The restoration of a 1988 [SUPER SPORT 13] is finished, and the boat now has a 2004 9.9-HP BIGFOOT engine with electric start, a battery, remote steering, and a 6-gallon fuel tank. The original four-cylinder 40-HP two-stroke-power-cycle engine has been removed; it was too much power for an 11-year-old to operate.
The 9.9-HP BIGFOOT propeller is 10-3/8 x 9.5-pitch. The maximum engine speed is now too low, only 2,400-RPM, and boat speed is only 9.4-MPH. That was with with myself (220-lbs) and my son (104-lbs). With just my son the boat accelerated to 13.2-MPH, which almost calculates to a propeller SLIP = 0.
The current propeller looks like a big, flat, pusher. I believe a lot of [engine speed] is being lost.
The engine propeller shaft has 10 splines, which limits propeller choices.. I plan to get a propeller with smaller diameter.
[Discussion about carburetor changes to increase power are now in their own thread.--jimh]
Readers: give me any thoughts you have [about the proposed change in propeller diameter]?
I am out of my comfort zone in choosing a propeller for this small engine.
SUPER SPORT 13 with Bigfoot 9.9-HP / 15hp
SUPER SPORT 13 with Bigfoot 9.9-HP / 15hp
Last edited by v12mac on Sat Jun 08, 2019 5:14 pm, edited 1 time in total.
Re: SUPER SPORT 13 with 9.9-HP
Merc spec is 5500 wot max
Yep the 3" gearcase on the bigfoot is working against us. So is all the additional weight. But it's the motor I have.
The prop looks like 3 table spoons. Looks like a tugboat prop.
It is only 9.5" of pitch but I think it might be out of wack.
Solas makes a few props for this motor but they start at 10' of pitch.
More data Friday.
Yep the 3" gearcase on the bigfoot is working against us. So is all the additional weight. But it's the motor I have.
The prop looks like 3 table spoons. Looks like a tugboat prop.
It is only 9.5" of pitch but I think it might be out of wack.
Solas makes a few props for this motor but they start at 10' of pitch.
More data Friday.
Re: SUPER SPORT 13 with 9.9-HP
Is the Mercury Bigfoot the 4 stroke model? If it is, I don't think you'll see much better performance since 4 stroke motors lack the down low torque of a 2 stroke to get the boat on plane and the engine to the upper RPM range where it makes power. I can tell you the difference between a 4 stroke 9.9 Mercury and a 2 stroke Yamaha 9.9 is night and day since in our cruising group I've had the chance to try many RIB dingies with various motors over the years. I can also tell you for certain that the Yamaha 2 stroke 9.9 is a simple carb change to change it to 15hp and several of my friends went this route with great results.
My suggestion would be to locate a good running 15hp 2 stroke for the kids since the 13' Whaler will run better and not be a speed demon with 15hp.
At that age, my kids had a 40 Johnson, bit I put a throttle limiter on the linkage, but my son was ultra careful and probably didn't need it.
D-
My suggestion would be to locate a good running 15hp 2 stroke for the kids since the 13' Whaler will run better and not be a speed demon with 15hp.
At that age, my kids had a 40 Johnson, bit I put a throttle limiter on the linkage, but my son was ultra careful and probably didn't need it.
D-
Re: SUPER SPORT 13 with 9.9-HP
v12mac wrote:The [propeller]...looks...like a tugboat [propeller].
I don't know that I can recognize a "tugboat propeller" on sight. Most tugboats have very deep draft and their propellers are far too deep in the water to be seen. And I don't know that I have ever seen a a tugboat on a graving dock with its propeller visible.
Most "tugboats" today use much more sophisticated drive systems than a single propeller on a straight shaft. I am not sure there is a genre for "tugboat propellers" now, if there ever was one.
Three-bladed propellers are by far the most common propellers, as they seem to provide the best all-round performance.
Re: SUPER SPORT 13 with 9.9-HP
[The 9.9-HP engine under discussion] is the larger 323-cc or 19.7-cubic-inch block made by Yamaha. I had to go with a 9.9-HP engine for local laws. (A 40-HP four-cylinder two-stroke-power-cycle outboard engine is now in my garage.)
By tug boat prop I meant prop is designed not for speed but to push (like a slow trolling auxiliary engine) and bite in reverse. My frustration is that at 9.5-pitch and still being under recommended RPM there aren't any propeller options on the market that I can find. The 3-inch gear case and 10-spline shaft are the challenges.
