Repair to hull under the water line

[rogersimms]

I have searched for this subject online but do not seem to get the right scenario or answer.

If a boat is holed under the water line and an emergency repair is carried out is there anyway the hull can be repaired on the external side with diving gear. There are some parts of my boat that is totally unreachable. I was looking for some sort of epoxy that can set submerged. I read some time ago that there is a cement for steel tanks that sets when the tank is full of water to stop it leaking allthough I have a GRP hull I am sure there must be something similar. I have seen to many large floating bits of drebri that I am sure would have holed my boat should I have been infortunate enough to have hit it.

Sorry if this has been covered before and I have missed it while searching. Just using the time to cover all the things I need to think about while I have the bandwidth

Thanks

 

[savageseadog]

If it's not too deep you could careen the boat over at a pontoon or use a heavy weight suspended from the top of the mast

 

[RobBrown]

I'm pretty sure most epoxy putties cure underwater and indeed I carry some on my boat for just such emergencty repairs, so I hope they do!

 

[oldsaltoz]

G'day Roger,

There are epoxy products that will cure underwater, however they are not designed as a permanent repair solution but rather a temporary fix.

The downside of this product is that it will seal some water in the hull and this alone can lead to major problems over time.

There are also some epoxy based patches available that can be applied underwater.
All available at almost any chandlers.

Pulling a sail or special strip of material around the hull with a sheet of plasic pushed into the hull will also work.

I hope this helps.

Avagoodweekend......

 

[Anonymous]

It all depends on how big the hole is. Last summer, at anchor off the Porquerolles, I decided to remove the grilles covering my bowthruster openings, using my hookah diving gear, as they were getting loose and could have caused a problem -- and are not really required anyway. I took the screws out, removed the grilles and then swam back to the stern to get aboard. Mrs L was in a proper lather....the bilge pump had suddenly started running every few minutes - were we sinking, or what? So we started the compressor again and I went back down and re-checked my work....nothing out of the ordinary but I could hear the bilge pump running from time to time, which it never does. Probably a coincidence?

So, back on board and take off my wetsuit and so on, and have a cuppa, the bilge pump is still cutting in and there is water coming out of the discharge pipe. Odd. Carpets up, cabin soles up, and I see that there is water coming down through the limber holes from the bow section. Open up the most forward section by the bowthruster and I can see a strong squirt of water coming in and daylight shining through the hull from two holes!! /forums/images/graemlins/shocked.gif The screws I had removed were about 3mm self-tappers only about 4mm beyond the end of the grilles I had removed. The bowthruster tunnel is little more than 4mm at the outside /forums/images/graemlins/shocked.gif Anyway, the problem was solved quickly by putting in, from the inside, the same PKs into those holes, drying and a splodge of silicone sealant which will have to suffice until we are out of the water next.

So, if a 3mm hole can do that, just think what a 6mm hole can do (think the fourth power of the radius for orientation) flow volume per second = pressure difference x pi x radius**4 / (8 x viscosity x length of pipe) -- for laminar flow. Keep in mind that these were holes of 3mm and only 0.5m underwater. Suppose we'd had a hole of 10mm at a depth of 1.3m (about the point that our keel starts)? The pressure would have been three times as much and the flow? Let's guess 10 litres per hour from the bowthruster holes, then nearer the bottom of the hull the 10 mm hole might have caused a flow of 7 x 7 x 7 x 7 x 3 = 7200 litres per hour.

Most people keep softwood bungs of various sizes (buy a bag of different sizes from the chandlery) keep them to hand and a darned big hammer to bash them in with.

I have found some figures from a US forum that suggest the same sort of flows....but I haven't checked their physics......

[ QUOTE ]
Flooding rates

Can a boat be made unsinkable? Yes, but it takes some planning and critical attention to engineering details. Boats sink because they fill with water. And given the smallest opening, water will enter and fill a boat at a mind-boggling rate. Because water can fill and sink boat extremely quickly, procedures for handling flooding must be fast and simple.

A quick review of water pressure and flooding are in order. Flooding rates for various size holes at selected depths are calculated using this formula:
Q = 20 x d x square-root of h
Q = flooding rate in gpm
d = diameter of hole in inches
h = depth of hole underwater in feet

[/ QUOTE ] When will the Americans learn metric?

 

[rogersimms]

Thanks for all your replies. I was looking at all possible nightmare scenarios for an ocean crossing. all though rags, sail cloth, and bungs is a very quick fix for letting the brain catch up with the situation I needed to look at something that would be semi permanant and what the general consensus was. I shall be looking for some epoxy that was mentioned above and hope that I never have to use it which just reminds me must get the liferaft serviced /forums/images/graemlins/smile.gif

 

[lenseman]

[ QUOTE ]
When will the Americans learn metric?

[/ QUOTE ]
If God had wanted us to use metric, Jesus would have had 10 disciples! /forums/images/graemlins/grin.gif

 

[Anonymous]

[ QUOTE ]

If God had wanted us to use metric, Jesus would have had 10 disciples!

[/ QUOTE ]I thought he did....ten plus one dodgy one (without whom the Grand Plan couldn't have happened) and a spare /forums/images/graemlins/wink.gif

 

[saltwater_gypsy]

I have found that the underwater epoxy sold by aquarium suppliers is handy for small underwater repairs. It has quite good adhesion in the wet as it is used to mount bits of coral onto stones for artistic effect.
My classic repair was when I noticed that the nut on one of the skin fittings was somewhat corroded.I started to remove it and it suddenly crumbled and the bolt disappeared. This was instantly followed by a jet of water/forums/images/graemlins/shocked.gif AQUARIUM EPOXY to the rescue!!!!!
Lasted for three months until the boat was lifted out. /forums/images/graemlins/smile.gif