CONTINUOUSWAVE

Posted: **Sun Jul 13, 2025 1:12 pm**

Q1: what does the performance data below tell?

Q2: what new propeller should I purchase for a 1986 MONTAUK 17 with an E-TEC 90 to improve its performance?

The performance data below is collected multiple runs at each data point from testing the following.

DATE: July 12, 2025
BOAT: 1986 MONTAUK 17 with 18-gallons fuel and 215-lbs crew weight
ENGINE: 2014 E-TEC 90 mounted two-holes-up
PROPELLER: BRG [later clarified to be three-bladed BRP] aluminum 13.25-inch x 17-pitch

ENGINE     BOAT
RPM        MPH
3000        19 
4000        26 
4500        29 
5000        33  
5500        34 
6000        37

REMARKS
I recorded the data as best one person can do. On-line discussions anticipated the top boat speed would be greater than 40-MPH. The top speed in the testing was only 37-MPH

I am not a speed demon, but, if a different propeller will be more efficient, then I want [the added speed a different propeller will provide due to its greater efficiency].

[Deleted remarks in the form of a narrative that attempted to describe what a graph of the above data looked like. Just include the graph as an inline graphic so readers can see the relationship. Describing something that can easily be a graphic illustration in a narrative is not a particularly useful way to demonstrate the data shown in the graph.]

The top boat speed was 37-MPH.

The boat reached planing speed at an engine speed of 3,000-RPM.

The feel of the boat at engine speed 4,000-RPM and 26-MPH boat speed is wonderful.

Acceleration [of either the engine or the boat speed] from idle is huge.

I am not a propeller expert.

To me it seems the engine is going past the point of maximum horsepower, which I believe occurs at 5,200-RPM.

--Glen

Posted: **Sun Jul 13, 2025 5:36 pm**

glen1941 wrote:PROPELLER: BRG [unknown brand] aluminum 13.25-inch x 17-pitch

I don't recognize "BRG" as a propeller manufacturer. Did you intend to write "BRP"?

You did not describe the number of blades or the family designation of the propeller.

For an E-TEC 90 model ABA [there are no model year designations for E-TEC engines after 2012] the recommended full-throttle optimum speed range is shown at

https://continuouswave.com/whaler/reference/ETEC_EngineRPM.html

and indicates a full-throttle engine speed of 5,000 to 5,200-RPM is best.

Your propeller test indicated the E-TEC 90 can accelerate to 6,000-RPM at full throttle (with the MONTAUK 17 at the total boat weight as tested) which is a greater-than-optimum engine speed. The general meaning of this data is that you ought to test a propeller with larger pitch than the 17-pitch you tested and repeat the test. The larger pitch propeller will have a greater load on the engine, which will tend to reduce the engine speed at full throttle. The greater pitch will improve the boat speed somewhat.

Also, if you want best boat speed results, you probably will find a steel propeller will produce more boat speed.

Assessing the boat speed results will be much easier if you include the GEAR RATIO of the engine. Please add that important data to the thread.

Posted: **Sun Jul 13, 2025 8:46 pm**

Thanks for the reply.

The propeller is a three-blade BRP, and the gear ratio is 2.0:1.

After reading the many discussions in continuousWave about similar boat-engine setups, it seems that the Stiletto Advantage 13-1/4 x 17 propeller might be a good choice.

Also, what I gather from these discussions is that while the existing propeller and the Stiletto have the same advertised pitch, the Stiletto does some magic through "cupping" and perhaps other design which produces an effectively greater pitch.

The advantages of the steel propeller over the aluminum propeller prop in efficiency would also help.

Knowing nothing about the various and many prop manufacturers, I don't know what other good choices there are, that is where you experts come in. Look forward to a consensus choice.

Posted: **Mon Jul 14, 2025 6:52 am**

With the gear ratio available, the performance data can be evaluated for the parameter SLIP. Using my Propeller Calculator, we now have:

ENGINE     BOAT  PROP
RPM        MPH   SLIP
3000        19   21.3
4000        26   19.2 
4500        29   19.9
5000        33   18.0 
5500        34   23.2
6000        37   23.4

The values calculated from SLIP from your engine speed and boat speed data are unusually high. Typically a properly working propeller that is at its maximum boat speed range will exhibit a SLIP value of more like 10 to 12, or even lower.

My inference from these numbers: the propeller is not working well. There could be several reasons for this:

the engine is trimmed out too far
the engine mounting height is too high
the propeller blades have some damage
the coupling between the propeller and the propeller shaft is not solid and the propeller is not turning at the proper speed
or, there is nothing wrong with the engine and propeller but the data recorded is faulty, either in engine speed or boat speed.

With regard to the data, please verify how you measured the engine speed.

Also verify how you measured the boat speed and what unit of speed you were using. There is often confusion between boat speed in statute-miles-per -hour and nautical-miles-per-hour.

For example, if your recording of 37 as speed were in nautical-miles (as often used when make long passages on the open ocean) instead of statute-miles-per-hour (generally universally used for small boats in lakes or inland waterways), that could account for the lower-than-expected boat speed. Converting 37-nautical-miles-per-hour to statute-miles-per-hour becomes 42.6-MPH.

Assessing the propeller performance at 6,000-RPM then produces a SLIP value of 11.8, which is very typical. All the other SLIP values will be similarly reduced.

Also, if there is any error in the engine speed, the SLIP value will be affected. Typical in most modern outboard engines the engine speed is available at very high accuracy via a NMEA-2000 data link. If the engine speed was being measured by an analog tachometer, then the accuracy of that data would be much lower. Also, if the tachometer were a universal type with a calibration setting, the tachometer could possibly be set to the wrong calibration notch.

I await your comments about these possible discrepancies and the errors they could introduce.

Posted: **Mon Jul 14, 2025 7:38 am**

glen1941 wrote:Q2: what new propeller should I purchase for a 1986 MONTAUK 17 with an E-TEC 90 to improve its performance?

Before buying a new propeller, we should investigate the data from the current propeller and try to determine what is causing such high SLIP values.

Posted: **Mon Jul 14, 2025 12:47 pm**

Jim--here are clarifications as asked for:

[Boat] speed was in units of statute-miles-per-hour from [the GNSS receiver on] a Lowrance Eagle 7; I verified with vendor Tactical Sonar today. The boat speed is corroborated by an iPhone speedometer app.

The propeller has no damage and is like new.

The gear ratio is 2:1 (0.5); I confirmed with a parts store and other sources

The tachometer is digital, but new and installed by Riverside Outboards.

The [engine propeller shaft] to propeller [hub] connection s solid. The Johnson-Evinrude shop and other boating repair professionals checked it; also, Riverside would never have let the installation go if otherwise.

