Since it is just a very small hole (less than 1/8 of an inch) in mild steel
hull you can just drill it out with an appropriate size drill bit and tap it
to be able to screw in the correct size threaded bolt/screw to use as a
plug. You have to make sure though before starting that you have all the
necessary tools (drill bit, correct tap with wrench and correct size
plugging screw) on hand since you have to accomplish the repair process
quickly to avoid getting in too much water. After you install the plugging
screw it's pretty much almost like a permanent repair and you can even weld
it in place if you want.

wrote in message
...
Hi all,
No rush for answers on this one, but I'm sinking... I found a bit
of water in the bilges and put it down to something benign, but on
inspection, found a blister on the paint inside the hull, which when I
burst revealed a ~2mm square hole in the hull on the bottom of the
boat. I've plugged it with gaffer tape, rubber mats and bits of wood
for now, but has anyone got any neat ways of fixing this without
taking it out of the water (boat is a 20 tonne wrought iron/mild steel
dutch barge, and a proper repair job would be ~£700)?
I'm thinking a bolt with a big rubber washer on both sides and
liberal use of silicon sealant. I'm hoping the rot is very localised.

cheers

Jim
UK