79 Mainship 34 Roof Repair

Hello,
We purchased our 1979 Mainship Trawler with full knowledge of the cabin top repairs required this past August. After a couple months on the St John river, with winter looming, I have her home and almost covered up. The roof repairs have required a slightly larger winter shelter, but I avoided cutting most lumber and it will be reused for something else later.
I am proud of my cradle, which was built by copying another mainship one and cutting up the yard stands taht came with the boat.
I will try to keep a good record of the process for those who may want to try this on their own.Plan is to brace and jack from inside to get the camber/centerline back to factory then start at the front, excavating approx 18" wide sections, recoring and glassing, working to stern.Thinking of foam over balsa, resin impregnated wood where items mount. Comments and suggestions will be welcomed!

First question: Anyone done this know what thickness core material is in roof of the old mainships?

Thanks, Mike

3/4 balsawood

Wow - that's quite a project. My roof had some moisture so I drilled out some 1 inch holes from the ceiling but not penetrating the top layer of fiberglass. I found a mix of plywood - mostly the rear section, and balsa core. There's a separate fiberglass headliner about 1/8 inch below the structural roof. When you're in the cabin looking up at the white ceiling that's the fiberglass liner.

At the Yahoo Mainship site I've read many a story about these fixes, you may want to take a look over there.

I'm not understanding " foam over balsa." I think the best fixes I've seen were cutting the top skin off with a circular saw, scraping all the old balsa out, replacing with same or core of choice of same thickness, replacing top skin.

The Flybridge needs to come off or be blocked high enough to work under as those screws holding it on are the source of many cases of water intrusion.

Great winter project, good luck

First question: Anyone done this know what thickness core material is in roof of the old mainships?

Nadia core is about as cheap and far easier to work with, and it wont begin to die the day you put the first fastening in.

Lay the roof up , figure about 3lbs per sq ft of assistance when having folks help put it in place. 10x10 ,,,300 lbs or so.

foam or balsa, oops

replacing with same or core of choice of same thickness, replacing top skin.

Click to expand...

Replace with material thinner than original and build up a new skin.
I used 5/8 plywood and layered the skin onto that while glassing all the plywood pieces together.

Nadia Core? Thanks

FF said:

First question: Anyone done this know what thickness core material is in roof of the old mainships?

Nadia core is about as cheap and far easier to work with, and it wont begin to die the day you put the first fastening in.

Lay the roof up , figure about 3lbs per sq ft of assistance when having folks help put it in place. 10x10 ,,,300 lbs or so.

Click to expand...

I will look it up.

mgardner said:

I will look it up.

Click to expand...

NIDA-CORE:
Core Materials
Lots of good materials here.

For those that prefer to use plywood as a core the hassle of sheet size is difficult.

IF you can find 3/4 in 10 or 12 ft ply in the most common sizes its a bear to bend to the overhead curve.

My solution was to use 1/4 ply and simply offset the seams , using 3 layers to get to 3/4.

PL structural was used to assist the laminating , but was expensive.

Now I learned that common roofing tar makes a better sealer between layers at 1/10 the price.

I chose wood as at the time I did not have a location to lay up a proper foam core .

Wood works , but like a wooden boat the sealants must be replaced eventually or it will rot, weather GRP covered or not.

Don't know if you've seen this, but there are lots of pictures on one owner's process here: Flybridge Deck Project - Complete Recoring of the Mainship Bridge

My solution was to use 1/4 ply and simply offset the seams , using 3 layers to get to 3/4.


I did a whole 36' x 13 1/2' hull deck and cabin tops this way.
Cut ply into 8' wide strips, applied diagonally using staples and
"Cold-Cure Epoxy". Super strong and would ring like a bell when struck.

Ted

Finally into the repair work. I have found plywood and Foam!! So am I repairing a repair or is it possible Mainship used foam? Never expected that but it does come up easy. I am going with MAS epoxy, foam and ply where needed. How about Peel Ply? Pros and Cons? Also planning on leaving a hole just aft the cockpit door so I can put a radar/light mast with a boom in the future.

Peel ply is used to protect a layer of laminate , and perhaps sop up excess resin.

Main advantage is NOT having to sand the laminate for a secondary bond if too many days have gone by.

Easier and cheaper with a cabin top just to lay it all up in one session.

Nice! I have a '78. I put some ventilation holes with aluminum louver caps in the underside. Hardly noticeable and lets the core dry out - especially when the hot sun is pounding on it. You never hope or intend for moisture to eventually get in...but it does. Although probably not in the timeframe you'll have the boat or plan to sell it.

Go to the Yahoo Mainship website. There are pix and dozens of people that faced your issue with pix and hundreds of post. Mine included.

FF makes a good point about roofing tar.

Well, first big head scratcher. There is an unbonded layer of glass between the roof and headliner ie I cleared the outer layers, wood and there is the underlayer and a layer under that, not bonded to the "middle" layer. Not sure to cut it out or not?!

Do not cut that out, you will bond your core material to that layer.The bottom layer is the headliner,try to bond the headliner screws to the new core

Thanks i did some small cuts and found that, headliner glue has let go in places, will fix that when my support wall is removed.

OK, so I am making progress. Bought most of my supplies from Composites Canada. Recored the entire roof. Replaced plywood with plywood and all old wet foam with new . All was covered with 2 layers of 45/45 stick matt. Lots of observations, lots of learning. 2 big ones are that the inner layer that you are rebuilding on will sag and needs support or you get an unfair hump so the support wall should have had plywood strips running to outer walls or something. The other biggie is the work to wet out the stitch mat, it is thick. The roof is still more springy than I think it should be in the overhang section but I will deal with it later. Main goal is to get the thing back together and in the water to salvage the last 3 months of the season. Made an album in flicker, will label them eventually but the idea of what was involved is there.I also replaced the rudder stuffing box backing block. That was a PITA , it has made me want to place another hatch in the cockpit! Please let me know if you can or cannot see my album. Thanks, Mike Link>>>>> https://flic.kr/s/aHskAS6PXP

So the verdict in my opinion is it was a success. The roof is solid, does not leak(it did before). The next one (Ha) will be a little different. Plan on keeping her in the water until Nov, next project ....Suggestions anyone?

Congratulations on completion of the bridge deck. Usually the biggest dragon to slay!

Have you streamlined the keel to prop to stop the captivation there? You will pick up 50 RPM or so. Have you ripped out the monkey fur in the v berth and recovered. Have you upgraded the electrical system? Bow deck area, near rails soft spots often appear. A boat this old often has headliner issues. Often the cockpit deck sags under the sliding glass door and needs attention.

There...any one of the above are more can keep you entertained if needed. Those 34's are tough boats, very sea worthy. Usually you can stay busy working on one, or not.

Omg, Our vintage Mainships are the easiest boats to work! Just keep at it a piece at a time, No worries about the next project, she will announce it! LOUD and CLEAR! Been at my "82" since 95 but damn, were a pair now. But.. If I were looking for a easy project, it would be to put in a beam under the sliding door supported by posts vertically between the doors and the stringers-- I'd love to be a fly on the wall to understand why it was built cantilevered.