Twin engine boat porposing problem
 

I'm looking at a twin big block 30 foot V bottom boat that the current owner says porposes at 85. I don't want to mention the brand of boat, but would like to hear reasons and possible solutions to the handling problem. The boat has standard Bravo drives with nose cones. The factory had the boat to 93 mph when testing it when it was built.

Drives trimmed to high.

Porpoises or chine-walks?

He said porpose. The owner has owned a few high performance boats, so I suppose he understands trim. I think the set up is the issue.

How old a boat? Sometimes when they sit on a trailer or lift too long the bottoms will "hook" or go a little concave. As speeds go up and you start running on the rear-most surfaces, the hook tends to want to push the nose down as the trimmed motors want to push the nose up, so you get this cyclical action called a porpoise. If you can, take an 8' level or machined straight edge and check the last 8-10' and see what you have. It's easy, free, and at least you can eliminate that in 5 minutes.

Mine's a chine-walk issue, tab has helped a lot but it's still a handfull.

Assuming its a straight bottom V, lab the props, put in a little cup. They will carry the bow better and the porpoise will go away.

It is a straight V bottom. Most of this model boat are single engine configurations and are very stable with high horsepower and 100+ mph. Not too many were built with twins, thats why I asked the question in a general manner, rather than specific Make/Model. How does drive placement come into play? As in, should they be high or low?

Caused by the boat not being able to carry the bow at that speed. It may be correctable with some prop tweaks or a prop style change.

If you mention hull others may know. Could he a known issue but tough to help with not knowing what it is.

The boat has full weekender cabin.

I did not want to say that it is a Checkmate 283 Convincor. I thought I would hear that all checkmates do the "Checkmate hop" which is mostly 251/253's and not get any good suggestions.

never really heard of that at that speed, but sounds like the props are wrong...maybe has hydromotives which are a stern lifting prop vs bravo 1's which are bow lifting ??? would think prop/trim changes would take care of that..

as Kieth, Griff and ez have stated, try changing your prop set up. Get with a prop guy as things change with a nose cone also.

Keytime has a twin bbc 283 Checkmate. I think with 454 or 502 mags.

Before touching props or spending money, i think i would experiment with switching the props rotation.

My straight bottom boat porpoised when... 1. I ran the drives spinning in, 2. no hydraulic steering, 3. Hydrmotives. 3 blade Mirages changed the attitude the best. Also Spinelli's. I have a plethora of Props Spinelli's, Bravo1's, and Mirages if you need to try before you buy.

Thanks Rookie. I sent the owner a message regarding what props are on it and what direction they spin. His reply:

They are 26p labbed Mach 1s. Small pitch due to the 1.36 drives. They spin out.

1 forget about the old owner. What he has to tell you may send you in the wrong direction. 2 What props are on it?

The props are Mach props. I think they are called "Stern Drivers" A lot of Checkmates came with these, they were round ear props. I think Reggie bought the company and shut it down after a while.

ON, Mach props were made by Second Effort/ Gary Garbrecht. Gary ran Mercury Racing for a lot of years.

Sounds like some Bravo props with a proper lab would fix this.

I'd try a set of Bravo1's before buying. My boat handles good with Bravo1's, but it runs to flat and never loosens up. Kind of rides hard up front in rougher water. The 3 Blades really soften up the ride and the bow rides soft and flightly, total different riding boat. They don't look as cool as my 4 blade Spinelli's though. :(