That's why triangular sections have the greatest rigidty for
their cross section area, and square sections are more rigid than oval
or round.


Nav wrote:
I think you may be confusing a truss with a section.

Nope.

... For bending in
plane

In what plane?

... the most rigid section per unit weight

Did I say "per unit weight"? No I said cross section area.

... is close to a T
section with the top under compression and the bulb (or smaller bottom
plate) at the bottom in tension.

You're describing an asymmetric I-beam.

Now, think for a moment... have you seen any sailboat booms shaped like
I-beams?

No, you haven't. But if you've looked at pictures of fancy hi-dollar
racing yachts, you have seen triangular section booms.

Why is that, Navvie?


Maybe you better go call up Bruce Farr and tell him he's been getting it
wrong. He'll probably offer you a job.

DSK

You may be confused. Perhaps you would like to re-read your earlier
post? I'll highlight it for you:


DSK wrote:
That's why triangular sections have the greatest rigidty for
their cross section area, and square sections are more rigid than
oval or round.

You did say most rigid didn't you? I'd say that rigid means best able to
resist bending -but perhaps you have some other use of the term? It's
strange but engineering texts say that the section that best resists
bending is an I or T section. But Doug is always right so we must all be
wrong!

Now, since you've neatly drawn and posted a diagram why haven't you
actually shown us where your cosine is or what the forces on the boom
are. I gave you a solution but you've not explained why it's wrong.
C'mon share your engineering expertise!

I'd say this is a smokscreen and you are trying to wriggle off the hook.

Cheers

DSK wrote:

So, I take that you've folded up a boom trying to lift something? Can
we assume that you learned nothing from it, other than "don't"?


Nav wrote:

Such vivid imagination.


Well, I have seen booms supported by rigid vangs that didn't fold up, so
obviously it can be done... if you do it right.

You think it can't be done, why? Conclusion: you did it wrong, and
decided it was impossible.


Yes a very vivid imagination. Dougs world -LOL


Funny you should say that, since you show no comprehension of how to
read the diagram, yet you pass judgement on my competence. The
resolution of forces is not obvious but it's also not rocket science.

If OTOH you *do* have some clue what you're talking about, tell us what
the mysterious symbol next to the mast represents.


Your statement makes no sense as you need to least show why my
calculation is wrong. After all I did solve the problem for the second
case for you -so either I can resolve forces and am correct or I cannot
and my answer is wrong! which is it? It would seem that you disagree
with my freshman solution so where's yours? So far you've only blustered
and obfuscated so I can't wait to see where the cosine in your diagram
gives the compression on the boom!

By the way, use of symbols does not mean that you understand them
-especially if _you_ put them in the wrong place.

Cheers

Try to keep up.
Scout

"Nav" wrote in message
...
I'm wondering what you are talking about.

Cheers

Scout wrote:

And I'm wondering what the formulation time has to do with how long
you've
been waiting to work it into a conversation.
Scout

"Nav" wrote in message
...

I wonder what "formuilating a problem" has to do with typing?

Cheers



Capt. Mooron wrote:

Heh... who cares... she gets paid.. she types.

CM

"Scout" wrote in message
...
| I'll bet she just loves being forced into asa ****ing contests.
| Scout
|
| "Capt. Mooron" wrote in message
| ...
| He uses a secretary ... she types about 120 wpm.
|
| CM
|
|
|
| "Scout" wrote in message
| ...
| | I don't believe you can type that fast.
| | Scout
|
|
|
|

"Capt. Mooron" wrote

Quit toying with the damn boom.... look think of it this way... how
many
lifting devices utilize a support located under the boom at less
than 25% of
the boom length? NONE!

Wrong, kanook.
Have you never seen an engine crane?
A bascule type draw bridge?
Any hydraulic crane with the boom out?
An excavator?

need more?

Scotty

OK Doug,

Since you made the statement; "Except for being used for a spare Back
Stay the Rigid Vang can do everything that a topping lift can do."

It's turned into a yes it can, no it can't.
So, let's change it to; A Topping Lift can be used as a Hoisting Device
even without the "BOOM".

Now, can the solid vang do that without modification?

Ole Thom

I extend my topping lift (quick disconnect fitting) and send it forward as
an assist line when stepping my mast. It's useless until I lift to about
25-30 degrees, but that's about where I'm stepping on the coach roof, and
can really appreciate someone holding steady at the bow.
On the other hand, I have no vang but see the need, especially in the case
of accidental gybes in strong breezes, in which cases I've had my boom
raised high enough to snag and hang up on my back stay.
Scout

"Thom Stewart" wrote in message
...
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)

Ole Thom
P/S I've used to tail as a temporary sheet while clearing an over-ride
on the main sheet wench

Scout,

You, my friend, Need the topping lift. The way you sail and the boat you
sail you should be considering a "Cruising Vang" set-up and be-damned to
the Std Vang.

