MT 34 Sedan - 1986 - Soft Decks

Bought the boat a couple of months ago aware that, among other issues, she has very soft cockpit sole and decks. I originally thought (and posted here) that the cockpit and decks were a fiberglass sandwich and that I could, as I’ve done before on sailboats, lift the top layer, replace the core, etc. Further access and inspection shows that the cockpit sole and decks are actually a top fiberglass skin laid on a plywood base. And, naturally, much of that plywood underlay is rotten. Has anyone here had the same problem and, if so, please, please tell me how you addressed it……….. its the biggest problem I have on the boat.

Simple. Pull off the fiberglass, rip out the wood and replace with new ply. Coat the ply liberally with epoxy resin first to seal it. Lay down new cloth and resin on the top and smooth to a new deck. Not as labor intensive as you may think, but a large project. Really no way around it. My deck, joists, support, etc all had to be replaced it was so far gone. Be prepared for what you may find.

How are the bulkheads around the windows?

Redhook - many thanks for the response. Insofar as I am aware, the bulkheads beneath the saloon windows are solid - and, to my amazement, the windows don’t seem to leak. Taking up the entire cockpit sole (she is a sedan so has a considerably larger cockpit than the DC versions) is going to be a major project - and I suspect that beams and stringers are going to be a problem, as maybe the under-sole bulkhead beneath the transverse cabin aft bulkhead that contains the aft cabin door and windows. It’s now very much the rainy season here in SW FL, so this will have to be a winter project. I also have a squishy spot on the foredeck - do you know if this is built the same way - FG skin on ply? Again, your response is much appreciated…..

I agree with Redhook98...... except do not coat both sides of the plywood with epoxy. Use Marine plywood and leave the underside open to the air. The reason it is rotted now is that the plywood very slowly became saturated and could not dry out.

Teak decks? If so, it might be possible to lay an epoxy glass layer over the top and simply raise the deck level 1/4 inch with roving and finishing cloth. The layer of fiberglass under the teak would become your tension surface, the rot resistant teak would now serve the purpose of the rotted plywood pieces, and your new deck surface is the compression layer (finished with non-skid). This assumes any beams are okay and that you can live with the idea that there remains a layer of rotted ply that is doing nothing. Given that time and materials would be greatly reduced, it's worth thinking about.

CharlieO and Marco - many thanks for the helpful input. Much food for thought and planning. Not sure about teak decks - for years I’ve been trying to avoid them on our boats. One of my concerns about putting a new layer of glass over the existing skin is that of adequate load-bearing - given that the current skin is saggy due to the rotten underlay - and probably the beams/stringers…… any additional advice/thoughts/suggestions will be enthusiastically welcomed!

Bluewater2 said:

Redhook - many thanks for the response. Insofar as I am aware, the bulkheads beneath the saloon windows are solid - and, to my amazement, the windows don’t seem to leak. Taking up the entire cockpit sole (she is a sedan so has a considerably larger cockpit than the DC versions) is going to be a major project - and I suspect that beams and stringers are going to be a problem, as maybe the under-sole bulkhead beneath the transverse cabin aft bulkhead that contains the aft cabin door and windows. It’s now very much the rainy season here in SW FL, so this will have to be a winter project. I also have a squishy spot on the foredeck - do you know if this is built the same way - FG skin on ply? Again, your response is much appreciated…..

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These mostly were all simply FG over wood. Not often sandwiched in. You can cut the upper layer of FG off, replace the wood, and reinstall the FG piece if you are handy enough. Almost as easy just layering in new FG though, and probably will make a better bond in the long run. I do prefer regular plywood over marine-grade for this. Marine-grade is a bit denser, no voids and has a better quality glue. But, if you saturate a standard piece of ply with penetrating epoxy, that builds (in my opinion), a more stable and stiffer foundation for flooring. Either way you go, marine-ply or properly saturated standard ply, you will have a deck that will last another 30 years, at least.

