Silicone

[irwinsailor]

I spent a great deal of time researching how to replace the 11 windows in our boat. And I decided to use the Sikaflex system, they were very helpful the three times that I called them when I had questions.
As for holding the windows in place while the Sika setup I cut some 3/8" strips of starboard and use them as spacers, kinda like the plastic stars used in tile setting. Then I used plungers with PVC pipe to hold the plexiglass tight. It worked flawlessly.

[Tnflakbait]

DOW 739

[Alan Wheeler]

GreatKetch said---There is a lot of mis-information (IMHO) in this thread about the appropriate sealant to use for bedding hardware.

Hmmm, no I don't think it is misinformation. Just different ways of doing the job. When I bed something down, I don't expect it to come off for a very very long time. Screws and bolts place the the load on a very small surface area. A winch base for instance. I have beeded my winch bases down as well as bolts. It ensures the load is taken over a far greater surface area. I have also had to shift them just recently and although it took some effort, they did come up in the end. I have not been put off by that effort and am happy to bed them down once again. By the way, once I have drilled a screw or bolt hole in timber, I then poor in thinned epoxy or evadure to ensure the timber is well sealed and provides a very strong screw hold.
I have had a winch disapear into the distance because it ripped out of the deck. It was a big heavey bronze winch and the sheet flung it as if it was a piece of plastic. It was scary. Never want that to happen again. And I hate to imagine what would of happend to me if I was either int he way or was still holding on to the sheet at the time
Silicon in my opinion is very good as a gasket medium. I don't think there is any other product out there that comes close to it for gasket uses.

[GordMay]

Not to beat this issue to death; but:
NOTHING (I know of) adheres to Silicone, or the silicone oil residue - not even Silicone (no cohesion between cured silicone & a new layer).

[ssullivan]

Originally Posted by Alan Wheeler

Screws and bolts place the the load on a very small surface area. A winch base for instance. I have beeded my winch bases down as well as bolts. It ensures the load is taken over a far greater surface area.

Wheels, I hate to question, but I do have one. How can using an adhesive give a properly mounted winch any more surface area to grab onto?

I mean if you have a proper backing plate (the size of the winch or larger), and it pulls out, it is going to take out the entire amount of deck under then winch, which is where your adhesive would be. Not understanding the logic.

Definitely not trying to start a big old debate, but not understanding how the adhesive would help hold a properly back-plated winch in any way.


PS: That winch story *is* scary! Wow.

[FrankZ]

Originally Posted by ssullivan

Wheels, I hate to question, but I do have one. How can using an adhesive give a properly mounted winch any more surface area to grab onto?

I mean if you have a proper backing plate (the size of the winch or larger), and it pulls out, it is going to take out the entire amount of deck under then winch, which is where your adhesive would be. Not understanding the logic.

Definitely not trying to start a big old debate, but not understanding how the adhesive would help hold a properly back-plated winch in any way.

Would the adhesive help spread sheer loads? Just guessing here.

[Pblais]

Would the adhesive help spread sheer loads? Just guessing here.

A backing plate would already do it better and the adhesive would add nothing significant other than acting as a water seal and a PITA down the road.

Pretend you used a few roofing nails to attach a primary winch to a solid wood deck (very dumb idea I'll admit) and nothing else. Now do the same thing with a second winch but add a strong adhesive as bedding.

The second winch takes more load but in a real working situation it still fails as the wood shears and the worthless nails pull out. That same situation is a failure to either winch as the first has no adhesive and fails far earlier as we all would expect.

At the end of the test both winches are gone. Does it really matter that the second one remained attached longer? You want both winches remaining after any test. The sheet should break before the winch gives way in a successful test. A through bolted backing plate give you the best chance of this AND lets you remove the winch if required (if it broke). Just how could you ever get it off if the adhesive really worked as well as a backing plate!

Originally Posted by GordMay

Not to beat this issue to death; but:
NOTHING (I know of) adheres to Silicone, or the silicone oil residue - not even Silicone (no cohesion between cured silicone & a new layer).

Gord, that is a little too general a statement, it does depend on the silicone, and silicone in some applications is used as an excellent adhesive. It is extremely good at gluing two pieces of glass together, for example. There are millions of aquariums, including very large ones, held together by silicone only.

I don’t completely discount the painful experience reported with painting over silicone, but it is not universal to all types of paint and all types of silicone. I certainly know and have first hand experience with the miserable pain that silicone polishes can cause furniture refinishers. Those &*#$ fisheyes!

I have painted areas on my boat that had silicone sealant extensively applied by a PO (inappropriately, I might add!). Using normal surface prep I had no problem with the paint I applied.

