This invention relates to a grounding protective device for sailing and similar boats provided with a fin keel.

Sailing vessels or sailing boats are in principle provided with a fixed keel, which may be designed in two different ways. One keel design comprises a αontfinuous garboard plate, which extends from prow to stern and mostly is comprised in the hull proper. The second design refers-to so-called fin keels, which consist of a garboard plate, which is attached in the central plane of the boat and approximately below the centre tRereof, and which is secured in the hull generally by keel bolts. The firstmentioned boat ^• type is called long-keeled boats, and the boat rudder generally is attached to the trailing edge of the keel. When such a boat touches ground, the boat runs aground with its middle line against the ground, and the grounding mostly proceeds cautiously, so that there are only small or no damages at all on the boat. The sliding movement of the keel on the ground implies a relatively soft braking of the speed of the boat, whereby a heavy impact on the boat is avoided. The risk of injuries for the crew, there¬ fore, is low. '

The present invention has the object to eliminate to the greatest possible extent the effect of the impact on a boat with a fin keel when the boat touches ground with the keel. It is essential that boat and crew are given a long braking distance in order to prevent damages on the boat and injuries of the crew. It is possible, within certain limits, to build boats, which are capable to withstand ground touchings, but human beings cannot be reinforced and, therefore, the braking must proceed mildly and through a long distance. A further object of the invention is to eliminate damages on freely suspended rudders of fin-keel boats.

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In order to achieve the said objects, the invention is characterized in that in the central plane of the boat a stay is provided which extends from at least either of the end edges of the fin keel at their lower end to a point so located that between the point and the fin keel the stay extends at least as deep as any part of the boat.

Pin-keel boats can be understood also to be boats similar to long-keel boats, which at some portion of the keel length show an inclination, which does not allow the boat to slide up on the ground.

Two embodiments of the invention are described in the following, with reference to the accompanying drawing, which is a lateral view of a sailing boat provided with a grounding protective device according to the invention. In the drawing, Fig. 1 shows one embodiment, and Pig. 2 shows a second embodiment of the invention.

As appears from the Figures, a sailing boat with fin keel is shown. The fin keel is presupposed to be rigidly secured in the lower surface of the hull. There exist also fin-keel boats, at which the keel can be retracted into the hull. Although the invention also can be applied to such a type of fin keel, it is hereinafter assumed that the fin keel is rigidly secured in the lower surface of the hull along the middle line thereof.

Groundings occur most often in such a way, that the ground is located below the water surface. Accordingly, it is the leading edge of the fin keel which strikes the ground, and the remaining part of the hull passes over the ground. As the ground hereby causes the boat directly and immediately to stop at the place of contact, a strong impact force arises which is transferred to the area of attachment between the fin keel and hull. The fin keel generally is so rigid that it is not deformed much.

This implies that in the contact between ground and keel

no substantial deformation work arises which could reduce the stress caused by the impact force in the area of attachment between the fin keel and hull. The size of the impact force depends on the weight and speed of the boat.

When the speed is not braked, and deformation work does not arise anywhe-re during the collision, then the stress to be taken up in the attachment between the fin keel and hull depends directly on the weight and speed of the boat. In order to limit the braking force on the boat to a size suitable in view of boat and crew, the braking distance must be relatively long, i.e. of about the same length as the keel. Deformation, for example of the leading edge of the keel, therefore, is not a practically possible solution. Already at moderate speeds, the damages can be disastrous for the boat. ^" It is more dangerous, however, that the strong and generally unexpected impact at grounding creates a highly riskful situation for the crew whose members often are injured. These injuries are serious per se, but in addition difficulties arise due to the fact that simultaneously the manoeuvring situation • of the boat must be managed. Even if no catastrophic leakage has been caused, the attachment between keel and hull has been damaged to such a great extent, that the boat is unfit and must be taken up on land for repair. The damages possibly occurring imply that the hull is smashed in the area where the keel is secured, due to the high torsional moment caused by the impact. In the area at the trailing edge of the keel, thus, pressure arises, and a tensional force arises in the area at the leading edge of the keel in the hull area. These forces are turned aboutby the present invention and remain turned about until the ground possibly strikes against the keel. The hull in the keel area can be deformed and, in addition, the keel bolts can break or be deformed permanently and must be replaced. It has happened that sailing boats with fin keel after having grounded at moderate speed can be

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regarded as substantially totally averaged, i.e. uncapable to continue to sail. In other cases and at milder ground¬ ings, considerable damages yet can be caused, although the hull is not destroyed so that leakage occurs. The keel bolts can be deformed so that the fin assumes oblique attachment relative to the central plane of the boat, which implies deteriorated sailing of the boat. It is to be mentioned, that fin-keel boats as they are at present manufactured almost all have the disadvantage, that grounding often causes serious damages. An extreme racing sailing boat always must be taken up as soon as the slightest ground contact with the fin keel has occurred. The greatest problem for fin-keel boats today should be to attach the fin keel so to the hull, that even at slight ground contact no catastrophe occurs and, of course, that in cases of sudden brakings ^' no serious risks are involved for the crew.

