hull/deck joint - 5200 or epoxy???

argonavis · Post by **argonavis** » Thu Sep 27, 2007 3:42 pm

Well I've been away for a long time(got rid of the original project in exchange for an even bigger one - oh dear....) and am back and in need of assistance. photos to come.

We are replacing the decks on a C-40. See pg. 89 in Chapman for the reason why. You'll be glad you did. It's a huge job, but we are actually laying down the new decks- a major turning point. We can't agree on which is the better adhesive for the hull/deck joint. Dad says epoxy, I say 5200.

The new decks are fiberglassed plywood and they are sitting on a 3" lip that is part of the hull. I'm worried that the epoxy won't flex enough to maintain a sufficient bond over time?

Thanks in advance
Chris

Hirilondë · Post by **Hirilondë** » Thu Sep 27, 2007 4:48 pm

Is the glue joint (5200 or epoxy) of the plywood to the 3" flange all that will hold the deck to the boat? Pictures would help a lot here.

argonavis · Post by **argonavis** » Thu Sep 27, 2007 5:47 pm

The glue joint is also backed up by ss bolts every 10 inches or so.

working on photos.

thanks

Rachel · Post by **Rachel** » Thu Sep 27, 2007 9:56 pm

I'm no expert, and I can't see exactly what you're talking about, but that's not going to stop me from opining.

I tend to think that when you use resin (epoxy), it should be in combination with a reinforcement (cloth, biax, etc.), and that if you're simply going to be "smooshing" something between two surfaces and then bolting them together perhaps 5200 would be better.

I don't think hull/deck joints need to (or should) flex independently of each other (the boat can flex as a whole), but, on the other hand, resin alone (without reinforcement) is a bit brittle, to my mind.

Rachel

CharlieJ · Post by **CharlieJ** » Thu Sep 27, 2007 10:11 pm

When I put the decks on my 35 foot trimaran I epoxied them - Ply deck epoxied to a solid wood stringer. But that's a quite different thing than bonding to a fiberglass lip.

Personally I think I'd use the 5200.

Jason K · Post by **Jason K** » Fri Sep 28, 2007 11:27 am

The deck and the hull can move independently and, given that epoxy can be brittle, I would also go with 5200.

deckhand · Post by **deckhand** » Mon Oct 01, 2007 8:06 pm

I think it really does depend on the cross section of the bond. I'm about 1/4 of the way through completely redoing my deck joints on my T30 and I chose fiberglass and epoxy. Why? From what I gathered about my old joint it was fiberglassed AND 5200ed. What time showed me was that the shrank a bit and failed after 30 years of service and then destroyed the fiberglass bond under neath it with ice expansion. I also have stainless bolts on 3" centers that were merely covered by the rub rail. This added to the failure of the bond. I think I remember reading that 5200 doesn't expand and contract so well, which is why polysulfides are used for decks and around things like chain plates.

Solution, grind it all flat (I ground down the dome shape of the bolts to make them flat but still with a good 1/16 of an inch lip), filled the shallow depression where the flanges meet with a mixture of colloidal silica and tons of chopped up fiber, and then covered the whole thing with two layers of 17 oz biax. Now that the outside it sealed I KNOW the inside can be reglassed without it failing. If you go with epoxy, make sure you thicken it up real good, epoxy is only brittle in an over cooked non filled state.

just my 2?

Dave[/url]

westsail42 · Post by **westsail42** » Tue Oct 23, 2007 10:10 am

I would agree with the previouse replies.

Epoxy with reinforcement sounds great, but, unless you are absolutely sure it will be a good bond, there is the risk of cracking under stress. Cracking leads to leaks.

5200, on the other hand, has some "give" to it and acts as a sealant as well as an adhesive.

I asked one of the Loctite guys about using hard adhesives for hull/deck joints (that would include epoxy, plexus, or any methacrylate adhesive). And he recommended polyurethanes like 5200 for this very reason.

Coupled with frequent thru-bolting, 5200 should be just fine. Besides, 5200 is probably easier to work with over epoxy as doing a hull/deck joint requires a bit of time.

Bluenose · Post by **Bluenose** » Tue Oct 23, 2007 11:54 am

I found the transition in the Aerospace industry from bolted joints to bonded joint to be an interesting one. When we first started bonding joints we also fastened them. We even called these fasteners "chicken" fastener because we were too chicken to just have the adhesive.

The thing that I think is important to remembers is that a bonded and bolted joint is not load sharing it is failsafe. What this usually means is that the bolts can't start taking loads until the bond fails because the bolts are relatively sloppy compared to the adhesive. What this means is that they need movement in the joint (to snug everything up) before they take any load. An epoxied joint is very, very rigid and won't budge unless it cracks and fails. Then you have the bolts in back pocket but you also have a leak path.

So I would decide if I felt more comfortable with a bolted hull to deck joint or a glass and epoxy one. If I went for the bolts I would want the most flexible sealing compound I could get so it absolutely wouldn't crack under deformation required to get the loads to the bolts.

