Aluminum hulls

[artdeluxe]

Hello there,
I have a question for you. I am doing research on 32-36 boat designs. Fiberglass is a material of choice. But I would like to try to special order hull made of aluminum. The reason – I would like to go off shore a lot, so I would like boat to be impact resistant and easy to repair. Also weight is an issue. So all your thoughts on this are welcome. Reason why I am asking for an advice is that I do not see too many 32-36 boats made of aluminum. Price in this case is not really an issue. And I am not talking about ugly hull. I found a ship yard where they can build a hull of almost any shape. I kind of like this idea, so your con’s for using aluminum for a boats of this size would be very welcome.
Thank you,
Victor

[duluthboats]

Here's one site that has some aluminum hulls.

http://www.stadtdesign.com/

Gary

[artdeluxe]

Thank you Garry, but what I am thinking is a little bit more contemporary form. I would like to try built a sail boat with a planning hull. So weight is going to be an issue. Most of the racing boats are made of composite materials based on epoxy. This finish boat might be a good example of what kind of shaping I am looking for: http://www.guydesigngroup.fi/.

[duluthboats]

The site was only to illustrate that an aluminum hull the size you want is very doable. With the right shop any shape can be done in aluminum if you’re willing to pay for the work or have the skill.

Gary

[gonzo]

Aluminum is a great material. It is more expensive than fiberglass on that size. Also, the skilled workers to weld a boat are more difficult to find. With proper tools and knowledge any shape can be developed with aluminum. Think of a canoe; each side is a single panel.

[SailDesign]

Artdeluxe - if you are looking to go "offshore" and want something with impact resistance and easy repairability, then stick to fiberglass.
Fiberglass at least has the advantage that you can take all the materials with you, and use them on the boat at sea. Would you really want to weld alu at sea? Can you carry enough power on a 35' boat to do that?
There is a reasonb that most of the Open-class boats are FRP - impact resistance, light weight, and eases of repair...

Steve

[Polarity]

"Can you carry enough power on a 35' boat to do that?"

Surprisingly, yes you can! Check this MIG welder out - runs on a couple of marine batteries : http://www.readywelder.com/

Can't you repair Aluminium with FG ?...

I am not sure about the numbers here, but I for one would rather be behind a sheet of Aluminium when meeting ice or a container on a dark night. Or dragging onto a reef for that matter.
However I understand that in any sandwich construction the core absorbs a lot of impact energy in a puncturing incident but the exterior has much less abrasion resistance.

I was under the impression that most of the new Open 60's are Carbon :
"Open 60s are one of the fastest boats in sailing - built in carbon fibre using the latest hi-tech structures, they are designed to be as light as possible (for speed) but strong enough to withstand the worst the seas can throw at them." - IMOCA

Of course this is one of those Steel vs Aluminium vs FRP questions, rather like Cats vs Monohulls!

Interestingly the 1993 Open 50, Branec III is a Glass/Kevlar/Airex Sand construction and displaces 8t. My 1990 Open 50 in Aluminium weighs in at (ocean race loaded) 7.3t, both by the same designer...- However Branec III is presently bashing into 35 Knts in the Channel lying 2nd in Class II of the TJV. Mine on the other hand is on the hard waiting for me to get sponsorship together for the STAR next year...

Paul

[artdeluxe]

Well, to patch aluminum hull you do not have to weld. Just drill holes and bolt a patch from the outside. After that concrete can be used to stop small leaks. But I am not talking about repair while at sea. I think that if there is a significant hull damage to a boat of this size – it is over, no matter aluminum or fiberglass.

[SailDesign]

Polarity,
Yes, most of the new ones are carbon. Personally, I have always felt that carbon is overkill in the hulls, although you will save a few grams. The current trend is to go for "monolithic" (read: solid) carbon below the DWL, and cored above. E-glass can be used for the skins if carbon is used to strengthen the sheer, keel, etc., resulting in a much cheaper boat although it may weigh (by last estimate dated 1998) some 250 lbs more.
That's my experience, and I'm happy to be corrected. I would rather be behind a proper crash-box, with a layer of Kevlar in the inner skin, than behind anything aluminum, but again, that's my experience and personal bias speaking.
Steve

[gonzo]

Impact resistance needs to be specified whether it is wave slamming or a hard pointy object. Metal is way superior for puncture resistance. For slamming wood is the best for its weight.

[SailDesign]

gonzo,
I'll agree that steel is better than fibreglass for sharp impacts, but aluminum better than Kevlar? Naaaahhhh...... ;-)

[betelgeuserdude]

Hi Victor.

As you were looking for cons rather than pros (of which there are countless), I thought that I would mention the hassles of underwater finishing. Even if one discovers the optimum wetted surface finish system, it becomes useless if damaged (when damaged). All other problems have decent solutions.

I would not paint an aluminium boat above the waterline.

I believe that any metal boat should be insulated. This provides positive and negative aspects. An insulated metal boat is quiet, and comfortable, but if (when) repairs become necessary, the hull must be accessible from both sides.


DC

[gonzo]

What about delamination on impact, even for Kevlar? I agree the fibers may not fail, but the resin will. I'm not sure about experimental data, but I am curious about how they compare.

[SailDesign]

gonzo,
Yes, Kevlar will delam, especially if it's just one layer out of many, but it still retains some integrity, unlike aluminum which splits and peels like..... like...... like an tin can ;-)
Steve

[gonzo]

My experience with aluminum boats is mainly canoes and john boats. They take a lot of abuse. A bit of hammering usually gets them back into shape. I've seen some Kevlar canoes and kayaks with cracked hulls. Does this not scale up?