Spinnaker boat, lee helm

Factory kite boats may drive much differently than a boat with a kite added. I had a N6.0 with a kite. There was quite a bit of lee helm with the kite up, on my N20, the boat is perfectly balanced.

But what is it about an N20 that allows it to be balanced downwind? Is it that the pole length and the kite foot length were better chosen?

It is most likely many factors combined. The N20 was designed from the very beginning with a spin in mind. The balance is probably a combination of sail area distribution (large main, small jib), dagger board location and aspect ratio, spin size, pole lenght etc. I am no expert, only speculating.

The only time I feel lee helm is when the spin is overtrimmed AND the main traveler is not high enough OR the main sheet is not tight enough.

I believe most of it (or lack thereof) has to do with the rake of the rudders and getting them very nearly balanced on their lift with the pivot point. If they're balanced, you won't feel any helm either way - I tune mine for a touch of weather helm upwind and it usually works out to a little lee helm downwind (even on the 20).

But the rake of the rudders doesn't balance the helm, just makes it feel like its balanced, right?

True - but compared to the alternative of moving the daggerboard trunks....

No catamaran is balanced so there is no load on the rudders - all rudders carry a bit of the side loading. The I20 carries a tremendous load on the rudders and you can stall them by sheeting the main too quickly after gusts and before the water flow over the foils is at a peak. I've seen plenty of rudders break just from the typical sailing side loads incurred on a 20 yet it feels balanced.

I don't know how much load is good load, but the rudders really do carry a lot more than you would think.

Are you leaving the main traveller central?
Coming from a 2 sail boat, you will be used to dumping a large amount of main traveller for downwind. F18s and 20s will go around the course with the traveller in the same place [except in light winds].

Ah, that makes a lot of sense. So one solution to my problem might be to rake my rig back and then re-balance the ruders.

Do you think the N20 rudders would be more or less likely to stall when highly loaded than the older Nacra rudder design?

I was trying to keep the telltales on the main flowing, which usually meant traveling out about a foot.

I won the regatta against boats I used to sail even with the first time with the new rig, so I don't think I was terribly slow. I still would have won with an F18 Portsmouth number, and would have tied for 2nd with an I20 Portsmouth number.

Congrats and hope Klamath was fun!

Some lee helm may be

normal

simply because you're hoisting a huge amount of sail in front of the center of resistance.

You could try a little more mast rake. But you'll probably find that there's a balance between weather helm upwind and lee helm downwind.

The new 20 rudders are definitely less likely to stall - the old pin-style rudders were very prone to stalling. I wouldn't change your rudders or the rake in the mast for whatever wind strength you were sailing in - there's nothing wrong with them and I wouldn't say there's anything wrong with the lee helm you are experiencing. You did win, afterall.

I would rake your rudders more forward to try and balance them a little more if the lee helm is uncomfortable. Certainly too much lee helm can make sailing fast difficult just from the pull on the tiller. You may have to grind a little on the rudder itself to get enough clearance for additional rake.

Thanks! Klamath was lots of fun, and for whatever reason the new rig worked perfectly. I thought we'd have lots of tweaking to do and lots of

we're going to die

moments. But actually with the self-tacker and the SNU snuffer it is very easy to sail.

The boat doesn't quite go upwind like it used to, so a little more rake might pay off there as well.

Yup, I'm fully raked on the rudders right now, so I'll have to grind to get more. I've been thinking of upgrading to the N20 rudders for next year - my current rudders are getting to be more patch than original anyway.

Rhino, are you using the original nacra 5.8 rudders? if you are they're probably too small, especially if you are using a spin.

Not that it would affect your helm. When I sailed the nacra 5.8 worlds a few years back the top guys were swapping out the standard 5.8 rudders with nacra 5.0 rudders which are bigger and the boat was supposedly going better.

And yes, if you don't have much rake on the mast, I would certainly put some in.

How are you setting your daggers?

The rudders are the original 5.8 rudders. I didn't realize that the 5.0 had bigger rudders.

I set the daggerboards about halfway up on the downwind legs. I figured pulling them all the way up would make the steering squirrely.

I certainly agree that you don't want your rudders to be too small! Otherwise you can literally spin out. My 5.0 rudders did not look bigger than the 5.8 rudders, but I could be wrong about that.

Rhino, as you know, the name of the game is to keep it wild the whole way downwind; the daggerboards are crucial to popping up the hull; how much the board should be down varies. My boat has much smaller boards than yours, and I only start pulling them up when it's above about 12kts.

It seems to me that the N20 rudders are smaller than the 5.8 rudders. Very different shape, though. I'd be more inclined to give the N20 rudders a try than the 5.0 rudders.

I'll have to start playing with the daggerboard settings. I would guess leaving them down will produce more lee helm, but help get the windward hull out of the water.

Are you referring to the original or newer N20 rudders? The original are much slimmer than the later ones.

Didn't know that there were two designs. The only N20 I've seen in person is Dave Spain's boat, which I think is fairly old.

There are actually three different I20 rudders:

The original

pin head

The

butterknife

(which came on boats for only three or four months - but was common on '04 and '05 F18s)
The

spade

- current fat, clover leaf looking rudder blade.

I use generation 1, 2, and 3 when describing them.

Spain's are generation 1, the narrow ones.

I still prefer those rudders - they do stall but because they are sensitive to proper sail trim...you can learn a little by learning to keep them from stalling.

how do you tell when a rudder stalls?

you move the tiller and nothing happens! <img src=

alt=

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And your crew yells

W T F

as you careen out of control... Usually happened to me when reaching too hot with the spin up and trying to drive down too quickly..

You feel it - it's pretty dramatic...you turn and the only thing that happens is a really huge rooster tail at the back of the hulls. With it blowing about 12 to 15, sail upwind and try to bear away sharply without easing the mainsail and observe the stalling. Do this on a crowded start line trying to duck a boat and observe the odor coming from your crew's shorts. <img src=

alt=

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If you're really cooking - like downwind with the chute up in waves, you can feel the rudders start to lose traction if you turn too sharply.