Aluminium deck on a steel hull ?

I'm looking at buying a steel hull boat, but it has an aluminium deck and cabin.

I always believed that putting two different metals together was a bad idea in boat building. Was I wrong?

I understand a gasket of some sort can go between the two, but how good a system is this practically?

I may be slightly biased as I had a Land Rover ( steel chassis, aluminium body) that died of corrosion !

 

You could have reason to be concerned. An aluminum house on a steel deck/hull is common but this boat is a bit unusual. Check to see if hull/deck is mechanically fastened( bolts, etc) or used a bimetal welded strip joint (Deta-Couple).
As a matter of interest, I know of a builder that did a boat like this and the 'connection' was so complicated (skin, frames, brackets, etc) he joked (seriously) it would have been the same price to build the entire boat in aluminum.
ps: you could also visit the MetalBoatSociety site 'forum' - you may be able to get some assistance there

 

Thanks,

How effecient is the Delta-Couple system? i.e. how long does it last?

If it's any good perhaps someone should tell Land Rover !

 

Don't remember any corossion problems with the old (1959) Rover 90.....

Well it was still OK in the mid 70s' ie no rust.

 

On a topic related to corrosion - my little story.
My first car was a 1956? used Hillman Husky. One day driving to work the brakes failed and I 'sailed' into a loading bay at about 20 mph. Fortunately the emergency (hand) brake worked so no damage was done. When the dealer's mechanic inspected everything, the entire system had to be replaced. The lines were copper, the slave cylinders were aluminum, and the master cylinder had a fair amount of aluminum. Living on the coast and exposed to moisture and salt air, why should anyone be surprised.

 

A steel hull with an aluminium deck and deckhouse/superstructure is very common. More than most realise. It is popular with patrol boats, especially in the middle east, where for some reason they still think steel is better for a hull. The ally is used to keep the weight down as they also want a fast patrol boat!. It is also used with passenger ferries too.

So long as the steel and aluminium are correctly isolated, all works well.

 

Almost all super yachts I have worked on (50m to 150m) Have aluminium super structure and steel hull. It Seems to be alright.
I believe they use explosion welding but I can't confirm that.

None have sunk yet. And there are almost as many paint repairs from steel corrosion as there is aluminium corrosion. But never at the joint.

 

Im still kinda new to this field as I have only been reading on it for about a year. However, From what I understand the issue you are worried about is electrolisis and that is mainly an issue for parts of the boat that lie under the waterline and can usually be combatted with a sacrificial cathode of some sort.