Casting the bulb

[noemar]

Hi Chad,
I would be happy to accept your offer for paterns for the keel bulb.
noemar
noemar@verizon.net

[Chad]

OK Noel, I'll get crack'n.

bulb plug.jpg

[Tim Ford]

I can say with a high level of confidence that Chad makes good plug. I can say that without reservation.

i550July4thb.jpg

[Chad]

Hmm, I see you added a little extra tail to it- I recall I left it blunt, maybe 1/2"-ish?

Would anybody rather see a beaver tail shape instead of the pointy tail? That seems to be generally more popular these days, whenever you see a new race boat's bulb. I imagine the beaver tail is also more robust and durable, especially if you want to extend it to a thin trailing edge...

Just an idea.

[Kevin]

I think the "beaver tail" is better for strength and durability. My pointy tip didn't survive the plug making process so mine is a little more blunt. Also, I did mine in halves and the joint wasn't that tight so it turned out to be wider then originally planned. My next bulb will be one piece and bolted from top to bottom to the keel foil. And the foil will probably be foam core with rod running top to bottom.

Kevin.

[ryderp]

Chad,

I do of course want to be on the "mailing list" for the new bulb core. Thanks for taking this on.

I think that the beaver tail would be better, as Kevin mentions, for strength. There could be some benefits to this in terms of minimizing the vortex that forms at the back end of the bulb. However, I'm not sure that anyone could tell the difference.

I was thinking about pouring in one piece. Any reason not to do this?

Phil

[admin]

While I'm certainly not opposed to "a little extra tail," as far as other people are concerned, I did not go for any extra tail. I'm just not that kind of guy, but, OK I understand if someone else feels that way, fine.

That's the original...maybe the pic distorts the aft end?? maybe?

[Chad]

Faulty memory then, Tim! I nipped my cast bulb off at about 1/2" tail diameter, and assumed the mold was that way too. Definitely not trying to accuse you of getting more tail than you are rightfully owed.

Ok, so here's what I'm thinking of. Self-imposed rules for this change were:
1- same weight as original (80kg).
2- keep the "curve of areas" the same. That is, each station is the same area as the original bulb design.
3- I arbitrarily chose about 2.5" wide as "good looking" for the beaver tail.
4- the point of max widths is kept level, just like the original bulb.

Good so far?

Thanks to our world of computers, you now get pics before it happens:

iso_1.jpeg

iso_2.jpeg

iso_3.jpeg

iso_4.jpeg

ortho_1.jpeg

[Chad]

And just because it's fun to look at, here's a (very) little movie of the beaver bulb....

i550_beavBulb.mov 2.zip

(should open in Quicktime, and you can use the slider to see it better than just pressing the play button.)
Try not to notice the funky streaking that is on the back end- just a relic of the kludgy method I had to use to generate this sorta odd 3d shape. But it makes a convenient demarcation line between the old bulb design and the new.

[jray]

Actually the original bulb was a round bullet style design. What we have been casting is a design of a friend of Andrews from down under. I can look up his name given enough time. Anyway the beaver tail looks great. Chad you have way to much talent and free time on your hands. Well done! And I agree, if Tim has a little extra tail, good for him.

[noemar]

Thanks, Noel

[M&S]

Nice renderings, Chad

[Chad]

Chad,

I do of course want to be on the "mailing list" for the new bulb core. Thanks for taking this on.

I think that the beaver tail would be better, as Kevin mentions, for strength. There could be some benefits to this in terms of minimizing the vortex that forms at the back end of the bulb. However, I'm not sure that anyone could tell the difference.

I was thinking about pouring in one piece. Any reason not to do this?

Phil

The way we worked this before, was that each person used the plug and then passed it on. Apparently the last person to use it destroyed it and fixed it, but I haven't heard of it being passed on afterword.

Casting in one piece is great, just make sure you can get a steady stream of molten lead applied since the stuff in the mold cools quickly and can block off the ends and cause voids. I think the beaver tail pattern will be a little tougher to extract from concrete mold halves since the tail is more parallel-sided, but it should work. I'll try to toughen the plug a little, so it can withstand a little applied persuasion.

And for crying out loud, don't paint it with solvent-based paints!

