More on Sail Twist

Nodak7 · Jul 17, 2012

Marc14857 said:
Hi Don

I'm working on fine tuning my boom vang on my Hunter 44..B&R rig in mast main no battens. Previous posts indicate that the vang has very little impact on these boats and I am trying to fix that by moving the attachment point to the boom further aft so the vang can be used for something other then supporting the boom. I've got it set up so when the boat is on a reach and the vang tension is light I have about 4 inches of vang travel to tighten the leech. What is confusing me is that in your sail trim guide you indicate that less tension increases twist and reduces power by spilling wind from the top of the sail. Makes sense to me. On the other hand on the sail trim card for a reach you indicate that as wind speed increases I'm supposed to tighten the leech aka less twist and flatten the sail. Wouldn't, I want to spill more wind as the wind speed increases? I understand the need for a flatter sail in higher winds by tensioning the outhaul but adjusting the vang has me confused.

Thanks
Marc

Marc,

You had the same idea as I did. I had always wondered why Hunter and Selden had attached the Vang in such a way that made it pretty much useless. I was just about to do it when I took a very close look at the design of the boat. I found that if you move the vang attachment aft 4" you have the possibility of lowering the boom below the arch and traveler. If you forget it is retracted and do a Tack or Jib you can damage your boom.

At least that was the case on my 33 and 41. Maybe you have not got that problem!

Nodak

Don Guillette · Jul 17, 2012

Marc: Expressed in a simple non scientific manner, because like Bill O'Reilly I'm a simple man and a common seaman, here's how you proceed through the range of wind speed. Let's take So Ca for the example where the winds are very light in the morning and proceed to pipe up through the day.

You'd start out with relatively flat sails with no twist because the wind doesn't have the power to get around the sail, even though you'd think a sail with draft depth (belly) would be more powerful in those conditions. You don't want to spill what little wind power you have with twisted sails so you're really cranked on the boom vang and adjust your fairleads. As the wind starts to slowly increase you gradually increse draft depth to power up the sails. When the wind speed gets up to say 12 knots and is still building you want to start to depower by gradually reducing draft depth (outhaul/fairleads) and twisting off the top 1/3 and spilling air, using your boom vang/fairleads. You're depowering the main and jib and keeping the boat on it's feet and under control.

Let's say you feel the boat slipping away from you. Twisting off the top isn't working because the bottom 2/3's are overpowering your efforts. Now you want to abandon that effort and flatten your sails as much as possible. On my Catalina 30, if the flat sail didn't work, I'd next roll up the jib. The next step would be to reef the main.

You're also working on the other 2 "elements of sail trim" draft positon and angle of attack to keep your boat under control. It's really a balancing act and like feathering an accelerator.

Obviously, it would be difficult to get all the above on a chart but the above is the idea I was trying to convey.

Nodak7 · Jul 17, 2012

Don Guillette said:
Let's say you feel the boat slipping away from you. Twisting off the top isn't working because the bottom 2/3's are overpowering your efforts. Now you want to abandon that effort and flatten your sails as much as possible. On my Catalina 30, if the flat sail didn't work, I'd next roll up the jib. The next step would be to reef the main.

Don, please clarify what you mean by "slipping away from you"?

Here is what I think you just said.

Light wind = flat sail
Increasing wind = fill the sail (increase draft) as wind increases
Once it begins to feel overpowered = Begin to flatten sail
If Overpowering continues = Reef sails

Does that summaries what you said?

Don Guillette · Jul 17, 2012

"Slipping away from you" means that when you lose your brakes in your car and it's like stepping on a grape or you're sitting in the cockpit and your rear end is sliding out from under you. Anyone out there ever experience those feelings??!!

Nodak7 · Jul 17, 2012

Don Guillette said:
"Slipping away from you" means that when you lose your brakes in your car and it's like stepping on a grape or you're sitting in the cockpit and your rear end is sliding out from under you. Anyone out there ever experience those feelings??!!

Would it be like seeing to much "weather helm"?

