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Old 07-12-2007, 22:42   #1
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deck fittings on a steel yacht


I'm looking for advice on attaching deck fittings such as winches, sail tracks etc to a steel yacht.

Is Duralac enough or should the fittings be bedded down on something like a UV resistant rubber?

Is there a better way of protecting the bolt holes than painting them?



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Old 07-12-2007, 23:34   #2
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Personaly I like to bed fittings down. It means that there is a gasket between the fitting and the material it is bolted to and it means all bolts/screws are watwer tight and in the case of things that take load, the load is spread over a little more area than just the screws. I would use Urathane adhesive sealant that comes in the tubes. Many here talk about a product called 5200 (?) I guess that must be one of those Urathane adhesive sealants.


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Old 07-12-2007, 23:40   #3
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Using the "Nike" method...

The PO of Boracay just bolted fittings to the deck with a black sealant, possibly some kind of Sikaflex. This has mostly worked worked well save where insufficient was used and a void remained that allowed oxygen rich salt water to sit on the paint. Rust then occurred.

The only major problem was when a hatch was packed up with epoxy putty. This pulled away from the steel taking the paint with it, salt water and oxygen got into the cracks and substantial rust followed.

I have used silicone rubber in excessive amounts with some success (The cleanup uses large amounts of turps and paper towels). It does seem to be water repellent though many have reservations about future painting. I have not noticed any problems so far.

I liked the silicon rubber (I used a cheap version) as if it pulled away the silicon gave way, not the paint, so there were no problems with rust.

The other advantage of excess silicon is that it reduces the need to be obsessive about painting.

In critical places (deck fittings) I have cleaned with turps and primed with an epoxy primer. Any rust is treated with phosporic acid. For the deck anchor winch switch that I am mounting at the moment I am going to paint with a single pack polyurethane as well.

Any rust, other than slight surface rust, has to be chipped and brushed to "bare" metal before priming.

I am about to try a polyurethane based sealant as it may be easier when painting later.

Whatever method you use I feel it is always necessary to monitor for rust round the edges.
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Old 08-12-2007, 01:58   #4
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As above, with the addition of ....Flex is the enemy of a water tight seal. If you are bolting on somthing that is to have a high load then have a serious look at the deck. For example, if you are not in a position to weld doubling plates to lessen the possible flex, can you add stainless plates below. These plates should be as wide as the application allows. Deck frames ALWAYS get in the way. Drill holes through for your application then glue with lots of sealant of your choice, a plate or plates (SS) to the underside. Now be patient and wait for the sealant to firmly hold the plates in place. Next, drill down through the plates using the pre drilled holes. Attach as per previous post, with one addition. Put a large squirt of sealant from the underside up through the hole after you have put the bolts down but before you put the nuts on. This is a messy business when tightening, but what ends up happening is that the nut forces sealant in compression back up the hole, creating a no void seal. For winches 10 mm plate in unsupported deck is a minimum (the wider the better to deal with shock loads). For other applications 6 mm twice the surface area of the footprint is the go. If you can weld SS fittings with SS wire and repaint the whole lot. Dont forget to repaint the under side. Join the Metal boat society and get a second opinion !!
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Old 08-12-2007, 02:55   #5
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The area the hardware goes onto should be finish painted and flat. After the fastener holes are drilled they should then be touched up with an epoxy primer/undercoat (assuming you are using an epoxy based system for priming/undercoating) - if a new boat the paint manufacturer will not have specified a zinc based primer so don't use one of those.

The deck hardware should be bedded over its whole base surface on a marine polyurethane type sealant such as Sikaflex 291 (a google will take you to the Sika site and the data sheets). Sealant should also be sufficient to squeeze down into and seal the fastener holes as well - important with steel as the fasteners will have likely damaged the touch up paint you will have used beforehand - and up into the fastener hole in the hardware to under the fastener's head so the fastener is sealed right through.

Tighten the fasteners up just enough to squeeze out excess sealant then clean up around the hardware. The polyurethane sealants are messy stuff - I find that a rubber coving tool as is sold for coving bathroom sealants when applied in corners is great for this job. Then wipe around with a rag wetted with methylated spirits (denatured alcohol in USA) which will remove uncured Sikaflex 291 but not too much alcohol else it will affect the cure of the sealant. Use the same to clean your hands which will be sticky by now .

After the sealant has cured, nip the fasteners up tight. If you have any sealant mess that you didn't clean up before you will have to mechanically remove the bulk of it now it is set but again alcohol will remove the final traces after doing that, if necessary.

For winches mounted on steel coamings, deck, etc makes sure that you don't seal up any drain holes there may be in the winch and that the sealant does not get up into the body of the winch through its base fastener holes to affect the operation of the gears, etc.

For things like turning blocks for sheets, etc that may need to be at an angle to the deck to give a correct lead for the sheet or whatever then a teak block can be shaped to go between the block and the deck with sealant top and bottom, but I recommend the use of as little wood as possible.

