Early alloy masts

[Michael4]

I have just taken over MR 950 (1959) from Steve Hawkins. Very happy and looking forward to getting her out on the water, she will make a nice contrast to a Tideway...

The boat has a tall hog stepped Proctor alloy mast which is presumably original and is not anodised.

It has probably spent most of its life in a fresh water environment. I'm going to use it in a salt environment (obviously I will be trying to keep the mast out of the water!).

From what I remember bare aluminium corrodes, or should I say oxidises, quite badly when in contact with salt. The result is that white chalky dust.

I don't know what alloys were used for masts or whether they are/were susceptible to oxidisation?

Do you think it would be worth my while trying to combat this in some way?

Not sure how, obviously oils etc would make a mess of the sails and I don't think I want to paint it. I could seal the exterior with something clear maybe or even wax it with something?

But...one would only be able to treat the exterior, the thought of trying to spray something like Waxoyl or a product like Fluid Film on the interior of a mast doesn't appeal much. It would probably achieve little more than greasy halyards and would tend to melt out again on warm days, messy.

I don't know if the interior of an alloy mast corrodes quicker than the exterior?

The mast appears OK right now so this is more a question of preservation for the future rather than something that needs attending to immediately, I shudder to think what a new one would cost!

Any ideas or suggestions (including leaving it well alone) much appreciated.

Michael

[chris]

Not sure about any modern finish on the outside, but I have a similar mast that was well 'marked' on the outside but when I took the bottom fitting off to do a modification Looking inside I was pleasantly surprised to see how clean and bright it still was (once I had washed out the spiders).
I cleaned the outside with soapy water and a washing up rough spongy scourer. It's as a spare vintage mast when I don't want to use a wooden one anyway but I have found it is splitting in the top section when you look closely down the luff slot as if the slot has been forced apart...maybe the structure of the alloy has deteriorated.

[davidh]

Michael,

One way of limiting the worst effects of future corrosion is to be careful with the halyards. Are you still using wire or are they rope? If you are using wire halyards, either pull them through when you leave the boat so they are not left up inside the mast or- invest in some lengths of dyneema and change them out!

On some of the contender masts, corrosion was a real issue, you had to wash the salt off after each sail AND make sure that the wire tail didn't get left inside

D

[solentgal]

As a salt water sailor I have seen many un-anodised masts with salt problems over the years.....cruisers and dinghies. They do seem to build up a patina that resists salt to a certain extent, and I have also seen several masts that appear to have been varnished !
I would avoid cleaning up the surface (which exposes new metal) but maybe the wax idea is worth a try..... I have seen many people do that with anodised masts, and have done it myself too. The inside seems to survive very well though, even on masts that show corrosion on the outside.

[Ed]

Anybody with an old Fairey boat with the Reynolds masts/booms will be familiar with this problem.....

although on Fairey boats, it tends to be the boom that gives way a long time before the mast does.

What can you do about it? Personally, I don't think any coating will do much. I think David is on the right track though. Remove as much contact as possible with any other metals, especially stainless and brass. Replacing halyards with dyneema seems like a good plan and of course lots of washing down with water.

I think the only place you are likely to have problems though is from cracking around fittings at head, hounds and foot. That is always the problems are with Reynolds mast/booms.

But on the whole, my thoughts are that most of the issues will already be there....and you won't be able to improve the situation much....so do what you can and sail as much as you can....with fingers well crossed.

cheers
eib

[PeterV]

I thought I remembered coating alloy masts with wax polish to resist corrosion?

[Michael4]

Thanks for the suggestions. The internal halyards are some sort of thin hard multi coloured braided cord. Not sure if it Dyneema but not wire.

The rest looks pretty much like common sense and apart from obvious maintenance, best left alone.

If I get really worried I could hire one of those drain inspecting camera/endoscope kits and send that up it for a bit of fun, or at least peace of mind.

Thanks again

Michael

[Michael Brigg]

Reynolds masts were not anodised and so in theory they are prone to corrosion if used on sea water but this was remarkably uncommon as a problem, I suspect because the "grade" of aluminium used was one that is relatively resistent to oxidation.

Aluminium is a highly reactive metal but is able to resist oxidation beacuse it forms a resistant layer of "Stoichiometric" (Meaning it forms a perfectly geometrical lattice) oxide on the surface. This acts like a self perpetuating layer of "almost diamond hard" paint. (Al2O3 is the chemical formula of Rubies Emeralds and Sapphires!) However if exposed to Chloride Ions, in sea water this Oxide layer is breached because Aluminium Chloride is "Non stoichiometric" and so ongoing oxidation of the mast will occur. This is simple Oxidation rather than electrolytic Corrosion and is a slower process as it is not driven by an electrolytic reaction.

The concept of the mast "corroding from the inside" is largely a myth unless the mast had been drilled to put a fitting on it and then not sealed. Corrosive seawater was then trapped inside and could not be washed out.

External corrosion was easily prevented with either a powdered metallic Aluminium laquer, or by painting with hard enamel. Both worked simply by sealing the metal away from the sea water and have nothing to do with any Electrolytic sacrifice.

Anodising will protect most modern era masts and is a treatment that ensures the Aluminium Oxide layer is formed in a manner that is able to resist the ion exchange at the exposed surface bewteen Oxide and Chloride Ions. However, scratches and breaches of the Anodised surface will react with sea water, so, although anodising seals both the internal and external surfaces, this will be scratched and rubbed away by wire halyards.

