1976 Seacraft 23 IB - Rear Deck/Hatch Core Replacement

[John3325]

Beginning a series of multiple items on the to-do list this year for the SeaCraft. First on the list, I had to get the rear deck out to investigate what's underneath. Tanks look good, exhaust hose should be redone I think. Anyways, removing the deck lead to the first thing to get done, the rear deck core. I wasn't planning on doing it this year since the top seems solid, but since it is out and I have a free table, so here we go.

I cut a seem essentially around the core and dug all the crap out. It was all mushy crap, the wood was fully saturated and must have been for a long time. I am amazed that the top skin was still rock solid. I got all the crap out so far, and for the most part the "first layer" which appears to be 1/4 ply or matting is still solid except for a few areas.

My game plan, is to counter sink a bunch of holes about a 1/2'' apart in the small soft areas that I now have exposed. Once that is done, I will replace the core with marine grade ply or maybe nida core?

Whatever the material is, I will layer resin, layer the core and put that in place. Then I will resin the core and cover with some commercial grade fiberglass mat I have.

Last, feather in the new core to the seem I cut. Sand her down, paint it up, and call it a day.

Any thoughts on the game plan? I have only done one of these before but I'd really like to get some insight from the forum before I dive into the repair.

[John3325]

And, this is the progress about 3 hours later. Letting the decking dry out for now since it's still pretty wet to the touch from all the soaked wood sitting underneath it.

Hopefully it will dry out. I'll start sanding it down tomorrow or over the next few days to start preparing for the glass work and core.

[fishlips56]

Good morning John,
I'm interested to see your progress and final product. I also have a 1976 23' inboard and the rear deck is basically solid with a couple small soft areas and a slight sag in the middle. My deck appears different underneath as it is only about 1/2" thick with 6 or so transverse sisters (1/2" - 3/4" x 1 1/2" high beams) running the entire width except for where the hatch meets the deck. Was your rear hatch seam caulked to eliminate water intrusion? Do you have any pictures of your hatch that mounts in front of the console and partially slides underneath? Mine appears to have been modified (molested) over the years. I'll send you a PM also. Thanks.

Barry

[aldo]

Hi John,
Did this a few years back on my 1976 inboard

[aldo]

I used 1" nidacore. The mahogony was a base for my leaning post screws.
I built a frame of 2x6's that would allow for the center of the floor to have a slight crown- (about 1/8") to shed water.
Looks like you have the hard work done. I would just suggest you plan where you will need to screw in your seats or leaning post, and a slight crown will keep you from stepping in water every time it rains. The nidacore will help to shed a lot of weight.
Good luck with your project.

[John3325]

Thanks Aldo! Great information.

How did you like using the Nida Core? Does it work the same way as if you were using marine grade plywood? I do like the idea of shedding some weight.

[aldo]

Nidacore is much easier to cut and work with than plywood.
It's incredibly light.
Just make sure you bond it the top skin with resin or a bonding agent, and remember that it won't hold hardware bolts. Just plan ahead like I did with the mahogany.

[Ed]

I did this on my 27 Tournament hatches a couple of winters ago. I vacuum bagged them but the same basic rules would apply.

Once all of the old rotten coring has been removed, I followed these steps:

1) Lay down a fresh piece of 1.5oz mat on to the inside of the cleaned out hatch.
2) Cut core to size. I drilled small holes in mine so that the bedding putty I made out of thickened epoxy resin would have a place to flow as the bag pulled down.
3) Then I laid down one layer of 1708, breather cloth and peel ply.
4) Being a glutton for punishment, I then applied System 3 Quick Fair over the 1708, faired it and then applied EMC Quantum Epoxy Primer followed by EMC Quantum paint.

[John3325]

Thanks Ed.

My next step is to determine whether I need to keep the core at 1.5" deep. Only thing I can think of is that it was made that the hatch was made that deep to rest on the "retaining walls" for the gas tanks, giving the deck added support. Going to measure this out and see what I find.

If there is no need to have it this thick, I think a 3/4'' core is all I need to reinforce this properly. If I go with Nida Core, I will use marine ply as my backing material.

Where do you pick up Nida Core? Does it have to be special ordered though a vendor or is this something they will stock at a lumberyard? I remember my last run at one of these my closest spot for marine plywood was Hingham Lumberyard in Hingham, MA.

[John3325]

Was able to get up in the boat after work while I had daylight.

The highest objects that are under the deck hatch are the gas sending units, which are 1 3/8" underneath the lip of the hatch. This would explain the 7" circle spots that had a center point 1.5" higher than the bottom.

My father helped me identify what was used before.....bulsa wood/core! I think that might answer some people's questions whether this was original or not. I am now leaning to think that this was done before.

I am thinking that I may sandwich a 1/2'" & 3/4" marine grade pieces together, and that creates my core. I will have cutouts on the 1/2" piece to leave space for the leaning post washers/nuts, and cut two holes to leave space for the fuel sending units. This will fill the entire void back up to 1 1/4", and will leave space to resin/mat the top surface back to that 1.5" mark. The more I thought about it, I want it back to 1.5" depth. It will get me essentially resting on the retaining walls for the gas tanks, and I doubt I'll ever have to worry about this thing getting soft again.

Took a few more pics, first one is of the stern area of the boat. The others are after sanding the deck hatch down and letting it dry out for a day. It's definitely a lot dryer in general than yesterday. I have cold temperatures working against me in NE, so I may have to invest in a space heater soon to continue progress.

Few pics of where I got a little chizel crazy. Nothing that can't be fixed but definitely a moment.