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Extension Question
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jfeehan



Joined: 27 Jul 1998
Posts: 129

PostPosted: Thu Oct 19, 2017 9:06 am    Post subject: Reply with quote

U2U2U2 wrote:
NOVAAN wrote:
Do not remove the collar and set the mast all the way down. You will break your mast


I've done this a few times never a problem, never heard of one


i've wondered about this as well.

it certainly seems as though the loading is not as intended, but i think it would take a lot to split a skinny mast
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U2U2U2



Joined: 06 Jul 2001
Posts: 4382
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Thu Oct 19, 2017 9:19 am    Post subject: Reply with quote

The loading could be more rigid with little flex, but once downhauled , should not matter.
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NOVAAN



Joined: 28 Sep 1994
Posts: 895

PostPosted: Thu Oct 19, 2017 9:22 am    Post subject: Reply with quote

The cone shape of the extension has a wedging effect on the bottom of the mast. It will eventually split the mast. I did it years ago with a standard mast.
Might be better with a rdm mast but why take a chance. Mast expensive proper extension cheap.
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jfeehan



Joined: 27 Jul 1998
Posts: 129

PostPosted: Thu Oct 19, 2017 9:38 am    Post subject: Reply with quote

NOVAAN wrote:
The cone shape of the extension has a wedging effect on the bottom of the mast. It will eventually split the mast. I did it years ago with a standard mast.
Might be better with a rdm mast but why take a chance. Mast expensive proper extension cheap.


exactly - it's the tapering of the extension that is potentially problematic. it will impart a circumferential stress that the mast is not designed to withstand.

it might not be enough to matter.., or it might be...
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bred2shred



Joined: 02 May 2000
Posts: 892
Location: Jersey Shore

PostPosted: Thu Oct 19, 2017 10:02 am    Post subject: Reply with quote

It's been discussed before.

Removing the collar is certainly not how the extension was intended to be used and likely puts undue "hoop" stress on the bottom of the mast as the extension tries to wedge itself into the mast. I suspect the mast could also start to wear into the base extension since the load is not being dispersed over the entire bottom surface of the mast and instead only right along its inside edge.

There's no real way of knowing whether or not the mast will break (until it happens). But this is a risky move if the only benefit is to shave off one or two centimeters of mast height.

If you're going to do this, you might want to consider wrapping several layers of half inch or one inch wide uni-directional carbon around the bottom of your mast to increase the hoop strength and prevent splitting. Also take a piece of 100 grit sandpaper and knock off any sharp edge on the inside circumfrence of the bottom of the mast to make it nice and "friendly" where it contacts the base extension.

sm
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zirtaeb



Joined: 03 Jul 2009
Posts: 3621

PostPosted: Thu Oct 19, 2017 11:29 am    Post subject: Reply with quote

All this for 1.25 inches, on a wave sail?
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manuel



Joined: 08 Oct 2007
Posts: 666

PostPosted: Thu Oct 19, 2017 11:53 am    Post subject: Reply with quote

The mast bottom cut a small lip/rim into the extension.
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techno900



Joined: 28 Mar 2001
Posts: 2802

PostPosted: Thu Oct 19, 2017 2:19 pm    Post subject: Reply with quote

As zirtaeb said.......... If racing slalom, then closing the gap 1.5 inches may be a good idea, on freeride or wave set ups, little if any advantage other than it may allow the perfectionist to feel better.
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dhmark



Joined: 04 Sep 2007
Posts: 256

PostPosted: Thu Oct 19, 2017 3:47 pm    Post subject: Reply with quote

Perfectionist wouldn't have this problem because a sail wouldn't be designed for a mast with only 6 cm extension, would be designed for the next smaller size mast.
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isobars



Joined: 12 Dec 1999
Posts: 18334

PostPosted: Thu Oct 19, 2017 5:37 pm    Post subject: Reply with quote

1. The 6.9 has a 486 luff according to Goya.

2. Why would anyone make a sail with a non-adjustable mast cap?

3. Do NOT remove the collar, for reasons stated. Log splitters are wedge shaped for a reason.


Each chop impact or hop landing is another hammer blow to a base without its collar ... aka a mast splitter. One second, it's fine; the next bump or chop hop the mast is destroyed.

Do I feel lucky? Well, do ya, punk?/



4. Nobody not competing for a World Speed Record gives a damn about an inch or three of gap between the sail and the deck. That inch or three gap will matter infinitely less than an improperly tuned sail, and matters only when the entire foot of your sail is rubbing the deck in a broad, pure speed run on flat, flat water with a race sail on a speed board with the reigning world speed champ on your tail.

5. When's the last time THAT happened? Smile

6. 5. US base Chinook skinny aluminum bases have a 10.7 cm/4.2" minimum extension.
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