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Author Topic:   Prop pitch-classic 15' w/ 50hp

bc posted 09-18-2004 09:32 AM ET (US)
Running a 15' with a Evinrude 48spl (1990). The dealer gave me both a 13 & 17 pitch props to try (both alum). The 17 pitch (11.5 X 17) obtained 32mph @ 5100 rpm-ok acceleration. I then tried the 13 pitch (12.5 X 13) and reached 31 mph @ 5800-great hole shot. mph checked with gps. I played around with the motor's trip, but it didn't really help much. Boat had two adults, full tank 12 gal and batteries..etc.
I would like to try a 15 pitch....Is anybody here using this same setup with a 15 pitch?...and if so what kind of performace are you getting.
Thank you,
bc
Peter posted 09-18-2004 10:55 AM ET (US)
I used to have the same engine on my 15 SuperSport. My 48 was turning the 11 3/4 x 17P aluminum propeller. Maximum speed with only me and a tank of gas was consistently about 36.5 MPH as measured by GPS in many directions. I had no tachometer but to achieve 36.5 MPH, the motor had to be turning at least 5800 RPM.
The 17P prop should be the right one.

jimh posted 09-20-2004 07:42 AM ET (US)
See this article:
http://continuouswave.com/whaler/reference/prop2.html
for results on a SPORT-15 with a 50-HP engine. Top speed was 33 MPH with a 15-inch propeller.
bc posted 09-20-2004 12:49 PM ET (US)
Jim, Great information...Do you know the boat's load when tested? Persons, batteries...etc...
bc
Peter posted 09-20-2004 01:56 PM ET (US)
Typical boat, motor, fuel, batteries, gear and single person load is in the 1100 to 1250 lb range for the 15 classic hull.
Theoretically, with 50 HP on the transom trimmed correctly with no lifted or offset mounting such as with a jackplate, a 15 classic typically loaded as noted above should be able to go about 37 MPH using a hull constant of 180 (bottom painted). With 70 HP, it should be able to go 43.5 MPH. My results using the same 1987 15 SuperSport powered once by the 48 SPL (50 HP) and now by a 70 HP Yamaha are remarakably consistent with that prediction.
In Jim's example, his motor ran the 15 inch propeller through a 2:1 gear case. Your motor runs its propeller through a 2.42:1 gear case meaning that every 2.42 turns of the flywheel, instead of just 2, make for one turn of the propeller. Thus, for any given engine crankcase speed, your motor will be turning the propeller more slowly as compared to his motor. To make up for that, you need to turn a propeller with a greater pitch. That's why I think the 17P propeller is the correct one if the motor is working properly and should produce a speed in the 35 to 37 MPH range.
Acceleration with the 48 SPL turning the 17P propeller was pretty good.
bc posted 09-20-2004 06:14 PM ET (US)
Peter, Thanks for the replies. Kind of funny, I started out with the 70hp (omc-with T&T) and then down-sized to the 48spl. My 70 was never "right" and only achieved 38 mph with a 19" SS. At our Tennessee rendezvous event, I rode/drove in a 15ss powered by the yamaha 70. That was a great combo. The 70 yam. seems to have a smaller profile than the 70 omc. I like the way this boat sits in the water with the 50hp....the splash well scuppers are rarely under the water now. I like the low profile of the omc 2cyl. fifty. Thanks again.
bc
AW posted 10-06-2004 09:00 PM ET (US)
For reference I had 1980 2 cyl 60 which is the same physical size as the 48. It turned a 19" aluminul prop at (up to) 6400 rpm. I'd guess that the 17" prop is right with a 48 or 50.

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Author	Topic: Prop pitch-classic 15' w/ 50hp
bc	posted 09-18-2004 09:32 AM ET (US) Running a 15' with a Evinrude 48spl (1990). The dealer gave me both a 13 & 17 pitch props to try (both alum). The 17 pitch (11.5 X 17) obtained 32mph @ 5100 rpm-ok acceleration. I then tried the 13 pitch (12.5 X 13) and reached 31 mph @ 5800-great hole shot. mph checked with gps. I played around with the motor's trip, but it didn't really help much. Boat had two adults, full tank 12 gal and batteries..etc. I would like to try a 15 pitch....Is anybody here using this same setup with a 15 pitch?...and if so what kind of performace are you getting. Thank you, bc
Peter	posted 09-18-2004 10:55 AM ET (US) I used to have the same engine on my 15 SuperSport. My 48 was turning the 11 3/4 x 17P aluminum propeller. Maximum speed with only me and a tank of gas was consistently about 36.5 MPH as measured by GPS in many directions. I had no tachometer but to achieve 36.5 MPH, the motor had to be turning at least 5800 RPM. The 17P prop should be the right one.
jimh	posted 09-20-2004 07:42 AM ET (US) See this article: http://continuouswave.com/whaler/reference/prop2.html for results on a SPORT-15 with a 50-HP engine. Top speed was 33 MPH with a 15-inch propeller.
bc	posted 09-20-2004 12:49 PM ET (US) Jim, Great information...Do you know the boat's load when tested? Persons, batteries...etc... bc
Peter	posted 09-20-2004 01:56 PM ET (US) Typical boat, motor, fuel, batteries, gear and single person load is in the 1100 to 1250 lb range for the 15 classic hull. Theoretically, with 50 HP on the transom trimmed correctly with no lifted or offset mounting such as with a jackplate, a 15 classic typically loaded as noted above should be able to go about 37 MPH using a hull constant of 180 (bottom painted). With 70 HP, it should be able to go 43.5 MPH. My results using the same 1987 15 SuperSport powered once by the 48 SPL (50 HP) and now by a 70 HP Yamaha are remarakably consistent with that prediction. In Jim's example, his motor ran the 15 inch propeller through a 2:1 gear case. Your motor runs its propeller through a 2.42:1 gear case meaning that every 2.42 turns of the flywheel, instead of just 2, make for one turn of the propeller. Thus, for any given engine crankcase speed, your motor will be turning the propeller more slowly as compared to his motor. To make up for that, you need to turn a propeller with a greater pitch. That's why I think the 17P propeller is the correct one if the motor is working properly and should produce a speed in the 35 to 37 MPH range. Acceleration with the 48 SPL turning the 17P propeller was pretty good.
bc	posted 09-20-2004 06:14 PM ET (US) Peter, Thanks for the replies. Kind of funny, I started out with the 70hp (omc-with T&T) and then down-sized to the 48spl. My 70 was never "right" and only achieved 38 mph with a 19" SS. At our Tennessee rendezvous event, I rode/drove in a 15ss powered by the yamaha 70. That was a great combo. The 70 yam. seems to have a smaller profile than the 70 omc. I like the way this boat sits in the water with the 50hp....the splash well scuppers are rarely under the water now. I like the low profile of the omc 2cyl. fifty. Thanks again. bc
AW	posted 10-06-2004 09:00 PM ET (US) For reference I had 1980 2 cyl 60 which is the same physical size as the 48. It turned a 19" aluminul prop at (up to) 6400 rpm. I'd guess that the 17" prop is right with a 48 or 50.