The engine mounting height has been mentioned as being too high by two shops that I had look at the boat. The engine is installed so that above the actual top bolt there are too empty holes. [This is more often called being mounted two-holes-up from lowest position]. The engine mounting height will be lowered [to become one-hole-up].

PROPELLER SLIP CALCULATION
I did my own slip calculation for the 4,000-RPM 26-MPH data point, and I got SLIP = 18.8

Something is really really wrong. Recently, I had [calculated SLIP values] in the single digits from data for a Key West 1720 with 70hp Yamaha 70-HP and Yamaha propeller, and data for a Pioneer 180 with Honda BF100 and and Honda propeller. Both propellers were aluminum.

If lowering the [engine mounting height] does not resolve the [excessive] SLIP, I will be not sure where to go with this.

Thanks
--Glen

Posted: **Wed Jul 16, 2025 1:30 pm**

Thanks for the additional data that clarifies the situation. If the data measurements are in MPH, that rules out the possible error of the speed units.

If the propeller hub is in proper condition that rules out the connection between propeller shaft and propeller hub not being solid as a cause of deviation in performance.

If there is no damage to the blades then the loss of effective propeller pitch or loss of propeller efficiency from damage can be ruled out as the cause of deviation in performance.

glen1941 wrote:I did my own slip calculation for the 4,000-RPM 26-MPH data point, and I got SLIP = 18.8

As for your different value in your calculation of SLIP for the data set

if you got a value different from the value calculated by my Propeller Calculator, you may be doing something quite different. The propeller calculator has been on-line for many years and has been used by many people, and I have never received any report of an error in any calculation.

It is actually possible to check all the calculations by just selecting a different value to be calculated. For example, after the calculator computes SLIP from the other data, you can then calculate any of the other data from the other values. If the SLIP value were wrong, it would cause all the other values to change when they were re-calculated using the SLIP value initially calculated.

CHECKING THE MATH

Because MPH was the speed unit in the above data, the value of "C" (for conversion of speed into MPH from inches-per-minute) will be 1056.

To calculate SLIP the equation is then:

SLIP = 100 x [ 1  - ( MPH x RATIO x C)/(RPM x PITCH) ]

FIlling in the data

(1) SLIP = 100 x [ 1 - (26x2x1056)/(4000x17) ]
(2) SLIP = 100 x [ 1 - (54912/68000) ]
(3) SLIP = 100 x [ 1 - 0.8075284]
(4) SLIP = 100 x  [0.1924716]
(5) SLIP = 19.24

Posted: **Wed Jul 16, 2025 6:09 pm**

Jim, Many thanks for taking your time on this.

I believe the difference in slip is actually due to my data gathering. I calculated the slip manually comparing theoretical [boat speed] to actual [boat speed] as if I were taking my PE exam again. Our slip [calculated values] are within ROM range. I also eliminated (or think that I did) the possibility of the engine mounting height.

I read umpteen threads and watched many youTube presentation. Then I used a 5-feet-long level to determine that the anti-ventilation plate is 3/4-inch above the keel, and that the engine mounting height is the popular "two-holes-up" position.

I am starting to believe that [the lack of higher boat speed results] is "operator error". Think I was depending on the engine trim gauge and not on feel, and I managed to trim-out the engine to the point where it was pointing down.

While the boat was on the trailer, I watched how little movement was required for the engine to go from [trimmed-in] all the way to the anti-ventilation plate being horizontal.

I will be out on the lake on Friday, July 18, 2025, to pay off a charity donation ride; I will get out early and experiment.

ASIDE
Riverside stills swears that this 1986 MONTAUK 17 hull is the driest older Boston Whaler he has seen. Also, with fuel and engine, at static trim the hull rests right on her chines.

--Glen

Posted: **Thu Jul 17, 2025 8:40 am**

glen1941 wrote:I believe the difference in slip is actually due to my data gathering.

I used the same values for my calculation of SLIP that you did, that is, I used the data you collected and posted.

glen1941 wrote:I calculated the slip manually comparing theoretical [boat speed] to actual [boat speed].

That is the same method I use to compute the value of SLIP. The "slip" factor is the difference between how the propeller would have advanced if it were operating in a solid like a screw and how it advanced operating in a liquid like water.

glen1941 wrote:Our slip [calculated values] are within ROM range.

I do not understand the acronym ROM. What is meant by a "ROM range"?

glen1941 wrote:I also eliminated (or think that I did) the possibility of the engine mounting height.

This is a bit unclear to me. I do not understand what was eliminated.

Posted: **Thu Jul 17, 2025 1:58 pm**

Good afternoon Jim,
All, maybe, will be revealed when I complete my silent auction debt tomorrow by taking a couple for a boat ride and lunch.
1. ROM = rough order of magnitude, as in "give me an ROM estimate for the cranage costs". Our different slip estimates were not that far apart, and it is due to the different numbers that I put into my calcs. If your slip had been 20 and mine 5, it would have been something to work on.
My calculation:
motor speed rev/min / gear case ratio x pitch in/rev x 1 ft/12in x 60min/hr x 1 mile/5280 ft = theoretical speed.
theoretical speed - actual speed / theoretical speed x 100 = slip
2. One of the several possibilities which you mentioned was the engine height. I eliminated that as a possibility through the process I described.
Again, I think it is down to me learning how to trim properly.
Thanks, Glen

Posted: **Fri Jul 18, 2025 9:28 am**

glen1941 wrote:ROM = rough order of magnitude...

Thanks for explaining your intended meaning for ROM. I have never encountered that usage before. In today's world, ROM is generally used for read-only memory.

Regarding an order of magnitude, my interpretation is a change in order of magnitude would be by a factor of ten.
Cf.: https://en.wikipedia.org/wiki/Order_of_magnitude

Posted: **Fri Jul 18, 2025 11:48 am**

I have been carefully reviewing all the calculations in the Propeller Calculator after a report in this thread that indicated the same data produced a different outcome in calculating the value of SLIP. An alternative method was described which was said to produce a different calculated value. Here is a look at that situation:

glen1941 wrote:motor speed rev/min / gear case ratio x pitch in/rev x 1 ft/12in x 60min/hr x 1 mile/5280 ft = theoretical speed.
theoretical speed - actual speed / theoretical speed x 100 = slip

I think you mean to write: (here you need to widen the browser window to see the full math expansions)

(1) (RPM/RATIO) x PITCH (inches/revolution/minute) = theoretical speed of advance

(2) (4000/2 revolutions/min) x 17-inch/1-revolution = 34,000-inches/minute

(3)Calculating a conversion factor (C) for inches-per-minute to miles-per-hour 

60-minute     1-mile       1-foot      1-hour	      60-minute-miles    1-minute-mile
 ________  x  ________  x  ________ x  _________  =   ______________  =  ______________
1-hour        5280-feet    12-inches   60-minutes     63360-hour-feet    1056-hour-feet

(4)Apply the conversion factor to your data of 34000-inch/minute advance

(34000-inches/1-minute)  x (1-minute-mile/1056-hour-inch) = 32.2-MPH theoretical speed of advance

(5) Calculate SLIP according to your definition using observed speed == 26-MPH

(32.2-26)/32.2 = 6.2/32.2  = 0.1925 x 100 = SLIP = 19.25

This is the same value of SLIP as produced by the Propeller Calculator.

