SUPER SPORT 15 Re-power - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  SUPER SPORT 15 Re-power

search | FAQ | profile | register | author help

Author Topic:   SUPER SPORT 15 Re-power

littlehandegan posted 03-14-2011 10:50 PM ET (US)
What [i]s the consensus [of opinion] on [re-powering a Boston Whaler SUPER SPORT 15 with a] Yamaha 90-HP two-cycle?
jimh posted 03-14-2011 10:57 PM ET (US)
I don't know what the consensus of opinion is going to be, but I will give you my opinion, which is about all any individual is going to be able to provide. If your article elicits enough opinions, you may be able to deduce what the consensus of opinion will be.
A Boston Whaler SUPER SPORT 15 with a 90-HP will have an engine that exceeds it maximum horsepower rating of 70-HP.
The Yamaha 90-HP two-cycle is a very refined three-cylinder two-cycle engine that has been in production for a long time and has a very good reputation as a light weight motor with compact size.
With extra horsepower the 15-foot Boston Whaler hull will go quite fast, and perhaps faster than it was ever intended to go, which may make its stability decrease.
Tom W Clark posted 03-14-2011 11:09 PM ET (US)
littlehandegan -- Welcome to continuousWave.
Russ 13 posted 03-15-2011 03:26 PM ET (US)
I own [a SUPER SPORT 15]. When I was reconditioning the boat I looked all over for a Yamaha 70-HP two-cycle, and found a 90-HP instead. The weight of the Yamaha 90-HP is close to the weight of a 70-HP two-cycle, so the boat does not squat in the stern. I have my battery forward under the console.
I use [the SUPER SPORT 15] for water sking and wake boarding and the extra power is a help. Top speed is around 50 [MPH?], but it is rarely run at that velocity. The Yamaha two-cycle 90 has been problem free now for five years, and does not burn much fuel. For an experienced boater, [powering the boat with more horsepower than its maximum] is no problem. I would not recommend the extra power for a beginner.
dgoodhue posted 03-15-2011 05:31 PM ET (US)
90hp on 15' whaler is overpowering the hull. I am getting 47mph with 70hp and a jackplate. Your probably not going to hit 50 mph without a jackplate and that yamaha. Basically you getting diminishing returns for that up. I would guess it have better hole shot and acceleration but a 70 on a 15' isn't lacking to begin with.
jimh posted 03-16-2011 10:07 AM ET (US)
There is a good article on the general topic of using engines with horsepower that exceeds the hull rating in the REFERENCE section. See
http://continuouswave.com/whaler/reference/ratedHP.html
littlehandegan posted 03-16-2011 10:27 AM ET (US)
DgoodHue may I ask what kind Brand 70 2 Cycle you are running?

Thanks guys!
dgoodhue posted 03-16-2011 11:41 AM ET (US)
I have an older Evinrude (1989). As someone likes fast cars, I would still be tempted to repower it with 90 up ETEC, but I am happy with the performance of the boat right now.
Tohsgib posted 03-16-2011 11:44 AM ET (US)
The 90 Yamaha is not the most powerfull 90 and more like an 80hp hence why the rebuttles. Len had a 90 E-Tec on his 15 with a power jackplate and his BEST was 52.5.
Tom W Clark posted 03-16-2011 05:57 PM ET (US)
The three cylinder, two stroke Yamaha 90 puts out 83.3 HP.
I would not put one on a classic 15' Whaler. I've owned quite a few Whalers including a 1979 Striper 15 with a 70 HP Johnson. It was fast.
The classic 15' Whaler is the one Whaler hull I would not overpower, the rest can take a little extra easily, but the 15 does just fine with 70.
