The weight of solid versus hollow wood masts
- The question naturally arises, then, of just what are the weights of a
solid wood mast vs. a hollow wood mast. The facts needed to address
this are: a hollow mast should have 10% greater diameter than the
equivalent hollow mast, the formula for the volume of a cylinder is pi
x the radius squared x the height, and the fact that hollow wood masts
should have a 20% wall thickness (not to mention solid inserts at the
masthead and partners (deck or upper point where it is held firmly.)
I think it is reasonable to use the average diameter to calculate
this, so since the mast head is 41% of the greatest diameter, so
(discounting any taper below deck) you want to use say .71 x the
greatest diameter to calculate the average. The weight of Douglas Fir
(aka Oregon Pine,) is @32 pounds per cubic foot, and a cubic foot is
12 x 12 x 12 inches = 1728 cubic inches.
(I'm not very good at math, so fellow posters, please feel free to
double check and correct my arithmetic.)
If your solid mast is 12" in average diameter and 70'long overall, its
weight would be (3.14 x 36 x 840 / 1728) x 32 = 1,755 pounds.
An equivalent hollow mast would be 13.2 inches in diameter, and its
"removed" space would be 11 inches in diameter, rounded for
convenience. So, you calculate the two, subtract the second from the
first, and there is your weight. So, 2128 - 1372 = 756 pounds for
the hollow equivalent.
That is a heck of a lot lighter. Does it matter?
If we are comparing junk masts to marconi masts, there are various
factors to consider. Junk masts are rather short compared to marconi
masts, and so the heavy masts have less effect on heeling than you
might expect. A 35' (length above deck) mast weighing a 1000 pounds
has the same heeling moment, roughly, as a 45' mast weighing 750
pounds. Also, let us not forget that shrouds, stays, tracks, tangs,
etc. have considerable weight.
Based on my experience of two boats 34 and 35' long, one a rather
tender 12,000 pound marconi sloop, and the other a very stiff 18,000
pound junk schooner with solid masts, not if you have a stiff boat
boat with moderate to heavy displacement. The sloop in question
usually went to windward with the lee rail and stanchion bases under
water. The schooner never touched its rail to the water. I sailed
the sloop about 6,000 miles, and the schooner perhaps 14,000 miles.
So, the stiffness issue aside, obviously, some boats were designed to
be light in displacement, and the weight of a solid mast (or 2) would
be undesirable, regardless of any effect on stiffness. Another issue
is the effect of weight aloft on the motion of the boat. In my
experience, weight aloft makes a boat more comfortable, as it slows
the boat's motion (roll, heave, and pitching.) The investigation
after the Fastnet race disaster also suggested that weight aloft would
make a boat less likely to capsize.
My conclusion is that a moderate displacement to heavy displacement
cruising boat should have sold grown sticks, if feasible, unless the
boat is tender, and light displacement boats should have hollow ones.
Tim Dunn, somewhere near Seattle
- Hi, Gary
Regarding mast height, my example of a junk schooner with a main mast
35' long above deck, and a marconi sloop with a mast 45' long above
deck: these were not theoretical boats. They were two boats I
actually owned, Batwing and the Artful Dodger, an Ericson 35. See
Batwing's rig was designed by Hasler, and its AR was 1.7 for the
mainsail and 1.8 for the foresail. You can see Batwing in PJR.
Batwing was 34' long and 18,000 in displacement, and the Artful Dodger
was 35' long and 12,000 pounds in displacement. -TD