how much lead in a centerboard?

[kng]

Hi people!! i would like to know how much lead to put into a centerboard, it is the centerboard for a 16 foot Hampton Flattie, i have only the plans and i can took the measurements from them but i don´t have exactly how much in pounds... (kilos better ;) ... the dimensions of the blade are... it´s made of 3/4 plywood, 41" x 18" in its widest section. The rectangle of lead in the drawings shows to be 7" x 3" aprox.
I have the experience of a boat that the centerboard didn´t get into the water... i really don´t know if the lead is the problem but i wouldn´t like it happens to me...

well thank you very much !!! bye !!

Emiliano.

[htom]

Without considering the rounded shapes, 7" * 3" * 3/4" = 15.75 cubic inches; this is 15.75/(12*12*12) = 0.009114583 cubic feet; lead weighs ~710 pounds per cubic foot ~= 6.47 pounds or 2.94 kg.

So 6.5 pounds or 3 kilograms.

[ion barnes]

the lead is there to help hold the board down and not to keep the boat upright. I have a 10' fiberglass dinghy with a plywood board - no lead insert and I have it pinned through the centerboard box to keep it down or at whatever depth I wish. As for inserting the lead, be carful not to breath the lead fumes, they are poisonous! That said, cut the hole in the board and start some common nails around the inside edge of the hole. leave about 1/3 of the nail exposed. About 1 nail per inch of perimeter is good and pour in the lead. A more eco-minded solution is to use lead pellets and epoxy with or without the nails. I have also heard of the lead being shaved with an electric wood plane. Actually I have a 20 liter pail of shavings, thats why I know. ANYWAY! Go for it ! I am all for the lead/epoxy version. Keep us posted, Ion

[kng]

thank you very much for the information. But do you think that 3 kg. will put the centerboard down ?? that is really what i don´t know exactly, if the weight of 3 kg. will do the job.. or i would need more?? or if you know how much lead do you need to keep down X plywood volume?

thanks again !!

cheers.

Emiliano.

[Don Olney]

Hola Emiliano, Earlier in the summer, I put about 9-10lbs (4.1-4.5kg) of lead in a centerboard that is 1" thick (solid Ash) and maybe around 20% bigger than your board. It stays down (so far) on all points of sail with that weight. Since it does not slam when lowering and it stays down, I'd say that weight is just right.

Based upon Htom's calculation and my experience with a slightly larger board, 6.5lbs (3kg) sounds like it should be sufficient to keep your board down.

If you put 3kgs in and it turns out (after testing under sail) that the board needs a little more lead, you can always take the board out and put in another half a kilogram by drilling another hole.

-Don

[kng]

Thank you very much Don Olney !! i will try with 3kg.
i have read messages in the forum about the same question and i think that i have it clear !!!

thank you everybody !!!

Emiliano.

[ahp]

I have another suggestion, but I have not actually done this myself.

Can you buy sheet lead, about 1/8 inch, 3.0 mm thick? Consider routing out an area on each side of the board by this much. Cut the sheet lead to fit the two areas, and nail it in place. You will need to encapsulate the lead and the board with epoxy and glass cloth to keep the water away from the raw edges of the plywood.

[Mac_Muz]

The easy way to figure this out is place lead on the wood, and sink it..... This is only ballast for the board as has been said already.... You don't want it so heavy that the board becomes a chore to use, and not so little that the board floats up in the box.

Earlier in summer i was testing my wooden dorry for real ballast, as I want as much as possible, but want to stop short of sinking....

So I placed 150 pounds of lead in the bottom, and pulled the cork... All I know right now is I need more lead, as the boat still floated swamped, with the stem, and transom high and dry...

The reason I want to know is that I will use this boat in cold water, and with weight of that ballast and a large gun for French and Indian War re-enactment, and I have no way to get a boat, and a gun of some value off the bottom of Lake George NY, which in spots is 200 feet deep.

In the event of a capsize, in cold water, I will be busy saving myself, and won't have time for a boat that goes down 200 feet.... So if I have the ballast set to still float, I may be able to save everything in time.....

