Mast step

I am replacing the steel step that is embedded in the fibreglass under the mast.
I am tempted to spend the extra $30 for stainless steel, the same size as before. I don't think flex is much of an issue there, and it gets exposed to water via the screws which can only be rebsealed when the mast is down i.e. inevitable slow drip.

Thoughts anyone?

Gareth
Freyja E35 #241 1972

stainless

Gareth,
I'm not a metallurgist, but my understanding on the properties of stainless steel is that, if it is not constantly exposed to oxygen it will corrode. I've heard that monel is a better alloy for strength and corrosion resistance in extreme conditions...but ymmv
Dave Hussey

Maybe bronze is the best choice. It's supposed to tolerate submersion in salt water very well, much better than stainless. I know that Nigel Calder had intended to ask Pacific Seacraft to make his keel bolts of bronze, but forgot. until it was too late.

I wonder if bronze can handle the 10000lb load?
Gareth
Freyja E35 #241 1972

Alloy for mast step

Hi Gareth,

Looks like you'll be addressing the same problem as myself, but a year in advance......let me know how it goes - whether she falls or stays upright!

Actually, stainless steel is only subsectable to crevice corrosion if denied oxygen AND in a continual wet environment such as with threaded stainless components underwater (i.e. S.S.thruhulls and valves). However, there are some interesting alloys now like as those used for propeller shafts such as Aquamet 17, 18, 19, 20, 21, and 22. But, the whole idea is too keep water out no?

Thinking it through it, I maybe a good steel plate that is well coated with the new chemistry paints and sealers on the market now-a-days. There is some amazing stuff being used on steel in ship's ballast tanks and cargo tanks that last several years when exposed to nasty ballast water, petroleum products and corrosive chemicals.

Actually, now that I think about it, mabe a Copper-Nickel-Steel alloy (CuNiFe) would be a good choice - it has enough copper and nickel in it to prevent corrosion, is quite strong yet won't cost very much in such a small piece like a mast step. It's rated @15,000 lbs /sq. in.

So, there you have it, my thoughts on it. I guess I'd go with Copper Nickel unless I'm told otherwise. I'll ask around if I get the chance.

John M.

PS...drop me an e-mail, I have an account card for you to send out.



I'm not sure bronze would be up for it as it is fairly flexible and soft. Al.? same problem I suspect.

How about galvanized steel? I know that X-Yachts uses it in the bilge for the grid that supports its keels. FWIW I questioned a sales rep about this and he said there had never been a problem.

Geoff,

I admit I didn;t really think of Galv. steel. A galvinized plate would work, but make sure it's well galvinized...like in 1/10ths of an inch and not microns like Home Depot junk. All too often galvinizing is only microns thick, flakes off easily, or is just poorly done (i.e. third world country recycled junk steel). Not to mention, you'll most likey need to cut the plate when buying a chunk of galv. steel. It may behoove oneself to take the cut piece of steel to a plating shop and have them galvanize it thick after cutting and prior fit out?

Just a thought

John M.

Fyi

just a general point ... monel is a trade name for cupra-nickel steel alloy...
I believe it is used quite extensively for screw shafts, to give an example.
Dave Hussey

Stainless

My initial thoughts are dissimilar metals and electrolytic corrosion. That would be my biggest concern. Assuming an aluminum mast, I would look for a metal that has similar potentials. For galvanic or dissimilar or electrolytic corrosion to occur, three conditions must be met: the metal join must be wet with a conductive liquid; there must be metal to metal contact; the metals must have sufficiently different potentials. Since a mast step will have these three conditions met, I would be careful about this issue. There is a good web site at http://www.assda.asn.au/asp/index.asp?pgid=18533 that will give much better information. Interesting enough, the potential difference between Monel and Aluminum Alloys is greater than Aluminum and Stainless. The lower potential metal is sacrificed. So for example, Zinc is one of the lowest potential metals, so for the Zinc/Stainless interface on your prop shaft, the Zinc goes first. Take a loot at the site, they also state that as a rule of thumb, if the potential difference is less than 0.1 volt, then it is unlikely that galvanic corrosion will be significant.

Deck Stepped mast plate

Al,

Keep in mind the E-35 MKII is deck stepped and the metal plate is actually imbedded in the coach roof. Therefore, there is little concern of mixing metals. I believe Gareth is thinking that if water did get into the deck step plate area (remote possibility but could happen), at least there will not be deck swelling if the metal corrodes, rusts, expands or undertakes crevice corrosion.

As for CuNiFe, there are heaps of alloys out there and the higher the Cu and Ni the better the corrosion resistance. The high Cu Ni content metal has a distinct brownish color that's shiny. Genrally the desired Copper-Nickel alloys are classified as 90 Cu/10 Ni or 70 Cu/30 Ni, while Monel tends to fall under a Nickel-Copper alloy (more nickel than copper) usually classified as 70 Ni/30 Cu and is more silver in color than true CuNiFe.....But there are tons of alloys out there and best to do homework and buy from a reputable metal works.


John M.

Actually, I would call water getting at the plate an inevitability rather than possiblity - there are four screws from the visible mast plate that tap into the plate beneath the deck. Since they routinely get exposed to water from the masthead, and since taking the mast down to rebed them is not going to happen very often, moisture will get in there. My old steel plate was very seriously corroded.

Does anyone know of a shop that would build me a plate out of monel mail order?

Gareth
Freyja E35 #241 1972

Why don't you fill the screw holes w/ epoxy so the hole is completely sealed. The loading is horizontal so the screws can't pull out.