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Old August 31st 03, 11:48 AM
Steve Lusardi
 
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Default Converting sloop to cutter

Jim,
The position of the mast is arranged so that the center of effort of the
sail plan is directly over the center of lateral resistance. In most cases
this places the mast over the leading edge of the keel, but it does not have
to be there.
Steve
"jimthom" wrote in message
m...
I was wondering if the position of the mast in relation to the
leading edge of the keel was sacrosanct, or indeed if there was any
significant reason at all to establish this relation.

I am planning to move the mast aft from station 4 to station 5
(approximate), but keep the CE of the sail plan where it is by
altering the sail plan to a cutter rig. The leading edge of the keel
is fixed around station 4.

Of course I will have a qualifed person design my new cutter rig, but
I was wondering in theory if this is a practical objective.

Thank you,
jimthom




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Old August 31st 03, 01:07 PM
Stephen Baker
 
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Default Converting sloop to cutter

Steve Lusardi says:

The position of the mast is arranged so that the center of effort of the
sail plan is directly over the center of lateral resistance.


Not in many cases, if at all. Usually the CE leads (i.e. is forward of) the
CLR by between 5 and 10% of the LWL. This may vary from designer to designer,
and they may or may not include portions of the rudder in the calculation, but
there is always some lead.

Steve
Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/pr...cbweb/home.htm
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Old August 31st 03, 05:03 PM
Stephen Baker
 
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Default Converting sloop to cutter

Ron whines (and spells my name wrong to boot!):

Steven, Tell um why please.


Well, since you ask, and since this is a Sunday so I can't charge for this.....

There are a "few" variables that affect the placement of CE. You have to allow
for things like the actual centre of effort not being the centre of area
(although this is simpler because that is the case for the keel as well), and
the fact that the sails are almost never on centreline, so the line of force
(vector for the tech-heads) doesn't act in the same plane as the drawing.
That last one is the kicker here. If you draw the boat from above, and draw
the sails in "operating" position, and then their respective force vectors, you
will note that the resultant is now acting _behind_ the CLR, giving some
weather helm (vastly preferable to the alternative) in most cases. Boats like
Open Class 50s and 60s, using autopilots most of their sailing lives, will have
little, if any helm at all. And the lucky designer is the one that has figured
out his own little system, and it works ;-))

Steve
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Old August 31st 03, 05:55 PM
P.C.
 
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Default Converting sloop to cutter

Hi

"Stephen Baker" skrev i en meddelelse
...
Ron whines (and spells my name wrong to boot!):

Steven, Tell um why please.


Well, since you ask, and since this is a Sunday so I can't charge for

this.....

There are a "few" variables that affect the placement of CE. You have to

allow
for things like the actual centre of effort not being the centre of area
(although this is simpler because that is the case for the keel as well), and
the fact that the sails are almost never on centreline, so the line of force
(vector for the tech-heads) doesn't act in the same plane as the drawing.
That last one is the kicker here. If you draw the boat from above, and draw
the sails in "operating" position, and then their respective force vectors,

you
will note that the resultant is now acting _behind_ the CLR, giving some
weather helm (vastly preferable to the alternative) in most cases. Boats like
Open Class 50s and 60s, using autopilots most of their sailing lives, will

have
little, if any helm at all. And the lucky designer is the one that has

figured
out his own little system, and it works ;-))


Don't you just design the boat so it perform well ?

P.C.



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Old August 31st 03, 06:18 PM
Ron Thornton
 
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Default Converting sloop to cutter

Thanks Stephen, sorry bout the name.

Ron



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Old August 31st 03, 09:59 PM
Stephen Baker
 
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Default Converting sloop to cutter

P.C. says:

Don't you just design the boat so it perform well ?


Usually ;-)
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Old August 31st 03, 09:59 PM
Stephen Baker
 
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Default Converting sloop to cutter

Ron says:

Thanks Stephen, sorry bout the name.


No problem - my own father used to forget from time to time. ;-))

Steve


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