boom vang for a low boom
matthe...@yahoo.com
I'm considering installing a rigid boom vang on our Pearson 35. Brian
Toss in his excellent book, the Rigger's Apprentice, recommends that the
vang be attached no less than a fourth of the boom length as measured
from the goose neck. This is so that the pivot is close to the center
of effort of the main. Further, both Brian and Garhauer Marine
recommended a 45 degree vang-to-mast (or boom) angle.
The problem is that our rig is a fairly low-aspect one -- the boom is
long, over 15', and low, just over 2' off of the deck. When I measure
out an arrangement with a boom mount that's about 4' out, the requisite
25% of the boom length, I end up with a vang-to-mast angle of around 63
degrees -- a good ways off the optimal 45 degrees.
Has anyone any experience with similar configurations? Would getting
"bigger" hardware be sufficient to make this a functional and safe
improvement to our rig?
Thankfully,
Matt Shore
sv Argosy
Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.
Rich Hampel
To change from the 45 degree angle you will need stronger attachments and a stronger vang.
At an angle of 63 degrees you will need a system of attachments and equipment that is at least 26%
stronger than recommended for 45 degrees.
Any of the manufacturers (especially Garhauer or Harken) will be able quickly give you the precise
recommendations.
:-)
Thomas Webb
Are you accounting for the increased leverage of the boom in your
estimate? In this case the leverage nearly doubles which, I think,
makes up for the poorer vang angle plus a bit... OTOH, there are other
factors at work, like increased vang size, weight and cost. So, I agree
that the folks at Garhauer will know the 'right' answer from past
experience and are the best source of information.
-- Tom.
Dave Hord
boom.
If the vang is a little closer to the mast than 1/4 of it's length, the
boom has the strength to keep its shape and the optimal strength of the
vang is used at about 45 degrees.
The vang is used to keep the best shape on the Main sail, and it's been
proves that
the 45 degree angle is the best for this, over all. It's main function is
to keep the end
of the boom from rising too high as the boom is swung out on different
points of sail.
You can check with a couple of sail makers, to verify this. Good luck.
brian whatcott
matthe...@yahoo.com,matthe...@yahoo.com says...
>
>Dear Sailors,
>
>I'm considering installing a rigid boom vang on our Pearson 35. Brian
>Toss in his excellent book, the Rigger's Apprentice, recommends that the
>vang be attached no less than a fourth of the boom length as measured
>from the goose neck. This is so that the pivot is close to the center
>of effort of the main. Further, both Brian and Garhauer Marine
>recommended a 45 degree vang-to-mast (or boom) angle.
>
>The problem is that our rig is a fairly low-aspect one -- the boom is
>long, over 15', and low, just over 2' off of the deck. When I measure
>out an arrangement with a boom mount that's about 4' out, the requisite
>25% of the boom length, I end up with a vang-to-mast angle of around 63
>degrees -- a good ways off the optimal 45 degrees.
>
>Has anyone any experience with similar configurations? Would getting
>"bigger" hardware be sufficient to make this a functional and safe
>improvement to our rig?
>
>Thankfully,
>Matt Shore
>sv Argosy
This increases the stress in the vang by 40% or so, (cos(60)/cos(45))
and specifically increases the force into the main from the boom.
But if the mast is supported at the deck, this is not important, as far
as I can see.
So just scale the forces by that 40% and you should be good to go.
But remember that the vang can sterilize some part of that deck
area if it wants to luff.
Brian Whatcott Altus OK
Rich Hampel
Stresswise the design is for 45 degrees.
Any change of that angle will INCREASE the tensile requirements.
For the stress-analysis minded among us. ... If 45 degress is the design angle; (sine 65 ) /
(sine 45) = .89 / .707 = 1.26 --- requiring 26% more strength (equipment strength and attachment
strength) to do the same job.
;-)
Jim Conlin
a useful amount of downward force on the boom from a point on the mast at
deck level. I'd be particularly concerned about axial loads on the
gooseneck against the mast. Didn't the Pearson 35 have roller reefing? If
so, the gooseneck was certainly not intended to bear loads against the mast.
