Aluminum boats

[Sartre]

Hi,
I am considering buying a Aluminum boat (~38ft-ish) and wanted to collect some opinions (both positive and negative are welcome). I'd be particularly interested to hear about maintenance issues (usual maintenance problems, costs etc). Is painting of aluminun hulls as difficult and expensive as some say?




Many thanks.

[gibbonsj]

From what I've seen the best option as far as painting goes is to only paint the bottom and to leave the hull above the waterline bare. Paint the deck in-order to get nonskid on. Aluminum has awesome self healing properties even before adding paint and the paint does nothing but to massively increase maintenance, obviously bottom paint is still very necessary.

[noelex 77]

Painting aluminium is not difficult, but it has a relatively short life (especially compared to gelcoat), particularly if you want it to look perfect.

The good news is that unlike other hull materials, 5 series aluminium that is used for hull and deck plating does not require any paint or other surface finish to prevent deterioration or corrosion.

The less paint the better in my view, but some owners take the opposite tack. A stunning immaculate paint job is possible, just look at super yachts (most of which are aluminium), but with the rough and tumble of cruising life a (mostly) bare aluminium finish is more practical than paint or a gel-coated fibreglass finish, especially when the aluminium is inherently more abrasion and puncture resistant than most other materials (except steel).

[dannc]

I was hoping that Noelex would show up.

If you have not read his thread about building an AL boat, you should, http://www.cruisersforum.com/forums/...47499-131.html.

We flip back and forth between wanting a steel hull vs AL but it is a 49% vs 51% ratio. Sometimes AL is 49%, other times AL is 51%.

What usually flips us to AL is the lack of rust and the need to paint to prevent said rust.

However, we were talking to a boat builder in the EU about AL and he pretty much wanted to paint the boat to prevent pitting. First I have ever heard of AL pitting because of lack of paint. The company has been in business for over a century so what he said was interesting. Unfortunately, we quickly went to a different subject. I wonder if he meant the pitting was below the water line which of course should be painted.

If you have not read through the Dashew's website, it is highly recommended. They are retired now but have built several series of boats in AL. https://www.setsail.com/

The Dashew's have also published their books as ebooks and they are available for free from their website. The books are a treasure trove of information about boats, materials, weather, seamanship, etc. The more technical information is sorta going out of date but much will be helpful. https://www.setsail.com/free-books/

Later,
Dan

[noelex 77]

Originally Posted by dannc

I was hoping that Noelex would show up.

If you have not read his thread about building an AL boat, you should, http://www.cruisersforum.com/forums/...47499-131.html.

We flip back and forth between wanting a steel hull vs AL but it is a 49% vs 51% ratio. Sometimes AL is 49%, other times AL is 51%.

No hull material is perfect. Obviously my vote would be for aluminium, but any material can make a great boat. Remember the sunsets look the same no matter what your choice.

[Cheechako]

I have some experience in Aluminum boats, from a manufacturer's standpoint as well as friends who owned a nice 48 ft aluminum.
-My friends had their boat painted 3 times in 10 years, spending probably $50k in the process. It was a quality boat built in Maine. The first of those paint jobs, after they bought the boat, was at a high end "big yacht" yard on the east coast.
-I had a trailerable powerboat , 24 ft. The trailer had outdoor plastic carpeting on the bunks that suspend the boat. Because I didn't leave it in the water, I had no bottom paint on it. I always tried to flush the trailer with fresh water after using the boat in salt water. After selling the boat, maybe 1-2 years later I got a call from the buyer saying there was deep pitting in the bottom. I helped him investigate it and we concluded that the pitting was where the bunks were. The area stays wet and the salt isn't completely removed by flushing.
-My conclusion from this is that any trapped areas of salt moisture will cause rapid corrosion.
-As a manufacturer we got a notice from the aluminum mill that there had been a batch of marine aluminum that was slightly out of spec. This material was already in several boats. On 3 boats we had to ship the boats back to us, remove the entire transom and replace it. The boats showed a lot of corrosion on those transoms.
-Aluminum's resistance to bending is only approximately one third of steel. So your aluminum boat, compared with steel anyway, is going to be a lot more "bendy" if not designed with that in mind.

