Fitting a through deck U bolt for jackstays

[gyoungs]

I have bought an 8mm U bolt to act as the mounting point for webbing jackstays on the foredeck. It has plates to spread the load. In the area where I want to mount the fitting there is no access to the underside of the deck directly. Down below in this area there is a moulded in head lining which is the ceiling of the fore cabin. I am not sure what the void between the two skins is filled with.

My plan is to drill straight through both the desk and the headlining from the top. Then with a hole cutter cut out say 25mm holes in the headlining from below. Insert plate (somehow) seal and tighten.

Any tips / alt suggestions welcome. Cheers.

 

[oldsaltoz]

G'Day Gilbert,

'U' bolts will leak if not properly installed, you don't say what your deck is made of, solid glass, sandwich with end grain balsa, timber???

The fixing method will vary depending on the material.

Let's assume it's solid GRP; dill your holes about 1 mm oversize so you can coat the raw glass with a little epoxy, as for the fitting of the backing plate, I would recommend you install a small (100 mm) 4 inch screw in inspection port, this make access easy when fitting and for checking later, don't forget to add plenty of sealant around the U-bolt when you first place it thru' the deck.

If the underside of the deck is curved, you will need to some form of packing, I normally apply a liberal coat of Vaseline to the bolts to prevent the epoxy grabbing them and fill the void with micro-fibres and resin, pull it up finger tight and fully tighten the next day.

Let us Know if your deck is solid glass.

Andavagoodweekend........

 

[gyoungs]

Good point.. what is the boat made of ;-). The boat is GRP. I am not sure what the construction is in the fore deck area. The thickness from the top surface of the deck to the bottom surface of the headlining must be about 2.5 inches so I doubt it is solid GRP. To be safe, I guess I need to know the method for either solid GRP and balsa core so that when I drill through, the hole is compatible with both methods (hopefully). What would the method be for balsa core?

Cheers.

 

[Swagman]

Re Balsa Core

It's the same as above but after drilling through the deck, put a short L shaped piece of metal into a power drill and inserting it into the hole - so the L piece goes between the two skins - use the drill slowly to rout out the balsa around your between the two skins.

Then fill the void with solid epoxy stiffened with strands of glass so that the gap between the outer skin and the inner skin is bridged - let it all go off - and re-drill your hole a second time.

If the jobs done properly you'll now find the hole is now going though the solid GRP you've created - and the fitting can be mounted without risk of compressing the two skins together when tightening it up - or any water ingress betwix the two skins if your sealant ever fails.
Cheers
JOHN

 

[oldsaltoz]

G'Day Gilbert,

The method for a core filled or Balsa deck is as follows:

If we simply drill through and bolt down onto balsa we will have two problems, water entering the exposed balsa will cause it to rot, soften and the effected area will continue to grow; also, balsa is a soft material that will crush under the loads imposed by through bolting, so we need to make a water tight hole that is strong enough to withstand the pressure of thru' bolting.

First drill your holes 10 mm oversize, find an old alen key and grind the short leg on one side at about 30* and with short end on a hard surface give it hit with a hammer to bend the still hot (from grinding) end to put a small bend in the tip, this will be your cutting edge.

Using a small screwdriver, remove what balsa you can by inserting the driver at an angle and turning it till you have enough space to put the alen key in, drop the alen key into your drill and remove the rest of the balsa to the depth of the alen key short leg; make sure you clean the balsa from both internal surfaces for a good bond, and blow out any remaining dust.

Put some tape over the bottom holes, mix a small quantity (a thimble full) of epoxy resin and put some in each hole, work it around inside with the alen key to wet the whole inside, remove the tape and drain off any left over, replace the tape and mix more epoxy resin adding some Micro-fibres or fine cut roving cloth to a thickness much like toothpaste. Fill the holes taking care not to trap any air inside, add small amounts and work them to the sides till full. Let this cure overnight.

Next day, drill your holes to the required size, add some sealant to the u-bolt and it's deck plate, cover the threads with Vaseline and push it thru' the deck.
Using more epoxy resin and Microfires or fine cut roving cloth apply a liberal coat to the backing plate and do the nuts up finger tight, clean up and resin that is squeezed out and let this cure overnight, next day fully tighten and your all done.

Note: adding the resin to the balsa prior to the fibre mix will help the resin soak into the balsa and not only provide a good seal but also improve the bonding.

A small 100 mm inspection cover of the screw in type will make access to rear easy and give a neat finish as well as provide easy access later if required.

Avagoodweekend.........

 

[William_H]

Now for a different approach to managing the interior lining problem. Abandon the U bolt and get a large saddle to suit. ie U shaped with holes at each end for screws. Get a piece of stainless steel bar about 1 inch wide 12 inches long and 6mm thick.. into which you tap holes and threads for bolts to suit the saddle.
Cut a hole in the deckat least 1 inch in diameter then file it to oval shape as necessary so that the bar can be slipped into the cavity under the deck but over the lining. Using temporarily extra long bolts hook the bar and pull it up to the under surface of the deck by pulling up with a wire loop or passing the bolts through a narrow plate on the outside.
Now fill the hole with epoxy with filler as described above. Put lots of grease onto the bolt threads so that when the epoxy hardens you can unscrew the bolts. Finally attach the saddle on top of the epoxy. The area of deck with smooth epoxy will be a little eyesore but being under the saddle may look as if it was intended. Paint the epoxy to protect from sun.
The strength of the attachment depends on good threads tapped into the bar( thicker the better) and the size of the bar. A suitable tap can be bought from tool shop but for large bolts be carefull not to smap the tap off when making the thread. The difficulty may be in getting the bar into position and also in getting the tempory bolts out of the epoxy filler.
Just a thoght no I haven't tried it but good luck. Olewill

 

[gyoungs]

Thanks all for the comprehensive answers. Much appreciated! G