Replating on the inside does it effect boats gravity?

[Judith Adams]

Hi we have bought a lovely Westlander Dutch Barge circa 1930. Following a survey the hull's new plating showed approximately 2.8 thickness replated steel. We've gutted it for a full refit, having it blasted before steel repairs. Question: we are going to replate 3mm inside because the inside steel has rusted. Will this effect it's gravity. Its has 0.5 draft and can only be suitable for river cruise. Don't want to compromise it's stability in the water further. I hope that makes sense? 

[matty40s]

Hi Judith,  I have reported your post so the moderators can remove your email address from your forum name. Otherwise you will be spammed to the moon and back. 

Proper replating(cutting out old and welding new) will not affect your boat as much as over plating (usual method of gaining insurance ok)

[Muddy Ditch Rich]

3 mm wont last long enough make the welding labour cost, cost effective.

You don't over plate from the inside.

Any over plate on the underwater hull will be the same as more ballast making the boat more stable not less.

 

[Bee]

Not sure if that is actually possible, your boat will have transverse angle running across the bottom and up the sides . Its probably riveted and a  really tricky job to weld between the frames. Its not a difficult shape to work on, all flat except maybe at the stern where it might be awkward. As you are stripping it out I think I would be tempted to re bottom it. Take a deep breath, cut the bottom right off, do it in sections of - say 6 feet at a time, shove the new plate in, jack it up to the boat then weld in new angle and weld it to the vertical angles and you will have a nice new bottom, it will be quicker than you think and a much better job, leave the engine alone and if you need to then overplate the last few feet from underneath. Your boat night have a rounded 'chine' in which case it might be best to ask a welder what to do. Whatever you do it will not make much difference to its stability. Some used to be sailed, a wet and scary experience I should think, look along the top edges and see if there are traces of plates where the shrouds that hold the mast up used to be.

[Judith Adams]

Thanks for the advice so far. I understand from the feedback that i should replate outside plate to 5mm but change the shape so it is less flush with the water line. Inside idescribed by Bee is accurate.

The welder seemed confident about inserting new steel pre-cut into each section. He mentioned that this may be a problem if water gets caught between new and old steel.  

I am very grateful for the in-put so far. We are keen to get it right first time.  

Judith 

[rusty69]

It maybe worth asking on the Dutch Barge Site too if you haven't already 

 

http://www.barges.org/

[Northernboater]

The new re-plating is showing 2.8mm? What percentage of the hull is this over and what was the original re-plating thickness? There is a Thread on here showing as barge that has had major surgery  not re-plating but cutting and replacing large sections of the hull, just can't remember the Thread.

Edited May 30, 2017 by Northernboater

[MtB]

Affect!

[WotEver]

26 minutes ago, Mike the Boilerman said:

Affect!

Very effective. 

[tomsk]

6 hours ago, Judith Adams said:

Hi we have bought a lovely Westlander Dutch Barge circa 1930. Following a survey the hull's new plating showed approximately 2.8 thickness replated steel. We've gutted it for a full refit, having it blasted before steel repairs. Question: we are going to replate 3mm inside because the inside steel has rusted. Will this effect it's gravity. Its has 0.5 draft and can only be suitable for river cruise. Don't want to compromise it's stability in the water further. I hope that makes sense? 

Sounds like a lovely boat, got any snaps?

Who's advised you to 'underplate' in 3mm, it's not something I've heard of before though I'm no expert.

Are you trying to avoid dry docking costs?

Whatever you do try to ensure it effects a robust, first time fix.

 

[Tam & Di]

14 hours ago, Judith Adams said:

 we are going to replate 3mm inside because the inside steel has rusted. Will this effect it's gravity. Its has 0.5 draft and can only be suitable for river cruise. Don't want to compromise it's stability in the water further. I hope that makes sense? 

You have some terminology problems here I'm afraid, and it does rather confuse. By 'gravity' do you mean the weight? Obviously any overplating (putting a patch of new steel over the existing, rather than cutting out the old and inserting new) will add to the weight. In fact of course even replating will make the boat heavier as you'd be replacing something extremely thin (2.8mm!) with something rather thicker (probably 5mm ideally). I don't quite understand what you mean by compromising the stabilty - if you add weight to the bottom then the boat will become more stable, not less. Do you perhaps mean draft - how deep the boat is in the water? Again, obviously extra weight will put the boat deeper in the water, but it would have been that deep initially when it was first built (to carry cargo of course) so that should not cause any problem.

If there is rust on the steel (or iron?) it means the steel is thinner than it was before rust started, and if your plating is 2.8mm then it has lost a lot of its thickness due to rust. The fact you can see this on the inside is not relevant - it is the thinness of the steel that matters, and if you are going to overplate this to make the boat less likely to get a hole and sink it is preferableto do it on the outside. If you did it on the inside there is still the liklihood of getting a hole through the present thin plating and you then have water between the two layers of steel which is not good. It is particularly "not good" as it is only then that the welds in the new plating would come under test to check they are actually 100% sound.

I suspect tomsk is right and you are trying to avoid going into a dock, but it would be even more chancey trying to weld something as thin as this when it is afloat.

Hopefully this has not added to any confusions.

[MtB]

14 hours ago, Judith Adams said:

Thanks for the advice so far. I understand from the feedback that i should replate outside plate to 5mm but change the shape so it is less flush with the water line. Inside idescribed by Bee is accurate.

The welder seemed confident about inserting new steel pre-cut into each section. He mentioned that this may be a problem if water gets caught between new and old steel.  

