Small boats are conventionally made of glass-fibre-reinforced plas- tic or other plastic using a mould. Water-craft of this kind include small motor boats, console boats, sport boats, ht-cabin boats, special boats made for vari- ous professional uses, and water scooters. The hull of such boats, comprising a deck, a bottom and sides, is made entirely of the same material by using a mould.

Boats built by using a mould have similar properties, and a new mould is necessary for each variation or technical modification of a boat type to enable a boat to be constructed. According to the use and motor power of a boat, a plurality of moulds is needed since for instance the lifting strakes and the shape of the bottom of the boat should be chosen as necessary. The drawback presented by the boats built in this way is that the moulds are ex- pensive. Furthermore, owing to the number of moulds involved and the pro- duction methods used, industrial boat production is inflexible.

US 3,871,043 discloses a boat comprised of two portions: a hull and a liner. The hull is constructed of aluminum, for instance, and the liner is made of plastic or glass fibre, for instance. The aim is to provide, by means of a liner, a functional interior construction in combination with a sturdy hull made of aluminum. The publication discloses how the hull and the liner both com- prise vertical side walls.

US 4,917,037 and US 4,821,667 also disclose a boat comprising two portions. In accordance with the publications, the boat is constructed of a metallic hull and a glass-fibre interior to be fitted therein. The portions are de- signed in such a manner that the interior and the hull only connect at the edges where the portions are also attached to each other.

The durability of glass-fibre boats depends on how they are used. A boat made of reinforced plastic has a long life span and it is easy to maintain, provided that the boat is used in such a manner that no damage is caused to the surface made of reinforced plastic. If, however, the surface layer of a glass-fibre boat is damaged in connection with beaching, running aground or docking, the reinforced plastic may absorb water through the damaged spot.

With time, the water causes embriftlements in the reinforced plastic. When the boat is damaged more seriously, for instance when it is scratched or torn, it is expensive to have the boat repaired since special craftsmanship is needed.

For the above reasons, the glass-fibre boat must be handled with care.

BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide a method which avoids the above drawbacks and enables a boat or the like to be built in a more reliable manner. The object can be achieved by the method of the inven- tion, which is characterized in that the method comprises steps in which a blank of the boat is produced, the blank being arranged to form an inner bot- tom, a deck and inner and outer sides of the boat, a bottom structure to be fitted into the blank of the boat is produced, the bottom structure substantially covering the bottom area of the boat, and the bottom structure is combined with the blank of the boat in order to provide a boat or a corresponding device designed to travel across water.

The method of the invention is based on the idea that a boat or the like is manufactured in several steps in such a manner that a blank of the boat, which comprises the an inner bottom and sides of the boat, and a bottom structure are manufactured separately. The bottom structure of the boat is combined with the blank of the boat, and the result is a boat with a strong structure.

An advantage of the method of producing a boat in accordance with the invention is that production costs can be reduced. The costs can be re- duced since every desired boat model does not require a new, expensive mould in which a hull made of reinforced plastic can be manufactured. Each bottom structure can be made as desired as long as motor power and the like are taken into account. This enables for instance the lifting strakes of a boat to be manufactured entirely individually into the bottom structure regardless of the shape of the blank made of reinforced plastic. Also, the V-shape of the bottom structure can be chosen as necessary.

When boats having inboard, outboard or water jet motors are in- volved, the method of the invention enables a quicker motor mounting, which makes a boat quicker to manufacture. The motor and power transmission equipment can be mounted already in the bottom structure, and the entire

bottom structure in the blank of the boat. Fewer steps are thus needed in the mounting.

The invention further relates to a boat or a corresponding device designed to travel across water, which is characterized in that it comprises a bottom structure manufactured separately and substantially covering the bot- tom area of the boat and arranged to be combined with the blank of the boat, the blank comprising an inner bottom, a deck and inner and outer sides of the boat.

A boat in accordance with the invention is based on the idea that a bottom structure of a boat can be manufactured mechanically of a strong ma- terial, whereby the most vulnerable parts of the boat are protected most effi- ciently.

An advantage of the boat in accordance with the invention is a con- siderable improvement in boating safety. When boating, there is always the risk that the boat hits a rock, drifting wood or the like. When a bottom structure in accordance with the invention is used, the risk that the boat should sink is significantly reduced, thanks to the strength of the bottom structure, the safety bottom and the material, and to the fact that another entirely water-proof bot- tom is provided on top of the safety bottom.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now described in closer detail in connection with the preferred embodiments with reference to the accompanying drawings in which Figure 1 shows schematically how the blank and the bottom struc- ture of a boat are combined; Figure 2 shows the shape of the bottom structure of a boat; Figure 3 shows the shape of the bottom structure of another boat; Figure 4 shows the shape of the bottom structure of another boat; and Figure 5 shows schematically how the blank and the bottom struc- ture of a boat with an inboard motor are combined.