[noemar]

Chad, That beaver tail looks interesting but do you still need the pointy end ?
Noel

[Chad]

The pointy end is just drawing the thing out until zero. I didn't bother to draw the last station, which would basically be a horizontal line. I would guess most folks would build this with about a 1/8" trailing edge, which would occur just after the last station. For the plug to survive concrete mold making, I think it won't be any thinner than 1/8" at the tail, either. So the extra tail in the renderings won't be in the finished plug, but will be part of the centerline pattern to guide the tail shaping, until it gets cut off.

Sorry for the confusion.

[noemar]

Chad,Thanks for the response,sometimes us old guys are easily confused.Senior moments occur more frequently.
Noel

[Chad]

How about a step by step, for folks that want to build their own?
Here's day one:
Buy a 1/4-sheet of something thin at the lumber store- I used 1/4" luan (about 3/16" thick) last time, and grabbed the 5-ply birch stuff this time. Also buy a small sheet of foam, 1.5-2" thick. In California, all they stocked was white EPS; here, all that's available is the pink XPS, and I had to buy a whole sheet. The white stuff shapes faster but is more chunky, the pink stuff is more expensive and tougher. I'd pick the pink, given a choice.

Print the patterns on letter sized paper, and cut out each one. Make you scissor cuts through the little extended vertical and horizontal lines- you'll line those up with similar lines on the plywood.

IMG_0219.jpeg

Cut the plywood. Cut one 5" strip for the centerline "spine", and (17) 5x7" pieces for the "ribs". Cut these parts very carefully, using a stop block or fence setup to get them really square and really identical.

IMG_0223.jpeg

Draw the layout lines on the plywood. Very carefully draw the centerline, and a line that will represent the horizontal datum on all the blocks. Test fit station #8 on one of the blocks, to see how high up to draw the datum lines. Then use spray adhesive to mount the patterns to the plywood.

IMG_0224.jpeg

Total time so far, about an hour and a half.

Tomorrow, I'll cut the notches for the egg crate assembly, and shape all the ribs and spine.

[jray]

Great start on a walk through Chad. Perfect for those just starting their bulb! I think the beaver tail idea you came up with is great, I will wait though, until It's time to replace the one I'm running. With luck it will be down the road some. Great stuff!

[Chad]

Thanks, Jon!
I don't need a new bulb yet either, but I'll be glad to have a mold already done and squirreled away should anything unfortunate happen to the current model!

No progress on the plug today- I spent the morning "boat time" putting together a sailplan to give my sailmaker. If he doesn't laugh too much at my whacky ideas , I'll post that here in a couple days.

[noemar]

Chad, You are a great asset to the I550 ommunity,thanks for all you do.
Noel

[noemar]

That was supposed to read community

[Chad]

Good. Someday, and that day may never come, I'll call upon you to do a service for me. But until that day – accept this service as a gift to help get this class rolling.

(please don't anybody make me explain where that's from)

[Chad]

First, I suppose I should say:

Don't do ANY of this if you're not comfortable around your tools. I'm just showing how I do things in my shop with my tools. Different tools, different comfort levels, and different levels of experience will cause you to do some things differently. Don't cut your fingers off, and say "Chad said to do it this way!"


Here's day two.

Notch the ribs and the spine, taking the notches all the way to the datum or "belly" line. Cut the rib notches from each side, so the notches are perfectly centered. Requires about a 3 1/8" deep cut on the ribs, like this:

IMG_0230.jpg

All notched:

IMG_0232.jpeg

Test assemble:

IMG_0231.jpeg

Rough cut with a jigsaw, about 1/16" outside the lines:

IMG_0233.jpeg

Sand the parts to the line. I like to use a belt sander cutting vertically like this:

IMG_0234.jpeg

...continued...

[Chad]

...continuation:

Smooth the parts a little bit more with a hand block sander, and assemble the framework:

IMG_0235.jpeg

IMG_0236.jpeg

Time today: about two hours.

Next up is to cut strips of foam and glue them into the gaps, using the same gluing operation to glue together the ribs to the spine.

[M&S]

Doesn't matter where your sharing came from. Everyone who reads your post will send good thoughts your way.