Hull hitting Cockpit - Normal / How to fix?

William Carwile

New Member
Hello,

I did a brief search and couldn't find anything so hopefully i'm not missing something obvious...

I just bought an old 1960's sunfish in pretty good shape except when i took it out on the water I noticed that when i hit waves a certain way it sounds like (and feels like) the bottom of the hull is hitting the bottom of the cockpit.... Overall the boat is pretty stiff--especially topside.

Is this normal? If not, is there a way to fix this? I already have an inspection port on the starboard side of the centerboard.

Looking forward to your thoughts and comments.

Thanks!
 
Soon, I hope to videotape the flexing of my (older, racer) hull through my "Ultimate Inspection Port"—located in the forward cockpit bulkhead. I suspect well-used hulls gradually become weaker through various "insults".

I've also seen circularly-arrayed "spider cracks" in the cockpit floor—directly opposite a corresponding circular "hit" in the hull's bottom. (Possibly from "over-sprung" trailer transport). A recently donated (to me) Sunfish has an actual fracture :eek: in the cockpit floor, again, directly opposite a hit in the bottom.

I wouldn't bother repairing this, although one member has looked into adding "splines" inside.

Hitting "normal" lake wave action wasn't a problem in the 1960's, but powerboat/"surfboat" wakes have become plentiful in recent decades.

.
 
The cockpit tub only contacts the hull at the outer edges. The factory was using glue pads somewhere along the line to counter the flexing. Also the hull was stiffer when new. It becomes a problem plaining-out when you hear the hull go 'braatttttt.. .' Fortunately the fix is as easy as putting some expanding foam between the tub and hull. Push on the hull under the cockpit and you'll probably find one side stiff and the other side flexing. I used Great Stuff foam in a can which someone mentioned absorbs water and is not a good choice. Worked for me but probably better to go with decent two-part foam.
 
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I am with Webfoot. The makers of Great Stuff also make a version that is black and designed for landscaping. They say it does not absorb water, so it could be a good choice.
 
I've used great stuff for these purposes. Works fine and doesn't initially absorb water. Sitting in it for a couple months...eh. drain the boat after sailing if it leaks, I say.
 
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Awesome, this coming week I am going to inject some foam and am looking forward to not having to worry about the hull hitting anymore!

Thanks for all your advice/opinions!
 
watch using TOO much expanding foam so your hull doesn't end up looking like a sausage!
 
Sounds like a good explanation. I in fact am doing the same thing on my puffer where the blocks popped loose on either side of the cockpit. I drilled 3" holes in the bottom about every 8 inckes...fore to aft. There's plenty of expansion room and the holes are kinda a "safety valve"...not to mention good 360 access. I used a whole can on each side...running about 4 ft in length and a about a 1-2 inch void...top and bottom of the block sides. No hull swelling and very minimal out the drilled holes. Bottom NICE AND RIDGED now! No flexing what so ever. Perfect solution. Good luck with yours.
 
Btw...I glassed a layer of woven roving and a layer of cloth+mat in that area too. Hull is super thin and this extra fiberglassing helped with stiffness while adding very minimal weight. BTW...the string in the pics, is holding the foam block in place so I could shoot foam on both bottom and top sides, not to mention the vertical sides too.
 

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Oh....one other item I did in addition to the foam...I tabbed the hull to the cockpit wall sides, while I had access . Just a layer of mat and roving, draped thru the holes, attached to the cockpit walls and the bottom of the boat. Now if the hull flexs, the cockpit will too! (Not now!). But the Puffer cockpit has seating and is much more substantial than the Sunfish, with double right angles, provided by the seating.
 
I was gonna drill a small hole in the cockpit at the center of the flexing them just shoot like 3 seconds of foam in there.

That's the way I did it because I already had holes in the cockpit floor. All the extra foam expanded horizontally.
You should be able to do it by reaching in through an inspection port. Most older Sunfish have cracks in the
tub because it is unsupported. Kids jump up and down on it when the boat is beached. Likewise the keel
has no internal support and gets crunched at the low point just behind the dagger-board.
 
I am with Webfoot. The makers of Great Stuff also make a version that is black and designed for landscaping. They say it does not absorb water, so it could be a good choice.
There is also a version of Great Stuff designed for wet areas, called "Great Stuff Pond and Stone". I've not used it, but, from the description, it sounds like it has the right properties.
 

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