All of the discussion so far has been good but controling the wind is only half the battle. As a single handed sailor it is often difficult to control the rock of the boat in waves. Especialy when the boat has a shorter waterline length. My recomendation when encountering any waves going upwind (Boat waves, chop, swells) is to move your body weight aft. By doing so on a small light boat it raises the bows a good 3-6 inches, reduces the rock of the boat, and allows the daggerboards/rudders on the windward hull to stay in the water. Many of you will say this will drag the transoms but in waves with the boat punching and bouncing through the water it allows the boat attack the waves at an angle which is what you want.
One thing I wouldn't do is rake your mast back. I have seen H-17s do this but with lighter I-17s and T4.9 I would think it would give you so much weather helm you would be fighting the boat in a hard puff to keep it from going into irons. I will probably regret giving you all this information on the race course.
Keep sailing
J.P. the Terrible
Isotope #186 the Shark Boat
Mark,
I dont remember how the jib sheeting is arranged on the I20, other than it sheets to the front beam.
When my old N6.0 started to feel the way you describe, i knew it was time to move the jib trims outboard/aft, to allow the top of the jib to twist off and depower at the top.
Give it try...
Mike Parsons
F24 mkII #121 Littlewing
A-cat USA 151
J.P.
Unortunately I've never had the priveledge of sailing an Isotope, but from what you say it may behave a little differently than my Taipan.
I agree there are certain conditions where trapesing further back is a definite plus.
I spent a season trapesing back in the heavy stuff to finally conclude it didn't pay off every time.
Now I consider the situation carefully as trapesing back on the boat does affect the boats pointing.
Not a lot but just enough to make a difference when you need it.
This is particularly bad in conditions where the increased windage from lifting the bows helps you to be blown to leeward from the tops of the waves. If I can manage it, in these conditions bow down works better.
But like everything else in sailing it's just getting the right balance because everything is a compromise.
So I trapese as far forwad as I can without taking the waves hard on the front beam as this slows the boat. If this is happenning I move back, suffer the loss of pointing, and rewarded with higher speed and a good ride.
The thing that really gets me is big waves or chop and light to moderate wind.I always find this a real pain.
Go to :
http://www.geocities.com/kustzeilen/heeling_pitchpole.html
and see how at example 0,4 speed of wind boat velocity the heeling reduces by 11 % when steering up and the trust by 33 % !!
Wouter
Wouter
JP, Phill and all,
1. I was out yesterday,..a changed the mast rake,..foward one hole on the aft,...funny thing,..it took 2 hole forward on the bow plates to 'tension' it correctly (...the split forwards are not a 1:1 relationship to the aft plates??)
RESULT,....weather helm (...it was 100% neutral before)....do not know if I like or not.....the neutral helm is comfortable,....but I always wondered how close I 'really' was to optimal pointing,..as you can agree, .1 to 2 degree angle on a 30 minute upwind leg is going to add up.
2. The comment I have on the 'big wave' jumping,.....I hit a few yesterday,...there is an area off the North shore where the seas pile up( steep, not a ocean swell),.....upwind , in a big sea(starting at 4+feet crest to trough),..the boat flies off the crest( winds 20ish E),.....no problem,....it is the wind that now 'sees' the bottom of the tramp as a sail too,...this is the problem for me,...I need to keep up the speed to get thru this zone of 'exposed tramp-sail area",.....so bow-down and speed-up,...is essential for me at this point. I usually am around the centerboard for weight placement.
regards,
Bruce
St. Croix
ps. going sailing after work today,...gonna look at this weather helm thing more...??
Bruce,
I know what you mean about wind under the tramp.
I was sailing in about 20 knots or so (on a 16ft Cobra) in a big swell with a Hobie 16 just to leeward (you could almost step from one boat to the other). We were beating into the wind and swell. We went over this big one and the wind got under the Hobies tramp and, the Hobie became airborne, thefirst thing to touch the water was the tip of the Hobies mast. This really got my attention as we were so close.
This was nearly 20 years ago and in that one instant I realised the value of bow down in those conditions.
If I understand your post correctly you are saying you raked your mast forward and got weather helm?
This is most peculiar.
Raking my mast forward speeds up my tacking but as it moves the C/E in the sails forward it can reduce helm and possibly reduce pointing angle,
It may pay to recheck your other settings to make sure nothing else changed that could account for the increased helm. I always check to make sure only one thing is changed at a time and evaluated before a second change.
Anyway I envy you. It sounds like your having a good time.
I have another month before our sailing season gets underway.
Phill
Personally I don't believe in sailing with much weather helm on the I-17. The daggerboards are the same as those of the I-18 and therefor are bigger than needed for the loads of the single hander. I would de-rake the mast. Move up one whole aft and tension the rig with the turnbuckle in the forestay. Best trick is to place one aft stay one hole up and the other 2 holes up. Now tigthen the forestay (not to much) rig your mainsheet system to a trapwire move traveller out and pull hard on mainsheet. The aft stay that was moved up two hole will be easy to put in the right hole. Rig is now nice and firm.
Why not much rake on I-17. Baords are already big (bigger than Nacra unis etc) and neatral helm is nice. You might want a lttle weather helm (not as much as you have now) so that the rudder are not just extra wetted surface drag but contribute a little to pointing too, this is more efficient. So I would say something between what you have now and perfect neutral helm.
