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Old 20 October 2009, 08:43   #1
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aluminium or Grp rib, characteristics and choice

Pardon me for being ignorant perhaps but, what are the benefits drawbacks of both. it would appear from reading this forum, southern hemisphere boaters love aluminium based boats. Over here, ribs have taken off massively in the last 10 years.

Why then aren't we using aluminium hulled ribs? Factors to consider that i don't know the answer to are:

Cost
weight
strength
durability
manufacture limitations
etc

Curious to know some answers?
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Old 20 October 2009, 11:00   #2
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Aluminium is very popular down under because Australia mines more Bauxite than any other country - double even what China produces!!!

Aluminium hulls are very tough and pretty light but you can't have shapes as complex as moulded GRP. We tend to use aluminium for tough commercial boats here like Ocean Dynamics.
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Old 20 October 2009, 11:08   #3
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Cost is just about the only reason we don't use aluminium. Stronger, lighter and easier to repair/modify.

As well as the high cost of ali material, you cant compare the labour time to laying up a grp hull once you got a mould to work from.

I don't think theres much you can do in grp that you cant in aluminium, again its just labour intensive.
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Old 20 October 2009, 11:20   #4
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hull comlexity

Anyone shed light as to whether you can or cant make as complex a hull with aluminium as you can with Grp? I would conclude from the comments that you could, it would just cost a lot.

To conclude to some degree, from an owners perspective, aluminium would be the choice if money no object? (subject to the success failure of carbon fibre hulled rib, a different thread)
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Old 20 October 2009, 11:29   #5
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I wouldn't choose an aluminium hull unless I needed one - for example constant bashing over rocks etc.

Even then fibreglass can be pretty tough - the RNLI boats are all GRP and they have plenty of money to spend.

Aluminium can crack at the welds and you have to be very careful with galvanic action - some ali hulls have just dissolved!!!
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Old 20 October 2009, 11:36   #6
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Quote:
Originally Posted by codprawn View Post
I wouldn't choose an aluminium hull unless I needed one - for example constant bashing over rocks etc.

Even then fibreglass can be pretty tough - the RNLI boats are all GRP and they have plenty of money to spend.

Aluminium can crack at the welds and you have to be very careful with galvanic action - some ali hulls have just dissolved!!!
Cheers codders, ever the oracle! Have to admit to not knowing what galvanic action is but i'm sure google will help me!!
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Old 20 October 2009, 11:42   #7
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Galvanic effects are probably the biggest drawback. Zincs need to be clean and inspected regularly; having a lot doesn't hurt, either.

Most plate boats (3/16" and thicker aluminum) are built from plates that are generally formed in one dimension. You can do more, but it gets rather complicated and expensive because of the tooling required to form it. So, in keeping costs down, most hull shapes for welded aluminum boats are fairly simple.

Advantages: Lighter for a given strength and size, more room inside (assuming you don't seal the deck to the hull), fairly simple repair if you have access to someone who can weld thick aluminum. No chipping of gel coat. Water intrusion generally doesn't hurt very much.

Disadvantages: Cost. Doesn't stay nice and shiny without a lot of work. Cost. Lighter boat usually means a rougher ride for a given size (though that is also hull-dependent.) People want to recycle it. And, of course, cost.

jky
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Old 20 October 2009, 12:15   #8
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I could be slightly biased as I am a welder/fabricator who can't fibreglass for s**t!
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Old 20 October 2009, 12:23   #9
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Quote:
Originally Posted by codprawn View Post
I wouldn't choose an aluminium hull unless I needed one - for example constant bashing over rocks etc.

Even then fibreglass can be pretty tough - the RNLI boats are all GRP and they have plenty of money to spend.

Aluminium can crack at the welds and you have to be very careful with galvanic action - some ali hulls have just dissolved!!!
Apart from the Atlantic 85 which is carbon fibre, the Tyne which is steel and the Mersey which is either alloy or fibreglass.

Ribcraft do alloy hulls too.
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Old 20 October 2009, 13:09   #10
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I could be slightly biased as I am a welder/fabricator who can't fibreglass for s**t!
Thats alright, I cant weld for soot either!

Did try welding ali to make a water tight seam a while back, got ok at it after loads of practice. Then moved and had to leave it behind.

There are pics on here somewhere to prove it.
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