Raising a sunken boat.

I guess this is an unusual DIY job, but think this is the best place to put it.

It looks like I am about to be tasked with raising a sunken cabin cruiser, I will try to post a picture in a while.

It has sunk on a mooring, and is only partially submerged.

It has gone down by the stern, and is held in place by the mooring ropes.

I have heard that it is possible to raise a semi submerged boat using a sheet of ply, a tarpaulin and one or two pumps.

The idea being that you place the sheet of ply over the open deck, place the tarpaulin over the ply, with weights to pull it as close as possible to the hull.

The theory being that as you displace the internal water, it pulls the tarpaulin tight against the hull and ply sheet, and provided you can pump water fast enough, it should raise the boat.

Whilst I appreciate that this is an army forum, I know that there is a wealth of knowledge here, and hope to avail myself of it.
Won't it depend upon how it sank in the first place?

I.e. if the hull is holed, or is leaking badly because of rot, pumping out won't have any effect.
Love this!
Are you a diver?
Is the water tidal?

If tidal, place lifting bags/empty LARGE plastic containers around the boat, inflate them and get the boat as high in the water as possible, then, then at high tide, get it as far up the beach as you can.

Tide goes out, get the oggin (technical RN term for water!) out of the hull ASAP using whatever you have to hand.

Remember to fix the cause of the initial sinking before the tide comes back in!

If non tidal, it can still be done using the principles above.

EDIT Damn, beaten to by by JS with seconds to spare!
You don't say if it is holed or not?

If it's not, airbags and pumps, if it is holed, revert to the old way,plug on the outside of the hull, airbags and pumps, as you pump out, water pressure will push the 'plug' into the hole, air bags will lift.
It’s on a non tidal part of the thames.

There is no access for a crane to lift it to get The gunnel rails above the surface.

It isn’t holed, the owner has failed to pump the bilges for a considerable time, and I expect that what has happened is that it has taken on enough water that it has reached the sink waste pipe/hole, which probably after the hard winter has split . This then ends up with the boat sinking.
The theory behind what I am proposing is that as you pump out underneath the sheet of ply, with the tarpaulin on top, it creates a small partial vacuum with the out side water pressure pushing the tarpaulin against the hull, and provided you pump fast enough, it should bring it up enough to get the gunnels above the surface.
The boat itself is trash, but as it’s on my mooring, I want it up and gone.
Tell British Waterways or whatever they are called this week. Surely they will drag it off?

Alternatively, get the stern raised and pump out - so long as there is not a large hole / broken valve or inlet.
Tell British Waterways or whatever they are called this week. Surely they will drag it off?

Alternatively, get the stern raised and pump out - so long as there is not a large hole / broken valve or inlet.
The EA tend to make matters an awful lot worse, and present you with a big bill for it.

There are people who we know who can do it, but rather fancy having a crack myself, mainly because I need it up quick before the weather turns.
I know of a boat that was raised using the method I have outlined, but also know that people like yourself frequent this forum, hence the post.
If nothing else, my posts on this could give everyone a good laugh, provided I don’t end up on the TV news as the bit at the end, that’s meant to make people laugh!
Archimedes principles apply. You are going to need a shedload of buoyancy devices/airbags/oildrums to match the water already in the hull.
2 or 3 44 gallon drums a side, weld cleats to the bottom ends, fill to about 80%, so about 6"of drum is above the water. construct some web of webbing/tarp under the hull, and attach to cleats.
You get some decent pumps which fit on the drums, but with some careful balancing, can discharge at a fair rate, from each side. that may lift it sufficiently for you to start pumping the hull out.

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