View Full Version : Mast Extension
21st January 2008, 11:08 PM
I am buying a 7.8m sail for light wind sailing as I have sails in the following sizes at present; 5.0m, 5.7m and 6.5m. Hopefully this will get me out as much as possible this year.
My question is this. I currently have a standard 40 cm mast extension which I use with my 75% carbon 460 mast. The 7.8m has a 489 luff. I can buy a NP 48cm carbon extension. Is this worth getting and will it give me the ability to go to 508 or does it not work like that?
22nd January 2008, 08:17 AM
Yes, the longer (48 cm NP carbon) extension will allow you to go longer on the mast and this will allow you to use larger sails.....
Unless you are racing and using 100% carbon masts on huge sails (you aren't anywhere near that with only a 7.8 m2 rig, but even an 8.5 m2 rig isn't really all that large by todays standards) I'm not sure if there's a real reason to get an expensive carbon extension.
I use aluminum extensions that weigh an ounce or three more than carbon extensions, but I've never had an aluminum allow extension "snap off" the way carbon extensions sometimes do.
The aluminum will bend or deform long before you "break it off".
So, unless you are looking to "hyper extend" your 460 mast, I think it's better, safer and perhaps almost as cost effective to use the 40-42 cm extension you have and get a longer/stiffer 490 mast if you need to go beyond 500 cm.
Remember, you really want to use (or at least try) the recommended mast (size/length and stiffness/bend characteristics) if you get a larger (8.0 m2 to about 9.5 m2) sail.
The larger sail really will "need" the additional stiffness.
460 cm masts are in the range of MCS/IMCS 24-26 (constant curve or CC) whereas longer 490 cm masts are IMCS 28-30 (which is still a constant curve, just stiffer over the entire length of the mast.
If you try to "hyper-extend" a 460cm IMCS 24-26 mast to use it in a sail that was designed for a 490 cm IMCS 28-30 mast, you will not get the correct profile as the top of the sail will "dump off" long before you get the correct tension in the lower panels because the overall bend characteristics are simply not stiff enough.
Adding extensions to the bottom of a mast does not really change it's overal bend characteristics very much, if at all.
Hope this helps,
23rd January 2008, 01:31 AM
Thanks Roger, that is very helpful. Think I will hold on to my dosh when it comes to carb mast extensions. I have bought the Tush Lightening 7.8m which is compatible with a 25 mcs mast so extended by 27 cm I should be spot on with my 460 mast. The boom is set at 220 though and my max boom length is 222. Do you think that this will be ok?
What do you think the minimum wind speed for planning my Carve 145 with the 7.8m rig would be. I am currently 175 pounds (and falling as I get a bit fitter!) and 5' 6" (unfortunately cannot do much about my height!). Hoping it will be around 15 mph as we get alot of days in the Summer where the wind does not get above this. I sail at Eastbourne on the south coast of England - sea, South Easterly and a little choppy.
I am also going to Boston this year in September. We will travel around a bit after a little stay in the city. We finally end up at Hyannis for a week on the coast. Is this any good for a spot of windsurfing? Can't wait to sample the American restaurants again!
23rd January 2008, 09:23 PM
Well, if your sail has a boom/clew length of 220 cm and you only have a 222 cm boom, you may have a bit of a problem.
The stated boom length on most sails is the median length required.
If you want the sail more fat and juicy (more draft) then you can simply not outhaul the sail as much (back off on the downhaul a bit as well so the top does not loosen up quite so much) and you will have an OK boom length with your 222 cm.
For median, if your Tush Lightning needs only 220 cm then you would be OK there as well with normal downhaul, but it leaves you with almost nothing if the wind comes up and you want to flatten your rig a bit.
Where you will really have the problem is when the wind is up (for this sail) and you want to add additional downhaul to get more top twist and flatten the mid level panels a bit more.
Anytime you downhaul more, you bend the mast more, and this causes the required clew length to increase (quite a bit on some sails).
Now you have the problem of a longer clew length and no way to extend your boom.
Also, booms all tend to be a bit more bendy and flimsy when extended to the max. possible. This is due to a very minimal tube overlap ( outer main tube over lapping the inner tail extension tube.
I like to stay at least 10 cm longer than what the sail requires (in your case that would mean a boom length of 230 cm min.) plus a little bit more tube overlap simply gives you a stronger boom with a mre solid feel.
As far as getting planing on your Carve 145 with the 7.8 m2 Tush Lightning, I think you will be planing pretty easily in a solid 14 knots and with some pumping and heading offwind to get up to speed, you might get going in 12 knots at your weight.
It will depend on your technique and how you rig the 7.8 m2 Tush.
Make it fat juicy and drafty and you can expect quite a bit of low wind power.
Rig your sail more lean and fast and you won't get going so early (or as easily) but you will be able to handle significantly more wind.
Boston in September should be quite good.
There are some places to sail right near Boston, but I'm not sure about renting gear there.
Most of the shops that used to be in Boston have moved down into the Narragansett Bay area or out on Cape Cod.
You will be fairly near the shops when you are in Hyannis, and there's a great sailing area just down the road.
So, when you pick a rental car, get an SUV or something with racks, drive out to the WS shops near Bourne and Falmouth, rent your gear and go sailing.
Here are a couple of links to shops I know in that area:
http://www.canamsailcraft.com/ (In Boston)
If you decide to make a side trip to the South, come down to Cape Hatteras and look me up!
Hope this helps,
24th January 2008, 12:12 AM
Thanks for the advice, particularly regarding the Hyannis sailing which I will look in to. I would love to get to your part of of the world but probably not this time. Hopefully on another trip.
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