Newbie with a speed boat

[andreshs1]

hi all

I just got my first speed boat, a 2003 22ft cuddy with a Mercury 200 EFI, and I have a very stupid question.

on Saturday I took her out for a while and I got worried about the hull strength, basically between 10 and 20 knots when the hull was hitting the water I could see the interior seat moving with every hit, as if the hull was flexing by about 1/2cm when hitting the water. Is this normal? should I apply fiberglass to the interior of the hull below the water line? or this would be of no use?

I used to have a sailing boat and the hull was rock solid but this one I don't know if it is expected.

Thank you for your time

Regards

 

[BruceK]

That does not sound normal no. I'd have the stringers cored to check they haven't rotted out.

 

[mlines]

There is a certain level of flex in GRP boats on fittings etc above the main floor pan. Not sure if you are referring to 0.5 cm or "1 to 2" cm. I would have though that 0.5cm on an interior seat was probably normal. I have a wakeboard tower fitted to mine which is rigid stainless steel and you can see this moving slightly when the water is not smooth, implying that one side of the boat is flexing with respect to the other side. The floor that the seat is attached to is probable Plywood

I would mind betting that if you had looked closely at your sailing boat that it was flexing, just more slowly than the speedboat.

 

[andreshs1]

Hi guys

thanks you both for the feedback.

it might not have been 1 or 2 cm, but definitely much more movement than I am used to, but you might be right and it could be normal.

I will most definitely will be doing research on the stringers and checking them out on the boat next weekend.

Regards

 

[BruceK]

If you core a stringer(s) be sure to fill it with cut glass strand and resin PB mix and cap it with some coarse weave if it turns out alright. i.e. dont leave the stringer exposed or leave it in a weakened state.

 

[andreshs1]

thanks Bruce for the reminder!
I'll update further after the weekend checks

Regards

 

[mlines]

If it helps here is the view inside ours at speed. You can see things moving as the boat flexes

 

[Rooster]

Can see the fender splashing around in the wake ;-)

 

[mlines]

Yes, we were doing short sharp experience trips with very frequent stops so we got rapidly tired of "Fenders out, Fenders in"

Martin

 

[BruceK]

OK, that's not 10 to 20 knots. At the speed you were doing yes some flex will be expected. But that chair is not a good reference point. Keep an eye on the stringers but I wouldn't rush to core them just yet as I didn't see anything that I'd have thought alarming.

 

[andreshs1]

do you have a video of what happens inside the cabin so I can compare.

Regards

 

[BruceK]

Not really. I have this as the closest but doesn't show much except a fender coming loose. But that cuddy was a bit old school i.e not so much skinned between stringers and bulkheads but layed up unusually thickly throughout with a weight to match.

You were pushing hard in your vid. The stresses at that speed are enormous and some flex should be expected. What threw me was the 10 to 20 knots. At that speed you shouldn't expect noticable flex unless you were slamming. Even in this vid below there was no flex that I could discern and the boat is significantly bigger again.

http://www.youtube.com/watch?v=A0L00nQdlnw

 

[mlines]

OK, that's not 10 to 20 knots. At the speed you were doing yes some flex will be expected. But that chair is not a good reference point. Keep an eye on the stringers but I wouldn't rush to core them just yet as I didn't see anything that I'd have thought alarming.

I think you have mixed up posters here. I was showing the original poster (Andreshs1) that boats flex, that video is of my boat, not his, and yes it is doing around 30knots. The rotating seat is not a good reference but the video shows that there is some flex to be expected.

 

[BruceK]

I think you have mixed up posters here. I was showing the original poster (Andreshs1) that boats flex, that video is of my boat, not his, and yes it is doing around 30knots. The rotating seat is not a good reference but the video shows that there is some flex to be expected.

Indeed, I have. Whoops.