hull speed under power

[Mike4116]

Hi Peggie:A friend of mine has a 1992 Catalina 28. The boat has a diesel engine which produces 23 HP at 2800 RPM. The transmission is rated at a 2:1 ratio. The trouble is that under flat water conditions the boat will only move along at 4 Kts at 3000RPM. With any kind of head wind at all the boat will be working hard to make 2 Kts. She sails easily at 7 Kts in winds of 12 Kts or more. My question is: If he improves the pitch on the prop will the boat make hull speed under most conditions or is the Catalina 28 a slow boat under power no matter what?He, my friend has written the Catalina owners web site and can't seem to get an answer to the question I have asked above. He has been in contact with a prop maker and they want to know the engine type, transmission type and what his current prop is in use.It seems intuitive to me that for a small sacrifice in fuel economy a steeper pitch on his prop will improve boat speed.Thanks,Mike

 

[Mike4116]

Hi Peggie:A friend of mine has a 1992 Catalina 28. The boat has a diesel engine which produces 23 HP at 2800 RPM. The transmission is rated at a 2:1 ratio. The trouble is that under flat water conditions the boat will only move along at 4 Kts at 3000RPM. With any kind of head wind at all the boat will be working hard to make 2 Kts. She sails easily at 7 Kts in winds of 12 Kts or more. My question is: If he improves the pitch on the prop will the boat make hull speed under most conditions or is the Catalina 28 a slow boat under power no matter what?He, my friend has written the Catalina owners web site and can't seem to get an answer to the question I have asked above. He has been in contact with a prop maker and they want to know the engine type, transmission type and what his current prop is in use.It seems intuitive to me that for a small sacrifice in fuel economy a steeper pitch on his prop will improve boat speed.Thanks,Mike

 

[larry w]

Your right,

an increase in pitch will result in more speed and lower engine RPMs; there's alot of mathmatical formulae that will prove all that and the more data you can provide the prop guy, the better he can match prop to hull/engine.

 

[larry w]

Your right,

an increase in pitch will result in more speed and lower engine RPMs; there's alot of mathmatical formulae that will prove all that and the more data you can provide the prop guy, the better he can match prop to hull/engine.

 

[Terry Cox]

Hi Mike, our 1989 H28 had a two blade ...

15X12RH fixed prop powered by an 18 HP 2GM. We typically ran the engine at 2,800 RPM while cruising, which resulted in a seven knot speed through the water. A quality prop shop can tell you what changes they can make that might improve your boat speed.Terry

 

[Chris Burti]

Has a diver checked the prop?

A fouled prop will produce these symptoms as well.

 

[sailaway78]

I agree with Chris

The first thing you need to do is check the prop. After Katrina, my boat had sat for quite some time without being used. First time I tried to take it out, it would barely move, forward or reverse, at full throttle. Checked the prop, and it had some barnacles on it. A quick cleaning with a putty knife and away we went. It doesn't take a lot to make a prop almost useless.

 

[Peggie Hall HeadMistress]

Why are you asking me, Mike?

This forum--and my field of expertise--is devoted to sanitation systems (toilets, holding tanks, plumbing, etc) and related issues. I don't do engines, even crappy ones.