Christian CG #103 and I arranged a weekend to cast the keel bulbs. Friday after work we met at Christian’s workshop to do the preparation. Christian ordered 320kg of scrap lead from a local wrecker / recycler. We sorted the lead and prepared it in 80kg portions to be sure that the pieces fit in the melting pot. To get clean pieces of lead we had to remove some dirt (silicone and roofing felt). Attention at this point! We discovered some parts that are not lead. Other metal parts and cartridge case from projectiles have been mixed in underneath. We had to sort it out carefully. The following saturday morning we started with setting up the casting station.

We were curious and a bit nervous how we would succeed in melting the lead. With an 8kw gas stove underneath and a gas flame from the top of the melting pot we were able to melt the 75kg in 15 minutes. When lead was melted we had to remove from the surface between 2 and 3 kg lead slag.

Before casting we heated up the cemented bulb mould with the gasflame. Then we pourred the lead into the mould.

After 4 hours of cooling we lifted the mould and turned it upside down to get the bulbs out.

In total we pourred 4 bulbs for our boats CG #103 and CG #66. This was a real succesful and funny day in building our ClassGlobe boats.

Christian CG #103 took care of the construction of the mould. We ordered from a model builder a 3D printed positive form of the keel bulb in styrofoam. Christian has doubled it up by 3cm to create enough space for the shrinkage during the casting process. The styrofoam model was covered with 2 layers of epoxy to get a smooth surface. Christian built a box with the external dimensions H 24 cm, W 40 cm, L 105 cm. He cemented the bulb model with steel reinforcements.  Small bubbles and bumps in the cement surface cannot be avoided. Thus the negative mould was smoothed with a thin plaster layer and sanding. The cemented form has to dry in the shed for a few weeks so that it loses moisture. Christian built 2 moulds because we had no experience whether the mould break and in addition to speed up the casting process.

Many thanks Christian CG #103! Awesome job!

I’ve been thinking a long time what is the best way for casting the bulb. The best option seems to me melting the lead in a gas cylinder. Luckily I found an old gas cylinder in my father’s shed. But what is the safest way to cast the 75 kg of hot liquid lead without putting yourself in danger. So my father (an engineer) and I made some thoughts. It makes you very creative when there is enough stuff lying around in your shed. The result was a very stable construction with scaffold tubes. It is transportable and detachable to a minimum size to be stowed away in the workshop or transporation in the car. We where able to do small adjustments to put it in the perfect position to the mould and set it up for the casting job. It was created from leftovers that have been lying around for years. This is how sustainable boat building works.

After we had planned the framework we set about preparing the melting pot. First i cut the top of the gas cylinder with an angle grinder. It is important that it is completely empty (danger of explosion). Propane and butane is heavier than air and so there is still some gas left in the tank even if you opened the valve properly. It is best to unscrew the valve and fill it up with water so that all the remaining gas escapes. Then we measured the level of liquid lead in the cylinder. This is important to determine the center of rotation when pouring the lead into the mould. 75kg lead has a volume of approx. 7 liters with a specific weight of 11 kg lead per liter. We filled 7 liters of water into the cylinder, measured the water level and marked this level on the outside. Above the middle of the water level we positioned the center of rotation. We made the fixing points for the axle and the liftingbar from bigger metal tubes and the handles that we cut off before. After a busy day I was happy with the construction which gave me headaches for a long time. I could hardly wait the big day of pouring the lead.