Gulfstar 37 3 blade standard prop

[svsamira]

Wondering if anyone out their might have a Gulfstar 37 with a 4-108 who has changed to a 3 blade prop? If so, what size did you go with and pitch?

Thanks,

Dan

[jlogan]

My GS 37 has a 15x12 3 blade. I think it actually should be a 15x10 to let the engine work more efficiently. The PO never used the engine above 1700 rpm. At that engine speed, the engine is quiet, uses little fuel, and makes only around 4.8kts, but it is pleasant to use that way. However if you want to actually get somewhere using the perkins, it would be better if you could use 2400-2500 rpm as a cruise rpm. Most Perkins in GS 37s will be overloaded and overheat at that rpm with a 15x12x3. Gulfstar evidently propped the boats orginally to only use a 2000 rpm cruise...at that rpm, the perkins only puts out about 16-18 hp, so it won't move a 20000lb boat very fast.

The specs on the perkins say 50 hp at 4000 rpm...but if you read all you can about the 4.108, you should probably prop the boat so it maxes speed at 3000-3100 rpm and cruise at no more than 2500 rpm. Even then, you have to keep your cooling system in top shape...regular cleaning of the heat exchanger and recondition/replace water pump">raw water pump reguarly. Most authorities consider the Perkins a 25-30 hp continuous use engine...it should be propped accordingly. If you join Boatdiesel.com, you can use their prop calculator. I've used it with several diesel boats, and it works well in most instances.

[SkiprJohn]

Aloha,
Long between posts on this one but I have to mention that you need to know your transmission gear ratio as well in order to determine what the proper prop size should be. Do a search on this forum and you'll find all kinds of help.
Kind Regards,
JohnL

[jlogan]

Good point about the Gear ratio....most, if not all of the factory GS37 installs seem to have a 2.10 Borg Warner connected to the 43.108. My answers above assume the 2.10:1 ratio...

[geoleo]

Originally Posted by jlogan

My GS 37 has a 15x12 3 blade. I think it actually should be a 15x10 to let the engine work more efficiently. The PO never used the engine above 1700 rpm. At that engine speed, the engine is quiet, uses little fuel, and makes only around 4.8kts, but it is pleasant to use that way. However if you want to actually get somewhere using the perkins, it would be better if you could use 2400-2500 rpm as a cruise rpm. Most Perkins in GS 37s will be overloaded and overheat at that rpm with a 15x12x3. Gulfstar evidently propped the boats orginally to only use a 2000 rpm cruise...at that rpm, the perkins only puts out about 16-18 hp, so it won't move a 20000lb boat very fast.

The specs on the perkins say 50 hp at 4000 rpm...but if you read all you can about the 4.108, you should probably prop the boat so it maxes speed at 3000-3100 rpm and cruise at no more than 2500 rpm. Even then, you have to keep your cooling system in top shape...regular cleaning of the heat exchanger and recondition/replace raw water pump reguarly. Most authorities consider the Perkins a 25-30 hp continuous use engine...it should be propped accordingly. If you join Boatdiesel.com, you can use their prop calculator. I've used it with several diesel boats, and it works well in most instances.

I recently thew away the 2 blade sailprop on my GS37 and installed a 3 blade 15x14--while very good motorsailing it max out at 2650 rpm motoring which cheats me out of about 8 hp _ I should have gone to the factory standard size of 15x12 which would max out right at the 3000 (39HP) WHICH IS THE RECCOMDENDED CONTINUOUS USE RPM.The 4000 rpm 50hp is good only for 15 minutes!!!!!

[Dennis1679]

4years later I'm wondering how your prop change worked I have a 2 blade on my GS 37 and eas thinking of changing it