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Author Topic: Lead into GRP hull?  (Read 4421 times)

rmaddock

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Lead into GRP hull?
« on: August 28, 2011, 09:35:08 AM »

Hello all!

One of the venerable tomes on model building that I have, suggests that it is possible to pour molten lead directly into the bottom of a GRP hull :o.  It suggests that sitting said hull in cold water will help.

The question is, has anybody actually tried this? Does it work?

Cheers,

Robert.
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Colin Bishop

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Re: Lead into GRP hull?
« Reply #1 on: August 28, 2011, 10:01:22 AM »

This has been discussed extensively a while back. Try doing a search and you should find it.

Colin
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DickyD

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Re: Lead into GRP hull?
« Reply #2 on: August 28, 2011, 10:56:46 AM »

If it doesn't work I wouldn't like to be anywhere near when molten lead meets water.
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Colin Bishop

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Re: Lead into GRP hull?
« Reply #3 on: August 28, 2011, 11:20:48 AM »

Have to agree with DD there, I know it has been done but it seems a crazy idea to me. The standard casting methods using plaster etc. are potentially dangerous enough unless you really know what you are doing.

Colin
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Shipmate60

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Re: Lead into GRP hull?
« Reply #4 on: August 28, 2011, 11:23:09 AM »

Why not just use lead flashing, it is thin and pliable enough to mould to the hull contours and you can add as many layers as you like.
If you use pva glue to hull and each layer you can remove it by prizing apart too.

Bob
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pugwash

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Re: Lead into GRP hull?
« Reply #5 on: August 28, 2011, 11:26:15 AM »

I think very recently one of our continental members cast a lead keel for his sailing yacht (made of plank on frame construction ) and
used this method and it worked perfectly for him - would be in the past six to eight weeks if you go looking for it.
Sorry I can't remember who posted it.
Geoff
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Colin Bishop

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Re: Lead into GRP hull?
« Reply #6 on: August 28, 2011, 11:37:52 AM »

I think DD's point was not that it wouldn't work but that pouring molten lead into something surrounded by water is high risk. Imagine if you were to sneeze just as you were pouring it in..... Or even worse, a hiccup!

Bob's idea is much safer. I always use flashing myself for ballast, you can bend and hammer it ito just about any shape you want.

Colin
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nhp651

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Re: Lead into GRP hull?
« Reply #7 on: August 28, 2011, 12:18:34 PM »

you are best using lead shot used and obtained from a gunsmiths for re loading 12 bore cartridge cases.....put a sheet of clingfilm into the bottom of your boat.......pour the lead shot in mixed with polyester resin, and then if you've put too much in, it will come out easily and you can cut a chunk off...also lead shot and resin mix gives you a flat surface to put things such as motor mounts and batteries onto.........AND it sits as low in the boat as possibly it can. :-))

being in the lakes district you have a great oportunity.....just ask a local farmer where he gets his shot from.....he'll know the cheepest place/

neil.
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andyn

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Re: Lead into GRP hull?
« Reply #8 on: August 28, 2011, 12:25:33 PM »

Neil's idea is by far the best, in my opinion. GRP hulls warp in heat, too.
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essex2visuvesi

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Re: Lead into GRP hull?
« Reply #9 on: August 28, 2011, 12:40:03 PM »

be careful with lead shot and PVA glue as there have been reports in the Model railway hobby of them reacting and swelling... with enough force to split soldered joints

Not seen it myself but it has been mentioned in a couple of magazines
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rmaddock

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Re: Lead into GRP hull?
« Reply #10 on: August 28, 2011, 04:46:31 PM »

Oh, oh, oh! Woe is me.  {:-{

It sounded like such fun too. I'll have to go down the dry casting route then.  I appreciate that all this resin mix thing works too but this is a hull which will sail well without a drop keel and so I want to keep the CoG as low as possible. Therefore the ballast needs to be as dense as possible.

My plan then is to line the hull bottom with clingfilm and pour in plaster. I'll then use that to make a mould.  I've smelted lead and cast previous keels in this way so I'm sure I can do it again....it just adds a whole extra set of complications.  As to sourcing lead...well, over the back garden wall is a small family owned scrap metal dealer.  They've let me have a few kilos of lead for a good price before now and I don't have to pay postage.

