Mainsail Rust Stains.... Does Anyone Know How Come?

[rardi : H36 ( Cherubini)]

There are lots of references on the internet about sails stained with rust and some suggested suggested DIY removal remedies (which haven't done hoot when I tried) ....

But how is it that with only stainless steel everywhere on a sailboat, a sail actually gets stained with rust?

In my case, the otherwise just fine Dacron type fabric Hood mainsail that was on my boat when I bought it last year has rust stains all over the place on its lower third area. The sail had looked to be well protected with a sound sail cover. None of the stain areas match up with any rigging, or blocks, or tackle.

And also a fully battened mainsail ex a Catalina 36 that I bought (price was very very right) also has some rust stains.

Mystery to me as to the cause.

My older sails aren't worth the expense of professional clean job. (Anyway, can the professionals actually remove rust stains.) So the best solution for me so far has been to be sure the rust is neutralized by dabbing on some some swimming pool acid, then after rinsing well with fresh water, to cover the stains with off-white rustoleum type paint. Sure, when close-up looking up at the mainsail from my boat's cockpit, I can see where I've dabbed the paint... if I am actually trying to notice. But nonetheless the effect is a big improvement compared to looking up at rust stains.

Eventually, brand new sails will be acquired. I won't want them to attract rust like my existing sails.

So back to the original question... what causes rust stains on a stainless steel rigged boat that also has a sail cover in place?

 

[Ed Schenck]

Not rust?

I guess you could take a sample(how?) to a lab for analysis. But maybe it is not rust. If only on the lower third of the main it almost has to be from the boom. When the sail is flaked over the boom at least one side but probably two(unless always flaked to the same side) are on the boom. The marks higher up would be from bleeding through. Are the spots aligned vertically? That would give some credence to the theory.

On the other hand my H37C boom has had chipped bare spots through the years and my main has no stains. Quite a mystery.

 

[Steve Dion]

Paint? You must be kidding?

I would review all of the sail cleaning techniques to remove paint from the sail before I would worry about the rust.

Once you have removed the paint (if there is any thing left of your sail) I would look for the source. It may be a sail that was made in the orient that has sub-standard S.S. rings, screws etc that are staining your sail.

Take your sail to Rooster Sails (Rudy) and have him install new S.S. hardware to see if this is the source of your problem. If there is no metal parts that are coming in contact with the fabric you are probably getting pollution from an outside source.

Maybe the birds are picking up metal scraps from Alameda Navel Air Station and nesting them in your sail? Do you have any better ideas?

 

[GuyT]

Stainless steel does rust!

It is quite common to get surface rust on stainless steel - maybe that is the source. Stainless has different grades - maybe your mainsail cover snaps are the source or maybe some hardware on your boom.
The other source may be the shrouds. When your boom is let out running with the wind, your mainsail may come in contact with surface rust on the rigging.

Have you ever used steel wool or a wire weel or ground metal around your mainsail while working on your boat?
These tasks create alot of fine particulate that may have deposited in a pocket of your sail and a little is all it takes.

Just some thoughts.

 

[rardi : H36 ( Cherubini)]

Yes Paint - Old Sail - Just Over the Dots - Didn't Get Out the Roller

Steve (and for Guy T further down):

The rust stains on my sail mostly are small spatters and dots of less than 1/2" diameter. Only a few spots in the 1” range. Entire sections of sail are not rust-stained. So it was with just dabs of paint with a medium artist's brush I covered each rust spot. Rest assured that I did NOT paint the sail with a roller. From what I can tell, Dacron is pretty much impervious to most solvents. The paint I used is mineral spirits soluble, which doesn't damage even the most sensitive of plastics. So I couldn't see much (any) risk of actual damage to the fabric. The sail is serviceable, but old. It is under a sail cover most of the time, so probably will take years for UV to discolor the paint. The sail will be history by then anyway. Worth the experiment was my thinking.

Your and GuyT's thoughts about external sources have merit. Yes, the boat was on the hard at the Alameda Navel Air Station for about 1.5 years before I bought it and then another six months while I worked on it. I and other boats were having a problem with black engine soot blowing from the Military Sealift Command vessels causing rust like dot stains on the gelcoat. So if the sail had been left on the boom without a cover for a while, and/or if steel grinding was being done nearby, some dust could have settled between the folds which would have rusted at the first sign of moisture. Presumably even a small grain of steel/iron that is rusting would bleed out over a larger area.

I have looked at the stainless steel hardware on the boom. No brown discoloration on them, at least where the sail would be in contact. Also the pattern of the stains doesn't correlate with where the sail fabric would be in contact with these parts.

 

[carl foster]

My "get even" rust stains

Several years ago had a deck sweeper jenny made by an unnamed sail maker in Coconut Grove Fl. She had previously made me a great main, so was confident in the results i would get.Wrong! Sail cut, fit and performance were great, but, one major problem. Having supplied old sail as basic pattern there was no excuse for her new partner to put Sunbrella on wrong side of sail while she was off to Olympic trials. Brought back immediatly and was told to run furler line up other deck. Wrong! So he proceeded to swap sides, very sloppily. Panels didn't match and i think to get even, several staples were left in. After several weeks of non use, unfurled and revealed were nice quarter sized rust spots. Guess this explains why he didn't replace company logo on sail.