Nodak7 · Jul 17, 2012

Marc14857 said:
Nodak 7

I think that your summary is correct. As far as slamming the boom into the arch, I have the same problem as you but giving Hunter or Selden the benefit of the doubt, maybe that is why they also supplied a topping lift. I have preset the topping lift to limit how far down the boom can actually fall. With the boom centered, my vang has about 1/2 inch extension ( not bottomed out) and the boom is supported above the arch just enough so the blocks between the traveller and the boom don't interfere with each other. The boom is being supported by the topping lift. When the boom swings out to say a reach position, The topping lift unloads and i have about 4 inches of vang extension to play with but in no circumstance can I pull the boom down low enough to interfere with the arch because the topping lift sets the absolute limit that the boom can be lowered to.

This is all still a work in progress and I don't yet have a feel for how much of a difference being able to adjust the vang will actually make, though not being able to use it bothered me and thus started me down this path.

Marc, I feel your pain! It has bothered the heck out of me as well. I see that pretty boom kicker out there and cannot use it the way I would like!

Anyway, if you leave the topping lift on you do have a safety but, I think, it negates what you are trying to do with the vang. It prevents you from pulling down on the boom thus losing that adjustment for twist. As it stands now you can always loosen the vang and allow the boom to rise, with or without the topping lift. I guess I cannot see the advantage.

I guess that is why I have not made the attachment change that you are suggesting and I am frustrated with having a piece of equipment I cannot use fully.

Nodak

Scott T-Bird · Jul 17, 2012

How to loosen the leech and keep the sail flat ...

That seems to be the issue as the wind gets stronger. From windsurfing in high wind conditions I know that the best sail shape is flat, draft forward for control, and a loose leech (twist). To do that on a windsurfing rig it is easy ... I would increase downhaul a lot, and increase outhaul slightly (just enough to make the trailing edge at the clew of the sail flat). Increasing the downhaul increases the bend in the mast giving me 2 things that I want - draft forward and a loose leech for twist. Increasing outhaul flattens the draft and the trailing edge.

Translating this to a sailboat isn't as easy, particularly for a masthead rig because the mast has no bend. As the wind gets stronger, I can make the draft more shallow with the outhaul and vang tension (or mainsheet tension), and move it forward with halyard tension and cunningham tension. But I can't loosen the leech by decreasing the vang tension (or lifting a rigid vang) without increasing draft depth. So we tend to draw the boom down to decrease draft and tighten the leech when the wind starts to over-power. It seems to be a compromise. You don't want a hooked leech because it results in ineffecient air flow and is slow. But you have to live with it to reduce the draft.

With a fractional rig, and a bendy mast, I would think you have some advantage here. Putting more bend in the mast for windy conditions seems like a way to keep the leech loose while decreasing draft depth and moving draft forward.

The vang always seems like the most imperfect sail contol anyway. It has a very difficult and ineffecient mechanical advantage as it is. It makes me wonder if there isn't an improvement for it somehow.

Nodak7 · Jul 17, 2012

Scott T-Bird said:
That seems to be the issue as the wind gets stronger. From windsurfing in high wind conditions I know that the best sail shape is flat, draft forward for control, and a loose leech (twist). To do that on a windsurfing rig it is easy ... I would increase downhaul a lot, and increase outhaul slightly (just enough to make the trailing edge at the clew of the sail flat). Increasing the downhaul increases the bend in the mast giving me 2 things that I want - draft forward and a loose leech for twist. Increasing outhaul flattens the draft and the trailing edge.

Translating this to a sailboat isn't as easy, particularly for a masthead rig because the mast has no bend. As the wind gets stronger, I can make the draft more shallow with the outhaul and vang tension (or mainsheet tension), and move it forward with halyard tension and cunningham tension. But I can't loosen the leech by decreasing the vang tension (or lifting a rigid vang) without increasing draft depth. So we tend to draw the boom down to decrease draft and tighten the leech when the wind starts to over-power. It seems to be a compromise. You don't want a hooked leech because it results in ineffecient air flow and is slow. But you have to live with it to reduce the draft.

With a fractional rig, and a bendy mast, I would think you have some advantage here. Putting more bend in the mast for windy conditions seems like a way to keep the leech loose while decreasing draft depth and moving draft forward.

