Attach Fittings onto Double Skin?

[MASH]

A question for the techies...

How easy/difficult is it to attach deck fittings to a double skinned boat like a Sadler 26? I am thinking of midships cleats and a second pair of tracks for genoa sheet traveller as the standard ones are never far enough fwd to set a rolled genny properly.

Is this doable or really something to avoid?

 

[cornell_b]

you may have to drill a 'test' hole to see if there is space between the inner and outer skins and perhaps find a way to add backing plate between skins...

 

[35mm]

What I'd be inclined to do without thinking too long about it (so it might not be the best method), is to get stainless tube just big enough for the bolts to go through. Drill the holes through the skins to the same diameter as the outside diameter of the tube so the tubes fit tightly. Cut the tube to length for each hole so that it will be flush inside and out. Put the tube in the holes so they are a tight fit and use sealant to seal them. Now put the bolts through the cleat and down through the tubes and put a backing plate on the other side before putting the washers and nuts on. Use sealant under the cleat and in the tubes to prevent leaks.

 

[fryewe]

Epoxy

Drill holes for what you want to mount then ream out the material between the skins and fill between the skins with epoxy through the holes. Some use a bent piece of coat hanger in a power drill to scrape out the material between the skins. When the epoxy has cured re-drill the holes in the solid structure you have built and mount your hardware.

Good luck.

 

[cliff]

Drill holes for what you want to mount then ream out the material between the skins and fill between the skins with epoxy through the holes. Some use a bent piece of coat hanger in a power drill to scrape out the material between the skins. When the epoxy has cured re-drill the holes in the solid structure you have built and mount your hardware.

Good luck.

Can you explain how to do that on a triple skin?
The Sadler deck fittings are mounted on glassed in aluminium plates bonded between the middle and outer skin - this spreads the loads from the fitting - a center cleat can take exceptional loads when the nut behind the throttle decides to use the center cleat to bring 4 tons of boat doing 6kts to a halt within a couple of feet - cleats can, and do, get ripped out of the deck - and how do I know this - well that is another story for another time.

To the OP, be sure you can fit appropriately sized spreader plates behind yout cleat(s) - I cannot remember the interior setup on the 29 but you may be able to slide a suitable spreader plate up behind the inner skin (interior moulding)

 

[bbg]

Drill holes for what you want to mount then ream out the material between the skins and fill between the skins with epoxy through the holes. Some use a bent piece of coat hanger in a power drill to scrape out the material between the skins. When the epoxy has cured re-drill the holes in the solid structure you have built and mount your hardware.

Good luck.

That is the correct way. I have used a cut-off Allen key to ream out material. You need to clear a void that is larger in diameter than the washer you intend to use, and several holes if you are going to use a backing plate. The idea is to replace the existing foam with solid epoxy. Epoxy needs to be slightly thickened so it doesn't spread out or run, and pushed in well.

If there is already a hole through, you can ream out from both sides, cover one side with duct tape with a pinhole in it. When epoxy starts coming outh the hole you should have filled the void.

I prefer to drill out from the side opposite the force, so the plug of epoxy is being pulled against the remaining skin.

 

[jwilson]

What I'd be inclined to do without thinking too long about it (so it might not be the best method), is to get stainless tube just big enough for the bolts to go through. Drill the holes through the skins to the same diameter as the outside diameter of the tube so the tubes fit tightly. Cut the tube to length for each hole so that it will be flush inside and out. Put the tube in the holes so they are a tight fit and use sealant to seal them. Now put the bolts through the cleat and down through the tubes and put a backing plate on the other side before putting the washers and nuts on. Use sealant under the cleat and in the tubes to prevent leaks.

That is not a strong or reliable way of doing it. It will allow the fitting to flex too much and inevitably water will get in. You either have to cut away inner skin and add stiffening/strengthening, or do a sort of "erk out any foam and inject resin between the skins" job.

 

[MASH]

Thanks everyone, great help!

 

[PCUK]

The correct method is to use tubes between the skins a la 35mm. But drill the outer skin to the size of the bolt and the inner skin to the size of the tube. Cut the tube flush with inner skin, fit a backing pad and tighten. Obviously use sealant before fitting. Using epoxy is another more messy way. Use whichever method you prefer, both will work well.

 

[vyv_cox]

There is no foam in the deck of a Sadler 34 and I doubt very much that there is any in a 26.

For the centre cleats I would be thinking along the lines suggested by Cliff. Cut a hole in the inner skin big enough to take a pad larger than the footprint of the cleat. Cover the hole with a decorative teak panel.

For the genoa track you will probably get away with bolting to penny washers. Drill a series of holes with a hole saw, bolt through the deck, then cover the holes with plastic furniture caps. B&Q sell them, brown or white, about 30 mm diameter.

