1979 4-108, Borg-Warner 71 combo in a Gulfstar

[Idratherbesailing]

I'm in the process of purchasing a 1979 37 foot Gulfstar aft cockpit sloop. The present owner says he very rarely runs over 1700-1800 rpm, and gets 5 knots or so that way....I took it out for sea trial the other day and indeed, it seems to be overloaded when you take it up past 2100 rpm or so...the documentation with the boat says it has a 15x12 3 blade prop.....my question is, does anyone else have a 37 with this combination, and what rpm do you cruise? Unfortunately, I do not know the exact rated rpm of this model 4-108 nor the transmisson ratio. Just trying to see if this is any other owners experience with this model.It would seem the rated rpm of the 4-108 should be either 3000 or 4000 rpm, and in my experience, a motor overpropped as much as this one seems to be would not be good...anyone got any comments/experience with this?...

 

[rvolsen2]

Same boat

I have the exact same boat but it is a 1977. The engine and prop are the same as installed on my boat and the transmission ratio is 2.1 to 1. The 4-108 engine has an intermitent rating of 4000 rpm, a 1 hr. rating of 3000 rpm and a continuous duty rating of 2800 rpm. If the bottom is clean, I can cruise at 2300 rpm and achieve 5.5 knots of boat speed in calm water. As other conditions (bottom not clean, wind, waves, etc.) degrade, the speed decreases proportionally. This is my experience and hope it helps.

 

[Idratherbesailing]

Thanks for the response on the Gulfstar 37

Thank you for your response...you confirmed what I thought...It is interesting that the boat is "overpropped" from the factory...I am more used to dealing with diesel powerboats in which you prop the engine to reach rated rpm, which in the case of the perkins 4-108, I assume is 50 at 4000, then cruise the engine at 70-80% of that number. the 2800 number you mention is 70% of 4000, so that is about right. I still think the 15x12x3 prop is a bit too much for this boat, but the 2:1 transmission limits your options...if this boat had the 2.57:1 version of the Velvet Drive transmission, the 15x12 would be about right, or a 9" pitch on a 15" prop would be about right...not very efficient, though, at the slow speeds a sailboat moves..thanks for your input...

 

[Richard]

Gulfstar 37

I purchased a 1979 Gulfstar 37 in November '05. During the process I came across an old condition report on a prototype Gulfstar 37 from 1976. It lists the 50 HP Perkins 4-108 with a 2.1:1 reduction gear as standard with a 16x14 2 blade prop. My boat was repowered with a 50 HP Volva Penta and transmission with a 16x15 3 blade prop. Sorry I can't recall the gear ratio at the moment. Rated at 3000 RPM I cruise at 2500 RPM and maintain 6.5 kts. You can make 7 kts. at 2800 RPM. In the past year I have averaged .6-.7 GPH fuel consumption. Hope this helps.

 

[Georgetheleo@hotmail.com]

Me too!

I recently bought a 1979 Gulfstar 37 with the original engine and prop-2 blade I cruise at 5.9kn @2500 and 6.9 @2800. seems to burn .75 gph @2500.