Can you ever have too much draft?

[Bill Roosa]

Not sure how your boat is set up but on my mid boom sheet when you let it out the sheet the boom moves UP and OUTBOARD. Up making the sail twist and increasing chamber in the lower sail and outboard decreasing the AOA. I don't really think of AOA in a gust the way you guys do apparently, a gust causes the apparent wind to move forward decreasing the AOA (and automagically depowering the main!!!)(but not that much), letting out the sheet or traveler DECREASES the AOA even further (depowering the main). Not at all sure why youall are saying it increases the AOA.
AOA is the angle between the apparent wind and the line horizontal between the leach and luft (at any horizontal point on the sail)
Perhaps I'm not reading my Annapolis seamanship correctly.

 

[Scott T-Bird]

That's funny ...

a gust causes the apparent wind to move forward decreasing the AOA (and automagically depowering the main

Perhaps I'm not reading my Annapolis seamanship correctly.

Bill, you must be sailing backwards! On my boat, the apparent wind moves aft in a gust.

As Jackdaw says ... ease out, steer up, sheet in as the gust gives you a lift!

I usually just steer up but I'm going to try to change that habit!

 

[Scott T-Bird]

By dumping the sheet however, you have now, in addition, twisted off the top making that part of the sail completely ineffective and not working at all to drive the boat.

Yes, that is precisely the point Jackdaw is suggesting is the best reaction (fastest overall boat speed) in overpowering conditions during a race, when reducing sail area is a losing compromise.

The difference is that blading is more effective in puffs where the whole sail working efficiently is faster vs twist in more boisterous wind conditions where the gusts are overpowering and spilling the wind at the top allows control without having to throw in a reef.

BTW, I do keep the vang snug, but I think it stretches. In my opinion, a soft vang is not very effective in upwind legs as you ease the mainsheet. The boom will still lift. I can say it is vang sheeting, but that don't make it so. Maybe it helps keep that twist in reasonable control, though.

 

[Stu Jackson]

As Jackdaw says ... ease out, steer up, sheet in as the gust gives you a lift!

I usually just steer up but I'm going to try to change that habit!

I've always felt lifts were helpful. Why wouldn't you?

 

[weinie]

I've always felt lifts were helpful. Why wouldn't you?

"In a velocity lift, you are...likely sailing too slowly for the increased wind speed. So rather than come up, which is the sailor's normal instinct, head off and ease sheets to build speed. Then once you near the target speed for the new wind strength, head up and trim sheets."
Dennis Connor - Sail Like a Champion p. 225

 

[Scott T-Bird]

Of course lifts are helpful ...

I've always felt lifts were helpful. Why wouldn't you?

Jackdaw (and weinie) says the 3-step process is faster (in boat speed) than my 1-step process.

 

[Bill Roosa]

So explain the vector math to me
I think:
using all relative bearings from the bow of the boat (0 degrees)
a 45 degree apparent wind at 10 knots
a 5 knot boat speed
So since I'm sailing into the wind the true wind is at a greater angle (>45 degrees) due to my boat speed bringing it forward. in a gust the wind will move aft........
OK I've convinced myself, I guess I use my tell-tails too much, takes the thinking out of it.

Still don't understand how letting out the boom will increase my AOA. If I let it out far enough it will luft (0 AOA)
thoughts?

 

[weinie]

 

[Bill Roosa]

So letting out the boom does DECREASE the AOA, or am I missing something?
In the picture above letting out he boom amounts to taking the right hand end of the sail up

 

[Daveinet]

AOA is like changing gears. at some point, if you are in too high of a gear, the "engine" does not have enough power to push the vehicle forward. So while bringing the boom in will increase speed, but only to a point, where the ratio is high enough that there is not enough forward force to move the boat forward.
So it depends on how easy the boat moves through the water as to what "ratio" or AOA can be used. Seems like there are two choices. If the wind speed increases, there is more force in the sail, so you can go either way. You can decrease AOA, which solves the healing problem, but then only uses the increased wind speed for increasing the boat speed. On the other hand, if you "top reef" meaning twist off the top of the sail, you are still keeping the same "gear ratio" or AOA, and just letting the increased force from the increase in wind speed. Seems to me that the best approach has a lot to do with your current boat speed, and possibly where you are relative to hull speed. If you are pretty close to hull speed, and your boat does not easily plane, then blading out will increase your power and possibly increase your speed some. However if you are planing, or your boat breaks into a plane easier, you may not need that extra power from decreasing AOA. You may be able to just reduce functional sail area.

Looking at it in this light, it seems like boats with a high sail area to weight ratio, are probably going to do better with "top reefing" as they probably have enough power for their current speed. Boat with lower sail area need all the power they can get.

Nor sure if any of this is right, but just trying to visualize logically and see if any conclusions can be drawn.

BTW: Are we OK to coin the expression of top reefing as term to describe excessive sail twist?

