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Old 15-03-2006, 14:34   #1
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Aluminium hull refurbishment

Ive got an 1982, aluminium, 42ft, round bilged, finn keeler that Im going to be pulling out of the water this winter (southern Hemi) to do a thorough interior strip-out and rebuild. The boat is built out of 4mm aluminium sheet over frames at 500mm centres. I also intend to strip the deck and cabin right back to metal and repaint.
The hull interior has been painted some time ago, but this paint is falling off and creating quite a mess in the bilge. Im wanting to find a good authority that can help me with the do's and donts for blasting and resurfacing aluminium. Im reasonably up to speed with the corrosion issues and how to prevent them, but there seems to be alot of differnet ideas/opinions on the blasting and painting (or not repainting?) of aluminium. Can anybody out there help? Any pointers would be greatly appreciated.
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Old 15-03-2006, 19:32   #2
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That's a very tricky subject mate. I suggest you talk to a sandblasting expert for starters. But special care is required.It won't be a standard sand blast. Then after the paint is taken back to clean alloy, you will need to etch the alloy with an etch primer. Major boat paint companies have the stuff. Get some advice here as well. There is a "system" to use and follow. It is expensive and I mean EXPENSIVE. Hence why many go the route of not painting. Although, I would suggest you don't have as long a life expectancy of the alloy as if it were painted, it will certainly be cheaper. A very well prepared and coated paint system can last for many yearsand add great protection to the alloy.
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Old 15-03-2006, 19:59   #3
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Anything dealing with aluminium, in a marine environment. You're looking at shelling out "ALOT" of money.

Have consultations, with people. Find out who works with the best on this type of alloy. And try to find the best price in dealing with this alloy.

That's my 2 cents!!
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Old 16-03-2006, 03:52   #4
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Something you may want to consider???
Read a story in the Tampa paper about a year back about an aluminum boat hitting a reef somewhere in the Carib. and the Capt/Crew escaped thinking the boat lost on the reef. Came back the next morning, and she had crossed the reef with a hole in her side, and was floating in the lagoon on the other side of the reef. Seems like the guy, when building her, had foam insulation sprayed in the hull for temperature control, the foam was also waterproof, and had basically saved the hull, even though it was holed. They put some kinda patch over the gash, and either towed/sailed?? it back to Tampa Bay.
Just something to consider in your overhaul of the interior.
Alan
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Old 16-03-2006, 14:50   #5
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Thanks for the feedback guys. Its really appreciated. Alan W you're bang on, it is turning out to be a real niche area of boat construction. Its going to be interesting to see what comes out of the woodwork during this research phase. The real dilema is the paint or not to paint question. I think its a forgone conclusion that blasting the interior and deck/cabin will need to happen, its just a matter of finding an experienced pro who can either do the job or provide input as to how I should do it, as at this stage its all whispers and rumour. Ive heard that in the car body building/restoration business they use walnut shell as the blasting medium as its (apparently) not as abrasive on the exposed metal as sand? Who knows?

What do people use to strip paint off aluminium masts? Probably a electric wire brush, but Id love to hear from someone who has tried something else, as I'm DEFINITLY not going to be wirebrushing the boat back!!.

Ive come across a product called Nyalic that advertises as a clear aluminium protectant.... has anybody heard/used it?
http://www.nyalic.co.nz

Id definitly have a preference not to paint the interior, but its a time/money/life expectancy debate that needs alot of info pluged in to get the right answer out (if there is one and not many?!)

Stardate, thanks for the insulation info. Highly beneficial side-effect of a sprayon insulation!!! - its something ill be needing to address at some stage. Strange how they abandoned ship without confirming it was sinking?!?! - I was taught that you should only abandon ship if you have to step up into the liferaft/tender. Ive also heard that insulation on a metal boat has the added benefit of reducing condensation build up in the cavity and therefore reduces moisture that may promote corrosion.

Im taking hommage in the fact that there is a large super-yacht builder in Auckland that speciallises in alloy yacht construction, Ive just got to get to the guys that do the hands on stuff and pick their brains! Also, theres a large number of alloy fizz boat builders here which will hopefully share their knowledge also.

So much to learn, so much to learn.

Thanks again for your input.
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Old 16-03-2006, 15:59   #6
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Seaquesta1

You're right about the foam insulation being used for insulation against reducing condensation build up.

Steel contructed sailboats have that installed in their boats as well. And Bruce Roberts the marine sailboat designer, highly recommended the foam against corrosion on the inside of steel boats due to condensation!!

Walnut shells. It's common nowdays. Automotive mechanics use a soap with walnut in it, cause it cleans the oil and grease, and dirt out better. Than regualar soaps do!!
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Old 16-03-2006, 16:25   #7
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The general consensus is, that except for cosmetic reasons, 5000-series Aluminum alloys don't have to be painted above the waterline. The bottom of an aluminum hull needs only compatible (copper-free) antifouling paint*, and zinc anodes to prevent galvanic corrosion, although a conversion primer and epoxy barrier coat is usually recommended.