Here is a sketch of a pearson 40 hull to deck joint I found on the web (so of course it is accurate). This seem like a very typical joint. From looking at this joint my guess is that this was designed from the very beginning to be a sealed bolted joint.

If someone is really wanting to go with an adhesive bonded deck joint is always good to remember how adhesives do and don't work. They absolutely love to work with inplane shear loads like this.

They are not nearly so good with uniform out of plane loads, which are called transverse tension loads, like this.

And they are absolutely terrible with peeling or prying loads like this.

And they also work best with a uniform, thin bond thickness. Thick non constant bond joints have built in prying loads that can crack.

The problem I would have with wrapping a hull to deck joint in fiberglass is that the epoxy between the layers of glass is an adhesive and I would find it difficult to not end up in peel somewhere.

Bill

Rachel · Post by **Rachel** » Tue Oct 23, 2007 12:19 pm

Thanks, Bill, that was very informative and clear.

I guess as a "this has worked in the real world and it surely wasn't made perfectly" example we could look at the Triton (most of them anyway), which only has a glass/polyester hull-to-deck joint, and seems to be holding together.

This came into my mind as I was thinking how hard it would be to get a perfect, only-in-plane stressed joint, and whether that meant it was a bad idea to try. I like the "no bolts to work and leak" factor, but of course not at the cost of the boat coming apart.

Bluenose · Post by **Bluenose** » Tue Oct 23, 2007 12:36 pm

Hi Rachel

I am not quite sure what you meant when you said "I like the "no bolts to work and leak" factor"

I guess as a "this has worked in the real world and it surely wasn't made perfectly" example we could look at the Triton (most of them anyway), which only has a glass/polyester hull-to-deck joint, and seems to be holding together.

This came into my mind as I was thinking how hard it would be to get a perfect, only-in-plane stressed joint, and whether that meant it was a bad idea to try. I like the "no bolts to work and leak" factor, but of course not at the cost of the boat coming apart.

In my mind either joint could be tight or end up leaking depending on the design and the components used. A poorly designed fiberglass joint (and I think it would be easy to do) could locally crack and leak. And a poorly sealed bolted joint could leak just as easily.

Part of the problem with composites, including fiberglass, is that when they came along they became wonder stuff and there was a tendency to throw out the old. Bolts are the king of handling out of plane loads and for compressing joints. The reasons to use an all composite joints are usually based on cost and schedule. I don't mind if someone makes these choices but what usually happens is they try to rationalize that their choices where actually the best all around.

I also think that many of sealant failure we see in these old boats (and I am not sure I would call something a failure that lasted 30 years) is due to older sealant chemistries reaching the end of their useful life and giving out. If I had a boat with a bolted and sealed hull to deck joint that had work well for 30 years I would clean up the joint and bed it with newer, better, stronger and more flexible adhesive/sealent and reinstall the bolts.

Hirilondë · Post by **Hirilondë** » Tue Oct 23, 2007 5:30 pm

Bluenose wrote:The thing that I think is important to remembers is that a bonded and bolted joint is not load sharing it is failsafe. What this usually means is that the bolts can't start taking loads until the bond fails because the bolts are relatively sloppy compared to the adhesive. What this means is that they need movement in the joint (to snug everything up) before they take any load. An epoxied joint is very, very rigid and won't budge unless it cracks and fails. Then you have the bolts in back pocket but you also have a leak path.

The first sentence is a little hard to understand, is there an "if" missing? I agree with you about the loose bolts not sharing load till the glue joint fails, but a job can be done where the bolts are under tension and so is the glue. I use screws and epoxy together a lot in woodworking and there is some additive strength when the two are combined. I don't however think that epoxy and bolts together is the best way to repair a deck to hull joint.

Bluenose wrote:I also think that many of sealant failure we see in these old boats (and I am not sure I would call something a failure that lasted 30 years) is due to older sealant chemistries reaching the end of their useful life and giving out. If I had a boat with a bolted and sealed hull to deck joint that had work well for 30 years I would clean up the joint and bed it with newer, better, stronger and more flexible adhesive/sealant and reinstall the bolts.

I agree with you assessment and conclusion, this would be my choice. And if you use 4200 or 5200 the bedding would also be an adhesive, and to an extent share loads as some circumstances may demand.

Rachel · Post by **Rachel** » Tue Oct 23, 2007 5:41 pm

Okay, that was a bit non-sensical.

I guess I was thinking of the choice of having a solely glassed joint. It would not leak at all, but it sounds like it's hard to keep it from having some kind of "peeling" load, and then if it did fail.... no back up in the form of bolts. The "working" of the bolts mention was a mistake on my part. But the bolt holes could still leak, just because they are holes. That's bad as I HATE leaks.

keelbolts · Post by **keelbolts** » Thu Oct 25, 2007 2:00 pm

Nobody is worried about not allowing movement where the one side of the hull meets the other so why is anything less then an inflexible joint OK where the topsides meet the deck? I suspect that the whole fastener/sealant hull to deck joint came about as a result of cheap and easy manufacturing methods and not having a trustworthy adhesive. I read that a number of the high end sailboats that were at the Anapolis Boat Show didn't have a 'deck joint'. The deck was 'glassed to the topsides the same way one side of the hull was 'glassed to the other side.

