Mainsheets

The Gnav could be made to work really easily if two obstacles can be overcome:
(This assumes the adjustment track is on the boom as in the pics above with the mast a fixed point)
1. There needs to be a pivot(hinge) similar to that used on the goose neck(but much stronger I would suggest) This pivot needs to be exactly the same distance away from the mast as the pin in the goose neck so as the boom/gooseneck and the gnav can turn in harmony without inducing any twist.

2. The sail would need to be cut to accomodate the gnav. Great on one tack, but not good on the other. Or do we allow a double sided sail with cloth either side of the Gnav, (like the 29er?)

Then adjustment strings for the track if mounted on the boom would be fairly easy, or even easier if the fixed end was on the boom, and the adjuster track mounted on the mast.

Alternately have a look at what they use on the musto skiff, where they use a cranked lever mounted 'upsidedown' See picture 37
www.mustoskiff.com/downloads/Mus ... e-v0.2.pdf



Sinker



Edited by - sinker on 29 December 2005 21:22:01

Edited by - sinker on 29 December 2005 21:33:12

Excuse my ignorance but the second photo shown by Simon L. seems to show a conventional boom vang and also a short strut from boom to mast. Is this to prevent the boom from lifting? And if so it presumably replaces the boom vang. How is the strut attached to the mast?

The second picture is a bit confusing, the GNAV strut was just placed on top of the boom, the kicker was accidentally left in place. In practice you do not need a kicker, with the GNAV doing the same job, this obviously frees up the space under the boom at its forward end.

Proctor Masts are producing us a demo rig with GNAV, this should be available mid Jan. This will allow us to test this arrangement.

In the meantime their technical sheet may help you understand how it works and could be fitted :
www.seldenmast.co.uk/pdfs/tech_g ... -485-E.pdf

MCA Secretary

So to adjust the gnav you can control it by bits of rope on the mast. Can someone explain please how it adjusts by pulling some rope. Can these bits of rope be fed back to the helm to control or does it have to stay on the mast?
It doesn't appear to be as easy to adjust as the kicker we have now is.

Emma Barry

The controls can come down the side of the dagger case as at present to 2 turning blocks on the front bulkhead to take the control line from horizontal to vertical, the take this up to a block, to form a 2:1 then a single line from the block up to the boom and the GNAV adjustment car.
This is nearly identical to the set up on our existing cascade kicker system.

Hi Emma

The GNAV works by the bar pivoting on one end and sliding along the other end in a track on the mast or boom, Simons mockup looks like it will slide on the mast. By pulling on it using a system as Sinker suggests you increase the angle between the mast and boom, until the leech is tight.

The disadvantages I see are

Using a kicker (hard in heavy winds)when you tighten the leech the whole rig is also pulled back an advantage for the sailor, this may not be able to be acheived using a GNAV as the kicker has a better pivot point. This could be overcome with a centre main, but with small crews a 2:1 would be necessary and would the boat be able to take this stress?

Loss of sail area boats such as the 29er have huge sails, can the Mirror afford to lose even a square foot, also boats using a GNAV have fully battened sails will it have greater effects on the foot of our mainsail?

Happy New Year everyone

Paul

Thanks Paul and Sinker, I think I'll stick to the kicker.

Emma Barry

is the mirror ever

going to get a centre main

because i think it would ruin the boats

I agree, part of what makes the mirror different is the mast and gaff and the transom main and these are the things which could be changed. This is making the mirror into a different boat and providing so many different options. Is this fair?

Emma Barry

the mirror wouldn't be the same

here here!<img src=icon_smile_shock.gif border=0 align=middle><img src=icon_smile_dissapprove.gif border=0 align=middle>

64799 "Dolphin"

whats is that

meant to be