Hull/Deck Joint Seal

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vizwhiz
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Hull/Deck Joint Seal

Post by vizwhiz »

I have pulled out all of the bolts around my boat's hull/deck joint, plan to re-seal and replace the rub-rail. Here are a few observations:
1. The "edges" of the hull and deck fiberglass (where the two come together) don't seem to be sealed well, and at least on my boat, there seem to be many small spots where the edge on one or the other is "crumbly" compared to how strong the fiberglass is on the rest of the boat or other fiberglass edges around the boat. My boat is a 1995, so not too old, not too young... This leads me to believe that nothing special is done at the factory to seal those edges, and that they are susceptible to being water damaged over time. I especially think that rough handling makes this worse. (Ask me why I think this...) :wink:
2. The original sealant between the joint flanges is one thin bead of sealant, still flexible (4200 or similar?), on the OUTER edge of the bolts (between the bolt and the edge). Each bolt was then sealed with a ball of sealant when it was pressed through the joint, and the blob was left in place after tightening. While apparently sufficient straight out of the factory, it is a wonder to me that they did not put enough sealant in the joint to cover the whole joint and/or at least go around the holes from the inside.
3. The stainless bolts had a small head (5/16" wrench) and a larger nut (3/8" wrench). Both sides dimpled the fiberglass but the top bolt head worse, and in many places, it cracked the gelcoat. I don't know if the PO(s) tightened the bolts down further, or if that was "factory tight". However, I plan to add a small washer to both sides to help spread the load and avoid dimpling the fiberglass so much, or cracking the gelcoat again. I think this is in part due to #2 above, which kept the outer edges wedged apart, and caused the line of bolts to pull the two pieces together, creating uneven forces.
4. The PO(s) put goopety-goop along the top-inner-edge of the rub rail in several places to help seal the joint. This might have helped, I don't know. I DO know it's a pain to get off of the boat. :x

My Question:
I'd like your opinion of my idea, please.
After messing with this joint, and stripping beads of goopety-goop off (and I haven't even taken the inner bead out yet!) I am toying with using something other than a tube-type sealant to re-seal most of this joint. I am instead considering putting something like an outdoor-rated, foam type weather-stripping in that joint, perhaps 3/4" to 1" wide, if I can find one I think will work, and compressing it as I tighten the two halves together again. Here's why:
1. The inner surface of that joint is not smooth, it is the same unfinished surface as the rough fiberglass you see in the bilge. I am thinking that it will do a better job of filling all the little gaps as it is pressed together, and won't get squeezed out when two "high spots" meet.
2. If wider, I think it will ensure a seal across the whole surface instead of just at one edge.
3. The joint is flexible. As the boat moves and the stresses of sailing, the waves, and such make the boat flex, that joint has to be able to flex slightly. (IMHO, this rules out using 5200 or anything that gets hard, even though I know the factory uses that on all new boats.)
4. It also would help take out the variations in how much sealant gets applied as I work my way around 50+ feet of deck joint. I'm pretty steady-handed, but it's nearly a gamble to try to get the same amount consistently applied around something that large.
5. It might help seal "unclean" areas better, where the sealant might not adhere well due to something on the surface (like old goopety-goop).

Any input, please? :)
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Divecoz
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Re: Hull/Deck Joint Seal

Post by Divecoz »

5200 has some degree of elasticity to it.. It is not brittle like say epoxy.. If In Doubt? Use 4200.. Ask DaveB.. does it for a living.....
Over size bolt heads are common.. We called them Pan Heads .. Trade Name .. so there must be a Real Name and IIRC KevinM. knows the real name of these. They are designed to distribute pressure over a larger area than a standard nut and bolt..We Used Them at work a lot.. Anyway you can get them for both nuts and bolts and they ALMOST...... look like a washer head??? Yep both the nuts and the bolts and I am pretty dang sure Kevin M. knows what the #$%^&* I am talking about!! :D :D HEY Moderator!!!!
You have a steady hand? So I suggest Two Lines one inside the bolt pattern and another outside the pattern.. IIRC I used Enamel Reducer to clean it up ... again ask DaveB or KevinM. DaveB works with this stuff and Kevin is a Chemical Engineer or something like that../// aka Egg Head .. :)
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RobertB
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Re: Hull/Deck Joint Seal

Post by RobertB »

