Releasing the Cap and Intermediate Shrouds

[GILow]

Hello Cruisers,

First, let me apologise if my terminology is a bit off, or plain wrong, I am a bit confused by the names of some of these bits of rigging and cannot be sure I have them right.

Anyway, our cap shrouds and our intermediate shrouds are attached to chainplates that are exactly perpendicular to the mast. On a Swanson 42, these chain plates are attached to a steel "hoop" which is glassed into the hull, meets the mast step compression post at the keel and also supports the deck. I gather the idea is that the hoop is well nigh impossible to compress and thus prevents the tension on the stays from distorting the hull. Not sure about that though.

Anyway, I would like to replace the bolts that attach the chain plates to the hoop, and while I am at it clean up some surface rust on the plates, inspect them for seaworthiness and generally make the whole lot a bit tidier.

It's a bit early in our refit plans to pull the mast off the boat (that's over a year away yet) so I would like to release the cap shrouds but not end up with problems such as the mast falling over the side and clobbering the dock queen in the next pen. I am assuming that I can let the four remaining baby stays (which have their own chain separate chain plates) support the mast?

Is this safe to do, and are there any "gotchas" I should be aware of, aside from marking the current settings on the stay adjusters before I release them?

Matt

[transmitterdan]

Matt,

What I do is attach the spinnaker halyard to the toe rail about even with the mast. Take up snug (not super tight) on the halyard. Then I release the shrouds on that side. Once I get the shrouds back on and tensioned then I repeat on the other side. Without sails up it doesn't take a lot of tension to hold the mast in column.

[roverhi]

The lowers will support the mast while you work on the chain plates. Tie off halyards for additional support if I have to go up the mast while cap shrouds or stays are disconnected.

[GILow]

Thanks guys, halyards it will be. Glad to hear that what I am planning is not considered crazy.

Matt


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[Jim Cate]

Matt, this is one of the times when having a keel stepped mast is nice! But don't take off too many wires at once...

Jim

[GILow]

Ok Jim, just one pair at a time, I promise.

Matt


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[gjordan]

One pair at a time is like the apple a day saying, IT WILL KEEP YOU AWAY FROM THE DOCTOR. What you are doing is safe and sensible, and you might want to have some OSPHO handy if you have rust stains on the metal, or the fiberglass. I used lots of Ospho on my steel boat and also a fair amount on my Taiwan built fiberglass boat. Stainless Steel is a misnomer, and can stain fiberglass, but Ospho cleans it up pretty well. Have fun. ______Grant.

[GILow]

Never met OSPHO, will look it up, thank you. Have some evil SS pickling gel in the shed... but that's overkill.

Anyhow, these chain plates are cast aluminium above decks, and mild steel below decks. Hence I am just a little concerned about the state of the bolts.

Matt

[GILow]

Hmmm... OK, I assumed that OSPHO was just for Stainless Steel, but it appears to be suitable for ferrous and aluminium... not sure about Stainless Steel though.

Interesting, thanks for the pointer.

Matt

[gjordan]

Matt, I was not aware that you had aluminum chain plates. I am not sure about using Ospho on aluminum. I used it a lot on mild steel, and stainless, but never on aluminum. What type of bolts hold the hoop and chainplates together? A combination of mild steel with stainless bolts and aluminum chainplates could create a nice little battery that could eat the least noble metal. I had never heard of aluminum chainplates, other than on welded aluminum boats, but on this forum, we learn something new every day. I will be curious how your inspection goes. ______Grant.

[GILow]

Hi Grant,

The OSPHO web site mentions using it on aluminium. And a quick google suggests that phosphoric acid on aluminium is not unheard of, though of course those sites trying to sell you something else will tell you it is not particularly beneficial.

I may be using the wrong terminology when I use the word chainplate to describe the bit that the stays attach to...? I mean, I know they are usually called chainplates but these are great big cast aluminium plate things that sit on the deck and reach through to the steel sections below deck that are glassed into the hull. I assumed they were still called chainplates in that configuration, but maybe they are called something else?

Thankfully the 1" diameter bolts that hold these aluminium "things" to the steel hoops are also steel, or as you say, there'd be an unholy trinity of metals to produce goodness knows what sort of reaction. As it is, a bit of leakage around the deck penetrations has caused what I HOPE is some mild surface rust, but closer inspection is required. The whole lot were behind some cupboards I pulled out so were not inspected during the survey.

Matt

[JPA Cate]

We, too had mild steel chainplates below decks on our first Insatiable. In the case of that boat, s/s chainplates were welded to the mild steel. Also, that boat had the webbing structure to the base of the mast.

What method was used on your boat to galvanically isolate the aluminium from the s/s bolts?

In any event, you are quite right to want to inspect the mild steel. One guy we knew of lost his rig to "lacy" rusty mild steel, in a sister ship to our old one.

Ann

[GILow]

Hi Ann,

No isolation between the aluminium castings and the mild steel. But, to be clear, the bolts are also steel, not stainless steel, so only two metals to deal with.

I think I should check with Banjo and see what setup he has, I assume mine is standard, but with boats of Manera's age anything is possible.

Catching up with the original owner, who fitted out the boat, in Perth next week, so I will be able to discuss with him also. (Quite excited about this actually!)

Matt

[banjoship]

Matt,

As far as I can tell, the chainplates on Banjo are monel. Very difficult to tell, but there is no sign of corrosion, above or below deck, even where the paint has been scraped off. With assistance from a rigger, I pulled a selection of the bolts for inspection, no problems whatsoever. Neither I nor the rigger could determine the composition of the bolts. They are not stainless, nor steel, maybe monel also? I have no experience with monel, and can't pick it. Everything looked perfect, so I bolted everything back together again.

The composition of the steel hoop and compression post on Banjo is not mild steel, possibly corten. Yours may be different.

As an aside, it might pay to give close inspection to the base of your compression post, where it joins the steel hoop. On Banjo, fresh water has gotten into there on a couple of occasions, and I now check it regularily. One of those cheap cameras on a flexible stalk are very handy for inspection in these tight spaces.

Hope this is of some help

Lee

[GILow]

Lee , you are my knight in shining armour. I have a funny feeling I was confusing Monel with aluminium.

So much to learn.

Matt


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