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Author Topic: Deflection table  (Read 8037 times)
DN 5449
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Posts: 366


« on: April 18, 2011, 09:39:26 AM »

http://www.csi-composites.com/iceboat%20files/DEFLECTIONS.pdf

Looking at the following table I cannott believe the Wide range of deflection #'s between different designs.If I read correctly they range from a max. of 211 mm to 121 mm.I assume these are tip to toe measurements.Also doea FA stand for fore and aft?
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Bob Rast DN1313
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« Reply #1 on: April 21, 2011, 10:00:57 PM »

I have a lot of deflections old and some what newer. The old deflection numbers when fiberglass first came out Sherry mast and others 2-6-99
side to side  deflection
the masts were measured with 100 lbs at center between the base and 11 ft
I dont worry about for and aft as I ve experimented with both and doesn't seem to matter.
deflection  of 5 Sherry masts mostly Glass  ranged from
1 9/16 "to 1 7/8"
I have built 40 masts and found that for lighter skippers 150 lbs to 170 you probably want a deflection on the 1 7/8 "end.  Heavier skippers 200 plus are probably better using some thing around 1 3/8 or 1 1/2"
I have a newer cracker ill deflect as soon as I clean out the trailer.

If your hiking too much and cant get mast to bend your plank is too stiff or mast is too stiff or both
I weigh about 155 and had a hard time getting mast to bend until I built something softer around 1 3/4" defelection.
You also might try sending mast forward untill you get some bend and fine tuning from there.
your plank should defect around 1 5/8" to 1 3/4" with your weight.Check Rons tuning guides
I have one of both using softer  for light air and stiffer for heavier.
Try deflecting mast see if it is soft or stiff??

Bob Rast DN1313
here is a pic of my son testing a Mast he is about 150lbs.
My Viagra Mast  plank is on the soft side as you can see in photo
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Bob Rast DN1313
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« Reply #2 on: April 21, 2011, 10:10:17 PM »

That deflection table is pretty old.
We use to deflect side deflection,base to 11 ft and base to tip
fore and aft base to hound and tip
I just do base to 11 ft seems to work
masts are always stiffer fore and aft as material is doubled up on front of mast and section design

to do base to 11 ft  side deflection I clampt he base so mast doesnt rotate, then tape about a 2 ft strip of wood at aprox 5'6" center to make level area to add weight,I use 25lb barebell weights carefull balanced .measure to bolt  rope slot before and after adding weight , repeat for other side if you want .should be about the same.

Happy measuring
Bob Rast DN1313
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DN 5449
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Posts: 366


« Reply #3 on: April 22, 2011, 10:08:13 AM »

Thanks for the info Bob.I can see how the Plank deflection is soly based on weight but I would have to believe the stiffness of your mast would not all just be weight related. I would think
sterngth of the sailor would be a factor in how much you could bend the mast.That is a stronger individual could get away with a stiffer mast.Any thoughts or info on that Bob?
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