The vang always seems like the most imperfect sail contol anyway. It has a very difficult and ineffecient mechanical advantage as it is. It makes me wonder if there isn't an improvement for it somehow.

As a former Windsurfer I understand completely what you are saying. Unfortunately Scott the B&R rig has no backstay or means of bending the mast (after the initial pre-bend), no Cunningham and Halyard adjustments are restricted to full sail only on furling mains. Additionally as we have been discussing the Vang is very limited due to Hunters Arch system. Sail shape is a much different cat when it comes to these rigs. The basics are there but with limitations.

Please don't get me wrong! As an "old guy" I would not trade my furling main in. There are trim limitations for sure but I really like it. We may lose a .1 kt in speed but the convenience and safety the rig affords me and my Admiral is very much worth it.

MsEmee · Jul 18, 2012

I had the same questions when I first got my boat. The original main did not have battens and the boom vang did not have the gas spring to hold up the boom. The sail shape was lousy and as an ex racer made me want to puke most the time. The boat was uncontrollable during gusty winds above 17 knots rounding up most of the time.
I bought a new mainsail with partial vertical battens, put in the gas spring in the boom vang and lead the boom vang sheet back to the cockpit adding another rope clutch on the port side. I also raked the mast back 6 more inches above the Sheldon recommendation setting and re-tuned the rig.
I cannot say enough how much this changed the sailing characteristics of the boat. For the first time I can now fly the top third of the mainsail. I now have a real working boom vang. I am amazed at how little adjustment on the vang is needed to get the full mainsail to fly. In light winds I get 3/4 of the wind speed in boat speed. In gusty winds the boat no longer rounds up like it used to. The sail plan is so balanced now the autopilot hardly is needed and when it is set hardly works. I easily now get to 6.5 kts. With average winds, twisting the mainsail really powers up and the boat takes off like a thoroughbred horse.

Nodak7 · Jul 18, 2012

MsEmee said:
I had the same questions when I first got my boat. The original main did not have battens and the boom vang did not have the gas spring to hold up the boom. The sail shape was lousy and as an ex racer made me want to puke most the time. The boat was uncontrollable during gusty winds above 17 knots rounding up most of the time.
I bought a new mainsail with partial vertical battens, put in the gas spring in the boom vang and lead the boom vang sheet back to the cockpit adding another rope clutch on the port side. I also raked the mast back 6 more inches above the Sheldon recommendation setting and re-tuned the rig.
I cannot say enough how much this changed the sailing characteristics of the boat. For the first time I can now fly the top third of the mainsail. I now have a real working boom vang. I am amazed at how little adjustment on the vang is needed to get the full mainsail to fly. In light winds I get 3/4 of the wind speed in boat speed. In gusty winds the boat no longer rounds up like it used to. The sail plan is so balanced now the autopilot hardly is needed and when it is set hardly works. I easily now get to 6.5 kts. With average winds, twisting the mainsail really powers up and the boat takes off like a thoroughbred horse.

MsEmee, just last weekend we were sailing in very gusty winds ranging from 18 to 34 kts. We had the foresail about 3/4 deployed with a bit of a draft to power thru the waves. The main was deeply reefed at about 1/3 deployed and flat. We averaged 7.3+ kts and topped at 8.2 kts. No problem with rounding up but in the big gusts we had to let out the traveler. Very little weather helm except in the very big gusts.

We have no battens in our main and I think I have a bit more bend in the main then recommended. We experience the performance you mention. Not certain what you consider "average winds". We generally maintain 1/2 or better wind speed on our boat. I am very pleased with her performance. The only real issue that I have is pointing. We just have not been able to get her to point the way I would like.

Nodak

MsEmee · Jul 18, 2012

The partial vertical battens helps tremendously with pointing ability. First, I have 10% more sail area than non-batten main. Second, I can control the 1/3 now with both the battens and boom vang modifications where as before I could not really control it. I can point up to 20 degrees and average about 1/2 the wind speed.
Average winds speeds = 10-15 knot range.
I start to tuck in a little main when the wind starts getting up over 18kts and over 20 start reefing the jib. The jib on my boat is very small as in most of the B&R rigs. Depowering the boat now with the boom vang mods gives me one more option in the cockpit along with the traveler.
The performance of the 36' boat Hunter got it right. It is why they made it into a race boat in last years model.