Russ 13 posted 03-21-2011 05:48 PM ET (US)
I agree with Tom, the 70-HP [two-cycle] is a great match for the 15-footer. I got a great deal on a friend[']s Yamaha [90-HP engine], and the extra 13-HP helps with pulling water toys. Both the two-cycle 70 Johnson [and] 90 Yamaha are great lightweight outboards that are proven reliable designs.
littlehandegan posted 03-26-2011 12:15 AM ET (US)
Found a 1997 Yamaha 90. Going to get it next week. Wish me luck!!!
Pics to come!
edwardschnog posted 03-28-2011 07:20 PM ET (US)
Hi guys, I never understood how you guys can reach that top speed @ WOT with the 90 Yammie... I GPS clocked my boat at 43MPH with that same 90 HP Yamaha 2 stroke engine.
My 15 is a bit heavier since it was built for the Coast guard, more layers of fiber is probably the cause of this extra weight. I have a 15 pitch Prop with lots of cupping which gives me a max rpm at WOT of 5800
By the way I just installed a state of the art Audio system in the boat. Sounds beautiful!!
Have a look: copy / paste the below link in your browser.
http://s186.photobucket.com/albums/x117/schnog/Alert15/
Cheers and happy boating,
Edward
Tohsgib posted 03-28-2011 07:28 PM ET (US)
15" you have your problem there, should be running at leats a 19".
pcrussell50 posted 03-28-2011 07:33 PM ET (US)
If you plan on obtaining liability coverage with an overpowered hull, please post up who you used, or contact me. Near as I can tell, no insurance company will cover you for liability if you are as much as 1 horsepower over the max rating for the hull. I hear there are some case-by-case underwriters, like Lloyds of London, but that is actually the only one I've ever heard of. Id like to know for sure if there are any others. One of my boats is rated for 120hp max, and I have a 135hp on it that is the same size and weight as the 115hp that came on it, so size and weight are not a problem. Just horsepower. With a 15 month old baby girl now, I would really like to have some protection of my assets if my barely overpowered boat were to be involved in a liability case.
-Peter
Binkster posted 03-28-2011 09:39 PM ET (US)
I assume your 135 is an OMC outboard. The simple way to address this problems is to get some 115 decals, find a marine boneyard and pop the motor Id plate off a 115. If you have a liability suit, do you think they are going to tear the engine down to see what the specs are? They only do that at the race course/track.
pcrussell50 posted 03-29-2011 01:05 AM ET (US)
Binks! Of course it's an OMC 135! :). You know me by now.
On a more serious note, I'm afraid that when it comes to saving an insurance payout of tens or hundreds of thousands of dollars, or millions, the price of a professional teardown is peanuts, and money well spent... by the insurance co. The stories abound. Apparently, some law enforcement agencies impound the motors right off the bat, in injury cases.
Anyhoo, this should be in a thread of its own. I was just wondering if anybody knew of any insurance companies you could deal straight up with, for a price, besides Lloyd's.
-Peter
Keeper posted 03-29-2011 11:34 AM ET (US)
I was on this kick for a while (90 HP Yamaha on a classic 15) . . . but have since changed my mind.
My 15 SS was originally powered w a Yamaha 70 2-Stroke. With the addition of a Bobs jack-plate I could consistently achieve 42-43 mph w/ 2 on board. This set-up had a bow mounted 24 volt trolling motor three batteries and a 15 gallon fuel tank. Lightly loaded I could only fetch a little more on the top end.
The boat sat well in the water, static trim was great, and the balance of the boat running was right . . . trimmed out at WOT it was a little 'flighty', but not dangerous. Basically it felt like the right power choice for the hull.
To add more wight on the transom for a few more hp's is not in my best interest. Static trim will suffer, the bow will climb higher on take-off (I hate that). Mileage will suffer, and I really don't want to have to move or add weight froward to keep things under control. Most of my time is spent in waters I can't run WOT in anyways.
It would be 'fun' to set up a 15 w/ a 90 (even more fun if you hopped it up a little) . . . but impractical for what I am trying to achieve. The liability of having an illegal boat on the water doesn't sit well with me either.
