Hull flex

[P323]

I have developed major hull flex. Yesterday I came off a large wave and hit flat, this was the loudest bang I have heard on this boat. After that it seemed to shake much worse than before. Today was even worse, coming off even small 1' wave made the boat shake from bow to stern. I could feel the cockpit shake and even see the deck flex a little. It feels like something structurally has come loose, everything looks to be intact and no leaks.
The boat is a 1975, so it's got some age on it.

So... any suggestions?
Thanks,
Paul

 

[Wayne]

I have developed major hull flex. Yesterday I came off a large wave and hit flat, this was the loudest bang I have heard on this boat. After that it seemed to shake much worse

You may have broken loose the styrofoam emergency buoyancy blocks that also serve to reinforce hull stiffness. You'll need to install an inspection port (deck plate) to get a look inside and evaluate further.

In the menu bar at the top of this page click on Sunfish KB & FAQ and follow these paths to get an overview of the next step:

Knowledge Base

• 
  
  [*]General Information​
  [*]Construction​

Knowledge Base

• 
  
  [*]Repairs and Upgrades​
  [*]Inspection Ports [PDF]​

More detailed information and complete illustrated repair guides can be found at these web sites...

Wind Line Sails - Sunfish and small boat repair pages.
http://www.windline.net/how_to.htm
http://www.windline.net/project3.htm

Sunfish Sailor
http://groups.yahoo.com/group/sunfish_sailor
Look in the file library under repairs, ask if you need assistance with details.

 

[P323]

I have an inspection port, I can see the two foam pieces by the centerboard well. One of the blocks looks like it could be loose... it doesn't feel loose when I push on them. The blocks my be compressed, loosing contact with the hull/deck, thus loosing stiffness.

Paul

 

[Wayne]

The blocks may be compressed, loosing contact with the hull/deck, thus loosing stiffness.

That, I would think, you'd be able to see clearly..., and should show movement when shoved on.

Get a work light in there and start moving and shaking everything...

• Mast tube
• Daggerboard trunk
• Cockpit tub
• Every block you can poke a stick at
• ...even look at the bottom's internal fiberglass fabric for splits resembling a broken piece of plywood.

. . . one last thought, my Catfish had this happen -
You may have had a hull/deck separation along an abnormally wide area.

Do a leak test for starters.

 

[Webfoot]

If something is shaking it's likely the hull bottom is 'Oil-Canning.' Turn the boat over and press on the hull bottom. There should be no flexing. Press on each side of the hull under the tub.

If the deck can flex the hull has lost structural integrity, you could have popped the seams between the hull and the deck, this would lead to the hull no longer being ridged. You'll have to remove the metal trim strips to inspect the seams, try doing a pressure test first.

Stick a light-bulb in the hull and turn out the lights. You'll see every crack, flaw and problem in the fiberglass.

 

[P323]

Yep, one whole side of the bottom is soft. I have looked in the front section of the hull and it appears the foam blocks are loose. The hull deck joint appears to be ok. I have lost the hull rigidity on that side. Looks like I have a winter project.

Paul