Hi,
I am considering MDM masts as the idea seems very good to me, slightly reduced diaameter in order to have proper bend with thicker walls and/or better carbon.
I enjoy fin slalom sailing and don't plan to foil.
But seems to me MDMs are mostly used in foil windsurfing, for some reason, and not much with fin.
Can anyone share his or her experience with MDM masts and slalom/race fin sails?

I have various SLAKE MDMs from 430 to 530, use them for fin and foil - HUGE fan - still have a Slake SDM that survived huge loads in a very nasty mowdown by a speedboat, these will be even more reliable - but feel very SDM in flex/performance, even with my 95+kg - and sweet rotation is a bonus

Thank you Searoamer!
Having tested on both, have you an idea about why MDMs seem the way to go for the foil and not (yet) for the fin?

I really don't know who is on what these days ...
Dedicated slalom/race sails (4 cams etc) can be very mast specific, and top racers will usually go with recommended mast??
I never liked RDMs for slalom sails designed for them (lighter sailors often do) so use MDMs instead
And when you catapult on the foil, you definitely want the strongest mast possible! maybe a factor ...

I have MDMs from 1995, but they aren't slake, they're kilwell. Fantastic masts, they have survived being catapulted into reefs, with the board suspended in the air and waves crashing into them. Multiple catapults that have destroyed booms, harnesses and hooks.
If slake are making something similar, they'd be well worth paying a bit more for.

Had a 400 RDM slake and 430 MDM Slake last year. Both masts failed just above the boom clamp. The 400 was my fault shallow water forward catapult, still strange it broke as I wasn't travelling at any speed just caught the fin on the bottom and a slow forward catapult, I still attribute the snap to sailor error.
The MDM on the other hand, snapped same place just as I was going to step on the board. No crashes on this mast, was a cool day so not attributable to heat, 15 months old mast.

Slake masts are very responsive and light to boot, so a good product. Any brand mast will snap if you hit something at speed and get thrown especially shallow water. I don't discriminate and have snapped NP, KA and tushy as well so can't blame Slake.

Biggest reason mine snap is that I don't let go off the boom so all the weight plus forward momentum in shallow water snaps the mast in the identical spot no matter what brand. Discipline I sail is Speed and Slalom.

Lightest and most responsive feel of all the masts was the Slake, but it's not unbreakable??

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Aus501 Boz said..>>> Any brand mast will snap if you hit something at speed and get thrown especially shallow water. I don't discriminate and have snapped NP, KA and tushy as well so can't blame Slake.

Biggest reason mine snap is that I don't let go off the boom so all the weight plus forward momentum in shallow water snaps the mast in the identical spot no matter what brand. Discipline I sail is Speed and Slalom.

Lightest and most responsive feel of all the masts was the Slake, but it's not unbreakable??

Pity the kilwell matrix 5 are no longer available. I doubt they are indestructible, but mine have had a hiding over the last 18 years, crashes, both in the surf and at speed. The old sudden stops that tears harnesses apart, snaps booms, and mangles the board nose.

So I think the slake MDMs have potential, as you said they probably just need more reinforcing around the boom area.

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Searoamer said..
...
Dedicated slalom/race sails (4 cams etc) can be very mast specific, and top racers will usually go with recommended mast??
...

Yes race sails are mast specific but unfortunately for some reason I can not have my '22 Venom 7.5 and 8.2 work on recommended masts.
The top guys tend to do things that we would never do. My home spot is Talamone, about an half hour drive from RRD's headquarter, so during past years I had lots of chances to meet racers here, Maynard, Dagan, Martini, and very often Rosati. Rosati used to select masts by a simple procedure: rig, hit water, do 1 or 2 jibes, get onshore, derig, change mast and repeat. One can be sure he always has proper masts in his sails after that, but that may mean custom masts or at least carefully selected ones ... and I think the same applies to the others.

I think north are using MDM for the new 3Di sails

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Aus501 Boz said..
Had a 400 RDM slake and 430 MDM Slake last year. Both masts failed just above the boom clamp. The 400 was my fault shallow water forward catapult, still strange it broke as I wasn't travelling at any speed just caught the fin on the bottom and a slow forward catapult, I still attribute the snap to sailor error.
The MDM on the other hand, snapped same place just as I was going to step on the board. No crashes on this mast, was a cool day so not attributable to heat, 15 months old mast.

Slake masts are very responsive and light to boot, so a good product. Any brand mast will snap if you hit something at speed and get thrown especially shallow water. I don't discriminate and have snapped NP, KA and tushy as well so can't blame Slake.

Biggest reason mine snap is that I don't let go off the boom so all the weight plus forward momentum in shallow water snaps the mast in the identical spot no matter what brand. Discipline I sail is Speed and Slalom.

