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[explorer750]

Hi all,

This is probably a silly question but how do you make a lead bulb for a yacht. The plan says to make up a mould and cast it but does not go on to say how. The bulb is for a 'Tinker' Rg 65 which on the plan needs to have a weight of 600 grams.

Any help would be much appreciated. Here it is so far.

[boatmadman]

Hi,

You need to make a wooden plug to the profile you desire, then use it to make a mould out of plaster of paris. make two half section moulds.

Leave the moulds for a couple of days to make they are absolutely dry before using it. If there is any moisture left in it when you pour molten lead in, it will shatter with the risk of molten lead being sprayed around - and on you - it hurts!

Then, wearing protective clothing, face mask, gloves, boots and apron melt some lead, I have use an aluminium pan on a camping stove - outside to keep away from the fumes - poisonous - and pour into the mould VERY carefully.

Allow to cool and tip out. Drill through the lead for fixing bolts to clamp onto the keel, fill, file and emery to shape and paint!

Simples! - but potentially very dangerous, so be extra careful and think through each step.

Ian

[john s 2]

Please do not look into the pan melted lead can without warning spurt out of the pan.No doubt this is caused by heating the lead to a high temp .John

[andrewh]

Ian has described the plaster-of paris method - which works well and safely as long as the plaster is COMPLETELY dry.

Simpler and cruder is to cast the bulb in two halves in a thermalite block.  Carve the half-bulb shape using drills, knives/ whatever, sandpaper smooth

Make sure the block is completely dry
Pour lead in and allow to fully harden

This method is rather quicker - but requires a lot more filing and fitting
andrew

[derekwarner]

  a good dusting of sulphur powder in the mould will reduce any potential for the molten lead to spit back at you

Naturally all of the H&S requirements as noted by  boatmadman are still applicable ......Derek

[malcolmfrary]

When doing my casting I gave the mould a long cooking in a low oven to make sure all the moisture was gone.  The preheating also reduced the thermal shock.
To get the right volume and shape for my intended weight, I dropped the weight of lead into a jar, filled it with water, reserved the water, removed the lead, put the water back and made up the volume with plasticine.  Then I made my shape from the plasticine and used that to make the mould.
If there is an accurately dimensioned plan of the bulb, life becomes easier.

[sinxalot]

two books which describe the construction of a mold, pouring the lead and stressing the inherent dangers of this activity,as mentioned in the previous posts :
  Radio Controlled RACING SAILBOATS by Chris Jackson --traplet publications, and Build your own Radio Controlled Yacht, the racing sparrow 750 by Bryn Heveldt www.RacingSparrow.co.nz
I made a mold and poured after first drying the mold for a week, fine weather all week,in Sydney in the summer,I thought 'no problems'! THEN, I left the molds overnight in my building shed
BIG MISTAKE TIN SHEDS CAUSE OVERNIGHT CONDENSATION guess how I know I'm not trying to 'put you off'pouring ,just stressing the dangers.
Cheers Col.

[pugwash]

I recently made a 1.5 lb lead bulb - same as everybody else made the mould in plaster of paris in two half sections
but I didnt have the camping stove or a suitable container to melt it in so I used a gas blow torch, cut the lead into
long strips and with a long pair of pliers to hold the lead I just melted into the mould and after giving it a final blast with
the torch was left with two rough and ready half moulds which I filed down and sandwiched between a keel made of
ply.  countersunk the bolt holes and used Nyloc nuts.  Covered both keel and bulb with west epoxy - final smooth down
and a perfect finish.
As it was to cure a ballast problem on a destroyer it had to be removal for going onto the display stand so glassed in two
brackets under the hull to which it can be bolted and they are almost invisible unless you get down on the floor to examine the
model AND most importantly the hulls watertight integrity has not been affected.

Geoff

[rmaddock]

I've been trying to find some photos of when I cast mine but cannot...sorry. 

It's not all that hard thought.  Just make sure you've planned out everything that you're going to do and that everything is in place and ready.

Are you aware that various people sell ready made keel bulbs? IE Sails Etc sell a 700g bulb: http://www.sailsetc.com/parbulb.htm Too heavy, I know, but it's an example...you could always shave a bit off 

[JayDee]

Hello,

As I am reading about casting Lead, I am shuddering at the thought of the injuries that doing this can cause!!.
Here is another, very safe way of making a Lead Keel Bulb.

It is made from layers of Lead Flashing, clamped together, then soldered to join the edges.
The finished weight can be fine tuned by removing Lead, or soldering some more on !.

A large Soldering Iron is needed, or a VERY small gas torch and a steel pallet knife.
With the gas torch, don't wait for the Lead to melt, just wipe it about like Icing a cake!.

Very, Very easy to do, and VERY SAFE !!!!!!!!!!!!!!!!.

John.     

[explorer750]

I was not too keen on casting either so I made it up from flashing expoxied together and lots of car body filler. It is not a brilliant shape but we will see how it goes. I went for a flat top and bottom one because it was easier and the other was to try and generate some lift to stop the front from nose diving.

Hope you like her.

[JayDee]

Hello,

At least you did not "Burn your Fingers".

John. 

[sinxalot]

there is a very good discription of laminating? a keel bulb at   www.rcsailing.net/forum1/showthread.php?5879-Ac100/page2     scroll down to post 15 by Claudio,
maybe a bit 'fiddley'but, no blistered fingers I might try this on my next build.
Cheers Col.

[blowdown]

Has anyone tried using fine lead shot in a resin matrix with a slight increase in dimensions to compensate for slight loss of density due to resin infill. Gunshops supply shot for cartridge making. this amounts to cold casting and the fin can be bonded in at the same time.  Cheers from blowdown.

[CF-FZG]

Has anyone tried using fine lead shot in a resin matrix with a slight increase in dimensions to compensate for slight loss of density due to resin infill. Gunshops supply shot for cartridge making. this amounts to cold casting and the fin can be bonded in at the same time.  Cheers from blowdown.

From what I've read - it's a common method as long as it's sheathed in fibreglass for protection


Mark.

[rmaddock]

Funny how these topics keep coming round in waves....

http://www.modelboatmayhem.co.uk/forum/index.php?topic=30888.msg345912#msg345912