I believe the above calculations have followed the same method you used and got a SLIP = 18.8.

Posted: **Fri Jul 18, 2025 1:11 pm**

jimh wrote:
glen1941 wrote:I also eliminated (or think that I did) the possibility of the engine mounting height.
This is a bit unclear to me. I do not understand what was eliminated.

I mentioned engine mounting height as having an influence on propeller performance, which would tend to cause the apparent SLIP to have a higher than expected value.

jimh wrote:My inference from these numbers: the propeller is not working well. There could be several reasons for this...the engine mounting height is too high

I guess that what you mean is that your intention to re-test with the engine mounting height lowered to one-hole-up will tend to eliminate a higher-than-appropriate engine mounting height as the cause of the high values of calculated SLIP.

Posted: **Fri Jul 18, 2025 8:10 pm**

I believe the mystery [that is, the cause of the lower than expected boat speed] is solved, but the likely problem remains and is likely terrible.

I was confident that the boat was dry, perhaps because I was told that it was dry, and because I really did not want to accept that water intrusion could be the problem. Remembering that I had only put the boat in the water two times before and that in both cases I had 12-gallons of fuel and that the drain plug was in. On my outing today, I put the boat in the water with 18-gallons of fuel and with the drain plug out. With nothing else in the boat, water entered the drain and scupper holes and went forward of the console and was 6 to 8-inches deep at the stern.

I was committed to provide lunch and a boat ride to others, and they were on their way to the dock, so I got the boat on a plane until most of the water had drained out. leaving only the sump full, and put in the drain plug.

Some other indicators are that the steering is really heavy, there was a marked drop in speed--maybe 4-MPH at 4000-RPM--from recent tests. Also, handfuls of granular material had been steadily and continuing to come out of the rigging tunnel into the sump. While I was standing in the shallow water, I saw the bottom paint waterline was 6-inches above the water at the bow and the stern chine was 2-inches underwater.

Riverside [the dealer] was and still is convinced that the boat is dry, but his experience was [based on] drilling four holes in the upper part of the transom.

Looking at a youTube presentation of a fellow removing foam from a Boston Whaler, I saw that the rigging tunnel on his boat was cracked in many places. I can envision the transom being dry and the hull being wet. To determine if the hull is wet, I can only think to cut out a piece of the cockpit deck , maybe 12 x 12-inches, just aft of the fuel tank, and close to the rigging tunnel. I had been trying to flush water through the rigging from under the console to remove the granular material, and in so doing, may have made a bad problem worse.

I really do not want to reinvent this wheel and would dearly love advice; also, I imagine this thread going to the repairs section.

I will try to locate a weigh station where I can weigh boat, engine, and trailer, with fuel and battery.

--Glen

Posted: **Sat Jul 19, 2025 7:46 am**

I am very sad to hear that the cause of the slower than expected boat speed might be due to the hull weight being higher than normal due to water ingress and retention in the Unibond hull.

The Crouch speed prediction method as implemented in my Crouch’s Calculator can predict hull weight from performance data. Let's look at what information can be taken from using the Crouch method to look at the data.

First, we look at the expected outcome: a 90-HP engine should push the boat to 40-MPH. To calculate the weight we need a value for the hull coefficient. Typically a round-bottom hull like the MONTAUK will have a coefficient of 190. So we turn to the calculator and enter:

POWER == 90
COEFFICIENT == 190
SPEED == 40

The calculator returns a value of WEIGHT = 2,031-lbs.

Now we use your observed speed. Previously in your testing the top speed was 37-MPH. Using that value for SPEED the calculator predicts the total weight will be 2,373-lbs.

Also, you mention that the maximum speed decreased by 4-MPH, so it is now 33-MPH. At that top speed the estimated weight would be 2,983-lbs.

If the normal total boat weight for a MONTAUK 17 with E-TEC 90 that reaches 40-MPH is about only 2,031-lbs, and if your boat now weights 2,983-lbs, that is a very significant difference in total weight, a gain of 952-lbs.

The density of water is about 8.3-lbs per gallon. In order to have 952-lbs of water aboard the boat, you would need the volume of water that has ingressed and is being held in the foam to be 115-gallons. The space occupied would be about 15-cubic feet.

As for measuring the total weight of the boat, engine, fuel, and gear, and doing this while the boat is on the trailer, you will, of course, need a very accurate weight measurement for the trailer.

One method will be to weight the boat on the trailer, then return to the same scale and weigh the empty trailer.

Before you conclude that the lower-than-expected boat speed is due to added water weight in the hull, you should re-test with the lower engine mounting height, with better attention to engine trim, and report the new data you observe.

Another cause for lower-than-expected performance could also be the engine. The E-TEC 90 is well known for producing somewhat less than 90-HP, and the variations depend on the particular model year. Apparently the engine was tuned in some years for more power and in other years for less power, presumably in order to hit certain targets for monitored exhaust gas emission levels. So the E-TEC 90 could be producing something like 82 to 88-HP.

Again using the Crouch's Calculator, if the hull weight is just 200-lbs heavier than expected (2231-lbs), and the engine is only making 82-HP, the boat speed predicted would be 37.1-MPH. That just about matches your data.

The other possibility is the engine is not in particularly proper tune, and perhaps there is a problem with the engine power output related to something amiss, like a fouled spark plug, or restricted fuel flow, or bad gasoline.

I recommend that before you conclude the hull is much too heavy, you re-test with the lower engine mounting height and better trim settings.

Posted: **Sat Jul 19, 2025 11:16 am**

Jim--thanks for staying with me on this.

On yesternday's [July 18, 2025] sea trial, I did trim more judiciously, and there was better response.

The [engine mounting height] t is set at the two preferred locations: the anti-ventilation plate is approximately 1-inch above hull keel, and the mounting position "two holes up".

If Riverside is anything, he is a Johnson-Evinrude expert. He claims the 2014 that I have is probably making more than 90-HP.

I ran probably 40 miles yesterday and used practically no fuel. I want to amend something from my last; Riverside did install three new drain tubes and found no water, but again those tubes do not intrude directly into the main hull. For me the main and clear indicators are the heavy steering, the constant granular stuff finding its way into the sump, the large difference between the bottom paint lines and the actual water line, and most positively, the large amount of water which came into the boat with the drain plug out and no one in the boat.