Lightest and most responsive feel of all the masts was the Slake, but it's not unbreakable??

...how did you get a 400RDM from Slake? I didn't see it available in the website and I would be really more than interested in getting one (and eventually also a 430 if available)... can you please advise me?

Does anyone have experience with the MDM foil mast/sail combination and what is the comparative feedback to the SDM in terms of performance?

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geoITA said..
Rosati used to select masts by a simple procedure: rig, hit water, do 1 or 2 jibes, get onshore, derig, change mast and repeat. One can be sure he always has proper masts in his sails after that, but that may mean custom masts or at least carefully selected ones ... and I think the same applies to the others.

That sort of testing results in finding the thing you are used to using, that feels familiar. That's fine if that's what you are looking for.
Improvements come from finding the thing that is higher performance ( or another metric)and it is likely that this will be unfamiliar and different and require adjustments to your sailing and or set up. You don't find them in one or 2 gybes.
There is the placebo effect as well, I am sure he feels like he did the work to find the right mast, and thinking he did is important, like board paint jobs or sail colours, it all has an effect.

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Maui74 said..
...how did you get a 400RDM from Slake? I didn't see it available in the website and I would be really more than interested in getting one (and eventually also a 430 if available)... can you please advise me?

I got in touch with Brett from Slake Masts, I just used the contact on the Slake website. The masts were for KA sails, I'm sure he can do other brands in RDM

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sheddweller said..

That sort of testing results in finding the thing you are used to using, that feels familiar. That's fine if that's what you are looking for.

.. . You don't find them in one or 2 gybes.

There is the placebo effect as well...

May also result in finding what one is looking for. Don't forget the guy is used to check masts that way and has huge experience. By sure such procedure would not work for me.

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Maui74 said..

Aus501 Boz said..
Had a 400 RDM slake and 430 MDM Slake last year. Both masts failed just above the boom clamp. The 400 was my fault shallow water forward catapult, still strange it broke as I wasn't travelling at any speed just caught the fin on the bottom and a slow forward catapult, I still attribute the snap to sailor error.
The MDM on the other hand, snapped same place just as I was going to step on the board. No crashes on this mast, was a cool day so not attributable to heat, 15 months old mast.

Slake masts are very responsive and light to boot, so a good product. Any brand mast will snap if you hit something at speed and get thrown especially shallow water. I don't discriminate and have snapped NP, KA and tushy as well so can't blame Slake.

Biggest reason mine snap is that I don't let go off the boom so all the weight plus forward momentum in shallow water snaps the mast in the identical spot no matter what brand. Discipline I sail is Speed and Slalom.

Lightest and most responsive feel of all the masts was the Slake, but it's not unbreakable??

...how did you get a 400RDM from Slake? I didn't see it available in the website and I would be really more than interested in getting one (and eventually also a 430 if available)... can you please advise me?

The North MDM Masts are produced in the "former" Slake factory (CST in NSW). They are manufactured with a variable pitch to allow different flex without changing the wall thickness.

More info from Pieter in the video below.

Please check the few last posts here:
www.seabreeze.com.au/forums/Windsurfing/General/S2Maui-Venom-The-Rotation-Problem-#2869088

The MDM 460/25 masts I was able to test as protos is now available in the Neil Pryde 2025 lineup.However, the stiffer (460/27) version could be probably better for different brand sails.

I brought a Slake MDM 430 mast from Brett last December. Best $1000 I have ever spent. Awesome product.

Totally enthusiastic about the MDM mast concept.
After testing a 460/25 past year, that solved 100% my S2Maui Venom '22 rotation issues.
This year I started testing a slightly stiffer and more constant curve option, 460/27. It proved even better than the 460/25. My sails (Venom 7.5 and 8.2, '22 and then '25) turned out more direct and responsive than with the 460/25, same rotation (good in the '22 samples instead of barely rotating if any with the SDM original mast, flawless in the '25 ones), no drawbacks, only better.
Best of all. The 8.2 size Venom sails are specified for 460 masts, which is unusual as all other brands race sails over 8.0 sq. mts. are specified for 490 masts. Probably because of this, the 8.2 Venom when rigged on its SDM mast, apart from rotation issues, feels as a "large medium wind sail" attitude, instead of a true "light wind sail". When rigged with the slightly stiffer 460/27 MDM mast the sail achieves a more direct and responsive feel that makes a proper "compact LIGHT wind sail" of it, while still keeping great control in gusts and all of its wind range.
I also received a 430 sample to use with the 6.7 Venom '25. Mind the Venom going on 430 masts did not show rotation issues, both the '22 6.8 and the '25 6.7 have great rotation with the standard SDM 430 mast. Rigged with the MDM, the 6.7 seems to me to behave just same as with the SDM, only with an even superior, incredibly smooth rotation.
This to say: no matter which MDM mast you have available, THE CONCEPT WORKS. Pieter Bijl was perfectly right when he chose to design the new North Sails Race based on MDM masts.

