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Old 11-23-2015, 09:09 PM   #1
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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
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Old 11-23-2015, 09:20 PM   #2
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3/4 balsawood
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Old 11-23-2015, 11:46 PM   #3
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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.
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Old 11-24-2015, 05:08 AM   #4
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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

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Old 11-24-2015, 06:35 AM   #5
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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.
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Old 11-24-2015, 06:44 AM   #6
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foam or balsa, oops
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Old 11-24-2015, 09:14 AM   #7
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Quote:
replacing with same or core of choice of same thickness, replacing top skin.
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.
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Old 11-24-2015, 10:05 PM   #8
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Nadia Core? Thanks

Quote:
Originally Posted by FF View Post
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.

I will look it up.
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Old 11-24-2015, 10:09 PM   #9
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Quote:
Originally Posted by mgardner View Post
I will look it up.
NIDA-CORE:
Core Materials
Lots of good materials here.
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Old 11-25-2015, 05:21 AM   #10
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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.
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Old 11-25-2015, 10:39 AM   #11
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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
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Old 11-25-2015, 01:02 PM   #12
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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.

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Old 05-16-2016, 07:06 PM   #13
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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.
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Old 05-17-2016, 05:23 AM   #14
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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.
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Old 05-17-2016, 10:28 AM   #15
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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.
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Old 05-17-2016, 11:02 AM   #16
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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.
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Old 05-18-2016, 11:52 AM   #17
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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?!
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Old 05-18-2016, 01:38 PM   #18
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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
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Old 05-18-2016, 03:23 PM   #19
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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.
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Old 07-30-2016, 07:01 AM   #20
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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
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