View Full Version : Long mast extension
25th March 2008, 05:09 PM
I'd like to hear your comments regarding two concerns I have when using a rather long mast extension (40-45 cm):
- situation A: Major part of the extension inside the mast. Let's assume that te mast has a constant curve characteristic. Will the extension inside the bottom of the mast spoil the performance? We' re talking about 30-40 cm alu piece that probably makes the lower part of the mast stiffer than should be.
- situation B: Using the extension at ful length, only 5-10 cm of it is inside the mast. Due to rather small conntact between the mast and extension, I think there's quite a pressure acting at the mast. Is there any risk to crack the mast?
Thanks in advance for your inputs,
25th March 2008, 05:25 PM
I have often contemplated your questions and at one point asked the same questions on the SB forums many years ago. My opinions ...
a) Yes. It makes the mast stiffer but it does not concern me too much. I think the effect is relatively small. If you have the cash just buy a couple of extensions, otherwise don't worry. It really won't cause you to lose the PWA championship.
b) No. All manufacturers basically have a similar minimum length with their extensions into the mast. They wouldn't put holes so high up on the extension otherwise. I am sure there are true engineers working on the design & spec of carbon masts - perhaps not with the brand names like Neil Pryde, North, etc but at least at the mast manufacturers like Italica, Maclean etc. Also the connection between the top & bottom section of mast has a similar length of insertion compared to the minimum length of mast extension into the mast.
26th March 2008, 01:47 AM
Regarding your situation B, you would be running a very high risk of mast failure unless you have a least 15cms (6") of the extension inserted in the mast. Any less than that doesn't provide a sufficient bearing surface and unduly point loads the mast. However, I think the minimum could be argued a bit contrasting RDMs and SDMs, since RDMs have a thicker wall structure. Still though, poster 2 offers a very good rule of thumb to follow by highlighting the length of the ferrule that joins the top and bottom sections of the mast.
26th March 2008, 09:38 AM
I'd have to disagree with the 2nd poster here.
I've seen some pretty bad results when too much extension was used up inside the mast.
This can definitely "stiffen" the bottom of the mast and can make the lower camber or even RAF battens very hard to rotate. (Your situation A).
The reason they make several length extensions is so you can use an extension that supports the mast well, but does not stiffen the bend characteristics apprecialbly.
In your situation B, even a 45 cm (long/tall extension has an additional 15-20 cm of tube at the top to support the base of your mast.
So, you can go out to the full adjustment (45 cm) and feel fairly confident that you are not unduly stressing your mast.
Certain size rigs (7.5-8.0 mostly) use 460 (IMSC 24-26) masts that are extended out to near 500 cm.
The bend characteristics of a 490 (IMCS 28-30) are just too stiff for these sails to work well on a longer mast, so the luff length specification is 460 cm + 35-40 cm of extension.
You could use a 490 mast here, but the sail would not twist of as designed and it might not rig well at all.
Also, if you are a big guy, then maybe (only maybe) you'd like the feel of a longer stiffer mast in this type of sail, but most sailors < 100 Kg. seem to prefer the "best" mast in these cases.
So, your situation A is almost worse than situation B.
I have seen several masts "point load" at the top of a long extension inserted 35 cm or more up into the mast.
The "point load" simply "snaps" the mast right at the top of the extension because the mast cannot bend with the extension inside it down lower and consequently breaks off at the first point were it can bend.
Hope this helps,
30th March 2008, 01:10 AM
I have some experiments of this kind last year.
I suggest you use not recommended mast if you have to use very long extension. ;)
In my MauiSails MS-2 9.5 I had to make custom extension. Otherwise it did not work properly.
sit.B If you use very small part of extension in mast(and too long extension), a backlash of extension in mast cause critically wrong shape of the sail.
30th March 2008, 02:45 AM
So what is the ideal amount of extension inside a mast ( i.e. how much is too much)? Is it more or less critical in RDM vs. SDM?
I have Chinook Carbon Tall extensions (both RDM/SDM) I use for my entire quiver.
(Severne Blades 5.3 -6.2 with PWX RDM 430, a 7.5 Gator with PWX SDM 460, and I also have a MS2 8.5 and Nitro4 9.3 on a FS7000 SDM 490).