If it's a fun project for you to play with for a while, go for it. But if it's a daily driver to be used heavily around a lot of people, kids, families etc., and perhaps driven by others . . . I'd be careful. It would suck to be involved in an accident . . . it would suck even more if the accident wasn't your fault but they pinned something on you because of an overpowered boat.
I guess once I saw what runpastthefence did with his 15 . . . all my hot-rodding ideas seemed feeble and were thrown out the window. : )
KEEPER
Tohsgib posted 03-29-2011 01:18 PM ET (US)
Peter many and most will insure an overpowered boat, not just LOL. I think some here are using State Farm, etc. Post it in the GAM and you should get some leads.
pcrussell50 posted 03-29-2011 02:54 PM ET (US)
Thanks Nick. I will. But before I do, are you sure they will insure you for liability? I know they will insure against hull loss. But that's not what I'm worried about. I'm worried about being sued for millions if I either hurt someone, or am accused of it.
-Peter
Tom W Clark posted 03-29-2011 03:11 PM ET (US)
Peter -- Nick is not an insurance agent. Just call an insurance agent and ask. I am sure you will find it can be done.
Russ 13 posted 03-29-2011 07:12 PM ET (US)
I am waiting to see how the poster's boat runs with the 90.
I could not be more pleased with my 90 Yamaha & 15' combo.
If you are close to the rated HP. you should be fine.
Were talking 20 HP, or really 10 to 15 prop HP.
To listen to some of the ideas....you would think that
someone wanted to mount a 150 Hp. engine on a 10 footer.
dgoodhue posted 03-30-2011 07:27 AM ET (US)
[/quote]I never understood how you guys can reach that top speed @ WOT with the 90 Yammie... I GPS clocked my boat at 43MPH with that same 90 HP Yamaha 2 stroke engine.
My 15 is a bit heavier since it was built for the Coast guard, more layers of fiber is probably the cause of this extra weight. I have a 15 pitch Prop with lots of cupping which gives me a max rpm at WOT of 5800[/quote]
As mentioned above, you need a bigger prop. The operating range of Yamaha 90hp 2-stroke is 4500-5500. At 5800 rpm your out of RPM.
The extra fiberglass weighs about 90# on your Alert. I would guess that it would take 1 mph off your top end.
Russ 13 posted 03-30-2011 01:46 PM ET (US)
I agree, I am running a 17P Stilletto - for pulling power for wakeboards & water toys.
My 90 is mounted one hole too low
for added bite, and my top speed is over 48 MPH.
For more speed increase the pitch, raise the A/V plate to above the bottom of the hull & use a good stainless prop.
littlehandegan posted 04-01-2011 05:38 PM ET (US)
Bought a 1990 90 Yamaha. 120 compression across the board.
It is at Dukes Marine near High and Dry boatworks being installed.
Will have reports in the next week or so.

Did I mention there was a 15 SS converted to a CC with a 200 there?
Russ 13 posted 04-01-2011 10:10 PM ET (US)
I think you will be VERY pleased with your Yamaha.
Again 90 HP is plenty for a 15'..my .02c.
A 15' with a 200HP....that's NUTS!!
conch posted 04-02-2011 06:31 AM ET (US)
Littlehandegan - is there any chance of getting some photos of the 15 with the 200hp ?
Thanks and good luck with your repower.
Chuck
Ridge Runner posted 04-03-2011 10:54 AM ET (US)
My 2005 Montauk 170 is over powered (rated at 90hp) with an E-Tec 115HO, I have liability cover with Cigna through BoatUS. The 115hp rated outboard was the highest horse power motor that they would insure with liability coverage. I had to talk to an insurance specialist to get coverage, I believe they ran the Coast Guard formula for maximum horse power, which I think came out to 119hp for my boat.
