The comPromise of Speed

There was once a young fellow named Bright
Who exceeded the Speed of Light.
  He left early one morning
  And returned  without warning
At dusk of the preceeding night.


Some things aren't meant to be rushed.


Speed is Relative.
-- Albert Einstein


The comPromise of Speed

Speed under sail is a glorious thing. But it isn't the only thing.

All boats are a balance of numerous compromises. One virtue at the expense of others. A vice tolerated for net gain. A good design is a good match with its owner's priorities. Such a balance is as precise, magical and rare as is to be found in any good relationship.

There are only two broad considerations concerning speed:

First one is easy. Generally speaking, displacement monohulls are limited to their hull speed, a mere one and a third times the square root of their sailing waterline length.

The only way to raise the hull speed ceiling is to lengthen the waterline. But a curious result of the math, here, is that short boats are faster for their length than longer ones. A long hull is an expensive way to gain speed. Cost rises exponentially at construction time, in maintenance, heavier gear and rig and linearly in harbor fees. Speed gains diminish exponentially with length, however... each extra knot of hull speed will cost you dear.

In effect, because hull speed is strictly relative to waterline length, it doesn't usefully distinguish fast boats from slow.

The second, more pertinent question is how easily does the boat reach its hull speed? Most boats achieve low fractions (to about half) of hull speed with little energy input. But diminishing returns apply as one approaches full hull speed. A fast boat will start ghosting sooner and reach hull speed sooner than a slow one. This is one reason that the crew's skill and attentiveness is such a big factor in any competition.

The faster boat, adjusted for length, is simply the one that, for whatever the reason, spends more time at higher fractions of the narrow range between zero and hull speed.

Hull shape plays a major role. Easy entrance (at the bow) and exit (aft) minimize plow and drag. Well placed curves ease water aside and return it to equilibrium with minimal disturbance. Hull shape may be optimized for specific conditions; flat water, steep chop or anywhere between. Wetted surface area (friction) from keels and such is a liability, balanced against lateral resistance and optimal ballast placement.

But these are hard to construct, and carve away volume and displacement. Angles of heel and motion are affected. Easy lines can make for relatively tender hulls, tamed with expensive ballast that reduces payload. Hull smooth and clean? No brainer, but what are the costs of keeping it so?

Then there's the rig. Bigger rigs supply more power, all things being equal, but size must be balanced with expense, stability and handling issues. Fail-safe vs fail-dangerous. Maintenance issues. Windward ability? Another round of compromises struggling for a point or two.

*****

Anke and I have a set of priorities for live-aboard sailing that runs in clusters approximately as follows:

• Ease and economy of construction -- If we can't get it built, it's a pipe dream.
• Ease and economy of maintenance -- A) We're lazy. B) We'd rather be sailing).
• Ease and economy of operation -- Ditto.
• Fail safer -- Hedge our bets.
• Ultra-shoal draft -- Opens up our world and safe harbors.
• Single handling in all weather -- If one of us is sick, hurt or otherwise occupied...
• Reliable windward ability -- We count on being able to make good to windward shy of storm force winds.
  
  
• Relatively heavy displacement -- We carry a lot of stuff.
• Relatively high interior volume -- For inside projects and hangin' with friends.
  
• Speed and efficiency under sail -- Suckin' hind teat.

Our solution has been box barge hulls sporting lee (off-center, actually) boards and simplified junk sails (on two+ masts).

It can be fairly said that each and every choice along these lines makes it just a little harder for us to achieve hull speed. It takes a little more wind or a little more time. Both of these, however, are free. We also tow a 16ft dory, which sucks up another erg of energy. One of these days, I'd like to take SLACKTIDE out for a spin without it, just to see what she'll do. But, around here, round-trips on windy days are never guaranteed.

Still and all, we don't find that our choices cut too deep.

Off the wind, we're surprisingly fast -- we objects in your mirror which are closer than we appear. On the wind... well... we'll get there, slow but sure, though it's often more pleasant to wait for it to turn around. In fact, it's only the last fifth of hull speed that we're reaching for. If we have wind, we cruise with a decent average for our size. We won't be placing in any races, but we get where we're going.

We do sometimes dream of speed, I won't deny it. A Bolger ROMP. A Wharram catamaran. A Brown JZERRO.

If we owned a magic wand, instead of a hammer, maybe things would be different.