What sealant to use between bowsprit and the deck?

[hilbert]

Any suggestions on a sealant to use between a new bowsprit and deck?
My first thought is to use BoatLIFE Life-Calk.

Thanks,
Jonathan

[Jim Walsh]

I used 3M 4000UV recently and suggest you look at its properties. I removed my mid-ship hatch and used it to fill voids found between the teak trim and the fiberglass. It didn't leak a drop over seven days of heavy weather offshore. I'm happy with it.

[John Stone]

I agree with Jim to use 3m 4000uv. But I'd take another step as well. Ensure the holes in the deck the fasteners pass through are chamfered. Wrap a small ring of butyl rubber around the shaft of the fastener after you have inserted it through the bowsprit. Apply the 4000 to the deck and install the sprit the chamfered holes will allow bedding compound to be forced down into the hole and around the fastener due to the compression of the bowsprit to the deck.

There is a fine I.illustration/explaination of how to do this on the PBBase Compass Marine website. I used this technique throughout the rebuild of the Far Reach and continue to so so. I have not had a bit of water intrusion.

[hilbert]

I will be working alone, under conditions that are not favorable for a fast curing sealant in the Summer.
The contact area between the bowsprit and the deck is large and there are 21 bolt holes that pass through the bowsprit and deck to backing plates.
If the sealant can be worked into a gasket between the two surfaces, then I only need to secure a few bolts during the application of the sealant and the rest can be inserted at leisure.

Does this seem to be a reasonable plan?

1) Drill out and seal all the holes with epoxy plugs as described in http://www.pbase.com/mainecruising/sealing_the_deck
2) Countersink the holes in the deck
3) Tape off the area of the deck around the browsprit.
4) Trowel the 3M 4000uv onto the deck area of contact.
5) Suspend the bowsprit above the area on a set of shims.
6) Insert the 6 main bolts pictured below, applying butyl tape to countersunk holes on the topside of the bowsprit.
7) Remove the shims, lowering the bowsprit onto the deck (quided by the inserted bolts).
8) Tighten up the bolts.
9) Have a Guinness.
10) After the 3M sealant has set, drill out the open holes to remove excess sealant.
11) Install the hardware using butyl tape in countersunk holes on the topside of the bowsprit.



The deck:

[John Stone]

I may miss something here as I am commenting via smart phone. My eyes just aren't that good anymore.

I believe You can get 3M 4000 in a regular cure speed vice fast cure. If not, there are several different sikaflex bedding compounds that will work just as well as 3M 4000 I just don't remember which ones they are off the top of my head.

Test run--install the fasteners in the sprit with the shafts protruding all the way through the bow sprit. Then see if you can lower the sprit into position. If the bolt holes are not all vertical it might now work as they will bind on the holes . . . that is what you want to find out before you apply the butyl and bedding compound. If it won't work, skip the butyl. With the bowsprit temporarily in position, tape off the deck with painters tape. I use 3M 233 tape as it is solvent resistant.

Remove the bow sprit.

With the fasteners in the sprit, install the butyl donuts around the fasteners--doesn't take much. Then apply the bedding compound on the deck guided by the tape outline. Then drop the sprit down onto the deck. Install washers and nuts (assuming the backing plate is already in position). Tighten the nuts. Clean up squeeze out with a West Systems black stir stick (or plastic putty knife). I use acetone or mineral spirits per 3m or sikaflex data sheet. I like to discard the paper towels, loaded with excess 4000, in a cardboard box. Then pull the tape right away and put it in the box too. I have used plastic garbage bags but as you will see it can be a real mess to get the pulled tape to go into the plastic bag.

Don't trowel it on. Use a caulking gun. Though you can use a notched plastic flat sided trowel to spread the bedding compound to an even surface depth--now that I think about it that's probably what you meant. I would wrap the donut of butyl around the shaft of the fasteners after they have been inserted into the bow sprit so that the butyl is between the sprit and the deck. I would be inclined to countersink the fastener heads in the bowsprit with wood plugs. I think its find to use head heads but you'll need to use washers and it might look clunky. Personal choice. I don't think there would be much use in applying compound or butyl under the washer on the topside of the sprit if you don't chamfer that hole too. And it would seem counterproductive to not have a flat surface under the washer.

I like butyl. But if it becomes a hassle combining it with the 4000 and trying to get this whole thing to line up I would not use it. Also, if you plan to remove the sprit ever now and again it probably is overkill. But you'll have to decide that.

[hilbert]

John, thanks for your thoughtful replies. I think that you are correct that the best approach will be to use a slow curing sealant and install all the bolts at the same time.

Also, if you plan to remove the sprit ever now and again it probably is overkill.

I doubt people ever plan to install a bowsprit more than once, but accidents happen. Even sealants which are relatively weak adhesives can make parts very difficult to separate when applied over a large area.

I would be inclined to countersink the fastener heads in the bowsprit with wood plugs. I think its find to use head heads but you'll need to use washers and it might look clunky. Personal choice. I don't think there would be much use in applying compound or butyl under the washer on the topside of the sprit if you don't chamfer that hole too. And it would seem counterproductive to not have a flat surface under the washer.

I could have prepped holes to hide the two exposed bolt heads in the fiberglass sprit, but I decided to surface mount them and call the look 'rugged'. All the holes have a modest chamfer and I will attempt to apply butyl under the hardware and even the two exposed washers (there will still be plenty of flat contact area).

