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 Post subject: sail trim question
PostPosted: Wed Nov 04, 2015 7:03 pm 
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Location: South Carolina
When beating into the wind, I feel the my Hobie 16 slow as I head up. The reason I head up is because the lee tell tales on the main are flying up or down, not straight back. This is telling me that my main is stalling and I can point up (or let out the sail) in order to get the wind flowing on the lee side again. Usually it is the very top tale doing this, sometimes the middle and top. Sometimes the jib lee tales flutter around.

I noticed this in about 6 knots of wind. I checked my mast rotation, and it is correct. I usually have my main traveler close to the boat's center. I usually leave my jib traveler car outboard a bit, and attach my jib sheets to the lower most hole on the clew to ensure I am not closing off the air flow. But I don't see too much difference when pulling the car all the way inboard.

Any thoughts on why this is happening? Is my fastest time to the mark pointing high but going slower? Or fall off, let the lee tales twirl around?

Thanks!


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 Post subject: Re: sail trim question
PostPosted: Thu Nov 05, 2015 6:10 pm 
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Sounds kind of anachronistic. Are your sails close-hauled beating upwind? Were there big waves? Were you close to any obstructions (like trees on shore)?

I generally pay more attention to the outboard telltales so they don't show stall. Sometimes on a reach my top main telltale may twirl a bit but usually I can move the traveler and get the top to twist off properly (I have square top sails). Upwind I can watch for flow and see that I don't pinch too high or foot off too much. I don't use a VMG computer but you have a sense for your progress I'm sure. Upwind it seems pretty clear to me usually, downwind I'd say the angle depends on wind speed and waves.

Scott

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 Post subject: Re: sail trim question
PostPosted: Fri Nov 06, 2015 7:06 am 
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IMHO, many beginners get hung up on trying to make all the telltales fly at the same time. With the complex flows across the sails, they almost never will.

If you plotted boat speed vs. angle to the wind, you'll end up with something like this:
Image
There's no continuation of the plot line to 0° because the line would go almost straight to zero - like falling off a cliff. You can feel this "corner" on the plot when sailing - the boat loses speed rapidly.

When setting up a Hobie 16 for the first time on the beach, I'll have the main traveler centered and both jib travelers as far inboard as possible. Tack the jib as low as you can, using the pin of the shackle (not the bow) to secure it to the forestay adjuster:
Image
Raise the jib to the point of taking the slack out of the side stays - not super tight, but snug.

Raise the main and downhaul it enough to take the winkles out of the luff. Attach the main and jib blocks (center / 2nd from bottom) hole in the and sheet in snugly. Stand behind the boat and continue to sheet in the main until the leech starts to hook (goes to weather of the mast). Basically, you want the leech parallel to the mast.

Here's what a hooked leech looks like: (it's a 17, but the principle is the same)
Image

That little strip of red you see above the mast is the leech of the sail. This sail is oversheeted. Oversheeting is slow.

If you can't get the main sheeted in this far, you need to 1) reduce the stack height on your mainsheet system, or 2) reduce mast rake (tighten jib halyard more or loosen side stays). The objective is to have the leech of the main parallel to the mast with about 6" - 8" between the blocks.

With the main sheeted in, check the slot between the main and jib - the objective here is to have about 3" sheeting distance when the leech of the jib parallels the shape of the main. If you two-block the jib sheet before you get to that point, you can 1) reduce the stack-up of your jib blocks:
Image
or 2) move the jib tack up in the forestay adjuster or 3) reduce mast rake.

You leave some sheeting distance on both systems to allow for the flex of the rig when sailing. You will be able to easily two-block both systems once you get going in enough breeze.

Now go sailing in about 8 - 10 knots - good pressure, but not enough to trapeze. Sheet both sails in snugly (not quite two-blocked, but more than you had on the beach) and practice steering upwind. Provided your helm is balanced (that's a whole 'nuther topic), you should be able to feel the "edge of the cliff" fairly easily. The objective is to sail on the "edge," but not go over. It takes practice. In lumpy conditions, the edge becomes less distinct and it's better to ease the sails just a bit to develop more power to punch through the chop and not try to sail so close to the "edge."

To fine-tune the placement of the jib sheet on the clew plate, you need three sets of telltales in the jib - all about 1/3 back from the luff in the middle three panels. Sailing upwind, head up slowly and watch to see which windward telltale "breaks" (flips up) first - top or bottom. If the top one breaks first, there's too much twist in jib - move the sheets to a higher hole in the clew plate. If the bottom one breaks first, move the sheets down. You can also move the tack to adjust this. The objective is to get all the telltales to break at approximately the same time.

Once you've done all this adjusting - remember which holes you attached things to (use nail polish to mark them if you can't remember) and put a piece of electrical tape on the jib halyard at the mast's black band to mark it's position. That way, you can recreate your tuning quickly.

Now go play with your boat!


