Boom Vang and Outhaul Questions

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Boom Vang and Outhaul Questions

Postby omin » Sun Jun 30, 2013 11:27 pm

Hi guys. I am a young sailor, who started on a sunfish, after that was destroyed on the beach by hurricaine irene, i had an opportunity to buy a daysailer 3, and wish to eventually buy even bigger. however, i have questions about how to utilize the outhaul, and boom vang.

please feel free to help with either or both of the questions

first the outhaul, there are two eyelets in the rear of the boom, and the rope attached to the clew of the mainsail is fairly long. there is also a cleat about 2/3rds of the way back up the boom on the port side. am i just supposed to run the line through the eyelet and tie it off to the cleat or am i missing some equipment?

The boat came with a boom vang that the previous owner never utilized, there is a clear place on the boom to attach the vang, but no place on the mast. what would be a good way of attaching? there is a pully on that side.

also there is a line attached to the gooseneck, that looks like it goes down into a clam cleat on the mast to keep the boom from slipping up when there is pressure on the sails. does that make sense?
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Re: Boom Vang and Outhaul Questions

Postby jpclowes » Mon Jul 01, 2013 7:52 am

Hi Omin
I have a block that I attached to one of the eyelets on the back of the boom, and then ran the line forward to the cleat. If it is big enough, the eyelet may be enough.
I have an eye strap on the mast, just above where it enters the hole in the deck, that I attach my boom vang to. Get it as close to the deck as you can, so you have the best angle for the most mechanical advantage.
The line on the Gooseneck is exactly for what you are describing, it is very useful in heavy air.

Enjoy!!
J .P. Clowes
Eastern Great Lakes Regional V.P.
DSI 14083
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Re: Boom Vang and Outhaul Questions

Postby GreenLake » Mon Jul 01, 2013 3:11 pm

You can get some mirco blocks with lashings. Lash one onto the sail, one onto the boom. You can construct a pulley system that way with various degrees of mechanical advantage. If you just tie the line to the sail and reeve it to the eyelet to go forward, you will probably have too much friction to be able to adjust the outhaul while under way.

If you just lash a single block to the eyelet on the boom that will reduce the friction, but you still don't get a mechanical advantage. My current system is a double block on the boom and a single on the sail. However, my boom may be to short for that setup, I've noticed the blocks being "chock-a-block" (touching) when I'm not sure I've run out of need for additional outhaul tension. I plan to investigate that when I get to the boat next. But you should have space for a single block and that might work for you.

Boom vang often attaches via a strop to an eyelet on the front of the mast. That way, the eyelet only has to hold the vertical component of the vang pull, not the much stronger horizontal pull. If that is missing on your boat, should be an easy retrofit.
~ green ~ lake ~ ~
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Re: Boom Vang

Postby csrguth » Wed Jul 17, 2013 10:08 pm

My DS1 Rebel does not have a boom vang. In what wind conditions does one begin to become of value and in what conditions does it become necessary?
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Re: Boom Vang and Outhaul Questions

Postby GreenLake » Thu Jul 18, 2013 8:00 am

Going downwind a vang will increase the projected sail area by keeping the sail flat. That would be the standard use for one. Going upwind, you can use a vang to separate the control of the leech tension from the control of sheeting angle (normally the main sheet does both). Used that way, a vang has the same function as a traveler. This is called vang sheeting and needs a rather beefy vang (20:1).
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Re: Boom Vang and Outhaul Questions

Postby K.C. Walker » Thu Jul 18, 2013 10:15 am

Is a boomvang necessary to sail a boat? No. Is it a desirable sail control? Yes.

In light air, less than 5 kn, the boomvang is not used, generally. As the breeze continues to build, the boomvang increases in value for maintaining a good sail shape.

For upwind sailing, when close hauled, the boomvang can easily help change the power of the sail on the fly. When using the two controls together upwind (mainsheet and boomvang), more mainsheet and less boomvang = a powered up sail with a closed leech, i.e. less twist. With a powerful boomvang applied the power in the sail can be decreased because the mast bows forward taking draft out of the sail and the leech is open, i.e. more twisted, so de-powered up high, as well. Using the boomvang as sheeting, i.e. controlling the height of the boom and therefore the sail twist, the mainsheet takes on more of the role of being a traveler.

Any time that the boom is beyond the rear quarter deck a boomvang would control the height of the boom. A powerful boomvang is not necessary for this purpose. When reaching or running without a boomvang, you will notice that the boom "skies", this puts a lot of twist in the sail. This uncontrolled twist can make the boat unstable when broad reaching or especially when running. If you let the boom out far enough, with this considerable twist, the upper leech can go beyond square and can be sailing "by the lee". With the upper part of the mainsail sailing by the lee the boat can set up a very unstable rolling momentum, which can lead to a capsize, given enough breeze.

So, obviously, you can sail a boat with out a boomvang but I like to be more in control than that.
KC Walker, DS 1 #7002
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Re: Boom Vang and Outhaul Questions

Postby TIM WEBB » Thu Jul 18, 2013 10:06 pm

Completely agree KC: it's just one more control that helps you stay in control (ain't English quirky?)
Tim Webb
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Re: Boom Vang and Outhaul Questions

Postby csrguth » Sat Jul 20, 2013 9:56 pm

Thanks, I'll put one on my wish list.
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Re: Boom Vang and Outhaul Questions

Postby bnnauti » Sat May 03, 2014 1:00 pm

Naive question by a newbie-purchased a 17' Spindrift last season that has mid-boom sheeting only (think there is a block for a topping lift in the aft end of the boom). Took it out in very low wind once at end of season (before the water turned hard here in upper MI) and noticed how easy the boom could "sky" (using anothers term my learning). Thinking I need a traveler of some sort and/or a boom vang though the mast has a fixed bracket on the mast (no down-haul) so the sail height adjustment is only with the halyard.

