Little RIB performance.

[corsair.p]

Hi,gentlemen,
We have troubles in testing our 12' RIB,the boat has too big trim angle when starting to planing.And even bad,when it's planing,always have porpoise movement make it very uncomfortable for people.
We are thinking to add one more sprayrails each side(currently only have one) and add an outboard stabilizer on the 50hp OB to test again.
But i am not sure it's gonna work,so if someone can give some idea to solve the problems we will very appriciate.
Or maybe someone can tell me where i can find some technical informations to study?

Thanks

David

[lewisboats]

What horsepower is the boat rated for...50 hp seems way to high.

Steve

[corsair.p]

we just test the boat at it's Maxium Power as calculated from ISO standard.And it's 50hp.

[marshmat]

I believe your problem is that the boat is way overpowered and thus way off balance.
For comparison purposes, Zodiac's 340 DL and 380 DL (11'2" and 12'6" respectively) are rated for no more than 30 hp and 40 hp respectively; Zodiac advises against using more than 30 on either.
A 50 hp outboard weighs about 100-120 kg. There will be a person sitting right in front of it, another 80 kg. So you have as much as 180-200 kg at the transom in a boat that is only twelve feet long. Couple that with a lot of thrust from a propeller down below the bottom and you have a recipe for excessive bowrise.
I have two suggestions before you start gluing strakes and foils onto the thing.
(1) Recheck the maximum power calculations.
(2) Replace the 50 with a 30, move the crew forward a bit, and try again.

[corsair.p]

Thanks,matt.We will try..