Again, water was up to the cooler and 6 to 8-inches deep at the stern. Talk about scary, if it had not been a Whaler I would have been concerned about it sinking. Someone said, "oh, that is normal".

I very recently had a Key West 1720, and there was always talk on their forum about water in the stern with a big motor and several adults in the stern, water maybe to their toes. I never had any water in my Key West boat with me and the F70LA.

The water I experienced yesterday was in no way "normal" and for me a big sign saying: time - money.

I am now going to put my engineer hat on and set several things in motion:

Have local shop raise boat on slings off trailer for close inspection of underside.
Take boat to weigh scale which has the most accurate scale, maybe go to two scales. The trailer is a new Venture, so I can get very close to what the weight of boat, motor, trailer, battery, fuel, and cabling should be.
Cut section of floor aft of fuel tank near to rigging tunnel for exploration.

Having a good idea where this is headed, I have watched every "Whaler, boat foam, restoration" youtube online, I believe. I will not put the boat with one of the several overpriced hard-to-talk-with fiberglass shops here. If, when, it comes to it, I will use several young men who work at local boat shop who will work at home with my guidance.

The fork in the road happens with either putting the foam in through floor holes, or putting foam into hull and then putting the floor over the foam after leveling. I like this method better. I may then let fiberglass shop install the floor glass. Maybe getting ahead of myself, but rather be ahead than always behind the power curve.

--Glen

Posted: **Sat Jul 19, 2025 2:03 pm**

I believe the maximum engine speed for your E-TEC engine is 5500-RPM, so 6000-RPM is 500 over maximum. I also believe that that engine is equipped with a rev-limiter. So one might I assume that your tachometer is not reading correctly. If that 13 1/4 x 17 aluminum prop was turning at 6000 RPM, your boat speed would be in the 45 MPH range, regardless of weight and bottom condition.

Posted: **Sat Jul 19, 2025 8:49 pm**

Too many things going on here. Riverside saw on his test run 6000-RPM. I have seen twice on the three times with the boat 6000-RPM. The tach is an OEM multi-function analog with the alerts. Web info says the [E-TEC 90-HP engine] can accelerate past 5500-RPM if [the rev-] limiter is malfunctioning. There is no pulse adjustment for this tachometer.

So I will take [the boat] to [the] only Evinrude shop in this part of world and find out what is going on. Maybe the tachometer is defective.

As to your other comment, the [engine] could be turning 6000-RPM with the 17-pitch propeller, and boat could be traveling at a slow speed with the weight that I suspect I will find over the next several days. Think of it as pulling a droge, and with the engine turned out to create additional slip.

Posted: **Sun Jul 20, 2025 10:53 am**

I had not considered that the report of the engine speed at 6,000-RPM might be incorrect. I do not know what engine speed would cause the rev-limited to act.

glen1941 wrote:Jim--here are clarifications as asked for...The tachometer is digital, but new and installed by Riverside Outboards.

From this earlier report, I thought the tachometer was "digital", which I interpreted to mean that the signal from the engine that was providing the engine speed was a digital signal. The tachometer is now also being described as "analog."

The E-TEC 90-HP engine has a NMEA-2000 interface, and it would be rather common that the tachometer gauge would be connected to the engine's digital signal. The digital engine speed comes from the Engine Management Module (EMM) and is precisely accurate. An analogue tachometer could have error in the display of engine speed.

Getting more information about the tachometer gauge and how it is connected to the engine would be helpful. Perhaps we can see a photograph of the tachometer gauge.

If the dealer (RIVERSIDE) is an Evinrude expert, he should be able to clearly describe the tachometer model name and clarify if the tachometer is connected to the engine via a digital NMEA-2000 signal or a conventional analogue signal.

ASIDE: the SystemCheck series of analogue tachometer gauges also have four lamps that illuminate to indicate four alert conditions. I do not recall an Evinrude OEM NMEA-2000 tachometer gauge that also had four lamps for alert signalling.

Posted: **Sun Jul 20, 2025 11:36 am**

Jim,
Today, I will do the following:
1. Weigh the boat at two certified weigh stations. Unfortunately, they require weighing the truck as well, but the truck is a 2025 Honda Ridgeline with only one weight. I have all the other weights ready to go.
2. Use a 5" hole saw to cut a section of the floor out for discovery.
3. Remove the multi function tach and try to determine manufacturer, etc. The tach as a large multi pin connector coming from the motor. I installed a nema 2000 system in the KW and this looks like a similar data source. A possibility is that the source from the motor is accurate, but that the tach is not accurate. Communication with Riverside is over, so any advice from you as to what the best tach to use would be great. I can even imagine installing another monitor on top of the console to read the engine data and blank off the existing tach hole. There is a new Lowrance Eagle 7 on the dash, but I can find a space.
This Montauk 17 will live again.
Thanks,
Glen

Posted: **Sun Jul 20, 2025 1:35 pm**

glen1941 wrote:There is a new Lowrance Eagle 7 on the dash...

Usually a multi-function display will be able to show engine data it receives from an outboard engine via NMEA-2000. I don't know the exact details of the EAGLE 7 model, but unless it is the lowest-tier model, it should be able to show engine data.

I have an old Lowrance HDS-8 and I have it configured to show three pages of engine data from my E-TEC. But when I bought that device it was the top-of-the-line product.

Usually a Lowrance device will have an editing feature so the user can add or remove pages, and the user can edit the contents of any page to show any data available.

If your EAGLE 7 can show engine data, and
If your EAGLE 7 is connected to a NMEA-2000 network, and
If your E-TEC engine is connected to the same NMEA-2000 network,
Then you should be able to see engine speed in RPM on the EAGLE 7 that is coming from the engine EMM and will be very accurate.

Posted: **Sun Jul 20, 2025 1:42 pm**

glen1941 wrote:If Riverside is anything, he is a Johnson-Evinrude expert. He claims the 2014 that I have is probably making more than 90-HP.

We have a whole new element to add to the uncertainty. Because you mention that the engine is a 2014 model "90" and your dealer says it makes more than 90-HP, we have to establish what model you actually have.

PLEASE give the engine model number in its complete form as you can find on a label on the engine midsection.

With the full model number we can discover if you have the typical three-cylinder in-line E-TEC 90-HP model or whether you have the four-cylinder V-block E-TEC 90 H.O. ("high output") model. The E-TEC 90 H.O. was a new product introduced in 2014. It is a completely different engine than the E-TEC 90-HP that we have been discussing.

There is more and more ambiguity in this discussion with each new post.

If you have the 90 H.O. engine it will be much heavier than the 90-HP model, and the 90 H.O will produce more than 90-HP; as I commented earlier, the 90-HP model produces somewhere around 85±3 horsepower, depending on model year and EPA tuning.

