Opinions on aluminium?

[Wardy]

I've been looking at most boat construction materials in my search for the perfect live-aboard; Ferro, Steel and GRP, but I haven't considered Ally! Now i find a boat that seems to have everything i could ask for internally and externally but i don't know if there are any problems regarding this material.
What should I look for? Is it a decent material for a live-aboard? What are the maintainance costs like in comparison to GRP?

Any help with anything that matters please

Steve

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[bruce]

have only seen one here in fla, owner had hard time selling, lots of electrolosis(sp) and other 'rotting', appears to require extra care in painting. just one impression, but lots of "glass' around.

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[Ovni]

Alu is a good option.

There are a lot of horror stories about alu, but most of them are nonsence.

The biggest problem is a wrong electric installation. If that occures the whole boat will be a wreck in short time on salt water.
There shouldn't be any current running from or to the batteries using the hull. This always happens on alumasts on grp boats; that's why alu get's a bad name. (e.g. the antenna of the vhf puts -12v on the mast)

So if everything is build mass free, including the engine, it's the most perfect material for fast yachts.

To look for a guide how to find out if the electrical system is oke use this:
John C. Payne in
"The Marine Electrical and Electronics Bible. A practical handbook for cruising
sailors", Adlard Coles Nautical, 1994, ISBN 0-7136-4110-X

Alu is more than 2.5 times as strong as grp when build on the same weight. The painting can be done by an hobbiest, allthough I will let it done the next time

<hr width=100% size=1>http://groups.yahoo.com/group/Ovnisailors/

 

[Birdseye]

I've been wondering too. My current boat has an aly outdrive leg held together by stainless bolts. Works reasonably well but does reuqire maintenance. Paint doesnt stick well to aly, even with etch primers. And once corrosion starts, it works its way between the aly and the paint and you have work to do! Probably why Ovni dont just paint the boat but run tape along the paint edges to give a seal.

I suspect that GRP is the least maintenance option, but aly seems to offer strength advantages at the cost of likely higher maintenance.

Also, electrical installattion in an aly boat seems to be a job for someone who is a specialist.

Still fancy it though

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[Capt_Scarlet]

For what its worth, a friend of mine has sailed on an ali boat, and commented that the hull was very noisy - ringing of the panels when hit by waves - so much so that he could not sleep.

May just have been poor construction or insulation, but may be worth considering.

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[ianabc]

Most commercial fishing boats on this coast are now built in aluminium !

In an interesting book by Brent Swain ( Of Oragami metal boat fame here on the West Coast of North America) he suggests that acid etech primers are akin to washing a boat in salt water before painting.......

Sandblasting with black grit ( fine 80 grade or so) provides a good key for epoxy paint. BUT the paint MUST be applied immediatly as the aluminum oxidises rapidly and paint does not key well to oxidised al.

Also it is my understanding that the marine series 5200 has less of the extra metals added to the alloy and is therefore less likly to corrode in seawater.

High strength alloys are prone to corrosion and weakening by welding.

We sandblast, ( well usually use black slag as it is less toxic and wear carbon double filterts protected by a 1/4 inch thick pre filter ) then have all al. items epoxy powder coated.......inexpensive and much simpler than the old etch and layers of paint method!

Ian ( of Worldwide Sailing Directions on CD )
ian.jean@shaw.ca

<hr width=100% size=1>Building a steel sailboat in Comox, B.C. Canada.

 

[Talbot]

epoxy powder coated work is fantastically hard wearing and gives a great finish, but the last ytime I checked, there was a problem of making good any areas that suffered scratches. AFAIK there is no real compatible touch up kit, unless of course you know better.

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[oldsaltoz]

G'day Wardy,

Did a delivery of an aluminium yacht some years back, it was during our winter, still warm during the day but very cool to cold at night.

I recorded the trip and have made some observations:

Condensation was a real problem, nothing was dry below decks, this was a racing yacht so she was pretty spars below decks, no heavy insulation, just a bit light carpet stuck to the hull in the berths.

After dark, cold to sit on, and cold to the touch, sailing gloves replaced with full finger gloves. Hot in full sun during the day.

Sleeping on board with even a small ripple running was all but impossible, gloop-plop-wish-gloop-gloop-plop, most of it from the stern, may have been a design fault, but it sure made sleeping a problem.

