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Help with keel weight

Robbe Atlantis

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Richard Caughey 115/02/2019 18:39:17
39 forum posts
21 photos

so I bought a Robbe Atlantis kit, nice kit, but no keel weight. The original weight I think was 11kg of cast iron, cast iron is too hot for me so i will be using lead. Lead is denser than iron, so the weight will sit lower, i.e. a lower c of g do I still need 11kg or shall I use less. I will be casting the lead in a solid block as I have made a mould. Any suggestions?

Tim Rowe15/02/2019 21:14:15
405 forum posts
440 photos

Hello Richard

How big is this Atlantis. I have searched some pictures on the web but it is difficult to judge the size. 11kg seems a whapping amount of weight.

If that is what it needs however to float at the correct designed waterline you will have to have 11kg whether it be cast iron or lead. If you cast in lead you will require less volume as I think lead is about 40% heavier than cast iron.

To reduce the volume I would take it off the top of the ballast perhaps adding as spacer and enjoy the benefit of a lower centre of gravity. Most model yachts would like that.

Tim R

Richard Caughey 115/02/2019 21:45:02
39 forum posts
21 photos

It’s big. Old school measurements 54 inches long, beam is 14 inches and depth is only 11 inches, twin masts so needs a lot of weight in the keel to stop it falling over. I might go with a bit less than 11kg and make it up with extra lead once on the water. The mould is part done I filled the keel with plaster let it set and pulled it out so now I need to do something to reverse it to make a mould to pour the lead into, I might use silicone or somewhere I read plaster of Paris should do it???

Tim Rowe15/02/2019 22:54:36
405 forum posts
440 photos


You have made the plug from which you now make the mould. As the keel sounds like it is hollow I would be tempted to fill the keel with lead shot sealed in epoxy (or even plaster of paris). I suspect the density would then be similar to that of the cast iron. You can keep on adding until you have the exact amount and no heat involved.

Tim R

Empire Parkstone15/02/2019 23:00:24
222 forum posts
8 photos

Can't remember the weight of mine but a lot more the 11Kilos I'd guess nearer 20+ its bloody heavy

Richard Caughey 115/02/2019 23:19:19
39 forum posts
21 photos

Tim, I wanted to make a removable keel weight as it will help with transport etc, I have melted small amounts of lead before, but I think the lead shot is going to be easier, I think I am going to go with your idea with an amendment . I will still make the mould from the plug and then use shot and epoxy in the mould That way I could still make it removable? Also sounds a lot less hazardous with no heat and no potential toxic lead fumes! And if As Empire suggests that it needs more then I can add more. Now to buy some shot, or go to the shooting range after they have finished and collect the spent bullets😀

Empire Parkstone15/02/2019 23:54:06
222 forum posts
8 photos

I would work out your winch positions before considering a removable I have two winches the main one having a double drum and that is dead central over the keel.

Ray Wood 216/02/2019 07:23:26
1991 forum posts
709 photos

Hi Richard,

As has been said already, making the ballast removable is not practical or feasible once you have a deck in place and the rigs above, I would buy a trolley for moving the boat

Regards Ray

ashley needham16/02/2019 08:37:04
6599 forum posts
150 photos

I bought lead shot for a project and set it in resin as suggested.

11kg of lead is a LOT of lead to cast! My shot was 0.5mm-2mm in diameter and for all practical purposes was just like having a liquid, very little wasted air space. It mixes really well with resin and and then can be poured easily into a mould, knowing that there will be no “dry” pockets in the cast


Richard Caughey 116/02/2019 08:52:17
39 forum posts
21 photos

I just bought a second hand diving belt off eBay for 30 quid with 14 kg of lead shot in it so that’s mi plan, Now where can I buy a large enough quantity of resin/ epoxy to hold it all together..... or how much will I need?

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