Thank God, someone else is as confused as I am

Hope you get some good replies, also I'm interested to know if the performance of the skinnies are worth the extra cost and whether cam sails are just for skinny masts these days?

Cheers Phil

I'll start the controversy...

1. It depends. There have been many forums on this topic. Generally, more carbon in RDMs = stronger, less carbon in SDMs = stronger. Sounds weird.

2. Yes. Skinnies last much longer.

3. Glass

4. Sail compatibility with masts still depends on mast curve. RDMs have different stiffness and curve character. Same as their fat cousins.

430 - depends on the sails you want to use. RDMs are simply better. Once you try one, you'll never go fat again.

G'day Howard. Its Friday night. Don't you have a life either?
mmmmm.... masts, not just sticks to shove up your luff.

Lets see... A lot depends on where you sail. A 100%C SDM is going to be the lightest and nicest to sail and throw around however they wont take the brutal punishment dished out by the shore pound so you can't use them in the waves. That said they are the best for everything else. According to the "Team" guys (a few years ago) that's all the pros use for freestyle.

There seems to be a trend towards RDMs for general use however, not just waves. Naish's speed sails for example only rig on an RDM.

75%C is a bit heavier and quite a bit more durable.

100%C RDM is definitely more durable than 100%C SDM by a long way. There are 2 reasons for this 1) 100%C SDMs are designed for racing so they tend to be as light as they can possibly be made. 100%C RDMs are still designed for rough use. 2) The reason d'etre for RDMs is simply the mechanical effect of being able to bend further before local overstressing. Of course the same effect means that the skinny needs a lot more stuff in it to achieve the same stiffness. This means that for the same stiffness they will always be heavier but not necessarily by a lot.

75%C means 75%C + 25% glass

All camless sails will work to some extent on RDMs. The difference in diameter of the mast doesn't matter much to the set of a camless sail. It has some effect but its trivial. The main difference to be aware of is with the bend curve. Most, but not all, RDMs have a bend curve of about 10% (relatively soft in the bottom and stiff in the top. Powerex are exceptions and NP). SDMs tend to be more like 12% to 15%. relatively stiff in the bottom and soft in the top. So the same camless sail rigged on a Pryde 15% bend SDM will feel totally different from the same sail rigged on a 10% skinny. If the sail suits one it will be totally RS on the other. There is an industry standard that says the 12% bend is the garden variety best all round most common and most compatible bend, except for short masts. For a 400 or 370 10% is the go.

Oh, some sails will only rig on a skinny.

What 430?.... depends on the sail and the conditions.

Puggy: I agree (but I don't think there is any controversy )

100% SDM race masts sometimes go bang when only used a few times. Their life is much less than a 75% and the performance increase is negligable.

RDM's are heaps stronger than SDM's..... but maybe they woudl be even better with less carbon (nobody ever made one with 50% I think?)

Its also the fact that for the same amount of bend the displacement in the wall of a smaller diameter mast is a lot less. This means the wall is under less tension/compression for the same amount of bend. Also meaning you need a thicker wall to maintain a similar bend stiffness, however with less force/mm^2 of carbon. Hence you can bend the mast a lot further before you reach the same breaking strain.