BYYB Forums

Recently repairing a broken centerboard, I wanted a better way. It was one of my designs and it snapped off when the board fell out of the slot (lanyard slipped on the cleat), while backing off a trailer.

The board has about 90 pounds of lead in it and was my typical strip planked construction technique, with a hole for the ballast casting to live in, all sheathed over.

Because the board was cut to fit this big hunk of lead, it was weakened and though any board would have broken, turned sideways on trailer in a cross wind, with the board down, I wanted a better way and it just dawned on me - smaller castings.

The new board wasn't going to be strip planked, but a plywood laminate using three layers of 1/2". I don't like plywood boards for a few reasons, but in this application I needed some additional cross grain stiffness, so plywood makes more sense.

The problem with the original board was a big hole, just aft of the leading edge was cut and filled with lead. The new board is a 3 layer sandwich, each with 6" diameter disks of lead, spaced on 8" centers, but still along the leading edge (yep, it's a big board). Each layer has it's lead "slugs" staggered from the opposing layer, which permits the integrity of the board to remain intact, once all glued together. The board was then covered in two 12 ounce layers of 45/45 biax and then again with Xynole for abrasion resistance.

The reason I'm posting is I can't imagine why I haven't thought of this before. It's such a simple thing, logical and easier too. Of course, you have to make a bunch of 6" round, 1/2" thick, lead slugs (16 on this board, 5 on each outer layer and 6 in the center), but the next time I do it, I'll cast them all in place, as they over lap, from one layer to the next. The lead castings only weigh about 6 pounds each, so handling them was easy. I made 4 at a time, by cutting 6" holes in an oak plank, then just pouring melted wheel weights in each "mold". I was so proud of my cleverness at the time, but now, I'm a bit disappointed it's taken the number of decades to "discover it" that it has. So, maybe I'm clever, but slow.

Great idea! Sounds like this method would be superior to the original for amateur construction as well.  Several smaller castings would be easier to pour and easier to handle than one large one.  Do you use straight lead, or alloys (a la  LFH)?

At Scamp camp 2 I was in charge of cleaning up the flippers (foils) and casting weights for both the center boards and rudders.  I used cat food cans to cast the weights for the rudders and a specially shaped form for the centerboards.  We were able to get 120 lbs of spent bullets from a shooting range for free which I melted down and separated out the copper down to about 70 lbs of lead.  It was kind of fun.  I'm not too sure that I would want to take on a 400 lb keel weight, but who knows, that might be fun too.

Al

Greetings Paul,

I still vote for a Tungsten polymer matrix ( Powdered Tungsten + an epoxy-like polymer ); just like mixing up fairing compound, only the cured material is much harder to sand and it weighs a little more than lead at 11 grams per cubic centimeter.

Details at ... Tungsten powder applications

The only down side is the cost, roughly $40 per pound at the volumes you would need for a rudder or centerboard. That is a tad more expensive than the $2.50 per pound rate for very pure lead.

I'm sure they would also be happy to make you a couple of dozen short cylindrical weights about the size of a hockey puck using their sintered tungsten process. At an even denser 18.5 grams per cubic centimeter, you would be able to reduce your hole size from 6 inches down to just 4 & 5/8 ths inches, or you could use twice as many 3 & 1/4 inch holes, which would be considerably easier to arrange in a satisfactory manner along the leading edge of the board and yield a stronger honeycombed matrix.

The real question is would the labor savings of not having to bother with the mess of melting lead make up for the more expensive material? Alternatively, if the board is for one of your no-holds-barred racing clients, I am sure you could dream up a suitable explanation for the added expense of such a high-tech appendage. 

Another benefit is that Tungsten in any form is significantly less toxic then lead, especially if you are being exposed to lead fumes during melting and pouring operations.

Cheers,
Tom

(If it is worth doing, it is worth over-doing)  ;D

I get lead (11.34 g/cm3) wheel weights for free and usually have a substantial supply on hand. If I buy lead, it's dirty and about 50¢ a pound. Once you boil it up, you can pluck the metal out and contaminates can be scooped off (steel floats in boiling lead). If I could get my hands on some spent uranium pellets (19.1 g/cm3), I'd make some serious ballast castings. I'm past my prime, so the fear of two headed babies isn't a concern anymore.

I just found the interlocking disks of ballast, in the 3 layer sandwich, clever and wondered why it took so long to figure it out.

I've revised the plans to now include the new centerboard arrangement.

If you study the drawing, you can see how the lead weights overlap each other, but don't affect the strength of the individual layers of plywood, because they're spaced apart enough to relieve stress concentrations. This ballast arrangement could be poured in one shot, though handling about 100 bounds of lead in a rough casting, is a pain in the butt.