mast loads, design
 

Does anyone have advise on how to calculate mast/sail loads? This is
actually for a solid wing ice boat, but I think if I can understand
traditional mast/sail loads, it should translate to my application. I
don't think aircraft design is applicable here, especially G-forces. The
key point for boats vs. airplanes is that you can only apply so much force,
and then the boat will start to capsize and spill the air. For sake of
example here are some parameters:
weight: 500lbs
sail area: 50 square feet
center of effort on sail (wing): 6 ft high
plank: 14 ft (7ft from hull to runner)
estimated speed (if it matters): 80mph

I don't know how to figure this out with an equation, but by simply
examining movement distances of the CE and hull, it appears that the sail
has a mechanical advantage so the load on the sail would never reach 500
lbs. I also have to account for loads encountered in a gust.

Am I on the right track here? Can anyone recommend some reading on this
matter?

Thanks for any assistance,
Dave

Assuming chain plate base =plank: 14 ft

500 lb. x 7 ft. = (vertical chainplate load) lbs x 14 ft.
max mast load compression =vertical chainplate load
max mast load compression= 250 lbs.

There is more going on here, but I need spreader information.

"Dave Schneider" wrote in message
...
Does anyone have advise on how to calculate mast/sail loads? This is
actually for a solid wing ice boat, but I think if I can understand
traditional mast/sail loads, it should translate to my application. I
don't think aircraft design is applicable here, especially G-forces. The
key point for boats vs. airplanes is that you can only apply so much
force,
and then the boat will start to capsize and spill the air. For sake of
example here are some parameters:
weight: 500lbs
sail area: 50 square feet
center of effort on sail (wing): 6 ft high
(7ft from hull to runner)
estimated speed (if it matters): 80mph

I don't know how to figure this out with an equation, but by simply
examining movement distances of the CE and hull, it appears that the sail
has a mechanical advantage so the load on the sail would never reach 500
lbs. I also have to account for loads encountered in a gust.

Am I on the right track here? Can anyone recommend some reading on this
matter?

Thanks for any assistance,
Dave

Hi Dave,
I think your on the right track. The capsize moment is simply the weight
times 1/2 the "beam", but dynamic loads (wind gusts, sharp turns, bumps,
etc.) are more difficult to quantify. On my last wing sail project I
doubled the capsize moment to account for dynamic effects. Crude, but you
have to start somewhere. The next step is to use the beam equation, Stress
= MC/I, to calculate the required mast size and thickness ( I ), for an
assumed stress level. If your building the wing out of composite materials
its a good idea to build some samples, test them to failure, calculate the
failure stress, and use a percentage of this stress ( 50% ) in the beam
equation to calculate the minimum I (moment of inertia) required. SKEN'S
ELEMENTS OF YACHT DESIGN has some examples of the basic process. You can
get more details on my wing sail projects at:
http://www.johnsboatstuff.com/Articles/rigid2.htm .
Good Luck,
John


"Dave Schneider" wrote in message
...
Does anyone have advise on how to calculate mast/sail loads? This is
actually for a solid wing ice boat, but I think if I can understand
traditional mast/sail loads, it should translate to my application. I
don't think aircraft design is applicable here, especially G-forces. The
key point for boats vs. airplanes is that you can only apply so much
force,
and then the boat will start to capsize and spill the air. For sake of
example here are some parameters:
weight: 500lbs
sail area: 50 square feet
center of effort on sail (wing): 6 ft high
plank: 14 ft (7ft from hull to runner)
estimated speed (if it matters): 80mph

I don't know how to figure this out with an equation, but by simply
examining movement distances of the CE and hull, it appears that the sail
has a mechanical advantage so the load on the sail would never reach 500
lbs. I also have to account for loads encountered in a gust.

Am I on the right track here? Can anyone recommend some reading on this
matter?

Thanks for any assistance,
Dave

If you give me the sail CE height from the ground,
I can add the sail compression load. Is there a forestay?
Height?


"ddinc" wrote in message
...
Assuming chain plate base =plank: 14 ft

500 lb. x 7 ft. = (vertical chainplate load) lbs x 14 ft.
max mast load compression =vertical chainplate load
max mast load compression= 250 lbs.

There is more going on here, but I need spreader information.

"Dave Schneider" wrote in message
...
Does anyone have advise on how to calculate mast/sail loads? This is
actually for a solid wing ice boat, but I think if I can understand
traditional mast/sail loads, it should translate to my application. I
don't think aircraft design is applicable here, especially G-forces. The
key point for boats vs. airplanes is that you can only apply so much
force,
and then the boat will start to capsize and spill the air. For sake of
example here are some parameters:
weight: 500lbs
sail area: 50 square feet
center of effort on sail (wing): 6 ft high
(7ft from hull to runner)
estimated speed (if it matters): 80mph

I don't know how to figure this out with an equation, but by simply
examining movement distances of the CE and hull, it appears that the sail
has a mechanical advantage so the load on the sail would never reach 500
lbs. I also have to account for loads encountered in a gust.