On entering a marina we had to deploy 6 wires with anodes attached and make sure the on board end had a good contact, this was to avoid the ravages of stray current from other craft and the systems used by marinas to prevent the piles rusting. Then haul them all back in and stow then (without tangles) for the next use.

But she was fast and very light, around 44 feet and not much over 9 feet wide, fantastic downwind.

It was very nice to get back into a glass boat and have a good sleep, no plonking and the berth was dry........

Avagoodweekend




<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[richardandtracy]

If you choose the right alloy you'll never have problems with aluminium. It's when you choose the wrong alloy that problems happen.

I've been out on the Great Barrier Reef on the 'Quicksilver' cat's. These machines had been in the water for 4 years when I went out. Un protected. In a hot very salty environment (equivalent to about 6 years in UK waters due to accelerated corrosion rates at higher temperatures).
No corrosion was visible near the waterline, or anywhere else for that matter. The alloy used was 5086-H8 (seen from some of the print markings still visible on both the extrusion stringers and plating).

Right, now for some other myths.
Myth 1. Aluminium boats get more condensation. The heat transfer rate is higher, yes. But the a steel hull will drip lots too if it's not insulated. When isulated the extra heat transfer due to the aluminium will be insignificant.

Myth 2. The boats slam more. Why? The behaviour in waves is a function of the shape and the boat weight. With an aluminium hull you can have a lower structure mass, which is not always wasted by a heavier keel - that is a designer issue not a material issue and is not to be blamed on the material.

Myth 3. They're weaker and more flexible. With correct design, taking into account the reduced stiffness of Al compared to steel, there is no reason for aluminium to be more flexible than steel. The strength issue is a bit more complicated. Aluminium breaks closer to its yield point than steel, but if the design is made for aluminium it can be as good as steel.

So, what it comes down to is if the design is for aluminium rather than an aluminium version of a steel boat, it will be structurally as good as a steel boat. If the alloy selection is right, there will be no corrosion problems in a reasonable vessel life.

Why are there not more aluminium boats then? I suggest you get a few quotes for aluminium in the quantities you'll need before you buy any plans. Then do the same with an equivalent quantity of steel. The aluminium will be about 3x more expensive by volume and in the region of 6x more expensive for an equivalent strength design.

Shame really, it's a nice material even if working with it takes more skill.

Regards

Richard.


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[Ships_Cat]

I agree with you Richard, they are all myths.

We have been putting into commission power boats capable of 40 knots, if the drumming myth was real we would know. They do not drum. Our own steel yacht we hear water sloshing when sailing but it is the water in the tanks - unless falling off large steep waves in which case any boat will make a bang - there is no reason for an aluminium boat to be any different.

Condensation is not a problem. The boat should be insulated. An insulated metal boat will be much better in this respect than a glass one and it will also have better thermal performance (retaining heat in cold weather or preventing it in sun).

Electroysis/galvanic action is driven in peoples' minds by marina myth and ignorance of the mechanisms - like any boat there should be isolation from the shore power earth and the boat be correctly wired. The ideas of hanging of anodes over the side, not mooring by steel boats or piles, etc, etc is all bunkum. For the naysayers, the majority of commercial vessels these days are made of aluminium and you will not see them doing those things - they know better.

If moored stern on to waves in a marina they will get wave slap under the counter but should not be any worse than any other boat and can be very easily made better than most. If it is an annoyance it is cured in any boat by gluing insulation (preferably closed cell flexible) to the inside of the hull in the affected area).

Problems with painting, well the majority of superyachts are these days built of aluminium, they seem to have finishes better than most of us.

Sure to generate a pile of responses from the mythmakers, removed from the metal boat marine industry, but the above is how the professionals see it - observing with interest.

John

<hr width=100% size=1>I am the cat but I am only 6.

 

[ovniowners]

Alubat offer closed cell insulation as an option on all Ovni yachts. We do not have it on our Ovni 385, and only suffer a small amount of condensation. I have not noticed much 'water noise' when sailing, however the relatively long bathing platform can slap the waves when at anchor. I must say that keeping the boat hot is not a problem - my father and I were sleeping aboard in Jersey in January (during force 10 winds) and were warm all night, having only run the heater for an hour that evening.

Paul

<hr width=100% size=1>The Ovni Owners' Club:

www.ovniowners.co.uk