The 5000-series alloy used to build modern aluminum boats consists of aluminum and magnesium, with a trace of silicon. Sailboat masts and spars are usually anodized 6061 alloy and contains a little copper, as well. Copper increases strength but reduces corrosion resistance: The copper in the 6061 reacts with the aluminum when salt water, or even salty dampness, is present to serve as an electrolyte. This causes bubbles to form wherever there's a break in the paint film and salt gets underneath. The result: Lifted paint, powdery white corrosion pockets, and other maintenance nightmares typicval of spars. The 5000-series alloys, used to fabricate quality hulls, are much more corrosion- resistant because they contain no copper.

* Antifouling paints that contain cuprous oxide or metallic copper should never be used on aluminum. Antifouling paints that contain cuprous thiocyanate can be used if the aluminum is primed properly.

Some on-line references:

Marine Applications of Aluminum Alloys
http://www.key-to-metals.com/Article99.htm

The Metal Boat Society:
http://www.metalboatsociety.com/

Aluminum for Boats - by Michael Kasten
http://www.kastenmarine.com/aluminum.htm
In which Kasten recommends 12- to 16-mil dry-film thickness of epoxy below the waterline.

Metal Boats For Blue Water - by Michael Kasten
http://www.pilothouseonline.com/curr...etal_boats.htm

The AluminumAssociation
http://www.aluminum.org/
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Old 16-03-2006, 16:49   #8
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Well said Gord.

Couldn't of said that better myself?
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Old 16-03-2006, 18:21   #9
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Thumbs up

Gord - you're a legend!
Thanks very much for that.
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Old 16-03-2006, 22:02   #10
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Gord is a legend all right.

Here is a picture of what happens when you put copper anti-foul on Aluminium.
http://cruisersforum.com/photopost//...sort=1&thecat=

Walnut shell can be used for such, but I doubt it would be used in this type of situation. More likely plastic beads or some such material. Maybe even glass. Sand can be used, but it has to be done very carefully. The objective is to remove the paint without the alloy. Alloy is still a fairly hard metal and it has one inherent strength, it is mallyable. Thus it will actually minutely dent with the sand particels rather than erode away. Providing it isn't enormouse particles , high pressume and so on. You may even find using one of those small hand sand blasters you can get from somewhere like supercheap or such, will allow you yourself to do the job. That way you can do it slowly and in small areas at a time and be able to clean up easilyas each area has been compleated. Having a commercial sandblaster in will leave a huge mess.
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Old 17-03-2006, 08:46   #11
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Aluminium boat

Steel Yachts is in your neighbourhood. They would know quite a bit about all types of metal boats. They have built quite a few. I am assuming they are still there as the owner died a few years ago.
Michael
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Old 20-03-2006, 17:04   #12
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Ive recieved the following email back from Nyalic NZ, thought it might be of interest, especially its use as a finish on aluminium masts, not just hulls. Certainly sounds as though it could be the business. I havent got comparative costs on paint v Nyalic yet so we'll see how that side of the equation stacks up. However, I do like the sound of something that can be easly recoated.

NB: I have no affiliation of any sort to these guys whatsoever.



Hi Tony ,

I am happy to discuss your vessel and any information that we can help you
with regarding your refurbishment.

Nyalic ..well take a look at who use Nyalic as a factory finish... any
search on "Google "will find us and who is using and comments about both
about our products and our service.

Here's a current list of just some who are our valued clients .


Stabicraft :Surtees :AMF :King Fisher : Image :Aqualite :Southern Spars:
Fosters Masts :Orams Marine: Touch Of Gloss Marine Painters: Southern Boats
:Evolution Boats : Sea Boss Boats : NZ Navy : Australian Navy : Australian
Customs: Australian Fisheries:NSW Police : NSW Waterways: Queensland Police:

etc etc

Nyalic has a proven long lasting guaranteed system for direct coating
aluminium hulls, mast sections, paintwork etc.We have boats looking great
after 7 years in the water, The system is simple and able to be done by any
adult following our instructions.

Its interesting to note that Nyalic NZ Ltd is the World Marine Distributor
and source knowledge for all marine applications ..We wrote the book and are
driving the world wide marine business on behalf of the American Patent
holders of the Nyalic product HBI inc of Atlanta GA USA.

Tony there are some specific do's and don'ts to look out for when sand/soda
blasting etc of aluminium and the plethora of different surface finishes
achievable prior to coating with Nyalic..

We would be pleased to send you or any other interested party our full media
kit with sample on request .

All enquiries should come to me at john@nyalic.co.nz We have support
distributors in Canada .USA .Australia New Caledonia ,UK;Maldives and
growing all the time.

You are welcome to post this information and reference to our website
www.nyalic.co.nz or the American site www.nyalic.com at any time.

I can be contacted by phone at 0800692542 to discuss any issues you may have
with your project and I thank you once again for your concern


Best Wishes


Sincerely

John Fielding
Director
Nyalic NZ Ltd
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Old 20-03-2006, 20:56   #13
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Well I have seen the finish on Stabi, Kingfisher and Southern Spars. I didn't know it was Nyalic. It is a very nice finish indeed.
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