The interesting question to me is how to design a boat which can sail in midocean in light winds, even with a left-over swell. I've been on a couple of racing
yachts where this is possible, but never a cruising vessel.
Such a swell is usual, at least in my favoured oceans. Even the Southern Ocean has calms, often one per weather
system, but there's almost always a swell travelling ahead of the next one.
For me, motoring on long ocean passages is not just impractical, it feels to me like skipping the slower-paced bits of a well-written book.
Those bits are often the best bits, and if I skip them, not only have I not read the book, but I won't even know what I've missed.
Here's my set of (hopefully!) enabling features:
1) Narrow waterline beam, wide beam on deck
(plenty of topside flare)
2) Shortish, bulletproof mast
, but a modernised sliding gunter, radial fathead, "light airs" mainsail
with massive sail area up high, and a vertical leech up to the fathead (sliding gunter projecting well above the standing rig).
Lightweight (nylon?) mainsail
cloth, replaceable (semi-disposable) rectangular panels
between lightweight full length battens, attached with velcro, to 'blow out' if caught with too much sail up, to save busting the sliding gunter topmast. Leech and luff loads taken separately from sailcloth (by leech and luff lines)
3) Water ballast, acting at the wide gunwhale (carried in hypalon 'pontoons' like a RIB
, full length) enabling heeling the boat the "wrong" way, ie to leeward, in light airs. The tall mainsail with the fat head
, once there's a bit of apparent wind, would increase and stabilise the heel -- a big tall main is an excellent roll damper, once there is a knot
or two of wind across it.
4) Swing keel
, enabling balancing the boat, both trimwise and CoE-wise, with a dagger extension with ballasted tip (dagger extension keeps the slot and keel
case short, and enables tailoring both the draft
and the righting moment to the conditions)
Here's how (I hope !) it could all work together.
- The thing driving a hull
to roll in a swell is the static stability. A wide plank (even with a ballast keel) will roll heavily when side-on to the seas. Shift the same keel to a round log and it won't roll at all. Cue the narrow waterline beam, and a keel with the shortest chord I can contrive. (Because in a big swell, the orbital motion extends well below the surface, and you don't want the keel to couple the boat to that motion)
- The reasons I'm aware of that sails slat in a cross-swell are:
a) insufficient area (particularly up high where there's more breeze)
b) insufficient boatspeed (sailing to windward - which is the best direction to sail in ultralight wind, even if it's the wrong direction; it'll get you to the new breeze more quickly, and in a much better frame of mind, because apparent wind is the key to stability)
c) insufficient angle of heel (gravity does wonders to keep the camber always in the correct direction
d) excessive hull-form stability, causing roll (see above)
The main sailhandling "enabling factor" is that the light-airs main would be reefed and stowed around a horizontal mandrel, enabling the medium-to-heavy airs main (battenless, hollow-leeched, "Swedish" style) to unroll from within the mast
A further enabling factor is stored-energy drive, enabling quietly trickling through the occasional lull, maintaining the apparent wind, without having to run an engine. Otherwise it can take forever to get the boat moving again, with the swell shaking the wind from the sails.