Jeanneau Structure

[Marc555]

We have a 43' Jeanneau with wet plywood core in 2 floors over the aft half of the keel. I know that some builders use plywood as a form and then laminate as if the core was non-structural. I'm wondering if someone can help us determine how thick the laminate should be if the core is non structural? Perhaps we can add more laminate if needed. They appear to be about 1/4-5/16" thick. There are no signs of any structural issues around the tabbing, hull, etc.

Appreciate any ideas.
Thanks,

 

[bajansailor]

Welcome to the Forum Marc.

Have you taken any photos of these floors that you can post on here?
Some photos would help a lot.

Re the thickness of 1/4" - 5/16", is this the total thickness (including the laminate on each side) or the estimated thickness of the plywood core?

That is good news re how there no obvious signs of stress cracks around the tabbing .

Re how the core in these two floors is wet, did you measure this with a moisture meter, or are the skins flexing, or........?

 

[kapnD]

Adding laminate to existing structures will most assuredly beef them up, but if there’s water in them I’d try to dry them first.
Vacuum is my favorite method of drying out. Drill some holes and apply suction.
It won’t actually dry it out, but you’ll probably be able to remove enough that the moisture won’t affect your new laminate.
Sistering is pretty simple, and allows you to be certain of the value of the new structure.

 

[wet feet]

I would completely agree that you would benefit from drying out the structure that is in place.What I might question is the justification for carrying out the work,is there any evidence of movement or weakness?If the builders were using the plywood as a former for an adequate amount of glass,there may well be sufficient to perform it's function.If there are keelbolts passing through the reinforcing grid,are they within tubes of any kind?A small access hole that would allow a camera within would possibly help you ascertain the condition of the interior and it's anatomy.Then there is the matter of perception if you ever decide to sell the boat on in that a pre-purchase survey would very likely reveal that reinforcement had been added and may raise questions about whether the boat had run aground and suffered damage of some kind.If the work is done,it would be a very good thing to document the process from start to finish so that you have evidence of it being a precautionary measure added to a structure that was not damaged prior to the modification.

 

[Marc555]

I appreciate all the thoughts. A buyer's surveyor discovered the moisture. Unfortunately, the surveyor we used when we bought the boat 14 months ago missed it. The laminate is about 1/4" to 5/16" on each side of floors that are about 3" wide. We drilled some holes vertically from the top down. The drill bit could be pushed into the plywood with little force. Attached is a picture of a sister-boat showing the geometry after the tanks are removed. The surveyor wants to cut them out and start over, requiring removing the interior, or cut the tops off and replace the wet wood. I'm wondering if there's a calculation to prove the existing laminate is adequate and then dry the wood and stabilize with penetrating epoxy. Or ... ???? Thank you again for your thoughts.

 

[bajansailor]

The laminate is about 1/4" to 5/16" on each side of floors that are about 3" wide.

I am estimating that the floor depth is perhaps about 10", if the overall width is about 3.5" including laminate?
And if the laminate is 6 - 8 mm thick on each side then the fibreglass alone should be a fairly strong top-hat section, if one considers the plywood to be just acting as a former.

Removing the interior furnishings locally, and then cutting the floors out sounds very drastic to me.
If you wallop the sides of the floors, do they flex much, if at all?
The existing laminates appear to be in reasonable condition generally (no reported signs of stress cracks or delamination), and I would be reluctant to start chopping out good structure unnecessarily.
Are the tanks a tight fit in these compartments?
If the tanks are not a tight fit, and there is room to make the floors a wee bit wider, and as you are worried about their strength, I am wondering about the feasibility of adding a core to the front and back of each floor, and then overlaminating this core - this would dramatically increase the stiffness of the sides of the top hat section.