I usually try and use the longest mast that will fit a sail in order to use the least amount of extension possible. Say for example, a 6 with a 438 luff gets a 430 mast, and a 5.3 with a 408 luff gets a 400.Now, lately I've been considering rigging slightly larger sails on a 400 mast. Say for example, that same 438 luff sail, on a 400 mast with a 38cm extension. As I understand correctly, a 400 mast on a sail like this might feel "too soft".
So.... Here are my thoughts?1. Good quality carbon extension? - I would suspect that if you are rigging a longer extension, at more than 30cm, you would want a good carbon extension instead of an aluminum one, right? You may want a bit of flex on that extension? I understand this might make the feel even softer, but having a rigid extension and starting the curve higher up may not be ideal, right?2. Higher reflex fast mast? - I would also suspect that using a mast with a very fast reflex in 80%-100% carbon would be preferable as well, right? It may help compensate for the fact that it's a litter shorter than recommended?
3. Large sails may be more adversely affected? I would also guess that the larger you go in sail size, the worse the effect of a shorter mast might be. For example, rigging a 400 mast instead of the recommended 430 on a 6.2 sail may not be as bad as rigging a 430 mast on a 7.2 sail where a 460 is recommended? Or even worse, rigging an 8.0 on a 460 where a 490 is recommended? Right?
First, I would not expect an extension to bend, actually you do not want it to bend because it will not match the bend curve of the lower part of your mast. But I stand corrected according to duzzi, but that is a brand specific extension, I was thinking of my Streamlined extensions and Streamlined does not make masts.
And it depends what you want in terms of sail response. For example, an Aerotech Freespeed 8.0 can be rigged on a 460 or 490 according to the manufacturer, on the 460 need 38 cm extension and will get a softer sail maybe better for fining, but with a 490 mast and 8 cm of ext. same sail will be stiffer and better for foiling because it will pump better.
All the sails I now use for foiling are on short extensions, most at 8 cm, one at 18 cm, and that puts them on a stiffer mast because several have adjustable head caps that are extended ~14cm.
Select to expand quoteeluviis said..
I usually try and use the longest mast that will fit a sail in order to use the least amount of extension possible. Say for example, a 6 with a 438 luff gets a 430 mast, and a 5.3 with a 408 luff gets a 400.Now, lately I've been considering rigging slightly larger sails on a 400 mast. Say for example, that same 438 luff sail, on a 400 mast with a 38cm extension. As I understand correctly, a 400 mast on a sail like this might feel "too soft".
So.... Here are my thoughts?1. Good quality carbon extension? - I would suspect that if you are rigging a longer extension, at more than 30cm, you would want a good carbon extension instead of an aluminum one, right? You may want a bit of flex on that extension? I understand this might make the feel even softer, but having a rigid extension and starting the curve higher up may not be ideal, right?2. Higher reflex fast mast? - I would also suspect that using a mast with a very fast reflex in 80%-100% carbon would be preferable as well, right? It may help compensate for the fact that it's a litter shorter than recommended?
3. Large sails may be more adversely affected? I would also guess that the larger you go in sail size, the worse the effect of a shorter mast might be. For example, rigging a 400 mast instead of the recommended 430 on a 6.2 sail may not be as bad as rigging a 430 mast on a 7.2 sail where a 460 is recommended? Or even worse, rigging an 8.0 on a 460 where a 490 is recommended? Right?
Point-7 claims that their carbon extension matches the curvature of their mast point-7.com/carbon-pro-extension/?v=7516fd43adaa I am not sure if that is true, (but their extensions are very well designed!).
When it comes to using a long(er) extension I think it depends. My Point-7 6.0 is supposed to be rigged on a 400 + 38 extension, and it indeed works great. I rig my 4.2 Spy not on the factory spec 370, but on a bottom 370 and top 340 , because I like a softer feeling. I used to have a HSM KS3 that supposedly could be rigged on 400 or 370, but even at my weight, 70 Kg, the 370 made it into a noodle.
And using a long extension can work with bigger sails too, at least at my weight. I rigged a Switchblade 7.3 on a HSM RDM 430, but it felt too soft. I use my Point-7 ACX 7.5 on 100% carbon Point-7 RDM and now SDM 430 with a 44/46 cm extension and it works great, with the SDM better.
So try ...
It makes huge differences on my NP V8 8.7 which can be rigged on a 490 or 520
Much less power on the 490 and the battens rotate much better . Feels like a smaller nicer sail . Probably better for a lighter rider . Heavy me is better on the 8.2 which seems to have the same power but is physically smaller .
As you drop down in mast length, you are dropping in stiffness. The main difference in going from 430 mast / 8 ext to 400/38 will be the degree of stiffness in the top 200 cm of your mast. That will have the biggest impact on your sail shape and response. Extensions are designed to carry the load of the Downhaul, not to flex or provide curve. I doubt any extensions curve more than a millimeter. The best example I've seen for what you are describing is Bruce Petersens description of the design of Sailworks' Flyer foiling sail. Their specs page shows all their mid-large sizes are designed around "soft" masts with 28-42 cm of extension as the reduced hull resistance means sail no longer needs a loose leach.
I'd be curious to get AWalkSpoiled's take on this.
See 05:00 in this:
Select to expand quoteduzzi said..eluviis said..