RichH · Jul 19, 2012

"Wouldn't, I want to spill more wind as the wind speed .....

"Wouldn't, I want to spill more wind (by easing the vang) as the wind speed increases?"

NO NO NO NO, when you ease a vang in high winds it causes the draft to increase but not uniformly over 'all' the sail and thus leaves the sail vulnerable to 'sudden power-ups' due to the nonuniform shape. A sail that has its vang grossly eased will not be able to be 'bladed out' ... all sail surfaces working 'evenly' during the blade-out. The extreme situation with a loose or no vang is a catastrophic goosewing gybe when sailing downwind. If the vang is insufficient to hold down the boom then ease out on the traveller to help to keep the leech tight during a 'blade out'.

With a slack vang to reduce 'overpowering' which allows nonuniform 'twist' youre always subject or vulnerable to 'a dunking' if that over twisted sail unexpectedly 'powers up'. Blading-out (heavy vang pressure and traveller dropped) so that the sail shape is 'controlled' is a MUCH better way to control when being 'overpowered' as when blading out you can 'open' the sail so much so that only the aft/leech sections are 'drawing'/attached.
With a grossly overtwisted sail ..... you never know where the air flow attachment will occur and thus be vulnerable for 'sudden power-ups' (and a stronger possibility for a 'dunking').

"Blading-out" works best with high aspect sails - long luff, short foot (ie.: a small LP jib).
Of course if you have roller furling/reefing, your best SA reduction is 30% max., then beyond more than 30% reduction, youre subject to uncontrolled 'powerups' because the roller furling/roller reefing sails get REAL BAGGY in the midcord sections beyond more than a 30% 'roll-up'.

FWIW - A boat set up with all roller reefing, to me, is a boat that should not be out in winds at greater than 25-30Kts, unless you can put up 'smaller' roller reefing sails before the conditions become 'gnarly' ... or if you definitely plan on NOT sailing above a beam reach.

Todd Smith · Jul 26, 2012

Scott T-Bird said:
...
The vang always seems like the most imperfect sail contol anyway. It has a very difficult and ineffecient mechanical advantage as it is. It makes me wonder if there isn't an improvement for it somehow.

Some boats ( like the star ) have the vang come straight down to a car on a circular traveller. Some use a detachable vang and clip it to the rail. Others just use a big and beefy hydraulic ram.

Nodak7 · Jul 26, 2012

RichH said:
"Wouldn't, I want to spill more wind (by easing the vang) as the wind speed increases?"

FWIW - A boat set up with all roller reefing, to me, is a boat that should not be out in winds at greater than 25-30Kts, unless you can put up 'smaller' roller reefing sails before the conditions become 'gnarly' ... or if you definitely plan on NOT sailing above a beam reach.

RichH, though I am no expert on this subject I would have to question your statement regarding furling. Can you explain your concerns? We sail quite often in winds that exceed 25 kts and sometimes 30 kts. I do find is that I am not terribly concerned about sail trim in those conditions. We usually deeply reef the main and jib and can handle the winds that way. I believe the advantage to a furling main is that you CAN deeply reef the main. At times I might only have 1/4 of my sail exposed. I keep it tight and flat. Granted the foresail when it is reefed is not "pretty". In those conditions it cannot be flattened. For the most part we do quite well.

RichH · Jul 26, 2012

Nodak7 ---
The real answer can only come from your own actual experiences --- what is your tacking angle when the boats mainsail is 'reefed' by 75%?

For 'normal' conditions and with an full exposure to the 'roundness' of shape that only 'broadseaming' or quasi-shperical shape that is in the area towards the luff can provide, one would expect your boat to tack through at least 80°, even with mainsail 'roller reefing' with a flattened main - probably at least 90°. When the broadseamed sections, those sections that provide the 'curvature' necessary to give lift are all rolled up and inside the mast ... then, what is your tacking angle? ... probably greater than 100+° or more .... and the now remaining FLAT shape that used to be the leech sections dont have much 'power', so you have to expose more sail area (with greater heeling potential) to make up the difference.
The higher the wind and the higher the chop - the more open or greater the tacking angles become until you simply cant point .... remembering that on a lake that there's ALWAYS a leeshore looming somewhere.

