slow catalina 32

[T. OReilly]

My '98 catalina makes about 5.5 knots at 3200 rpm with my Yanmar GM30 27HP. I have checked it with GPS and my knot meter. The books says, 6 knots @ 2800 rpm and 7Kts at 3200rpm. The bottom is cleaned monthy, Is it the wrong pitch on the stock 3 blade prop? or ?

 

[Eric Lorgus]

Are you SURE of the speed?

Whew! max 5.5 kts on a 32? Ouch!1st, are you SURE you're only doing 5.5? What about under sail, say close-hauled or reaching, in say 15 kts? If you're still only indicating 5.5, then it sounds like your knotmeter is wrong.When checking speed using a GPS, remember that's speed over the ground, while knotmeter is speed through the water. They difference is the current. When trying to calibrate speed, is best to use a triangular course so that the current affect is minimized.But if your knotmeter is correct, it does sound like you may be under-propped. Usually if you're over-propped the engine can never make it up to the top of its operating RPM range, which yours is doing.Good luck.Eric LorgusS/V Explorer

 

[v.a. kinsey]

prop pitch

i have the same engine in my beneteau and had the same problem you describe. i had the yanmar rep look at and test the boat and was told the prop pitch was incorrect for the engine. after re-pitching the prop, i am now able to reach hull speed at 3200rpm. mine is a 3 blade prop and it has now worked well. interesting that the boat dealers or engine people may be placing the wrong pitched prop on this engine.

 

[Steve Dion]

Don't they test these things?

I am not sure that the specs for props on any of these boats are correct. We have a '85 H'31 w/a 2GM20F Yanmar. The specs call for a 15 x 12 2-blade. From what I have be able to determine a 15 x 9 2-blade would be the propper prop for this engine. If you go to a three blade you would probably reduce the pitch by 1 degree or the diameter by 1 inch.

 

[Kevin L. Woody]

Speed

Dear T. Oreilly:Thank you for your letter. In order to confirm if the propeller is producing the correct load on the engine, you will need to take the boat out and give the engine maximum throttles. If the engine is capable of obtaining maximum rated rpm’s you can assume that the propeller is producing the correct loads. You will not see additional speed to the boat by simply adding pitch if the current propeller is correct. You could actually harm the system by changing pitch or diameter. You will need to keep in mind that your propeller is only as efficient as your power plant. If the power plant is being used for other things, like high output alternators, refers and alike your engines capacity at max torque may not be enough to push the vessel at your desired speeds. If however the propeller is not pitched correctly and you can increase your pitch to maximize the load, you will most likely see an increase of speed. I hope this helps.Sincerely, Kevin L. Woody