If the engine were a 90 H.O, then the added weight would account for the static trim of the hull being down-by-the-stern more than usual, and having more water allowed onboard by the open cockpit drain.

Posted: **Sun Jul 20, 2025 3:56 pm**

I am back from the adventures in weigh scales.

WEIGHTING AND CALCULATING

I went to a CAT certified scale. I twice weighed truck [and boat on trailer] in different positions of a three-platform section scale; the [two sets of weights] were were consistent [with each other].

I then weighed boat and trailer only on the center section of the scale.

[Moderator's note: a CAT scale intended to weigh trucks will that three sections: truck steering axle, truck drive axle, and all trailer axles.]

The scale operator said the scale weights are very accurate, and the scale has an upper limit of 20,000-lbs but can weigh a [human] body.

Using the two weights sets, I calculated that the 1986 MONTAUK 17 weight is 140-lbs greater [than I expected based on the following assumptions of the weights involved:]

950-lbs boat
560-lbs trailer
52-lbs battery
84-lbs fuel
30-lbs cables
320-lbs engine

[Assuming that the variance in expected weight is a result of water ingress and retention into the hull, I interpreted these measurements as] indicating there is 2.24-cubic-feet of water in the hull.

[A volume of water of 2.24-cubic feet] does not sound like a lot.

A small adult.

But if the [cockpit sump drain] plug is out, a lot of water comes in [the cockpit].

TACHOMETER IDENTIFICATION
On the tachometer there is a sticker that says: BRP # 177107. Date: 08-G-1R; and TC3002E. Also [a sticker says] pulse for 6 pulse/rev OMC.

The pulse setting is not a positive click-to-click for the different setting, and the setting was set between 5 and 6, closer to 6, maybe 3/4ths of way between 5 and 6. The tachometer has an 8 pin female connection.

ENGINE IDENTIFICATION
The engine model is E90DSLABB; Serial No.: 5408858; date of manufacture: 5/2012.

I have not drilled the hole yet in the floor. Tomorrow for sure.

More tomorrow.
Glen

Posted: **Mon Jul 21, 2025 8:59 am**

glen1941 wrote:The engine model is E90DSLABB; Serial No.: 5408858; date of manufacture: 5/2012.

More new information.

The model number decodes as follows:
E = Evinrude
90 = rated horsepower
D = Evinrude E-TEC
S = Saltwater Approved
L = 20-inch-long shaft
AB = second major model variant
B = second revision

The production date of May 2012 coincides with the format of the model number, because in 2012 Evinrude stopped using model year designations with their engines. Evinrude just identified the sequence of the variations or changes in production beginning with AA , then AB, then AF, because these two-letter codes skipped using the letters C, D,E, I, N, O, R, S, T, U because they were previously used as production year identifiers. A third letter was also appended to the first two to indicate minor revisions, beginning with A and continuing through the alphabet to Z.

What we now know:

the engine is actually a c.2012 engine, not a 2014 engine as indicated before;
the engine must be a three-cylinder in-line model because there is no letter "H" in the model designator, which is used to indicate High-Output (H.O.) versions.

The dealer's comment that the in-line three-cylinder 90-HP E-TEC engine will produce more than 90-HP power output is in conflict with the actual horsepower reported in the EPA emission certification testing data and with the general experience of boaters with the engine. This model makes anywhere from about 84 to 88-HP, and to base boat speed potential using a horsepower figure greater than 90-HP is not going to be realistic.

Posted: **Mon Jul 21, 2025 9:07 am**

glen1941 wrote:On the tachometer there is a sticker that says: BRP # 177107

The BRP part number indicates positively that the tachometer that has been used in all engine speed measurements is a SystemCheck tachometer that uses an analogue signal to operate the dial pointer mechanism with scale graduations every 100-RPM, with the dial face marked 0 to 7 as in 0 to 7,000-RPM.

What we know now:

the tachometer is an analogue type, and
there is nothing "digital" about its operation, as neither the display is a digital display and the signal provided to the tachometer is not a digital signal.

The use of an analogue tachometer raises some question about the accuracy of the engine speed measurements obtained.

glen1941 wrote:The pulse setting is not a positive click-to-click for the different setting, and the setting was set between 5 and 6, closer to 6

The idea that there is a movable calibration control setting on the rear of the tachometer further adds to the uncertainty that the engine speed is being measured accurately.

For example, if the calibration setting was still in the "5" setting, then the tachometer would read the engine speed higher than actual by a factor of 6/5 or 1.2:1, which would suggest that the engine speed seen on the tachometer as "6,000" would actually be 5,000-RPM.

If we change all the engine speed data by a factor of 0.833 and recalculate the SLIP, the SLIP numbers are going to be much closer to normal.

For example, using the maximum boat speed data:

RPM = 6,000 ---> and now using 5,000
RATIO = 2
PITCH = 17
MPH = 37
SLIP = 8.1

This new calculated value for SLIP is much closer to expected SLIP values than previous calculated value of 23.4.

RECOMMENDED CHANGE IN MEASURING ENGINE SPEED
You really need to use the NMEA-2000 data from your E-TEC engine to display the engine speed. Earlier I described how you may be able to use your multi-function Lowrance display to show the engine speed.

Your REALLY need to get better engine speed data, and especially BEFORE you start cutting holes in the cockpit deck.

Posted: **Mon Jul 21, 2025 9:23 am**

glen1941 wrote:...Using the two weights sets, I calculated that the 1986 MONTAUK 17 weight is 140-lbs greater [than I expected based on the following assumptions of the weights involved:]
950-lbs boat
560-lbs trailer
52-lbs battery
84-lbs fuel
30-lbs cables
320-lbs engine

[Assuming that the variance in expected weight is a result of water ingress and retention into the hull, I interpreted these measurements as] indicating there is 2.24-cubic-feet of water in the hull.

Previously the effect of a weight variance that could be the cause of the significantly lower maximum boat speed performance showed that an increase in weight on the order of 900-lbs or more.

Also, my feeling is your assumed "normal" weight for the boat and all its gear is probably lower than the actual weight. You probably did not account for normal gear on the boat, such as an anchor, mooring lines, fenders, mandatory safety equipment such as a fire extinguisher, flares or signalling devices, personal floatation devices, a Type-IV throwable cushion, and other gear routinely found on any boat.

Because you assumed a "normal" boat weight that was somewhat lighter than what would be more likely probable, you found that the hull was overweight. Then you assigned the extra weight to be due to water ingress into in the hull.

If you could PLEASE just state the actual measured weight of the boat and trailer, and cite your source for the weight of the trailer, then we could known a reasonably good measured weight for the boat.