I'd look for other options, like a house-top traveller and an old-style
vang tackle to the rail. The traveller will provide leech control for
windward through beam reach points of sail and the vang tackle for broader
than that. A plus- In that use. the vang tackle to the rail serves as a
jibe preventer.
matthe...@yahoo.com wrote:
> Dear Sailors,
>
> I'm considering installing a rigid boom vang on our Pearson 35. Brian
> Toss in his excellent book, the Rigger's Apprentice, recommends that the
> vang be attached no less than a fourth of the boom length as measured
> from the goose neck. This is so that the pivot is close to the center
> of effort of the main. Further, both Brian and Garhauer Marine
> recommended a 45 degree vang-to-mast (or boom) angle.
>
> The problem is that our rig is a fairly low-aspect one -- the boom is
> long, over 15', and low, just over 2' off of the deck. When I measure
> out an arrangement with a boom mount that's about 4' out, the requisite
> 25% of the boom length, I end up with a vang-to-mast angle of around 63
> degrees -- a good ways off the optimal 45 degrees.
>
> Has anyone any experience with similar configurations? Would getting
> "bigger" hardware be sufficient to make this a functional and safe
> improvement to our rig?
>
> Thankfully,
> Matt Shore
> sv Argosy
>
Thomas Webb
>
> Yup I did [take the boom's leverage into account].
It seems to me that your analysis assumes that the vangs are attached to
the boom at the same place. They aren't. The 63 degree vang doesn't need
to apply as much force as the 45 degree vang to do the same job.
-- Tom.
brian whatcott
Brian Whatcott
On Tue, 17 Aug 1999 15:38:29 -0400, Rich Hampel,rhm...@att.net says...
brian whatcott
>
>Yup I did.
>Stresswise the design is for 45 degrees.
> Any change of that angle will INCREASE the tensile requirements.
> For the stress-analysis minded among us. ... If 45 degress is the design
angle; (sine 65 ) /
>(sine 45) = .89 / .707 = 1.26 --- requiring 26% more strength (equipment
strength and attachment
>strength) to do the same job.
>;-)
Try cos(45)/cos(60) :-)
Brian Whatcott Altus OK
meuz...@my-deja.com
situation for a hard boomvang. If the angle between vang and boom
becomes too small, the resulting forces on vang and gooseneck
may become unacceptably large. On the other hand, by moving the
vang attachment point to the boom further forward you may be
asking for a broken boom (I would certainly check with the
manufacturer of the boom on the proposed configuration).
With all due respect for Brian Toss, when you are reefed in
high winds (and thus essentially have a loose-footed sail)
nearly all of the sail's force transmitted to the boom acts
on that point where the clew is attached to the boom.
Consequently you don't want to attach your hard vang too far
forward from there. Where the sail's center of effort is in
that situation would appear to be largely irrelevant.
Flying Dutchman
SAIL LOCO
point is located the LOWER the loads would be. It's the same as the mainsheet
loads. End of boom sheeting always offers lower loads than the silly out of
the way cabin top mainsheet arangement. Example: Average 30 foot sailboat
with end of boom sheeting can be trimed by the helmsman. Average 30 foot boat
with cabin top traveler and sheeting must be controled by a winch in any kind
of a breeze and the catalogs tell you to go up a size in the parts used. So if
your controling a lever it's always easier the further you get from the pivot
point.
"Trains are a winter sport"
Paul Kamen
>The vang is used to keep the best shape on the Main sail, and it's
>been proves that the 45 degree angle is the best for this, over
>all...
Not true. The idea is to maximize the moment about the gooseneck, and if
you do the math (or draw a simple free body diagram) you'll find that the
further aft the attachment is on the boom, the more vang effect you get
for a given amount of vang tension.
The only downside from moving the vang attachment point aft is a modest
increase in compression in the boom and gooseneck. But for most real
installations, the boom is much more likely to fail in bending at the
point of vang attachment, so the aft location usually makes for a more
robust rig with better control.
And, BTW, there's no rational basis for the 1/4 boom length attachment
point, either.
