1998 Checkmate 251 Convincer
 

Friend just bought anniversary addition boat with a Merc 500 HP. The boat has a crazy porpoise at 30-50 MPH. Is this common? What should he be looking for to fix the problem. Using a Hydro 4 blade PX. The only way to get it better is to use tabs and negative trim but that isn't enough to make it smooth. I had this same boat and it didn't handle like this. Mine was also a 253 version. Help please.
Randy

What prop did you use with yours? The P5X is a bow lifting prop. Is that what Checkmates like?

Padraig

The 251 likes to porpoise under 40. On mine I didn't use any trim until 35. Even at 35 just a little trim. On smooth water id trim it up a bit, feel the speed pick up and you could feel it get on top of the water, but the smallest ripple would start a porpoise session. Once I was over 40, you could trim more and more with speed.
I ran both a Hydromotive 4 blade (Quad IV) and a Bravo 4 blade. I liked the Bravo a little better because of the mid range drivability, but got my top speed with the Hydromotive. I don't think I had the extreme porpoise you are describing with my props though.
As stated above, if that's a bow lift prop, not good on the 251.

My buddy has a 251 convincer, his hops bad without a bunch of trim tab. These boats need the big trim tabs. They are a fast hull and built well.

Does the 251 have a pad???

Padraig

yes

Might be better off with a hydromotive P5 instead of the P5X. Talk to Tom at Hydromotive. Good guy and knowledgeable.


Padraig

When I had mine, they only had 3 blades LOL

Was he running the merc big tabs or short? HE did a little testing yesterday playing with the tabs but has to drop them almost all the way down and full negative trim under 40-50 on calm water. Are these boats known for having hooks in the bottom? When you get it up to speed and start to raise the tabs and drive it gets better.
Thanks for the advice

I was just going to say, throw a Mirage + on it.

I had a 1999 251. Had a hydromotive on it. Had XZ Drive with 1" short. Had to use a little tab at the 40-50 range to settle. Might have been a 27 if I recall, That was almost 25 years ago. So Not sure about the prop size.