IMPROVEMENTS IN BOAT HULLS

Abstract: A hull for a high speed motor boat has a bow section of V-form having a hard stem (6) which merges into a keel (7). The keel is divided amidships into two hard keel after-sections (8, 9) which diverge in the sternward direction and between which is provided, on the underside of the hull, a tunnel (10) which is open at the stern and extends forwardly while tapering inwardly. The forward end of said tunnel may be determined by a bulkhead (11) at the after end of the forward hard keel section (7), and the tunnel may be vented to atmosphere through the hull, for example through the bulkhead (11).

Description: I MP R O VE ME NT S I N B O A T HU LL S This invention relates to an improved boat hull, especially for a high speed motor vessel. High speed motor vessels, in particular those which are used for racing, have hulls which are of one of two types: there are deep-vee hulls and catamaran hulls. Deep-vee hulls have, as their name suggests, have a hull cross-section of V-form with a hard keel, which may be stepped, running the full length. Such hulls have good sea-keeping qualities because the deep V-form of the main part of the hull cushions buffeting from an uneven sea, and the V-form cross-section extends to the bows of the hull. The hard stem of the boat is readily able to cleave through and ride over waves at cruising speeds. At higher speeds, such hulls are designed to rise out of the water so that the boat planes, the wetted area of the hull being then confined to a rather small area around the keel at the stern of the boat. This gives rise to instability at high speeds, and die boat is liable to suffer from a rolling and pitching motion which can ultimately result in total loss of control of the boat. Catamaran hulls comprise a pair of parallel sponsons which are connected by a centre wing section which rides clear of the water. Such hulls are also designed to plane at high speeds, and because of their twin keels they are not subject to rolling motion in still water and consequently, in still water, they are more stable and capable of higher speeds than a deep-vee monohull. In moderate or heavy seas, however, the relatively blunt bow of a catamaran hull rides the waves much less easily than a deep-vee monohull, the boat has much impaired sea-keeping qualities, and it is therefore not capable of such high speeds as a deep-vee monohull. Various proposals have been made to achieve a compromise between these two basic hull designs. For example some such designs incorporate a twin bow section which merges into a deep-vee stern section. Other such hull designs incorporate a deep-vee bow section which is stepped in a plane amidships aft of which there is a box-section tunnel beneath the hull so that the latter has twin parallel keels. None of these proposals has found wide acceptance. It is an object of this invention to provide a new form of hull which has good stability and sea-keeping qualities. According to this invention, there is provided a hull, especially for a high speed motor boat, which hull has a bow section of V-form having a hard stem which merges into a keel, characterised in that the keel is divided amidships into two hard keel after-sections which diverge in the stemward direction and between which is provided, on the underside of the hull, a tunnel which is open at the stern and extends forwardly while tapering inwardly. Such a hull form has good sea-keeping qualities and good resistance to roll, even when planing. Preferably, the hull has a hard chine which rises in the forward direction. It is also preferred that the dead rise angle should progressively increase in the forward direction. It is preferred that each of the two keel after-sections is substantially straight. It is also preferred that the two keel after-sections converge in the forward direction towards a point which is between one third and one half of the length of the hull from its bow. The tunnel preferably has a transverse cross-section which is geometrically similar along substantially its whole length. Such cross- section is preferably curved, and it may with advantage be a part conic section, for example part-circular or part-elliptical, and it is preferably semi-circular or semi-elliptical. The tunnel may thus have the shape of a cone on a circular or elliptical base which is bisected by an axial plane. In some preferred embodiments of the invention, the forward end of said tunnel is determined by a bulkhead at the after end of a forward hard keel section which merges into said hard stem. This can give particularly good sea-keeping properties, especially in relation to the reduction or avoidance of a possible tendency for the hull to porpoise. The tunnel preferably extends forward of the stem to a distance from the stem which is between one quarter and two thirds of the overall length of the hull. It is advantageous for there to be provided means for venting said tunnel to atmosphere through said hull. This permits air to enter the tunnel to displace the water therein as the hull rises to plane, so easing the transition of the hull from displacement mode to planing mode as its speed over the water increases. In embodiments in which the tunnel terminates in a bulkhead at its forward end, it is especially convenient to vent the tunel to the atmosphere through that bulkhead. The hull is suitably driven by twin propulsion means. Two preferred embodiments of this invention will now be described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view of the underside of the hull of a first embodiment o this invention, Figures 2 to 5 are respectively a side elevation, a plan/under plan view, a view on the stem, and an end view showing transverse hull external cross-sections at various distances from the bow separated by equal increments, all of the embodiment of Figure 1. Figures 6 and 7 are respectively a side elevation and an underplan view of a second embodiment of hull according to this invention, and Figures 8 and 9 are views showing transverse hull half cross-sections at various distances from the stem, Figure 10 is a view showing a full cross-section of the hull, and Figures 11 to 13 are further views showing transverse hull half cross-sections at various distances from the stem, all of the embodiment of Figures 6 and 7. In the drawings, the hull generally indicated at 1 has sides 2 which meet the bottom 3 at hard chines 4. In accordance with the invention, the hull has a bow section 5 of V-form having a hard stem 6 which merges into a keel 7, and the keel 7 is divided amidships into two diverging hard keel after-sections 8, 9 between which is provided, on the underside of the hull, a tunnel 10 which extends forwardly from the stem and. tapers inwardly in the forward direction. The hulls 1 illustrated each have a hard chine 4 which rises in the forward direction. The chine 4 also rises with respect to the keel after-sections 8, 9, with the result that the dead rise angle α (best seen from Figures 5 and 8 to 13) progressively increases in the forward direction. It will be noted, especially from Figures 2 and 3 and Figures 6 and 7, that in each hull, each of the two keel after-sections 8, 9 is substantially straight. It will also be seen that each pair of keel after-sections converges in the forward direction to a point which is between one half and one third of the overall length of the hull from its bow. In the embodiment of Figures 1 to 5, such keel after-sections meet at a point M which is at a distance aft of the bow of about five twelfths of that overall length of the hull 1. In the embodiment of Figures 6 to 13, the projected lines of such keel after-sections meet at a point M which is also at a distance aft of the bow of about five twelfths of that overall length of the hull 1. Figure 5 is an end view showing transverse external hull cross-sections A, B, C, D, E, F, G, H, K on the corespondingly lettered lines of Figure 2 at various distances from the bow separated by equal increments. The tunnel 10 of each embodiment of hull has a transverse cross-section which is geometrically similar along substantially its whole length. In the embodiment illustrated in Figures 1 to 5, such cross-section is semi-circular along substantially the whole of its length. That tunnel thus has the shape of a cone which is bisected by an axial plane. Figures 8 to 13 are hull cross-sections of the embodiment also shown in Figures 6 and 7. In those Figures: Figure 8 right half is a section along line A of Figure 6 and Figure 8 left half is a section along line B of Figure 6. Figure 9 right half is a section along line C of Figure 6 and Figure 9 left half is a section along line D of Figure 6. Figure 10 is a section along line E of Figure 6. Figure 11 right half is a section along line F of Figure 6 and Figure 11 left half is a section along line G of Figure 6. Figure 12 right half is a section along line H of Figure 6 and Figure 12 left half is a section along line J of Figure 6. Figure 13 right half is a section along line K of Figure 6 and Figure 13 left half is a section along line L of Figure 6. In the embodiment illustrated in Figures 6 to 13, such tunnel cross-section is part-elliptical along substantially the whole of its length. That tunnel is terminated at its forward end by a bulkhead 11 as shown- in the cross section of Figure 10 and in Figure 6. A single central hard keel 7 extends forward of that point to merge with the stem 6 of the hull. The tunnnel 10 is vented to atmosphere through the hull by means of vent tubes 12 (see Figures 6 and 10) which terminate in openings in the bulkhead 11. It is preferred that spray rails 13, 14, as shown in Figures 8 to 10 should be provided along the line of each keel after-section, and other spray rails may be provided as desired. Other features of the shapes of the two illustrated embodiments of hull will be readily apparent to those skilled in the art from the drawings, in particular from Figures 2 to 5 and from Figures 6 to 13. The hull is suitably driven by twin propulsion means.

