I had a barrel tapered mast that had very good strength and stiffness through the middle but, unlike a more traditionally built barrel tapered mast as Skeene would have analyzed, my mast was unusually light, I believe, in the upper few feet.  It was built lightly enough that the very top of the mast flexed under halyard and sail forces which I guess that would be consistent with  Arne’s “case 1”. 

My first junk rig mast was barrel tapered and designed for me by Phil Bolger in 1994.  At the time he wrote “I have no personal experience with Chinese lugs.” This was before he drew his hybrid Chinese gaff rig.  (Which incidentally powered Jim Melcher’s  Alert and which is now owned by a friend and has been at one of our north east junkets albeit with a different rig) The mast was in keeping with Phil’s amateur friendly philosophy. The 27 foot O.A., 24 ft above the tabernacle, 4 3/4 inch square tabernacled mast was for a 3200 lb. boat, an O’day 23.  Two of the scarfed staves were 1 1/2 “  X  4 3/4” X 27 feet. Two were 1 1/2” X  1 3/4” X 27 feet. When glued up the hollow center of this 27 ft box was 1 3/4” throughout its length.  The barrel shape was sawn from this and the corners radiused. 

The barrel shape, of course, allowed for wider sections. For example at 25% above the partners (tabernacle) the mast was 96% of the 4 3/4 inches and at mid point it was still at 87% .  In this design wall  thickness was reduced as well. At midpoint it went from 1 1/2 inches to 1 3/16 inches. Six feet from the top, the walls were three quarters of an inch thick and at a station three feet below the top the wall thickness was just one half inch.  

The mast head was at 42% but the walls in the last three feet were quite thin and, despite a little possible help from a long tapered mast plug, the top of the mast flexed. Despite that I was very happy with the mast and its tabernacle. I’m sure it would be better for a junk sail if this amateur buildable mast it could be designed with a with a stiffer top section, perhaps with top closer to 50%. Being square with well radiused corners worked fine in all respects and matched my building skills and the tabernacle was the utmost in simplicity. Of course it was highlight for me to meet and converse with a most gracious Mr. Bolger. 

I agree, David & Arne. A mast that bends evenly is highly desirable. The "elongated half-a-barrel", or entasis, shape (thanks for teaching me a new word, David!) gets nearest to that ideal. The tapered aluminium flagpole (usually parallel over its bottom half) and the hybrid aluminium tube + wooden topmast are both good approximations. My current mast has a top diameter of 46% of the diameter at partners, and that's as small as I'd want it to be.

I think you are right Arne; I have noticed that cone tapered masts always bend more about 2/3 of the way up from the base, and this appears to be where they mostly break. I have found that entasis tapered masts seem to have a more even bend. The Greeks obviously got it right when building their columns!!

Thank you again David, and Len.  Perhaps some FAKE news :)

And your discussions makes sens.

  Raymond Liljeros wrote:

I read somewhere that a mast for a Junk Rigged sailboat

made of a tree would be much stronger than from metal.

It is true that I have rarely seen a tree broken in half,

usually it is the roots that give away.  Then to be on the safe

side, I suppose that it would be quite easy to change

from a metal mast to a tree mast on any junk rigged sailboats ?

Almost all the stories I have read of broken masts have been tree and wood masts. The only metal mast failure I have read about was not the mast but the deck structure. Certainly I have not read or heard of everything that goes on and metal stayed masts have been known to fail as well. I think in both cases, do the math and get to know your material before making a decision. A wooden mast (solid or hollow) will be of greater diameter and heavier for a given strength. So to change from metal to wood likely means making a bigger partner, using more interior room, changing any rigging to deal with a larger mast, possibly changing the location of ballast for trim, etc.

Aside from the PJR Arne Kverneland also has some good documents on this for both wood https://junkrigassociation.org/Resources/Documents/Arne%20Kverneland's%20files/Chapter%206,%20THE%20(wooden)%20MAST.pdf and alloy masts https://junkrigassociation.org/resources/Documents/Arne%20Kverneland's%20files/Chapter%206b,%20The%20Hybrid%20Mast.pdf  

Honestly, I think wood masts can be strong and long lasting. I do think that a lot of unstayed wooden masts are calculated by "That looks good enough to me" or "that is the best I can find". But many are just "It broke at a flaw in the wood that was not visible when I selected it". I think selecting a tree for a mast takes some talent and experience of knowing what to look for. I would not use a wood mast (even though they look nice) for this reason, I know I don't know...