Skin tank

[Hawkmoth]

I've just been looking at one of the blogs I read. One of then is having trouble with an undersized skin tank, and they've been advised not to move the boat for warranty purposes.

The seem to think that it must come out of the water for this work.

Is this right? Surely as the tank is on the inside of the hull, a new one or second one could be welded in without dry docking. Or am I wrong?

Bob

[Graham Davis]

Some skin tanks are fitted externally.

[Tony Brooks]

You need good access all around the tank for the welder and it may possibly have to extend into cabin depending upon swim length. Experience seems to to show that a thin skin tank welded to the outside of the swim has a minimal effect on handling so this is often the most cost effective way. Otherwise I expect you would have to take the engine out.

[Neil2]

You need good access all around the tank for the welder and it may possibly have to extend into cabin depending upon swim length. Experience seems to to show that a thin skin tank welded to the outside of the swim has a minimal effect on handling so this is often the most cost effective way. Otherwise I expect you would have to take the engine out.

I had the skin tank on my last boat repaired where one of the welds had failed, and it was touch and go because the boatyard concerned were not happy to MIG weld it. It's the view of many welders that anything that has to contain water should only be "stick" welded but in a tight space MIG welding is a lot easier. I can't imagine stick welding in a new tank without removing the engine, and ideally you would do it under cover, - most boatyards would find this easier to perform with the boat in dry dock I guess.

[Hawkmoth]

Thanks all for your views.

It was simply that seeing mine was on the inside that it may be possible to do the job without dry docking.

I see now some of the pitfalls.

Cheers all

Bob

[alan_fincher]

OK, complete numpty question from someone who admits they know sod all about welding.......

 

To what extent (if at all) the fact that your hull is sat in canal water able to cool the outside of it affect any ability to weld to the inside of it?

 

Where I have had welding done out of water, the heat generated inside had clearly caused some charring of internal woodwork nearby, and I felt lucky it had not turned into a fire.

 

So does having the plate you are attempting to weld to "water cooled" not affect things at all then?

[Hawkmoth]

OK, complete numpty question from someone who admits they know sod all about welding.......

 

To what extent (if at all) the fact that your hull is sat in canal water able to cool the outside of it affect any ability to weld to the inside of it?

 

Where I have had welding done out of water, the heat generated inside had clearly caused some charring of internal woodwork nearby, and I felt lucky it had not turned into a fire.

 

So does having the plate you are attempting to weld to "water cooled" not affect things at all then?

Not sure Alan, I think that problem could be gotten around with more power in 'the stick', but better welders than I will know.

I must admit that I didn't know about the MIG v stick welding came into it, and that probably has a bearing on it.

Bob

[blackrose]

OK, complete numpty question from someone who admits they know sod all about welding.......

 

To what extent (if at all) the fact that your hull is sat in canal water able to cool the outside of it affect any ability to weld to the inside of it?

 

Where I have had welding done out of water, the heat generated inside had clearly caused some charring of internal woodwork nearby, and I felt lucky it had not turned into a fire.

 

So does having the plate you are attempting to weld to "water cooled" not affect things at all then?

 

I part it depends on the thickness of the hull it's being welded to. (Not that I know anything about welding either).

 

When I was at Uxbridge Boat Centre buying some fittings for my new skin tank, I mentioned to Alan, the owner, that my plan was to get the tank pre-fabricated according to a template of the curve of the swim I'd made, and then get it welded in while in the water.

 

He was adamant that it wouldn't work on both counts - the prefabrication and welding it while in the water. He got quite impatient with me when I tried to ask why, but basically according to him a prefabricated tank would pull away from the swim as the welding cooled and the welding itself would be brittle and lack penetration because it would cool too quickly while in the water.

 

I carried on regardless. The 4-sided prefabricated tank cost me 70 quid (about 6ft2) from a local fabricator on the river who also welded it in for another 60 quid. The guy doing the welding had to put plenty of power into the mig welder and at one point he had to stop to let the machine cool down, but he said that the weld was still hot 10 minutes afterwards because the hull steel was 6mm thick, so the concern about the weld cooling too quickly wasn't a problem. The fabricators just shook their heads and laughed when I told them what Alan had said. They told me that once tacked into place the tank wouldn't move and if the welder knows what he's doing then it can be done in the water (dependent on hull thickness).

 

Anyway, what would have cost me 500 quid + dry docking at UBC ended up costing me 130 quid + fittings and hoses. It's been fine and works well.

Edited July 14, 2013 by blackrose

[system 4-50]

I have a vague idea that I've seen underwater welding on TV with pictures of oil rigs in the North Sea. I suppose it would be awkward trying to get a narrowboat out to the North sea?

[alan_fincher]

I suppose it would be awkward trying to get a narrowboat out to the North sea?

Probably even more awkward trying to get it back again!

[blackrose]

Thanks all for your views.

It was simply that seeing mine was on the inside that it may be possible to do the job without dry docking.

I see now some of the pitfalls.

Cheers all

Bob

 

If it's a narrowboat then the welder may not even have enough room to get in and weld it from the inside, so it may be a non-starter on that point.

