Aluminium Keel Ballast

[mydauphin]

Don't put lead in a aluminum boat unless you seal it very, very well or you end up with a battery and no boat.... SIMPLE

I have seem some big boats using lead sheets for engine room sound insulation. After a few years eventhough aluminum was painted the lead leeched something into bilge and corrode unpainted bilge and area around shield. Very bad, holes in hull bad. Same goes for copper pipes, people do it but it is a problem in no time.

[MikeJohns]

Another issue has been the corroding of inbuilt water tanks, many have corroded through within a short time when unpainted. The Chlorine and other contaminants such as minute traces of dissolved copper from copper water-pipes quickly corrode unpainted alloy. Interestingly alloy gutters on buildings quickly corrode if there is any copper roofing just from the minute amounts of dissolved copper in the rain water. The same can occur from condensation that forms on more noble metals and drips onto bare alloy, as incredible as it may seem this is probably what happened with the lead insulation.

[Brent Swain]

For my current boat I made a mold the shape of the keel fore and aft and made ingots to fit, then stacked them in and poured concrete around them. I started the engine for vibration and the air came bubbling out. Don't overdo the vibration or cement and sand will separate.
I've seen major distortion with hot lead pored in an aluminium keel. It's very unpredictable. No such problem with steel keels I've seen.
Brent

[cvzzr]

I am currently looking for aluminum hull ballast options as well. One thing I had dreamed up was to pour concrete inside the keels (I am considering a twin keel design), then bolting on a lead bulb at the end. This would concentrate the weight lower, and the concrete inside the keels would keep the size of the bulb manageable.

Any ideas about how this could work? Of course, the lead and the bolts would have to be isoloated from the aluminum with some HDPE or something...

Here's the pic that got me thinking:

http://www.boatdesign.net/forums/att...n-g2612179.jpg

[cvzzr]

Sorry for posting again, but here's another pic that I find interesting and it may be relevant to the original poster:



It seems that as long as the lead and bolts are electrically isoloated from the keel, it should be no problem, with the added benfit of a lower COG...

[Crag Cay]

Alu has a further disadvantage, it can burn....

This need squashing: aluminium doesn't burn or else you couldn't weld it, melt it to cast anything, recycle it or even smelt it.

After the Falklands War the newspapers started all the nonsense about the aluminium used in British warships 'burning', but all the subsequent official reports completely refuted this. A google search will find all the relevant papers.

Contributors to a Boat Design Forum should know better than to recycle these flights of fancy that spout from the backsides of sensation seeking tabloid journalists.

[Brent Swain]

Those bulbs at their aft end will be nasty for fouling anchor rodes. I had that problem before I ran a heavy flatbar vertically from the tip of the trailing edge to the hull. I now make the trailing edge vertical, for that reason. Experimenting with a piece of string and couple of keels on a board will make obvious what works and what doesn't . When you foul a rode there in a bit of wind or current it is very difficult to get it unfouled. Could be dangerous on a lee shore.
On those keels, being more vertical, the trailing edge or flatbar should run slightly aft to where it meets the hull. This is another example of how what works well on paper and in the math, doesn't work out in the real world , or shows the importance of hands on cruising experience.
The rudder looks as flimsey and fragile as they could possibly make it, and very prone to fouling.
Brent

[mydauphin]

It is amazing that people build Aluminum boats to make them lighter and then add lead to make them heavier... Oh, Aluminum, Lead, Copper, Concrete, or anything touching Aluminum will corrode it. Buy and read the boat Metal Hull Construction. Aluminum is great, but electrolysis, crevice corrosion, poultice corrosion, electrolysis will all eat your boat a live and turn it into swiss cheese. Many people will tell you what you want to hear. Learn it for yourself before you pour anything anywhere... CONSIDER YOURSELF WARNED.

[cvzzr]

Originally Posted by Brent Swain

Those bulbs at their aft end will be nasty for fouling anchor rodes...
The rudder looks as flimsey and fragile as they could possibly make it, and very prone to fouling.
Brent

Hi Brent,

I agree with the fouling and rudder comments. This designer has a bit of a better setup on his 31', with the rudder skeg triangulated back to the hull via the propeller shaft skeg. I would change the design of the keels to eliminate the extension of the bulbs.

I do like the idea of the bolt-on lead as it gets the COG lower, though. I would still want some ballast in the keels (concrete, maybe) to maintain some stability if one lost the lead off the bottom due to a severe impact or whatever.

I am still considering your 36' hull, but I am finding that aluminum is relatively cheap right now, and I have some experience working with it having built a welded aluminum 17' skiff. I want to stay with the twin keel idea for the ability to keep a boat without moorage (it may be a little more crowded down where you are once I get a boat in the water )

[Ilan Voyager]

Originally Posted by whoosh

what I usually do is throw in as big a pieces as possible, some up 20 30kg, then pour molten around it then seal then TEST USING NOTHING OTHER than manometre If the keel is properly constructed designed and built and welded there will never be a problem But if you have overlooked a pin hole and you say crack a plug weld, then you are introuble, because then you would have to cut open one side, flush with fresh water and dry , the slightest and I mean slightest hint of moisture and alloy will not weld
In 30 years I have not had a prob, but saw Taberlys Pen Duick, with spent uranium or was in plutonium waste, was cracked in 78 Whitbread in AK , IMPOSSIBLE to fix in that short time
To reiterate the manometre is the only test that is failsure

Happily it wasn't plutonium a very toxic metal (a part radioactivity) it was waste uranium. Almost as inert as lead. The lone problem with "poor" uranium that it must be very well sealed as it dissolves in salt water maybe as fast as sugar in hot coffee.

All the hot pouring I have seen (2 or 3 times) were finished after the tests of leaking with compressed air, by pouring a very fluid epox resin and making a very slight vacuum to take out any air bubble. Sorry I have no more infos, I was just looking as spectator

[Brent Swain]

Originally Posted by cvzzr

Hi Brent,

I agree with the fouling and rudder comments. This designer has a bit of a better setup on his 31', with the rudder skeg triangulated back to the hull via the propeller shaft skeg. I would change the design of the keels to eliminate the extension of the bulbs.

I do like the idea of the bolt-on lead as it gets the COG lower, though. I would still want some ballast in the keels (concrete, maybe) to maintain some stability if one lost the lead off the bottom due to a severe impact or whatever.

I am still considering your 36' hull, but I am finding that aluminum is relatively cheap right now, and I have some experience working with it having built a welded aluminum 17' skiff. I want to stay with the twin keel idea for the ability to keep a boat without moorage (it may be a little more crowded down where you are once I get a boat in the water )

It will get a bit more crowded, as another 36 is due for launching in a couple of weeks, but there is still room, if we pick some good spots out . The recession probably killed plans they had to extend the breakwater further west.
Brent