 

[Jackdaw]

AOA is like changing gears. at some point, if you are in too high of a gear, the "engine" does not have enough power to push the vehicle forward. So while bringing the boom in will increase speed, but only to a point, where the ratio is high enough that there is not enough forward force to move the boat forward.
So it depends on how easy the boat moves through the water as to what "ratio" or AOA can be used. Seems like there are two choices. If the wind speed increases, there is more force in the sail, so you can go either way. You can decrease AOA, which solves the healing problem, but then only uses the increased wind speed for increasing the boat speed. On the other hand, if you "top reef" meaning twist off the top of the sail, you are still keeping the same "gear ratio" or AOA, and just letting the increased force from the increase in wind speed. Seems to me that the best approach has a lot to do with your current boat speed, and possibly where you are relative to hull speed. If you are pretty close to hull speed, and your boat does not easily plane, then blading out will increase your power and possibly increase your speed some. However if you are planing, or your boat breaks into a plane easier, you may not need that extra power from decreasing AOA. You may be able to just reduce functional sail area.

Looking at it in this light, it seems like boats with a high sail area to weight ratio, are probably going to do better with "top reefing" as they probably have enough power for their current speed. Boat with lower sail area need all the power they can get.

Nor sure if any of this is right, but just trying to visualize logically and see if any conclusions can be drawn.

BTW: Are we OK to coin the expression of top reefing as term to describe excessive sail twist?

You're pretty close; most of your observations are on track.

I'm not sure of the term 'top reefing' but I see why you went there.... and I'd also disagree with the notion of 'excess twist', in fact it is the absolutely correct amount of twist for that situation.

You are correct in the notion that most modern high performance boats (SA/D > 20) are fully powered up and starting to over-power in 14-17 knots of breeze. At this point the game is not NOT about idealized sail trim, it is about sailing fast and flat.

I think it's funny that people are arguing against this point with theory and drawing of idealized sail flow from books. Most people know me here; I'd guess there are maybe 5 regulars on this board that care as much about sail management and boat speed as I do. I'm also a degreed scientist that understands how to conduct observations. So when I present a observable, measurable, repeatable phenomenon that is also backed by peer review, common sense and (in fact) theory and they argue the point with quotes from books on ideal sail flow it kind of makes me chuckle.

 

[Daveinet]

I'm not sure of the term 'top reefing' but I see why you went there.... and I'd also disagree with the notion of 'excess twist', in fact it is the absolutely correct amount of twist for that situation.

Yes, you are clarifying what I mean by "excessive twist". I was contrasting an assumption of "correct twist" meaning the correct twist to cause the AOA to be correct for the wind speed increase as you get higher off the water. I was using excessive twist to mean twisted far enough to result in no load (effective reef). HOWEVER, you are causing me to think this through even more so, and realizing that there isn't any optimum AOA for any part of the sail except for that which moves the boat at the fastest speed. As long as there is enough force to move the boat, one can keep increasing AOA over the whole sail, till the boat heels. I keep thinking back to motorcycles which often achieve a higher top speed in 5th gear, as opposed to 6th gear.

You are correct in the notion that most modern high performance boats (SA/D > 20) are fully powered up and starting to over-power in 14-17 knots of breeze. At this point the game is not NOT about idealized sail trim, it is about sailing fast and flat.

So I'll put one back at you, It is about idealized sail trim, idealized for the conditions and the boat capability . The optimum AOA is much better pictured in a performance multihull, where one can sail faster than the wind speed. Not because the boat "makes its own wind", but rather the increased AOA changes the "gear ratio". So once you can control the heel, then one is converting wind speed into boat speed, based on maximum AOA.

I've always theorized that once you have too much wind, that a lower aspect ratio is better, because for the same amount of force against the sail, it will produce less heeling.

 

[weinie]

Jackdaw,
I was just tossing my 2 cents in and hope i didnt come off like an ass. Apologies if i did.

Im sure id have a ton more to learn from you than you would ever have from me.

 

[Scott T-Bird]

Weinie, from where I stand, everything you posted is on target and appreciated. All worthy of discussion, that's for sure. That's why I like it here, whether we're argumentative or not ...

 

[Jackdaw]

Jackdaw,
I was just tossing my 2 cents in and hope i didnt come off like an ass. Apologies if i did.

Im sure id have a ton more to learn from you than you would ever have from me.

No worries at all. All good and +1 to what Scott said!

 

[Roadking Larry]

Just when I think I'm almost starting to get a grasp on sail trim along comes this thread.

Great stuff guys, much appreciated.

 

[jstyers]

Terrific Thread

What a great read! Passionate and informed insight from multiple points of view. I thoroughly enjoyed this. Thanks for the education and explanations. I grasped only a fraction but I'm fired up to get out and experiment!

 

[Daveinet]

Sorry to switch subjects, but I may have found where my boat speed went, which is what triggered this thread. I digging around trying to figure out where to mount my fish finder, which I plan to use for depth and speed. In looking through the center board slot, I found my center board has a very significant amount of rust on it. When I got the boat last year, the board had some surface stains on it, but no real penetrating rust. Now there is rust that is pitted over most of the board. So can anyone confirm that much rust will knock a knot or more off the boat boat speed?

 

[Jackdaw]

Now there is rust that is pitted over most of the board. So can anyone confirm that much rust will knock a knot or more off the boat boat speed?

No. Some but very little, in particular not when in enough breeze to get you moving well. What it will do is effect your ability to point. Loss of attached flow on the keel will destroy that.

 

[Daveinet]

Interesting. I did notice some difficulty sailing up wind. Last year this boat would sail any direction you wanted to go. I blamed it on lack of speed, but maybe not. This time sailing, I actually missed a tack. First time that was ever even a remote issue with this boat.

Hopefully I can get the boat in the water again this weekend. The weather has been so lousy on the weekends, I've not been able to sail.