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Old 04-23-2012
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Seeking opinions for deck and hull-deck joint repair

I have a three part question and would like several opinions.

I am replacing the soft deck in my Balboa 20 which is best described as a swing-keel pocket cruiser. Water infiltrated several places where previous owner and even the factory did not protect the core when fastening through-deck. The hull-deck joint is NOT the usual flange-and-lid arrangement but a sort of "cookie-tin" lid. (See Figure A.)

Since the bulk of the deck build is in the upper surface and since water has infiltrated the fiberglass skin below the core in several places, I have removed all of the old glass skin and plywood core from below. Now, it turns out, the hull deck joint is loose in several places. It was originally held together by some kind of adhesive and a skillion 3/16 bolts that hold the rub rail on.

Separating the hull and deck sufficiently to clean the joint and make an effective application of new adhesive is out of the question.

Please consider the repair options shown in attached Figures B and C.

In Figure B I've shown the hull-deck joint glassed together (blue) then glued in the core and additionally supported it by a glass flange (red) before applying a finishing layer (green) on the inside overhead.

In Figure C I've skipped explicitly glassing the hull deck joint. I've simply glued the plywood core in and then installed a glass flange for support (red) and the overhead finishing layer (green). The hull-deck joint is somewhat stabilized especially when you consider the rub rail screws, but not as good as in option B.

QUESTION 1: Option B or C? This boat never sees heavy seas but trailering (especially loading and unloading) can result in significant stress.

QUESTION 2: What weight of cloth or biaxial tape and how many ply for glassing the hull/deck joint (blue) in Option B?

QUESTION 3: What weight of cloth or biaxial tape and how many ply for providing a flange for the plywood core in Options C & B
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Old 04-23-2012
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Re: Seeking opinions for deck and hull-deck joint repair

Quote:
Originally Posted by gregor1234 View Post
The hull-deck joint is NOT the usual flange-and-lid arrangement but a sort of "cookie-tin" lid. (See Figure A.)
Commonly called a "hat box" or "shoe box" joint.

Quote:
Please consider the repair options shown in attached Figures B and C.

In Figure B I've shown the hull-deck joint glassed together (blue) then glued in the core and additionally supported it by a glass flange (red) before applying a finishing layer (green) on the inside overhead.

In Figure C I've skipped explicitly glassing the hull deck joint. I've simply glued the plywood core in and then installed a glass flange for support (red) and the overhead finishing layer (green). The hull-deck joint is somewhat stabilized especially when you consider the rub rail screws, but not as good as in option B.

QUESTION 1: Option B or C? This boat never sees heavy seas but trailering (especially loading and unloading) can result in significant stress.
A: None of the above. Glue the core to the upper skin with thickened epoxy, then laminate the layers onto the hull/deck joint - all layers over both the hull and the underside of the deck. Stagger them - one layer say, 2/3 on the hull, then a layer 2/3 on the deck. If you want to make it indestructible short of nuclear attack, add a third layer 1/2 on the hull and 1/2 on the deck. Considering the size of the boat, I don't think you need heavy glass - something around 12 Oz. should be plenty. Use the stuff that is a layer of woven glass with a layer of mat attached - used to be called FabMat.

Your diagram does show the correct way to handle the fasteners IMO - too many people simply glass them over when doing a job like this - removing them, glassing the joint then redrilling and reinstalling them is the best practice. Do this a section at a time though - don't just pull all the fasteners on one side before doing any glassing. Pick logical start/stop points - bulkheads etc. and do it in stages.

Good luck - nasty job but it will make a BIG improvement in the structure of your boat.
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Old 04-23-2012
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Seeking opinions for deck and hull-deck joint repair

Wow, got a similar issue in our Newport 30. In places, when crawling around the hull, I can look up and see a gap at this joint! Yikes! Good to know we can address the problem.
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Old 04-23-2012
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Your deck/hull joint is bolted? Mine is screwed through the rub rail into the fiberglass. Hardly seems right. I did have to replace some of the screws on the transom because they had pulled through, presumably from the stress associated with the motor mount. I bolted those, but can't imagine replacing the bazillion screws all the way around. Haven't noticed any soft spots on the deck yet. Seems sound, but with everything else i have had to do, i have not really checked it out too thoroughly.

Steve
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Old 04-25-2012
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Re: Seeking opinions for deck and hull-deck joint repair

Thanks to all for replying with good advice.

What I'm taking home here is that I should glue up the core then put up three staggered layers of 12 oz cloth or biax/csm to join the hull to the underside of the core. Then I assume put a finish skin over entire core with light cloth.

RE huill/deck... Oops, too late all the screws are out. The adhesive is still holding in sevarl places so the joint doen;t really "want" to move. I think I'm ok at this point. If I see tendency towards movement, I'll put some of the screws back in.

