Recore from below

Post photos and descriptions of your ongoing projects here. No project is too big or too small.
Post Reply
Jason K
Boat Obsession Medal Finalist
Posts: 741
Joined: Fri Mar 18, 2005 10:41 pm
Boat Name: Rambunctious
Boat Type: J/30
Location: Mandeville, LA
Contact:

Recore from below

Post by Jason K »

I know this topic has been covered a bit, but I spent last weekend in my anchor locker and I'll be spending much of this weekend in the same place. So, I thought I'd hit this horse one more time and reiterate the importance of properly sealing hardware.

I knew about these spots when I bought the boat last year, but I've waited until now to repair them. A good section of the foredeck forward of the bulkhead needed to be replaced, as did a smaller section near the anchor locker. The foredeck was inundated with water from a deck plate and the waste pumpout fitting. The area around the anchor locker was damaged by the hinge screws.

Here's the cross section of deck with the deck plate removed:

Image

I did this from below so as not to ruin the deck finish. Here's the first cut:
Image

Here's the exposed core with the lower skin removed. Note the two pieces of wood right in the middle of the deck. This came from the factory as there was no indication of a previous repair in this area. An old foredeck cleat had two fasters through the wood (see the epoxy plugs), but the other two were through regular balsa. It's strange and I'd love to why these two pieces are here. Did TPI run out of balsa?
Image

I don't have any photos showing the new core exposed as I laid up the new core and replaced the lower skin in the same operation. I wasn't about to touch my camera. So, the two photos below show the lower skins replaced. In the anchor locker photo, I put that brace back for the picture. There were three braces in place while the epoxy cured.

Image

Image

Since these photos, I've water washed the repair to remove amine blush, sanded the area, and solvent washed it.

This weekend, I'm going to grind the seam back several inches on each side and reinforce with two layers of tape. Eventually, I'll repaint both lockers with Bilgekote, but that will be done later.

This work could have easily been avoided if the core was isolated from these fittings with thickened epoxy. Before the new hardware is installed, all fasteners or through-deck hardware will pass through the epoxy, not the new balsa. I omitted a lot of the core in the area where the deck plate passes through and I'll ream out the area around the waste pump out fitting. Fasteners will be installed in the standard way - potting the overdrilled holes with thickened epoxy and drilling and tapping the holes for the fastener.

The first time I did a recore from the inside I made a few mistakes. The largest mistake was not sufficently preparing the braces for shoring up the new core. This time around, all of the braces were cut and set near by, so that went much, much easier.

Another difference is that I was able to reuse the bottom skin. On the Triton, the skin was not salvageable so I just laminated a new lower skin. I had some issues with trying to install pieces (particularly the biax) that were too large and therefore were a real challenge to keep from falling back off the overhead surface. It went a lot easier when I started using smaller bits of glass.

This time, the old skin was replaced. However, I'm not convinced that's really the best way. You still have to clean and prep the old skin, it has to go back in precisely the same location (meaning your going to hold in place until the epoxy kicks and you can add the braces), and you'll still have to grind and glass the cut seam. It seems that with that much effort, it may be easier just to lay up new glass.

The only minor downside this time was gluing myself to the drop cloth. Last time I stuck the back of my head into fresh glass, so things are improving with practice. No haircuts needed (yet).
- Jason King (formerly #218)
J/30 Rambunctious
http://www.rambunctiousracing.com
Quetzalsailor
Master of the Arcane
Posts: 1100
Joined: Fri Aug 26, 2005 9:53 am
Boat Name: Quetzal
Boat Type: LeComte North East 38
Location: Philadelphia, PA

Post by Quetzalsailor »

I've done this to the bottom of the cockpit floor in the Morgan 27. I used a couple useful variations: Ground the perimeter of the cored area to disconnect the whole of the cored area. Ground the disgusting remains of the balsa off and the new perimeter tabbing surface clean. Laid up fiberglass onto the new plywood core at home, in comfort. Cut to shape. Coated out the plywood and buttered it in thickened epoxy. Propped the mess up tight to the bottom of the cockpit on pre-prepared sticks wedged in. Cured. Tabbed all around the perimeter. I was lying on polyethylene sheeting and wearing a huge black trash bag.

Friend of mine did the whole of the underside of the foredeck on his dad's cruising boat. Vacuum bagged the face and core in two halves in the shop and then vacuum bagged the two assemblies to the underside of the deck. He had lots of help.
Tallystick
Skilled Systems Installer
Posts: 177
Joined: Fri Sep 09, 2011 10:54 am
Boat Name: Nostalgia
Boat Type: Pearson Triton Yawl

Re: Recore from below

Post by Tallystick »

Bringing back an old thread to mention a technique that worked well for me. The only area that I recored from below was under the mast support. To hold the plywood in position while the thickened epoxy cured, I used high temp hot glue at the corners of each section of plywood. This was sufficient to hold the plywood in place while the epoxy cured. This made the process fast and easy, while having little to no affect on the overall strength of the repair. I cut the plywood pieces in sections to follow the curvature, applied thickened epoxy to the pieces, added a small bead of hot glue at the corners, pressed the pieces into position until epoxy oozed out the edges, and then sanded it all smooth with a belt sander after the epoxy fully cured.
Post Reply