Once we have the measured weight for the empty boat, we just need to know your weight, and then we would have a good estimate for the actual boat weight during your testing of the boat performance.

Posted: **Mon Jul 21, 2025 9:47 am**

glen1941 wrote:On ...[July 18, 2025] sea trial, I did trim more judiciously, and there was better response.

PLEASE provide the new performance data you gathered when you changed the engine trim settings and the performance improved.

Posted: **Mon Jul 21, 2025 3:42 pm**

Hello Jim,
The CAT scale weight for the boat, motor, trailer and rest of the stuff is 2100lb. I made sure the rig was sitting on the middle section of the scale. The source for the boat and motor are on the internet, the weight for the trailer [new] is from Venture's information and the shipping weight. Monday morning is weigh in day and I was 214lb. I no longer trust the 2008 tach, and have ordered a new Seirra International Lido which will have better quality and more positive pulse selection. I just came in from cutting a 4 1/4" dia. hole in the deck, 12" to starboard of centerline of sump, with leading edge of hole aligned with forward edge of sump. Dug down to the glass. Absolutely dry. I can see the fibers in the glass, no moisture at the bottom. If water was to accumulate in the foam, I would think it would find itself there, in the stern and near the rigging tube. Everything is out of the boat now except the console. In the immortal words of Butterfly McQueen, I just don't rightly know what to do.
Here is what I think I see now:
1. There does not appear to be water in the boat where water would be if there was any appreciable amount. Maybe Riverside's yelling was correct.
2. If the scales and my calcs are right, there would only be the effect of a young adult moving to the stern of the boat. That should not cause the great bow up stern down attitude and the scary amount of water coming into the boat with the plug out.
3. The tach is giving incorrect rpm readings, and it will be replaced by a new unit which takes its pulse directly from the motor.
4. Which leaves me with:
a. Why the really heavy steering, its not turning the wheel, its the difficulty of making the boat change course?
b. Why the very noticeable bow up stern down attitude?
c. And the really big problem for me, the water coming all the way to the cooler when the drain plug is out? Can this really be normal?
d. Why the continuous flow of dark granular stuff, like sand, coming from the rigging tube? In a worse case, and only if required, installing a new rigging tube would not be difficult.
e. My calc that the boat is 140 lb more than the ideal weight of boat et al, would only be 7%. One of the first courses that I took in school was on the theory of errors. There could actually be no weight problem as the boat might weigh above average [more glass], the trailer the same [spare and tongue jack], I might be light with my estimates of the gear.
I have two items on the way: new tach and 19P alum prop. I will put the boat back in the water when the new tach is installed. Also need to fill the hole in the deck, I can reuse the wood and glass. The saw has a very thin kerf.
I was not in the boat or on the scales, when these things showed themselves.
Glen

OK, really need help on b. and c. above.

Posted: **Tue Jul 22, 2025 3:10 pm**

I have two modifications to be made to the 1986 MONTAUK 17:

The "heavy" steering, my description, is now, as I better understand, the effect of propeller torque. I am now going to install a UFLEX hydraulic steering assembly. This should cure most of the steering torque.

I will move MOELEER 22-gallon fuel tank to be forward of the center console. The cooler will be moved to be aft of the reversible pilot seat.

I read {somewhere} of a MONTAUK 17 with a 70-HP engine; with [the cockpit sump drain plug removed] a ton of water came into the boat

jimh wrote a great article explaining how once the water begins to come in to the boat that it continues until the boat reaches equilibrium. That point would be unique to each boat.

I am guessing my MONTAUK 17 reached [a new equilibirum of water in the cockpit] after I changed to a 22-gallon fuel tank from a 12-gallon fuel tank.

To NOT see any comments [from people with the older 90-HP engine and having water in their MONTAUK 17 boat] surprises me. [I attribute this lack of comments about higher than expected instances of water in the cockpit with an open cockpit sump drain to be caused] by people not wanting to say bad things about an icon.

I anticipate moving the 22-gallon fuel tank [to be ahead of the center console] will eliminate some or much of the bow-up stern-down [static trim].

In my mind the design of the MONTAUK 17 hull and its cockpit sump drain is a bad design.

I love my MONTAUK 17, and it is my forever boat, but it is like being in love with a bad woman.

When the fuel tank is relocated and the new tachometer goes in, will get all the data again and see what they say.

An aluminum 19-pitch propeller has been purchased. But I will see what happens with the aluminum 17-pitch propeller.

Posted: **Tue Jul 22, 2025 5:01 pm**

Glen--another effective way to reduce weight in the stern on a MONTAUK 17 boat is to move the engine cranking battery to be in the center console. That moves about 50-lbs from the far end of the boat to the center of the boat.

If you are thinking about moving the battery, it is a big project because you need to significantly increase the size of the conductors that run between the battery and the engine in order to reduce added voltage drop from the longer cables. The conductors need to be increased in size, and these days the proper, marine-grade, multi-strand, all-copper cable is quite expensive per foot. If you want to discuss that in more detail, start a new thread in SMALL BOAT ELECTRICAL, and I can offer more specific advice.

Posted: **Tue Jul 22, 2025 5:38 pm**

Using a boat weight of 2315-lbs (2,100 + 215), the Crouch Speed prediction for 88-HP and 190 Hull Factor is 37-MPH.

Posted: **Wed Jul 23, 2025 6:41 pm**

It's all coming together. Surprisingly, the critical path item is the teak boards for the relocated tank platform.

While the boat was in New Hampshire, I had Riverside install new [4-AWG] battery cables to the console, when I got the boat down here, I installed a new Group 34 Marine AGM battery by cutting a section from the console floor so the battery would rest directly on the deck.

I am not familiar with the formula that you refer to, so do not know how it is derived. In most formulas, there is a component that is most sensitive to the result. Be interesting to see how sensitive the formula is to the fairness of the bottom [bottom paint].

--Glen

Posted: **Fri Jul 25, 2025 12:24 pm**

glen1941 wrote:...not familiar with the formula that you refer to, so do not know how it is derived...

Glen--I am not sure what "formula" you are asking about.

If you are asking about the methodology of the Crouch Planing Hull Speed Predictor, I have already mentioned it and linked to my web page where I have implemented the method and also explained the basis for the method. I don't know if you have visited the page, but there are several links to in already in this thread. Here is another link:

Crouch's Calculator
https://continuouswave.com/calculators/crouchCalc.php

The Crouch method of speed prediction is based on the concept that boat speed varies a function of the ratio of power to weight to the 0.5 exponent. There is no separate variable input for the condition of the bottom paint on the hull. The ENTIRE influence of the hull is combined into one factor, the hull coefficient. The value of the hull coefficient also includes the conversion to the unit of speed measurement.

The method allows for the hull coefficient to be deduced by input of the the other parameters: POWER, WEIGHT, BOAT SPEED.