Cross section of fiberglass bowsprit:

[CD_Sailor]

J ... the best approach will be to use a slow curing sealant and install all the bolts at the same time ...

John Stone is the "man" on matters like this, but I will chime in anyway just for drill.

Regardless of sealant choice or specific sequence, you may find it effective to avoid fully tightening the major fasteners initially. This gives the sealant a chance to cure slightly and therefore not be forced out under pressure. In effect you are building a custom gasket. After the sealant cures bring the fasteners to tension with a strain gauge or similar.

Also, although I believe it has been mentioned elsewhere in the thread, it is a very good idea to over-drill all fastener holes, fill with West epoxy (high strength mix), and then drill the actual fastener holes through solid epoxy rather than any cored material. There is then essentially no chance for water to enter the deck. Using a counter-sink on the holes will also allow your sealant more "work area."

Good luck with this big and important job.

[hilbert]

CD_Sailor, thanks for chiming in.

I have sealed all the deck holes with thickened epoxy and did the same with the sprit during construction. I have also considered the idea of using a 3/16" sheet of neoprene rubber as a gasket between the bowsprit and deck. This would be a cleaner install and it would have the advantage of making both assembly and dis-assembly easier. It would still necessitate a good seal under the hardware or bolt heads to prevent water penetration into the hole and setting up for anaerobic corrosion of the stainless bolt shafts.

The other "man" on all boat matters, Maine Sail, explains sealing the deck in detail at his post http://www.pbase.com/mainecruising/sealing_the_deck.
Rather than overdrilling, he prefers to preserve the skin which is a structural component and dig out the the core with a Dremel. Main sail also has some strong opinions on the 'two step, wait to tighten and form a gasket" method of bedding deck hardware with a "curing" marine sealant.' Well worth the time to read through it.

Does anyone have any thoughts on cutting a gasket from a neoprene rubber sheet to seal between the sprit and deck?

Here is a picture of the interior of the bowsprit with epoxy plugs, before glassing the bottom. The holes in the top skin (red U-Channel) are sized much smaller to match the diameters of the fasteners.

[Sea Hunt Video]

Hilbert:

Thank you very much for posting the link to Maine Sail's tutorial on deck sealing. As always, his tutorials make a lot of sense, are detailed, great photos, etc. For someone like me who knows so little about this stuff his website is a gold mine.

From his discussion and explanation I will be following Maine Sail's advise when I install a deck winch, etc. later this Summer I will be fully tightening each bolt initially and will not be doing the epoxy "two step".

Thanks again Hilbert for starting this terrific thread.

[John Stone]

"The man" Ha. Hardly. But, I do have what I consider an informed opinion. But, its just that . . . my opinion. However, I think there is almost always a number of ways to tackle a project. The only way that is no good is the one that does not work.

When I see the term "over drill the holes" I always assume it is as described by Hilbert. Drill the hole, dig out the core, fill the whole thing with epoxy, etc.

Nonetheless, regarding the gasket. It might work. Who knows. My concerns:
1. One of the advantages of quality bedding compound is it flows and fills slight (or sometimes not so slight) voids and hollow spots in the deck or hardware. Bronze is a perfect example. When bronze is cast, the pattern will have "draft" built in so the pattern can be pulled from the sand without disturbing the hollow left behind. You try to file/machine base surfaces flat but it doesn't always work that way. I bet the deck is not perfectly flat. You might think it is but if you get down on it with a straight edge there will probably be some imperfection. The bowsprit might be perfectly flat but might not. The gasket, when a large flat surface like the underside of your bowsprit pushes down on it might not press evenly into the deck. If water can find it's way into a gap, it will.
2. Bedding compound, especially 3M 4000 or it's Sikaflex counterpart, is a pretty good adhesive just not as aggressive as 5200. There would be no adhesive holding the gasket to the deck or the bowsprit. Also, the gasket won't compress flat and perhaps there could be some give at some point allowing the sprit to move and that could break loose compound around the chamfered holes.

So, I don't see any advantages and only negative consequences to using a gasket for a piece of hardware that for all intents and purposes will likely not be removed for more than 10 years. True, I made my bowsprit removable but it's an entirely different design and does not require any bolts to be removed. It also does not touch the deck at all.

One thing I would recommend you do it to router a recess on the underside of the bowsprit, about 1/2"-3/4" inside the outer edge of the sprit all the way around the perimeter of the bowsprit "where it rests on the deck. Use a 1/4" to 3/8" diameter bull nose router. Set it for about 1/8" to 3/16" deep. When you apply the bedding compound to the deck, you can also apply some to this trough on the underside of the sprit. When the sprit makes contact with the deck the compound will ooze along and the compound in the trough will also be force down and out along the surface of the deck and create and thicker ring of compound all the way around the edge of the sprit. So if any part of the surface between the deck and the sprit gets starved of bedding compound you will be certain you have a seal all the way around the circumference of the bowsprit. This caulking groove ensures that all the compound can't be forced out and leave an area starved of bedding compound where water can sneak in. I use this technique whenever I can. You can usually accomplish it with just a trim router or you can use a larger router with a guide bar. Just remember to not router a groove past the stem of your bow!

The attached picture is a piece of teak for the flue of the reflecks heater I installed in the Far Reach that sits on the cabin top. You can see the groove I cut with the router. I cut this one on the bench top router and you can see the router bit in the back ground. But, I have used that same bit in a trim router and cut the groove free hand and it does the same thing . . . just not as pretty.