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Think of carbon fiber mast as an exercise in load distribution. The fibers are very strong in pull strength but lousy in side force, after all it's just thread similar to sewing thread. The way the fiber is woven is what gives the mast it's strength. I'm imagining some of the threads could be 15-20 ft long, and there are likely thousands of threads weaved into the mast in all kinds of orientations. Each thread takes it's fair share of the entire load in a carefully balanced manner.
I think we all know the highest point of stress on these masts (where they are most likely to break).
If I was concerned about my mast breaking (I'm not too concerned) I would go to Home Depot and buy a fiberglass ax handle. Strip the yellow molded pp plastic cover off, what your left with is a white oval fiberglass pultrusion around 3/4x1" x 30" long. These suckers are extremely strong, I'm one of the guys who developed them originally, in the factory while developing the thing we used to place the pultrusions each end on a brick and jump up and down on the middle like a trampoline, for something to do, yea their that strong.
Actually both my mast topper and my bow sprit are made from those same pultrusions, (they were just sitting in my garage for the last 25 yrs (development samples), so I thought I would just use em, (I'm an engineer, not the kind of guy who would ever chop down a tree myself (lol).
If it was me I would take one of those pultrusions cut out a couple cardboard stars (to center the pultrusion inside the mast). I would then drop the pultrusion into the base of the mast. I would then get a couple tubes of GE silicone (the quick dry stuff) and a length of 1/2" dia pp plastic tubing (probably 5-6ft long). Put the tubing to the bottom then start pumping in silicone filling the space around the pultrusion. Thats the poor mans method. A better way might be to use 2 part pourable silicone (available at hobby stores), mix it up and pour it in, (obviously more expensive, silver based silicone is hyper expensive). Two part (2lb) urethane foam may also work just fine if you want to save weight, (also hyper expensive)).
What this does is slightly re-enforce the lower 30" inches of the mast, (where it's most likely to break) with a non rigid flexible piece that prevents the point load at the area just above the delrin bearings, basically making the mast a little little stronger down near the bottom without comprimizing the rest of the mast.
Whatever you do don't fill with epoxy, or use aluminum (not flexible), if you do the mast will simply snap 33" up instead of 15" up from the end (lol).
I've been running up to 260sqft of sail on my TI's for 7 yrs now with no mast breaks, but keep in mind all my stuff is carefully engineered to compensate for all the stresses with stays and strategic re-enforcments.
Also always keep in mind the weakest link in the system is not the mast. That little 1/4" stud in the bottom of your hull is the weak point, if your adding a bunch of massive sails that area needs to be re-enforced. I have an aluminum plate epoxied to the base of my hull to take the excess strain, that the boat was not designed for.
I'm not recommending anyone add that much sail area unless you really enjoy pitchpoling often, it's basically the same hp as strapping a 50hp outboard to your boat, lol yea sails can generate that much power.
PS if your running the Hobie spinnaker, you pretty much need that rear stay.
FE
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