Hi Simon,
I think that 2 piece masts were made so that the cat was readily car-top-able - in 2 pieces there would be little or none of the dismounted mast sticking out at the front or the rear. So, for example, you could car-top your cat AND tow a caravan if you had a 2-piece mast. Or if you took it abroad car-topped then you woudn't have to pay ferry costs for a vehicle between 6 and 6.5m long.....
If you have a 1 piece mast then you're pretty much bound to have some of the mast sticking out at the front and the back if you car-top. You might have to tie a cloth (flag) on the end(s) of the mast if you had one on top of a small car in order to be legal on the road. A very small car might be too short to transport a 1 piece mast on the roof legally......
If you have a trailer, then the mast support is often (but may not be on some trailers....) adjustable up and down, so that any mast sticking out at the front can be raised high enough to clear the back of the towing vehicle. If you have a cat trailer for a 15 ft cat, the angle you need may be quite high if the van is one of the tall varieties - eg a Transit with a high roof. This may mean that the front of the mast will be quite high over the van, and you would be advised to note just how high in case you have to go under low bridges..... You'd be less likely to have trouble with a trailer for an 18 ft cat..... I have an 18 ft cat trailer, and my mast on the lower crook of the mast support in its lowest possible position is higher than the rear of my 4x4 (around 1.6m high). I have only recently thought about having a higher gap - when going to Shanklin it dawned on me that there was quite an angle between the ramp down to the ferry and the ferry ramp onto the ferry itself, which might have caused the gap between the mast(s) and my car to "go negative"; we did some adjustments..... On my 18 ft trailer, if I stuck a bit of the mast out over the tailboard the front of the mast could be behind the tow hitch.
Sailing wise, there is different bend in the 2 types of mast - I think that the 1 piece masts are generally stiffer and need more downhaul to produce the same bend as you'd get from a 2 piece mast. You can also get some wear in the jointing area on a 2 piece mast. And if you look at some recent threads you'll see that a 2 piece mast was broken in strong wind conditions recently at Shanklin (gusts at Gale Force
. I saw it happen; I thought it broke due to the capsize being in shallow water when the mast head hit the bottom; the helm said it happened when the mast and sail hit the water; whatever, there had been some corrosion around the rivets holding the jointing section. I've only known of a handful of mast breakages.