Babywhaler posted 04-05-2011 09:19 PM ET (US)
My 1988 15' CC has the original 70 HP Merc motor and will
do about 41 MPH at WOT. My Boston Whaler manual states that the boat is rated for 70 HP max and with that HP it is considered a "high performance" boat and further warns that caution should be used in operating the boat due to potential "chine walking condition" at higher speeds. I wouldn't install a higher HP motor myself due to liability/insurance concerns.
Tohsgib posted 04-06-2011 02:20 PM ET (US)
41 is it? Len had a 1988 Merc 70 on his 15 before the 90 E-Tec and he did mid+ 40's. My 1983 70 Merc was a dog but I thought the newer ones(70/80/90) were pretty slippery. My 1989 70 OMC did 48+. My 48SPL did 37.
Peter posted 04-06-2011 03:03 PM ET (US)
My 1987 SuperSport 15 with a 2003 Yamaha 70 mounted all the way down turning an aluminum 13 x 19 Yamaha K series propeller would consistently reach 42.5 MPH per GPS with 1 person. Same boat except with a 1988 48 SPL would get 36 MPH (saw 37 a few times) turning a 11 3/4 x 17 aluminum prop. Would probably do a little better than that if the 48 SPL had power trim. There was a big difference in the way the boat handled above 39 MPH. It gets on that rounded pad. I would not put a 90 on the 15 hull. It doesn't need it.
Babywhaler posted 04-07-2011 02:06 PM ET (US)
I should add that I'm getting about 41 MPH using a 12.75 x 21 MW aluminum prop. It seems to take a little long to get up on plane, I'm not sure why, as I've never used a different prop. My boat may be a little heavier due to the center console and other accesories I have, such as bimini top, electronics box, SS handrail around console, antenna, etc. Its looks like a mini-Montauk.
Russ 13 posted 04-08-2011 12:41 PM ET (US)
BabyWhaler if you are pushing that 21P prop with a 70 HP Merc, that is why your holeshot is shot.
Time to plane...15 min.
Try a 17 pitch stainless, Stiletto.
Hang on, and see what youve been missing.
Babywhaler posted 04-15-2011 02:11 PM ET (US)
I was wondering about that. But that was the prop that came with the boat when it was new. I will try a different prop, but stainless isn't in my budget right now.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: SUPER SPORT 15 Re-power
littlehandegan	posted 03-14-2011 10:50 PM ET (US) What [i]s the consensus [of opinion] on [re-powering a Boston Whaler SUPER SPORT 15 with a] Yamaha 90-HP two-cycle?
jimh	posted 03-14-2011 10:57 PM ET (US) I don't know what the consensus of opinion is going to be, but I will give you my opinion, which is about all any individual is going to be able to provide. If your article elicits enough opinions, you may be able to deduce what the consensus of opinion will be. A Boston Whaler SUPER SPORT 15 with a 90-HP will have an engine that exceeds it maximum horsepower rating of 70-HP. The Yamaha 90-HP two-cycle is a very refined three-cylinder two-cycle engine that has been in production for a long time and has a very good reputation as a light weight motor with compact size. With extra horsepower the 15-foot Boston Whaler hull will go quite fast, and perhaps faster than it was ever intended to go, which may make its stability decrease.
Tom W Clark	posted 03-14-2011 11:09 PM ET (US) littlehandegan -- Welcome to continuousWave.
Russ 13	posted 03-15-2011 03:26 PM ET (US) I own [a SUPER SPORT 15]. When I was reconditioning the boat I looked all over for a Yamaha 70-HP two-cycle, and found a 90-HP instead. The weight of the Yamaha 90-HP is close to the weight of a 70-HP two-cycle, so the boat does not squat in the stern. I have my battery forward under the console. I use [the SUPER SPORT 15] for water sking and wake boarding and the extra power is a help. Top speed is around 50 [MPH?], but it is rarely run at that velocity. The Yamaha two-cycle 90 has been problem free now for five years, and does not burn much fuel. For an experienced boater, [powering the boat with more horsepower than its maximum] is no problem. I would not recommend the extra power for a beginner.
