Jerry
I have followed this discussion with interest since I am the designer/builder of the Stealth F16, one of the boats mentioned.
Most of the posters are right, and are actually agreeing with each other, but unfortunately the argument has become a personal one and the answers to your questions are a bit lost in the mud that's flying around.
Your question about whether spinnakers produce dificulties in certain types of boats.
Well I think that it is too simplistic to put cats into these two camps of Hoppers and ploughers, my experience is that all the cats around today are pretty easy to sail with spinnakers. Some respond better than others but I suggest that the main difference is in the developement that has gone into the boat in the first place so that it is more a question of refinement rather than, the effect that the hull shape has.
next on the point of weather helm or lee helm
It is a simple fact of life that if you stick up a spinnaker you move the centre of effort forwards, now if you have a balanced boat to begin with you will end up with lee helm, if the boat is balanced with the kite up, there must have been weather helm before you put it up. You cannot have a balanced boat both ways unless you mave the daggerboards forward when you put the kite up.
Some boats, the I20 is one, have very balanced rudders, so that you cannot tell if there is weather or lee helm, but it is still there.
Bill is right in that his design will make a more neutral helm when the kite is up, but he failed to mention that his design must have more weather helm when the kite is down, its just that he has balanced rudders so you can't feel it.
The real question is whether or not any of this is a problem, and the answer is that it is not, just select a boat that has been designed by a good company, and develeloped with the spinnaker on it and you will have no problems with any of this.
Any of the boats you are looking at will do in this case
Bill,
I have some questions on slip angles going to WINDWARD, and ballpark numbers are good enough, for as they say 'government work'. What kind of relative numerical difference between board vs boardless?
For say SC20 catamaran (which I have had the pleasure to sail on):
Is slip angle more practical as a design tool, than for practicing by yourself to improve VMG?
The slower you go the higher the slip angle, and the converse, the faster you go the slip angle approaches zero to the same true wind angle?
Going to windward, what angle to the true wind will the slip angle begin to zero out?
(mathematically never, but for practical use go to windward)
Is there a boat speed at which point the slip angle almost zero's out?
Did anything supprise you, while you were doing your research on SA?
ie. the rate of change of slip angle from 1kn to 10kn.
Using a slip angle you can determine the optimum amount of board to use for a given wind speed? and if so, any comments?
The higher a cat points into the wind the higher the SA? For practicing to improve VMG would you sail lower angles to the true wind until SA plateau's out? If so when does it plateau out?
Bill, should I buy North's SA meter-z1, or Elvstrom's SA A04-meter? (LOL)
Thanks again,
Chris
Thanks for making the answer so clear, John, as with all your advice. A while back I asked how to get rid of lee-helm, the answer came from John : Rake the mast back until the lee-helm is neutral, or at least not too unmanageable. Then rake rudders forward so that the weatherhelm upwind from increased mast rake is not a problem. It`s still there, it still loads up the rudders, but it isn`t transferred to the tiller, so you get to keep your shoulder joint in one piece. Apparently some weatherhelm helps the boat track upwind as the loaded up rudders create lift. (If I`m mis-informed here please don`t kill me, I spend my time designing buildings, not boats, and very seldom consider the hydrodynamic properties of concrete, although I imagine they`re not worth discussing. No, this is not an invitation to ressurect the thread about concrete canoes ).
Although my boat was designed without a spinnaker in mind, I`ve found that this advice has helped tame the rudders.
Cheers
Steve
“Perhaps Maugan was a bit strong...but the manufacturer and designer bashing is wearing on me too. If everybody else is so bad why do they sell so many boats?”
Come on Jake…you already know the answer to that one…LOL…MARKETING!!!! More than quality of design... More than quality materials... More than after the sale support...it’s all about MARKETING! If you can get a person emotionally involved with a product, logic goes out the window.
What do you think was the cause of Hobie selling so many H16? A stellar beach cat design? Or the most brilliant advertising campaign in catamaran history selling the “Hobie way of life”?
