Subject: loads on masts


Hello,
need to get some data on load figures on masts for sail boats.
Various pulling forces from forestay, halyards,shrouds , backstays etc
plus
pushing forces from spreaders
act on the mast.
Need some real numbers in lbs for standing rigging as well as under sail
for
variable conditions.

Of course each boat and size have different value ranges.
Have looked into various books but real data are scant.
Can somebody help with links or bits of wisdom? Just assume and make
references to boat length , mast heights etc.
help is much appreciated
thanks mik

Skene's Elements of Yacht Design has a good section on calculating these
loads. I don't know if it's still in print, but you can probably find a used
copy on the web (or try the library).

Tom Dacon

"noexpert" wrote in message
...
Subject: loads on masts


Hello,
need to get some data on load figures on masts for sail boats.
Various pulling forces from forestay, halyards,shrouds , backstays etc
plus
pushing forces from spreaders
act on the mast.
Need some real numbers in lbs for standing rigging as well as under sail
for
variable conditions.

Of course each boat and size have different value ranges.
Have looked into various books but real data are scant.
Can somebody help with links or bits of wisdom? Just assume and make
references to boat length , mast heights etc.
help is much appreciated
thanks mik

Hi
What do you want these points for ?
The forces from the rig is not just those at the mast , wires take most
anyway and when you calculate the forces they are often situated at the
first third of the main sail, not at the mast --- even unstayed masts
distribuate the force to a rope at the far corner of the sail acturly
these forces can be bigger than those affecting the mast that then pull
the wires in the rig.

On Wed, 31 Aug 2005 15:52:14 +0000, noexpert wrote:

Subject: loads on masts


Hello,
need to get some data on load figures on masts for sail boats.
Various pulling forces from forestay, halyards,shrouds , backstays etc
plus
pushing forces from spreaders
act on the mast.
Need some real numbers in lbs for standing rigging as well as under sail
for
variable conditions.

Of course each boat and size have different value ranges.
Have looked into various books but real data are scant.
Can somebody help with links or bits of wisdom? Just assume and make
references to boat length , mast heights etc.
help is much appreciated
thanks mik

Well, one way to look at it is that the torque cannot exceed the righting
moment of the boat. It may be easier to guesstimate the righting moment of
a boat than aerodynamic forces.

I am not a naval architect (or marine engineer).

--Mac

You have asked an interesting question. Of course these forces change all
the time as the wind, sea state, heading and sail set change. If you knew
these numbers exactly, what would you do with the data? A prudent designer
would multiply the forces by a safety factor (like 10 or more) and then
develop the stresses. For practical purposes, assuming you are interested
in rigging a real boat, take a look at similar successful boats in your area
and plagiarize.

The gotcha with that approach is the inertial loading.

Sure, a steady pull of umph pounds will hold the boat at a forty five degree
angle, but lurch against the mast to try and move from level to heeled
rapidly and the forces become huge, depending on the angular moment of
inertia. (Keep the weight out of the ends of the boat.) Then too, in
really rough weather, the forces are chaotic.

Remember that the standing rigging pulls up as well as down. If your chain
plates will only withstand 1000 lbs, it's silly to use shrouds that will
pull 2000 lbs. Also, two shrouds at 1000 lbs each means an additional 2000
lbs on the mast step.

Too complex for my brain.

Roger

http://home.earthlink.net/~derbyrm

"Mac" wrote in message
news
On Wed, 31 Aug 2005 15:52:14 +0000, noexpert wrote:

Subject: loads on masts
Need some real numbers in lbs for standing rigging as well
as under sail for variable conditions.

Well, one way to look at it is that the torque cannot exceed the
righting moment of the boat. It may be easier to guesstimate the
righting moment of a boat than aerodynamic forces.

I am not a naval architect (or marine engineer).

Hi
Now if what you need is to see if the sail have the right size compared
where the mast are compared the size of the jig ---- the shape of the
sail aso. there are one easy way to find out, the way these things been
"calculated" for centuries. It will not thell you if the sail is big
enough but it will tell you if the boat can sail.
Just draw a sideview of the boat with sails up, then cut it out and
place the cut out pieces on a point needle untill it ballance
------Then you have the geometric center point for the forces of the
sail. Do the same with only the underwater hull and by ballancing it
over an edge, find the center point for that. Now when you have both
the point you can say the sail forces will work from and the point that
tell you how to push the hull sideverts thru the water, it is easy to
point out a point or line to place the mast, so the forces from the
sail effect the hull. In some old books you can find some rules about
what the ideal distance between these two points or lines must be for
the boat to be able to tack.
Cut out a sideview and ballance it over an edge, --- that's
boatbuilding math ) and it work.

This and other matters dealing with sizing of rigging, spars, and scantlings
is dealt with quite well in Dave Gerr's "The Nature of Boats." Perhaps you
could take a SWAG at the safety factors which were applied and work
backwards to the loads?

Roger

http://home.earthlink.net/~derbyrm

wrote in message
oups.com...
Hi
Now if what you need is to see if the sail have the right size compared
where the mast are compared the size of the jig ---- the shape of the
sail aso. there are one easy way to find out, the way these things been
"calculated" for centuries. It will not thell you if the sail is big
enough but it will tell you if the boat can sail.
Just draw a sideview of the boat with sails up, then cut it out and
place the cut out pieces on a point needle untill it ballance
------Then you have the geometric center point for the forces of the
sail. Do the same with only the underwater hull and by ballancing it
over an edge, find the center point for that. Now when you have both
the point you can say the sail forces will work from and the point that
tell you how to push the hull sideverts thru the water, it is easy to
point out a point or line to place the mast, so the forces from the
sail effect the hull. In some old books you can find some rules about
what the ideal distance between these two points or lines must be for
the boat to be able to tack.
Cut out a sideview and ballance it over an edge, --- that's
boatbuilding math ) and it work.

Thanks so far;
good comments. Shall get the books mentioned.
I am reworking a mast arrangement and needed some details.
Naturally stresses are different along the lenght and calculatiuons are not
done with a simple formula.
So any references are welcome.
regards mikl

"Dave W" wrote in message
...
You have asked an interesting question. Of course these forces change all
the time as the wind, sea state, heading and sail set change. If you knew
these numbers exactly, what would you do with the data? A prudent
designer would multiply the forces by a safety factor (like 10 or more)
and then develop the stresses. For practical purposes, assuming you are
interested in rigging a real boat, take a look at similar successful boats
in your area and plagiarize.

On Mon, 05 Sep 2005 00:08:34 GMT, noexpert said:
Thanks so far;
good comments. Shall get the books mentioned.
I am reworking a mast arrangement and needed some details.
Naturally stresses are different along the lenght and calculatiuons are not
done with a simple formula.
So any references are welcome.
regards mikl

Another book you may consider: Larsson and Eliasson, _Principles of Yacht
Design_ deals with these forces in a full chapter on rig construction,
and also their effect on the hull.

--Damian