Anodizing Aluminum Mast

[Calliste]

Ahoy Sailors, I have been fabricating a new aluminum mast for my BCC , here in Singapore, and now is the time to choose the metal finishing for corrosion resistance, with a "Reserve Of Neglect", included.

As I see it, I have 4 choices . My first choice is to anodize , second choice is to powder coat , third choice to LPU paint , and forth choice is to polish and leave the aluminum bare.

The longest section is 20' , with 2 other sections at 12' and 14' long.

There seems to be 3 types of anodizing to choose from ,,, Type I , Type II , and Type III , with a Class 1 or 2 , with each Type.

I think that Type III Hardcoat clear, class 1 , would be my best choice, for long lasting durability, and corrosion resistance .

Does anyone have information on what Type anodizing , Spar Manufactures specify for their sailboat masts, and how durable it has been ?

I have a price quote from a Singapore Company , to "Hair-Line" polish the 3 pieces of aluminum extrusion, and anodize them with the Type III , Class 1 , for USD $ 2600.00 ,,,,, does this seem a reasonable quote from an ISO Certified Company , in this area ?

Douglas

[MMNETSEA]

Hello Douglas,

Best bet would be System 3s LPU, which allows you to control the amount of paint to be applied. Anodizing is usually applied in the last process of extruding an Aluminium product, doing it to an article later in its life is hard to control the amount and the quality- confirm that the mast sections are not already anodized?

Richard

[SteveW]

I modified and installed a used aluminum mast in my Ingrid 38. It was un-anodized but painted. This was the original paint from the spar builder and had held up well. However, I did find corrosion under the paint in areas where the paint was scraped, scratched or abraded. from that point, the corrosion would advance under the paint. Not at all uncommon with any type of paint on aluminum. No paint is "bullet proof" and even hard anodizing will eventually be scared in some manor, allowing the bare aluminum to advance under the protective coating. You can't repair the anodized damage in the field, so you would have to paint the surface to stop oxidation.

My solution: I stripped all the paint off the mast and polished it to the best of my ability. Then just left it to oxidize naturally. The natural oxide becomes a barrier to further oxidation, just not as hard as anodizing or paint. Note: the higher the polish on most any metal, the less the oxidation. This is especially true of aluminum, brass or bronze. Something to do with the surface texture. I learned this years ago on my brass bell.

An way, most of the above is based on my humble opinion and experience. My mast has been in the boat for 8 years and the surface is a dull gray and the surface is not effected by halyard or sail contact or chafe. There is not evidence of corrosion.

Another note: Serious corrosion will occur on any aluminum mast where stainless steel fitting, screws or bolts are used. Here, the best preventive measure is to use a laniline coating on the threads or faying surfaces. West Marine carries it under the name of LaniCoat (or something like that). It is just a grease. I've never had any proble with frozen screws or corrosion under hardware when using this product.

My opinion, FWIW.

Steve

[redbopeep]

Steve,

I'm glad you brought up the Lanolin for use between dis-similar metals. It is also available via a brand call ProLan. Here is a link to a source http://www.greenboatstuff.com/prolan.html

[Calliste]

Thank You guys for your replies.

Richard, yes, you are correct, that aluminum extruders usually anodize just after extruding, but we wanted to machine the mast before anodizing, so we ordered the mast sections, un-anodized.

There is a simple check to see if aluminum is anodized,,,, just use an ohm meter,,, anodized aluminum does not conduct electricity,,,, gosh ,,, I wonder about enhanced lightning protection ???

My first choice would be to anodize, because I just hate to see paint bubbling and blistering from corrosion under it, like my mast has now.

Steve, that's a good report on polishing and leaving the aluminum bare, this is one option I had considered, but I can't polish inside the tube.

Choices / Choices ,,, which coating to use to isolate the ss screws from the aluminum ? I have had reasonable results with aluminum "Never-sieze" from Permatex,,,,, some riggers only use Boatlife 101 silicone adhesive, many use lanolin, some use Tef-Gel , it is obvious that you must use something, but what is best to chose ???

