Lead ballast

[Graham_Wright]

Has anyone tried pouring molten lead straight into a fibreglass keel?

Although it sounds horific, the specific heat of lead is very low and I have received splashes of the molten variety on my neck without any blistering. I wonder if a small quantity is poured, allowed to cool completely and then added to gradually monitoring the temperature rise continuously, no damge would ensue. Having tried to melt a resin/glass assembly with a heat gun, I know it will take a tremendous amount of heat before softening.

The advantage, of course, is that a space can be completely filled with no voids.



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[Althorne]

I don't know the effects but it's not something I would like to do to my boat especially if grp. Even when I built my steel boat I made moulds for the lead ballast and resin glued the lower sections in place. Upper sections were lose, but captivated to stop movement in rough sea, for trim when laden for cruising.

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[richardandtracy]

Just Don't.

Epoxy gets heat damaged above 120C, Polyester slightly less.
Lead melts at 327C or thereabouts (depending on alloying elements) and it's likely that it'll be poured at temperatures nearer 350C. There will be thermal damage to the resin (not the glass admittedly). I agree that the quantity of damage can be minimised by small pours and carful monitoring - but given how valuable a boat is compared to the small cost of making external moulds, don't risk it. Also, however good your monitoring, I would be amazed if you could unequivocably say that the resin is only surface damaged & to what degree.

On steel it's unwise to cast in the keel, in grp I think it'd be downright foolhardy.

Regards,

Richard.


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[Graham_Wright]

Thanks for that;- I just wanted to check the wimp factor before ruling out going ahead.

I agree on the melting point of pure lead (=roofing lead in my case?) but I didn't know the damage temperature of the resins.

Academically, I wonder what temperature the resin at the contact interface would reach v poured lead mass bearing in mind the low specific heat. Taking this to extremes, one drop would presumable result in no detectable temperature rise; a bucket-full would go straight through. Somewhere in between would lie reality.

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[snowleopard]

in order to avoid a build-up of heat you'd need to let each small pour cool completely before adding the next, say 6 hours. that would make it a very long job indeed!

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[BrendanS]

There was a post on this fairly recently. The recommended solution was to cast blocks roughly to shape in moulds, then drop into place in the keel when set, filling in any gaps with small ingots or scrap, then pouring in lead to fill in the spaces. Alternatively, fill the keel with ingots and scrap, then pour in molten to fill (probably in stages)

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[William_H]

Hello Graham I added some lead to the tip of my trailer sailer drop keel by making a fibreglass mold over the existing tip. I then poored the molten lead into the f/g mold. Only about 10kg but the smoke and smell was horrendous. The mold worked ok but the fibreglass was totally knackered with loss of the polyester resin. Make a mold, you could try plaster in the keel space using wax paper etc to ensure you can remove the plaster. Don't forget lifting handles. Use the plaster to make a fibreglass mold into which the lead is poored. Better still break up the lead and drop it into the keel space use a hammer to compress it then seal in with resin. BE CAREFULL regards will

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[richardandtracy]

There was.. In a steel keel.

Regards

Richard.


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[Bodach na mara]

It's not the specific heat that is the problem, it's the latent heat. The likelyhood is that the interface temperature would reach the melting point of the lead as the thermal conductivity of GRP is not high. I have poured lead (about 200 grams) into holes bored in wood to make fishing weights and there is lots of smoke and charring.

<hr width=100% size=1>Ken Johnson

 

[oldsaltoz]

G'day Graham,

The last time we filled a GRP keel we used ingots and lead shot to fill the voids then added epoxy resin thinned with 30% methylated spirits, glassed over the top when cured; that was about 12 years ago, no problems at all since then.

No huge blow lamps, no burns, no smoke no worries, also note, adding hot lead to a cold block of lead can lead to separation as the two do not bond very well at all.

Avagoodweekend..........



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