[dannc]

Originally Posted by noelex 77

No hull material is perfect. Obviously my vote would be for aluminium, but any material can make a great boat. Remember the sunsets look the same no matter what your choice.

Yep. Which is why we flip flop back and forth between AL and steel.
Both materials have good and bad points, and for us, they are closely matched.

Later,
Dan

[dannc]

Originally Posted by Cheechako

...
-I had a trailerable powerboat , 24 ft. The trailer had outdoor plastic carpeting on the bunks that suspend the boat. Because I didn't leave it in the water, I had no bottom paint on it. I always tried to flush the trailer with fresh water after using the boat in salt water. After selling the boat, maybe 1-2 years later I got a call from the buyer saying there was deep pitting in the bottom. I helped him investigate it and we concluded that the pitting was where the bunks were. The area stays wet and the salt isn't completely removed by flushing.
-My conclusion from this is that any trapped areas of salt moisture will cause rapid corrosion.
-As a manufacturer we got a notice from the aluminum mill that there had been a batch of marine aluminum that was slightly out of spec. This material was already in several boats. On 3 boats we had to ship the boats back to us, remove the entire transom and replace it. The boats showed a lot of corrosion on those transoms.
...

Your pitting issue is interesting and the first I have ever read. I really wonder if in our discussion with the builder he thought I meant we did not want to paint the bottom of the boat. The wife and I discussed this later. What is ironically funny is that the builder and us are native English speakers but he talks funny. Or maybe it was we who talked funny? I really think we had a misunderstanding due to language even though we were speaking English.

I also wondered if maybe the pitting he had seen was due to a bad batch of AL.

Flip side is that another boat builder we met showed us a steel boat that had pitting in the hull but that was a lack of zincs.

Later,
Dan

[dannc]

For the OP, I should have mentioned Kasten's website. He was the editor of the Metal Boat Society for many years and his website has some very informative pages on AL, steel, and other metals for boats. Here is a link to one page on AL, Cruising World Article - Aluminum For Boats . He has more so dig around the website.


Later,
Dan

[Cheechako]

Originally Posted by dannc

Your pitting issue is interesting and the first I have ever read. I really wonder if in our discussion with the builder he thought I meant we did not want to paint the bottom of the boat. The wife and I discussed this later. What is ironically funny is that the builder and us are native English speakers but he talks funny. Or maybe it was we who talked funny? I really think we had a misunderstanding due to language even though we were speaking English.

I also wondered if maybe the pitting he had seen was due to a bad batch of AL.

Flip side is that another boat builder we met showed us a steel boat that had pitting in the hull but that was a lack of zincs.

Later,
Dan

Yeah. The French have a ton of unpainted boats in the Carribean.

[noelex 77]

Originally Posted by Cheechako

-I had a trailerable powerboat , 24 ft. The trailer had outdoor plastic carpeting on the bunks that suspend the boat. Because I didn't leave it in the water, I had no bottom paint on it. I always tried to flush the trailer with fresh water after using the boat in salt water. After selling the boat, maybe 1-2 years later I got a call from the buyer saying there was deep pitting in the bottom. I helped him investigate it and we concluded that the pitting was where the bunks were. The area stays wet and the salt isn't completely removed by flushing.
-My conclusion from this is that any trapped areas of salt moisture will cause rapid corrosion.
-As a manufacturer we got a notice from the aluminum mill that there had been a batch of marine aluminum that was slightly out of spec. This material was already in several boats. On 3 boats we had to ship the boats back to us, remove the entire transom and replace it. The boats showed a lot of corrosion on those transoms.

This is classic crevice corrosion.

It is why aluminium fuel and water tanks are a bad idea on anything other than an aluminium boat. It is very difficult to support the tank wihout the support brackets preventing oxygen reaching the area.

If supporting an aluminium hull on carpet, even plastic carpet, crevice corrosion is guaranteed. Fresh water will not help significantly.

There was a defective batch of 5 series aluminum that caused significant problems. It was 5086 produced by a major supplier, I think from around the early 90’s from memory, but it is unlikely there are any boats with this aluminium left, as there were extensive court cases and litigation. If building an aluminium boat make sure the aluminium used is certified and tested to meet the specifications.

