Help with keel weight

[Richard Caughey 1Participant @richardcaughey1]

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?

[Richard Caughey 1Participant @richardcaughey1]

Robbe Atlantis

[Tim RoweParticipant @timrowe83142]

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 1Participant @richardcaughey1]

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 RoweParticipant @timrowe83142]

Richard

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 ParkstoneParticipant @empireparkstone]

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

[Richard Caughey 1Participant @richardcaughey1]

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 ParkstoneParticipant @empireparkstone]

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 3Participant @raywood3]

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 needhamParticipant @ashleyneedham69188]

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

Ashley

[Richard Caughey 1Participant @richardcaughey1]

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?

[ashley needhamParticipant @ashleyneedham69188]

Richard. Put the requisite amount of lead shot onto a plastic bac and add water to just cover. Will give you a rough indication for the amount of resin needed! I realise There are more scientific methods available for calculation, but? You will obviously need a bit more than this but likely the tin you have to buy will have more in it anyway.

Ashley

[Kev.WParticipant @kev-w]

For resins I use these **LINK**

I have always used their poly resin **LINK**

I find it easy to use & with a reasonable cure time.

[Ray Wood 3Participant @raywood3]

Hi All,

Even with the lead shot mixed in beware of the heat generated by the chemical reaction in that volume of resin !! Could easily damage the hull .?? I speak with some bad experiences, I'd put the shot into the keel void and cap it of with a P38 layer, then maybe glass cloth and resin over that ?

Regards Ray

[Malcolm FraryParticipant @malcolmfrary95515]

A removable internal weight is likely to be even more trouble than a fixed one. Yes a big heavy boat can be very awkward to handle in and out of a car, but having access through the deck at the poolside can be even worse. It will still need transferring into and out of the water fully laden, it isn't the kind of thing that can be added with the boat floating.

Bagged shot of various sizes to get good packing density in the right place, covered with a layer of fibreglass to keep it there. The FG layer only needs to be strong enough to hold the bags in place should the hull be inverted, shot that has had resin poured into it eventually becomes a PITA. A layer of FG that can be attacked with a dremmel later keeps options open.

One thing about the Atlantis – it was a big model with lots of possible extras that all added more weight upstairs, where you really don't want it, so one without the optional exras, should have some leeway as regards ballasting.

Edited By Malcolm Frary on 16/02/2019 11:43:37

[Tim RoweParticipant @timrowe83142]

Hi Richard

I wonder if we have some mission drift? Are you still planning to make the weight removable? Are you still going to make a mould in plaster of Paris. Ray is quite right about the heat generated but that may not matter too much in a plaster mould.

You could also choose a less reactive epoxy that cures more slowly and of course you don't have to fill the mould in one go. You can wait for the temperature to drop and then add some more and so on. Provided you don't let the epoxy fully cure between pours and the surface is kept clean, you will get a true chemical bond.

I am a bit limited in my ability to lift heavy weights. If this was mine, my over the top solution would be to cut the keel off at a suitable level. Close and reinforce the bottom of the hull / keel and use the cut-off portion as a pattern for the lead. Then to devise a way of bolting the keel on externally but then, I am a glutton for punishment

Tim R

Tim R

[Richard Caughey 1Participant @richardcaughey1]

Never thought about the heat, but that could be a problem if done in the keel, not a problem if I put in in a mould to make it removable. I think I like the cap idea , put the shot in the keel and cap it with a bit of fibreglass resin and matting, I can always add more lead on top of it mixed with a bit of resin.

The removable keel weight sounds like it’s going to be too difficult. All ideas you have all sent me are very much appreciated for me a newbie yacht builder.

thank you

Richard

[Richard Caughey 1Participant @richardcaughey1]

Malcom Frary, OMG, I just re read all the posts, and I must have missed the comments you made about optional extras/ fittings, so I just weighed the two fittings packs that came with the kit and their weight is 3kg, that doesn’t include the masts or booms, paint, varnish, wooden decking, servos, radio gear and battery. I think I am going to have to think carefully about what I leave out, otherwise this will be a 20 + kg monster that never leaves my garage!

[Richard Caughey 1Participant @richardcaughey1]

Don’t know how to delete this pos, posted the same thing twice so just ignore this

Edited By Richard Caughey 1 on 16/02/2019 17:06:33

[Malcolm FraryParticipant @malcolmfrary95515]

Posted by Richard Caughey 1 on 16/02/2019 17:03:04:

Malcom Frary, OMG, I just re read all the posts, and I must have missed the comments you made about optional extras/ fittings, so I just weighed the two fittings packs that came with the kit and their weight is 3kg, that doesn’t include the masts or booms, paint, varnish, wooden decking, servos, radio gear and battery. I think I am going to have to think carefully about what I leave out, otherwise this will be a 20 + kg monster that never leaves my garage!

I was thinking about the roller reefing and suchlike, which is all extra weight upstairs. One of my members way back had one (without most of the options, but he did have the auxiliary folding prop). Looked great, sailed like a dream, needed a pack of friends to help get it in and out of the water. I think he had to rig it at the poolside, it probably needed a Transit van (as opposed to his small Kia) to carry it around ready rigged. In a long-ago mag article, a horse box trailer was used for rigged transport.

[Empire ParkstoneParticipant @empireparkstone]

As said mines is well over the 20+k weight I used to take it on my own inthe back of my Volvo noprob lengthwise . Rigged it at the pondside quite easy as the Masts adjust all the tensioning from the top single screw and have a sturdy carrier to launch with . Though could not manage it today she just gathers dust I have toyed with getting one of those carriers that go on the towbar and then I could take her fully rigged

[Richard Caughey 1Participant @richardcaughey1]

After spending most of last year in France I didn’t get to build the Atlantis…. But now we are in lockdown I thought time to get on with it. I haven’t put the keel weight in yet, and I am really glad I didn’t, moving the boat with it would have been difficult.

still not finished but here it is so far

[geconParticipant @gecon]

Looks really great Richard! Lovely contrast between the mahogany and pine, spruce, obeche or?

I can back up Ray about keel ballast. In the Comtesse I filled the keel with the Krick supplied tiny iron shot and covered/sealed the top with a thick layer (1cm) of P38 filler. Krick iron shot is so small that it 'flows' like thick soup.

I put small amount of resin in the bottom of the keel first so I could drill for a wing keel without all the iron shot 'flowing out' of the boltholes in the bottom of the keel!

George

[Richard Caughey 1Participant @richardcaughey1]

Thanks George, the deck was not fun to stick down but I got there after two full eight hour days of glueing. On you comtesse did you use the “ parts that cam with the kit or make your own? I have a Smaragd with nothing on the deck. I have the “stickers” but was thinking something else might look better?

[geconParticipant @gecon]

Sorry for the late reply…been away all afternoon/evening hanging up curtain poles and curtains, helping a grandchild (26 years old lady!) move into a new flat..

The kit did not come with much in the way of 'adornments'. I bought the accessory packs for the Comtesse. ie. The motor drive set, the wing keel set (which reduces the amount of required internal ballast) and the fittings set.

Also made a seagull or two for the decks of the two yachts (so far) in build. Ref. 'albums'

George

Edited By George Edward Connery on 12/05/2020 23:01:13

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