Have seen images of DS1 rigging that employ both. Just want to keep sailing simple, safe and understand what I'm doing with any mods. Unfortunately did not have access to previous others experiences.

Thanks for any suggestion. :?
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Re: Boom Vang and Outhaul Questions

Postby Swashbuckley » Fri May 23, 2014 12:29 am

The main purpose of a boom vang to prevent "skying" of the boom. It controls the sail shape by controlling the booms ability to move up and down. The mainsheet should be used primarily for moving the boom in and out. When sailing off the wind the boom will tend to rise with each puff of wind, causing a loss of power and control. The boom vang prevents this movement (that is why some call it a preventer). A boom vang is a simple and extremely helpful addition to your rigging. It will help you in more ways than a traveler if you have to choose between them. Hope this helps.
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Re: Boom Vang and Outhaul Questions

Postby Interim » Mon Jul 28, 2014 2:27 pm

GreenLake and KC Walker--

I've ordered a 4:1 Boom vang, but after reading this thread I have some questions (one related to your posts, and one not).

Safety first: You will see in my gallery a picture of a slight bend to aft in my mast. It seems to me that a vang applies forward pressure on the mast at the point of the gooseneck (coincidentally where my mast bends). If this is so, is there risk of mast failure from this pressure?

1726
1727

I realize this is hard to answer without seeing the mast in person, but your best guess would be appreciated.

Second, I am trying to understand the value of a vang when close-hauled. As the boom moves inboard, doesn't the main sheet increasingly pull down (the same action as the vang)? I imagine the vang increasing my ability to tighten the leech (perhaps to the point of cupping). In lighter winds I would be more efficient because I am reducing twist, somewhat, but it seems like this is almost the same vector as the sheet.

Is that right? (I don't think so, but I don't know why).

And, can the vang help de-power when close-hauled in heavier winds? It wouldn't seem to be able to do so beyond the point of where I would be without a vang. My alternate hypothesis is that less twist = more forward speed, and thus the apparent wind is more forward and pushing the boat over to a lesser degree.

A messy set of questions, I know. Sorry.

Regards,

--john
1979 DSII
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Re: Boom Vang and Outhaul Questions

Postby K.C. Walker » Sun Aug 03, 2014 11:10 am

So, I've got a new twist, so to speak, on my boomvang. I replaced my mast last summer after breaking my original AllSpar. The bend characteristics are different now as this one is stiffer. With my bendy mast I could easily put on enough boomvang with a 20:1 to get both mast bend, flattening the sail, and open the leech for twist. So far, with this one it does not seem to bend enough to open the leech when the boomvang is fully applied. Or…It may be that the top of the mast is stiffer and does not de-power automatically as well with gusts as the old one did. I guess it's still a work in progress…

What I'm finding now is that I am resorting to reefing more often when the wind gets piping, especially when I'm single-handed. It does, of course, still separate the twist control (boom height) from sheeting with everything except hard on close hauled sheeting. If I'm using 1:1 at the end of the boom for sheeting purchase power, the boomvang can supply the down force for the boom and then all I need the sheet to do is control the boom centering, or angle off-center which greatly reduces the force needed.

Another thing that using vang sheeting does that simplifies things is; when you ease the sheet for a gust, because you don't have a lot of downforce with the sheet, the jib stay sag does not change much. If you get a puff and you want to ease the sheet to keep the boat upright you don't want the jib stay to sag and power up the jib, just at the wrong time. So, this is definitely a good use for the boomvang when close hauled.

I don't think a 4:1 boomvang will put all that much forward force on the mast. It's not really enough purchase power to use it for vang sheeting. It's still a useful sail control, though, as it will control the boom height to some degree. It will be more useful on other points of sail than close hauled.
KC Walker, DS 1 #7002
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Re: Boom Vang and Outhaul Questions

Postby Mike Gillum » Mon Aug 04, 2014 3:10 pm

K.C., What is your rig tension as that will also greatly affect mast bend because a "loose" rig won't bend as easily as a "tight" rig?
I've been running 300# on the forestay (Loos Gauge) forever on all of the fractionally rigged dinghies like 5o5, Thistle & Day Sailer that helps to create at the dock the positive prebend of around 1-1/2" measured by holding your main halyard taught between the top of the mast and gooseneck at the backside of the mast.
The outboard end of the boom is pulled downward as tension is applied via the Boomvang helping to close the leech while the forward end of the boom at the mast is driven forward towards the bow which in turn bends the lower 1/3-1/2 of the mast that in turns helps to flatten the bottom 1/3-1/2 of the Main as well as in most cases twist open the upper half of the leech allowing it to fall to leeward quickly depowering the sail plan. A tight outhaul is also very important to this equation!
This past weekend at the Morro Bay DS Invitational we had flat water, predominately light winds and a heavy flood tide both days that didn't allow much use of my 20:1 Boomvang but the few opportunities when the breeze popped up for a minute or two I was using the Boomvang to quickly help shape the Main before dumping it almost as quickly.
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Re: Boom Vang and Outhaul Questions, plus mast

Postby scitfrostbite » Fri Aug 08, 2014 10:38 pm

On the subject of mast set up, how much do you slide the butt aft at the dock? This seems to flatten the lower part of main and open the slot. I've been trying one hole on my super spar step (about 3/4" I think). Do you do this? Does moving the butt aft help in other ways? Thanks
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Re: Boom Vang and Outhaul Questions

Postby Mike Gillum » Sat Aug 09, 2014 12:21 am

I haven't touched the butt location since 2007 when I installed the adjustable base.
My rig was originally setup per the North Sails Tuning Guide based off of Dave Keran's DS #316.
Those tuning guide numbers are a great starting point for any DS.
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