Thanks Redhook. Very helpful. Unfortunately, after too many boats and oceans, and unlike Vagabond, this owner will never last another 30 years!! ����

I would be very surprised if the decks were not sandwiched. The decks on my 1977 DC are. You can see it from underneath.

I also would be surprised if the stringers and beams were rotted. Those are usually solid teak not plywood. The crappy plywood is the problem. I just had to replace 1/2 my aft cabin floor due to crappy plywood. Underneath the dust of the flooring were perfect stringers and beams. I was surprised too.



You won't know what you have until you start pulling it apart. Marine Traders were all built by different builders so one man's opinion is based only on what he has seen. By 1986 they all had gotten their act together pretty much.

Al - I am unpleasantly surprised by the decks being fg skin over ply. But from what I can tell, this was not unusual in Taiwanese trawlers of this vintage from certain yards up to about 1985. I certainly hope that your thoughts on the stringers and beams are correct!

Bluewater2 said:

Al - I am unpleasantly surprised by the decks being fg skin over ply. But from what I can tell, this was not unusual in Taiwanese trawlers of this vintage from certain yards up to about 1985. I certainly hope that your thoughts on the stringers and beams are correct!

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The above type of deck construction was usual for all these Taiwanese builds, so nearly all suffered the ingress of water through the screw-holes they used to hold the teak deck down, which ultimately, (and unnecessarily) ruined the integrity of the upper layer of GRP. If only they had not done it that way, how much trouble all of us who bought these boats down the track would have been saved..? Later models used a synthetic stiffener core and just laid non-skid GRP over it - voila..! No such issues.

Anyway, they didn't think that far ahead, so it is what it is. However, my boat was repaired from soft decks, by the person I bought it off, the way Marco Flamingo suggested above.

Just rip off the teak - or leave it down if still fairly free of rot - which it often is, and then lay down about 15mm ply, in place of the teak, if the teak is stuffed, then re-fibreglass over the lot.

It ends up the deck raised a tad - not an issue - and plenty stiff, and the old damp core is sequestered safely away in between the fibreglass layers, so not going anywhere and as long as the underneath layer of GRP is intact - and no reason why not usually - then it is fixed quite nicely and way more cheaply than ripping out all the damp core then re-glassing over that.

Hi Pete - the boat doesn’t have teak decks, and, as far as I can ascertain, never did. No signs of old fastener holes and the single skin seems seamlessly (other than old-age cracks) bonded to the bulwarks and cabin sides. When I bought the boat I was happy about this - had nothing but trouble with teak decks on multiple boats (with the exception of our two Hans Christians….). So I seem to be stuck with the single skin on ply. When it stops raining here I’m going to get back under the cockpit deck and conduct an autopsy on the ply - maybe its not completely dead…..! But I’m certainly not holding my breath. I’m thinking about using some 2x4s to help support the cockpit sole until I can address the problem in the dry/winter season. Please please keep the thoughts/advice/suggestions coming - I love this forum…..

Sorry, Bluewater2, I was mistaken re the original issue, and thinking it was the old teak screw-holes leaking thing. I understand now. However, it sounds like somehow, probably because of badly sealed perforations in the upper GFP deck layer installing fittings, water has got into the core. The rest, as they say, is pretty much the same as for the old teak deck thing actually. The damp core has lessened the stiffness of the deck.

Point to note. This damp core cannot go anywhere, or cause any other significant issue, it is sandwiched in between two layers of GRP. Nor will the deck collapse.

You have three choices.

1. Accept the fact you have springy decks, and live with it - no-one is going to fall through them.

2. Basically do what I and Marco Flamingo suggested, but you don't have to strip off old teak, as there was none in the first place. Just ignore the damp core, lay a stiffening layer of ply, treated with an anti-rot epoxy preferably, over the top of the existing deck finish, and then another layer of GRP finished in non-slip surface over that. That would definitely work. I can vouch for that.

