My plan was to convert to junk rig this last summer but things didn't quite according to plans. In any case I don't have to worry about my appendix getting infected while at sea anymore. One issue I've had while planning the conversion, since buying the boat in late 2012, was the fact that it seems impossible to get a hold of tapered aluminum poles in Finland. Which leaves me with a few alternatives:

1. Wooden mast, solid
+ easy construction
+ inexpensive
- heavy

2. Wooden mast, hollow
+ lighter than solid wood
- construction is more difficult, somewhat depending on build method

3. Aluminum + wood (or GRP) hybrid
+ relatively light
- construction difficulty somewhere between 1 and 2

4. Steel
+ not much construction at all
- about as heavy as a solid wooden mast

As the winter is approaching I won't have the luxury of a) finding a suitable piece of spruce and b) drying it in time to go sailing next summer, and a full lenght hollow mast would also require space I don't have access to at the time being. This leaves hybrid and steel (carbon fiber is way too expensive).

As for the boat specs, my humble ship is 8.3 meters LOA (27 ft), 2.4 m (7 ft 10 in) beam, 3 tons displacement. It's pretty similar to a Pearson Triton.

I've been leaning towards a steel mast, as I recently got a decent price quote for hot dip galvanized tapered steel poles. The two options are:

#1
Length: 10600mm (~34 ft 9 in)
Base: 188mm (~7 3/8 in)
Top: 60mm (~2 3/8 in)
Wall: 3mm (~1/8 in)

#2
Length: 11100mm (~36 ft 7/16 in)
Base: 208mm (~8 3/16 in)
Top: 76mm (~3 in)
Wall: 3mm (~1/8 in)

I've decided on a 34 m2 Fantail-type sail, so I would need a spar of 10 meters, more or less.

After reading Arne's article on mast scantlings I did some calculations. According to the "guess formula" my boat has a righting moment of roughly 1800 kpm. Using the ultimate tensile strength of steel[1] (400 MPa) and the spar base as the diameter (don't know if/how we should account for the pole being tapered?) I calculated[2] the breaking strength of the 188 mm mast to be 3238 kpm, which gives a "safety factor" of 1.8. With the 208 mm mast it would be 3982 kpm and a "safety factor" of 2.2.

Weight is obviously a factor to consider. At 10 meters, the 188 mm mast would weigh roughly 90 kg while the 208 mm mast would weigh about 105 kg.

So, the first question would be if 3 mm wall thickness is enough to use as a junk mast? The second question would be if the 188 mm pole is strong enough or if I should go with the 208 mm? I would preferrably avoid dismasting if possible.