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.