I have a board that must be similar to yours, but I did not build it, so I do not know how to weight it, and tell what part is lead from what is wood.... Maybe someone knows how to do that here? Mac

[LoonyToo]

Yes, I have part of a roll in my garage. Roofers use it for flashing and valleys. The stuff I have is about 1/16 though.

Hal

Re:
Can you buy sheet lead, about 1/8 inch, 3.0 mm thick? Consider routing out an area on each side of the board by this much.

[James R]

Hi Emiliano. If you can calculate the specific gravity of the ply you're using you can calculate the amount of lead you'll need.

Typically plywood weighs about 615.1kg per cubic metre, salt water weighs 1026.5kg and lead 11340kg. You will want the ply and lead together to weigh the same as an equal volume of salt water. IOW 615.1+11340X=(1+x)1026.5. Solving for x gives you ~0.0399. Multiply that by 11340 and you get 452.35kg which is the amount of lead you need for every 615.1kg of plywood to have a neutrally buoyant board. IOW you'll need 0.7354kg of lead for every kg of ply.

So just weigh your board after you finish building it and mutiply that weight by 0.7354. Remember, of course, that part of the daggerboard will be above the waterline so this amount of lead will keep the board down.

And that's enough math for today. :rolleyes:

[ 10-15-2002, 02:33 PM: Message edited by: James R ]

[Frank Pellegrino]

You can buy sheet lead in various(to some degree) thickness. Plumbers use it, or used to use it to make pans for showers. Sheet lead is sold in different weights per square foot. Common weights were 4 pound, 6 pound or 8 pound. A plumbing supply house, especially in a larger city, should stock this material. You can also search out a plumbing contractor and he may have some small pieces that he would sell.

[Keith Wilson]

An an easy alternative to melting lead is to use lead shot in epoxy, as follows:
- Cut a hole in the centerboard.
- Drive some bronze nails partially into the edges of the hole.
- Clamp a board covered with waxed paper to seal one side of the hole
- Fill the hole with shot
- Pour in epoxy until it's flush.

The lead is an excellent heat sink, so it won't exotherm. The hole will, of course, have to be somwhat larger than one for a solid lead plug. You can buy lead shot relatively inexpensively at gun stores (I assume for these who like to load their own shotgun shells?). Quick, easy, and doesn't require any special equipment.

[kng]

Hi !! Thanks again !! i think i will make it the usual way.... pouring the lead into the hole with nails. But in the book of Howard Chapelle says that you can paint the interior of the hole wiht "watter glass" someone could tell me what is this ??

thanks again !! bye !!

cheers !!

Emiliano.

[stef]

Water glass = sodium silicate

It is used in a variety of products including refractory mortars.

It is difficult to comment on the use of sodium silicate in this application. It should act as a barrier (physical and thermal) to the molten lead on the plywood surfaces but inorder to prevent charing a very thick layer would have to be added in order to act as a thermal barrier. Charing of the wood during the casting would seem to lead to a loose plug which is subsequently bonded in with glass and epoxy anyway.

Nails would probably be best in keying or locking in the lead plug to the board. Epoxy is still required with this method to fair and seal the board.

Alternately, an epoxy and lead shot plug would bond quite well to the plywood. From a materials standpoint epoxy does stick quite well to plywood while, molten lead does cause some charing, disbonding and has other issues as well.

In my humble opinion bonding the lead in epoxy would be the best choice for an operation of this size. It would work for both a plug or sheet installation.

(I will now duck)

Best regards

Stefan Shelenko

[Beowolf]

Hi there,

You might want to check out the following thread..

Casting Thread (http://media5.hypernet.com/cgi-bin/UBB/ultimatebb.cgi?ubb=get_topic&f=1&t=004003&p=)

I tell ya, this guy's a genius

Take Care

Jeff

[Thaddeus J. Van Gilder]

You guys are killing me. It is so quick and easy to pour 5 pounds of lead into a centerboard or a rudder, why would one considered doing it any other way?

