Aluminium Keel Ballast

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.

 

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.

 

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

 

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/at...159817634-brewer-aluminum-design-g2612179.jpg

 

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...

 

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.

 

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

 

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.

 

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 )

 

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

 

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

 

Here are some practical long term solutions for the lead/aluminum keel problems, even though this thread is very old, it is a very significant one.

I designed and built my aluminum 65 footer with retractable 12' centerboard, launched in 1999 (variable draft of 4.5' to 12'). I designed a long, shallow draft keel using a NACA computer generated foil section with a deep centerboard case that penetrated it in the form of a quadrant board (eliminating board trailing edge suction when extended that way) designed volume to hold precisely 21,000 pounds of lead, with the board itself being a solid aluminum foil shape.

We smelted our own lead, and found it much quicker and COOLER on the plating (the plating WILL warp if heated too much, and NO, it will NOT burn) by lining the keel areas with solid lead pigs as much as is possible but still allowing space for the molten lead to flow around them, and lock the mass together as it cooled. There was undetectable lead shrinkage in this manner, and the cooler mass of the lead pigs cooled off the temp of the molten lead, allowing for zero aluminum plate distortion.

After many test panels, I found that it is not practical to pre-coat the aluminum NACA keel box prior pouring the lead, simply because there is no paintable covering that will resist the heat. After sealing the top of the keel box, I drilled and tapped two 3/8" fittings on the top, at opposing ends. The forward one was plumber to a Hynautics pressure pot, like the one used on their engine controls, and filled with extremely high viscosity food grade silicone, with the viscosity of honey. After researching all the possible dielectric oils, I found that this gave the best dielectric qualities, does not burn if you have to weld on exterior plating in the future, and will not poison you if you use integral water tanks and there occurs a pinhole leak. All you do is fill the pot, close the cap, and use a bike pump to bring the tank up to 5 psi (don't go any higher, as pneumatic forces increase astoundingly of large areas) and rig a hose to the exit line and into an overflow pot. I is preferable to do the initial out of the water, and could take as long as 2 weeks before you see anything from the return line. Of course you will need to keep check that the pressure does not go below 1 psi. This system will forever keep your lead/ aluminum keel free of electrolysis, and be forgiving to allow for any pinhole leaks due to the extremely high viscosity.

As for a little aluminum oxide (AL2-O3) found on the the inside of your plating, that this is not the end of the world. Understand that alu oxide is an excellent dielectric by itself, from DC to GHz frequencies, it resists strong acid and alkali attack even at elevated temperatures, and is used as high voltage insulators and in electronic substrates. That little bit of corrosion should actually slow down future corrosion. However, this is no excuse not to provide for a solution to the problem, which is securing the leak, drying it out, replacing the overly diminished plate in only the localized area, and pumping in an excellent dielectric oil, such as very high viscosity food grade silicon.

 

Resplandor
Welcome to the forum. It would be great if you could post some pics of your boat. People are always interested and it's good to a project that made it to fruition.

I'm afraid you are mistaken about Aluminium oxide, it reacts quite readily with both acids and bases. Also the reaction between lead and alloy is galvanic corrosion, electrolysis needs an impressed current from an external source, it's a common confusion.

 

Esteemed Mike Johns,
Thank you for your reply, and your welcome to the group. However, with all due respect, there is no confusion. I am very aware of the galvanic voltage difference between lead and aluminum, but this has nothing to do with my point, which was that aluminum oxide itself has dielectric properties, and actually helps protect from further galvanic corrosion in alu/lead keels. If this were not true, you would be seeing death sentences given to most alu boats over 5 years old. Galvanic corrosion manifests itself as aluminum oxide when inside a sealed environment. If water was flowing freely over it, obviously the alu oxide would be washed out. Additionally, an impressed current galvanic system would have no effect in stopping such corrosion in alu/lead keels. The area of contact is simply too great. Frankly, I am terrified of impressed current systems, and I have studied them in depth. At best they are precarious when diligently watched and maintain, and are a Damoclean sword when not. I think it is far better to properly wire the alu boat so that ALL electrical has breakers on BOTH poles (DC and AC), all electrical gear is double checked so as to be ground isolated (including starters and generators) or installed on a good dielectric base such as Star-board, and to ALWAYs run your AC through an isolation transformer. When wired this , troubleshooting stray currents is a simple matter of opening breakers.

In short, the only solution I have been able to come up with to tackle the alu/lead keels was what was described in the previous post, and it works.