For those who had so much trouble with paint and silicone, did anybody contact the manufacturer of the sealant to see if they had suggestions or comments?

[Alan Wheeler]

Once again, I think their are two views and they are widening and neither totaly right or wrong here. Because it really depends on the situaton.
For sealing, I have found many many times where something has supposedly been sealed by silicon, has failed and leaked. Now it is quite possible that the original installer did not do the job properly.
As for beddign, a backing plate is not always posible. Very common and essential on fibreglass construction to have a backing plate. Not always so easy on timber construction. But I use adhesives to bed down winches on the mast as well. I like the idea of not having all the load taken on only 4mm(1/4") of thickness that the little 6mm screw holds onto.
As I said, I have had no issue with removal, I just use a sharp knife and cut through it.

[FrankZ]

Originally Posted by Pblais

A backing plate would already do it better and the adhesive would add nothing significant other than acting as a water seal and a PITA down the road.

Pretend you used a few roofing nails to attach a primary winch to a solid wood deck (very dumb idea I'll admit) and nothing else. Now do the same thing with a second winch but add a strong adhesive as bedding.

The second winch takes more load but in a real working situation it still fails as the wood shears and the worthless nails pull out. That same situation is a failure to either winch as the first has no adhesive and fails far earlier as we all would expect.

At the end of the test both winches are gone. Does it really matter that the second one remained attached longer? You want both winches remaining after any test. The sheet should break before the winch gives way in a successful test. A through bolted backing plate give you the best chance of this AND lets you remove the winch if required (if it broke). Just how could you ever get it off if the adhesive really worked as well as a backing plate!

The original question I replied to asked about using adhesive with a properly backed winch which is where my conjecture went.

Nails are used in constuction all the time because they are a cheap way of joining things that you don't want shearing apart. The do not provide tensile stregth very well.

In your example if you were pulling the winch straight up the nails would be useless. The adhesvie would slow the failure but, unless it was some magical adhesive that had 100 % resisteance to tensile pull, it would fail sooner or later.

I don't know if adhesive would help slow the side load shear, but I also suspect if the load was parallel to the backing plate it isn't doing much to help either and the winch would be trying to shear the bolts straight across. That being said the loads on a winch shouldn't be parallel to the backing plate as the sheet should be going in at an angle which is where the backing plate comes in.

Of course this is pure conjecture on my part and not the area of background for me. And when it comes to loaded hardware a backing plate does make sense to me to use.

I suppose a bedding compund that has some sort of adhesion also would help with seal integrity if something is moving about even a little bit. With a pure gasketing material one would think the gasket and bits sealed could move away from each other and allow water in. And, over time, that may get worse due to friction and chafe of the gasket material in the joint. Again, it seems reasonable to me that this could occur, but I have not tested this out nor am I an expert here.

It would have been a lot cheaper for me to just nail the new winches to the gunwales instead of by those nice stainless bolts, washers and backing plates and likely quicker. The cost may have risen in the end when they flew off the boat and I needed to replace them.

When I refit the deck I rebedded everything in polysulfide. The only leaks I had were where I didn't get enough goop in to get everything touching or didn't crank down well. I have had to pull a couple things back up, to make changes and it wasn't difficult to get things apart with it, but they didn't just seperate when the bolts were pulled and I pulled a litte. A sharp putty knife cut it away nicely though.

[GordMay]

A “simple” gasket has to be:
~ thick enough to accommodate any compression on one side,
~ elastic enough to expand into the corresponding peel gap on the other,
~ and resilient enough to recover from both.

An adhered gasket also requires enough thickness to absorb compression, but will be will be pulled into the peel gap.

Silicone sealants, having only moderate adhesive qualities, act like a simple gasket.
Polyurethane, Polysulfide, and some Modified Silicone adhesive sealants act like adhered gaskets.

The prime advantage of Silicone, is that it doesn’t adhere too well – which can also be a distinct disadvantage.
Silicone’s prime disadvantage is that NOTHING sticks (well) to it.

If either require removal – it’s a mechanical job (polyurethane due to it’s adhesive strength, and silicone due to it’s pernicious residue, to which nothing will adhere).

Why not get the significant benefit of polyurethane’s adhesive strength?

Polysulfides have the added benefit of oil-resistance, which is why they are used in bedding teak.

[Pblais]

Shearing the through bolts is a whole lot of pull. I don't think the sheet could handle that much force. That force would be far greater than the holding power of the adhesive to the deck surface or the deck suface itself.