30th March 2008, 10:01 AM
QUOTE - RUS_12 ---- "sit.B If you use very small part of extension in mast(and too long extension), a backlash of extension in mast cause critically wrong shape of the sail."
Huh !?!? That is crap. Why guess? .... Just follow the manufacturers recommendations, then it is easy.
If you need flexibility & you are on a budget, then you could use North gear to make things cheaper with their Carbon Xtenders. The recommended mast in numerous sails, is actually using the Carbon Xtender often with 30+cm of extension. I use mine as per their ideal mast recommendations and they rig perfectly ... and I also am complying with their specifications in case there is any warranty issues.
30th March 2008, 10:37 AM
Think the extension designers have pretty much answered this question.
Take any short, medium or long extension, slip the adjustment collar up to the highest
setting, and measure the amount of extension from the seat on the collar to the top of the extension.
My guess would be about 5.0" (12.7 cm) based on a NP 26 cm max (medium size) extension I just found under my chair.
As far as how much is too much, measure the front of the lowest batten in your sail from the foot, then see how far up inside the mast your extension goes.
If it extends beyond the height of the lowest batten (the foot batten) then you need a little shorter extension.
This is not critical on RDM masts and probably not on small wave and freeride sails, but the higher end sails, with lots of shape in the foot of the sail, can have some real problems if the mast base extends beyond the front of the lowest batten and "stiffens"
the mast in an area where the designer intends it to start bending to allow the foot batten to rotate freely.
Yes, you can often "fix" the poorly rotating foot batten by backing off the tension, but then you get wrinkles and less than the design amount of draft in the draftiest and most power making area of your sail.
Hope this helps,
30th March 2008, 05:34 PM
QUOTE ... "As far as how much is too much, measure the front of the lowest batten in your sail from the foot, then see how far up inside the mast your extension goes.
If it extends beyond the height of the lowest batten (the foot batten) then you need a little shorter extension."
Yes, this is a rough guide but if in doubt dont waste your time trying to be a windsurfing engineer .. just read the designer's recommended specs.
Plenty of my North sails have the Xtender connection much higher than the foot batten, and that is as per the OEM spec!
So make it easy .. just read the specs.
30th March 2008, 10:49 PM
The north mast extenders are a different issue. As I understand it, the problem is a long extention INSIDE the mast. The extention collar is the main contact point with the mast and is kept tight with the downhaul. If there is a long extention deep in the mast, when downhaul is applied, the mast flexes and the end of the extension makes contact with the mast, stopping the flex in this area (possible damage??). This would to have most impact on sails that require a lot of flex in the mast in the initial rigging (my retros flex alot, my north ices don't).
30th March 2008, 10:59 PM
Ummmm.... last time I saw one, the North "Carbon Xtender" was made in exactly the same way and of exactly the same materials as the mast it extends.
So, it will bend by design.
Putting a rigid aluminum or carbon (with a different fiber axis bias and not designed to bend) mast base extension up inside a mast that is already reinforced for hoop strength
from the boom area to the bottom really makes the bottom of the mast very rigid and unable to bend.
I guess the std. extension lengths are:
Stubby .....0 amount of adjustment
Short..... 10-12 cm of adjustment
Medium.... 26 cm of adjustment
Long/Tall.... 46 cm of adjustment
So, if your sail specification calls for the mast to be 455-460 cm, use a stubby.
If your sail calls for 462-472 cm use a Short extension
If your sail calls out a 474-486 cm use a Medium extension
If your sail calls out 488 cm or greater (up to 506 cm) use a long/tall extension (unless your sail specifies a longer/stiffer 490 cm IMCS 28-30 mast.
Hope this helps,
P.S. As suggested above, this is for getting the optimum tune from your race/slalom sails on standard diameter 75-100% CARBON Race masts.
RDM masts/Low carbon economy masts used in freeride and smaller wave sails probably are not as sensitive to having the right mast/extension geometry.
The North Carbon Extender System works well in North Sails designed for that mast Xtension system, but does not work so well in sails from other lofts.