dgoodhue	posted 03-15-2011 05:31 PM ET (US) 90hp on 15' whaler is overpowering the hull. I am getting 47mph with 70hp and a jackplate. Your probably not going to hit 50 mph without a jackplate and that yamaha. Basically you getting diminishing returns for that up. I would guess it have better hole shot and acceleration but a 70 on a 15' isn't lacking to begin with.
jimh	posted 03-16-2011 10:07 AM ET (US) There is a good article on the general topic of using engines with horsepower that exceeds the hull rating in the REFERENCE section. See http://continuouswave.com/whaler/reference/ratedHP.html
littlehandegan	posted 03-16-2011 10:27 AM ET (US) DgoodHue may I ask what kind Brand 70 2 Cycle you are running? Thanks guys!
dgoodhue	posted 03-16-2011 11:41 AM ET (US) I have an older Evinrude (1989). As someone likes fast cars, I would still be tempted to repower it with 90 up ETEC, but I am happy with the performance of the boat right now.
Tohsgib	posted 03-16-2011 11:44 AM ET (US) The 90 Yamaha is not the most powerfull 90 and more like an 80hp hence why the rebuttles. Len had a 90 E-Tec on his 15 with a power jackplate and his BEST was 52.5.
Tom W Clark	posted 03-16-2011 05:57 PM ET (US) The three cylinder, two stroke Yamaha 90 puts out 83.3 HP. I would not put one on a classic 15' Whaler. I've owned quite a few Whalers including a 1979 Striper 15 with a 70 HP Johnson. It was fast. The classic 15' Whaler is the one Whaler hull I would not overpower, the rest can take a little extra easily, but the 15 does just fine with 70.
Russ 13	posted 03-21-2011 05:48 PM ET (US) I agree with Tom, the 70-HP [two-cycle] is a great match for the 15-footer. I got a great deal on a friend[']s Yamaha [90-HP engine], and the extra 13-HP helps with pulling water toys. Both the two-cycle 70 Johnson [and] 90 Yamaha are great lightweight outboards that are proven reliable designs.
littlehandegan	posted 03-26-2011 12:15 AM ET (US) Found a 1997 Yamaha 90. Going to get it next week. Wish me luck!!! Pics to come!
edwardschnog	posted 03-28-2011 07:20 PM ET (US) Hi guys, I never understood how you guys can reach that top speed @ WOT with the 90 Yammie... I GPS clocked my boat at 43MPH with that same 90 HP Yamaha 2 stroke engine. My 15 is a bit heavier since it was built for the Coast guard, more layers of fiber is probably the cause of this extra weight. I have a 15 pitch Prop with lots of cupping which gives me a max rpm at WOT of 5800 By the way I just installed a state of the art Audio system in the boat. Sounds beautiful!! Have a look: copy / paste the below link in your browser. http://s186.photobucket.com/albums/x117/schnog/Alert15/ Cheers and happy boating, Edward
Tohsgib	posted 03-28-2011 07:28 PM ET (US) 15" you have your problem there, should be running at leats a 19".
pcrussell50	posted 03-28-2011 07:33 PM ET (US) If you plan on obtaining liability coverage with an overpowered hull, please post up who you used, or contact me. Near as I can tell, no insurance company will cover you for liability if you are as much as 1 horsepower over the max rating for the hull. I hear there are some case-by-case underwriters, like Lloyds of London, but that is actually the only one I've ever heard of. Id like to know for sure if there are any others. One of my boats is rated for 120hp max, and I have a 135hp on it that is the same size and weight as the 115hp that came on it, so size and weight are not a problem. Just horsepower. With a 15 month old baby girl now, I would really like to have some protection of my assets if my barely overpowered boat were to be involved in a liability case. -Peter
Binkster	posted 03-28-2011 09:39 PM ET (US) I assume your 135 is an OMC outboard. The simple way to address this problems is to get some 115 decals, find a marine boneyard and pop the motor Id plate off a 115. If you have a liability suit, do you think they are going to tear the engine down to see what the specs are? They only do that at the race course/track.
