Porpoising dinghy

[Pete7]

Originally Posted by poiu

Thanks. I wonder if there are other people with experiences like that?

I did wonder if I could jack the lower bolts back a bit to put more nose down thrust to try to improve things.

"Jacking the lower bolts" outwards will raise the bow!

You can add wedges with the fat bit at the top so that the upper bolts are further from the transom to gain some additional trim in. and help bring the bow down. The theory is then the longer water length helps stabilize the boat.

However, you still have a short stubby boat with a big engine on it so its never gong to be great. I would try the Dole fins or one of the other makes first.

[darylat8750]

A Dole fin was helpful on my boat. I would first try to get them to take it back for a different model first but a dole fin would be worth a try if they won't.

[poiu]

Originally Posted by Pete7

"Jacking the lower bolts" outwards will raise the bow!

You can add wedges with the fat bit at the top so that the upper bolts are further from the transom to gain some additional trim in. and help bring the bow down. The theory is then the longer water length helps stabilize the boat.

However, you still have a short stubby boat with a big engine on it so its never gong to be great. I would try the Dole fins or one of the other makes first.

Yes, of course, I meant the top bolts.

I think it is more than just the boat length and power. I had a 1 foot longer dinghy before so 8% longer , but with a 20hp bigger engine, so 66% bigger, relatively a much worse situation yet I had no porpoising at all unless I was abusive with the nose up trim.

Noted re the fins.

[Privilege]

I second the idea of fins. You are correct that they are designed to get you up on a plane quicker, but they do that by keeping the bow down. It might be a $50 fix to your problem. It made the world of difference on my 11'.

[HopCar]

I’ve cured porpoising on two boats with trim tabs. On one boat I installed powered tabs and on the other fixed tabs. I think it was a matter of getting more lift aft to compensate for heavy engines.

The fixed tabs ended up just extending the bottom further aft. They had no angle to them.

They also made it much easier to get on a plane without moving a lot of weight forward.

I imagine engine fins like the Dolfin would accomplish the same thing.