Am I on the right track here? Can anyone recommend some reading on this
matter?

Thanks for any assistance,
Dave

I forgot to mention that the wing has shrouds and a forestay, probably
around the 8 ft mark. CE is around 6 ft.


"ddinc" wrote in message
...
If you give me the sail CE height from the ground,
I can add the sail compression load. Is there a forestay?
Height?


"ddinc" wrote in message
...
Assuming chain plate base =plank: 14 ft

500 lb. x 7 ft. = (vertical chainplate load) lbs x 14 ft.
max mast load compression =vertical chainplate load
max mast load compression= 250 lbs.

There is more going on here, but I need spreader information.

"Dave Schneider" wrote in message
...
Does anyone have advise on how to calculate mast/sail loads? This is
actually for a solid wing ice boat, but I think if I can understand
traditional mast/sail loads, it should translate to my application. I
don't think aircraft design is applicable here, especially G-forces.
The
key point for boats vs. airplanes is that you can only apply so much
force,
and then the boat will start to capsize and spill the air. For sake of
example here are some parameters:
weight: 500lbs
sail area: 50 square feet
center of effort on sail (wing): 6 ft high
(7ft from hull to runner)
estimated speed (if it matters): 80mph

I don't know how to figure this out with an equation, but by simply
examining movement distances of the CE and hull, it appears that the
sail
has a mechanical advantage so the load on the sail would never reach
500
lbs. I also have to account for loads encountered in a gust.

Am I on the right track here? Can anyone recommend some reading on
this
matter?

Thanks for any assistance,
Dave

Thanks John.

I looked at my movement drawings a little more and I think I understand the
static loads. As I said, the mast/wing does have a mechanical advantage
for lifting the hull. Using the lee runner as the radius center, the
capsize moment is the ratio of the hull circumference and the CE
circumference. With pi factored out, the algorithim is:
|
|
|
h |
|
|
+------+------+
| b |

500 * b/sqr(h*h+b*b) (the CE radius is simple trig)

Actually the base in this example is less than b because the movement isn't
actually against the lee runner, but against a line that is tangent to the
hypotenuse of the triangle formed by the rear plank and the front steering
spring board. This omission actually errors on the side of safety so I'm
not going to worry about it.

I'm ok with designing the wing if I know the loads. I purchased a spar
designer that is used for designing airplane wings. The program isn't
perfect for this application because it assumes a cantelevered wing
(unstayed). Only the portion of the wing above the stays is cantelevered.

So now I'm still left with the dynamic loads encountered in a gust. I'm ok
with just doubling the loads if that works.

FYI: here is a web site that I'm co-managing. I'm co-managing only because
I helped instigate the forming of the group, not because I know anything
about wings. :-) My alias in that group is Sllingblade.

http://groups.msn.com/LandsailerandI...ndconstruction



"John Holtrop" wrote in message
...
Hi Dave,
I think your on the right track. The capsize moment is simply the weight
times 1/2 the "beam", but dynamic loads (wind gusts, sharp turns, bumps,
etc.) are more difficult to quantify. On my last wing sail project I
doubled the capsize moment to account for dynamic effects. Crude, but you
have to start somewhere. The next step is to use the beam equation,
Stress
= MC/I, to calculate the required mast size and thickness ( I ), for an
assumed stress level. If your building the wing out of composite
materials
its a good idea to build some samples, test them to failure, calculate the
failure stress, and use a percentage of this stress ( 50% ) in the beam
equation to calculate the minimum I (moment of inertia) required. SKEN'S
ELEMENTS OF YACHT DESIGN has some examples of the basic process. You can
get more details on my wing sail projects at:
http://www.johnsboatstuff.com/Articles/rigid2.htm .
Good Luck,
John


"Dave Schneider" wrote in message
...
Does anyone have advise on how to calculate mast/sail loads? This is
actually for a solid wing ice boat, but I think if I can understand
traditional mast/sail loads, it should translate to my application. I
don't think aircraft design is applicable here, especially G-forces.
The
key point for boats vs. airplanes is that you can only apply so much
force,
and then the boat will start to capsize and spill the air. For sake of
example here are some parameters:
weight: 500lbs
sail area: 50 square feet
center of effort on sail (wing): 6 ft high
plank: 14 ft (7ft from hull to runner)
estimated speed (if it matters): 80mph

I don't know how to figure this out with an equation, but by simply
examining movement distances of the CE and hull, it appears that the
sail
has a mechanical advantage so the load on the sail would never reach 500
lbs. I also have to account for loads encountered in a gust.

Am I on the right track here? Can anyone recommend some reading on
this
matter?

Thanks for any assistance,
Dave