--
fish...@netcom.com
http://www.well.com/~pk/fishmeal.html
-"Call me Fishmeal"-
Pierre Boudier
australian 18 footer ?
Jim Conlin wrote:
>
> Given the long boom/low gooseneck combination, it's going to be hard to get
> a useful amount of downward force on the boom from a point on the mast at
> deck level. I'd be particularly concerned about axial loads on the
> gooseneck against the mast. Didn't the Pearson 35 have roller reefing? If
> so, the gooseneck was certainly not intended to bear loads against the mast.
>
> I'd look for other options, like a house-top traveller and an old-style
> vang tackle to the rail. The traveller will provide leech control for
> windward through beam reach points of sail and the vang tackle for broader
> than that. A plus- In that use. the vang tackle to the rail serves as a
> jibe preventer.
--
Pierre Boudier - Marseille - mailto:pbou...@altern.org
" Le pays des rêves est la seule région au monde où personne n'est
interdit de séjour. "
thoma...@my-deja.com
thoma...@my-deja.com
way) comments:
The torque the vang applies to the boom about the
gooseneck is exactly equal to the compressive
force the vang applies to the boom times the
distance from the gooseneck to the vang mast
attachment point.
So, in order to maximize the torque for a given
compressive force, mount the vang as low on the
mast as possible. (Obvious I know) The ratio of
compressive force to torque is independent of the
vang boom attachment point. (Not so obvious)
Moving the vang boom attachment point aft does
increase the compressive force (for a constant
vang tension) while commensurately increasing the
torque. So move your vang boom attachment point
as far aft as practical. You will get the most
torque for the least vang tension.
Regards,
Tom Thomas
Phil Arnold
Also remember you will be stressing a boom where it may not have been
designed to be stressed. A doubler may be in order, particularly if
the vang attachment is to be some sort of fabrication that involves a
slot or holes in the bottom of the boom. The gooseneck will also be
heavily loaded with a low angle vang. A track on deck may be another
alternative.
Phil
Paul Kamen
>Just to amplify on Fishmeal's (welcome back by the
>way) comments:
Thanx! I'm back in rec.boats.racing, but haven't found time yet to catch
up in r.b.cruising.
>The torque the vang applies to the boom about the
>gooseneck is exactly equal to the compressive
>force the vang applies to the boom times the
>distance from the gooseneck to the vang mast
>attachment point...
Agree. But an equivalent statement, and I think one that makes more
intuitive sense, is that the moment about the gooseneck equals the vang
tension times the length of a line perpendicular to the vang and passing
through the gooseneck. Sketch it out and it should be clear why the aft
location on the boom reults in less vang tension (and less boom bending)
for a required gooseneck torque.
It's really Just another way of saying that moment is the vector
cross-product of R and F.
Terry Schell
Rich Hampel wrote:
>
> 45 degrees is the angle at which the stresses will be at a minimum for the application.
> To change from the 45 degree angle you will need stronger attachments and a stronger vang.
<snip>
This is a popular misconception. Work through the calculations and you
will see that moving the mast attachment down or moving the boom
attachment aft will reduce the required vang tension... regardless of
the angle of the vang.
If you want to reduce the bending moment on the boom or the required
vang tension for a constant unit downforce on the clew, move the boom
attachment as far aft as is practical.
If the boom vang is rigid and will be used to support the mast, the
optimal attachment varies somewhat since you have to worry about the
euler buckling of the vang.
Terry Schell
Rich Hampel wrote:
>
> Yup I did.
> Stresswise the design is for 45 degrees.
> Any change of that angle will INCREASE the tensile requirements.
> For the stress-analysis minded among us. ... If 45 degress is the design angle; (sine 65 ) /
> (sine 45) = .89 / .707 = 1.26 --- requiring 26% more strength (equipment strength and attachment
> strength) to do the same job.
> ;-)
I think the problem here is that you haven't included the "job" that
needs to be done into your calculations: creating a downforce on the
clew of the sail.
