no, i’m right
Bruce Parsons attempts to criticise my modest efforts in hull development with a wonderful array
of erroneous assertions and non-sequiturs, but he trips up at the first step. He castigates me for
suggesting that the displacement hull speed of an 18 ft LWL hull is 6 knots, asserting that it is
5.5 knots, and that therefore I do not know my own business. Actually, the calculation for hull
speed on this type of hull is 1.4 x square root of the waterline length, which amounts to 5.94
knots. I rounded this up to 6 knots because all my other figures were rounded up (or down) to
whole numbers for brevity. Unfortunately, a misleading statement followed by a libelous
assertion is typical of Parsons’ technique throughout.
As an illustration of Parsons’ unique reasoning powers, he refers to an earlier published article in
Sailing Anarchy outlining an 18 ft prototype which I have designed and have just begun to test. In
that article it stated, as a matter of principle, that reducing the hull wave has been a key element
of marine design. One example (among others) of the attempt to reduce the hull wave is the
forward projecting bulb on large cargo vessels and tankers, which are designed to create a wave
which interferes with the bow wave in such a way as to reduce the hull wave and so reduce drag.
Parsons then makes the ludicrous assertion that the bow on my 18 footer must be an example of
the forward bulb used on tankers and merchant vessels.
Anyone who took the trouble to look at
that bow would see that it is an entirely different way of reducing bow and hull wave, almost the
exact opposite of the voluminous bulb on a tanker. My bow shape reduces the bow wave by
extreme fineness. In static trim the half-angle of entry is 10 degrees. When the hull rises into
planing trim, because of the V-shaped form, the half-angle of entry on the planing waterline
reduces to approximately 3 degrees. It is as sharp as a knife.
Here are two photographs of the 18 ft prototype showing that slicing bow in more detail. The
first is in build, the second shows how the hull sits at rest in water.
On an 18 ft hull, the chine is 6 ins above the waterline, and the ledge has the additional function
of deflecting spray. The combination of a very fine entry, a V-shaped hull, and a ledge above the
waterline which suppresses spray should result in a dry boat with a soft motion in seas. This
appears to be verified in early tests, but we will have plenty more opportunity to study this
prediction in detail.
The bow shape is not the only attack on the hull wave. In due course I will list other key methods
of reducing hull wave which are embodied in the hull, some of which may be obvious to students
of hull form and some of which may not. The aim has been to bind all these aspects together in a coherent multi-purpose shape.
Although I think Mr Parsons is unwise to cast me as a fool, I do plead guilty to ambition. I do
believe it is possible to combine a large, commodious hull shape with an underwater form which
is economical at all speeds and which can plane easily with a minimum of hull wave.
Regarding sailing boats, the same generic hull shape forms a potential base for the development
of future sailing boats. It seems to me odd that in the 21st century we continue to rely on
deadweight ballast, rather than pure hull form, for stability in sailing monohulls. The design
waterline beam on this hull is 3.5 ft, half the overall beam of 7 ft. Upright, the boat is easily
driven. As the wind increases, the hull heels gradually until the chine touches the water typically
at 7-10 degrees, considerably increasingly righting moment and power, not unlike the outer hull
of a trimaran.
Unlike a multihull, this form of hull, with proper design (including placing the engine and fuel and
water tanks in the lowest part of the V hull), is capable of recovering from high angles of
knockdown comparable with most keelboats.
We are at the early stages of testing, but so far every prediction made has been verified, if not
Quite apart from the visual evidence of a minimal hull wave, there are clear signs on the you tube
clip of a hugely diminished hull wave under engine. One is the clean acceleration through hull
speed (6 knots) to planing speed (16 knots with 15 h.p motor). Another is its capacity to take 6
people without falling off the plane on a small 15 h.p. engine (not shown on this clip). As we test
further, I will disclose further elements of performance in my own good time. It is a rich field,
and requires careful and patient understanding, not least on my part.
Meanwhile, I hope your readers will keep an open mind, and not be put off by Parsons’ attempts
to impose his own misleading interpretations upon my efforts.