For large based items such as anchor windlasses I would avoid using a wooden block to take out any camber in the deck to give it a flat base to sit on. The best way for sure on a steel boat is to make a low dam on the deck the same shape as the windlass base but a little bigger all around. Fill that with epoxy thickened with fibres (you will find instructions for this on the West site I think) so that you end up with a flat surface for the windlass base to sit on with enough thickness at the crown of the deck so that it has some integrity (say 1/4 inch or so). When the base is cured cove around the outside with epoxy thickened with microballons. Then fit the windlass with sealant, etc as described above.

If the windlass motor DC supply is not isolated completely from the windlass (I think most are but pays to check) then you need to consider if you need to isolate the fastenings from the steel deck with insulating bushes or not, that depending on how you have done your electrics. The general recommendation is to insulate anyway as the chain is electrically connected to it and the zinc on the chain thus may act as an anode to noble metals underwater on your boat. But if your boat is well painted underwater with an epoxy system I have not found it any problem and our own is not so insulated (we only have one anode that on one side of the fin keel and that lasts a couple of years so we have a galvanically inert steel boat).

While on windlasses, if it has an integral chain pipe as many vertical ones do, or when fitting a stand alone chain pipe it pays to weld a short piece of stainless steel pipe under and up through the thickness of the deck (welded above and below to seal) so that as the chain goes down it does not whip against the edge of the hole in the steel deck which will create a big rust problem but rather whip against the ss pipe. If the windlass is of the type with an integral chain pipe and is mounted on an epoxy base then the ss pipe can preferably come up through the deck sufficient for fillet weld around the top, that all then buried in the epoxy base.

Hope that is of some help.

EDIT: I note the mention of backing plates above. These should not be necessary on a well constructed steel boat and will introduce problems of their own, for example with respect to insulating over them and also a hidden area which condensation will wick under (you will get condensation of the fasteners). In our own case our deck is a mixture of 4mm and 3mm plate (3mm being used as much as possible to keep weight down). The big sheet winches for 500 sq.ft. genoa are mounted on the cockpit coamings pressed out of 3mm steel and these are no problem at all (but stiffness is given by the box shape of the coaming). The windlass is on 4mm deck with no doubling or stiffening whatsoever, but mounted quite close to a deck beam.

If a doubler is needed then I would suggest a plate welded all round but would actually lead you to just stiffening the deck underneath with a bar welded on edge and which only needs to be 3/4 inch or so high.

In the case of our bollard made from ss pipe for taking the anchor load when anchored there is a ss doubling plate welded on top of the deck of sufficient diameter only to stop the chain damaging the deck and under the deck just one bar about 1 inch x 1/8 inch welded on edge aligned fore and aft. None of this has ever been a problem even though we operate in a boisterous area.
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Old 01-01-2008, 00:33   #6
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Thanks for that. Lots of good advice.
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Old 01-01-2008, 01:47   #7
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If you use 3M 5200, you will need dynamite if you ever need to take the deck fitting off. 3m 4200 would be a better choice or a Silkaflex product.
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Old 01-01-2008, 19:21   #8
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Another way

Well, there is another way to do it that avoids having holes in your steel deck which you don't need. You can figure out the mount locations, then weld stainless acorn nuts of the appropriate size flush into the deck at the appropriate locations, first fill the threads with clay to protect them. In fact you can put acorn nuts all over the place where you might later want to fasten stuff down, like teak gratings , hand rails, fairleads, snatch blocks etc., i.e. all sorts of stuff. If the deck where you want to mount isn't strong enough, get under it and weld on some big backing plates, extra reinforcement angle iron, or whatever you need to ensure, its SEAcure , alternatively, weld down a stainless mounting plate, and screw your fitting into that.

ANY bolt hole in a steel deck that carries any substantial load is eventually going to 'work'. When it does, you're going to get moisture, abrasion, and rust..just a matter of time unless the load is trivial. using the acorns solves that problem and leaves the steel deck's watertight integrity intact.

If you're worried about burning paint or causing fires, either use a mig, borrow a tig, and/or use wet towels to keep everything except the immediate area you're working on, from becoming too hot while you're putting in the acorns, then touch up as you would any other area of the boat.

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Old 01-01-2008, 20:18   #9
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Lots of good ideas above ! We have been using silicone where we may need to remove an item for adjustments at some stage and Polyurethane sealants where we do not intend to remove the item. Underneath the item we sometimes use a hypalon sheet to make a gasket or if it is a big item or needs packing we use a HDPE chopping board, the cheap ones you get from supermarkets, cut these to profile of the item and use the sealants as well.
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Old 01-01-2008, 21:14   #10
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I use teflon or nylon pads or washers as electrolytic isolators between my aluminum boat and two steel oceanographic cable winches. I also do the same with my stainless steel stanchions which are thru-bolted. I "bed" them down with Tef-Gel which forever remains flexible. I also use nylon sleeves over the bolts. Paint will not stick where electrolysis is well as losing good metal to electrolysis.


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