There's no discussion of flexibilty at the deck joint in a wooden boat.
If there's movement there, somebody screwed up. You fix it.

I vote epoxy.

feetup · Post by **feetup** » Thu Oct 25, 2007 2:46 pm

It seems to me that the "shoe box" style joint would be the ideal candidate for a glued fastening. It would be the closest thing to pure shear that would be available. The origional rub rail bolts would be adaquate for clamping purposes.
I think the hard part would be to get the glue surfaces properly prepaired for the adhesive. Perhaps one could remove all the fasteners and rubrail, and spread the joint with wedges, preferably UHMW or Nylon and use a thin abrasive disc gently to prep the surfaces.

Feetup

Give generously, epoxy can be cured.

PGplastic · Post by **PGplastic** » Sun Oct 28, 2007 1:00 am

I agree with the idea that the "shoebox" style of joint would be a good candidate for a glassed joint. The Com-Pac-16 has a flange joint which would be a bad candidate for such. 5200 and hundreds of tiny bolts. It's a small boat after all.

deckhand · Post by **deckhand** » Mon Oct 29, 2007 12:11 am

I just finished my deck joint overhaul. I have the shoe-box style joint with some sort of mastic and stainless bolts every 3-4". The joint was then packed solid with gel coat and the stainless rub rail was screwed in over that. I took off the rub rail, ground out the gel coat, stripped the gel coat off the two halves of the joint, ground the heads of the bolts smooth and about 1/16th thick, and put 2 layers of 4" 17oz biax over the whole thing. The original joint is holding fine so I figure that my fix will make sure it never leaks again so that I never have to rebuild another stringer... ever.
now its just time to fair...and fair.... and fair some more.

Bluenose · Post by **Bluenose** » Mon Oct 29, 2007 2:10 am

Did you by chance take any pictures?

Bluenose · Post by **Bluenose** » Mon Oct 29, 2007 2:57 am

I read that a number of the high end sailboats that were at the Anapolis Boat Show didn't have a 'deck joint'. The deck was 'glassed to the topsides the same way one side of the hull was 'glassed to the other side.

I also tend to feel comforted when a certain type of construction has lasted a long time and therefore "must be good". But at the same time I highly recommend everyone read the chapter on "What Happened at Cabo San Lucas" in Lin and Larry Pardey's "The Capable Cruiser". Many high dollar well "respected" boats broke apart in the surf while other boats survived. I realize we may have different requirements of our boats but I still think it is a good read.

I also think that by owning an old boat and "getting" to replace these type of joints, we have the opportunity to substantially improve the design and the quality of the work.

I recently stumbled onto this Coast Guard rescue that happen on the south end of our Island and it very much help remind me that the design requirement of our boats can be exceeded and lee shores are everywhere when you sail in a group of Islands.

Small Video
http://www.youtube.com/watch?v=6i-HtlQa2I0

Large Video
http://cgig.uscg.mil/media/main.php?g2_itemId=124954

Post by **dasein668** » Mon Oct 29, 2007 8:58 am

It's kind of amazing that the boat was still floating...

keelbolts · Post by **keelbolts** » Mon Oct 29, 2007 10:47 am

It's been some years since I read the Pardey's account of the storm at Cabo San Lucas, but the lesson I took away from it was that many people are cruising on boats that are too big for them. As I recall, several couples got a costly lesson in the size of crew required to sail a 50 foot boat. Boats weren't so much broken up by the storm as they were broken up by the beach when they were blown ashore when their too small crew was unable to get them underway in the deteriorating conditions. Most of my old books on cruising say that, for an individual or a couple, a boat of between 25 and 32 feet is about the right size. That modern 50 foot floating luxury condo that, with the electric winches and windlass and wide-screen TV, is so pleasant in good conditions can just be too much to handle when things hit the fan.

Having said all of that, there's no doubt that more expensive isn't necessarily more seaworthy.

deckhand · Post by **deckhand** » Wed Oct 31, 2007 1:09 am

Bluenose wrote:Did you by chance take any pictures?

damn, I don't think I took any pics of the glassed up joint. I'll snap some pics of the joint with the glass with fairing compound over it .

I started replacing the joint because of the extensive repairs to the stbd joint amidships. When I got the boat it was basically disintegrated for about 10 ft from slamming into a sea wall (very similar to that coast guard video I guess). I glassed all that up and made some new deck segments. Theres is some other back story as to why I'm re-doing the joint (see "stringer re-core" on the my site for some ugly pics). There are some pics and you can read about it on my site.

www.dkyrejko.com/hobyn

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hull/deck joint - 5200 or epoxy???

hull/deck joint - 5200 or epoxy???

hull deck joint