GB2042987A

GB2042987A - Improvements in or relating to boats

Info

Publication number: GB2042987A
Application number: GB7907668A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-03-05
Filing date: 1979-03-05
Publication date: 1980-10-01

Abstract

A boat (1) having a first substantially planar boat bottom portion (2), a second substantially planar boat bottom portion (6) abaft and adjacent the portion (2), the portion (6) extending upwardly abaft and at its aft end merging into a lower portion (5) of the stern (4) of the boat, and the portion (6) in the longitudinal direction of the boat (1) forming an obtuse angle (7) with the portion (2), and at least one air conduit (9) for passage of air through the bottom of the boat (1), the or each air conduit (9) being located at the transition between the first and second boat bottom portions (2, 6). <IMAGE>

Description

SPECIFICATION Improvements in or relating to boats This invention relates to boats, more precisely to a boat construction effecting a favourable water flow around a boat both at low and high speeds.

Such boats may be relatively small, such as leisure boats.

Small boats, for example open leisure boats, generally are constructed either as rowing boats, the hull bottom of which in the longitudinal direction of the boat is bent upward uniformly at the aft and joins the stern with a uniform rounding-off, or as so-called planing boats, whose hull bottom in the longitudinal direction of the boat is substantially planar, approxirnately from midship to aft, and forms a sharp edge with the stern.

To construct a rowing-boat as mentioned above presupposes the advantage, that the water flow around the boat is uniform, and turbulence behind the stern is substantially prevented, so that the water-resistance to the boat is low, and the boat, therefore, is easy to row. Such a hull design, however, is entirely unsuitable for use at higher speeds. At high speeds the bottom portion curved upwards to the stern gives rise to the formation of low pressure beneath said bottom portion, because the water travels through a longer distance beneath said bottom portion than to the side thereof. Due to the low pressure, the stern is sucked down into the water, whereby the waterresistance to the boat increases.For this reason, at higher speeds planing boats are used, which as mentioned have an aft bottom portion of the boat which is substantially planar, which bottom portion forms a sharp edge with the substantially planar stern. When planing boat reaches the speed, at which at planes on the water, only a portion of the hull astern is in contact with the water, and substantially the entire stern is above the water surface. Owing to the planar form of the aft bottom portion, no low pressure, or only a slight one, arises beneath the planar bottom portion, and the aft of the boat is not sucked down. The hull design in the aft region, thus, presupposes that no turbulence, or only a slight one, is caused in the water behind the boat when it is propelled at a speed causing the boat to plane.

Planing boat hulls, however, are entirely unsuitable for use at low speeds, such as at rowing. Because of the planar bottom in the aft region and at its sharp transition to the planar stern, which at low speed partially is below the water surface, a significant reduction of pressure occurs behind the stern and gives rise to heavy turbulence in the water behind the boat.

It has not been possible heretofore to design a boat hull so that a boat is suitable for use both at rowing and low speed and at high speed.

The present invention solves or minimises the aforesaid problems and renders it possible to manufacture a boat, which is suitable for use both at low and high speeds.

According to the present invention there is provided a boat comprisng a hull having a first substantially planar boat bottom portion, a second substantially planar boat bottom portion abaft and adjacent the said first substantially planar boat bottom portion, the said second boat bottom portion extending upwardly abaft and at its aft end merging into a lower portion of the stern of the boat, and the said second boat bottom portion in the longitudinal direction of the boat forming an obtuse angle with the said first boat bottom portion, and at least one air conduit for passage of air through the bottom of the boat, the or each air conduit being located at the transition between the said first and second boat bottom portions.

Preferably said first bottom portion shows a flattened V-shape in a transverse cross-section.

The bottom of the or each said conduit may be disposed between the rear edge of the said first boat bottom portion and the forward edge of the said second boat bottom portion. Preferably for the boat in its normal position in use the or each said air conduit comprises an upstanding channel the upper end of which communicates with the atmosphere and the lower end of which opens into a substantially horizontal channel which communicates with one or more apertures in the bottom of the boat. The or each said aperture in the bottom of the boat may be elongate and extend transversely of the longitudinal axis of the boat. There may be a plurality of the said apertures in the bottom of the boat, the apertures being disposed transversely of the longitudinal axis of the boat.

