Flexing of the cabin

Bryant · Posted: Sat Jan 24, 2009 4:04 am Post subject: Flexing of the cabin

I posted this message but it didn't seem to come up.
I have a 1999 C Dory 22 and the cabin seems to flex alot in moderate seas. Does anyone else have this problem?

matt_unique · Posted: Sat Jan 24, 2009 8:28 am Post subject: Re: Flexing of the cabin

tsturm · Posted: Sat Jan 24, 2009 10:40 am Post subject: Re: Flexing of the cabin

thataway · Posted: Sat Jan 24, 2009 12:27 pm Post subject:

We need more information: As above, how do you know it is flexing? Where do you notice any changes or movement? Is the floor flexing? Is the cabin top flexing or are the sides flexing?

Agree--we need to know what seas you are referring to.

The Boat should not flex. There have been some boats (very few) which have flexed. But your boat is way out of warranty. There are some things which can be done diagnostically, as well as to repair the boat is there is a problem.

Bryant · Posted: Sat Jan 24, 2009 2:20 pm Post subject: cabin flexing

I have noticed that even in 1 to 2 foot chop the sides of the cabin between the deck and cabin top visibly vibrate and flex as the boat hits the bottom of the wave, similiar to the way a 1/4" piece of plywood would do if you held it on each side and shook it back and forth.

Larry H · Posted: Sat Jan 24, 2009 2:51 pm Post subject:

On my 1991 22 Cruiser, the cabin sides flexed near the galley counter top. I had to move the counter top away from the cabin side about 1/8 to 1/4 in to stop the squeaky sound.

I owned the boat for 16 years and the flexing never got worse and never caused any cracks or other problems.

thataway · Posted: Sat Jan 24, 2009 4:57 pm Post subject:

It sounds to me if the boat is pounding. Do you have trim tabs and a Permatrim? If you do,you can put the bow down--and decrease/stop the pounding.

How fast are you going?

The cabin sides are solid fiberglass, and not very thick (maybe 1/4" max)--and if you are pounding the boat, may be appearing to flex. The deck and cabin roof are cored and thus much stiffer.

There are ways to stiffen up the cabin sides--but this involves putting stiffners in place. These could be wood, or fiberglass/foam. But if you are pounding, you may be abusing the boat.

Adeline · Posted: Sat Jan 24, 2009 5:10 pm Post subject:

thataway · Posted: Sat Jan 24, 2009 5:46 pm Post subject:

Why not seal the sides of the cabin to the galley with 5200? I have done this on several boats. Another option would be to tab glass to the cabin sides and the underside of the galley counter with epoxy.

Tortuga · Posted: Sat Jan 24, 2009 7:32 pm Post subject:

My 1994 CD 22 cruiser will flex like that if I really drive it hard -- it's the pounding -- my fix was to trim the bow or slow down.

I believe it is the same on all the cruisers -- if you approach the boat from the outside as it lies on the trailer and gently pound between the aft and middle window with the bottom of a closed fist you can get some pretty good vibrations and flexing. I actually went down to the dealer to pound the new boats to see if this was unique to my boat when I first discovered it. The new boats flex exactly the same way.

Interestingly, the port side flexes less -- but on my boat I have a teak grab rail between the aft and middle window which I assume is stiffening the boat up in that area.

My conclusion (after pounding every C-Dory I could find in Ventura Harbor) was the flexing was God's way of telling me to slow down. I never found any resulting cracks or loosening of hardware/ windows etc.

Matt

T.R. Bauer · Posted: Sat Jan 24, 2009 7:43 pm Post subject:

Everything we make has some flex. Buildings flex, airplanes, bridges, huge ocean ships, and even our C-Dory boats. My 93 does exactly what you guys are describing.

But, the "fix" is very simple as all you have to do is slow down to the speed where it doesn't do it anymore. Our boats do not run through sloppy chop at high speeds very well at all. And once you get that through your head and adjust your actions by reducing your speed, this flexing will become a distant memory. I have no idea what happens if you just ignore it and let the pounding continue. But my intuition tells me it just isn't good.

Others have suggested adding stiffeners and you can. It probably will help. However, the engineers that design things take into account the natural oscillations that ocurr while cars, boats, trains, and planes have while in operation and adding stiffeners may add a problem somewhere else.

Unless you have a serious hull problem, and I doubt that you do, I would just slow down. If you can't just slow down, I think you maybe you should be looking at a deep-v boat as they deal with the chop much better.

C-Hawk · Posted: Sat Jan 24, 2009 8:49 pm Post subject:

Are you getting any rush of air out of the v-berth when you pound?
I hope not.

Tortuga · Posted: Sun Jan 25, 2009 12:24 am Post subject:

I haven't noticed anything like that on Tortuga. Is that part of what you experienced on Fishtales?

T.R. Bauer · Posted: Sun Jan 25, 2009 1:10 pm Post subject:

thataway · Posted: Sun Jan 25, 2009 4:35 pm Post subject:

As I recollect there was a piece of wood glassed into the hull on the port side for the table suoports.

It would be interesting to see if the newest CD 22 (molded interiors) have as much movement.

I had to retab some bulkheads etc on the 25. I suspect it had been driven at too much speed into chop.

I'm not sure about how much "engineering" goes into this flex type of issue on the small boats. There are laminate schedules which are acceptable for boats this size, and most builders adhere to these. Where-ever the cut cross section of the CD 22 is, would tell us how thick the laminate is. It does not need much strength at this point. Another question is how the aluminum frame window fits in this equation, if any?

Agree, slow down. This is understanding the C Dory boats.