Would I be correct in assuming that, if the hull is supported so that the waterline is horizontal, then plaster poured inside will settle where it would need to be to keep that balance correct?
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DickyD

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Re: Lead into GRP hull?
« Reply #11 on: August 28, 2011, 10:45:48 PM »

Depends how runny your plaster is.  :-))
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rmaddock

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Re: Lead into GRP hull?
« Reply #12 on: August 29, 2011, 08:23:26 AM »

Depends how runny your plaster is.  :-))
It's runnier than you like it, Sir.  %%
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cos918

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Re: Lead into GRP hull?
« Reply #13 on: August 29, 2011, 10:43:10 AM »

making a plaster mold is the corrct way to go. Molten lead and GRP dosent sound correct. Make sure you do a balast check on how much lead you will need . Water plaster will go all most leavel when set.

John
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rmaddock

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Re: Lead into GRP hull?
« Reply #14 on: August 29, 2011, 04:20:25 PM »

making a plaster mold is the corrct way to go. Molten lead and GRP dosent sound correct. Make sure you do a balast check on how much lead you will need . Water plaster will go all most leavel when set.

John

Cheers John!

My rough calculations say between 10kg and 11kg of ballast in total. I thought I might put in 3/4 of this (or so) in the bottom and leave the rest a bit more flexible for later addition as, and where, necessary.
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barriew

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Re: Lead into GRP hull?
« Reply #15 on: August 30, 2011, 08:53:40 AM »

be careful with lead shot and PVA glue as there have been reports in the Model railway hobby of them reacting and swelling... with enough force to split soldered joints

Not seen it myself but it has been mentioned in a couple of magazines

I've used PVA and chopped lead wire in a couple of boats - no problems yet! What I tend to do is pour in the lead and level it, then pour on PVA to soak into just the top layer. This stops it moving about and fixes it to the hull.
Using resin can generate quite a bit of heat which has the potential to distort a thin hull.

Barrie
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malcolmfrary

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Re: Lead into GRP hull?
« Reply #16 on: August 30, 2011, 09:53:33 AM »

From the point of view of undue excitement, pouring molten lead into cold water produces some steam and lead shot and very little drama.  The hot lead sinks below the surface and the steam given off condenses before it gets to the surface and the rest of the water just warms up a bit.
Pouring molten lead into an enclosed space with any damp involved is a very different matter, since the very small quantity of water is suddenly turned into very hot steam and tries its best to take up about 1600 times its original volume causing a fountain of steam and whatever was there, mostly lead that would still be molten.  This applies to a few drops of condensation in the bottom of a hull and any residual damp in a plaster mould.  When trying this sort of thing, I have always cooked the mould for a considerable time in a low oven to make sure that there is no moisture there - as a bonus, if the mould is pre-heated, it is less likely to suffer thermal shock and crack when the lead is poured.
However dry I got the inside of the hull, I would still be very uncertain about pouring anything as hot as molten lead into an expensive hull, no matter how certain anybody else was about the water on the outside being able to keep the hull from overheating to the point of damage.  Fibreglass is a pretty good insulator, and the weighing merits or otherwise of a thin or thick hull to either withstand damage versus conducting heat away into the water is a journey into the unknown that I would not care to take with something that I had paid for.
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pugwash

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Re: Lead into GRP hull?
« Reply #17 on: August 30, 2011, 10:33:56 AM »

I totally agree with you Malcolm but I have now found the build thread for the wooden boat cast with a lead keel
iwhilst it was sitting in a bucket of water.  It can be done but I personally wouldn't like to take the risk.

Geoff


http://www.modelboatmayhem.co.uk/forum/index.php?topic=31496.0
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Nordsee

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Re: Lead into GRP hull?
« Reply #18 on: September 07, 2011, 08:27:30 PM »

I did the pouring direct into a GRP hull with my latest. Better with a helper to hold the boat steady,and the interior of the hull is completely dry, then with the lead good and hot and fluid, pour into the hull, start at one end and go slowly but steadyily to the other. Keep the hull deep enough that the lead is below the surface. Leave boat in the water for a while after pouring so the lead has completely cooled.Always wear Leather gloves and Safety Glasses! If you use old wheel weights they melt at a lower (slightly)temperature as lead.
 I would never use a plaster mould as it always retains some moisture. I make a wooden "Master" and purchase Moulding Silicone from a Specialist Store, this is safe upto 300C. Not cheap, costs about 25 pounds a Kilo, but that will make several moulds.  You can  use the mould many times.  I have made a very large half mould and measure the correct amount of lead needed, divide by 2 and pour two halves which go either side of the Keel. Final shaping can be done with a file and car filler.
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