Star 45

Star 45

Wednesday, July 05, 2006

Star 45 R/C model sail boat , making a keel bulb mold and Castings

From Jim Adams:

I made a plug from balsa and finished it to a smooth finish second I used two aluminum pans (the kind that you throw away) I filled the first one with plaster took the bulb (well waxed) and placed it in the plaster half way in I used two pins through the center to hold it down. let that dry then pull out the plug next put thin saran wrap over the mold and place the plug back in the hole.

Now comes the fun part I used rubber bands to hold the plug in place (remember I had two pins that extend past the mold walls) next fill the second pan with plaster and lay the first on top it is kind of messy but it works. When the second half dries (about two hours) pull them apart. You will need to plug the holes at the ends on the sides and create small air path upward in the and a spur (looks like a funnel when you
are dune this needs to be big enough to pour in the led) at the end.

Billie Geisler's comments regarding "Keel Bulbs 2006 August 1:

I advise against using tire weights for ballast bulbs, because the tire weights seem to be some sort of alloy, and not pure lead. The markings on the weights are a good indicator, as different physically sized weights have the same ounce values stamped on them. So, if you use tire weights, you will have a physically larger bulb to achieve the necessary weight, thus more wetted surface friction, resistance through the water.

I go to the plumbing supply store to buy lead. This lead is much denser than tire weights. The lead comes in various shapes, some like hocky pucks, and some like Snickers bars. The Snickers bars fit into my lead pot better.

Incidentally, fishing supply stores sometimes carry electric lead pots, along with fishing weight molds. Good use for your tire weights. I was lucky enough to find a lead pot at a garage sale, sold by a rifleman who no longer cast his own bullets.

Consider mounting the ballast bulb on the keel fin at an angle, about 1 to 3 degrees up at the front. You can find info on performance of this arrangement on some IOM sites. It makes a substantial difference in boat speed on an IOM.

I cast my bulbs in two plaster of paris molds. One mold for the outer cheeks of the bulb(split fore and aft), and one for a center peice, to go between the cheeks. The thin (about 1/8 inch thick) center peice can be easily cut for fitting the fin, and drilled for adjusting the weight. If I need filler, I mix buckshot with epoxy. I can rough sand the lead with a belt sander, with very course belt. The course belt doesn't fill with lead.