RDM is witchcraft - smaller diameter for same weight and strength!!! Theres no way this should work!!! Someone please .sort out string theory and quantum gravity so we can answer this question and travel the universe through wormholes.

Plus SDM works fine for me!

longwinded said...

RDM is witchcraft - smaller diameter for same weight and strength!!! Theres no way this should work!!! .

Plus SDM works fine for me!

Simple.

If you bend two tubes the same amount, the walls of the fatter tube have to stretch more to achieve that same bend.

Sidenote:

string theory Rubbish
and quantum gravity Well quantum means amount and yes we have sorted out the amount of gravity we have. Just enough, and not too much.
travel the universe through wormholes hmmm. I'd rather take the bus, i don't think i'd fit in a wormhole... if you wanna try you go for it but be reminded that it may be painful for the worm, and illegal.

Gaz

I would change tack - having all sails the same is nice, your quiver has very different handling sails. Strongly consider getting all the same sails.
For about the price of 2 new RDM's, you can probably get 3 x 1y/o sails and 2 x 1 y/o RDM's.
I know it is tempting to buy all new shiny stuff but if I had 3 different sails I'd not be buying a couple of Ezzy RDM's.

IMHO

I'd go RDM, especially as your largest sail is a 6m. I have 2 RDM masts which I use with my 6.6m, 5.3m and 4.7m (none of these have cams) I have a SDM which I use with my 7.5m KA Koncept which has 3 cams.

I buy 2nd hand gear BUT, never again a 2nd hand mast.....(unless I know its owner/history)...

All my old Masts fat diameter are used to hold tents up or wind direction things.

Reduced diamiter are the go ,finer entery through the wind ,and and give the rig a lighter feel when throwing it around, sweeter balance...........there pritty dam strong .......hard to bust.

Also you really want to get a set of rigs of the same brand.

But even then a skinny will feel better ................sailing and gyding.

one thing you will notice is the mast sleeve will and can become full of water and you will have to swim up the rig further to get it out of the water and or wait longer when its stuck under water , although this is a little determined on the cut and width of the sleeve in your riggs case for a fat mast ,,,,,!!!!!

aNY EXTRA WEIGHT IN THIS AREA ie water in the sleeve half a liter requires extra energy . to pop it out of the water and to recoverit as you have to swim further up th mast to pop it out and then back before water starting
Which ****s me especially if you have had rigs can pop out easly with one hand on the boom
Becomes very noticible year to year when different mast sleeve widths are used.

This can make the difference between geting taken out by a monster wave and or getting going

Mark _australia said...

Gaz

I would change tack - having all sails the same is nice, your quiver has very different handling sails. Strongly consider getting all the same sails.
For about the price of 2 new RDM's, you can probably get 3 x 1y/o sails and 2 x 1 y/o RDM's.
I know it is tempting to buy all new shiny stuff but if I had 3 different sails I'd not be buying a couple of Ezzy RDM's.

IMHO

Mark,

I've had numerous same brand sail quivers in my 25+ years of windsurfing and whilst what you're proposing sounds good in theory, it doesn't always work out that way (e.g. previous NP Combat and Excess sails handled very differently and my old 5 cam NP race sail was a completely different animal to these!), unless your lucky enough to be able to try before you buy which I've never had the opportunity to do.

Actually, you'd be surprised how similar my 5.3 KA Koyote and 6.0 Tushingham Lightning feel (when rigged on a NP 430 X6) if you had the chance to try them. The Koyote performs just like a smaller version of the Lightning minus cams. Koyote may sacrifice a bit of top end stability with no cams (though gains a lot of durability from full x-ply construction) but they're both very much similar in feel when blasting around.

I have considered selling the 6.0 Lightning and getting a 6.6 Koyote to make my 3 sail quiver a bit more brand/model consistent but the Lightning is such a nice freeride sail that I will probably wait until I trash it before updating!

longwinded said...

RDM is witchcraft - smaller diameter for same weight and strength!!! Theres no way this should work!!! Someone please .sort out string theory and quantum gravity so we can answer this question and travel the universe through wormholes.

Plus SDM works fine for me!

They are not the same weight. If you compare an SDM with an RDM of the same specs for length stiffness and carbon content and prepreg layup the RDM will be a bit heavier. They are making RDMs for non wave use these days and they are as light as they can make them. The equivalent SDM is a bit lighter but more fragile.

I think what is happening with masts is the prepreg high modulus carbon that they use in the most expensive masts enables them to make the walls very thin. In the case of SDMs it is arguably too thin. That's my guess :)

Best value for money non wave use is SDM.

^^^
(I can't believe you said that!)

Interesting sub-topic emerged on this thread which I interperated as "the depth of your commitment to the sport is measured by how much money you spend on it".

longwinded said...

RDM is witchcraft - smaller diameter for same weight and strength!!! Theres no way this should work!!! Someone please .sort out string theory and quantum gravity so we can answer this question and travel the universe through wormholes.

Plus SDM works fine for me!

To answer you question, it is all about the "moment of inertia". The higher the moment of inertia the better the ability of the mast to handle bending moments (ie horizontal forces from sail, boom etc. The moment of inertia is dependent on the shape of the mast, for example the larger the diameter of the mast the thinner the walls need to be. Moment of Inertia for a slender beam (mast) taking out the fixed variables is proportional to: (outer diameter^2 - inner diameter^2). So if the mast is skinner (ie rdm) the wall thickness must be greatly increased to achieve the same resistance to bending (keep the same stiffness). Which answers the weight part as a RDM has a smaller outer diameter it needs significantly more wall thickness to achieve the same stiffness.

The "strength" is a tad bit more complex, trying to keep its simple I will assume the mast fails in bending, bending stress is depended on the distance of the outside wall of the mast to axis it is bending around. So for a RDM this is a lot less than a SDM, thus at the same bending moment it will be exposed to less stress. Or put another way you have to bend the RDM more than the SDM to acheive the same stress. As both masts are the same material they will break at the same stress. I hope my rambling is understandable i just found it an interesting question I had not thought to hard about before.

Side note

For the Shear and Torsional loading the mast experiences the amount of stress occurred is depended on the cross sectional area of the mast. So a RDM has a greater area and thus again less stress for same deflection. If we all want to get really technical we have to pull Mohr's circle out....

Mark _australia said...

Pretty much what I said in one line Beebles

Very true,

This discussion doesn't interest me much but I thought I'ld let you see this recent quote from Monty Spindler on his Loft Sail forum.
-if you sail on flat water/lakes it could be that you prefer the sdm
-if you are heavy maybe the sdm suits you better
-if your trim is better on the sdm- maybe it suits better
-if you consistantly sail in the low end of the wind range maybe the sdm suits better...

Rubby said...

This discussion doesn't interest me much but I thought I'ld let you see this recent quote from Monty Spindler on his Loft Sail forum.
-if you sail on flat water/lakes it could be that you prefer the sdm
-if you are heavy maybe the sdm suits you better
-if your trim is better on the sdm- maybe it suits better
-if you consistantly sail in the low end of the wind range maybe the sdm suits better...

That would indicate that I need an rdm!!! (more to it than that)