Footie buylb dims & shapes


Yes, I’m still building. (I have a few other projects on the go!)

I’m at the “melt lead to make bulbs” stage, and I’m wondeirng what are some typical dims you all have…

(Boats are new to me, and I’ve never “poured lead”!)

I’ve worked out some numbers, and I’m looking at about 12cm long, and 2cm dia at it’s fattest point. And that should give me about 160g… Considering it’ll be easier to remove material rather than add it…

Am in the ball park? Too long? too fat? not long enough, nor fat enough?

This’ll be for a Papaya & Razor hulls…

i use an 6-8oz do-it mold 8 oz bulb ends up being about 4" long and 3/4" wide at its widest…

Attached a few aids I have picked up from somewhere.
Supplemental questions:

  • Is it worth pitching the bulb up a few degrees to align with the average running angle?
  • Where does the centre of mass go on the fin? I have seen it all over the place, but assume it ‘should’ be below the thickest part of the fin’s foil? May waunder a bit to trim a hull if the fin is not in the right position.
  • What are some favorite ways of attaching a detachable bulb? I am thinking of inserting a stainless steel bicycle spoke end in the fin and attaching the bulb with a counter sunk matching nipple.

Dr Wogz,

160 gm is probably too light. Most boats use 8 oz (27 gm), with some going as light as 6 oz (170 gm).

There are a few threads on this and related subjects. Try the search feature.


A comment on molds for bulb casting.

If you are planning to cast multiple lead bulbs then I would recommend using a harder gypsum material than plaster of paris. Hydrostone or Ceramical are good choices for gypsums and will hold up better to multiple castings. Cement is another option for a home grown mold. Each of these mold materials should be reinforced with hardware cloth and thoroughly dry before the first cast (most lead mold accidents are due to steam expansion from pouring a hot metal into a mold with residual internal moisture).

Witch ever of the above mold materials you go with one precaution to take is to preheat the mold in an oven before the first cast in a session. This will reduce the chance of a shock fracture occurring during the pour.

Of course the ideal mold for bulb casting is a two part aluminum one. For a foundry to cast the parts for a Footy size bulb mold would probably not be that expensive. The adjoining faces would have to be milled flat but that and a keyway system would be the extent of the machining involved to make the mold halves ready for casting.

An elegant method for casting bulbs is sand casting. Since it involves a mold frame and casting sand it is a bit more advanced technique. It has the advantage of being flexible because you form a sand mold around your bulb shape each time you cast. This way, if the first bulb you cast comes out too heavy or too light you can reshape the master and cast the new size right away. No waiting for a plaster mold to dry enough for safe casting.

Good luck and be careful!

Yeah… What he said.

At least give a Plaster-of-Paris mold a good chance to get fairly dried out, and remember that it will shrink a little as it dries.

Otherwise, I’ve never had one fracture, even though it stays in the cool basement. But things dop happen. :eek: I also make a form out of blsa or wood (or plastic even) to help in pouring & handling.

You might even consider casting half- bulbs, like Mr. McCallister does.