If you aren't aware of what I'm talking about, I'll explain;

Sailing on the Delaware River
(especially on that bend at St Mary's Hall)
You need a Vang that is also a "Preventer" It is cheaper and more
effective on your size boat.

Set a block on each Toe-rail directly under the Boom's position when the
Boom is fully let out. If you have a metal toe rail. If not you can use
the hand rail stanchion base.
( Close enough is good enough) Run a lite line from the Boom thru the
block and back to the cockpit. If you don't have a cleat, use the stern
mooring cleats. I hook my lines to the Boom with loops to a cleat on the
Boom at about the Vang location. That's it!!

When on a reach, I can pull the Boom down with the off side sheet winch.
When running free, I use it as a preventer to stop the Accidental Jibe.
I use it also as a Boom brake while Jibing.

Try it. A lot cheaper than a vang and you get a preventer you can set
from the cockpit.

Let Doug have his solid vang

Ole Thom

"Scott Vernon" wrote in message
...
|
| "Capt. Mooron" wrote
|
| Quit toying with the damn boom.... look think of it this way... how
| many
| lifting devices utilize a support located under the boom at less
| than 25% of
| the boom length? NONE!
|
| Wrong, kanook.
| Have you never seen an engine crane?

Is the brace located at 25% of the arm's length? I believe the hydraulic ram
is located at 50% or more of the arm length.

| A bascule type draw bridge?

It's only lifting the bridge [boom] .. and again not at only 25% of the span

| Any hydraulic crane with the boom out?

Not at less than 25% of the boom.... extend the boom and the capacities
decrease exponentially.

| An excavator?

Double Hydraulic rams to the main boom at 50% distance or better to the
elbow and a third along the top of the stick to control breakout and curl.
Limits imposed are with bucket size and hydraulic capacity.

|
| need more?

Sure... the examples you provided so far hasn't done anything to convince me
that the capacity of a lifting device secured to a location less than 25% of
the span of the boom can lift as much as one located at the end of the boom.

Make note I never claimed a device secured to the bottom couldn't lift a
weight... only that the location of the vang in this instance is far too
short to accommodate the capacity of a topping lift.

Look Scotty... if you place a pair of hydraulic rams to the end of the
boom.... or a distance greater than 50 % of the span.. then the issue
becomes moot. The specific point I'm making is that the rigid vang is badly
situated to handle loads delivered to the end of the boom.

I'll stand by that claim...

CM

"Capt. Mooron" wrote |
| Wrong, kanook.
| Have you never seen an engine crane?

Is the brace located at 25% of the arm's length? I believe
the hydraulic ram
is located at 50% or more of the arm length.

So you've never seen one. It is at 25% and less when the
boom is extended out. Here's a pic of one my little Canuck
friend.
http://www.jcwhitney.com/autoparts/P...lay/s-10101/p-
1498/c-10101


| A bascule type draw bridge?

It's only lifting the bridge [boom] .. and again not at
only 25% of the span


Only the bridge? You have any idea what a bridge weighss?
And the gear is at about 5%, I'd say.



| Any hydraulic crane with the boom out?

Not at less than 25% of the boom.... extend the boom and
the capacities
decrease exponentially.

Here's a pic of a Grove Crane, very popular in this area.
See where the hyd cylinders are connected to the boom? I'd
guess that's about 10%. What do you say?
http://www.marcelequipment.com/Misc/grovert58c.htm




| An excavator?

Double Hydraulic rams to the main boom at 50% distance or
better to the
elbow and a third along the top of the stick to control
breakout and curl.
Limits imposed are with bucket size and hydraulic
capacity.


Guess again office worker. Here's another pic for you.
Can you say 10%?

http://usediron.point2.com/Xhtml/Equ...ails/P2/Excava
tor-Long-Reach/CATERPILLAR/320C/153870/ByManufacturer.html


| need more?

Sure... the examples you provided so far hasn't done
anything to convince me
that the capacity of a lifting device secured to a
location less than 25% of
the span of the boom can lift as much as one located at
the end of the boom.

How about a diving board?

look at the pretty pictures again. Study them, measure them.
Take a few days, then get back to me.

Scotty