Reinforcing main bulkhead

It is hard on boats to be on the hard.  Last summer Reach was blocked up high enough for us to work on the rudders.  Then hurricane Matthew came along.  Manta catamarans can sit on their keels due to the placement and strength of the bulkheads.  She was well-secured with straps and stands on the sides, yet must have gotten wracked in the process.   After the passing of the storm we noticed a bulged main bulkhead that was not there before.

This portion of the main bulkhead under the settee is 1 1/2" nidacore.  It is about 18" tall under the seat and 36" tall in front of the refrigerator.  On later boats, Manta placed 3" bulkheads here.  Despite being smaller, the main issue with ours is that it had not been capped-off with fiberglass.  Nidacore is strong in compression, but not in shear.  You can see how the bare honeycomb was subjected to shear in the photos.

At this point, we had just completed grueling months of projects and were anxious to get back to the Bahamas.  We decided to sail with the bulge for a winter season before fixing it.  This worked out fine, but it still weighed on the mind.  As soon as we returned to the US, Mark started on the repair that he’d been visualizing for the past six months.

The plan was to double the bulkhead to 3" width, straighten the bulge and cap the new bulkhead with fiberglass.  

This was best accomplished by sandwiching the existing bulkhead with two, 3/4" plywood sheets.  

We could access the space from both sides after cutting off the front of the settee.

To ensure that we could get the entire new bulkhead straight, we needed to loosen the rigging.

Here we propped-up the mast with our car jack to relieve the pressure on the compression post that sits on the main bulkhead.  

We’ve been here before... when we re-rigged two years ago & took the opportunity to inspect and paint the compression post.

After cutting the reinforcements to size and sanding them down, he first glassed the outer portions of the new bulkheads.  


The attachment of old bulkhead to new required sanding of both old and new surfaces prior to gluing them together with epoxy, milled fiber[-glass] and Cabosil fumed silica.

Besides using C-clamps over temporary 2x4” lateral clamps, he drilled holes through the sandwich to place through-bolts in for the straightening and curing process.  These were later replaced with screws and glassed over.

The final step to complete this bulkhead fix was to fill and glass over the entire sandwich to cap-off the structure and tab it to the existing glass.  This is an important step and if our old bulkhead had been capped we might not have gotten a bulge in the first place.  In any case, we’re happy to have the main bulkhead at 3" and plan to continue this reinforcement through the main bulkheads in both hulls.

© M&M 2019