Once you have a good sense or value for the hull coefficient, then you can predict the BOAT SPEED.

The hull coefficient of 190 (for speed in MPH) that I have used comes from many reports of the performance of Boston Whaler boat hulls with a rounded semi-V design, like the hull used in the MONTAUK 17.

Certainly a hull that has attached marine growth such as barnacles will produce more drag than a hull with a clean bottom.

So far you have made no mention of the condition of the hull you are using and testing for performance. It seems unusual that at this point into the discussion you introduce a new parameter: hull bottom condition. If the hull being tested for performance in this discussion is fouled with marine growth, you should have mentioned this in the first post.

If you have any actual data that shows the effect on boat speed from a particular state of the hull bottom compared to a perfectly clean hull bottom, please share that data and where you got the data from, that is, did you perform testing to get the data or did you rely on another person's testing or did you just read some old dock chatter about it. A good concept for a metric for hull bottom condition would be a figure that was a percentage of reduction from optimum speed caused by each different state of hull bottom condition. I leave it to you to work out this augmentation of Crouch's very useful work in explaining how moderate speed planing hulls respond to the effects of power, weight, and hull design.

If you have more interest in understanding the effect of propellers on boat performance, you should purchase a copy of PROPELLER HANDBOOK by Dave Gerr. This book is mentioned in the explanatory material that accompanies the Crouch's Calculator page. Unlike many technical reference books, the cost of the PROPELLER HANDBOOK is quite modest.

Posted: **Fri Jul 25, 2025 8:31 pm**

Glen,

You seem to be concerned that there’s something majorly wrong with your boat. After reading this entire thread, I'm not sure that's the case. It sounds like you may have a perfectly normal 1986 Montauk 17. It does, however, sound like you may be getting incorrect readings from your tachometer. It would probably be helpful to resolve your tachometer problems before making any further changes, or drawing any more conclusions, so you can accurately assess the performance of your boat.

With respect to your concern about your boat’s static trim (that it’s floating too low at the stern), it would be helpful if you could describe the relationship between the waterline and the splash-well drains, or better yet, provide a picture. As a point of reference, there’s a classic Montauk 17 moored in my marina. Like your boat, the Montauk in my marina is equipped with a three-cylinder, 90 horsepower E-TEC, a 22-gallon fuel tank mounted under the reversible pilot seat, and a battery mounted in the factory (stern) location. The waterline is just below the splash-well drains on this boat.

Hope this helps.

Posted: **Sat Jul 26, 2025 8:59 am**

Regarding comparison of boat performance of your boat to published reports from others with the same set-up, a major influence that will cause different outcomes is the effect of environment. In particular, the air and water conditions have a significant influence.

Let us begin with the water: the density of the water affects boat performance. Water density is affected by salinity and temperature. If one test is conducted in very cold saltwater and another is conducted in tropical freshwater, there will be an influence: the cold saltwater will create better performance.

Now let us look at the air: the air temperature and humidity also affect performance by their influence on the engine power output. Hot air and humid air is less dense than cold, dry air. The engine tested in cold, dry air will produce more power.

Altitude also affects engine performance. Air density decreases with altitude. The engine tested at higher altitude will produce less power.

If BOAT A is tested at sea level in very cold saltwater on a cold dry day, it will exhibit better performance than an otherwise identical BOAT B tested at higher altitude, in very warm freshwater, on a hot and humid day.

Posted: **Sat Jul 26, 2025 2:53 pm**

[Deleted comments in which no intention was meant to suggest that the Crouch performance predicting method could be modified, but then suggested two additional factors that could be added to modify the formula. If you have any idea for a method to predict the speed of a moderate-speed planing hull, you are welcome to invent a new method, test the method, and present your new and more refined method as a possible replacement for naval architect George Crouch's work. But please do not make that part of this discussion.]

FUTURE WORK AND TESTS

[Soon] I will complete the relocation of the 22-gallon fuel tank, [and after that work I] should see the completion of the hydraulic steering. [Moderator's note: it is not necessary to give the names of the days of the week when each job is scheduled. Identifying the time span in terms of what day of the week relative to when you are writing your post makes it difficult for readers to understand the particular epoch when you expect to perform the task.]

[Next] a Sierra International Lido tachometer gauge [will be installed]. I have selected the "6P" setting as accurately as I believe it can be done.

[After the new tachometer gauge is installed] I will re-launch the boat.

Then I will see where the bilge drain holes are relative to the waterline, but of course, this reading will be under different conditions from when the boat took on all the water; but the plug stays in the drain.

I will take [engine speed and boat speed] readings; I will not rely on the TRIM gauge. I will use the aluminum BRP 17-pitch propeller.

[Also deleted was another entirely new topic about the effect of use of a transom-mounted transducer on the performance of a depth sounder. Please start a new thread in SMALL BOAT ELECTRICAL if you want to discuss how a transom-mounted SONAR transducer could be improved.]

Guidance from CW was responsible for resolving several of my problems.

Posted: **Mon Jul 28, 2025 5:16 pm**

bjohn wrote:With respect to your concern about your boat’s static trim (that it’s floating too low at the stern), it would be helpful if you could describe the relationship between the waterline and the splash-well drains, or better yet, provide a picture.

I found a photo of the boat in the water with two 6-gallon fuel tanks under the seat and the Group 34 battery under the console.

The waterline is right at the bottom of the scupper drain holes, but no water was coming into the scupper area.

FUTURE OBSERVATIONS
When I put in the boat next time, will be able to see the effect of moving the 22-gallon fuel tank forward of the console, and the tank will only have 15-gallons of fuel.

Posted: **Wed Jul 30, 2025 10:56 am**

glen1941 wrote:
bjohn wrote:With respect to your concern about your boat’s static trim (that it’s floating too low at the stern), it would be helpful if you could describe the relationship between the waterline and the splash-well drains, or better yet, provide a picture.
I found a photo of the boat in the water with two 6-gallon fuel tanks under the seat and the Group 34 battery under the console.

The waterline is right at the bottom of the scupper drain holes, but no water was coming into the scupper area.

In order to talk intelligently about this topic, we need to use a common language. The inquiry asked specifically about the position of the engine splash well drains relative to the water line in static trim.

The answer provided invented new drains ("scupper drain holes") and a new part of the hull ("the scupper area").

We need to share a common understanding about what particular features of the hull are called and what their function is.

The classic 1986 MONTAUK 17 hull does not have any scuppers and there is no part of the hull called "the scupper area". A scupper is an opening, typically a hole or channel, designed to drain water from a surface, commonly from a ship's deck. The purpose of the scupper to allow water trapped on the deck to drain immediately into the sea.

