BB,

Don't bother with anymore replies. Doug knows he FU and is trying to get
a reply that he can bebunk.

The example of the plank supported at both ends is good for the Topping
lift at the end of the boom. It doesn't hold for the Solid vang. With a
solid vang one of the horses would have to be done away with.

Doug knows that. Its just to much for him to admit, as stated
originally, that a rigid vang cannot give the same lifting power as a
topping reinforced main at the end

Ole Thom.

If you change to a rigid vang, you still have the
topping lift for all these things--unless you take it
off.

"Thom Stewart" wrote
Bart,

I know that topping lift can be a PITA but it still has a lot of
advantages over the rigid vang. Just to mention a few;

A spare and ready back stay

A man overboard hoist

An end reinforcement of the boom when you want to use it as a crane
(Dingy recovery)

Thom Stewart wrote:
BB,

Don't bother with anymore replies.

Yes. Please.

... Doug knows he FU and is trying to get
a reply that he can bebunk.

???

So far I haven't "debunked" anything. I have tried to explain some basic
engineering.


The example of the plank supported at both ends is good for the Topping
lift at the end of the boom. It doesn't hold for the Solid vang. With a
solid vang one of the horses would have to be done away with.

???

A better analogy would be a plank locked in place at one end, and
supported somewhere along it's length.


Doug knows that. Its just to much for him to admit, as stated
originally, that a rigid vang cannot give the same lifting power as a
topping reinforced main at the end

Yes it can, and many of them do.

DSK

| Why not? If the boom can take the torsion in one direction, then unless
| it is a very weird asymmetric structure, then it will take the same in
| the opposite direction.

Capt. Mooron wrote:
This is where you stray from engineering principal... that is not the case
at all nor is it the rule.

Oh? Are you saying that a symmetric structural member is stronger one
way than the other? If you nail a board into a frame, you have to be
careful to put it label side up or something?




| Sure it is. It's exactly the same in both directions.

No Doug... it is most assuredly not the same in both directions if only by
the points of compression

Well, go explain that to Newton. He had a little to say on the subject.

.... forget the boom or assume it indestrutructable and unbendable.

OK


| The max forces are limited by the righting moment of the boat. On a 30
| footer, it doesn't need to be that massive. On bigger boats... take a
| look at the vangs on IACC racers...

Nobody is discussing righting moment here Doug...

Well, if we're not discussing the strength of the boom, nor the limit of
force on the whole system, then the only thing to complain about it the
compressive strength of the vang itself (which with a proper one, should
not be an issue) or the strength of the connections between vang, mast,
& boom.

If you break the gooseneck, then it probably wasn't strong enough
anyway. The vang connections take greater strain than the gooseneck (due
to the greater leverage) and thus they have to be stronger yet. So that
rules them out.

Now all you're left with is the strength of the vang itself.

How about a hydraulic cylinder? Some are. How about a very thick solid
SS turnbuckle with machine threads? Some are. That leaves the little
fiberglass rod ones (which I agree are not going to hold up much load)
and the spring loaded locking kind. I suggest you take a look at the
specs on several and see if you can't find one or two that look strong
enough to hold up a substantial load. They're there.



... we are discussing the
ability of basic mathematics in regards to the placement of the vang and the
loads you expect it to encounter.

Not really. You were trying to obfuscate the basic point that a vang
needs to be strong enough to stand up to hard sailing, and if it will do
that, it is almost certainly strong enough the other way too (unless
it's one of those wimpy hen-pecked little fiberglass rod ones).

| For using the boom as a lifting device.... you will stress the vang
unduly
| with a set-up located that far back on the load arm.
|
| ???

Well come on now Doug.... it's basic common sense engineering principal!

It can't be that basic, I have no clue what you're talking about.
Doesn't seem to pertain to vangs, though.


| ... It's not designed for
| that.
|
| It should be. Anything less would not be safe for sailing IMHO.

No it's not... it's designed as a VANG!

I guess a tackle employed as a vang would not be strong enough to use
for anything else?

I do one thing... you can't push a rope.

DSK

Bart,

That is what started this discussion. I believe it was you that
said,"That with a Rigel Vang you could get rid of the topping lift."

I mentioned that although TL is a PITA it does have other function. You
should weigh them all before doing away with it.

On Wed, 18 Aug 2004 07:33:02 -0400, DSK wrote:

Thom Stewart wrote:
If you use the solid vange to hold up the boom when using it for a
crane, it will soon be like Neals Boom, with a pipe in it. The topping
lift bears the load. The boom only position the lifting location.

Not if it was built properly in the first place.

I must be more spoiled than I realize, having sailed boats with strong
spars and decent rigging. Oh well.

If your boom will not lift a dinghy then it will not stand up to hard
sailing either. A topping lift might "bear the load" but it also puts
the boom under more compression than the weight of the load.

The usual failure point (in my experience) is the gooseneck.

Fresh Breezes- Doug King

I am no engineer, but my boat does have a well built boom (Hall) and a
solid vang (Offshore Spars) and a topping lift. I am not worried
about any of the three under any conditions. My vang does have a
means to "lock" it with a quick release pin and a number of holes into
which it can be placed. Last year I was sailing when the water levels
were VERY low and we managed to find a shallow sandy spot and run
aground. Hey, not the first time or the last, I am sure. We were
able to swing the boom out over the side and my friend climbed out on
the end of it to give us some heel as we had very little wind to work
with. We managed to sail off and enjoy the day. No big deal. I keep
the topping lift because it is quick and easy to lift the boom for
extra clearance above the bimini when the sail is down, rather than
screwing with the vang. Just my preference, but it works well for me.
If my main had more roach to it that was creating a chaffe issue, I
would probably get rid of it as I don't really *need* it, but I like
it, so there

Doug,

I mentioned early in this discussion that with a topping lift hoisting
boom, the boom only positions the location of hoist. There is very, very
little force on the boom. The hoist is on the topping lift.

Mooran re-stated this.

You are the one insisting the force is the same on the end of the boom
supported on the other end by a Vang and a gooseneck. We say BS and sign
off.

Ole Thom

No they don

DSK wrote:

Maybe if you sailed anything other than a cheap old beater, maybe if you
had some experience with other than obsolete gear, maybe if you hung
around sailors who know how to sail and how to rig their boats properly,
you'd know that solid vangs have locks.


Since you are always right, I can only surmise that my locks were lost
at the factory.

Cheers

Hi Thom

Actually the force is revealed as compression on the boom in the topping
lift case and bending in the vang lifgt case. I wonder how many booms
Dog has bent lifting loads that way??? In our case, the solid vang only
serves to hold the boom up is the sail is dropped (and no topping lift
used). Just another thought, do you suppose Doug thinks that compressive
and tensile strengths are the same in symmetrical structures???

Cheers

Thom Stewart wrote:

Doug,

I mentioned early in this discussion that with a topping lift hoisting
boom, the boom only positions the location of hoist. There is very, very
little force on the boom. The hoist is on the topping lift.

Mooran re-stated this.

You are the one insisting the force is the same on the end of the boom
supported on the other end by a Vang and a gooseneck. We say BS and sign
off.

Ole Thom

DSK wrote:


Think about this, Thom... the force on the end of the boom is going to
be very great when sailing hard... enough to lean the boat over a lot.


Good lord! I wonder why I can pull the end of the boom to windward by
hand on the traveller but not lift the side of the boat up???? superman!!!

Cheers