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Author Topic:   SPORT 15, Yamaha 90-HP

offshore27miami posted 06-03-2011 02:48 PM ET (US)
I just finished my CC conversion on my 15 and replaced my tired Evinrude 70-HP with a Yamaha 90-HP two-cycle outboard engine. Give me your idea for a propeller. The current propeller is a 13.25 x 17 and is revving way too high. RPM will hit 6,200 to 6,300 if I let it, but of course I won't.
Tom W Clark posted 06-03-2011 02:53 PM ET (US)
I'd start with a 13-1/4" x 19" Stiletto Advantage 4.25 or a 13-1/4" x 20" Yamaha Performance Series three blade. They are essentially the same propeller.
Be sure the motor is mounted as high as it can go.
offshore27miami posted 06-03-2011 03:42 PM ET (US)
Thanks Tom, I appreciate the input. [There is] room to go up two more holes, I was worried that [the propeller] may cavitate if I did. As it is now I can tell [the engine mounting height on the transom] needs to go up. I will give [raising the engine mounting height on the transom as high as possible] a try.
Rob
whalersailer posted 03-31-2012 08:57 PM ET (US)
Hi Rob and Tom--Sorry to revive an old topic, but I'm wondering what propeller ended up working for this setup. I just acquired an 1981 Sport 15 with an 2007 Yamaha 90 on it, and it has the same OEM Yamaha propeller as Rob stated he had in his first post. My new 15 also performs identically to what Rob stated initially.
Any feedback you can offer as to the correct prop for this combination would be greatly appreciated. Thanks!
-WS
Teak Oil posted 03-31-2012 09:12 PM ET (US)
Well, since you have the same motor and the same boat as the original poster, how about using the same props Tom suggested above?
You are going to need a 19" or 20" prop for sure. Also make sure the motor is mounted at least two holes up.
whalersailer posted 03-31-2012 09:34 PM ET (US)
Hi Teak,
I was just looking for feedback as to whether one those 2 props ended up making the final cut.
I have had great luck with Tom's advice and Stiletto props in the past. Unless there is any feedback to the contrary, I will go with the Stiletto Tom recommended below.
Thanks,
-WS
Teak Oil posted 03-31-2012 09:51 PM ET (US)
After I read my post I didn't like the tone of the way I worded that post, but we can't edit anything lol.
If you do a search for 15 AND Yamaha you should get a lot of data on this combo, as it is a very popular setup since that Yammie 90 is so light. There are quite a few guys running this setup
Russ 13 posted 04-01-2012 12:38 AM ET (US)
The Stiletto 19 pitch works great for me--same engine on a 1985 15-footer. Good hole-shot, good top end.
Perry posted 04-01-2012 03:39 AM ET (US)
What is the top speed of a 15 CC with a Yamaha 90 two-cycle outboard engine, by the way?
Peter posted 04-01-2012 07:37 AM ET (US)
Expected top speed is 48-MPH based on Yamaha 70 being able to push the 15 Sport to 42 to 43 MPH. That's with the motor mounted all the way down.
pcrussell50 posted 04-02-2012 02:18 AM ET (US)
Those performance predictions sound about right. For reference, I have a light weight (hand laid), 16 foot v-hull that does 52-MPH--did 55 once when all the stars lined up--with a 22" prop and an old 135-HP Evinrude (or 110'ish modern day equivalent). So 48-MPH with a 20" prop and 90-HP sounds about right to my shade tree speed guesstimator.
-Peter
dgoodhue posted 04-02-2012 03:44 PM ET (US)
I have seen reports of 48/49 with the 90 yamaha mounted on the transom. It should be able to do over 50 with a jackplate since I can hit 48mph with a 2 stroke 70 Evinrude and a jackplate on my 15'
Tohsgib posted 04-06-2012 12:13 PM ET (US)
Don't count on the 90 being much more faster than the old 6k rpm 70 OMC's. The 70 was a strong engine and the 90 is weak. I was running a 20" SS prop on my 70 mounted all the way up on the transom and could always hit 47/48 on the GPS with bottom paint.
whalersailer posted 04-06-2012 01:39 PM ET (US)
Nick,
I wonder what makes the Yamaha 90 "weak" compared to the "strong" OMC 70. Given that the Yamaha has roughly 25% more displacement (1140cc vs. 912cc), I would expect that generation of roughly 28.5% more horsepower would be reasonable.
I received the new Stiletto yesterday and will be trying it out this evening. It will be interesting to see how it performs.
