"IanM" wrote in message
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Cornelis Koger wrote:

"IanM" wrote in message
...

"Cornelis Koger" wrote:


My Draco 2500 twincab has been repowered with VW td engines and tunnel
drives of my own design, for which I have added a 1 ft long box to the
stern. In fact it is an extension of the hull that supports the 2
tunnels, rudders etc.
Although I've spent many hours on my back under the hull laminating and
painting, now that the boat is back in the water, a steady trickle of
water is entering the bilge through one of the holes where the stern
tube is bolted to the stern. The bolts are not visible outside, they
are in a grp walled cavity filled with polyurethane foam.
I would have bet anything that the construction is watertight, but I'm
glad I didn't.

My plan is to locate the hole by pressing a sponge soaked in dye
against the suspected area, with a helper inside who looks for a color
change of the incoming water.

Is anyone familiar with a product or procedure that can successfully
seal a small hole in a submerged object?

Steve Lusardi wrote:


Perhaps your dilemma is far worse than you suspect. If you have a leak
into a foamed area and that foam is not closed cell, you have foam that
will be waterlogged. If also in that same cavity you have end grain
glass exposed, you will also suffer osmosis. I am afraid you have a
winter project redoing the entire area. The cost of NOT doing that will
be far worse.
Steve

Haul out, rip out stern tube, remove waterlogged foam and dry out, grind
back to sound GRP, replace the bonded in nuts. laminate up a GRP tube to
sleeve the stern tube, bond in place checking alignment carefully, fair
and make good. When fully cured, bed the stern tube and its end fittings
in with plenty of a good quality sealant. (Assuming metal stern tube, a
GRP one gets glassed in directly.) There is NO shortcut. OTOH the leak
could be anywhere along the joint of the hull extension so you may have
an even bigger job as if its leaking at the joint, the structural
integrity of the whole addition is questionable.

If foam wasn't involved you *might* have been able to bodge it with epoxy
putty applied underwater. The dye isn't going to be any use as the
volume of water allready in the foam will dilute it to the point that you
dont get a clear colour change in anything like a reasonable time to keep
the sponge in place.

Been there myself and spent a winter on the hard fixing it right.



Did you write this to cheer me up?
The stern tube, 2,5" diameter, has a welded on flange of 10x12", bolted
to the outside of the 2" thick stern. A short 3,5" tube is welded on the
inner side, laminated in the 2"stern with just glass and resin, almost
flush with the inner engine bay wall. The 4 holes in the flange served
the purpose of assembling and aligning the construction only. All metal
parts are marine grade stainless steel.
The stern tube protrudes 2 ft behind the stern, has ball bearings and
tapered roller bearings to take up axial and radial forces and is oil
filled. Ripping that all out really is no option!
The tunnels are 15" half circles, a little over 2 ft in length, made from
GRP and laminated to the stern and the extension, no leakage there. At
that point of the job, I should have smeared some Sikaflex around the
heads of the 4 bolts, but at the time I didn't think about it.
Because the tunnel entrance was blunt and fairing impossible, I made
something that could best be described as a sloped ceiling. Six layers of
GRP form a warped disc, laminated to the tunnels and the boat's bottom
with roving and expoxy. When that was done, I left a small gap to stick a
plastic tube in and filled the cavity with a polyurethane product used
for sealing sewers and wells. Over 98% closed cells, doesn't rot, but
hates UV. After it hardened, I cut off the excess foam and closed the gap
with epoxy/glass.
Finally, I quickly gave it a coat of anti-fouling and put the boat back
in the water with the next high tide.

The water started coming immediately, so my guess is I overlooked a small
hole in a corner or somewhere along the seam between the bottom and this
"ceiling". Probably a maze in the roving that was too large for the epoxy
to fill. As you know, epoxy looks quite capable of filling gaps when
applied, but when it warms up during curing, it is thin as water.

This concerns the starboard tunnel, the port one, with identical
construction, does not leak.

Haul out *IN PERSON*, wipe down and look for drips (dont let the yard
pressure wash). If you get lucky you *might* find the gap. Otherwise
drill into the cavity and apply air at a pressure of no more than 6" water
gauge, and wet all suspect areas with a 1/3 solution of dish detergent in
water and look for bubbles. You've then got the problem of drying out the
foam.

If the leak *IS* round the stern tube, it will almost certainly have to
come out. I would never trust a directly glassed in metal stern tube as
unless there is a resiliant sealent between the GRP and the metal, thermal
shock alone can break the bond, let alone shaft vibration.

You haven't left youself any maintenance options with a one piece welded
up stern tube and flange directly glassed in :-(

Ideally one should be able to pull all bearings etc. from the stern tube
and heat it up to break the bond and remove it non-destructively for
repairs etc. Some light cleanup of the GRP shell round it and some fresh
sealent and it would all go back together sweetly. Bit late for that now
though.

I hope for your sake the leak is elsewhere.

Thanks for your advice, I'll post my findings later.
I did think about maintenance when I designed this, but I expected possible
problems to be inside the tube, not around it. There are removable covers at
both ends of it to renew oil seals or bearings in case a seal would fail and
water has entered the tube.