As noted, the idea of Internal corrosion of the Reynolds mast is not an issue because they were sealed This was regarded as one of the clever aspects of the design as the top mast made of wood contained sealed air pockets, and the tight seal at the top of the extrusion and the heel plug were similarly watertight. The Diamond struts are also a single rod , lying within a tight rivet, passed right through the mast. The result was a superbly lightweight, bouyant mast, advocated as a means of preventing invertion on capsize though this in the firefly was as much as anything due to its own lack of effective hull bouyancy!

When I have shown my reynolds to the modern firefly set they are regularly astonished by how lightweight it is. About half the weight of a modern Seldens D section!

The rotating mast design means that the Jib hallyard was on pulley outside the mast and led back down to the bow fitting and thence under the deck for tightening on the infamous rack. The system requires the halyard to be wire, so that was technically a minor source of power between the aluminium and iron to produce corrosion. The same can be said for the main halyard, but although these were generally wire, spiced to a rope tail when the sail was down the only wire left in the luff groove was only in contact with the wooden topmast so not much of a problem. The brass pulley at the head for the main hallyard again was within the wooden part of the mast.

Shrouds were galvanised steel so not a problem until the zinc had all gone. Rust marks were an exellent warning of imminent failure and need to replace.

A real problem was the use of shroud plates screwed into the inbord hull with just six 1" brass screws... these secretly dry out or corrode , and then pop out in the midst of a gnarly reach and the mast is inevitably lost. A tragic end to a beautiful piece of early post war developmental engineering that fused the art of the oar and spar maker (Collars of Oxford) with the best of aeronautical engineering. The "Rocket science" of its day.

The other weak spot was steel or worse, brass bottle screws to adjust the diamonds.

The more standard alloy masts will corrode around the rivets even if they are anodised unless the rivets are properly sealed at the time of fitting, with Zinc Chromate paste. This is absolutely essential on all rivets! These post a far bigger problem than any amount of wire halyard.

[JimC]

The "Rocket science" of its day.

I know I shouldn't quibble pedantically over such a useful and informative post, but you know the rocket science of those days was rocket science...

[Rupert]

Made me want to go and get another Reynolds mast for Saskia... almost.

[Ian Malcolm]

I plated over a hole in a mid-60's aluminium boom (on a CO26 yacht) about five years ago using ordinary aluminium sheet. the repair patch was bedded on a 50/50 mix of white Sikaflex and Duralac (to avoid poltice corrosion) and I thinned the residual mix and painted the patch with a thin coat of it for additional protection. After five years of salt spray exposure, the patch is in excellent condition with no significant corrosion. A dinghy mast may get immersed, but unlike my boom, is likely to be washed down immediately after use so probably leads an easier life.

[davidh]

Far be it for me to argue with a 'man of learning' but the internal corrosion is anything BUT a myth. Nor was it just the early masts, but some of the last alloy sections used on the Contender (before they changed to Carbon) could suffer very badly. When they broke (!!) it was clear that the there had been a significant loss of material from the inside - with interaction with the steel halyard tail being identified as the probable cause. Certainly, ensuring that the steel section of the halyard was pulled through (or replaced with a halyard lock) solved many of the problems.

At the heart of the problem is the mistaken belief that aluminium is aluminium - there are huge variations in make up for varying applications. Marine grade aluminium is far more resistant to corrosion! (I get a reminder of this every day! Living at Ventnor, the air is heavy with salt coming in from the Channel - things like zips can quickly fur up!).

In the search for lightness and bend characteristics, many different alloys have been trialled - some are superb, others are really a risky proposition in a salt water environment. I personally have lost masts to corrosion - got to the leeward mark, sheeted in, pulled on plenty of kicker (as one did in the ways pre-hoops) - the stick didn't go 'bang' - it didn't really make much noise at all, but the mast just folded aft at the break like a gaff rigger! Once back ashore it was clear what had happened. The break was not at a fitting (all those went on with loads of zinc chromate) but just mid tube........

So, a lesson learned.....switch to dyneema and /or a halyard lock

D

[Michael Brigg]

Hmm....

Dampness in the Zip area and furring up. Sounds like you need an appointment David...

I was writing mainly about the Fairey Reynolds mast. A different beast indeed to the Contender which I suspect uses huge rig tension by comparison and is Not a sealed unit as is the Reynolds. Traditionally the Firefly has always had shrouds tension set to a level of "swinging in the breeze."

Also no trapeze.

And as has been noted, the stiffer Aluminium alloys used for modern masts may be less resistant than the relatively soft, malleable marine grade Aluminium which resists cracking and puncture and is less prone to sea water oxidation. I suspect this would have been the grade used in the Reynolds. The more modern Contender will have undoubtedly got a more sophisticated lead in its pencil! The down side is that it might not last as long once it gets moist!

As Contender masts are built in the era of Anodizing, and this is done as part of an immersion process, I would envisage that the internal surface is also anodized. The issue of wire halyards is that with the mast bend and high halyard tension the wire will bear on the internal surfaces, rubbing away any surface protection. Then as these masts are not sealed, (carrying internal halyards being the clue) there will be salt water and dampness inside to set up corrosion. Rope will retain the dampness. So a combination of both wire and rope must be the worst case scenario.

[davidh]

"The more modern Contender will have undoubtedly got a more sophisticated lead in its pencil! The down side is that it might not last as long once it gets moist!"

Except that these days it tends to be more HB than 3H!!!!

Interesting observations though Michael......

They other consideration to the debate is the use of acid to promote corrosion, thin down the spar walls and change the bend characteristics. So, we ended up in the situation of etching tubes, then resleeving them to give localised strength and rigidity. Of course, once Carbon masts came along, all this stopped; you just played with the lay up in various places in the tube and achieved the same result

D