Perkins Single screw problem

[SeaKoon]

I recently bought 34' boat that has a 240 Perkins with a 1.5:1 Borg Warner tran. The transmission is shot and I'm looking to replace it, it seems that the boat is a little over propped?, (20 inch wheel) she only tacs to 2500 rpm and is rated for 2600. I'm new to this diesel inboard thing, so I'm a little confused.<br /><br />Should I replace the tranny with a 2:1, and then see if I could possibly step up the prop? <br /><br />This boat is really heavy and is underpowered, I plan to replace the setup with a 450 Cummins, but in the mean time, I was wondering if anyone had an opinion on how to handle the situation.<br /><br />I see that this engine has different ratings from 2100 rpm to 2800. Does that mean I can load her up with as big a wheel as I want?, like a 24 inch square? <br /><br />Help please. <br /><br />Thanks

 

[DJ]

Re: Perkins Single screw problem

Trip,<br /><br />Going from a 1.5 to 2.0 is a big jump.<br /><br />The rpm range you have sounds good to me. Diesels are not particularly happy with more rpm. They do not mind a little lugging, which I do not think you're doing.<br /><br />If you can, see if you can get a hold of the hp/torque chart for your Perkins. You'll probably find you're just about right.<br /><br />By the way, I'm not a big fan of Cummins power in marine, or any other application for that matter. I belive the 450 is based on the "C" series block of 8.3 liters.<br /><br />In automotive (truck) applications that engine is only certified to 300 hp, and that's for emergency vehicles only.<br /><br />I think I would shop around a little more for power.<br /><br />My favorites are: Caterpillar, Yanmar and Volvo.

 

[SeaKoon]

Re: Perkins Single screw problem

Thanks for the help. <br /><br />The point of a bigger prop and a 2:1 would be to try and get more speed. She weights 15,000lbs and runs 12kts at 2200 rpm. I have 5 inches of prop clearance now so I could possible step up from the 20 incher that is on there now. I have no idea on pitch. I'm clueless about how all of this stuff fits together.<br /><br />Thanks

 

[DJ]

Re: Perkins Single screw problem

Tripp,<br /><br />As I mentioned, I think you are right in the middle of your "sweet spot" as far as rpm goes. <br /><br />The only way you are going to get more speed is to increase pitch, not diameter.<br /><br />Yes, you could go to a 2:00/1 trans but then you would be experimenting with props, etc.<br /><br />If you are going to repower anyway, I think I'd just fix what I have and worry about all those set up gyrations when you do repower. <br /><br />Any marine engine sales house should be able to set your new engine/trans/prop package up just about perfectly on the first try.

 

[SeaKoon]

Re: Perkins Single screw problem

Thanks. I'll probably just look for another 1.5:1 VD.<br /><br />Thanks

 

[steelespike]

Re: Perkins Single screw problem

If your hull is a displacement hull it is probably close to its designed hull speed now.<br /> More horsepower may only help the fuel dock.

 

[SeaKoon]

Re: Perkins Single screw problem

I would call this hull semi-displacement. With the right setup these boats will rise up and scoot.

 

[magster65]

Re: Perkins Single screw problem

What kind of boat is it?

 

[SeaKoon]

Re: Perkins Single screw problem

A 34' Crusader. Built by grant fiberglass in Miami in 1977.