Butyl tape underwater

[brak]

As a continuation of ground plate story, I need to figure out something to be used to seal ground plate bolt holes. Using sealant is not a great idea - it can smear on bolts and interfere with electric contact. What about making "washers" out of butyl tape and placing them around the holes (may be in a bevel), then clamping down with the plate? Does butyl stand up to immersion in water or will it dissolve over time?

[sailingdog]

I wouldn't use butyl tape in a below-the-waterline application. Use 3M 4200 or something made for below waterline use.

[Freesail99]

BoatLife Life-Caulk is a long lasting, permanently flexible marine polysulfide sealant which can be sanded, painted and used above and below the waterline. That was from there web site. I have used it and found it does a good job.

[Maine Sail]

I would not use butyl under water either. There is no known rating for below water use of butyl that I know of. Products like 101, 291 or 4200 would be far better choices and should not interfere at all with the electrical conductivity if done correctly.

[brak]

The "done correctly" part is difficult for me to imagine. I would have to place at least some amount of caulk in the hole and, preferably, around.
I could probably maintain enough pressure on the bolt on the outside to make sure caulk does not get between the bolt and the plate. But there is no way to not get caulk on the bolt as it passes through the hole. Once it is on the bolt, no matter how much I clean it, there will be caulk film left in the grooves of the thread and it will reduce electrical contact.

If there is another way that would let the bolt pass through caulk and not get covered in it - I'd be glad to find out, it would make the project so much easier.

[sailingdog]

Why not apply the caulk to the bolt on the outside of the boat, and then insert it into the hole. The caulk will not get on the threads, since it won't get onto the hull until the bolt is already most of the way in place.

To clarify MS's post. Sikaflex 291, 3M 101 or 3M 4200...

[tager]

Brass washers might work... a galvanic cell might be created though, if you are not careful. Nylon washers would work too. If what you want is a washer, they can be bought!

[Maine Sail]

Originally Posted by brak

If there is another way that would let the bolt pass through caulk and not get covered in it - I'd be glad to find out, it would make the project so much easier.

If your palte has threaded holes use bronze studs, not bolts, and pre-thread them into the plate first then apply the caulk then go inside and put nuts on and suck it down.. If you can't find bronze studs simply make them out of bolts by cutting the threaded end off. This will also give you a removable nut, if you double them, on the inside of the hill for ground attachment to the studs.

Generally, at least with DynaPlate's, you bed between an internal backing block & the hull but it does not sound like you have a DynaPlate? On the last DynaPlate I installed we made a fiberglass backer that was slightly bigger in surface area than the DynaPlate and then routed a continuous groove, with a router v-bit, in the bottom of it to capture & retain a thick bead of sealant. I also beveled both of the holes on the inside of the hull as an added safety measure. With both the chamfer and the v-groove it was a double fail safe against leaks.

[brak]

The plate comes with bronze flat-head machine screws that fit flush into the countersunk holes in the plate. Putting the screws in place and then applying sealant as a "collar" behind the plate seems like the most workable solution for using sealant, I will keep this in mind.

I think, though, that I will try butyl this season. My boat will be back out of the water in fall, and I can see then how well it fared. It certainly won't be any worse then previous condition when holes were not sealed at all.
And, since I just sealed the entire surface and inner edges of holes with epoxy anyway - the only job seal should do is keep water from entering inside the boat.

So next season we'll know if butyl dissolves

[AjariBonten]

One Comment About Butyl Tape in Underwater Applications:

I work with underwater buoys that are deployed as deep as 2000 meters. The main body of these buoys is comprosed of a glass sphere that comes in two parts. The hemispheres are mated, a light vacuum is applied, and we seal the joint (on the outside of the joint) with butyl tape. Standard, off-the-shelf, glaziers butyl tape; and the tape has remained intact, pliable, and removable after as long as two years submerged.

(edit: we then wrap with a layer of Scotch 5200 electrical tape as a mechanical protectant)

While this is not a statement that it is the ideal candidate for Brak's application ; I can state emphatically that it will come out of the water in nearly the same state that it went in. Personally, If I were to do this job I might choose it over 5200 for the ability to remove it without using the nuclear option.