911 mast center of gravity?

[gregshay79]

Hello brain trust,
On my Olson 911, where is the mast COG, below or above the lower spreaders?

Thank you
Greg Shay
Sail # 41324

 

[G Kiba]

I don't know? I have this nice picture and can likely make a guesstimate.

 

[gregshay79]

Thanks for the photo.. looks like above the lower spreaders.

 

[bgary]

the easy answer is that for a straight extrusion, it'll be slightly *above* the midpoint of the total span (above because the masthead structure adds some mass up high)

For a tapered extrusion it'll be lower. But if the question is about where to put slings on the mast when it is being pulled from the boat, the safe answer is to have the slings above the midpoint.

And, yeah, for a double-spreader rig that's usually just above the lower spreaders. (don't forget to consider the below-deck parts of a keel-stepped mast in figuring the total length...)

 

[gregshay79]

Thanks for the photo.. looks like above the lower spreaders.

For future reference, I put that photo G Kiba kindly provided into a paint program, added about 6ft of mast below the deck level,
and measured above and below the marked CG point. This is ignoring the taper of the mast and the weight of the spreaders, but
about 55% is below the marked CG point. (Ignore the inches units on the markup, that was just what the image editor used, the ratio
is valid, though..)

 

[bgary]

Looks good. just keep in mind that if the sling is secured too low, the mast will be top-heavy when pulled. Far better (and no detrimental effect) to have the sling secured higher than you expect you need to.

 

[Ed Valente]

It’s been a while. But if memory serves me correctly, the mast COG on the 911 is approximately 12” above the lower spreaders. Emphasis on “memory “