From other reading I've learned that 1708 as a skin on the underside is way overkill and I can easily get away with much lighter cloth.

For gluing up the core I intend to:

Prepare the core by drilling holed every 2 inch or so to allow epoxy and air pockets to escape. Also epoxy extending into these holes will greatly improve anchorage when hardened.

Plaster the overhead with viscous epoxy filled with chopped cellulose and thickened to peanut butter consistency with with cabosil.

Paint the core upper surface and edges with low viscosity epoxy.

Marry the two wet and shore up well from underneath at many locations.

Screwing down from top to draw core up I think not really very effective as will likely dimple the upper surface rather than draw up the core, will leave many holes to be filled (and act as future sources of water infiltration) and will be hard to place screws in central locaitons 'cause can't put my weight on deck to screw the screws in when deck has no supporting core.

Minnow1193: In my boat the rub rail screws in the stern section are simple sheet metal screws bacause you don't have access from inside to put a wrench on a nut in the stern because the lazarette is in the way. Once you go a couple feet forward, there are regular screws with nuts. These regular (machine) screws are mostly (all?) hidden behind a carpet-covered piece of trim tha covers the hull/deck joint all the way up to the bow.

Last edited by gregor1234; 04-25-2012 at 01:07 AM.
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Re: Seeking opinions for deck and hull-deck joint repair

Quote:
Originally Posted by gregor1234 View Post
Thanks to all for replying with good advice.

What I'm taking home here is that I should glue up the core then put up three staggered layers of 12 oz cloth or biax/csm to join the hull to the underside of the core. Then I assume put a finish skin over entire core with light cloth.

RE huill/deck... Oops, too late all the screws are out. The adhesive is still holding in sevarl places so the joint doen;t really "want" to move. I think I'm ok at this point. If I see tendency towards movement, I'll put some of the screws back in.

From other reading I've learned that 1708 as a skin on the underside is way overkill and I can easily get away with much lighter cloth.

For gluing up the core I intend to:

Prepare the core by drilling holed every 2 inch or so to allow epoxy and air pockets to escape. Also epoxy extending into these holes will greatly improve anchorage when hardened.

Plaster the overhead with viscous epoxy filled with chopped cellulose and thickened to peanut butter consistency with with cabosil.

Paint the core upper surface and edges with low viscosity epoxy.

Marry the two wet and shore up well from underneath at many locations.

Screwing down from top to draw core up I think not really very effective as will likely dimple the upper surface rather than draw up the core, will leave many holes to be filled (and act as future sources of water infiltration) and will be hard to place screws in central locaitons 'cause can't put my weight on deck to screw the screws in when deck has no supporting core.

Minnow1193: In my boat the rub rail screws in the stern section are simple sheet metal screws bacause you don't have access from inside to put a wrench on a nut in the stern because the lazarette is in the way. Once you go a couple feet forward, there are regular screws with nuts. These regular (machine) screws are mostly (all?) hidden behind a carpet-covered piece of trim tha covers the hull/deck joint all the way up to the bow.
Sounds like a solid plan. I have a question though - do you not have an inner deck skin "under" the core? (see highlight). Putting an inner skin on from underneath is going to be the ultimate in a nasty job - extremely difficult to fight gravity.
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Re: Seeking opinions for deck and hull-deck joint repair

Yes, the highlighted text indeed refers to a skin on the under side of the core... Any advice on cloth vs csm, material weight or method to avoid drips?.

I really can't see myself putting up one continuous piece overhead in that cramped space so I thought i would opt for 2 layers of lighter, narrow material and overlap the seams.
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Re: Seeking opinions for deck and hull-deck joint repair

Quote:
Originally Posted by gregor1234 View Post
Yes, the highlighted text indeed refers to a skin on the under side of the core... Any advice on cloth vs csm, material weight or method to avoid drips?.

I really can't see myself putting up one continuous piece overhead in that cramped space so I thought i would opt for 2 layers of lighter, narrow material and overlap the seams.
Ouch - going to be a NASTY job. It's a small boat - any possibility of turning it over on haybales or something so you can work downhand? I saw the bottom of a Cal 20 done that way a couple of years ago.
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Re: Seeking opinions for deck and hull-deck joint repair

No real chance of turning it over. The good news is that l'll be lying on my back with the overhead within easy reach rather than working overhead while crouching or standing. One idea I had would be to use wide tapes say 8-10 inches. Have my wife wet the tapes out with a medium viscosity mix on on a scrap board squegeeing out all excess resin. Then fold and hand them below where I position them. Once they cure to a medium tack I can skim over with a peanut butter mix of resin to fill in the weave.

Minnow1193 I can't reply to your PM cause junior members w/less than 15 posts can't PM (or apparently reply to PM's). So I sent email to your gmail address.
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