I actually have a container full of propellers at work, but none are for under 200-HP applications.
By tug boat prop I meant prop is designed not for speed but to push (like a slow trolling auxiliary engine) and bite in reverse. My frustration is that at 9.5-pitch and still being under recommended RPM there aren't any propeller options on the market that I can find. The 3-inch gear case and 10-spline shaft are the challenges.
I actually have a container full of propellers at work, but none are for under 200-HP applications.
Re: SUPER SPORT 13 with 9.9-HP
A propeller pitched at 9.5-inches will have a rather flat look to the blades.
According to Boston Whaler literature (c.1998) a 9-HP engine should get a 13-footer on plane with a minimal load and a bare, dry hull. I think that is what was achieved with your boat with just your son in the boat and the 13-MPH boat speed.
According to Boston Whaler literature (c.1998) a 9-HP engine should get a 13-footer on plane with a minimal load and a bare, dry hull. I think that is what was achieved with your boat with just your son in the boat and the 13-MPH boat speed.
Re: SUPER SPORT 13 with 9.9-HP
More data:
Engine: stock 9.9 Mercury Bigfoot; 2.42:1 gear ratio;
Propeller: 9.5-pitch propeller
Speed are in statute miles-per-hour and are speed-over-ground from GPS receiver
WITH STOCK CARBURETOR
Crew: 220-lbs Dad and 95-lbs kid
MPH = 9.4
RPM = unspecified; tachometer unreliable
As above but
Crew: kid alone
MPH = 13.2
WITH CHANGE OF CARBURETOR (to one from the 15-HP model; otherwise same conditions)
Crew: Dad and kid
MPH = 16.3
RPM = limited by Rev-limiter.
Crew: kid alone
MPH= 19.4
RPM = limited by Rev-limiter
[Extensively re-organized data to a more readable tabular presentation. Reduced size of giant screen captures to show only relevant information--jimh]
Engine: stock 9.9 Mercury Bigfoot; 2.42:1 gear ratio;
Propeller: 9.5-pitch propeller
Speed are in statute miles-per-hour and are speed-over-ground from GPS receiver
WITH STOCK CARBURETOR
Crew: 220-lbs Dad and 95-lbs kid
MPH = 9.4
RPM = unspecified; tachometer unreliable
As above but
Crew: kid alone
MPH = 13.2
WITH CHANGE OF CARBURETOR (to one from the 15-HP model; otherwise same conditions)
Crew: Dad and kid
MPH = 16.3
RPM = limited by Rev-limiter.
Crew: kid alone
MPH= 19.4
RPM = limited by Rev-limiter
[Extensively re-organized data to a more readable tabular presentation. Reduced size of giant screen captures to show only relevant information--jimh]
Re: SUPER SPORT 13 with 9.9-HP
In conclusion and support of prior suggestions:
- if you want to run a 9.9-HP get a light, pull-start, two-stroke engine and a can of diet coke.
- avoid the heavier super sport
- BIGFOOT gear case robs speed
- buy the 15hp
Re: SUPER SPORT 13 with 9.9-HP
I ordered a Solas three-blade with 11-pitch. I'll post data about performance after it arrives.
Re: SUPER SPORT 13 with 9.9-HP
It looks faster already, just from the picture.
Re: SUPER SPORT 13 with 9.9-HP
When you are 11 years old, this boat is plenty fast. I'm having a great time squeezing every bit out of this rig with my son.
New prop Solas 11-pitch; same test conditions as before
Dad and son
MPH = 21.4
RPM = 5400
Son only
MPH = 22.2
RPM = 5700
New prop Solas 11-pitch; same test conditions as before
Dad and son
MPH = 21.4
RPM = 5400
Son only
MPH = 22.2
RPM = 5700
Re: SUPER SPORT 13 with Bigfoot 9.9-HP / 15hp
Wow! That is great for a 15 hp on a 13-footer. Good pick on the prop.
Re: SUPER SPORT 13 with Bigfoot 9.9-HP / 15hp
I'm super happy with the performance, ran 20-MPH most of the day and did a bit of fishing.
The prop selection was 1/2 voodoo and as I shocked my son. had to use math--he liked that line.
Also l've had some great advice from lots of good folks around the web.
The prop selection was 1/2 voodoo and as I shocked my son. had to use math--he liked that line.
Also l've had some great advice from lots of good folks around the web.