Type of Aluminum for Marine Environment

Dec 02, 2004 9 Replies

I recently purchased a Questus self-leveling radar mount off of Ebay. Unfortuantely this unit was designed to be mounted on a backstay, and my boat (a Freedom 40/40 with a carbon fiber mast) doesn't have one. I've designed an adapter for it, which I will machine out of 3" round Al stock.



It seems that there's primarily 2 types of Al stock available: T6511 and



6061. The part will be painted. Which of these (or some other varient) should I use considering the salt water marine environment?


-- Thanks, Geoff


6061 is fine

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Bill

T6511 is a specific heat treat designation for 6061. 6061 does fine in a marine environment. IIRC 5086 is the preferred alloy for fuel tanks, etc, but is more commonly seen as sheet and plate.

Ned Simmons

Alloy 5456

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Hey Geoff,

5052 is good, and sort of available. Easy to work with, an used for fuel tanks too, and can be welded.

It is just a formed "L" bracket you need isn't it? I have to wonder why you don't go with marine grade stainless though. Gage-to-strength versus aluminum would keep the weight aloft very close, and would be the material of choice I would think.

What point or height are you going to mount it? Masthead? Spreader??

Take care.

Brian Laws>I recently purchased a Questus self-leveling radar mount off of Ebay.

Brian Lawson wrote in news: snipped-for-privacy@4ax.com: The adapter has to accept the 2.5" long shaft of the self-leveling radar mount and fit within the existing round housing. Basically this will be a 3" long x 3" diameter rod. Then I'm going to mill 2 flats along another 3" length of it down to 1.5" thick and bolt that to the existing radar platform. That much stainless would weigh too much.

-- Geoff

6061-T6 is about the commonest form of extrusion (such as pipe, channel, T's, etc. - I guess 3" round bar is one of the extrusion forms 5086, 5052,5083 are the common forms of plate 5456 is pretty uncommon though it has higher "as welded" strength

Uhh, you're not planning to put this right on your mast are you Geoff? Aluminum and carbon fiber get along like, well copper and aluminum. Basically the potential for the aluminum to disappear is very high. If you do this, make sure you insulate the two. One simple way is a couple light layers of E-glass on the mast to isolate the CF.

"Evan Gatehouse" wrote in news:41b01bb4$1 snipped-for-privacy@news.cybersurf.net:

This will be mounted onto an aluminum radar mast on the stern of the boat.

-- Geoff

Hmm, I never considered this. Are you saying that carbon fibre is a good conductor and that aluminum is "less noble" and therefore prone to corrosion when directly affixed to carbon fibre in the presence of current?

I mean, I learned the hard way about using fibre washers between my aluminum spreaders and my SS deck light mounts, but in my mind I think of carbon fibre as being in more or less the same class as fibreglass, i.e. an insulator. I gather you are saying it's more like a conductive metal... R.

Right - if you have it in contact with aluminum, the aluminum disappears quickly.

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