Your advise please...
After dusting the cobwebs off my gear and finally getting on the water again, I've discovered a build up muck around the metal cleat on the clamp thingy that holds the loop of rope that attaches boom to mast. (great technical terms there!!) The rope is stuck in there so you can't adjust the length of the loop.
The outhaul and downhaul cleats are OK, but could do with a clean.
What can I use to clean this metal, and to remove the build up on the third, so the rope can come out and it will be functional again?
It's oxidisation
you can clean it up with some vinegar and a brush, please be aware that you will be removing material from the cleat and thus weakening it
Thanks Elmo.
After cleaning, is there something I can use to protect the metal to avoid it oxidising in the future?
Aluminium oxidation generally just surface, but can get nasty with tie and worse where aluminium is directly on stainless (electrolysis effect? of a more inert conductive metal against the alumimium). One thing we used to do when sailing dinghies (many many moons ago) was to give a light varnish over the cleats (when fully cleaned) when approaching a non-use period. The varnish would wear off very quickly when first used again, but only on the parts actually doing most of the gripping on the rope. Always wash out with fresh water after each sail as well. Ever notice how many factory aluminium wheels used to have a varnished surface to protect the aluminium. PS: don't use a two pack - won't wear off and your cleats will be useless. :))
pull the rope thro the cleat rather than across the cleat which is way u normally release the rope. Dont leave the rope in contact with it during storage. As said clean with vinegar & hot water- not boiling as that can affect the plastic too much. Between sails u can spray light coat of wd40 or innox on em just remember to wipe off before u use.
As Elmo said, a stiff brush and a mild cleanser will clean the surface oxidation off. He lies about removing material, however. What you are removing is the cruft that has already oxidised and is useless material. It's pretty damn difficult to remove the base material with a stiff brush, or even a scouring pad.
Try it if you like.
Do NOT use any cleaner with chlorine in it. It will quickly destroy the aluminium (and any stainless steel as well).