3. Rip/cut all the top layer off, re-core, then replace top layer as above. The issue with that is you will then breach the integrity of, and the deck to cabin join of, the existing deck finish, and will end up with a result not much stiffer than it is now.

Option 2 would definitely stiffen it the most. It would also be a lot easier and cheaper to do, than option 3. Option 1 is to leave well alone, see if you can identify where the water got, or is getting in, and repair locally. Could be quite tricky to do. It sounds like this is your first choice at present.

Point to note. Whatever you do, it will end up looking the same, and you'll just have a stiffer deck...or not...good luck...

Please don't just leave the rot. You're a steward of your boat, there will never be any more of these Taiwanese Trawlers built, when the last one is scrapped they are gone forever. They represent an important milestone in recreational boat history - the era when ordinary people could afford one!

If you're going to enjoy it for a few years and pass it off so you can get a bigger boat you can stop reading now.

With all due respect Peter B there is no deck to cabin structural joint on an MT/CHB. There is a shelf of thick fiberglass that is part of the original pour of the two halves of the hull. There is a lip about 3" high on the inboard part of that shelf.

https://www.trawlerforum.com/forums/members/158-albums1121-picture6917.html

You can see the lip quite clearly in this picture.

In the double cabin design, the forward and aft cabins have teak planks on the inside, that are screwed into the lip to add strength. Some families screwed these through the lip and into the deck coring. The cabin walls (marine ply) sit on the outside of this lip. There's a top frame that is attached at the front and aft corners of the two doghouses. The stick frame and the walls hold up the cabins.

The main salon - on the D/C and the sedan - is held up by a stick frame that's supported by the forward and aft bulkheads, and that same lip, which is reinforced by the hollow stringer boxes that run up the side of the hull to the underside of the deck. In the sedan the forward house is built the same as the D/C.

Cabin to deck is a layer of caulk under the coring, a thin layer of chop gun glass, and typically a piece of quarter round.

When the decks go, the thin layer of chop gun goes, and the water wicks up into the cabin walls. If you crawl around the deck on your hands and knees and check the bottom of the cabin walls they will be lumpy and/or soft. The deck coring actually slides UNDER the cabin walls as the decks were cored first, and then the cabin walls were set on a strip of caulk which enabled them to expand and contract.

The decks themselves are torsion boxes, grp underneath, teak struts, and either plywood or balsa core. The teak decks are screwed into the struts, not the core. People ruin the decks by adding additional screws in the wrong places.

Adding a bunch of weight on top of the torsion boxes in the deck works, but if the core is badly saturated it is very heavy and you're adding more weight, which puts stress on the structure that supports the house. You'll get cracks in the walls as they can't stretch enough to handle the new weight. You're going to accelerate the rotting of the walls, as the original GRP shelves are going to sag under all that weight.

Amatuer repairs are often overdone and and as a result are very heavy.

The only proper fix is to recore the decks, and along the way you're going to end up scarfing new core into the bottom of the house.

If someone tells you to drill holes in the deck and squirt epoxy in the holes they don't know what they are talking about. The PO of my boat did that, when you take it apart you'll find pictures of little puddles of fiberglass floating in rotted wood.

Injecting antifreeze - advice you may also get - will slow the rot down as it kills the bacteria that's eating the wood. It won't add any strength.

Drilling holes and putting it under heat for a few months, and then laying new cloth is another approach. This works, but rotted wood then dried has about as much strength as a styrofoam coffee cup it crumbles in your hands easily.

BlueWater2 I have hundreds and hundreds of pictures of literally every piece of your boat taken apart so you can see how it is built, send me a PM.

There was so much rot in my 76 D/C that after I removed it all I raised the waterline TWO INCHES.

All this being said these are awesome boats, that can be repaired by the average guy, are surprisingly sea worthy for a coastal cruiser, and will give you years and years of pleasure at very low cost. It's hard to find a better value for the money, which is why they remain the most popular small cabin trawler ever built.