You rightly point out that moving the boom attachment out decreaces the
downward force of the vang on the boom... however it moves that force
closer to the clew and farther from the gooseneck. (BTW...I think you
also used sine when you mean to use cosine) You need to redo the
calculations only looking at the downforce at the clew.
According to your method, the optimal vang would be a attached directly
to the gooseneck (angle of zero). This is clearly incorrect.
Terry Schell
Dave Hord wrote:
>
> Matt, I'd stick closer to the 45 degree factor than the 1/4 length of the
> boom.
> If the vang is a little closer to the mast than 1/4 of it's length, the
> boom has the strength to keep its shape and the optimal strength of the
> vang is used at about 45 degrees.
>
> The vang is used to keep the best shape on the Main sail, and it's been
> proves that
> the 45 degree angle is the best for this, over all. It's main function is
> to keep the end
> of the boom from rising too high as the boom is swung out on different
> points of sail.
>
> You can check with a couple of sail makers, to verify this. Good luck.
I second your recommendation to check with some riggers/sailmakers...
however I disagree with the rest of the post. 45 degrees is relatively
standard on smaller boats with a relatively large gap between the boom
and the deck (relative to boom length that is), but this is far from
being 'proven optimal' for sail control across a range of boats.
Thomas Webb
>
> Not true. The idea is to maximize the moment about the gooseneck ...
Ok, I'm very confused. It seems to me that the idea is to get the
correct amount of twist in the main or to support the main when it's
down (since this is a rigid vang). If the 45 degree vang could do this
then the 63 degree vang ought to be able to do it at about 80% of the
tension with about the same compression on the boom... No?
-- Tom.
mocap
Phil Arnold <phi...@home.com> wrote in message
news:37bb9b59.17171671@news...
I used two vangs, one led to the deck on each side of the trunk cabin. When
changing tacks I released one and took up on the other. Worked fine. If the
foot of the sail uses slides rather than a bolt rope, there are devices that
look like a short mooring snubber that you can put over the boom between the
slides, and attach the vang to.
Mort
Wes Gardner
Did you get your vang question worked out? There are things like
preventers, JC straps, etc. Star boats have a semi-circular track that
the vang "sheets" directly down to - the boom is almost two-blocked to
the car on the vang track - there really is no angle as the boom is just
inches off the deck and vang car - not comfortable when tacking at all,
but...
Every boat is a compromise and looking for "ultimates" often leads to
frustration. I'd use a hard vang if you could, if not install the
typical one at an angle that "looks good from my house" and carry a
preventer that can be rigged via a strop around the boom and down to the
toe-rail - in a big blow off the wind, this is what you'll want anyway -
really does eliminate that "all standing" jibe when you least expect
it...
Hope this helps
Wes
Scott Truesdell
With a solid boom vang we are trying to do five things:
1. Control twist in the mainsail leach by exerting
a downward force at the clew.
2. Accomplish #1 without breaking the boom.
3. Accomplish #1 without breaking the gooseneck.
4. Accomplish #1 without localizing lots of force
in a small area (#2 and #3, in essense)
5. Hold the boom up when the sail is down (or in light
air.
We can discount #5 because any reasonable solution will work satisfactorily.
We will look at #2 and #3 as extreme examples. If the vang attaches only a
few inches AFT of the gooseneck, the force is almost directly down, making
the shear loads on the gooseneck relatively high. But worse than that is
that the shear force on the varg attachment point of the boom is almost
equally as high at an area less equiped to handle the load. The force is
trying to break the boom at the vang attachment point using a very long
lever. If the boom is sufficiently strong to take this abuse, leach
control will take a very powerful vang to counter-act the long lever of
the boom.
In the opposite condition, if the vang is attached only a few inches BELOW
the gooseneck and out along the boom a ways, the vang force will be trying
to pull the boom forward, not down. The gooseneck will be under heavy
compression AND shear while the boom will be fairly lightly loaded. It
will again take a lot of force to control the leach, much of which will be
dissipated loading up the gooseneck. This engineering conundrum was solved
in Stars and 12 Meters by installing semi-circular tracks directly beneath
the vang attachment point on the boom and pulling straight down with a
relatively light force.
