Anonymous wrote:

The weights in Reply # 7816554 on 7815815 are shipping weights. These poles are cone-tapered such that the bottom half or so are straight wall (see ECXA25 pdf attached). So using the you can estimate the weight of the pole alone . I got an estimate of 70 lbs weight for the ECXA25 which is 5" x 5/32" x 33 ft, 6063-T6.

David Webb:

I did a quick calculation on Arne's mast for Ingeborg and came up with comparative figures at 0.8 of 18,140 Nm and at 0.88, 19,954 Nm. The latter figure is very close to his calculated strength for his mast and is a much simpler calculation.

I hope this is of some interest/use.

All the best with the project, David

David, where do the factors 0.8 and 0.88 come from?

Arne

When in College I had a lecturer in Structural Engineering who told us Architects "you don't need to know how to design something to a "gnats ass", all you need is a rule of thumb that will get you approximately the same result and is quick and easy to calculate as well as easy to remember". I have always remembered that advice and it has saved me from mistakes on a number of occasions.

So when calculating the strength of tubes in bending I imagine the tube as an I beam with a top and bottom flange, each equal to a quarter of the circumference of the tube multiplied by the wall thickness. The flanges of the tube are separated from each other by the diameter of the tube, but because of the curve of the tube not all is at this distance. I use a correction factor of 0.8 which is a little more conservative than the actual .88 or thereabout. The simple bending moment formula is then used to calculate the strength.

I did a quick calculation on Arne's mast for Ingeborg and came up with comparative figures at 0.8 of 18,140 Nm and at 0.88, 19,954 Nm. The latter figure is very close to his calculated strength for his mast and is a much simpler calculation.

I hope this is of some interest/use.

All the best with the project, David

Scott wrote:

Shemaya wrote:

 But also, my flagpole mast on AUKLET was a lot thicker at the top, where it had been tapered. About 1/4 inch, when the butt was 1/8. So maybe in the interest of being lighter weight, the straight tube and wood topmast might be an advantage. 

The tapering technique usually takes a uniform tube and squeezes it down by rolling it.  You don't save weight with a tapered aluminum pole, but do save windage.

Not so, Scott. Some of the material moves inwards, thickening the wall, and some is extruded lengthways*. For example, a parallel tube 9.2m long, 17.7cm dia x 3.2mm wall: 43.4kg. My actual mast tube, after tapering: 36kg.

* exact proportions dependant on the machinery used, I suppose.

Oh my goodness! I go off to the country for a few days without phone service or internet and return to all this wonderful discussion and input. It’s going to take me a sec to digest it all!

Thank you all yet again! Huge amounts of gratitude to Shemaya for acting as proxy. I have no doubt that without her I’d be totally lost with all this