pcrussell50	posted 03-29-2011 01:05 AM ET (US) Binks! Of course it's an OMC 135! :). You know me by now. On a more serious note, I'm afraid that when it comes to saving an insurance payout of tens or hundreds of thousands of dollars, or millions, the price of a professional teardown is peanuts, and money well spent... by the insurance co. The stories abound. Apparently, some law enforcement agencies impound the motors right off the bat, in injury cases. Anyhoo, this should be in a thread of its own. I was just wondering if anybody knew of any insurance companies you could deal straight up with, for a price, besides Lloyd's. -Peter
Keeper	posted 03-29-2011 11:34 AM ET (US) I was on this kick for a while (90 HP Yamaha on a classic 15) . . . but have since changed my mind. My 15 SS was originally powered w a Yamaha 70 2-Stroke. With the addition of a Bobs jack-plate I could consistently achieve 42-43 mph w/ 2 on board. This set-up had a bow mounted 24 volt trolling motor three batteries and a 15 gallon fuel tank. Lightly loaded I could only fetch a little more on the top end. The boat sat well in the water, static trim was great, and the balance of the boat running was right . . . trimmed out at WOT it was a little 'flighty', but not dangerous. Basically it felt like the right power choice for the hull. To add more wight on the transom for a few more hp's is not in my best interest. Static trim will suffer, the bow will climb higher on take-off (I hate that). Mileage will suffer, and I really don't want to have to move or add weight froward to keep things under control. Most of my time is spent in waters I can't run WOT in anyways. It would be 'fun' to set up a 15 w/ a 90 (even more fun if you hopped it up a little) . . . but impractical for what I am trying to achieve. The liability of having an illegal boat on the water doesn't sit well with me either. If it's a fun project for you to play with for a while, go for it. But if it's a daily driver to be used heavily around a lot of people, kids, families etc., and perhaps driven by others . . . I'd be careful. It would suck to be involved in an accident . . . it would suck even more if the accident wasn't your fault but they pinned something on you because of an overpowered boat. I guess once I saw what runpastthefence did with his 15 . . . all my hot-rodding ideas seemed feeble and were thrown out the window. : ) KEEPER
Tohsgib	posted 03-29-2011 01:18 PM ET (US) Peter many and most will insure an overpowered boat, not just LOL. I think some here are using State Farm, etc. Post it in the GAM and you should get some leads.
pcrussell50	posted 03-29-2011 02:54 PM ET (US) Thanks Nick. I will. But before I do, are you sure they will insure you for liability? I know they will insure against hull loss. But that's not what I'm worried about. I'm worried about being sued for millions if I either hurt someone, or am accused of it. -Peter
Tom W Clark	posted 03-29-2011 03:11 PM ET (US) Peter -- Nick is not an insurance agent. Just call an insurance agent and ask. I am sure you will find it can be done.
Russ 13	posted 03-29-2011 07:12 PM ET (US) I am waiting to see how the poster's boat runs with the 90. I could not be more pleased with my 90 Yamaha & 15' combo. If you are close to the rated HP. you should be fine. Were talking 20 HP, or really 10 to 15 prop HP. To listen to some of the ideas....you would think that someone wanted to mount a 150 Hp. engine on a 10 footer.
dgoodhue	posted 03-30-2011 07:27 AM ET (US) [/quote]I never understood how you guys can reach that top speed @ WOT with the 90 Yammie... I GPS clocked my boat at 43MPH with that same 90 HP Yamaha 2 stroke engine. My 15 is a bit heavier since it was built for the Coast guard, more layers of fiber is probably the cause of this extra weight. I have a 15 pitch Prop with lots of cupping which gives me a max rpm at WOT of 5800[/quote] As mentioned above, you need a bigger prop. The operating range of Yamaha 90hp 2-stroke is 4500-5500. At 5800 rpm your out of RPM. The extra fiberglass weighs about 90# on your Alert. I would guess that it would take 1 mph off your top end.
