the semi foiling "Xer"

Semi foilers

A combination of two arts: the whole bethwaite and aussie hard chine , ultra low weight philosophy to the sandal wearing bearded joy riders who have expoused, for many years now, the virtues of sailing on hydrofoils ...for short distances at restricted wind angles and in narrow wind stregnths...go go gadget moth foils....

Improving speed and efficiency are recognized as the primary goals and activities in the !"naval arts "...there with decreasing frictional resistance is seen as the key to these goals.

An additional goal has been to improve the ability to operate in disturbed water, including heavy seas, where pitching and slamming, spray, yaw and roll severely limit navigability.

The 9er boats go faster than the maths would predict and the small motor boats with wings achieve a stability and lift by trapping air and spray under curved side wings. The "fluids" probably act in a chaotic manner as detached flow , not defined by current maths, but they generate both lift, reduced friction and to some extent dynamic stability by virtue of their "cushion" effect.

In my challenge to bethwaite design and allan andrews I cite the following principle in relation to much work done by naval arc's

-the descendents of both the International 14 and the NS14 have come to dominate the fast end of unballasted monohull racing craft ie no keels, viz dinghies. Unlike a planing naval vessel a sailing boats crew weight is both sizeable and mobile..for instance in the recently evolved 59er design the payload is approximately 150 kg for a boat weight of well under 100. The key issue for planing vessels is to 1. achieve plane quickly 2. not dig the stern in excessilively. In the 59er drag has been reduced so significantly as to negate the previous convention of the "drag bump " to climb before planing.

That crew weight can perform lateral balance is central to sailing ....but that it also provides for-aft trim is of course essential to planing craft with the crew movng ever more aft with speed. However in the case of my proposed foil assisted planing-spray cushion craft, the semi foilers, this is useful in moving the wieght forward to premote

1. stern trim after initial planing
2. freedom of the greatest area of planing "wetted area" over to cushion .- spray detached flow surface

I 14s already use trim tabbable rudders to achieve something like this, but in addition to forward hydrofoil forces, the rudders could act to further free the hull from conventional, dense fluid, attached flow.

Further to my principle I believe that due to the relative ballast weight and mobility of crew in a high performance dinghy, the need for adjustable trim on hydrofoiling surfaces would be negated.

Current and previous patenting in this area of trim is applied to motor vessels while refering to sailing planing as now applied on I Moths and I14s and various experimental dinghies like the Foiling 18s. In a motor vessel of any size over say 20 feet, the crew weight begins to become negligble in relation to trim due to the forces acting to sink the aft and usual position of motor weight. Trim tanks, as in the atlantic rib, are practical in combination with trim tabs in smaller craft but become both too slow and weight disadvantagous in larger planing vessels. In essence they cannot move trim fast enough to promote either planing or increase stability once planing is achieved. Most unlike this, crew in a performance sailing dinghy are habituated to moving their weight frequetnly to acheive optimum balance and trim. It is in effect totally and intelligently dynamic!

In my proposed development of the arts, Stability is achieved by replacing the "dense fluid" attached or wetted surface, with the air -spray cushioed surface held in suspension by the balance of-

a. forward or midships hydrfoils -primary lift

b. aft or rudder-integrated foils - secondary lift

c. trim aft to promote planing then re trimmed for'd to assist stern lift achieved by crew movement.

The 59er is in essence a boat designed to perform outstandingly in light air venues whilst carrying a heavy pay load. In my trial experience in the boat, while either in a wave train sailing big apparent wind, or crossing the deep wake of a tug boat, the hull also delivers outstanding stability in aggressive wave forms while planing. I contest that this is a virtue of a compressed cushion of spray and air which generates dynamic stability over that of just the wetted area. The boats foils contribute to this.

.... but I propose that the cushion be utilised in a "2nd planing" or totally detached dense fluid plane where hydrofoils lift no more than required to keep this cushion, or detached semi fluid lift.

Planing vessels normally are designed to (and must) operate at a positive trim angle, usually two to ten degrees, so that the stern remains in the water enough to maintain the stability of the vessel, not only against roll and yaw but also against pitching forces that could take the bow under, and to keep the propelling mechanisms submerged. (Loss of trim is usually measured as an angular deviation of the vessel's horizontal center for gravity line from true horizontal, zero degrees being perfect trim.) Such deviation from trim imposes a substantial penalty of increased friction and drag due to sinking of the stern, increased pitching, slamming and yaw, wind action against and air entrainment under the upraised bow and a substantial spray root at the bow entrance, as well as a decrease in the efficiency of the propelling system in most cases. Thus, maintaining trim is an additional objective in the art to further the primary goal of improving speed and efficiency.

BACKGROUND ART for the US Patents in this area

Numerous vessel designs have been proposed for reducing resistance. Planing hulls are widely used in moderate size and smaller vessels. The planing surfaces on the hull cause the vessel to rise in the water as speed increases, thus decreasing the wetted surface area and thereby decreasing the frictional resistance and drag. This decrease can be substantial. Nevertheless, a substantial amount of the wetted surface remains, together with its associated frictional resistance and drag, and the trim limitations impose the substantial penalties on efficiency mentioned above. Aside from the efficiency problems associated with trim, as speed increases water flow past even the most streamlined planing surfaces becomes turbulent. This turbulence has been yet another barrier to increased speed and efficiency for which a solution has long been sought.

Hydrofoils, like airfoils (e.g. wings) in the aeronautical arts, are streamlined bodies which create a useful reaction ("lifting force") from a fluid stream moving relative to them. In practice hydrofoils are given a different curvature (camber) at the opposed surfaces. The resulting unbalanced profile is designed to create an efficient lifting force in the water at the selected angle of attack of the hydrofoil, i.e. the angle between the chord (straight line connecting the leading and trailing edge) of the hydrofoil and the direction of movement of the vessel. The hydrofoils are secured to the hull of the vessel and usually extend transversely amidships, at and/or below the bottom of the hull.

Hydrofoils are capable of lifting the vessel almost completely from the water, thus reducing friction and drag to that imparted by the remaining relatively minor amount of wetted surface (principal portions of the propulsion system, and the relatively hydrodynamically efficient rudder and hydrofoils). However, the formidable structural and other design problems involved in lifting an entire vessel onto hydrofoils and continuing to propel it limits their use to smaller vessels. These vessels have additional serious shortcomings. They have poor stability and are difficult to handle. They have limited service speed. Hydrofoils are highly vulnerable to floating debris. Moreover, hydrofoils, as designed and positioned, can only impart a lifting action and they serve no appreciable function of heave or trim control, of countering yaw or pitch or of decreasing the friction or turbulence of the water on the vessel hull when a portion of the hull is under water at slower speeds. Indeed, the foils likely add to turbulence and drag when the hull is in the water.

further to this new art, I would propose that there may be other features advantagously involved to promote dynamic under hull spray and air flow while adding to stability ...most noteably the addition of under stern and trans-transom waterline skegs so as to train the flow whilst not contributing noticeably to non planing drag.

Most preferably the new art would utilise two laterally mounted fore hydrofoils, with a simple one continuous form design. Includable would be either a single hyrdofoiling dagger board or centre board midships or actualy a wieght ballast on a central keel in combination wiht a two laterally, hull mounted foils. This is for now a weight assisted dinghy variant but paves the wave for "reserve righting lever, foil -lift neutralised in forward velocity" keel boats of all sizes.