On my Dory, I rounded the Mast all the way down. I also decided not to use my router and did the job with a spoke shave. Why? Just for fun. I did a lot of work with hand tools on my Dory. It was fun figuring out how to get the best and smoothest cut with hand tools. And the quiet in my shop was very soothing. The sound the spoke shave made when it was cutting well was really fun, and since I worked nights at the time. I could work at 3am and not worry about bothering my wife or the neighbors.

We rounded our Passagemaker Dinghy mast (lug rig) the full length.  We used a router, but you want to be careful.  We caught a bit of cross grain at one point and created a divot which needed to be filled with thickened epoxy.  Hadn't planned on varnishing the spars, anyway, so it was no big deal for us.

I suppose that the rounding is to make it handier in the hand, less ugly to the eye, and maybe a little more likely to hold paint or varnish; the sharper the edge, the quicker the paint rubs off.

.....Michael

  Northeaster Dory, Lug rig. I chamfered mine down to the foot angle change. Posed an interesting problem when it came time to fit the hole in the mast partner.  If you use a 1/2” roundover bit you can drill the corners of the partner with a 1/2” bit for a near perfect fit. Michael is right about sharp edges and paint/varnish. Plus, the mast edges don't get beat up as badly or do they do as much damage to the interior of your boat when transporting.

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   On my Passagemaker I only rounded down so about 4 inches of square was above seat.  I think it looks pretty good, and the square on square fit made me feel a bit better.