GNAV v's Kicker

Now one of the burning reasons for returning here and potentially facing
another firestorm was because of this question which has been vexing
me. After travelling the best part of 40 miles without one how effective is
a GNAV really?

Now I haven't had a great deal of experience of conventional kickers, my
Laser 3000 had one, but the Musto had a wiered cantilever thing and the
RS and my Alto both have Gnavs.

I am wondering, if the GNAV actually does the job that the original kicker
came about to do as well as it did.

So to refresh my recollection of how kickers came about some old boy
noticed without one, the older style sails would lift the end of the boom,
collapse the leech, more air escapes than required, boat slows down, or
more the reverse of that, he found by additionally pulling the boom down
it kept the leech tight when required, or so I assume I forget who it was,
some wooden masted boat it was that long ago and he won by quite a big
margin.

We used to mess about with boom vangs in the early days of windsurf
racing when we had no full battens and CYT sails, but they made no
appreciable difference and along with topping lifts got left in historys
wastebasket.

The thing that appears to happen that is different with a GNAV, is the
bending of the lower mast section, I must admit it was more pronounced
on the RS than it is on the stiffer mast of my current ride, but it is still
there just the same. The effect this has, is to both flatten the sail and
narrow the entry at that point of the foil, making it shallow, so rather
than just powering up the sail with a tighter leech whilst retaining a nice
deep foil, it has the opposite effect.

So that's just my perception, I'm wondering if anyone else has any recent
experience of both systems, I'm almost of the view that having both
would be beneficial. O.K. Jumanji might have to divert his stampede and I
realise that is a bonus for lots of boats.

But does this happen? Do other craft combine both, Does anyone else
feel the GNAV aint quite as effective as a full blown kicker system..

Am I placing to much importance on it, it's all you hear folk talking about,
kicker this kicker that, is it boat park rhetoric?

I don't think I can, the boom would probably fall off the way it's cobbled
together right now, round gooseneck into a square hole, but I have been
thinking about it adding one in parallel, amazing how having to sail without
anything focusses the mind.

Well an here's another redundancy, it's rear sheeted, in fact the sail is
hopelessly inefficient unless I'm almost block to block it's that slack leeched.
(There again if it hadn't been this year we'd have stayed on the shore).

So you really need the Gnav to be functioning if you want to sail sheeted out
or your left with a flogging mess where the main should be..

Edited by G.R.F.

A conventional kicker produces a forward thrust at the gooseneck which is proportional to the amount of kicker tension (thus proportional to the leech tension) which induces bend (there may be strut(s) or lower(s) to counteract it).  The kicker pulls back at the heel of the mast with a similarly proportional force, but because it's at the heel it has no effect.   So put simply, more kicker equals more bend trying to be induced at the gooseneck.

A gnav swaps these 2 forces over - the forward thrust is induced further up the mast where the hardware meets the mast.   This is countered by the boom being thrust backwards with a similarly proportional force.  In this case the backward force on the boom (which presumably is bolted to the gooseneck in some way otherwise it would just fall off) will to some extent mitigate the forward force at the top of the lever.  In practice this 'push-me-pull-me' act some way up from the heel of the mast will be trying to induce an S-bend - imagine you've got a long whippy cane, both ends clamped, and then you get hold of it with both hands and pull with one hand whilst you push with the other.

I would have thought from the above that the gnav would induce less bend, albeit subject to positioning of struts/lowers/gooseneck/heel etc.  That's an intuitive guess rather than an engineering/mathematical proof - although it wouldn't take too much of an engineer to come up with the proof (or otherwise).

The only boat I've sailed with a gnav is an RS300 - it's the best kicker system I've ever used.  It automatically gears - the more tension you've got the more purchase you have due to the way the angle of the lever changes as you wind it on.

Mike

You could try one of these.

A Temple vang. No funny mast bending to deal with and improved room in the cock pit. Less blocks / wire etc
.

GRF,

The temple vang is basically a prodder extending out of the back of the foredeck. The kicker is then attached in a vertical plane between the prodder and the boom. In theory this only increases leech tension without all the lower mast bending. The picture shown by Jack shows the prodder on the mast stump.

However there are drawbacks with the temple vang. Sometimes it is desirable to induce bend in the lower mast. For this reason the Scorpions experimented with having both a conventional kicker and a temple vang.

I have to say though I reckon there is more chance of snagging yourself on the prodder than there is of getting caught by a standard kicker.

Alternatively GRF, you could fit your boat with a full width cockpit traveller and then you'd only need the kicker for downwind work. Sheet the main on hard upwind to control leech tension and play the traveller!