My point of the example was that if you did almost nothing as far as bolts, screws, or nails then the adhesive really isn't enough to hold the winch on it's own. Adding bolts won't make the adhesive hold any better. The through bolts are far stronger. The adhesive adds really nothing since the bolts alone are far stronger than the sheet. Using a good sealant will just make it easier to remove the winch later on and prevent water from going down the holes.

Nothing says you have to use a tiny backing plates or tiny bolts. Larger is better.

If you are thinking sealant I wouldn't think of adhesives as being better sealants. There are not.

[ssullivan]

Originally Posted by Pblais

Nothing says you have to use a tiny backing plates or tiny bolts. Larger is better.

This is the philosophy I used when mounting my deck-mount genset (hi DefJef). He loves deck mounted gensets.

Anyway, I used 1/2" bolts and huge, oversized washers that were close to, if not, 2" in diameter. The genset weights about 200lbs and rests on a custom steel frame. I also sealed the whole thing with silicone. Hasn't leaked a drop in a year and a few months, which is a good thing, since the bolts are direclty over the master stateroom berth!

Not sure what that says about the thread's main point, but I think Paul is correct above. It's all in the mounting hadware.

[Pblais]

I also sealed the whole thing with silicone. Hasn't leaked a drop in a year and a few months, which is a good thing, since the bolts are direclty over the master stateroom berth!

Trust a man who bets his sleep on it!

[FrankZ]

Ok. Just for fun (I really need my head examined if this is my idea of fun) I decided to go hunting for the techinical side of all this. As I have said I am not an engineer, nor am I trying to be obtuse, argue, fly in the face of conventional wisdom, or otherwise say people should attach high load hardware to their boat with shoestrings and bubblegum.

I was able to find out that 316 SS has a tensile strength between 75 and 90 Ksi. Ksi is 1000PSI. I found references to sheer strength being .6 x tensile stregth. It also appears that the proof or yeild strength is around 30Ksi. This seems to be the point where it starts to deform, which leads to failure.

I then decided to work with my winches. I am messing about with the numbers so I get to chose which winches we are dealing with. I put on new Harken 16STs last offseason and they require 1/4 bolts. If we use the upper and lower tensile figures from above that would mean (if I can use Excel properly):

KSI Tensile(pounds) Shear(pounds)
90 4415.625 2649.35
75 3679.688 2207.812

This would be for a single 1/4 bolt if the load was entirely on the shank and not thread. The threaded cross section would be less. I am not going to deal with that bit as you would need to know how deep the threads are and then.. well.. this is supposed to be fun right?

As I stated before I am not an engineer so I am not sure how this will translate into the bolt pattern itself. Are the 5 bolts (one bolt spot is where the drive gear is and faces the load entry) that hold the winch down simply additive, or does it get more silly than that with the diameter of the bolt pattern itself? I suspect for tensile strength or sheer it would be additive. If it isn't an additive thing then below wouldn't work and we can stop reading and go sailing.

KSI Tensile(pounds) Shear(pounds)
90 22078.13 13246.88
75 18398.44 11039.06

The next thing was to look at sheets. I use 3/8 inch, and again I get to pick the ones we use. I am also using New England Ropes for reference.

Type Tensile(pounds)
Sta-SET 4400
Sta-SETX 5500
Regatta Briad 4200
V-12 16800
Endura Braid 10000
Endura 12 19000


So with 5 x 1/4 bolts having a estimated sheer strength of 11039 at the low end. It seem there are a couple of lines that would be stronger than the bolts. If we go to the top end of 22078 pounds we come close with the Endura 12 in 3/8 size, but going up one size to 7/16 we get a tensile strength of 24000 pounds.

Of course the final bit is the adhesive. (I bet you were wondering when I would get to that)

3M lists 5200 as having a tensile strength of 700PSI.
The Harken 16ST has a base diameter of 4.75 inches. With a perfect bond and without the water channel in the base we would get 12389 pounds of tensile strength. There is no data for sheer that I could find. They do mention a whopping 1350% elongation before breaking which I thought was interesting.

Since I use the Sta-SET X 3/8 line for sheets all the above could boil down to you can glue your winch to the deck. This Of course that would mean the deck has to be able to hold, including all the layers needing good bond and such. 3M lists 5200 as high strength on gelcoat, fiberglass, wood and metal. Not as good on rubber or plastic so I suppose glueing down the winch on a rubber deck wouldn't work as well.

All in all this points to a situation where it "could" be done. Not that it should be done. I do realize that a lot of this is over simplified as well.

Just to make everyone sleep better at night I used a 3/4 inch wooden backing plate under the winches that was as large as I could fit in the space and large fender washers too. And bedded with polysulfide just in case I ever think I might need to remove them.

If I fuddled this all up and someone has a better answer I am all ears.

Apologies for the length as well.