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Author Topic:   90hp Yamaha on a 15 what size prop???

pimpinawhaler posted 01-17-2004 05:15 PM ET (US)
I just bought a 2004 90hp yamaha I would like to know what the best prop would be for top end. I dont need much out the hole power but would like to have a high top end speed so what prop side do I use Thanks Taylor
Moe posted 01-17-2004 07:41 PM ET (US)
Using the resources in the continuousWave Reference section:
With a hull factor of 180, the performance formula says 90HP will move 1100 lbs at 51.5 mph.
With 2.0:1 gearing, the prop calculator says that to reach 5500 rpm at 51.5 mph, with the 6% slip typical at WOT, would require a 21" pitch propellor.
These calculators, and 6% slip, seem pretty accurate for those using the 70HP (2.33:1) on the 15' getting 43 mph at 5900 rpm.
--
Moe
Perry posted 01-17-2004 08:14 PM ET (US)
2004 Yamaha 90 2 stroke or 4 stroke? I hope it is a 2 stroke because a 4 stroke 90 will be HEAVY on that 15 footer.
lhg posted 01-17-2004 08:24 PM ET (US)
What does your handle mean?
pimpinawhaler posted 01-17-2004 11:26 PM ET (US)
the motor is a 2 stroke
Peter posted 01-18-2004 06:33 AM ET (US)
Just to add a piece of data to Moe's post here -- in the 70 HP speed reference the propeller is an aluminum 13 x 19.
Moe posted 01-18-2004 10:33 AM ET (US)
Thanks, Peter, I meant to include that.
--
Moe
Peter posted 01-18-2004 10:59 AM ET (US)
No problem Moe. Question for you: have you estimated what the hull factor is for the 150 based on your boat's performance?
Moe posted 01-18-2004 11:36 AM ET (US)
Peter, I responded via email so as not to hijack this thread.
--
Moe
pimpinawhaler posted 01-18-2004 08:08 PM ET (US)
thanks you guys .....Taylor
Clark Roberts posted 01-19-2004 08:15 AM ET (US)
If boat is classic 15'3" hull then hull factor (K) of 200 might be appropriate since there will be virtually NO hull in the water; If boat is a new 150 then K=180 may be best. Only some accurate testing will determine and remember to keep K constant (no pun intended) for engine comparisons and predictions. The classic 15 can obtain some truely amazing performance figures when set-up (height on transom, prop pitch, trim out, load balance, etc) is optomized and an engine that actually produces 90hp will be a handfull!Happy Whalin'... Clark... Spruce Creek Navy
Bigshot posted 01-21-2004 03:18 PM ET (US)
I had the 17" on my 17' and she would hit 54-5500. Normally I would say a 21" on a 15' but that 90hp is more like an 80hp in all reality so somewhere between a 19 & 21" is where you need to be. I would go with a 19" and you can double cupp it to make a 20" or repitch to a 21". It is easier to add pitch then to remove it. I HIGHLY recommend a manula jackplate.
Peter posted 01-21-2004 06:19 PM ET (US)
I agree with Bigs' suggestion on starting with the 19 inch pitch. I come up with a predicted top speed of about 48.5 with standard mounting (~80HP and ~1200 lbs). A 19 inch stainless prop with an inch's worth of cupping should just about do it. If you get fancy with a jack plate and optimize the motor's height then that motor might be able to turn a 21. However, I imagine that will be one squirly boat. Hold on tight. ;)
Bigshot posted 01-22-2004 11:16 AM ET (US)
My 17 did about 41.5 so 48+ sounds about right being 300+ lighter. Scary thing is my 70hp Johnson would do that on a good day. I used to swing a 20" SS at 5900 and best speed was 48.6 on the GPS but that could have been with a current etc. My boat would hit 46-47 any given day though. I may have had a really good 70 as well being I did have bottom paint.

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Author	Topic: 90hp Yamaha on a 15 what size prop???
pimpinawhaler	posted 01-17-2004 05:15 PM ET (US) I just bought a 2004 90hp yamaha I would like to know what the best prop would be for top end. I dont need much out the hole power but would like to have a high top end speed so what prop side do I use Thanks Taylor
Moe	posted 01-17-2004 07:41 PM ET (US) Using the resources in the continuousWave Reference section: With a hull factor of 180, the performance formula says 90HP will move 1100 lbs at 51.5 mph. With 2.0:1 gearing, the prop calculator says that to reach 5500 rpm at 51.5 mph, with the 6% slip typical at WOT, would require a 21" pitch propellor. These calculators, and 6% slip, seem pretty accurate for those using the 70HP (2.33:1) on the 15' getting 43 mph at 5900 rpm. -- Moe
Perry	posted 01-17-2004 08:14 PM ET (US) 2004 Yamaha 90 2 stroke or 4 stroke? I hope it is a 2 stroke because a 4 stroke 90 will be HEAVY on that 15 footer.
lhg	posted 01-17-2004 08:24 PM ET (US) What does your handle mean?
pimpinawhaler	posted 01-17-2004 11:26 PM ET (US) the motor is a 2 stroke
Peter	posted 01-18-2004 06:33 AM ET (US) Just to add a piece of data to Moe's post here -- in the 70 HP speed reference the propeller is an aluminum 13 x 19.
Moe	posted 01-18-2004 10:33 AM ET (US) Thanks, Peter, I meant to include that. -- Moe
Peter	posted 01-18-2004 10:59 AM ET (US) No problem Moe. Question for you: have you estimated what the hull factor is for the 150 based on your boat's performance?
Moe	posted 01-18-2004 11:36 AM ET (US) Peter, I responded via email so as not to hijack this thread. -- Moe
pimpinawhaler	posted 01-18-2004 08:08 PM ET (US) thanks you guys .....Taylor
Clark Roberts	posted 01-19-2004 08:15 AM ET (US) If boat is classic 15'3" hull then hull factor (K) of 200 might be appropriate since there will be virtually NO hull in the water; If boat is a new 150 then K=180 may be best. Only some accurate testing will determine and remember to keep K constant (no pun intended) for engine comparisons and predictions. The classic 15 can obtain some truely amazing performance figures when set-up (height on transom, prop pitch, trim out, load balance, etc) is optomized and an engine that actually produces 90hp will be a handfull!Happy Whalin'... Clark... Spruce Creek Navy
Bigshot	posted 01-21-2004 03:18 PM ET (US) I had the 17" on my 17' and she would hit 54-5500. Normally I would say a 21" on a 15' but that 90hp is more like an 80hp in all reality so somewhere between a 19 & 21" is where you need to be. I would go with a 19" and you can double cupp it to make a 20" or repitch to a 21". It is easier to add pitch then to remove it. I HIGHLY recommend a manula jackplate.
Peter	posted 01-21-2004 06:19 PM ET (US) I agree with Bigs' suggestion on starting with the 19 inch pitch. I come up with a predicted top speed of about 48.5 with standard mounting (~80HP and ~1200 lbs). A 19 inch stainless prop with an inch's worth of cupping should just about do it. If you get fancy with a jack plate and optimize the motor's height then that motor might be able to turn a 21. However, I imagine that will be one squirly boat. Hold on tight. ;)
Bigshot	posted 01-22-2004 11:16 AM ET (US) My 17 did about 41.5 so 48+ sounds about right being 300+ lighter. Scary thing is my 70hp Johnson would do that on a good day. I used to swing a 20" SS at 5900 and best speed was 48.6 on the GPS but that could have been with a current etc. My boat would hit 46-47 any given day though. I may have had a really good 70 as well being I did have bottom paint.