Pete and SeaMoose - thank you both for thoughts and suggestion. Very much appreciated. And thank you SeaMoose for the construction details - I will be PMing you. I actually squished myself into both the port and starboard aft quarters yesterday and got a good look behind each water tank (both of which seem in excellent condition outboard - and I found treasure - two mismatched shoes and a completely rusted out emergency tiller!) and so I have a better idea now of what you are saying about the build methodology SeaMoose. As I’ve previously noted, it’s the “very wet” season here and so taking up any parts of the top skin must await winter. In the meantime I’m thinking about using some 2x4 as temporary framing to support the cockpit sole. Any thoughts on this? And BTW, I do not believe in injecting into the sandwich - I have every confidence that the sandwich material is liquid mush…. Again, grateful thanks to both of you

IMO if you have soft core in the decking then the only proper way to fix it is bite the bullet and cut the top skin off and dig out all the rotten core. Assuming you have a bottom fiberglass skin that is. Then replace the old mushy core with new core, whether plywood or something like Coosa board. Use thickened epoxy on top of the new core and then lay the top fiberglass skin back into the thickened epoxy and weight the skin down. Then grind a shallow trough along the cut line in the top glass skin and lay in some 1708 and fill. Then paint with Kiwigrip. Done.

I'll pull out at this point, but have to admit this...

I agree that the recommendations from Seamoose and Comodave are the better repair - just 'cos. And if the situation had not been pre-empted in my boat's case by the PO, who repaired the soft decks as I described, by leaving the damp core, and rebuilding a new deck over them, I would, being a bit of a perfectionist myself, probably have done - or rather had done - as being a rather busy family doc, I would not have had the time or expertise to do it myself, what Comodave and Seamoose suggested.

However, would doing that have made the boat function better over the next 16 years we owned her - I think not.

Would it even have added to the final re-sale price I got for her..? Again, I think not, bearing in mind her age, engine hours, etc, (1975 hull lay).
As even thought she was still in better condition when I sold her than when we bought her, because over the 16 years I had done a lot in terms of internal teak, improved electronics, lighting, outside canvas, etc, and had the hull professionally 2-pack resprayed, she was still 44 years old, and I got $Aus45k for her.

Thanks Pete. That’s a very good price for a “mature” MT. You must have put a lot of work into her…….

Commodave - that’s roughly what I intend to do. I have done that in a small area on one of our sailboats - but the cockpit sole on an MT Sedan is a very large area with a large lazarette “hatch” in the middle of it.

Bluewater2 said:

Thanks Pete. That’s a very good price for a “mature” MT. You must have put a lot of work into her…….

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As a bit of a PS, and reminded Bluewater, of where you said...

"Hi Pete - the boat doesn’t have teak decks, and, as far as I can ascertain, never did. No signs of old fastener holes and the single skin seems seamlessly (other than old-age cracks) bonded to the bulwarks and cabin sides."

...it gave me a bit of a brainwave.

I suspect it did originally have teak decks, as they virtually all did of that period, so it would be very unusual for it not to have had teak deck originally, but possibly several owners ago..?

If that was the case, then what you are dealing with now is the end result of a PO removing just the teak, and re-fibreglassing over the original GRP which was under the teak. It would be quite a thin layer, and hence still a bit flexible, but actually might still be a reasonable fix if the springy deck does not worry you too much. I therefore suggest that before you go 'rip-rip-wood-chip' too much, just select somewhere where it would not be too hard to disguise and do a plug repair, and with a hole-saw, carefully drill out through the whole deck, a core sample.

That should prove it once and for all, as if that has been done, there will be one bottom or lower layer of GRP, then the core, and two upper GRP layers above the damp timber core, not just one. If so, you may well be worrying and planning a major and costly repair unnecessarily. Best of luck anyway.