By way of example a preferred form of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a lateral view of a hull embodying the invention; Figure 2 shows a section on the line A-A of Figure 1; Figure 3 is a view from above of the hull of Figure 1, and Figure 4 shows the aft portion of the hull of Figure 1 to an enlarged scale.

In Fig. 1 a boat generally designated by 1 is shown from the side and embodying the present invention. Fig. 2 is a cross-section of the boat 1 along the line A-A in Fig. 1. The hull comprises a substantially planar portion 2, which extends from about midship in a direction to the aft. Said planar portion 2, more precisely, is a bottom portion where the bottom is slightly V-shaped, as appears from Fig. 2. The V-shape shown in Fig. 2 prevails astern to a device 3 for air intake beneath the boat, which device constitutes an essential part of the present embodiment. The bottom of the hull successively transforms in the direction afore from said slight V-shape to a more distinct V-shape.

Abaft the planar portion 2 in the longitudinal direction of the boat planar portion 6 is formed, which extends upward to the lower edge 5 of the stern 4. Said upwardly extending portion 6, thus, forms with the planar portion 2 an angle marked by the arc 7.

At the transition from said portion 2 to said upwardly extending portion 6 a connection 3 through the hull is formed between the water and the free atmosphere. Said connection 3 includes one or several substantially vertical channels 8, the upper end 9 of which opens into the free atmosphere, and the lower end of which opens into a substantially horizontal channel 10. Said horizontal channel 10 has connection through the hull with the water beneath the boat, and said connection through the hull includes one or several apertures 11 in the boat bottom which extend transversely to the longitudinal direction of the boat. The apertures may be designed as a series of round apertures located by the side of each other, or as apertures arranged in some other way, or they may be designed as slots or the like.

The apertures 11 are formed in the lower wall of said horizontal channel 10, which wall thus is the bottom 12 of the boat. The horizontal channel may be designed as a pipe bisected in longitudinal direction and attached to the bottom of the boat.

The vertical channels 8 preferably are formed along the hull side. These channels 8 also may be designed as a pipe bisected in the longitudinal direction, which pipe is attached to the hull side and is connected at the lower end to the horizontal channel 10.

The majority of open leisure boat now are manufactured of a plastics material. It is suitable also to make the channels 8, 10 of a plastics material and to attach them with a plastics material to the hull during the manufacture of the hull. It is, however, also possible to mount such channels 8, 10 on a hull already manufactured.

In order to effect a uniform water flow at low speeds, the said upwardly extending portion 6 will have a length marked by the distance 13 in Fig. 1, which is 1% to 20%, preferably 2% to 10% of the boat length. As mentioned above in the introductory portion, a hull for low speeds, such as for rowing, further will be formed so that the bottom is curved upward in the aft and joins the stern with a uniform rounding-off. According to the present invention, the upwardly extending portion 6 will form with the planar portion 2 an obtuse angle marked by the arc 7, which angle is 1350 to 175 , preferably 1450 to 1650.

Between the rear edge 14 of the planar portion 2 and the forward edge 15 of the upwardly extending portion 2, a difference in level in vertical direction exists, which is marked in Fig. 4 by the distance 16 and will generally be 1 to 25 mm, preferably 2 to 6 mm. Owing to this difference in level, with the propulsion of the boat air is sucked down by ejector effect through the channels 8, 10 and via the aperture or apertures 1 1 is sucked inward beneath the bottom of the boat.

A boat, to which the present invention is applied, operates as follows. At low speed, such as with rowing, the hull shape produces a uniform water flow about the boat, owing to the upwardly extending portion 6. The water line at the centre line then is approx. at the line marked by 17. At low speed, not much air is sucked down through the channels 8, 10 and out beneath the bottom of the boat, but the air, which is sucked down, has a positive effect on the water flow, viz, by reducing the low pressure, which may tend to develop beneath the upwardly extending portion 6.