Russ 13	posted 03-30-2011 01:46 PM ET (US) I agree, I am running a 17P Stilletto - for pulling power for wakeboards & water toys. My 90 is mounted one hole too low for added bite, and my top speed is over 48 MPH. For more speed increase the pitch, raise the A/V plate to above the bottom of the hull & use a good stainless prop.
littlehandegan	posted 04-01-2011 05:38 PM ET (US) Bought a 1990 90 Yamaha. 120 compression across the board. It is at Dukes Marine near High and Dry boatworks being installed. Will have reports in the next week or so. Did I mention there was a 15 SS converted to a CC with a 200 there?
Russ 13	posted 04-01-2011 10:10 PM ET (US) I think you will be VERY pleased with your Yamaha. Again 90 HP is plenty for a 15'..my .02c. A 15' with a 200HP....that's NUTS!!
conch	posted 04-02-2011 06:31 AM ET (US) Littlehandegan - is there any chance of getting some photos of the 15 with the 200hp ? Thanks and good luck with your repower. Chuck
Ridge Runner	posted 04-03-2011 10:54 AM ET (US) My 2005 Montauk 170 is over powered (rated at 90hp) with an E-Tec 115HO, I have liability cover with Cigna through BoatUS. The 115hp rated outboard was the highest horse power motor that they would insure with liability coverage. I had to talk to an insurance specialist to get coverage, I believe they ran the Coast Guard formula for maximum horse power, which I think came out to 119hp for my boat.
Babywhaler	posted 04-05-2011 09:19 PM ET (US) My 1988 15' CC has the original 70 HP Merc motor and will do about 41 MPH at WOT. My Boston Whaler manual states that the boat is rated for 70 HP max and with that HP it is considered a "high performance" boat and further warns that caution should be used in operating the boat due to potential "chine walking condition" at higher speeds. I wouldn't install a higher HP motor myself due to liability/insurance concerns.
Tohsgib	posted 04-06-2011 02:20 PM ET (US) 41 is it? Len had a 1988 Merc 70 on his 15 before the 90 E-Tec and he did mid+ 40's. My 1983 70 Merc was a dog but I thought the newer ones(70/80/90) were pretty slippery. My 1989 70 OMC did 48+. My 48SPL did 37.
Peter	posted 04-06-2011 03:03 PM ET (US) My 1987 SuperSport 15 with a 2003 Yamaha 70 mounted all the way down turning an aluminum 13 x 19 Yamaha K series propeller would consistently reach 42.5 MPH per GPS with 1 person. Same boat except with a 1988 48 SPL would get 36 MPH (saw 37 a few times) turning a 11 3/4 x 17 aluminum prop. Would probably do a little better than that if the 48 SPL had power trim. There was a big difference in the way the boat handled above 39 MPH. It gets on that rounded pad. I would not put a 90 on the 15 hull. It doesn't need it.
Babywhaler	posted 04-07-2011 02:06 PM ET (US) I should add that I'm getting about 41 MPH using a 12.75 x 21 MW aluminum prop. It seems to take a little long to get up on plane, I'm not sure why, as I've never used a different prop. My boat may be a little heavier due to the center console and other accesories I have, such as bimini top, electronics box, SS handrail around console, antenna, etc. Its looks like a mini-Montauk.
Russ 13	posted 04-08-2011 12:41 PM ET (US) BabyWhaler if you are pushing that 21P prop with a 70 HP Merc, that is why your holeshot is shot. Time to plane...15 min. Try a 17 pitch stainless, Stiletto. Hang on, and see what youve been missing.
Babywhaler	posted 04-15-2011 02:11 PM ET (US) I was wondering about that. But that was the prop that came with the boat when it was new. I will try a different prop, but stainless isn't in my budget right now.