Claims: C LAIM S 1. A hull, especially for a high speed motor boat, which hull has a bow section of V-form having a hard stem which merges into a keel, characterised in that the keel is divided amidships into two hard keel after-sections which diverge in the sternward direction and between which is provided, on the underside of the hull, a tunnel which is open at the stem and extends forwardly while tapering inwardly. 2. A hull according to claim 1, wherein the hull has a hard chine which rises in the forward direction. 3. A hull according to claim 1 or 2, wherein the dead rise angle progressively increases in the forward direction. 4. A hull according to any preceding claim, wherein each of the two keel after-sections is substantially straight. 5. A hull according to any preceding claim, wherein the two keel after-sections converge in the forward direction towards a point which is between one third and one half of the length of the hull from its bow. 6. A hull according to any preceding claim, wherein spray rails are provided running along said two hard keel after-sections. 7. A hull according to any preceding claim, wherein the tunnel has a transverse cross-section which is geometrically similar along substantially its whole length. 8. A hull according to any preceding claim, wherein the tunnel has a transverse cross-section which is curved. 9. A hull according to claim 8, wherein the tunnel has a transverse cross-section which is part-circular or part-elliptical. 10. A hull according to any preceding claim, wherein the tunnel extends forward of the stem to a distance from the stem which is between one quarter and two thirds of the overall length of the hull. 11. A hull according to any preceding claim, wherein the forward end of said tunnel is determined by a bulkhead at the after end of a forward hard keel section which merges into said hard stem. 12. A hull according to any preceding claim, wherein means is provided for venting said tunnel to atmosphere through said hull. 13. A hull according to claim 11 and 12, wherein said means is provided for venting said tunnel to atmosphere through said bulkhead. 14. A hull for a motor boat substantially as herein described with reference to and as illustrated in Figures 1 to 5 or Figures 6 to 13 of the accompanying drawings.

Inventors: BONNER HENRY WILLIAM, BONNER, HENRY, WILLIAM
Applicants: MONOCAT POWERBOATS LIMITED
Application year: 1988
Main classification: B63B1
IPC codes: B63B1