Do you add spacers to the cams when using mdm? If not, there will be less pressure on the cams and no doubt that will lead to better rotation.
No mention of speeds on the GPS in this thread. 2s, 10s average,
, 500m, alpha.

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PhilUK said..
Do you add spacers to the cams when using mdm? If not, there will be less pressure on the cams and no doubt that will lead to better rotation.
No mention of speeds on the GPS in this thread. 2s, 10s average,
, 500m, alpha.

It would make no sense at all for me to publish GPS speeds attained in order to prove one setup is better than another. That would be meaningful if I was a good sailor reaching say 42 kts with setup "A" instead of 41 kts with setup "B", but I do not think that talking about reaching 29 kts on a bumpy choppy ride instead of 28 would be of any interest. And, that would be "just" speed, and say nothing about accelleration or cam rotation or comfort ...Talking about the '25 Venom sails, I am not adding spacers, as the luff sleeve looks already OK: taut on the leeward side and slightly abundant on the windward side when onshore. Once sailing, the windward side is OK too. And visible differences vs. the same sail rigged on an SDM mast (of course I did) is negligible.
Almost all of the difference in outer diameter between SDM and MDM masts is in the lowest 70 - 80 cms. So we are talking about the lowest cam. Therefore, (almost) any possible cam pressure reduction due to slack between cam and mast will be in an area where aerodynamics are less important (slower flow, lots of disturbances) and the draft is bigger (meaning, few mms if any will make a relatively small difference).
Anyhow of course I understand what you say 100%: the FIRST suggestion one gets when asking how to fix a cam rotation problem is ALWAYS to shed off some material from the cam. So let's say, with an MDM you may get the same result without using sandpaper ...
BUT I think the real (or most important) reason is another one, and that is the "bottleneck" shape of SDM masts ("drop shape" or similar, they are mostly made that way, meaning you don't need the extra diameter size other than to fit the 48 mm extension ...) cause the mast to be too stiff in that area. On the other hand, MDM masts have a progressive OD reduction (simple conical shape) and therefore progressive flex from the base up. In order to better understand this, please read something about "buckling" or geometric instability. You will see that we always talk about how much carbon and what quality, BUT actually the shape of the mast plays a paramount role in its flex qualities.
I only changed the # 2 (from top) cam from 52 to 47 mm size on my 7.5 to test, but really it changes nothing, regular cams are OK. On the '22 ones I used to add spacers at cam # 3 and 4 (from top) but just to take out some excessive creases (even with SDM mast), rotation was not affected at all. Rotation on my old '22 7.5 even got better when, after breaking a batten tip (# 2 from base), I changed it for a stiffer one that I had at hand. The stiffer tip helped to make for a leaner entry, and that in turn helped rotation, despite the stiffer tip by sure did not ease any pressure out.

I have had a North 'Drop Shape' for many years, worked really well with my KA Sails and standard cams, and now is useful on Naish no cams because can be inserted more easily in the luff pocket

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geoITA said..
The MDM 460/25 masts I was able to test as protos is now available in the Neil Pryde 2025 lineup.However, the stiffer (460/27) version could be probably better for different brand sails.

Hi, what extension did you use? I don't see any Neilpryde MDM extension. Thanks

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ekramers said..

geoITA said..
The MDM 460/25 masts I was able to test as protos is now available in the Neil Pryde 2025 lineup.However, the stiffer (460/27) version could be probably better for different brand sails.

Hi, what extension did you use? I don't see any Neilpryde MDM extension. Thanks

Hi, I bought a NorthSails alu extension and also have machined Delrin adaptors to work with RDM extensions.The NorthSails extension is the way to go. Simple and nice, and with oversized pulleys.

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ekramers said..

geoITA said..
The MDM 460/25 masts I was able to test as protos is now available in the Neil Pryde 2025 lineup.However, the stiffer (460/27) version could be probably better for different brand sails.

Hi, what extension did you use? I don't see any Neilpryde MDM extension. Thanks

I forgot an important thing.If you use an MDM mast with an RDM extension + adapter, the extension pulley will easily be positioned too much inwards (close to the mast center axis) than desirable, resulting in pulling the sail too much towards the mast, more or less same as if you were pulling the tack strap a lot. This may result in too much profile down low, possibly with undesired wrinkles that will not be cured adding shims to the cams.So definitely at this time a NorthSails extension is BY FAR the best solution. The RDM extension + adapter may be useful as a backup.