Casting lead for P22

[Antony Harvey]

I have decided to pay for the keel ballast to be done in a casting yard so I am making a wood pattern. This is really a question for Charlie Jones: You mentioned there was not much contraction in the 3 1/2" x 3 1/2" section but was there any lengthwise? Any advice on oversizing the pattern would be much appreciated. :?:

[Travis Votaw]

Antony, Charlie is off on a six weeks sailing trip to Florida and back to Texas . He might not be back on the board for some time. And I don't know the answer to your question - sorry .

[Guest]

In the mean time, here are two threads for reading material.

http://www.messing-about.com/forum/viewtopic.php?t=2881&highlight=moulding+lead+keel+charlie+jones

http://www.messing-about.com/forum/viewtopic.php?t=2843&highlight=moulding+lead+keel+charlie+jones

[Designer]

The standard allowance for shrinkage when making a pattern to cast lead is to make the pattern 3/16" in each foot larger or 1 in 64.

It is not super critical in your case as whatever size your keel casting ends up, you will match the deadwood to it.

[Klaus]

For my NIS26 sharpie I cast the ballast in 12 slabs of 5"x2"x36" lead. I used upside down steel channel with ends welded on at an angle as molds.

There was far less shrinkake across and lengthwise than I would have thought. Quite minimal. Certainly nowhere near the dimensions mentioned by the designer above.

The shrinkage all occured on top of the surface, which would crater deeply unless I played a gas torch on it to prevent the rapid solidifying of it. Even so, I later refilled the hollows and dips with more poured lead. I needed a reasonable flat surface for mounting the slabs.

I then had the tip of the centreboard cast in lead. Professionally done in a sand mold, using the cut off portion as a pattern. I glued a 3mm thick plywood bit to the pattern where the cut was made, to allow for the thickness of the lost cut. The part came back and fitted perfectly, again showing how little shrinkage had occured. I was prepared to use a lot of bog for fairing but almost none was needed.

My personal experience, yours may differ.

Good luck with your casting and take care.

Klaus

[Designer]

Klaus,

That was a good tip for the masts.

I too have found that the shrinkage is usually less than the textbooks say, but as I said, "it is not that critical". I would rather the ballast came out heavier, if you are right rather than lighter, if you are wrong.

[Antony Harvey]

Thanks to Graham, Klaus, Oyster and Travis - I will continue with confidence thanks to the forum.