[almeyer]

Pourly melted lead directly into a hole cut into the centerboard as described above certainly seems easiest if you have the apparatus to melt that large an amount. Only drawback is that lead shrinks as it cools from liquid to solid - this I learned from casting bullets. Be careful if you try to use lead shot encapsulated with epoxy - it will probably turn out too light. Lead shot is not legal anymore for hunting - they're using some sort of other material, which will almost certainly have a lighter unit weight.
Thanks for the math lesson. The plans I've got for an upcoming project show no ballast in either the centerboard or two-piece swing rudder, but I've learned from experience some lead counterweight is going to be needed.
Al

[capt jake]

seems easiest if you have the apparatus to melt that large an amount. The volume of 6.5 lbs is very small. I cast a 12 lb lead disk that was inserted into the center board that I made. It was very easy. I bought an old heavy pan from Goodwill and melted wheel weights in it over the coleman propane stove.

BTW, I bedded it in place with thickened epoxy and then glassed over that. Seems to be holding fine.

[ion barnes]

As I previously posted, the lead/epoxy route is the way to go these days. Yes you may wish to increase the size of hole a very small amount but it could be the thickness of the saw blade OK? As for the epoxy, well, you only want enough to bond everything together because it is the lead you want in the hole. First, prime the edges of the hole with epoxy until the plywood has absorbed all the epoxy it will take. my experience is two coats, wet on almost set, and allow to set up over night. Next, mix an amount of epoxy that is equal to, hmmm, maybe about 1/2 of the volume of the 3 kilos of lead. Mix the epoxy well and only then add to the lead shot or shavings. Have one side of the hole covered with a patch of plastic and plywood. Pour in your paste and tamp down into the plywood edges and continue adding and tamping down untill all the mix is in place. Hopfully it will be a little over full and with the tamping the excess epoxy will be squeezed out. Anything else can be filed or sanded off after everything has set. Or if it is a little shy of filled you can repeat the process or just add some filler to make it flush. One suggestion I have is to make the hole round or with radiused corners because they will fill easier than squared corners. Another thing, do not worry about the precise amount of lead you need. If it turns out that you have insuffient ballast, you can drill another hole and add some more. If you have too much, drill into the lead pocket to reduce the amount of lead, and fill with epoxy filler. To find lead shot,find a scuba diver, they use it ballast themselves! or go to a sportsfishing tackle shop. All the best, ion

[kng]

Hi people !! the job it´s done... i finally have poured lead in the hole and secured it with nails to the plywood. I tested it in a small lake i have in my house (5´ x 4´ don´t think bad smile.gif ) and it sinks very well i hope when installed do the same.

i have images but they are a little ugly... my webcam doesn´t take nice images.

well thanks again !!

bye !!

[John of Phoenix]

"It sinks."

Does that mean, "If it falls out of the slot in a capsize it sinks and I've lost it."?

[kng]

smile.gif i really don´t know that becouse my little lake is 1´and a half deep..... but if i lost it in a capsize i won´t be thinking in it.....
you have gave me another problem now !! smile.gif

i have some images at http://www25.brinkster.com/kng/hampton.html

if you want to see....

bye bye !!

[John of Phoenix]

MY mistake, my mistake. So sorry. I was thinking it was a daggerboard, but you clearly said centerboard. Looks like you're making good progress. Good luck.

[Don Olney]

I'm curious as to what makes the lead/epoxy method more "eco-friendly" than just pouring lead. After all, this method combines lead (albeit solid lead) and epoxy, a material that has its own hazards.

There's no risk of getting burned accidentally with the lead/epoxy method but that really has nothing to do with "eco-friendly." As far as hazardous fumes are concerned, this should not be a problem with proper ventilation.

It seems to me, that unless one is a total reckless klutz, pouring a few pounds of lead is neither dangerous nor hazardous to the environment. There is a greater risk of personal injury in operating your table saw. Lead is just another material that needs appropriate care when handling, like epoxy, acetone, bottom paint, etc.

Special equipment necessary? For my centerboard, I melted 10lbs of lead in my driveway on a Coleman propane burner using a two-quart stainless steel pan I bought in Chinatown 15 years ago for $7.

It took about five minutes to melt and a couple of seconds to pour. Quick and easy and fun too since I don't get to play with fire and molten metal often enough.

No humans, animals or vegetation were killed or injured in the process and none were subjected to testing.

[ion barnes]

Nice progress. Keep us informed. And remember; Rule #1 Don't sweat the small stuff. Rule #2 Everything is small stuff!