31st March 2008, 05:03 PM
Interesting discussion. Iíve gone through specs for major brands slalom/race 7,5-ish sails and just about all manufacturers recommend 4,60 masts and long extensions for these sails. Except for my Gaasta gtx 7,5 which have a 4,90 mast specified as ideal. What do you think about running a 4,60 with long extension in my gtx instead? Reason for asking is that Iíve read a couple of post from people arguing that slalom / race 7,5ís will be not rig ok on stiff 4.90 masts. Which in turns contradicts to Gaastraís specifications.
31st March 2008, 07:32 PM
North Extender is a usefull item, the only thing I fear is according the mast durability: anyone has some feedbacks on using the north extender?
Anyway the north system works becouse the sails are designed to be used with the carbon (and flexible as Roger said..) extender, so the mast curve is optimized.
According 7.5-ish sails, I have a 2 cambered R_type 7.8 (460 + 42cm alluminium extention) and it works great..
31st March 2008, 08:18 PM
Sounds fine, will try the 460 + extension on my 7,5 gtx. I do have a brand new 490 Gaastra 75% mast for larger sails, just interesting to try other combos and see if that does any difference.
31st March 2008, 09:09 PM
My experience with "alternate" masts has always been that you can achieve some differences in the handling and performance of the rig by using a mast that's either
shorter/softer (460cm IMCS 24-26 in a sail designed for a 490cm IMCS 28-30 mast) or
stiffer/longer (490 IMCS 28-30 in a sail designed for a 460 IMCS 24-26).
If you are a lightwieght sailor, often the softer/shorter mast will give the sail the ability to twist off sooner and at less pressure so you can handle gusts more easily.
Sometimes, by very careful rigging (not "by the numbers) you can get a bit more draft and make the sail a little more powerful.
Conversely, if you are a heavier sailor, you can use a stiffer/longer mast and get the opposite effects.
More tension in the upper panels of the sail will put more power higher up in the sail and if you are big/stong enough to handle this, the sail can be rigged more powerfully and not twist off as much, and at a higher pressure.
The Sailworks Hucker sails are the most "tuneable" this way.
Take the 5.6 m2 Hucker and put the recommended std. dia. 430 IMCS 21-23 100% carbon race mast in it and you get the designed power and twist. The Huckers have more power up high and this is most evident on the 100% 430 Race Std. dia. mast.
Put in a 430 cm IMCS 21-23 Sailworks Backbone RDM and you get less power up in the top of the sail, and a deeper draft (due to the luff sleeve sizing around the dia. of the mast) down lower in the sail when it is fully loaded.
Put in a 460 cm Sailworks Backbone IMCS 24-26 RDM and you get a full on slalom tune (BP has used this combo with lots of success in the Gorge Cup Races) with a flatter head and more power down lower, but still fully tuneable with the adj. outhaul and on the beach downhaul adjustments.
So, give the softer 460 cm mast a try. You might like it. Do not go by what it looks like laying on the beach. Take it out and get it fully loaded up. That's the only way you can tell if it's better or not.
I'd guess that since Gaastra recommends the longer stiffer 490 IMCS 28-30 mast, you are going to see the top of your sail dump off at much lower downhaul tension and it will dump off alot more than it will on the 490 mast.
Whether this is good or bad...... only you can make that judgement out on the water.
Hope this helps,
1st April 2008, 01:24 AM
For a number of years now, I have been using 30-40cm of extension in my older 7.0 Windwing and my new 7.1 Hansen with great success. Although a 460cm mast was recommended for both these sails, a 430cm mast was cited as an alternate. Similarly, I used to go with a 460cm mast for my old 8.1 Windwing Race sail that recommended a 490cm mast.
Now, I probably wouldn't have normally deviated from the optimum recommended masts, but the path to the alternates was unexpectedly found due to broken masts. This led me to some experimentation with shorter masts and longer extensions. What I found is that I liked the result. The only important thing to keep in mind is adherence to the proper bend curve masts that the sail designer recommends. More and more today, going with recommended bend curve has increasingly been a prerequiste for optimum sail performance. Although it's sometimes it possible to use a different mast brand than recommended, it's often very dicey. I would hate to confront the dilemma that many NP sailors face after repeated X9 mast failures.
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