Life Expectancy of Alloy Hull?

[mattplowman]

Am looking at purchasing a Sparkman and Stephens designed 44ft Alloy yacht. She was built in New Zealand by a professional yard in 1976.

Assuming that there has not been any electrolysis / corrosion issues (full survey will be conducted) what is the half life of Alloy in the marine enviro?

Cheers
Matt

[s/v Beth]

Alloy of what metals?

[downunder]

Originally Posted by s/v Beth

Alloy of what metals?

Allumimum I presume.

[noelex 77]

Of all the commonly used boat building materials marine aluminium is the most resistant to salt water. Polyester resin and wood absorb moisture and gradualy loose their structural properties. Steel corrodes. Epoxy resin solid laminates and aluminium are virtually unaffected.
Aluminium boats need to well designed, free from electrical problems, contact with dissimilar metals. Oxygen has to reach the surface if the corosion resistance is to be maintained.
These goals are not difficult, if they are met aluminium will be unaffected by saltwater and have the longest life of all the boat building materials.

[mattplowman]

Originally Posted by s/v Beth

Alloy of what metals?

Allumimum

thanks
Matt

[noelex 77]

Originally Posted by mattplowman

Allumimum

thanks
Matt

Not such a silly question the aluminium grade is grade is critical. It also must be welded by people that know what they are doing. If these " details" are not satisfactory run, no matter how good the boat is otherwise.

[Factor]

Looked after - like any boat - they can be very long lasting, had a mate with a 43ft aluminium cat that was 20 years when sold recently, passed survey with flying colours and was in excellent condition. If I was building myself, an aluminium cat of 45-48 foot would be the go I think.

[mattplowman]

Originally Posted by noelex 77

Of all the commonly used boat building materials marine aluminium is the most resistant to salt water. Polyester resin and wood absorb moisture and gradualy loose their structural properties. Steel corrodes. Epoxy resin solid laminates and aluminium are virtually unaffected.
Aluminium boats need to well designed, free from electrical problems, contact with dissimilar metals. Oxygen has to reach the surface if the corosion resistance is to be maintained.
These goals are not difficult, if they are met aluminium will be unaffected by saltwater and have the longest life of all the boat building materials.

Thank you for your reply. So are we talking 50yrs, 100yrs etc.

Thanks
Mayy

[mattplowman]

Originally Posted by noelex 77

Not such a silly question the aluminium grade is grade is critical. It also must be welded by people that know what they are doing. If these " details" are not satisfactory run, no matter how good the boat is otherwise.

Have been trying to get grade details and will post once I have them. As for build quality, was built by top end Kiwi yard so quality of build will not be an issue

Thanks for the helpful replys thus far

Matt

[David M]

That's interesting because I run a custom designed aluminum Sparkman and Stephens power boat built in 1975, which was built at a yard in Maine....yes S&S designed some stinkpots.

To answer your question. I don't think there is a half life for aluminum. It all depends on how well you prevent the electrolysis and how well the boat was designed and welded together.

The boat I run has held up just fine. If you are interested I could list all the things I do (and don't do) to prevent electrolysis.

[downunder]

Originally Posted by David M

That's interesting because I run a custom designed aluminum Sparkman and Stephens power boat built in 1975, which was built at a yard in Maine....yes S&S designed some stinkpots.

To answer your question. I don't think there is a half life for aluminum. It all depends on how well you prevent the electrolysis and how well the boat was designed and welded together.

The boat I run has held up just fine. If you are interested I could list all the things I do (and don't do) to prevent electrolysis.

yes please.

[mattplowman]

Originally Posted by David M

That's interesting because I run a custom designed aluminum Sparkman and Stephens power boat built in 1975, which was built at a yard in Maine....yes S&S designed some stinkpots.

To answer your question. I don't think there is a half life for aluminum. It all depends on how well you prevent the electrolysis and how well the boat was designed and welded together.

The boat I run has held up just fine. If you are interested I could list all the things I do (and don't do) to prevent electrolysis.

That would be great

Matt

[leftbrainstuff]

Aluminium is fatigue limited unlike steels which have no such limit. The fatigue limit is a product of the microstructure of the alloy. 10,000,000 cycles is the design norm.

In reality useful life is consumed according to miners law. Expect 5083 or similar to be used for hulls. Aerospace speciality aluminium alloys have issues with corrosion but aren't used for marine applications.

It's not possible to answer your question in terms of years. In reality corrosion and gouging will be the limiting factors. Both are easy to determine from visual inspections.

[stillbuilding]

I owned a 35 year old 38' John Lidgard alloy cruiser/racer which took some effort to cope with corrosion around the s/s bolts used for the toe rail but otherwise was in great shape and still going strong. It was the first larger alloy yacht built in Victoria, Australia. Built by Haulmaster trailers which were doing alloy bulk truck freighters! Did a good job. Original mast and boom still good too.

[Andrew Troup]

OP: Which yard?