[onionbargee]

I had the skin tank on my last boat repaired where one of the welds had failed, and it was touch and go because the boatyard concerned were not happy to MIG weld it. It's the view of many welders that anything that has to contain water should only be "stick" welded but in a tight space MIG welding is a lot easier. I can't imagine stick welding in a new tank without removing the engine, and ideally you would do it under cover, - most boatyards would find this easier to perform with the boat in dry dock I guess.

old wives tale.

 

No qualified welder beleives that.

 

Your entire hull is MiG 'ed.

[Guest]

old wives tale.

 

No qualified welder beleives that.

 

Your entire hull is MiG 'ed.

I was thinking along the same lines. I am not a welder, but do know many NB's are mig welded, as is a lot of overplating. I worked in a road tanker fabrication shop, and much of the tanker shells were mig welded too.

[lynalldisocvery]

Maybe the boatyard are thinking they dont know how thick you bottom or sides are? and are frightened about getting the weld to hot and burning right through, cant see it myself not with all that water about.

Stick welding is a pain in a confined space, but then so is mig as the torch never seems at the right angle.

 

Lynall

[bizzard]

Stick and mig welders use different techniques. The mig torch needs a little more room to be able to sight around the nozzle shroud to see where your going, also you need a little more room to weave the torch to fill as mig wire is a lot thinner than a stick. You don't generally weave with a stick and you can cut the electrode in half to give yourself more room, albeit shortening the runs. When welding any thing that needs to be watertight I always scrupulously run over all the welds afterwards with a hammer and centre punch checking for any dodgy or porous bits.

[onionbargee]

 

I part it depends on the thickness of the hull it's being welded to. (Not that I know anything about welding either).

 

When I was at Uxbridge Boat Centre buying some fittings for my new skin tank, I mentioned to Alan, the owner, that my plan was to get the tank pre-fabricated according to a template of the curve of the swim I'd made, and then get it welded in while in the water.

 

He was adamant that it wouldn't work on both counts - the prefabrication and welding it while in the water. He got quite impatient with me when I tried to ask why, but basically according to him a prefabricated tank would pull away from the swim as the welding cooled and the welding itself would be brittle and lack penetration because it would cool too quickly while in the water.

 

I carried on regardless. The 4-sided prefabricated tank cost me 70 quid (about 6ft2) from a local fabricator on the river who also welded it in for another 60 quid. The guy doing the welding had to put plenty of power into the mig welder and at one point he had to stop to let the machine cool down, but he said that the weld was still hot 10 minutes afterwards because the hull steel was 6mm thick, so the concern about the weld cooling too quickly wasn't a problem. The fabricators just shook their heads and laughed when I told them what Alan had said. They told me that once tacked into place the tank wouldn't move and if the welder knows what he's doing then it can be done in the water (dependent on hull thickness).

 

Anyway, what would have cost me 500 quid + dry docking at UBC ended up costing me 130 quid + fittings and hoses. It's been fine and works well.

how out of character !

[Biggles]

The problem with MIG is people (armatures) think that one gas delivery setting is right for all situations. The gas IS the flux. If its outside and windy you will need 3, 4, 5 x more gas and or shielding from the wind no matter how slight the wind is. Welding bright well prepared joints on a bench indoors is totally different to welding a new bit to a boat hull outside in less than ideal conditions. Bench welding is totally different to field welding. Truth is stick copes with outside or less than ideal conditions better but is still totally dependent on the rods used as they are made to different situations. MIG has 2 main variations, gas mix type and gas delivery volume. The 3rd and much less available or used is fluxed wire used in addition to or without gas. With the latter at 400 amps I have seen super high pressure boilers constructed (indoors) with one pass filling a 1" x 1" 45 degree fillet weld with a weld pool the size of a £2 coin. These welds can't be ground out and re-done it has to be right first time. These boilers work at 400psi!

 

So basically what I'm saying is the type of weld method is not the issue its the choice and skill of the welder which is why some are on minimum wage and others are in great demand at any price.

[lynalldisocvery]

Reminds me when i was a steel erector years ago, a weld tests van had written in the dirt, (welders hate weld testers) and underneath someone had written (yes but everyone hates welders!)

 

 

Lynall

[NB Lola]

I've just been looking at one of the blogs I read. One of then is having trouble with an undersized skin tank, and they've been advised not to move the boat for warranty purposes.

The seem to think that it must come out of the water for this work.

Is this right? Surely as the tank is on the inside of the hull, a new one or second one could be welded in without dry docking. Or am I wrong?

Bob

Our old lister lpw4 (I think) died and we had a canaline 42 fitted. Part of the dead engine diagnosis led to a way too small internal skin tank so we had an external tank fitted by Paul barber on the Erewash. Excellent job and we have had no issues at all with either engine temp or skin tank performance. Biggest lesson on that change was to remove ballast as the uxter plate was way down int watter

[Arthur Brown]

Commercially the RISK that there is a pit or thin patch on the outside that may meet up with the weld pool and cause a hole spewing water is too great for most small businesses. If the boat is in the dock and supported then the chance of a burn through and sink is truly nil. Many businesses are risk averse these days because if the cost should things go pear shaped.