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Old 15-04-2008, 11:50   #1
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Aluminium Boats

Just seen a nice aluminium 42footer for sale, I pretty much know the pros and cons of GRP,Wood,Steel and ferro but don't have a clue about aluminium. Can anyone tell me the pros and cons or personal experiences.
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Old 15-04-2008, 12:13   #2
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First off, NO material is perfect. Aluminium just gives a different list of pro's and Con's. It is light for it's strength of course. Corrosion resistant, however, electrolysis can destroy it faster than any other material. It is often difficult to get paint to adhere. Not impossible, but because of the difficulties, it requires the job to be done right with particular care. Repairs can be difficult. Aly tends to tear upon impact and will deform and stretch to the point of where the damage would have to be cut out and replaced with a new panel. It also tends to be noisy, with wavelets etc slapping against the hull.
Apart from that, there are a lot of Aly boats out there and some very nice boat's built from the material.
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Old 15-04-2008, 12:19   #3
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Oh and one major rule. Never Ever Ever use a copper based Anti-foul paint on the hull.
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Old 15-04-2008, 12:23   #4
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There is an article on a Kanter 56 in the April PassageMaker magazine called "Aluminum Boat Building Done Right" that you might be interested in.
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Old 15-04-2008, 13:41   #5
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Alloy yachts have as Alan says just another set of paremeters to go by, Aluminium will deform and stretch long before it will tear, for you to be in a situation for that to happen would have to be extemely serious and would write off any/most other hulls (other than steel) before the deformation became a risk of penetrating and sinking the hull. ie. on a reef / rocks etc.
Many commercial fishing, Govt, pilot, boats in NZ are built of alloy and are subject to much more rigorous use than pleasure craft. One of the advantages of alloy is that it doesn't have to be painted, apart from antifouling. If you want paint, it will work OK, you just have to be more particular about how you apply it with the correct preparation and application of undercoats etc. Treat copper with care don't drop electrical wire strands into the bilge etc. Noise is no worse that any other hull material/design, flat runs aft can be noisy at anchor but insulation will overcome that, we find Gwalarn as quiet as anything we have sailed on and in many cases better. Any metal boat requires insulation from the water line up as a matter of course. My yacht is 30 + years old the hull survey in all the areas likely to have suffered from corrosion measured 5mm thick, (original spec 5mm) the only part at all affected was the rudder which didn't have an electrical bond to the hull (it does now) so it has some minor pitting. Would I buy another alloy yacht, Yes and yes again.
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Old 15-04-2008, 17:13   #6
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My main experience is with aluminium - most commercial vessels and the larger end pleasure vessels are now made from it. It would now be my probable choice if we were to ever have another boat built for ourselves (unlikely ).

Ignore all the stuff people talk about corrosion if you park next to steel piles, other boats, etc but not connected to shore power (commercial boats and superyachts do so all the time with not a care). For when you are connected to shore power ensure the boat you are looking at uses a properly installed marine isolating transformer.

If the boat is 10 or more years old have a close look for any corrosion issues under insulation or where debris (dust, etc) may be lying on longitudinals against the plating, etc - a problem there may indicate an alloy problem. If possible check the bottom of the fuel tank, pitting is common where water may collect in the lowest point - not normally a big problem if accessible for repair (crop and weld).

Painting should not be a problem - if you are faced with painting bare aluminium usual is coarse power sand back to remove the oxide layer then straight on with the paint manufacturer's recommended epoxy primer and undercoats. For any repairs or recoating get a paint specification from a reputable marine paint manufacturer (International/Interlux, Jotun, etc) they are normally very helpful. Castings of aluminium may be less resistant to corrosion.

As already said it should be insulated inside above the waterline for both control of noise and environment (need not be so outside of the accomodation areas but, as mentioned by another, may be useful under the stern counter to stop the noise from wave slap if in a slip stern to the wind). In my view the prefered insulation should be a sheet closed cell foam such as Korex or Armaflex or else sprayed foam - if the boat has a porous type insulation used (eg fibreglass or mineral fibre panels) then I think I would walk away from the boat unless I knew for sure the condition of all the plating behind.

I would suggest having someone who is professionally knowledgable and familiar with aluminium boats check it out for you. Like steel boats one can often get a good idea of what the overall quality of the boat is likely to be if one has an eye for boats in just the detailing of its construction and fitout - some you can walk away from without even going on board. Ensure that as it is not a new boat there have not been adventurous amateur escapades into its electrical and galvanic protection systems (the DC system, including engine, should preferably be one entirely isolated from the hull and with some means of monitoring that the isolation has not been compromised).

As others have said, all materials have their problems. But I would suggest that now with better coatings which stay on and modern alloys (both of which may not apply to an oldish boat though) and its widespread use through the commercial and superyacht building industry greatly increasing the knowledge of it, aluminium is now probably the material with potentially, if properly built, the very least problems.
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Old 15-04-2008, 19:24   #7
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Midlandone, do you have any thoughts on antifoul for an alloy hull, as you have experience with the super yacht industry what do they use? I contacted Alloy Yachts but any info from them was harder than extracting teeth from a crocodile.
I get 1 year + from International trilux with the boat kept in Tutukaka, if I were to go back into the Kaipara and then it would come down to single figures.
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Old 15-04-2008, 22:40   #8
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Steve, my involvement was from a wider quality point of view and while that included the permanent coatings I have no idea what went on for antifouling. I have been involved in the detailed specifications of big aluminium power boats but the antifouling specified for those (generally International/Interlux Intersleek) needs boat speeds of 25+ knots to work well .