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 Post subject: Re: sail trim question
PostPosted: Fri Nov 06, 2015 8:18 am 
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That chart of angle to speed is interesting. I've never seen anything like that. But the shape of that curve threw me off a bit at first. Based on my experience on my H16 I think that shape might hold true at low wind speeds (like < 10) but going faster I would expect the plot to bulge out in the lower angles like this

Image

Still doesn't change the excellent rigging advice above, and the excellent advice to not obsess on the telltales too much. My most general rule is to make sure the lee tale is flowing first before worrying about the windward tale. When the pressure gets heavier I have no concerns about that inside tale pointing straight up if the back one is flowing, if that means I have control. Stay in control then get into the zen of it and you'll feel it (and maybe hear it) when you're doing the right things, which I am sure is not news to you.

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 Post subject: Re: sail trim question
PostPosted: Fri Nov 06, 2015 8:55 am 
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I.P. Freely wrote:
That chart of angle to speed is interesting. I've never seen anything like that. But the shape of that curve threw me off a bit at first. Based on my experience on my H16 I think that shape might hold true at low wind speeds (like < 10) but going faster I would expect the plot to bulge out in the lower angles like this

The Hobie 16 chart (it's called a polar velocity diagram) actually bulges out more than the one you showed. A comprehensive polar diagram has a line for different wind speeds (like the one you showed) so you can determine the VMG (Velocity Made Good) for different speeds and angles.

The Hobie 16 plot I showed has a single line, which I suspect is for about 10-12 kts of wind.

You determine maximum VMG by drawing a horizontal line tangent to the plot curve. For the Hobie 16, the maximum downwind VMG on that curve is ~9 kts @ 130° true wind angle. For your Multi 23 diagram, it's about 6 kts @ 130° on the "TWS 12nds" curve (not sure what "nds" is, but I'm assuming it's knots).


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 Post subject: Re: sail trim question
PostPosted: Fri Nov 06, 2015 9:24 am 
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Quote:
You determine maximum VMG by drawing a horizontal line tangent to the plot curve. For the Hobie 16, the maximum downwind VMG on that curve is ~9 kts @ 130° true wind angle. For your Multi 23 diagram, it's about 6 kts @ 130° on the "TWS 12nds" curve (not sure what "nds" is, but I'm assuming it's knots).


Thank you. I am learning new stuff all the time. I've seen VMG computers but the displays were only numeric. Having a live plot like this would be an interesting smart phone app if you entered a target waypoint and wind direction.

SC

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 Post subject: Re: sail trim question
PostPosted: Fri Nov 06, 2015 4:12 pm 
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Location: Harsens Island, Michigan
Matt, the knowledge that you have and are willing to share freely is amazing.

I just want to say, thank you!

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 Post subject: Re: sail trim question
PostPosted: Fri Nov 06, 2015 4:42 pm 
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I.P. Freely wrote:
Thank you. I am learning new stuff all the time. I've seen VMG computers but the displays were only numeric. Having a live plot like this would be an interesting smart phone app if you entered a target waypoint and wind direction.

If you have a GPS, you can download the track data into your computer and bring it into a program like GPS Action Replay to display the polar. It's not nearly as pretty, because the wind is never blowing just one velocity from one direction:
Image
To generate clean polars, you need wind speed and instruments tied into your GPS data (current adds another dimension of complexity, requiring boat speed instruments). Big boats have their polars programmed in to their instruments, so as a skipper, you strive to meet your "target speed" for a given wind angle and velocity. More instrumentation = more $, and makes it more like a video game than sailing a boat.


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 Post subject: Re: sail trim question
PostPosted: Sat Nov 07, 2015 2:13 pm 
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ASDASC wrote:
Matt, the knowledge that you have and are willing to share freely is amazing.

I just want to say, thank you!


X2!

Now all i need to do is read it over and over until i get it and can remember it, then apply it and understand.

When I see things like this it makes me realize how impossible to answer a question I've had is, which is,...if two boats sails are set the same and one goes faster does that mean I need new sails because his boat is 20 years newer? lol, MAYBE I do but with all that could be different in the details the only way someone could say would be looking at/sailing my boat I think would be the answer.

I really don't care to much about speed, Flying a hull and being trapped out are what I'm in it for, but speed is still great, certainly with another Hobie sailing next to you, you just can't help but try to be faster can ya? :) me neither.


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 Post subject: Re: sail trim question
PostPosted: Mon Nov 09, 2015 11:46 am 
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greensnopro wrote:



I really don't care to much about speed, Flying a hull and being trapped out are what I'm in it for, but speed is still great, certainly with another Hobie sailing next to you, you just can't help but try to be faster can ya? :) me neither.


That's how it all starts. Don't go for it !!! It's a trap !!! I use to be the same way. I just wanted to be out on the water, then one day, a boat just like mine whizzed by me with the two on board sticking off the side of the boat. Immediately, I knew that this is what I wanted to do, especially since I already had the boat. My suggestion is, "run for your life !!!" :lol: :lol: :lol:

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 Post subject: Re: sail trim question
PostPosted: Mon Nov 09, 2015 12:57 pm 
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Quote:
To generate clean polars, you need wind speed and instruments tied into your GPS data (current adds another dimension of complexity, requiring boat speed instruments).


