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Old 9th June 2011, 06:52 PM   #11
Floyd
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Tend to agree with original poster. Think its to do with weight.Heavier sailors seem to prefer SDM .For same weight they are stiffer , by definition. Strength /stiffness propotional to depth ???

Last edited by Floyd; 16th June 2011 at 10:24 AM.
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Old 10th June 2011, 08:53 PM   #12
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Tend to agree with original poster. Think its to do with weight.Heavier sailors seem to prefer SDM as I do.
For same weight they are stiffer , by definition. Strength /stiffness propotional to depth ???
that is not true "everything else being equal, then an sdm will be stiffer than an rdm" may be true, but same weight could mean wildly different materials and construction techniques.

Im 95kg and use RDM masts on sails cut for RDM masts and am perfectly happy with them. If the sail is cut for the RDM masts there should not really be any issue.
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Old 10th June 2011, 09:16 PM   #13
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Ok
Should have said for same weight/same carbon content/same construction/same laminate direction etc etc SDM will be stiffer and stronger (OK not tougher) than equivalent RDM. !!!!

Cant change physics. Strength (and stiffness?) is/are proportional to depth. (ie in this case diameter )

IAnybody who has converted over to RDM as an experiment try your sail on an SDM ???? See how it feels.??

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Old 10th June 2011, 10:27 PM   #14
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Ok
Should have said for same weight/same carbon content/same construction/same laminate direction etc etc SDM will be stiffer and stronger (OK not tougher) than equivalent RDM. !!!!

Cant change physics. Strength (and stiffness?) is/are proportional to depth. (ie in this case diameter )

My 430 RDM would only cover 4.7 to 5.4. Which is probably why they are been pushed at us !!! New bases and more masts for us to buy !!!???
It is the thickness that makes RDMs masts so strong: to make a SDM as thick as a RDM it would weight a ton.

And in this case the conspiracy theories are quite misplaced: my Hot Sails HotRod 430 is used from my 4.7 Superfreak UL (you could go even smaller if you wanted), and is the recommended mast for my GPS 6.6, a race sail requiring 24cm extension. Quite a range of use: one mast for one of the softest sails around, used in extreme B&J, all the way to a multi-cambered sail. In addition tops and bottoms of the mast line are all exchangeable, so you can buy just the bottom of the next larger mast if you need something longer. Hot Sails and others have whole lines of sails that are designed to be rigged on a single RDM mast, take the Liquid: 5.0 to 7.5 can be rigged on a 430.

How a sail designed for a RDM would work with a SDM, and vice-versa? Who knows, some would work worst, some maybe better, some the same. What's the point?

Last edited by davide; 10th June 2011 at 11:03 PM.
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Old 10th June 2011, 11:04 PM   #15
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In general, lighter guys <70kg prefer RDM in most cases, and >100kg prefer SDM, if you weight is in between things are a lot more blurry... case closed.
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Old 10th June 2011, 11:53 PM   #16
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Davide
Putting it other way around
An SDM doesnt need the thick walls to be strong/stiff.;but the thinner wall makes them more fragile.(A relative term)

I

Last edited by Floyd; 16th June 2011 at 10:25 AM.
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Old 11th June 2011, 12:23 AM   #17
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I`ve yet to use an RDM on a sail over 5.4 that I`ve been impressed ;infact I`ve hired 5`s on RDM and swapped them for same rigs on SDM but totally agree with Sergio over the weight classification/choice.
Think I mentioned earlier I`m 105 kg;we are almost involved in different sports !!!???
Yep, that's a gap in weight! although you might want to check out http://martynogier68.blogspot.com/ Martyn Ogier is 110Kg and he was rated 2nd fastest in the world speed circuit last year, just in front of Dunkerbeck. Last time I noticed he was using RDM + Hot Sails GPS (not sure what he is using this year) ...

Last edited by davide; 11th June 2011 at 12:28 AM.
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Old 11th June 2011, 01:32 AM   #18
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Bet he`s not buying them !!!

Last edited by Floyd; 16th June 2011 at 10:27 AM.
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Old 11th June 2011, 01:48 AM   #19
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This is another debate that will run a nd run. Just checked boards Forum to see what opinion was on there. Rik (of Rik`s Windsurfing) posted this;
Originally Posted by Rikster


"A RDM sets a sail flatter so immediately you have less power from a standing start. In use the softer relative flex of the smaller diameter spar prevents the sail from delivering the same amount of power as the SDM. The extra deflection causes draft instability when sailing heavily powered-up.

Like with so many things it’s all rather subjective to the user, the conditions they sail in and the equipment combinations being used. I know many sailors swear by the softer more forgiving flex the RDM provides but that is often making up for other deficiencies (technique or equipment set-up). In general terms however, easier conditions that do not require the extra strength of the RDM benefit from the extra power and wind range offered by the SDM. "

Best regards,

Rik
This is the NP line on issue. I use NP sails ...nufsaid.
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Old 11th June 2011, 03:41 AM   #20
davide
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Bet he`s not buying them like us though !!!
Not sure what this is supposed to mean ... he is 110Kg and using RDM he almost won the world speed tour, and you just said that RDMs were not good for people above 100Kg ... I don't personally care if they are or not but this is just a counterexample to show that you can happily compete at the highest level on a RDM as a heavy-weight ...

As far as the (cherry picked!) comment of the guy from ... rik's windsurfing (sic) ... sails do not rig more flat on a RDM (or fatter on a SDM, sigh ..). Sails rig exactly as they are supposed to rig by design on a specific mast, RDM or SDM. (I'll skip commenting on range ... my 6.6 GPS is very happy when people are on 4.7s and I am 72Kg).

BTW to talk of RDM vs SDM is actually silly. For optimal performance a sail should be rigged on the mast it was designed for. One should not rig a sail designed for a, say, SDM NP on a, say, SDM North. This of course, unless you want to buy a dozen of SDMs from different manufacturers and investigate which one give you more "performance"!!!!!!

Ok, off to go sailing: 20knots in the forcast!

Last edited by davide; 11th June 2011 at 03:45 AM.
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