I am very grateful for the in-put so far. We are keen to get it right first time.  

Judith 

 

In that case I can't really see how putting 3mm plating on the inside can be anything even approaching the way to do it 'right first time'. 

I'm not a DB expert though. Who came up with this idea of putting 3mm steel on the inside? Was it your surveyor? Or your welder?

[hounddog]

if you have a welder willing and skilled enough to replate (i.e. cut out and replace sections) then do it. You will end up with a 'good as new' boat that will last another 90 years.

If you overplate then, as advised, do it from the outside.

Overplating will add weight and I know from experience that, if it's an old barge with low freeboard amidships you could cause problems with the freeboard (indirectly as a result of increased draft). In this case it would be a case of looking at removable ballast. Unfortunately, a lot of dutch boats are ballasted with concrete and this is a right pig to shift.

[Judith Adams]

Thanks for the reply and as a novice I do not have the termimology as yet. Peripheral language skills in boat terms so bear with me.

The boat is in dry dock and has been replated in Holland with 2.8 mil the ultra sound test could only test the new plating so not entirely sure what the actual thickness on the outside hull is.  She is 11m so not a big vessel and i was concerned that putting more weight would drop her down further in the water. I think you've answered that for me. She cannot go in tidal waters and we had to take her out of a tidal marina because she rocks and this was a concern pointed out to us. Her hull is flat. 

The steel on the inside had rusted the steel on the outside looks fine, surveyor said it should last another 30 to 40 years.  I thought that adding a 3mm steel skin inside would assist with stability from rocking. 

We are now considering rebottoming the hull. We also want to add more weight by converting wheelhouse and raising some parts for more headroom. 

I was concerned that all of this would have a negative impact on her integrity in the water. 

Sorry it's so long a post and I'm grateful for your thoughts. 

 

[Judith Adams]

[Alan de Enfield]

On ‎31‎/‎05‎/‎2017 at 08:46, Judith Adams said:

We also want to add more weight by converting wheelhouse and raising some parts for more headroom. 

That will reduce the stability and will make the boat much more 'tender' in that it will roll much more.

You need to add weight as low as possible NOT as high as possible.

I am not sure that this is the correct boat for you to do what you want to do with it.

Edited June 1, 2017 by Alan de Enfield

[Tam & Di]

3 hours ago, Judith Adams said:

Thanks for the reply and as a novice I do not have the termimology as yet. Peripheral language skills in boat terms so bear with me.

That’s OK, I was just trying to understand quite what the problem is. It sounds odd that it had repairs using 2.8mm plate - Dutch insurers generally require minimum 4mm hull thickness. Perhaps the welder used something thinner to be able to get the necessary curves, but it could have been down to a problem with weight too. One snag with a Westlander is that they are very shallow in the side of course, and if you add too much weight to the hull they don’t have much freeboard (the height of the hull above water). They were only built to carry fairly light cargoes - bulbs etc mostly.

If I understand you correctly, your surveyor says the hull is good enough for another 30-40 years (though I’ve NEVER heard one commit himself to anything so extravagant), but you are thinking of rebottoming it simply to stop it rolling as much as it does.

Adding some heavy ballast would achieve that same end at far less cost. Its also easier to move about and to adjust how much you put in. However you probably don’t have a lot of room to play with. As Alan says, if you add weight by raising the cabin and converting the wheelhouse it is going to rock a lot more, and the amount of ballast then needed could leave you with very little freeboard indeed. The previous owner obviously had the same problem and has fitted bilge keels (the little fins on the chine) to help stability. I certainly don’t think you should be having welding done to the hull unless it is absolutely necessary.

[WotEver]

4 minutes ago, Tam & Di said:

... you are thinking of rebottoming it simply to stop it rolling as much as it does...

Possibly you are correct, but my impression was that OP noted that it was rusty inside and hence wanted to replate/overplate the interior hull. I could well be wrong. 

Either way I agree with your last comment that she shouldn't consider any welding unless absolutely necessary. 

Judith - exactly why are you considering having this plating done, and exactly which part of the hull?

[Tam & Di]

26 minutes ago, WotEver said:

Possibly you are correct, but my impression was that OP noted that it was rusty inside and hence wanted to replate/overplate the interior hull.

I think she actually said she was replating internally, hence the initial guess she might be avoiding the cost of a dry dock, but you've asked my implicit question - how much rust is rust? Lot of nasty flakey stuff could be of concern, but otherwise it might only need wire brushing and application of Fertan or some other rust converter.

I don't see any skin fittings in the hull for water inlets/outlets, but that would be something else to bear in mind if the OP is thinking of adding weight in some form.

[Judith Adams]

Thanks for that i have attached a view of inside where we need or think we need new steel plating.  We are going to blast inside to see what we are dealing with

Thanks for all the comments so far

[rusty69]

Is it made of iron? 

[MtB]

Looks pretty normal and fine to me. Why do you think it needs any plating at all?

[Judith Adams]

She is constructed from steel plates running longitudinally, overlapping and riveted in place 

[Judith Adams]

Thanks Mike

Do you think just patching the corrosion will do? I thought that as the plates are exposed to have it all cleaned and relined with steel. Might be over-kill ? 

Outside doesn't need plating just that insurance won't cover the hull because it's not 5mm. A prerequisite for fully comp! Considered getting that up to specification but hence my concern about the increase weight on freeboard versus stability. 

  

[rusty69]

What did your surveyor suggest?