I am on the boat at the moment but have some specifications for some big yachts at home and will have a look to see if the antifouling is mentioned when I get home tommorrow night - but I don't think it is. I suspect one of the commercial vessel coatings would be used though.

Have you tried having a talk with Altex in Tauranga, they are generally very helpful and do pleasure and commercial aluminium friendly antifoulings (they also have product data sheets on their web site, but you may be familiar with that already). We are steel so don't need the aluminium safe antifouling but we have gone back to Altex after several goes with International/Interlux and while they have been fine for us the Altex is definitely superior (ablative coatings in both cases). But, of course, water temperatures are cooler here plus we get get brackish water through the marina when the nearby river gets in flood which I think does knock some things a bit (barnacles are not a problem for use, for example), but we do need to last 2 years between lifts.

We actually sail off to Nelson next week to get antifouled the following week and I will ask the yard there what the aluminium commercial boats are going for if you like.

John
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Old 15-04-2008, 22:51   #9
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John, Thank for your response, If I could get 2 years I would be quite happy, I have just been looking at a Niwa site that says that they are testing marine animals / plants etc. for natural antifouling properties and are working with Altex to develop a natural based antifoul.
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Old 15-04-2008, 23:14   #10
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I have been skippering an aluminum research vessel now for 17 years. MidLandOne is right on with his analysis of aluminum hulls. The only thing I might add is that since TBT paint was banned it has been impossible to find decent anti-fouling paint that is legal in the USA. The only option I have found is a non-copper, not TBT Interlux bottom paint which is not very good at all. I hear US government boats are allowed to use some sort of special paint which is not allowed on civilian boats. The skipper of a NOAA boat told me this...he has this paint on his aluminum hulled boat and he says it works fine...too bad for us civilians.

If I were to start it all over, I would not paint the boat anywhere above the waterline except for perhaps a boot stripe and the boats name of course. The oxide that forms on aluminum is an excellent anti-corrosive.

Aluminum sheds paint like a shaggy dog sheds hair on a hot day. One little ding in the paint and the paint blisters start creeping like cancer. Not even the best professionally applied Awlgrip paint job stops the blistering.

As far as electrolysis goes, a good epoxy barrier coat, electrically isolating dissimilar metals from the aluminum, keeping up on your sacrificial anodes, floating your DC system (nothing grounds to the hull) and isolating stray DC currents coming from your shorepower, stops electrolysis in its tracks.

One of the nice characteristics of aluminum is that modifications are very easy...all you need to do is find a person who is good at welding aluminum. I have made modifications to the aluminum research boat that would have been extremely difficult and much more expensive with a plastic boat.

I like aluminum boats for workboats. There are some magnificent aluminum workboat designs out there now but they are not for everyone. I do not want to own an aluminum boat for myself when I retire. It will probably be a plastic foam core boat of some sort.

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Old 17-04-2008, 21:25   #11
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Steve, I am on the boat at the moment but have some specifications for some big yachts at home and will have a look to see if the antifouling is mentioned when I get home tommorrow night - but I don't think it is.
Typically just says something like "4 coats of selected antifouling" so not much help. But I will ask in Nelson when we are there the week following ANZAC weekend even though most of the aluminium fishing boats are power and semi displacement so higher speed.
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Old 17-04-2008, 21:45   #12
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Thanks John, I have asked the oyster men on the kaipara that have alluminium oyster barges but they don't antifoul at all, they pull out and waterblast whenever the growth gets started, roughly between 2 and 4 weeks depending on the season.
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Old 20-04-2008, 07:05   #13
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Jimmey Cornell has taken an Aluminiun yacht too all lattitudes and back he sweaes by them,
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Old 28-04-2008, 16:16   #14
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Steve - I asked the yard what the commercial vessels were favouring on aluminium vessels down here.

Apparantly International Trilux was the usual choice but they are now using Trilux 33 which is apparantly a big improvement. I could not see anything about Trilux 33 on the NZ International site but a Google of it turns it up on International/Yachtpaint's other sites.

May need to remember that this experience will be on commercial power craft so generally faster than sail boats so performance may differ.

Altex are now doing the Pettit antifouling here in NZ for aluminium boats but while the yard had done some boats with it, there has not been enough time to see how it is performing.

John
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Old 28-04-2008, 16:40   #15
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Originally Posted by bg9208 View Post
Just seen a nice aluminium 42footer for sale, I pretty much know the pros and cons of GRP,Wood,Steel and ferro but don't have a clue about aluminium. Can anyone tell me the pros and cons or personal experiences.
TIA
if you speak french
go to hisse-et-ho.com
lots of aluminium boat in France
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