aluminium hull w/ wood deck ?

[shipwreck]

Hello Boatdesigners, I am about to build a 30ft. aluminium hull sailboat and still contemplating the deck material. The normal way is to just have an aluminium deck which is good for strength and waterproof but worried about it feeling like living in a tin can and the cabin not able to breath much. Could be unbearable in hot weather ? I'm thinking about having a wood roof/deck ...maybe just have one layer of thick teak as deck and roof ? I want to stay away from plywood ontop of aluminium deck ideas.
Does anyone know someone that tried this ? Thanks to all.

[Dean Smith]

It has been done many times,once by me. the time saving is when you get to your house structures. You have a (SHELF) running around the hull at the correct angles to pick up camber. you can either land the beams atop the shelf or slung under it
However I would not advise it, alu is easily insulated will not sweat with proper ventilation. Is integral, strong and forever.

[shipwreck]

Hi Dean Smith...thanks for the tip...love the "forever" part of aluminium. I see that you are from New Zealand. The boat I'm interested in making is a
Hartley 30 sailboat (from NZ?), bilge keel but in aluminium. It has been difficult getting opinions about this boat. What do you think about them ? Thanks again for the response.

[Ad Hoc]

Shipwreck

A "composite" of any combination can be made. But as always you need to be carefull you don't make matters worse.

Im not sure what Dean means by "will not sweat"....perhaps he means the wood will leak and the ally not...im not sure what the implication is?

The two real issue would be corrosion and movement.

1) Corrosion....if bare wood, or any 'wick-like' material is placed in direct contact with ally, you'll get Poultice corrosion. Basically a sticky white hydroxide will ooze out and push the ally from the wood, or vice versa. Therefore you need to use extreme care in protecting the wood to ensure it is 100% waterproof, such as an epoxy. Hence maintain regularly to ensure the water-tight barrier is not harmed is paramount.

2) Movement. The thermal expansion of ally is very high. However you attach the wood to the ally, you’ll have to take into account the relative movement between the two materials. Under a very hot med or tropical sun the ally will move a lot, this may introduce unwanted or unaccounted for strain into the wood/ally joint.

Also, any stress that is imposed under sea loads, of whatever nature, the load path from the ally to the wood, requires more investigation. Since the difference in strength of ally and wood shall effect the behaviour, and also the joint between the two.

Doesn’t mean can’t be done, as Dean notes above. But longevity and peace of mind requires more investigation and “belt and braces” approach then just accepting a wood deck as ‘nice’ to do.

[shipwreck]

...very interesting and you convinced me to go with the aluminium deck. Do you have any ideas to ventilate the aluminium cabin ? Size is about 3m x 1,80 x 5m.....would two or three cowl vents do the trick ?

[Ad Hoc]

Originally Posted by shipwreck

...very interesting and you convinced me to go with the aluminium deck. Do you have any ideas to ventilate the aluminium cabin ? Size is about 3m x 1,80 x 5m.....would two or three cowl vents do the trick ?

If it is a normal cabin as such, then natural ventillation should suffice. Just place a couple of vents at either end of the cabin to allow a free flow of air. If you find it is not enough, add an extractor fan on one of them.

[Dean Smith]

you really need hatches, , on a smallboat have them hinging on fore side
You need a big one say 550 sq to hand sails down , one over heads and so on, these days they are so good
All the around world yachts built here use Weaver I fitted over 100 , they do not leak
When you are anchored you can make a shute suspended from a halyard or stay to guide air down
The reason for hinges fore, is so IF they are not closed a wave wont slam em back and rip em off