First, I believe you need to both fill gaps and provide an adhesive bond - not all sealants/adhesives do this. Urethane such as 4200/5200 probably a good choice. Make sure the substrate (flanges) is clean and intact - no flakes or delaminated areas. If you need to treat the flanges before hand to solidify them, use a thin/penetrating resin (sounds like you should do this around the fasteners) - epoxy products come in thin penetrating versions. Then, keep in mind that any bond has three equally important steps: surface preparation, adhesive application, and curing. Follow the directions exactly. I would then make sure my fasteners had bearing surfaces larger than the original. Yes, you could use pan head, or washer head types - or just find washers with a large enough diameter (fender washers come in all sizes). Finally, your choice of adhesive should have a long open time before the adhesive takes a set - long enough for you to install and tighten down all the fasteners (here applying the adhesive in a cooler time of the day may help).
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Steve K
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Re: Hull/Deck Joint Seal

Post by Steve K »

Viz,
I know the hull/deck joint on the X boat was sealed with 5200.

Foam?....... Have an idea!
Home Depot sells 50 foot rolls of 4 inch wide, closed cell foam that is used for expansion joints in concrete work (About $15 on the left coast) Easy to cut.
It's 1/2 inch thick and as I said 4 inches wide. It has a narrow tear off strip on one edge. It's grey and I think PVC.
Bullet proof :!:

Your hull/deck joint is like the X joint? ( turned flange... all bolts on outside, right? The rub rail clamps down over the joint?)
The D boat has the traditional joint, where the deck fits over the hull and bolts run from outside to inside and also hold the aluminum part of the rub rail to the boat. It had a foam piece from the factory, in between the pieces (hull and deck) and was also sealed with something like 5200.

Anyway, this foam will have to be replaced on the D boat so I will used the above mentioned item, when I do mine. They used this foam as a filler, because the joint wasn't very accurate. In places the deck flange fits very tightly over the hull and in other places there is a large gap. Guess the molds weren't perfect.

Best Breezes,
Steve K.
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Catigale
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Re: Hull/Deck Joint Seal

Post by Catigale »

The only caveat I would have about the foam gasket idea is to make sure that the rub rail will still fit over the new joint....imagine you getting this all together and then finding out that it didn't..... :|

I think the foam that the home stores sell goes by sill sealer...the application is for the sealing of the top of the foundation to the first piece of lumber on traditional construction, called the sill. It's in the aisle with concrete block, anchor bolts, mortar, etc.
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FinallySailing
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Re: Hull/Deck Joint Seal

Post by FinallySailing »

Might Butyl tape work ? I've had really good experience with this stuff so far for rebedding hardware on my "S". I wonder if this would give a good seal between the hull and deck where adhesion is provided by bolts and not the sealant. It will stay flexible and allow for movements whilst being able to cover any irregularities of the surface. And it is easily removed should you ever have to open up the hull/deck joint again.
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Ixneigh
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Re: Hull/Deck Joint Seal

Post by Ixneigh »

I don't like the way the joint is in the newer boats. Any impact will damage the joint. IMHO the best solution is Fiberglas tape. It can be a chore to match the gelcoat though. On my boat part of the hull is painted so it will be much less of an issue to clean up and smooth the edges of the tape if I ever decide to do that. I can just repaint that area with the off the shelf marine paint I used.
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Divecoz
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Re: Hull/Deck Joint Seal

Post by Divecoz »

Ix..? How do you figure tape is better that the adhesive and then over run/ covered over and protected with the rub rail.??
What am I missing?.
Ixneigh wrote:I don't like the way the joint is in the newer boats. Any impact will damage the joint. IMHO the best solution is Fiberglas tape. It can be a chore to match the gelcoat though. On my boat part of the hull is painted so it will be much less of an issue to clean up and smooth the edges of the tape if I ever decide to do that. I can just repaint that area with the off the shelf marine paint I used.
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RobertB
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Re: Hull/Deck Joint Seal

Post by RobertB »

I highly recommend against foam or butyl tape unless you are willing to re-engineer this joint. Both these solutions only provide a gasket/seal. You are missing the adhesive component these joints are designed to. If you do omit this component, then you need to change the relatively small spaced out bolts holding the flanges together to something that can take and spread out all the load the adhesive component provides.
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Catigale
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Re: Hull/Deck Joint Seal