 

[cliff]

There is no foam in the deck of a Sadler 34

Got to disagree with you there - I recently had the decks on my Sadler 34 epoxy injected to get rid of some "springing" - deck cored drilled to reveal the foam core which was sound but debonded in a few places - a grid of holes were cored out and epoxy injected until it appeared in the adjacent hole(s) - a partial vacuum was applied to adjacent holes to help pull the resin through - excellent job - decks now "solid" again

 

[vyv_cox]

I am guessing that they vary, not only across an individual deck but from boat to boat. I have drilled in the area of the chainplates to add two U-bolts and there was definitely none there. The sun shines brightly through both skins of my coachroof and much of the deck. Looking forward in the port side locker I can see open space, there might be foam further forward where I cannot see but none for a couple of feet.

A friend with another 34 has pulled cables through between the skins at the top of the coachroof after removing the centre hatch, definitely all hollow.

 

[cliff]

I am guessing that they vary, not only across an individual deck but from boat to boat. I have drilled in the area of the chainplates to add two U-bolts and there was definitely none there. The sun shines brightly through both skins of my coachroof and much of the deck. Looking forward in the port side locker I can see open space, there might be foam further forward where I cannot see but none for a couple of feet.

A friend with another 34 has pulled cables through between the skins at the top of the coachroof after removing the centre hatch, definitely all hollow.

What hull number is yours?
Along the edge of the deck where it joins the hull there is no foam - the two skins are bonded together there, neither is there any foam in the sides of the coach roof where the windows are fitted. The "roof" itself is foam cored as is the deck. I too have had to rewire the center light in the salon - new cables fed between the inner moulding and the inner skin of the cored roof - sounds to me as if Sadler may have changed their build method somewhere along the production if your and your friend's boats are lacking the foam core in the deck and coach roof.

 

[jwilson]

The correct method is to use tubes between the skins a la 35mm. But drill the outer skin to the size of the bolt and the inner skin to the size of the tube. Cut the tube flush with inner skin, fit a backing pad and tighten. Obviously use sealant before fitting. Using epoxy is another more messy way. Use whichever method you prefer, both will work well.

If it is a fitting which may take substantial load, and the core is of any significant thickness, you need to somehow remove low-strength and compressible material ( ie foam) from the core around an area at least corresponding to and preferably larger than the fitting and its backing pad/washers. Tubes between skins alone do not stop the ends of (for example) a cleat pushing down under load and compressing the foam through the top skin. As it relaxes, the foam/outer skin may not move back fully, letting a leak path appear.

As I said, tubes alone, even if epoxied in, can lead to leaks, and you do not want water in the foam, or even worse balsa, if a core is balsa. I have had a sodden balsa deck core on one previous boat, thanks to a previous owners bad attachment of fittings.

 

[vyv_cox]

I think mine is number 38 but only because that is written on the foam of the cushions throughout the boat. No other number anywhere. When I fitted a horizontal windlass many years ago the aft bolts were sited just above the shelf in the forecabin, plugged with plastic funiture caps. There was no foam there, I bolted to the deck.

My friend found his 'roof' to be completely foam free, he was able to push a wire from the centre hatch aft to the slot above the aft cabin door.

 

[vyv_cox]

If it is a fitting which may take substantial load, and the core is of any significant thickness, you need to somehow remove low-strength and compressible material ( ie foam) from the core around an area at least corresponding to and preferably larger than the fitting and its backing pad/washers.

This is the method proposed in 'Glassfibre Boat Manual'. Works well, even where there is no foam, just needs thicker epoxy.

 

[bbg]

This is the method proposed in 'Glassfibre Boat Manual'. Works well, even where there is no foam, just needs thicker epoxy.

That is what I was trying to describe, although your series of photos does it in more detail and better. Picture / 1000 words and all that.

 

[PCUK]

So the filler is just a tube replacement!

 

[bbg]

So the filler is just a tube replacement!

No. Using your method you could cut a nice plug of outer skin using the tube. If you keep tightening the nut it will draw the outer fitting down onto the outer skin, against the sharp circle of the tube. The outer skin could be crushed against the tube.

Using epoxy spreads the load. Your suggested way is, IMO a bodge. Less messy than using epoxy, but a bodge nevertheless.

 

[vyv_cox]

No. Using your method you could cut a nice plug of outer skin using the tube. If you keep tightening the nut it will draw the outer fitting down onto the outer skin, against the sharp circle of the tube. The outer skin could be crushed against the tube.

Using epoxy spreads the load. Your suggested way is, IMO a bodge. Less messy than using epoxy, but a bodge nevertheless.

Exactly. In fact, I tried the tube method when adding a U-bolt for parking my inner forestay but I found it less than satisfactory. The biggest problem is that the inner skin is unsupported and able to move about. I reverted to the better epoxy method shown above.