Shape of a flexins mast, pros/cons?

[Gades]

Hi guys,

I'd like to know the opinion of different sailors/designers on the shape of a mast. I'm talking about the transversal deflection. For example, looking to the drawing I attached, you can see different shapes. Obviously they're not real (not properly scaled), but it's easier to appreciate this way.

So, playing with the spreaders (size and position) and the different diameters, I can get different bending shapes. Which one would you suggest, and why?

[Gades]

The attachment didn't work properly, so here it's the image.

[Polarity]

A....

lets the top fall off in the gusts and changes the sheeting angle according to the windsheer.

Paul (Sailor!)

[Gades]

Thanks Paul,
I was waiting for your answer

[DavidG]

I agree A,

Main twists off at the head, allowing for wind sheer.

Jib leach opens up in the gusts, giving a nice parallel slot.

More practically, the spreaders will clear the jib leach.

The rig will be easier to set up.

The sailmaker will understand what you are talking about!

David

[Gades]

Thanks DavidG,

I also have another question about the mast, actually about the spreader.

I think I know how to calculate the horizontal angle (let's say the one you'd see in a plan view); but I do not know how to calculate the vertical angle (if I want/need it). Any information/formulas about this?

Thanks again

Fernando

[Polarity]

As far as I know they should bisect the angle of the shrouds so that they are purely in compression.

Paul

[giramonti]

Yes, the spreader should bisect the angle of the shrouds that cross its tip. This can be a bit difficult to determine, because theoretically, the two or three or four shrouds that cross a tip must be weighted then divided by the sum of the loads to determine the final angle (e.g. on a 1-spreader rig, at the bottom spreader, the cap shroud has a Br.str. of 5000kg, the bisect is 5.4°, V1D2 has a br.str. of 4200kg w/ bisect of 6.8° – to determine spreader angle: "(5000kg*5.4° + 4200kg*6.8°) / 5000kg+4200kg = 6.039°").

Practically speaking, a sparmaker is not as precise as setting the spreader at small fractions of degrees. So, in this case the spreader will be set at 6°. At Carl Schumacher's office we set all of our spreaders at 6°, because experience told us that spreaders were always 6° +- 0.3°. I haven't analysed why this is the case, maybe its the way we designed our rigs, but it worked well.

-Roberto

[Gades]

Thanks again guys,

I think I understand what you say/mean (I don't always do )
I'm going to post my load calculations and a drawing (with proper dimensions), with the spreaders as well (my first time).

Cheers

Fernando


P.D.: Paul, I think there were some problems with your site today. I couldn't get to your links page (this morning).

[Polarity]

my personal site Polarity2 or work site Nonstopyacht Supply ? they both seem to work ok now, maybe just a glitch...

But thanks for the heads up..


Paul