http://home.cfl.rr.com/irwin104/specs.html

Foresail SheetLoads
100% Foretriangle @ 30 Knots: 834.8 lbs
100% Foretriangle @ 35 Knots: 1136.3 lbs
100% Foretriangle @ 40 Knots: 1484.1 lbs
135% Foretriangle @ 20 Knots: 500.9 lbs
135% Foretriangle @ 25 Knots: 781.4 lbs
135% Foretriangle @ 30 Knots: 1127.0 lbs
150% Foretriangle @ 5 Knots: 34.8 lbs
150% Foretriangle @ 10 Knots: 139.1 lbs
150% Foretriangle @ 15 Knots: 313.1 lbs
150% Foretriangle @ 20 Knots: 556.6 lbs
Lead Block Loads
#3 Genoa @ 30 Knots: 1093.6 lbs
#3 Genoa @ 35 Knots: 1488.4 lbs
#3 Genoa @ 40 Knots: 1944.2 lbs
#1 Genoa @ 6 Knots: 37.6 lbs
#1 Genoa @ 12 Knots: 150.3 lbs
#1 Genoa @ 18 Knots: 338.1 lbs
#1 Genoa @ 20 Knots: 417.4 lbs
#1 Genoa @ 25 Knots: 652.2 lbs
Maximum Genoa Turning Lead Block
60 Degree Turn: 1136.3 lbs
90 Degree Turn: 1602.2 lbs
135 Degree Turn: 2090.8 lbs
180 Degree Turn: 2272.6 lbs

Mic 67

Mic wrote:
http://home.cfl.rr.com/irwin104/specs.html

Foresail SheetLoads
100% Foretriangle @ 30 Knots: 834.8 lbs
100% Foretriangle @ 35 Knots: 1136.3 lbs

That's just plain silly. An Irwin 10/4 is not going to be
carrying a 100% jib in 35 knots of wind, nor a 150 in 20 knots.

Fresh Breezes- Doug King

DSK wrote:
Mic wrote:

http://home.cfl.rr.com/irwin104/specs.html

Foresail SheetLoads
100% Foretriangle @ 30 Knots: 834.8 lbs
100% Foretriangle @ 35 Knots: 1136.3 lbs


That's just plain silly. An Irwin 10/4 is not going to be carrying a
100% jib in 35 knots of wind, nor a 150 in 20 knots.

Fresh Breezes- Doug King



Thanls for the sanity check.

DSK wrote:

Mic wrote:

http://home.cfl.rr.com/irwin104/specs.html

Foresail SheetLoads
100% Foretriangle @ 30 Knots: 834.8 lbs
100% Foretriangle @ 35 Knots: 1136.3 lbs


That's just plain silly. An Irwin 10/4 is not going to be carrying a
100% jib in 35 knots of wind, nor a 150 in 20 knots.

Fresh Breezes- Doug King




Good Sanity Check!

It's seldom realized but wind forces are not used in engineering
sailboat rigs. To design a rig properly, you have to know the
vessel's stability. You determine the maximum normal sailing angle
and the righting moment associated with it. That righting moment is
then divided by the sail area and the distance between the center of
effort and a point usually taken as half the draft. This give the
load on each square foot of sail which is then used to design the
spars and rigging.

The theory is that sail will be reduced or the wind loads eased by
sheet handling or course change when the vessel is heeled beyond
normal angles. This won't always be the case but that's what the
factors of safety are for.

For very conservative rigs, such as on a solo (non-racing) long
distance ocean cruisers, you might look at the righting moment at the
peak of the righting arm curve. No amount of wind can put more
pressure on the rig than at that point because the boat will simply
blow over farther to where there is less righting moment.

You also sometimes want to look at loads under reduced canvas because
they will be much higher per unit area and may locally overstress
components that would be fine heeled to the same angle under the full
sail plan.

--

Roger Long



"DSK" wrote in message
.. .
Mic wrote:
http://home.cfl.rr.com/irwin104/specs.html

Foresail SheetLoads
100% Foretriangle @ 30 Knots: 834.8 lbs
100% Foretriangle @ 35 Knots: 1136.3 lbs

That's just plain silly. An Irwin 10/4 is not going to be carrying a
100% jib in 35 knots of wind, nor a 150 in 20 knots.

Fresh Breezes- Doug King

Roger Long wrote:
It's seldom realized but wind forces are not used in engineering
sailboat rigs.

Oh, I dunno, probably a lot of designers spend at least a
little bit of time on stuff like that.

... To design a rig properly, you have to know the
vessel's stability. You determine the maximum normal sailing angle
and the righting moment associated with it. That righting moment is
then divided by the sail area and the distance between the center of
effort and a point usually taken as half the draft. This give the
load on each square foot of sail which is then used to design the
spars and rigging.


Yes, but at that point, haven't the basic sailplan &
dimensions already been worked out?



For very conservative rigs, such as on a solo (non-racing) long
distance ocean cruisers, you might look at the righting moment at the
peak of the righting arm curve. No amount of wind can put more
pressure on the rig than at that point because the boat will simply
blow over farther to where there is less righting moment.


Sure. This is one reason why it's funny to hear people
talking about making their boats more seaworthy by upsizing
their shrouds. Unless they were undersized to start with,
and the chainplates etc etc also upgraded, this accomplishes
exactly nothing (expect the unnecessary expenditure of money).


You also sometimes want to look at loads under reduced canvas because
they will be much higher per unit area and may locally overstress
components that would be fine heeled to the same angle under the full
sail plan.