Cheers,
-WS

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Author	Topic: SPORT 15, Yamaha 90-HP
offshore27miami	posted 06-03-2011 02:48 PM ET (US) I just finished my CC conversion on my 15 and replaced my tired Evinrude 70-HP with a Yamaha 90-HP two-cycle outboard engine. Give me your idea for a propeller. The current propeller is a 13.25 x 17 and is revving way too high. RPM will hit 6,200 to 6,300 if I let it, but of course I won't.
Tom W Clark	posted 06-03-2011 02:53 PM ET (US) I'd start with a 13-1/4" x 19" Stiletto Advantage 4.25 or a 13-1/4" x 20" Yamaha Performance Series three blade. They are essentially the same propeller. Be sure the motor is mounted as high as it can go.
offshore27miami	posted 06-03-2011 03:42 PM ET (US) Thanks Tom, I appreciate the input. [There is] room to go up two more holes, I was worried that [the propeller] may cavitate if I did. As it is now I can tell [the engine mounting height on the transom] needs to go up. I will give [raising the engine mounting height on the transom as high as possible] a try. Rob
whalersailer	posted 03-31-2012 08:57 PM ET (US) Hi Rob and Tom--Sorry to revive an old topic, but I'm wondering what propeller ended up working for this setup. I just acquired an 1981 Sport 15 with an 2007 Yamaha 90 on it, and it has the same OEM Yamaha propeller as Rob stated he had in his first post. My new 15 also performs identically to what Rob stated initially. Any feedback you can offer as to the correct prop for this combination would be greatly appreciated. Thanks! -WS
Teak Oil	posted 03-31-2012 09:12 PM ET (US) Well, since you have the same motor and the same boat as the original poster, how about using the same props Tom suggested above? You are going to need a 19" or 20" prop for sure. Also make sure the motor is mounted at least two holes up.
whalersailer	posted 03-31-2012 09:34 PM ET (US) Hi Teak, I was just looking for feedback as to whether one those 2 props ended up making the final cut. I have had great luck with Tom's advice and Stiletto props in the past. Unless there is any feedback to the contrary, I will go with the Stiletto Tom recommended below. Thanks, -WS
Teak Oil	posted 03-31-2012 09:51 PM ET (US) After I read my post I didn't like the tone of the way I worded that post, but we can't edit anything lol. If you do a search for 15 AND Yamaha you should get a lot of data on this combo, as it is a very popular setup since that Yammie 90 is so light. There are quite a few guys running this setup
Russ 13	posted 04-01-2012 12:38 AM ET (US) The Stiletto 19 pitch works great for me--same engine on a 1985 15-footer. Good hole-shot, good top end.
Perry	posted 04-01-2012 03:39 AM ET (US) What is the top speed of a 15 CC with a Yamaha 90 two-cycle outboard engine, by the way?
Peter	posted 04-01-2012 07:37 AM ET (US) Expected top speed is 48-MPH based on Yamaha 70 being able to push the 15 Sport to 42 to 43 MPH. That's with the motor mounted all the way down.
pcrussell50	posted 04-02-2012 02:18 AM ET (US) Those performance predictions sound about right. For reference, I have a light weight (hand laid), 16 foot v-hull that does 52-MPH--did 55 once when all the stars lined up--with a 22" prop and an old 135-HP Evinrude (or 110'ish modern day equivalent). So 48-MPH with a 20" prop and 90-HP sounds about right to my shade tree speed guesstimator. -Peter
dgoodhue	posted 04-02-2012 03:44 PM ET (US) I have seen reports of 48/49 with the 90 yamaha mounted on the transom. It should be able to do over 50 with a jackplate since I can hit 48mph with a 2 stroke 70 Evinrude and a jackplate on my 15'
Tohsgib	posted 04-06-2012 12:13 PM ET (US) Don't count on the 90 being much more faster than the old 6k rpm 70 OMC's. The 70 was a strong engine and the 90 is weak. I was running a 20" SS prop on my 70 mounted all the way up on the transom and could always hit 47/48 on the GPS with bottom paint.
whalersailer	posted 04-06-2012 01:39 PM ET (US) Nick, I wonder what makes the Yamaha 90 "weak" compared to the "strong" OMC 70. Given that the Yamaha has roughly 25% more displacement (1140cc vs. 912cc), I would expect that generation of roughly 28.5% more horsepower would be reasonable. I received the new Stiletto yesterday and will be trying it out this evening. It will be interesting to see how it performs. Cheers, -WS