Prop choice

[dieselboy]

So i have a Cal 29 which the last owner repowerd with a Volvo 2002 Diesel.
I am sure it still has the 3 blade prop from the A-4. Being the a4 prop was designed for rpm not torque. What prop should i be using? Everyone i ask just scratches their head " or something else" and says... " No clue, then walks off..
Any suggestions?

The reason i ask is plain that the boat in heavy stuff just seems to loose ground while the engine never seems to load up. As if the engine wants a prop with a higher pitch.

Thanks in advance for your time.

[jrd22]

You'll have to figure out what prop you have on now, the diameter and pitch are usually stamped into the prop. A prop shop should be able to calculate which prop should work with your boat and engine.

[dieselboy]

Originally Posted by jrd22

You'll have to figure out what prop you have on now, the diameter and pitch are usually stamped into the prop. A prop shop should be able to calculate which prop should work with your boat and engine.

Actually i did. Clueless was what i got. While im sure they know how to sell a prop and to repair one. The repower prop selection left them in the dark.
But it was a good idea, maybe i just need a better prop shop. lol

[Faster]

Originally Posted by dieselboy

...., maybe i just need a better prop shop. lol

I'd say so!

There are several on line prop vendors that will give you that data as long as you have your displacement numbers, boat type and engine/gear combo.

Here's one... input your numbers and you should get some idea.. I'd still check this with a sailboat prop outfit.

http://vicprop.com/displacement_size.php

[CalebD]

So, Cal 28' weighs about 8000# (4 tons)
Volvo Penta 2002 is an 18HP diesel
Prop is probably an Indigo A4 optimized prop which is a 3 blade 10" x 7.4" pitch Boat Seem Underpowered?
Other factors to consider: your prop is not in an aperture and thus should get good bite out of the prop flukes.
If you feel under powered (what rpms do you run your engine at?) it is not so much the pitch (~7") as the diameter that I'd question as being inadequate.

I know that this is not entirely comparable but folks with an Atomic 4 in their Catalina 30's use a 2 blade 12"x6" (or 7") prop and report that it works fine.
I use a 13" x 8" on my 7200# boat with our A4 but our prop is in an aperture between the keel and rudder.
The wider diameter of the prop gives it much more surface area to push against the water. The pitch will always be in the 6" - 8" range most likely.
Try to find a used 12"x6" (or7") 2 blade prop and try it out.
If you want to stay with a 3 blade prop I'm not sure what dimensions would work best for you as I'm more familiar with 2 blade fixed props. You can have a good prop shop take your existing 3 blade 10" prop and they can add material to the flukes to make it 11" or 12". They can also modify the pitch if you want.
First you need to find a good prop shop though.

[JimsCAL]

If its the prop from the A4, its almost certainly too small and with too fine a pitch. Most A4s are direct drive while most diesels have a 2:1 or higher gear ratio. That means the correct prop will be larger in diameter and with a higher pitch. You need to know the engine model number and reduction ratio to get a proper selection. Take the info to a local prop shop or go to one of the online propeller suppliers and they should have no trouble giving you a recommendation.

[jsaronson]

You need to be sure a bigger prop will not be too close to the hull. On myP28 they put in a shaft that was 1 inch longer when it was repowered with a diesel to accommodate the bigger prop.