How can you get mad at Bill for stating known facts about the H 16?? How can we move toward better catamaran designs if everyone pretends “it doesn’t get any better than this”, and ignores the glaring short comings of past designs? They call that denial…LOL
What I see in this thread is, logic clashing with emotional brand loyalty.
Bob
FYI:
I'm far from brand loyal to hobie. In fact, I'm still quite bitter about quite a few things about my boat, and feel that hobie should have given me a more straight forward answer about it.
Which is why my next boat is non-hobie. Its actually manufacturer-free, which I love.
Hi Jerry,
In answer to your first question: 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.
Further discussion:
How did we get where we are? Why are CB trunks on beach cats located at or very close to the shroud chainplates? Answer: Because that is where the CB trunk should be located relative to the CE for the SLOOP rigged sail plan. Now add the spinnaker. Does anything change relative to the CE and CLR locations? I think so and the proof of it being so is that so many boats have lee helm with spinnakers up. What can be done about this? Lean the mast back which moves the spinnaker aft. This moves the whole sail plan CE aft and brings the CE and CLR into better alignment with spinnaker up and may be sufficient to get close to a neutral helm for most spinaker sailing situations. Now, how does this leave the CE/CLR situation without spinnaker or sloop rigged? We have moved the CE well aft from the normal position with the large amount of mast rake. We have unloaded the daggerboard and loaded up the rudder. (Remember the N6.0s, Worrell boats, with spinnakers; the masts were raked way way back. This was the correct trim because they were going to sail all day with spinnakers up.) This will make the rudder prone to stall sailing to windward but once you know it is touchy, you can live with it. A larger rudder would be an improvement in this trim/balance situation because the rudder is carrying a larger side force than it was originally designed for.
This situation of trying control the CE migration due to adding the spinnaker to the sloop rig led me to the CLR design scheme that I call "shared lift". The increased sharing of sail generated side force is being sharred between the centerboard and an oversize rudder. Instead of running a large amount of mast rake to move the CE aft, I have chosen to move the CB trunk forward and run a more normal amount of mast rake. The rudder side load increases with more mast rake or moving the CB trunk forward so the rudder is upsized in both cases. The CB side load has been reduced; it can be downsized. Sizing the centerboard and rudder to match the loads they carry will reduce the drag they generate due to making lift.
Good Sailing,
Bill
Hi Bill,
I have often wondered why there are not good slip (call them leeway) indicators on the market. They give information that is not unavailable from a GPS and a compass in practice. An inexpensive flux gate compass might be within 2 or 3 degrees - just no good at all for measuring leeway.
One tough part is keeping the vane perpendicular to the water. A pendulum seems like a good way, but then you have to damp the swing somehow (maybe use an Airpot?) AYRS once had plans for a leeway indicator but it mounted to the bottom of the hull, and did not remain vertical. Maybe there is an updated version. Now, if you could indicate apparent wind direction on the same display...
I really appreciate the technical portions of your posts.
Thanks for taking the time.
Talk to you later
-colin
Bill,
What I understand from your post is that putting a larger rudder set on the boat will have the same effect of "load sharing" whether you move the CB forward, or rake the mast back ?
If you upsize the rudders, is it necessary to make the CB`s smaller in area ?
Obviously can`t move my cb cases forward, so I`ll go with the "more rake" option.
Steve
I think you guys are making this way more complicated than it needs to be.
All older designs that add a chute end up with lee helm because there COE was not designed to work with a chute. Some people try to correct for this some by raking the mast waaayyyy back but it can't correct for all of the lee helm.
New boats like the I20 have Neutral helm upwind and downwind because they were designed to balance the helm. They moved the front crossbar forward to balance the boat. The I18 is also designed like this.
However the Hobie Tiger still seems to suffer from lee helm issues. However that lee helm doesn't seem to slow the Tiger down any as it is competitive with any F18.
I just heard this past Sunday that Performance Catamarans has a larger rudder now available for the I17R. It is not class legal yet but is available.
As it is now, I can only rack back so far until I get some rudder stalling problems going to windward.
Tom Turlington
I17R #124
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