Hi Colin,
Here's a trick; things are easier than they seem. The compass gives the direction the boat is headed. The GPS gives the direction of the path of the boat. The difference is the slip angle.
Good Slipping,
Bill

Hi Jerry,

I have been sailing/racing my I-17R since spring 2000. I have adjusted my rudders between neutral (no weather helm) going to weather and having "some" weather helm. In both modes, I experience some lee helm after raising the spinnaker. The amount seems minimal. I prefer the neutral setting going to weather...there are times I want to set the helm down to do something else. Under these conditions, I can set the helm down going downwind and not suffer significant change in speed or direction, although I try to minimize the time that I am not holding the tiller. I always let the tiller go when taking the spinnaker down, usually very close to the leeward mark. The I-17R behaves beautifiully all around the race course! In my 23 years of racing catamarans, 19 years on single-handed Catamarans, nothing is as much fun to sail as the I-17R!

Regarding Tom's comments on the new rudders, I would like to have the new rudders also! Although I have had my rudders stall, I have been able to get them to re-attach by oscillating the tiller. I think they would help with coming out of tacks, too (anytime the boat is going very slowly). We should contact Performance and get it made Class legal. Just join the I-17R Class first...they are the only ones who get a vote! Membership runs from 1-Jan thru 31-Dec, no matter when you join!

Hi Tom,
I think you now understand why this larger rudder is being made available.
Bill

Bill,

Exactly! I understood as soon as I read your post. I immediately thought about trying to get my rudders out of a stall once they went in.

I stopped getting too technically involved in the boat a couple years ago and decided instead to concentrate on the " nut on the tiller. " If I am in the ball park on setup, I am happy. But it sure is nice to know what causes what on some things. Thanks for taking the time to explain terms easy to understand.

Tom Turlington
B.A.History; Memphis State

I thought a small degree of weather helm upwind was a good thing on a boarded boat. Countering the helm with the rudders puts a slight angle of attack to the daggerboards making them generate lift to windward and compensate for some of the leeway.

Hi Steve,
Up sizing the rudders will help the rudder stalling problem when sailing to windward. You do not have to downsize the CBs. Leave them alone. My comments about upsizing and downsizing parts is for boat designers and sailors who build their own stuff.
Good Sailing,
Bill

Hi Bill,

Well, it is not quite that easy. Your leeway sensor idea is a much better idea. Ignoring the obvious problem of current there is an accuracy problem.

The bearing accuracy of a good commercial flux gate compass is plus or minus 2 degrees. The bearing repeatability is typically plus or minus 1 degree. I am interested in measuring leeway with greater accuracy than a 2 degree range, and certainly better than a 4 degree range (really absolute accuracy is what matters comparing to a GPS track). Four degrees is right around the leeway angle I am expecting when the hull just starts to fly on a close reach. I also want to be able to read leeway angle while sailing.

I know comparing course and heading works for finding the set and drift of ships with enough accuracy for navigation.
Sailboat performance is a different problem.

Talk to you later
Best regards
-colin

Thanks, John, for the great input.

I actually wasn't sure that all of these boats were designed for a spi (and balanced as such).

Still, lee helm aside, it does seem to be the experience of some good sailors that a modern spi equipped design can have a tendency to bury it's bow (and pitchpole) in heavier air (under spi) whereas others will not.

Jerry

Bill,

Thanks for your insights. One question, though:

You said "A balanced rudder, a rudder swept forward until 20% of the rudder area is in front of a line through the pintle axis, will feel neutral, light touch, no matter what the side load on the rudder"

Why is it that sweeping a rudder forward only 20% in relation to the pintle axis will fuly neutralize the helm (regardless of the load)? I understand why this shift in rudder position has the effect that it does, but would have guessed that it would be necessary to end up with closer to 50% of the rudder surface area in front and 50% behind the pintle axis to get the balanced helm you describe independent of rudder load.

Jerry

Hi Mike,

Good input. Do you know if the I17 was designed like the I18 and I20 with a more foreward front beam? And, in your (or other's) experience does the I17 have a neutral helm under spi like the I20 without over raking the mast and rudders?

Jerry

Jerry,
If a boat burys its bow with the spin up, the pole is too short. I have found from testing that the spin pole needs to be half as long as the spinnaker hoist. Also look at the Australian dinghys. These guys have been sailing/developing very high performance boats with spinnakers for 50 years. They know how to do it and they know what the proportions of the mechanical arrangement should be. Their poles are 50% plus as long as the hoist of the spinnaker and they lift the bows of their dinghys high. No more questions; no more argument. I'm convinced!
Bill

Sparky,

I appreciate hearing about your experience with the I17. If I understand you correctly, with an overall "neutral helm" (non-spi) you feel comfortable briefly letting go of the tiller even on a broad reach while snuffing the spi? Do you ever need to let go of the tiller going upwind?

Jerry

Thanks, Bill

Jerry

Hi Colin,
I think much of the error you are concerned about can be eliminated with proper testing technique. First repeat each test several times.
Take the same measurements on both port and starboard tacks.
When setting/approaching a position for taking a data point, approach the point from both sides and take data on point. That is sail low and rotate the boat clockwise to test point and then sail high and rotate the boat counter- clockwise to test point. I think this will wash out most of the errors you are concerned about.
Good Testing,
Bill

RBJ,

Like an aeronautical wing (or any basic foil shape), the rudder's center of lift is generated at it's thickest cross section (chord)...a dirty estimation would place this 1/3 of the way behind the leading edge.

Hey Jerry,

You ask if the I17R has neutral helm with spinnaker flying. It better! Think about it a second. We have no crew. We are lowering the spinnaker as we approach " C " mark. My boat will track straight after I have dropped the tiller and am in the process of lowering the spinnaker. Sometimes the damn think will get stuck or the halyard will tangle and I have to fix it all this being done while the boat is sailing itself.

Another thing, I'll let the engineers explain the why's and wherefore's, but the I17 does great in heavy air with the spinnaker up! Actually, the only reason boats were flipping during the heavy wind days at the Nationals was because the wind direction was jumping around so much after the front had gone through!

Tom

ps. The big bows on the I17 have save me on countless occasions however. I have buried the boat half way to the front beam and brought it back out before due to a wind change while flying the spin. This was because of the boat not me!

Thank you Bill,

I think I figured out a cheap way to measure leeway directly. Sorry for straying off topic. Thank you for the suggestions.

Best regards
-colin

Tom and Les,

Please descibe this 'stalling' of the rudder upwind,....this is the 3rd year I am sailing my 2000 I-17normal( no-spin, heck, I can barely handle this, as it is!),.......and we sail every week of the year here,.... and we get some light airs in the summer ( between hurricanes, you know..)

What exactly happens..?

What are you doing with your boards at this time?.....are they full down?

I have not seen this,.... yet.

regards,

Bruce
St. Croix

Bill,

Since we seem to be getting alot of Uni rig sailors asking questions here,....can you make a comment about the design of your 17?

Specifically in respect to what you decided to do with board placement?

regards,

Bruce
St. Croix
I-17n
ps.....it was 83 f again today,....13 E mph

Bruce,

It usually happens when the wind is up a bit. I cannot explain it though. The rudders just don't work right. I usually have to head up to get them to come out of the stall which slows the boat........not good. Of course, as we have learned, it is due to mast rack. I would tell you where my rack is but I am now running the single forestay setup so it would not help. If I was still running the two bridle wires ( I think they call them that ) I could tell you where the boat stalls out. At what setting.

I guess you could rack the hell out of your mast, like top hole and try it when the wind is 14-15 or so. But you have the shorter mast. Might not work!

Tom