As a point of reference, my last boat, a Santa Cruz 27, has a low boom and
due to my proclivity for vang-sheeting combined with a sufficiently
powerful vang to do so, resulted in cracking of the boom extrusion at the
attachment point. If the boom were higher, the attachment point could have
been further aft and there would have been less stress there.
--scott
--
remove the hot dog to sent me mail.
Newsgroups are the beginning of 90% of the spam I
get, so if I want to participate at all, I have to
take this stupid measure. Thanks a million, spammers!
Roy Smith
> With a solid boom vang we are trying to do five things:
>
> 1. Control twist in the mainsail leach by exerting
> a downward force at the clew.
>
> 2. Accomplish #1 without breaking the boom.
>
> 3. Accomplish #1 without breaking the gooseneck.
How about Accomplish #1 without tearing the mainsail?
I'm told that in a J/24 in a lot of wind, you can tear out the main leach
with the vang. Sheet in hard, then crank on lots of vang, then lots of
backstay. This lets you sheet in a bit harder, which lets you crank in
more vang, which lets you crank in more backstay. Repeat for a few
cycles. Now, without touching the sheet or vang, release the backstay.
The main leach now takes up all the tension that used to be in the
backstay. Well, at least it does for a microsecond or so :-) Never
tested the theory myself, but I am careful to release vang and sheet
before backstay!
Terry Schell
Roy Smith wrote:
>
<snip>
> I'm told that in a J/24 in a lot of wind, you can tear out the main leach
> with the vang. Sheet in hard, then crank on lots of vang, then lots of
> backstay. This lets you sheet in a bit harder, which lets you crank in
> more vang, which lets you crank in more backstay. Repeat for a few
> cycles. Now, without touching the sheet or vang, release the backstay.
> The main leach now takes up all the tension that used to be in the
> backstay. Well, at least it does for a microsecond or so :-) Never
> tested the theory myself, but I am careful to release vang and sheet
> before backstay!
I don't think you need to vang to pull this little trick. The mainsheet
is the culprit.
Leo Voorneveld - The Netherlands
Terry Schell heeft geschreven in bericht <37C563EC...@uwf.edu>...
>
>I don't think you need to vang to pull this little trick. The mainsheet
>is the culprit.
Yep, I thought that the vang became usefull when the mainsheet is not
pulling the boom in, like on reaching and running.The mainsail and boom
tends to go upwards, there is the vang designed for.
With dinghy sailing like the Laser it is different, but hack no backstay
there either.
regars Leo
alan...@my-deja.com
"Leo Voorneveld - The Netherlands"
J24 sailors like to use a upwind sailing method
called vang sheeting. You sheet the main for the
conditions and tighten the vang. Then you can play
the main up and down with the main sheet rather
than the traveler. Very popular in the J24 fleet.
J-World has a nice video covering the technique
called something like J24 Upwind Sailing. Ken Read
drives the boat and does all the talking.
Roy Smith
> J24 sailors like to use a upwind sailing method called vang
> sheeting. You sheet the main for the conditions and tighten the
> vang. Then you can play the main up and down with the main
> sheet rather than the traveler.
Really only useful in heavy air (above about 15-20 kts). The problem on
the J/24 is that the traveller is too short. Most of the time, I like to
just keep the mainsheet cleated and play the traveller and backstay in the
puffs. It's only when you've run the traveller all the way to leeward and
you're still overpowered that you need to to go vang sheeting so you can
ease the boom out beyond the end of the traveller and still keep leach
tension.
Leo Voorneveld - The Netherlands
>Really only useful in heavy air (above about 15-20 kts). The problem on
>the J/24 is that the traveller is too short. Most of the time, I like to
>just keep the mainsheet cleated and play the traveller and backstay in the
>puffs. It's only when you've run the traveller all the way to leeward and
>you're still overpowered that you need to to go vang sheeting so you can
>ease the boom out beyond the end of the traveller and still keep leach
>tension.
Yeah, I forgot that with mainsheet I mean main sheet/traveller combination,
is it rude to say that the vang takes over when the boom is past the use of
the traveller ? You can reckon at huge vang loads in boats without
travellers.