Post by Catigale »

Not an expert on this but I would think the adhesive is an important component of the strength of this joint.
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DaveB
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Re: Hull/Deck Joint Seal

Post by DaveB »

The 3M 5200 used in many sailboats deck to hull flange is the 7 day cure 5200 not the 24 hr cure 5200.
These boats flex all the time due to no bulkheads and fastened with thru bolts every 6 inches OC.
Over time these bolts have to be retorked to prevent leakage.
Takeing out these bolts will deform the hull to deck fitting. If one has to rebead take out 2 than skip one than another two so you don't deform the hull.
Even saying this takeing out all the bolts, the 3m 5200 should still keep the hull to deck joint togeather.
Personally I would just retork the bolts and add the 7 day 3M 5200 on the outside of hull to deck joint and put the rubrail back on.
Some like to reseal the rubrail after it's installed, that can be very messy and best done while putting the sealant on the bottom of U shape rub rail, this is after you already sealed the hull to deck joint to make it a double seal.
7day cure 5200 will remain flexable and holds up very well on those hard landing docks and flexing the hull when the rail is down.
Dave

Catigale wrote:Not an expert on this but I would think the adhesive is an important component of the strength of this joint.
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Ixneigh
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Re: Hull/Deck Joint Seal

Post by Ixneigh »

Because fiberglass will bond the two halves together, not just glue it like a bead of sealant. I'm talking wide tape six inches. Three layers. This will stiffen the hull and sheer area. Its the nuclear option grented. That's what I would do. Course I'm insane :D
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DaveB
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Re: Hull/Deck Joint Seal

Post by DaveB »

You have to alow stress, fiberglass/epoxy joints will not alow stress.
Thats why boat builders put the #M 5200 at hull/deck joints.
They don't rely on 5200 but include the thru deck bolts also.
Butal or any type of hull to deck on flexable hulls on this type don't work. High/low temps will desolve over time and this has been well documented.
Most Builders still use the 5200 since 1981 or before. ( I have in 1981 to repair a leak in my dingy, only full repair I could find at that time , Hypolon)
It's like quick glue but much better on dinks and boat deck to hull joints.
Dave
Ixneigh wrote:Because fiberglass will bond the two halves together, not just glue it like a bead of sealant. I'm talking wide tape six inches. Three layers. This will stiffen the hull and sheer area. Its the nuclear option grented. That's what I would do. Course I'm insane :D
vizwhiz
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Re: Hull/Deck Joint Seal

Post by vizwhiz »

I'm hearing what you guys are saying about the strength of the adhesive bond and its contribution to the strength of the bolted joint, and I appreciate the input...but I'm not sure I agree with that idea, at least not on my boat. Perhaps that became a consideration on the later models, but it certainly isn't a contributing factor in the way the sealant was applied to the S. I could go into a couple reasons why...size of the bead (or lack thereof), where it was applied (the wrong side of the joint for strength), the way it peeled apart when I separated hull/deck joint, etc. just doesn't fit into what would be "common" engineering practice for a structural joint. Perhaps changing to 5200, which has true adhesive properties, gave that joint an added component of strength...so I can understand where a change like that could have been made. Also, watching the video, it appears that a lot more adhesive is used in the M construction than was used on my S.

So if we temporarily set aside the idea of adhesive strength, are there any reasons related to sealing properties that you think would make the idea of using a compressible foam seal undesireable?
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RobertB
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Re: Hull/Deck Joint Seal

Post by RobertB »

vizwhiz wrote:So if we temporarily set aside the idea of adhesive strength, are there any reasons related to sealing properties that you think would make the idea of using a compressible foam seal undesireable?
Fatigue loading/failure of the hull to deck fasteners and tear-out of the fiberglass where the fasteners are installed - I stay with my point that if you change the way the joint is assembled by omiting the adhesive, you need to reengineer the joint. Are you prepared to use metal backing strips or additional layers of fiberglass and larger fasteners? As long as you can hold the two flanges together, you can hold in a gasket and keep out water - but keep in mind, a gasketed joint needs to be more rigid than an adhesive one to maintain integrety.

The way you describe the joint put together and the way it did not hold up may be more indicative of a Friday afternoon on a holiday weekend assembly job, not of the way the joint was supposed to be assembled.
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