[MMNETSEA]

Hi,

This is what is used often (you should be able to find it in tube form)

CLICK DUROLAC

[SteveW]

The inside of a aluminum extruded mast it just about as polished as you well ever get on the outside, just from the extruding process. Within hours or days of extruding the surfaces exposed to air oxidize and undisturbed that oxide forms a barrier against further corrosion. True, not as tough as anodized but still protected from further corrosion. (Let's not confuse oxidation and corrosion.) If you go to the Island of Yap, you will still see the thin aluminum aircraft wreckage of WWII sitting along the runways. Most of the bare surface, both inside and out are un-corroded, still only lightly oxidized since the exterior was highly polished 70 years ago. However, you will find corrosion around rivets and hardware.

I would be careful about various sealants on aluminum. Some have serious reactions with aluminum. Almost like there is an acid 'in the mix'. I have seen areas where someone has sealed around cable entries with Big Gobs of silicone, so thick that the interior of the mess hadn't cured and the aluminum was eaten away. Not the normal corrosion, but chemical reaction. The Lanocoat I mention is mostly pure lanoline from sheep's wool. They use to make "hair care" products in the '50-'60 and it was just as good for this purpose. Low tech, but it will keep threaded hardware from seizing and surrounding surfaces from corroding. Never hardens, doesn't wash off without some effort or detergent. My SS mast steps are each secured with 4 machine screws that at tapped into the aluminum mast. No sign of corrosion under them nor any seize threads. Lanocoat is easy to use since comes in a plastic container and has a consistency of grease. Just dip the threads of you screw into it and drive it home. I purchased one 'shoe polish' size container and still have 90% of it left in my rigger bag, after several boats.

Sorry, none of the above was intended as a Rante. Just my opinion FWIW.

Steve

[redbopeep]

Steve, you sure don't go thru the lanolin at the rate we do. In 2008, we purchased a 4 oz tub of Prolan (that's about 3 shoe polish tins stacked) as well as one each of the 8 oz spray bottles of the light, medium, and heavy "liquid" versions of Prolan. We've just got about a tablespoon of the grease in the tub left, about 2 oz of the heavy, 4 oz of the light, and 4 oz of the medium liquid. About to make another order.

We do use it all over the place--anywhere that we don't want a thread seizing or corrosion problems. From rigging screw, wiring harnesses, parts of rig. Great stuff.

[SteveW]

Yah! it sure sounds like you use it a lot. However, I would like to make a point since you mentioned using it on rigging screws. Since these are seldom disimilar metals I would rather use a petroleum grease that is better suited for lubrication. I like Lubriplate since it stands up in wet enviorment well. Similarly, in my opinion, I don't consider WD 40 as a good lubricant. It's a decent penetrating product but I prefer Kroil and for the really tough jobs or oil of wintergreen (if you can stand the smell).

Then, while I'm on the topic about freeing frozen screws and bolts. I frequently resort to heat and as an (very old)navy shipfitter I will point out that the main advantage to heat is to expand the nut and keep the heat off the bolt it's self. Even a ordinary propane torch can save the day. Just be careful to avoid blowing up or burning the boat down. Aluminum responds best to the heat/expansion method. My example would be an old Aries windvane that I purchase on eBay. It has about 30 SS set screws and all were frozen. I managed to free them all with a propane torch.

Different topic, but worth mentioning. Sometimes you might find double set screws in equipment. One behind the other. It is seldom obvious and worth a double check before you start hammering or pressing on a bushing. It has happened to me. And of course put some anti-seize on those threads.

Steve

[anacapa]

We painted our mast some 20 years ago with Rustoleum, it has held up VERY WELL, just the odd touch up from scrapes and floggings ....... cost $20, also looks beautiful, used Forest Green to match boat trim ... stunning

Bill

Challenger 32

[svtadpole]

I apply a liberal annual slathering of wax to my boat aluminium ( mast - boom - windgen pole - Aries gear ) .... any brand of boat/automotive wax does the trick .... I put it on with a nylon washing up brush & leave it ( no polishing off or buffing ) ...... cheap, quick & easy