At higher speed, but below the speed at which the boat planes on the water, an ever increasing air amount is sucked down beneath the bottom of the boat, whereby low pressure beneath the upwardly extending portion substantially is prevented. Owing to the prevention of low pressure, the aft portion of the boat has no tendency of being sucked down. At speeds, at which the boat planes on the water, large air amounts are sucked down beneath the bottom of the boat. Owing to these large air amounts, the boat will not be sucked down during the acceleration to planing speed, because low pressure beneath the upwardly extending portion substantially is prevented. When the boat is propelled at planing speed, the water line at the centre line is approx. the line marked by 18, i.e. a water line corresponding to that prevailing with a planing boat.Due to this low water line, air sucked down can fill the space between the water surface and the upwardly extending portion. If air were not to be supplied through the apertures 11 , said space would always be filled with water, i.e. at acceleration from low speed the aft would be sucked down, and the water would not be relieved from the upwardly extending portion 6.

At a planing speed, thus the present embodiment behaves like a planing boat, where the stern 4 is located immediately after the plane portion 2, i.e. at the position for the apertures 11.

Thus, an artificial stern can be visualized at the posiiton for the apertures 11.

The advantages resulting from the present invention are very great, especially for small open or partially decked leisure boats. Such boats embodying the invention can be provided both with very good rowing properties and with very good properties at high speed, which has not been possible heretofore.

As is clearly apparent from the aforesaid, it is simple and cheap to design boats according to the present invention, especially during the manufacture of the boats, but, of course, as already mentioned also a boat already manufactured can be converted to a boat embodying the present invention.

The invention, of course can be applied also to large boats. Channels and apertures as required, for example, can be attached to large planing boats in order thereby to reduce the sucking-down effect on the aft portion which occurs when the boat accelerates to planing speed.

The invention must not be regarded restricted to the above embodiment, but can be varied within its scope defined by the attached claims.

Claims

1. A boat comprising a hull having a first substantially planar boat bottom portion, a second substantially planar boat bottom portion abaft and adjacent the said first substantially planar boat bottom portion, the said second boat bottom portion extending upwardly abaft and at its aft end merging into a lower portion of the stern of the boat, and the said second boat bottom portion in the longitudinal direction of the boat forming an obtuse angle with the said first boat bottom portion, and at least one air conduit for passage of air through the bottom of the boat, the or each air conduit being located at the transition between the said first and second boat bottom portions.

2. A boat according to Claim 1, wherein the said first bottom portion shows a flattened Vshape in a transverse cross-section.

3. A boat according to Claim 1 or Claim 2, wherein the length of the said second boat bottom portion is 1 to 20% of the boat length.

4. A boat according to Claim 3, wherein the length of the said second boat bottom portion is 2 to 10% of the boat length.

5. A boat according to any preceding claim, wherein the obtuse angle is 135 to 175 .

6. A boat according to Claim 5, wherein the obtuse angle is 145 to 165 .

7. A boat according to any preceding claim, wherein the bottom of the or each said air conduit is disposed between the near edge of the said first boat bottom portion and the forward edge of the said second boat bottom portion.

8. A boat according to Claim 7, wherein for the boat in its normal position in use there is a difference in level in a vertical direction between the said rear edge and the said forward edge and the said rear edge is disposed below the said forward edge in order to obtain an ejector effect when air is drawn downwardly through the or each said air conduit.

9. A boat according to Claim 8, wherein the said difference is 1 to 25 mm.

10. A boat according to Claim 9, wherein the said difference is 2 to 6mm.

11. A boat according to any preceding claim, wherein for the boat for its normal position in use the or each said air conduit comprises an upstanding channel the upper end of which communicates with the atmosphere and the lower end of which opens into a substantially horizontal channel which communicates with one or more apertures in the bottom of the boat.

12. A boat according to Claim 1 wherein the or each said aperture in the bottom of the boat is elongate and extends transversely of the longitudinal axis of the boat.

13. A boat according to Claim 10 or Claim 11, wherein there are a plurality of the said apertures in the bottom of the boat, the apertures being disposed transversely of the longitudinal axis of the boat.

14. A boat substantially as herein described with reference to Figures 1 to 4 of the accompanying drawings.