I almost feel bad about hijacking this thread, but the VMG stuff is interesting to my geek side. I always thought of VMG as being used to measure your rate of progress toward a mark or waypoint, not that I race (except when there is another boat on the water). Back when we used to sail wing-and-wing downwind the change to a zig-zag strategy was explained to me in terms of VMG. The context was that you actually make it faster to the downwind mark by going a longer distance faster on reaches and gybing (in the right conditions) than by going straight at it on a full run, because of these speed/angle differences. Our charts seem to just show "land speed" at different angles, which I did not think of as Velocity Made Good. What do you call the concept of progress toward a mark?

I was thinking it would be interesting to have some kind of app that, if you just input a wind speed and direction (as constants), would show your projected rate of closure to some waypoint so you could try different angles to see how to get there fastest. But I agree, I'm not going to spend time looking at a screen when I am sailing - just a point of intellectual curiosity.

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 Post subject: Re: sail trim question
PostPosted: Mon Nov 09, 2015 3:26 pm 
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This stuff is exactly why I got annihilated in my first race last weekend. I didn't even come close to correcting up over anybody. I had the best start in the whole multihull (yes, even over the large corsair trimarans) fleet, but then I found out that long distance catamaran racing is completely different from short distance collegiate FJ sailing. Good tips on here, thanks all!

I'll worry about tout tales less in the future.

Is the rigging/tuning process described above for all wind velocities? Or does exactly what hole you attach here, and how far you rake the mast, differ for various wind velocities?


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 Post subject: Re: sail trim question
PostPosted: Mon Nov 09, 2015 4:44 pm 
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DavidBell47 wrote:
greensnopro wrote:



I really don't care to much about speed, Flying a hull and being trapped out are what I'm in it for, but speed is still great, certainly with another Hobie sailing next to you, you just can't help but try to be faster can ya? :) me neither.


That's how it all starts. Don't go for it !!! It's a trap !!! I use to be the same way. I just wanted to be out on the water, then one day, a boat just like mine whizzed by me with the two on board sticking off the side of the boat. Immediately, I knew that this is what I wanted to do, especially since I already had the boat. My suggestion is, "run for your life !!!" :lol: :lol: :lol:



To late, I got the boat in july, since then I used only a half tank of gas in the jet ski that i used to burn a tank a day, and all I think about is sailing and learning to do it better ! :lol:


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 Post subject: Re: sail trim question
PostPosted: Mon Nov 09, 2015 4:54 pm 
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BboySlug wrote:
This stuff is exactly why I got annihilated in my first race last weekend. I didn't even come close to correcting up over anybody. I had the best start in the whole multihull (yes, even over the large corsair trimarans) fleet, but then I found out that long distance catamaran racing is completely different from short distance collegiate FJ sailing. Good tips on here, thanks all!

I'll worry about tout tales less in the future.

Is the rigging/tuning process described above for all wind velocities? Or does exactly what hole you attach here, and how far you rake the mast, differ for various wind velocities?


yes kinda like you said, and I can't remember what I read on here but I "think" more wind more rake, and lots of other things lol
so good luck! someone will maybe link it but if you start scrolling back you will find a fairly detailed tuning discussion that addresses wind velocity


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 Post subject: Re: sail trim question
PostPosted: Tue Nov 10, 2015 6:15 am 
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I.P. Freely wrote:
I always thought of VMG as being used to measure your rate of progress toward a mark or waypoint. Back when we used to sail wing-and-wing downwind the change to a zig-zag strategy was explained to me in terms of VMG. The context was that you actually make it faster to the downwind mark by going a longer distance faster on reaches and gybing (in the right conditions) than by going straight at it on a full run, because of these speed/angle differences. Our charts seem to just show "land speed" at different angles, which I did not think of as Velocity Made Good. What do you call the concept of progress toward a mark?

VMG is a velocity vector with a specific direction - not to a specific point. For example, if the wind is from due south (180°) at 10 kts, and you're headed towards a mark dead downwind (0°) with a jibing angle of 90°. The boat will do ~7 kts dead downwind. To make gains by tacking downwind, your VMG needs to be >7 kts. With a little trigonometry, your can calculate that the tacking downwind speed over the ground needs to be 9.9 kts in order to have a VMG of 7 kts to the 0° direction.

If the mark is a long way away, then the VMG and progress towards the mark (which, if it has a name, I can't think of it right now) are very close, but as soon as the angle to the mark changes a few +/- degrees, then they diverge - until the extreme case of the layline to the mark, when progress to the mark on one tack will be 0 kts and your actual boatspeed on the other tack since you're pointed right at the mark.

Quote:
I was thinking it would be interesting to have some kind of app that, if you just input a wind speed and direction (as constants), would show your projected rate of closure to some waypoint so you could try different angles to see how to get there fastest. But I agree, I'm not going to spend time looking at a screen when I am sailing - just a point of intellectual curiosity.

You can do this with a GPS (or a GPS app on a smart phone) - just set a waypoint that is sufficiently far away (200 miles) in the direction you want so that the bearing angle doesn't change significantly when you're tacking back and forth.


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