Wouter
Phill,
What part of the world do you sail in?
Bruce
St. Croix
WOuter,
1. OK,..will do.
2. Actually, the boards and rudders are the same on ALL the INTER line,....17, 18 and 20. (...at least here in the USA)
3. Exactly where are you from Wouter?
regards,
Bruce
St. Croix
Click on my name and you'll see my personal info. You can do the same with Phill's name and see where he sails.
Anyways, I'm from the Netherlands.
OKay I've read my own post again and thought that I should explain the
not so much weather helm
better. As you said boards are all the same on the I-XX line. Now you rig will produce considerable less sailforce than the I-18 for which the original boards were designed / optimized.
Your maximum righting moment Ratio is about 60 % (assuming you are 75 kg's and boat width is 2,6 mtr. and boat weights 150 kg's; I-18 150 kg crew weight, 2.6 mtr wide and 180 kg's boat)
Your rated sailarea ratio = 12,31 / 14,80 = 83 %
Mastheight ratio = 8,5 / 9 = 94 %
Heeling moment rig ratio = sailarea ratio * mastheight ratio = 78 %
So your rig is producing about 78 % of the heeling force as a I-18 would in the same windforce. Your maximum righting moment is only 60 % of that of the I-18. Your thrust ratio and heeling force ratio are then = 60 % / 78 % = 77 % of that of the I-18. This means that your daggerboards are about 1/77 % = 130 % is about 30 % to big for your loades. The daggerboards won't be working at their optimal angle of attack on your boat but at smaller angles. There is often a range of rather optimal angle but 30 % to big might be pushing it a bit. So when you go for alot of weather helm like many asymmetric sailor are eager to advice than the only thing you'll do in relatity is to take load from the already underlaoded daggerboard and load up you rudders. Thus the angle of attack of the daggerboards descreases even more and efficiency drops even more. You could end up (in the extreme case) with annoying weatherhelm and equal or less pointing ability due to a rapid decrease efficiency as a result of small angles of attack. You might want to lift your boards a bit before the other boats do for the same reason.
Anyways, with perfect neutral helm your daggerboards might be working rather acceptable but your rudders are simply added wetted surface only creating drag when not used for steering.
What is wise ?
Well, it can be argumented that alot of weatherhelm is bad. Perfect neutral helm can work quite well but is almost certainly not optimal for your rudder are doing nothing most of the time excepot adding drag. Best bet would be to lift your boards a bit and to induce a little weather helm This way you :
- Load up the daggerboards more per sq.ft. and go back to the optimal design angle of attack
- reduce daggerboard wetted surface that you don't really need
- Open up the possibility to induce weatherhelm without a negative backlash. This weatherhelm will load up your rudders so they will need to contribute to the sideforce resistance. Your rudders will still create drag but at least they now contribute positively. With neutral helm you will never use the rudders even when you lift the boards.
wel 30 % to big would make raising your boards by 30 % a good starting point.
Guys (Phill ?) , please correct me when I made an error
Wouter
(designing is all about striking the optimal balance between different features)
Wouter,
1. Ok,..see, now I know.
2. I am a numbers person. I am a professor at University of the Virgin Islands in CIS(comp info science).
3. The Danes have a rich history in these Islands ( St. Thomas, St. John and St. Croix) you know.
4.The site referreed to a few posts ago confirm what you have numerically plotted out,...he said lift the boards too( with out the math).
5.OK, ...NEXT QUESTION.......mast -spreader- configuration. The I-17 mast was previously set up on PRE -BEND mode( spreaders back 4 inches, super tight wire). I changed it to a 1 inch bach-tight configuration. This is the only other factor I changed ( ..the other factor being the mast rake foreard 1 hole,...which, I believe did not matter much).
6. Knowing the above factors, and that before there was 100% neutral helm,....and now it is weather helm and slo....comment?....analysis?,....suggestions...
regards,
Bruce
St. Croix
Bruce,
In raking your spreaders forward you have straightehed your mast.
It is great that you have adjustable spreaders because it will assit you in setting up your masts bending characteristics to your sail and body weight.
I suspect what you have done is made your sail fuller but more importantly you have made your leach tighter.
These things induce drag and also give the weather helm.
(Slow and weather helm.)
If you want to sail with your mast set like this you will have a lot of power off the breese but your going to pay for it upwind.
Once again you will either have to sail upwind with your traveller out further or get some more bend back into that mast.
As you sail upwind ease your traveller an inch at a time and eventually the helm should go nuetral again. If your mast is too straight you may still not be able to get it going the way you want it. Give it a try and see.
You have two variables to play with, diamond tension and spreader rake. They can both be set in different combinations to give the same prebend at rest but once you start applying sheet tension and downhaul the mast will behave differently. The more spreader rake the more the mast will bend under load.
If you're not happy I would suggest you measure your prebend now and then gradually remove pre bend and measure and document your settings and observations.
My veiw is that basically a lighter person will benefit more from more spreader rake and a heavier person less spreader rake even if the pre bend is the same unloaded.
There are a lot of variables and it is essential to keep track of your tuning progress that you do your best to change only one variable at a time.
Just something for you to think about.
Phill
Phill,
1. Looks like I will be adjusting things this weekend.
thanks
Bruce