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Venture 25 Bulb Casting

If you are just joining this story you need to know a little background. We were given a free Venture 25 sailboat. It was free because it lacked both a trailer and a keel. Building a keel is a big process and this story chronicles just one of the many steps.

The big picture plan was to replace the 600 pound steel keel with a 150 pound steel fin carrying a 300 pound lead bulb. To make the bulb fit I decided to go with a lead buld that was basically NACA 00xx shaped and bolted to the bottom of the steel fin. Pouring molten lead didn't sound like a project I would want to be around if something went wrong so I decided to build a mold that the lead would also be melted in.

A paper cutout of the NACA 00xx shape was used to trace the shape for the plywood form. Eighteen guage sheet metal was bent around the form and screwed in place until the welding was done. My Hobart Handler MIG welder was used for all welds. A quarter inch thick piece of low carbon steel was then added as a bottom. Rusty scrounged rebar was cut and welded into a brace/handle combination to control mold flex and also allow easier movement of the mold when it was full of lead.

Sheet metal keel bulb form
NACA derived keel bulb shape

When I started this project I didn't know that scrap lead had become valuable. Here is a breakdown of how I acquired my raw materials:

* 110 lbs used wheel weights free from Kitsap County Craiglister.
* 20 lb leftover East Coast 12 Meter radio controlled sailboat ballast free from from father in law.
* 204 lbs of lead and copper swept up from indoor gun range floor for $100.
* 10 lb lead pipe free from Frank's Barn.

On a free day I drove out to my Friend Frank's farm. I started by digging a fire pit and placing a few bricks around it. Some plywood scraps were propped around the fire to block the wind that would have liked to steal the heat out of my mold. I placed the mold so that each end rested on a brick but the body of the mold sat over the fire pit. Once in place I started filling the mold with lead. I had planned to put all my raw materials into the mold to avoid having to add raw material to the molten lead. It turns out only about a third fit.

Building the fire that will melt the lead scraps
Wind block for the lead melting fire

Next I started the fire under the mold using wood scraps I had been collecting. Frank and I chatted while I stoked the fire. I guessed I would have the lead melted about one hour after the fire was going well. Frank guessed about four hours. Frank was pretty close.

John Deere lifts the Venture 25 keel bulb
A Sawzall is used to free the bulb from its form

The melting process was slow to start. The first batch took a couple hours to melt. The second about one hour. The third was ready to slag just a few minutes after dropping it in. As the day went on I also realized that the fire burned hottest when I burned mostly cedar fence boards cut into small pieces. After removing the last of the slag with my custom scoop, a ten foot piece of rusty rebar with some field fencing wired on, I removed the wind blocking plywood chunks and enjoyed a corndog lunch with Frank.

During lunch we discussed how long it would take before the bulb was solid and ready to be moved. I thought about an hour. Frank guessed over night. Just thirty minutes later we checked on the bulb. The top was solid and the mold was radiating much less heat than before lunch. Frank asked how I planned to move the assembly. I showed him a 4 by 4 and explained we would tie the mold to the center and each lift an end. He declined. About this time Frank's neighber drove down the road on her John Deere tractor. We realized the cavalry was at hand. The tractor cared not about the weight or the heat and the mold and bulb were soon in the back of my truck.

Although Frank passed on the 4x4 lever, I was able to use it successfully to remove the bulb from the back of my truck the next day. I dropped it into my daughter's wagon and pulled it to the back yard. Once there I used a block and tackle to invert and lift the mold but the lead wasn't budging. Even my largest hammer applied forceably to the bottom of the mold did nothing to let it free.

I had hoped to keep the mold in usable condition to pass to the next keelless Venture 25 owner but that was not in the cards. My Sawzall was drafted into service. I cut down the trailing edge of the mold allowing it to open and the lead to drop free.

Stay tuned for my next challenge. Attaching the bulb to the strut.