What a classic MONTAUK 17 actually does have is a engine splashwell that is designed to catch any water that splashes over the transom near the engine (and hence the name, engine splashwell), and then to drain off that water into the sea via one or more drain holes in the transom. The amount of water that can accumulate in the engine splash well is limited, and in order for the engine splash well to overflow and begin to flood into the cockpit, the boat would need to be severely out of trim such that the waterline at the transom was higher than the upper lip of the engine splash well. For this reason the engine splash well drains are virtually never plugged. They are always open so that they can immediately drain the water in the engine splash well back to the seal. Even if the trim on the boat puts the engine splash well drains below the static waterline, this only allows water into the engine splashwell, where it does NOT flood into the cockpit.

For most of this thread, and as far as I have been able to figure out, what has been a concern for this particular hull is another drain that is ACTUALLY here, and that is the COCKPIT SUMP DRAIN which is located in the stern of the boat and is a rectangular depressed well, close to the engine splashwell and transom, on centerline in the cockpit deck. If the cockpit sump drain is left open, then water from the sea will flow into the sump via its drain. This is, of course, the opposite direction of flow in the sense that the drain is supposed to drain water in the sump into the sea, not let in water from the sea to flood the boat.

Depending on the particular boat and distribution of weight in the boat, it is possible that, with the cockpit sump drain left open, the waterline will be higher than the top of the sump. This means that water will rise in the sump, and if the waterline is high enough, then the water will begin to flood into the cockpit.

Let's discard newly invented names for features in the hull that do not exist, and, please, let's use the common language that has been used for the elements of the hull for decades on this forum.

Also, the cockpit sump drain can be opened when the hull is making forward way, and from the Bernouli effect, water will not flow into the boat, but water will be sucked out of the drain, clearing all the water in the sump in a few moments.

Posted: **Wed Jul 30, 2025 11:05 am**

glen1941 wrote:...a Sierra International Lido tachometer gauge [will be installed]. I have selected the "6P" setting as accurately as I believe it can be done..

Measuring the engine speed with a non-OEM tachometer that is universal in calibration and is adjustable is not a particular improvement. The E-TEC engine can provide extremely precise data about engine speed from its EMM via a NMEA-2000 network connection to a display device, allowing engine speed to be known to a resolution of about 10-RPM out of 6,000-RPM.

Posted: **Wed Jul 30, 2025 11:15 am**

glen1941 wrote:Then I will see where the bilge drain holes are relative to the waterline...

A MONTAUK 17 Unibond hull does NOT have a bilge space. The area between the hull bottom and the deck, which on a typical boat would be open and could accumulate water, on a Unibond hull is filled with foam.

Your use of the plural "bilge drain holes" is confusing. If you are trying to describe the cockpit sump drain, it is a singular drain. There is only one.

If you are referring to the engine splash well, there could be more than one drain in the splash well, I honestly do not recall exactly how many are used on a 1986 MONTAUK 17, but I believe there are two.

Posted: **Wed Jul 30, 2025 11:22 am**

glen1941 wrote:In my mind the design of the MONTAUK 17 hull and its cockpit sump drain is a bad design

When the 17-foot hull was designed, outboard engines were lighter weight. When a 17-foot Unibond hull is new its weight is probably lighter than your particular 39-year-old hull. Boats often gain weight as they get older.

Posted: **Thu Jul 31, 2025 1:50 am**

Using a boat weight of 2315-lbs (2,100 + 215), the Crouch Speed prediction for 88-HP and 190 Hull Factor is 37-MPH.

Jim,

I believe the 2,100-lbs figure used in your calculation above includes the weight of the the boat trailer (560-lbs).

Hello Jim,
The CAT scale weight for the boat, motor, trailer and rest of the stuff is 2100lb.

Assuming that's true, I think the actual weight of the boat and operator is 1,755-lbs (1,540 + 215). Using this revised weight figure, the Couch Speed prediction is 42.5 MPH. Is this correct?

Glen,

The reason I asked about the relationship between the splash well drains and the waterline is because you suggested your boat was floating too low at the stern.

b. Why the very noticeable bow up stern down attitude?

If the waterline is below the bottom of the splash well drains, I don't believe there's anything unusual about your boat's static trim.

With respect to your other concern, about "the water coming all the way to the cooler when the drain plug is out", yes, this is probably normal. I haven't removed the drain plug from my 17 Montauk while the boat's in the water for a long time, so I couldn't tell you exactly how much water in the boat would be "normal", except to say it's not an insignificant amount of water.

Posted: **Thu Jul 31, 2025 10:03 am**

bjohn wrote:
jimh wrote:Using a boat weight of 2315-lbs (2,100 + 215), the Crouch Speed prediction for 88-HP and 190 Hull Factor is 37-MPH.
I believe the 2,100-lbs figure used in your calculation above includes the weight of the the boat trailer (560-lbs).
glen1941 wrote:The CAT scale weight for the boat, motor, trailer and rest of the stuff is 2100lb.

Assuming that's true, I think the actual weight of the boat and operator is 1,755-lbs (1,540 + 215). Using this revised weight figure, the Couch Speed prediction is 42.5 MPH. Is this correct?

Yes, Using 1,755-lbs as the total weight the Crouch Calculator predicts 42.5-MPH for 88-HP and 190 HULL FACTOR.

Sorry about my mistake. I am glad someone could figure out the boat weight, as the OP never clearly stated it. You had to deduce the boat weight from a column of various weights.

[Moderator's note: I am closing this thread, which has gone on at great length trying to get to the cause for reduced performance from a particular boat, engine, propeller, and testing conditions. The boat is in the process of being revised with changes in weight distribution, steering mechanism, propeller pitch, engine trim, instrumentation for measuring engine speed, and possibly engine mounting height. Then GLEN1941 is going to re-test the boat. I invite GLEN to start a new thread in the PERFORMANCE forum laying out the results of his testing, and, if possible, clearly stating what he believes was the total weight of the boat, engine, fuel, gear, and people when the performance data was recorded, along with information about the test conditions, such as air temperature, water temperature, salinity, currents, and winds. A clear and unambiguous presentation of the new data from testing with all the revisions will be much better provided in a new thread, as opposed to a continuation of this thread which is rather cluttered with numerous sidebar discussions, such how to calculate SLIP, how to revise the Crouch Method, and in general has become perhaps the longest, most confusing discussion of the performance of a MONTAUK 17 with E-TEC 90 ever conducted in the former. A new thread with clear, concise, accurate data about the boat and the performance of this boat will be the best way to continue this saga. See you all in the new thread that GLEN1941 can start if he wishes to continue his reporting. GLEN1941 has been notified by PM about the thread closing and encouraged to start a new thread about the performance data he will be obtaining in his new tests, and recommended to read the pinned article about performance data collection before posting his new data. ]

CONTINUOUSWAVE

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