I usually try and use the longest mast that will fit a sail in order to use the least amount of extension possible. Say for example, a 6 with a 438 luff gets a 430 mast, and a 5.3 with a 408 luff gets a 400.Now, lately I've been considering rigging slightly larger sails on a 400 mast. Say for example, that same 438 luff sail, on a 400 mast with a 38cm extension. As I understand correctly, a 400 mast on a sail like this might feel "too soft".
So.... Here are my thoughts?1. Good quality carbon extension? - I would suspect that if you are rigging a longer extension, at more than 30cm, you would want a good carbon extension instead of an aluminum one, right? You may want a bit of flex on that extension? I understand this might make the feel even softer, but having a rigid extension and starting the curve higher up may not be ideal, right?2. Higher reflex fast mast? - I would also suspect that using a mast with a very fast reflex in 80%-100% carbon would be preferable as well, right? It may help compensate for the fact that it's a litter shorter than recommended?
3. Large sails may be more adversely affected? I would also guess that the larger you go in sail size, the worse the effect of a shorter mast might be. For example, rigging a 400 mast instead of the recommended 430 on a 6.2 sail may not be as bad as rigging a 430 mast on a 7.2 sail where a 460 is recommended? Or even worse, rigging an 8.0 on a 460 where a 490 is recommended? Right?
Point-7 claims that their carbon extension matches the curvature of their mast point-7.com/carbon-pro-extension/?v=7516fd43adaa I am not sure if that is true, (but their extensions are very well designed!).
When it comes to using a long(er) extension I think it depends. My Point-7 6.0 is supposed to be rigged on a 400 + 38 extension, and it indeed works great. I rig my 4.2 Spy not on the factory spec 370, but on a bottom 370 and top 340 , because I like a softer feeling. I used to have a HSM KS3 that supposedly could be rigged on 400 or 370, but even at my weight, 70 Kg, the 370 made it into a noodle.
And using a long extension can work with bigger sails too, at least at my weight. I rigged a Switchblade 7.3 on a HSM RDM 430, but it felt too soft. I use my Point-7 ACX 7.5 on 100% carbon Point-7 RDM and now SDM 430 with a 44/46 cm extension and it works great, with the SDM better.
So try ...
The AC One 6.2 rigs with a 42cm extension
More extension = more hard top yet rubbery mast.
Good for lightweight, bad for heavy weight.
^^^ Unless the sail was designed on the shorter mast/more ext combo .......
Wavesailing I notice bugger-all difference. I like being able to get a 5.7 on my 400 so I only have two masts for 4m to 5.7 that covers pretty much all my sailing
Facts:
If you add base extension to a 370 mast to make it 400cm:
- the extended mast tests SOFTER then the 400 on the IMCS test
- The extended mast tests more flex top on the IMCS bend test
I have tested this on the IMCS test rig, and in real life in Cammed race and speed sails. Sometimes it is a good strategy for a lightweight sailor to create a more flexible, reactive sail with a deeper lower profile and a softer more open upper profile. But it depends a LOT on the individual sail, mast, use conditions and sailors size and weight. 
I was wondering this when I was foiling but my girlfriend was wanting to use a sail that required the same mast size (430). She's a lot lighter than me, so I was considering using a 400 with long extension on the sail that had short enough luff for it to be enough length. I just hadn't tried. Seems like ok for her but bad for a heavier person.
Otherwise I'm going to need another 430 mast so I can foil while she fins.
Thank you all for the responses. Makes total sense. I understand now that extension flex is not a thing. Regardless, I'm going to go with a carbon extension.
After giving this a lot of thought, I think I can get away with just having two masts... a 400 and a 430.
I just ordered a new Goya 100% 400 for a Cypher 5.4. But I intend to use this mast from 4.7 to about 5.6. Then from 5.7 up to 7.0, a 430 (The Flyer 7.0 rigs on a 430). I have an old 430 that I'll use for now. It's Italian, but I bought it used and the markings are all rubbed off. I'll see if I can gather what it is. And I still have a 6.5 that rigs on an old 460 SDM I have. I don't particularly care for SDM masts as I tack grabbing the mast, and I prefer the grip on RDM masts.
But anyway, point is, that regardless of what old masts I have lying around at any given point, I can away with my main masts being 400 and 430, with a couple of difference extensions, since I don't really plan to rig higher than 7.0. At least not for now. If I ever get the itch to fly an 8.0, we'll see. But I'm learning to wing foil too, so maybe I'll do that instead in light air.
Select to expand quoteaeroegnr said..
I was wondering this when I was foiling but my girlfriend was wanting to use a sail that required the same mast size (430). She's a lot lighter than me, so I was considering using a 400 with long extension on the sail that had short enough luff for it to be enough length. I just hadn't tried. Seems like ok for her but bad for a heavier person.
Otherwise I'm going to need another 430 mast so I can foil while she fins.
I'd say it's definitely worth a try. If it works OK will depend on many things, but definitely worth a try. 
also makes sense to me. shorter mast for more curve. often times sails need a bit more downhaul than usual so I guess shorter mast helps with that.
I have a 7.9m sail that takes a 490 recommend / I rigg it with a 460 + 30 ext. Seems to do the trick never had any issues still sails in all directions.