Sails are 'curved', roller reefing equipment is not curved and even with foam luffs and differential reefing the rolled up sail always get 'bunched' in the middle, has only the FLAT sections exposed at more than 30% WSA reduction. Flat shape is for SPEED SAILING (high gear), powered up or 'full drafted' (low gear) is for 'punching though' and you simply cant do that if all the 'important' lift generating sections of a sail are 'all rolled up'. With a roller furling mainsail you will HAVE to expose much much more sail area (enhancing heeling) to get the same results as a simple slab or 'jiffy' deep reefed sail ... and if you get 'powered up' suddenly because you cant control the shape of those mid height panels, you risk a severe 'dunking' ... and your pointing ability will rapidly decrease/deteriorate the more you 'roll up'.
If sails were able to be used as like you'd unroll a roll of carpeting or 'lineoleum' things would be great; but, sails arent board flat (like a sheet of floppy plywood), they are quasi-spherical especially near to the luff and when you roll them up past the area that is 'rounded' you dont have a sail anymore. Also with roller reefing the CE of each sail always 'goes forward' the deeper you reef; and, the terminal possibility is that you become dominated by lee helm and become 'unable' to come up into the wind when necessary unless you let fly a sheet, etc.

Next time out in moderate-heavy conditions do some trials of determining your 'tacking angle' vs. progressively more and more rolled up sail(s). If you were sailing a major ocean you could always 'run off' sometimes hundreds of miles because your tacking angle went all to hell when you 'rolled up' ... different story on a lake where you cant always 'run off' ... and there usually always is a 'lee shore' in quite close proximity.

;-)

Bowedtoothdoc · Aug 31, 2012

Nodak7 said:
RichH, though I am no expert on this subject I would have to question your statement regarding furling. Can you explain your concerns? We sail quite often in winds that exceed 25 kts and sometimes 30 kts. I do find is that I am not terribly concerned about sail trim in those conditions. We usually deeply reef the main and jib and can handle the winds that way. I believe the advantage to a furling main is that you CAN deeply reef the main. At times I might only have 1/4 of my sail exposed. I keep it tight and flat. Granted the foresail when it is reefed is not "pretty". In those conditions it cannot be flattened. For the most part we do quite well.

Nodak,
I have a battenless furling main as well...The PO had the new sails made in 2011 and they are Doyle Bluewater sails and still like new. I am also looking into ways to use the vang to maximize sail shape. Is your rig fractional? Mine is a masthead rig with a 110 jib.

Nodak7 · Aug 31, 2012

Bowedtoothdoc said:
Nodak,
I have a battenless furling main as well...The PO had the new sails made in 2011 and they are Doyle Bluewater sails and still like new. I am also looking into ways to use the vang to maximize sail shape. Is your rig fractional? Mine is a masthead rig with a 110 jib.

Bowed, if you find a way to use your vang effectively please let me know.

It seems to be a pretty useless piece of equipment when it come to the B&R rig and the arch system. The only time I can really use it is when we are going down wind and I have the boom out.

My sails are battenless as well and are the original sails. The PO did very little sailing (dock queen) so they are in good shape. However my previous boat had vertical battens and I liked the way they shaped the sail. Someday when I change the main sail on this boat I will replace it with a battened sail. Ours is a fractional rig with a 110 jib as well.

Bowedtoothdoc · Aug 31, 2012

Nodak7 said:
Bowed, if you find a way to use your vang effectively please let me know. It seems to be a pretty useless piece of equipment when it come to the B&R rig and the arch system. The only time I can really use it is when we are going down wind and I have the boom out.

My sails are battenless as well and are the original sails. The PO did very little sailing (dock queen) so they are in good shape. However my previous boat had vertical battens and I liked the way they shaped the sail. Someday when I change the main sail on this boat I will replace it with a battened sail. Ours is a fractional rig with a 110 jib as well.

Will do! Do you have an asymetrical?