Cheers Leo
Scott Truesdell
> Roy Smith wrote:
> >
> <snip>
>
> > I'm told that in a J/24 in a lot of wind, you can tear out the main leach
> > with the vang.
>
> I don't think you need to vang to pull this little trick. The mainsheet
> is the culprit.
It's the vang, typically. Here's what happens.
Vang-sheeting upwind, everything fine and dandy.
Get to weather mark, ease sails, pop chute.
Dump backstay ... DOH!
Tom Speer
Paul Kamen wrote:
>
>...Sketch it out and it should be clear why the aft
> location on the boom reults in less vang tension (and less boom bending)
> for a required gooseneck torque.
>
> It's really Just another way of saying that moment is the vector
> cross-product of R and F.
>
For an even easier way of visualizing it, I think you'll find
that the effectiveness of the vang is proportional to the area of
the triangle between mast, boom, and vang.
Cheers,
--
Tom Speer
tsp...@gte.net
http://home1.gte.net/tspeer
fax: +1 206 878 5269
brian whatcott
On Sun, 05 Sep 1999 06:47:56 GMT, Tom Speer says...
>Paul Kamen wrote:
>>
>>...Sketch it out and it should be clear why the aft
>> location on the boom reults in less vang tension (and less boom bending)
>> for a required gooseneck torque.
>>
>> It's really Just another way of saying that moment is the vector
>> cross-product of R and F.
>>
>
>
>For an even easier way of visualizing it, I think you'll find
>that the effectiveness of the vang is proportional to the area of
>the triangle between mast, boom, and vang.
>
>Cheers,
>--
>Tom Speer
Hehehe... I expect Tom's late entry in this interesting thread;
which was a mix of trig, horse sense, racing tips and seamanship,
could fire up a few late fizzles.
You see, the Tom approach leads to an aft attachment - but purists
want a boom attach at a given fraction of the boom length which is
meant to provide a favorable boom curve and hence desirable sail
shape.
Brian Whatcott Altus OK
Paul Kamen
>For an even easier way of visualizing it, I think you'll find
>that the effectiveness of the vang is proportional to the area of
>the triangle between mast, boom, and vang.
I don't think that's true. If, for example, you double the distance of
the attachment point on the boom back from the mast, you double area
(assuming boom and mast make right angles, etc.). But the R in R X F, and
hence the moment about the gooseneck for a given amount of vang force,
does not double.
Terry Schell
brian whatcott wrote:
<snip>
> >For an even easier way of visualizing it, I think you'll find
> >that the effectiveness of the vang is proportional to the area of
> >the triangle between mast, boom, and vang.
> >
> >Cheers,
> >--
> >Tom Speer
>
> Hehehe... I expect Tom's late entry in this interesting thread;
> which was a mix of trig, horse sense, racing tips and seamanship,
> could fire up a few late fizzles.
> You see, the Tom approach leads to an aft attachment - but purists
> want a boom attach at a given fraction of the boom length which is
> meant to provide a favorable boom curve and hence desirable sail
> shape.
>
I don't know of any modern sailmaker that makes as sail that uses the
boom for flattening... certainly none who would promote deliberately
bending the boom to flatten the sail. Even if they did, this method
wouldn't work when you need it most, when the sail is reefed.
Steven Shelikoff
Windsurfer?
> wouldn't work when you need it most, when the sail is reefed.
Well, you don't reef a windsurfer. Just put on a smaller sail.
Steve
--
/ / /
\ \ \ mailto:shel...@averstar.com
/ / /
Terry Schell
Steven Shelikoff wrote:
<snip>
> > I don't know of any modern sailmaker that makes as sail that uses the
> > boom for flattening... certainly none who would promote deliberately
> > bending the boom to flatten the sail. Even if they did, this method
>
> Windsurfer?
I wasn't very clear, I mean bending the boom to flatten the sails. This
was common back when sails were made from cotton and spars were wood.
The boom outhaul is routinely used to flatten sails, but that wouldn't
be helped by mounting the vang so that it could bend the boom.