A further problem with fin-keel ^" boats is that the rudder is suspended freely from the keel and, thus, a certain distance aft of the trailing edge of the fin keel. It happens quite often that at mild groundings the boat bounces with the keel over the ground in such a way, that the ground will be located between the trailing edge of the fin keel and the rudder, and that the rudder will be exposed to the next impact. A rudder in no way does with¬ stand such an impact, but the rudder axle breaks or there occurs total rudder average. The aforesaid applies to entirely freely suspended rudders as well as to rudders provided with a supporting yoke. The present invention, at a second embodiment, prevents to a great extent damage on the rudder when the boat with fin keel bounces over a ground.

The invention idea becomes apparent from the drawing. It implies that a stay 1 is positioned in the central plane

of the boat and extends from the leading edge 3 of the fin keel 2 at the lowermost point thereof to the leading edge 4 of the stem. When ths stay 1, for example, is a steel wire, it is understood that the wire, due to its elasticity, will deflect aside for a ground located below the draught of the hull but above the lower edge of the fin keel. During a certain period of the grounding the stay, for example, can assume the line shown in the Figure by a dashed line. The impact force 8 thereby receives two composants, viz. a horizontal one H and a vertical one V. The vertical composant, thus, tends to lift the boat over the ground while the horizontal compos¬ ant is the one which brakes the speed of the boat against the ground. It is understood that the ideal case would be the one when the vertical force, i.e. the lifting force., on the boat gives rise to such a great work, that- the entire work for braking the boat can be taken up thereby. In such a case the impact force is zero at the moment when the ground meets the keel fin. When the fin, in spite of the fact that a braking work is carried out, should meet the ground, the stay acts as a reinforcing stay and reduces the stresses on the fin attachment.

The stay, as mentioned, can be a steel wire, but also other materials can be imagined. The essential feature is that a braking work is brought about with the stay, and that the ground is prevented from meeting directly the leading edge of the fin keel. It also is important that the stay is formed so, that the smallest possible water resistance is brought about by the stay. The stay, therefore, is to be placed in the central plane of the boat and must be streamlined in a section in parallel with the water line of the boat. Due to the inclination of the stay of about 25 to the horizontal plane, its section in the flow direction is extended and, thus,, more favourable than what applies to a vertical stay.

A second embodiment, which also appears from the drawing, implies that a stay 5 is inserted between the trailing edge 6 of the fin keel -nd a point located at the lower edge of the rudder at the pivot centre 7 thereof. When, thus, the boat bounces over a ground, the ground is prevented from landing between the trailing edge of the fin keel and the leading edge of the rudder 8, and the boat continues to slide so that the ground cannot strike the leading edge of the rudder. The stay 5 also protects a propeller possibly located between the fin keel and rudder from being damaged when the boat bounces over a stone at grounding.

The stays 1 and 5 should be dimensioned so as when being extended plastically never to be capable to yield forces so high, that the mountings of the stays are overloaded and thereby cause hull damages. In Pig. 2 a variation hereof is shown schematically, which consists of that the stay 1 is designed superstrong, but the mounting in the leading edge of the hull is made by means of a force- limiting member 9 , for example a built-in shear rod, which is attached between the stay 1 and the leading edge 4 of the stem, and which breaks before the stresses on the leading edge of the stem and/or the leading edge 3 of the fin are so high that damages arise here.It is also understood that the member 9 can be formed so that it extends at the taking-up of work at tensile load, which implies that the stay can be designed rigid so that the braking force is taken up by means of the member 9 instead of or as complement to the taking-up of work in the stay 1 at a collision thereagainst. The member 9 may be a spring or a deformable, exchangeable body.

It is understood that the stays 1 and 5, within the scope of what has been described above, can be designed in diff-

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erent ways and also can be given different tension. It should be advantageous to be able to attach the stay 1 as far as possible ahead, so that the inclination relative to the water line is great. The invention idea, however, is not restrictory in this respect, but depending on the form of the stem line and the form and location of the fin keel two points are selected for attaching the stay which provide the best possible capacity of-taking up collision.. It also can be mentioned that _. it may be suitable to design the stay mountings detachable, so that for example at racing sailing boats the stays are attached only during the transport to and from the place of racing, but during the race the stay are removed. It cannot be avoided that the stays yield a certain water resistance, but it should be possible to reduce the resistance so much that it can be accepted in relation to the usefulness yielded by the stay, at a possible grounding.

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