One way to figure loads on various hardware, deck fittings,
and the like, is to look at how much strain would be on a
tow line pulling the boat at speed. Then imagine letting the
tow line veer side to side, slacken for a moment and then
pop tight, etc etc. If this would break it, then it needs to
be beefier. In fact, on many points the load is higher
because the rig is not only pushing the hull at speed, but
the force on whatever given bit of rig/hardware is at a tangent.

And one point I like to keep in mind, no sailor ever
complained that his rig was too easy to handle because the
winches were so big

Fresh Breezes- Doug King

"DSK" wrote

Oh, I dunno, probably a lot of designers spend at least a little bit
of time on stuff like that.


Nope. There are other design aspects where the designer is concerned
with wind speed but not when determining rig strength. (I muddied the
waters a bit by saying "force" instead of "speed" farther up the
thread.

If you were designing an exhibit boat fixed in a concrete berth on
land, you would have to figure out the maximum wind speed likely to
occur and then design the rig to withstand that. A boat in the water
heels. No amount of wind can put a greater force on the rig than that
which would heel the boat to the peak of the righting arm curve. You
resolve that back to a corresponding load to design the rig. That
does give you a force that can be converted to wind speed. However,
to get the wind speed that would be measured, you have to first divide
by the Cosine squared of the heel angle to account for the wind
blowing horizontally and not coming down perpendicular to the sails.

When determining sail plan or hull characteristics, the designer will
ponder wind speeds in order to produce a boat that will carry its full
sail plan at optimum heel in a specified wind velocity. The design
question is not, how much wind the rig should withstand but how much
strength is required to match the loads which are determined by the
hull's stability.

This is all a complicated way of agreeing (which is what I was trying
to do in my reply to your post) with your statement that it's silly to
talk about the rig loads of a 150% Genoa in a 35 knot wind.

--

Roger Long

Roger Long wrote:
Nope. There are other design aspects where the designer is concerned
with wind speed but not when determining rig strength.

Well, that's what I was getting at, in my unclear muddled
way of speaking

A deigner has to have an idea about how much sail area the
boat will need in order to achieve the desired performance,
be it a super-zippy hi-tech speedster or a crab-crusher.
After that part is worked out, and then things like desired
aspect ratio are fiddled with, the designer knows
approximately what the boat will need in terms of mast
height, etc etc. Somewhere in there, a desired range of
righting moment is worked out (the shape of the curve as
well the max).



If you were designing an exhibit boat fixed in a concrete berth on
land, you would have to figure out the maximum wind speed likely to
occur and then design the rig to withstand that.

Right.

... A boat in the water
heels. No amount of wind can put a greater force on the rig than that
which would heel the boat to the peak of the righting arm curve.

Agreed. I was not saying you were wrong about that, not at
all. In fact I have said the same thing a few times, in
years past.



.... You
resolve that back to a corresponding load to design the rig.

I think we are using the words "rig" differently.


When determining sail plan or hull characteristics, the designer will
ponder wind speeds in order to produce a boat that will carry its full
sail plan at optimum heel in a specified wind velocity. The design
question is not, how much wind the rig should withstand but how much
strength is required to match the loads which are determined by the
hull's stability.


And I think at this point, the word "rig" encompasses the
mast section, the shroud base & spreaders, as well as sizing
the standing rigging... somewhere in there, the deck layout
has to be planned too, completing the circle back to winch
size & sheet load


This is all a complicated way of agreeing (which is what I was trying
to do in my reply to your post) with your statement that it's silly to
talk about the rig loads of a 150% Genoa in a 35 knot wind.


Yep. Even though a few of us have done it!

Fresh Breezes- Doug King

On Sun, 04 Jun 2006 19:48:53 -0400, DSK wrote:

One way to figure loads on various hardware, deck fittings,
and the like, is to look at how much strain would be on a
tow line pulling the boat at speed.

Interesting idea but that is not how the professionals do it. I once
had the pleasure (or misfortune) to work with Ben Hall designing a new
rig for my old Cal-34. I wanted to increase sail area by turning it
into a fractional rig, same fore triangle, larger mainsail.

The first thing that Ben wanted to know was the righting moment
(stability) of the hull, because that was the ultimate determinant of
how much rigging load could be created.

One way to figure loads on various hardware, deck fittings,
and the like, is to look at how much strain would be on a
tow line pulling the boat at speed.


Wayne.B wrote:
Interesting idea but that is not how the professionals do it.

Perhaps I should have said "Figger" instead of "figure,"
since I did not mean to imply how to calculate the load
mathematically. Instead, just trying to get an intuitive
idea of how much force is involved. A lot of people can't
seem to grasp the idea that to move a big boat at speed
takes a lot of grunt, and all that force (and more) is
transmitted to the hull by the rig.

.... I once
had the pleasure (or misfortune) to work with Ben Hall designing a new
rig for my old Cal-34. I wanted to increase sail area by turning it
into a fractional rig, same fore triangle, larger mainsail.


That's a great idea. Did you go ahead with it? While I have
sailed a lot of mast head rigs, I've always liked fracs more.


The first thing that Ben wanted to know was the righting moment
(stability) of the hull, because that was the ultimate determinant of
how much rigging load could be created.


All that tells you is when you'll have to reef. You could
put a 70' mast on the boat and a 1000 square foot mainsail,
if you didn't mind tucking in your third reef in 15 knot winds.

Fresh Breezes- Doug King