Trying to get rid of porpoising
 

I have a 28 Pantera with 425hp 454's and number III drives. Right now it has 4 blade 28 pitch props on it. It will only turn those to around 4200 rpm's and it porpoises bad. I was wondering if going to a set of 3 blade 27 pitch props would help it out? I have only used the boat for one weekend so far and the water was smooth so I don't know how bad the porpois is in rougher water.

Sorry they are 26 pitch 4 blades right now.

You have too much prop for one. What shape are the ears on the current props? Does your boat have tabs? If so , at what deployment do they alleviate the porpoise?

I think the 23-24 P will be close. If you can't find a set to test with, BBlades has a nice loan/swap program.

K planes need to be about 3 to stop it and it does not run free at all, you can feel the bow being held down. Which props are better for porpoising 3 or 4 blade? The boat used to have 600 plus hp and ran in the 80's with these drives and props. The guy I bought it from put these 425 hp motors in it. Will weight in the bow help, you think?

What diameter are your props now? If they are under 16 I would say try A larger diameter and down in Pitch.

My 33 fountain had III's on it and I had the same problem. I went up in diameter and down in pitch. I had 26x16.5 and I picked up 8 mph. Felt like a different boat. I also tried some 29 x 17 three blades and they ran the same top end but lost some on the cruise.

I think they are 15 3/8 x 26 now.

So more diameter would increase transom lift, correct? Is that what I need to stop the porpoising, transom lift? Do I need to get 16 or bigger, or would a 15 3/4 3 blade be better than what I have?

Excaliber, did you also have the same rpm problem or were you always able to turn around 5000? How many hp you have?