[Fence Man]

Originally Posted by Cheechako

I have some experience in Aluminum boats, from a manufacturer's standpoint as well as friends who owned a nice 48 ft aluminum.
-My friends had their boat painted 3 times in 10 years, spending probably $50k in the process. It was a quality boat built in Maine. The first of those paint jobs, after they bought the boat, was at a high end "big yacht" yard on the east coast.
-I had a trailerable powerboat , 24 ft. The trailer had outdoor plastic carpeting on the bunks that suspend the boat. Because I didn't leave it in the water, I had no bottom paint on it. I always tried to flush the trailer with fresh water after using the boat in salt water. After selling the boat, maybe 1-2 years later I got a call from the buyer saying there was deep pitting in the bottom. I helped him investigate it and we concluded that the pitting was where the bunks were. The area stays wet and the salt isn't completely removed by flushing.
-My conclusion from this is that any trapped areas of salt moisture will cause rapid corrosion.
-As a manufacturer we got a notice from the aluminum mill that there had been a batch of marine aluminum that was slightly out of spec. This material was already in several boats. On 3 boats we had to ship the boats back to us, remove the entire transom and replace it. The boats showed a lot of corrosion on those transoms.
-Aluminum's resistance to bending is only approximately one third of steel. So your aluminum boat, compared with steel anyway, is going to be a lot more "bendy" if not designed with that in mind.

With regard to the pitting on the trailer boat, treated lumber bunk boards will also cause that problem, even if saltwater is never part of the equation. I would assume that it is the same chemical reaction that you experienced with the saltwater exposure.

[a64pilot]

My aluminum water tank touches nothing I don’t think.
I believe it’s hung, suspended if you will from metal tabs, however they still fail, mine is overdue. I hope they fail from chlorine as I keep that out.

However what tripped the replacement of my aluminum wast tank was corrosion from the outside, it did sit on the floor and apparently stayed wet due I assume to condensation, but the corroded aluminum formed a sort of sand that stayed wet and pressed against the good aluminum, and accelerated the corrosion, I think.

Point is I guess is aluminum requires someone who knows what they are doing and needs to be designed with it in mind, just as steel does.

The tanks are 5000 series aluminum, which specific alloy, I’m not sure

[dannc]

I read of a very nice AL sailboat which I believe was built in the 70's? The original owner sold of the boat, or his estate did, and the boat was not well maintained for many years. Eventually, the boat was bought by someone who had a connection to the original owner and had the money to refurbish the boat.

One problem area was the top of the AL water tanks which had pitting. When the boat was built they use copper pipes for the water supply, they did not have anything better to use back then, and there was a leak. This leak was on top of the AL water tanks and they had some pitting/corrosion. They blamed the itty bit of copper that had leached into the fresh water which had then leaked on top of the AL water tanks. Maybe they were wrong and it was just the water sitting on the tank.

Later,
Dan

[noelex 77]

Originally Posted by a64pilot

However what tripped the replacement of my aluminum wast tank was corrosion from the outside, it did sit on the floor

This looks like another classic case of crevice corrosion.

A good rule of thumb is to be very careful if aluminium is sitting against another surface.

If the aluminium is sitting against another surface with a free flow of oxygen and water, the aluminium will be fine and will not corrode. The other option is to completely seal the surface so no oxygen or water can enter.

These two options are very hard to do when installing an aluminium tank in a fibreglass or wooden boat. The aluminium and the fibreglass will change dimensions with temperature at a different rate, making the second option difficult to achieve, at least long term. An aluminium tank contacting a floor or stringer is common. Debris and crud will acumulate under the tank if there is a gap, although often the heavy weight dictates the tank rests on the bottom at some point. The aluminium will corrode and the only hope is that the corrosion will be slow enough to have a reasonable life.

Aluminium is great in the correct application, but aluminium tanks on a non aluminium boat are nearly always a bad idea, as this case shows.

If you do have an aluminium tank you also need to be careful if an electric tank gauge is installed, or if there is any other electrical connection to the tank. In simple terms, electrical systems on an aluminium boat are isolated. Unfortunately frequently boatbuilders familiar with other materials do not understand the simple but specific requirements of aluminium.