newbie question - sorry, I have searched but not really found an answer

I have a 6.0 Gastra Hybrid with a 445cm Luff and need a mast for it. I have been told that I could run a 400cm mast with a 48cm extension, but I'm just not sure if this is a good idea. The reason I'm asking is I'd also like to buy a smaller (5.3-5.5) sail as expect I'd need a 400cm mast for that.

I have been borrowing a 430 mast, but I need to give it back. Should I look at a 400cm mast, or go for 430 and then find smaller sail (5.3-5.3) that can rig with a 430cm mast?

thoughts?

400 rdm forms the core of my wave sail kit. My wave sails are 4.2,4.7 and 5.3, which I use 400 and a 370 but I can get by with just 400. For bigger masts I use SDM so 430 for 6.2 and 7 then 460 for 7.8 which are all slalom, but could just as well be freeridey sails.


So a 400 rdm and 430 SDM can make a good combination.

48 extension is fine for a SDM NOT used for wave sailing. But if you miles from the correct mast you might find the sail not as stable than if you had a stiffer mast.

Longer masts are stiffer.

I would never use a 4m mast with anywhere near 40cms of extension.
If the mast is an RDM then any extension over 32cms would not be safe in waves, strength wise.

But the main reason I wouldn't use a long extension is that you end up fitting the boom to the wrong part of the mast - and probably too close to the extension. The mast bend would also be affected.

A sail with a 445 luff length clearly needs a 430 mast as a starting point.

The bend thing is perhaps interesting.
If you make a 4m mast 30cms longer then in theory you get the right IMCS stiffness as for a 430 mast.
But the bend curve will not be the same for three reasons.

Firstly if your 4m mast was a soft top then it would be relatively less-so at 430.
Secondly, most extensions have a little play in them, so that they don't jam in the mast, and that tolerance allows extra effective bend at the mast base, with the extension base/tack pulleys sitting further aft.
With a fully inserted extension which is more a 'snug fit' then you may find the opposite is true, with get extra stiffness created in the mast bottom section due to the doubling up of the tubing.

But the answer, as ever, is to use the correct mast length and recommended extension in the first place. And there ARE other 6m rigs that will fit on 4m masts - with just a 30 cms extension required.

On topic, has anyone here actually ever run a 4m mast with 48cms extension?

Basher said..
On topic, has anyone here actually ever run a 4m mast with 48cms extension?

not 48... yes to 44cm (before I lost that extension). Only when sailing flat-water in light-medium wind strength, and I was quite careful to not over-stress the boom-clamp.

Is he talking about an RDM or SDM (unclear), because I highly doubt an RDM would care where you clamp the boom.

Been using 45-46cm extension for years on some sails and here is my take on it that may be helpful for you. Afte15 years of windsurfing I feel all of us find what works for them and there is no wrong or right once you reach a certain level.

I never heard of 48cm RDM extension. You can drill a few holes but max I saw is 46 RDM. I have 3 masts: 400, 370, 310. All Nolimitz. (strange combo I know). I use my Naish Boxer 6.2 and HotSails KS3 5.8 on 400cm and all rest Naish Choppers on 370. Chopper M and S I sometimes set on 310cm mast to add softness. I'm not planning to buy 430cm mast ever nor buy a sail larger than 6m. Nor I will buy a sail that needs > 400cm + 46cm extension. If my 6.2 sail breaks, I don't care to replace it.. will foil..

My typical long extension usage:
----
Boxer 6.2: 400 + 46cm
KS3 5.8: 400 + 38cm
Chopper M: 310 + 42cm

I never had any problems. I sometimes sail in the ocean too. I jump a lot. Agree with people that if your sail gets trashed in waves good and in wrong position under water, it may break easier with very long extension. Also I feel that other factors are at play here or at least for me:

1. My level of windsurfing is pretty good.
2. I'm tall.
3. Fairly light weight and light on my feet.
4. I don't race (meaning I prefer to be a touch under powered than massively overpowered)

I also agree with a person who said that for RDMs higher boom attachment point probably not as critical. Again, all my experience.