DETAILED DESCRIPTION OF THE INVENTION In accordance with Figure 1, a separately manufactured bottom structure 1 of a boat is combined with a blank 2 of the boat, the blank prefera- bly being manufactured of reinforced plastic. The blank made of reinforced

plastic is typically manufactured by using a mould. The material of the blank can be wood and plywood, according to use. The separate bottom structure to be attached to the blank is preferably made of aluminum or steel. In certain solutions, such as in connection with water scooters, the bottom structure can be made of a strong type of plastic with high resistance to impact and abra- sion, such as HD-polyethene. The separate bottom structure which, combined with the blank of the boat, forms a safety bottom 1 of the boat, is typically manufactured using a jig in which the bottom structures can be almost indi- vidually produced. When the jig is used, pieces of metal are preferably joined by welding.

Thanks to the separate safety bottom, it is easier and considerably tess expensive to change the shapes of the bottom structures 1 than to manufacture a new mould in which an entire boat made of reinforced plastic is conventionally built. The shapes of the safety bottom can be changed as nec- essary. The boat can thus be made suitable for different motor powers and uses by merely changing the bottom structure 1 of the boat, while the parts made of reinforced plastic need not be changed unless thus desired because of design. The bottom structure fitted in the blank is arranged to cover the bottom area of the blank, in which case the joint between the blank and the bottom structure is typically positioned below the water line when the boat in accordance with the invention is used. Hence, the blank of the boat forms both the outer and inner sides of the boat.

The blank and the bottom structure of the boat can be combined in many ways. In accordance with an embodiment, the bottom structure 1 of the boat is combined with the blank 2 of the boat at several different points.

Hence, the bottom structure pieces can be secured to the blank of the boat in such a manner that they partly overlap each other to ensure a strong safety- bottom structure. Using several partly overlapping parts, for instance the prow, middle part and stern of the safety bottom can be formed of different pieces.

The bottom structure 1 and the blank 2 can be attached as neces- sary. The attachment can be performed for instance by glueing, bolting or screwing the pieces together. In accordance with an embodiment of the inven- tion, the attachment can also be performed by means of resilient intermediate pieces to provide resilience and damping between an intermediate bottom 3 formed by the blank 2 and the bottom structure 1. The bottom structure can

also comprise an attachment flange by means of which the bottom structure can be attached reliably to the blank of the boat.

As a result from a potential serious accident, the strong metallic bottom may also be damaged or even punctured. When the bottom structure 1 combined with the blank of the boat is punctured, the boat does not sink, how- ever, since the blank which forms the inner bottom 3 is made entirely water- proof. Thanks to the safety bottom 1, boating safety can thus be considerably improved.

In case the metallic bottom structure of the boat is damaged, it is less expensive to have it repaired than a bottom made of reinforced plastic. To repair reinforced plastic involves special tools, great craftsmanship and correct temperature to ensure that the plastic is hardened, while to repair a metallic bottom structure only involves welding equipment or the like enabling metal sheets to be combined.

In accordance with an embodiment of the invention, the space be- tween the bottom structure 1 and the blank 2 comprises supporting structures 4 which carry and support the inner bottom. The supporting structure can be a separate framework attached to the blank of the boat and by means of which the inner bottom 3 of the boat becomes sturdier and stabler. The space be- tween the inner bottom 3 and the outer bottom 1 can also comprise cellular plastic or the like to provide an insulating layer.

In accordance with an embodiment of the invention, the junction of the bottom structure and the aft of the blank of the boat is left at least partly open. Hence, when the boat stops, a free space 5 between the bottom struc- ture and the blank can be filled with water. The advantage of the lower space being filled with water is the high stability achieved, whereby potential acts on- board can be safely performed when the boat is stationary. When the boat starts moving, the water flowed into the intermediate bottom is drained via the aft of the boat, so the structure with the open aft thus does not affect the char- acteristics of the boat when it is moving.

If a boat equipped with an inboard, outboard or jet motor is in- volved, several advantages can be achieved by using a method in which a bottom structure is attached to a blank of the boat. In accordanc with Figure 5, to enable an easier mounting of a motor 5 and components closely related to it, such as power transmission system, the devices in question can be first at- tached to a bottom structure 1, whereupon the bottom structure can be com-

bined with the blank of the boat. In the example of Figure 5, a boat with an inboard motor and a keel at the bottom is combined in accordance with the method of the invention. Thanks to the manner of mounting of said type, the motor of an inboard-motor boat can be mounted considerably quicker. In the known methods of producing a boat, the mounting of the motor of boats equipped with inboard motors or the like is cumbersome and ergonomically difficult. Furthermore, thanks to the mounting method of the invention, the re- sult of the mounting is better than by using the known methods.

By using the mounting method of the invention, sound insulation and fire insulation are also essentially improved. The motor is encapsuled in a cover made of aluminum or steel, which improves the important safety and convenience characteristics of boating.

Changes related to the bottom structure 1 which affect the boat characteristics include the V-angle of the bottom, the lifting strakes and the keel. Thanks to these changes, optimal characteristics for use can be achieved by motors of different power. The changes in the bottom structure enable a similar blank of the boat to be used for various uses. Figures 2,3 and 4 show a simplified cross-section of the bottom structures and blanks of a boat. The bottom structure in accordance with Figure 2 is suitable to be used particularly in console boats or the like designed for higher speeds. The bot- tom structure 1 in accordance with Figure 3 is highly suitable to be used in fishing boats or the like equipped with a keel, which require high stability in lateral direction. The bottom shape of a boat with a keel can also be round or a wide V. The bottom structure 1 shown in Figure 4 illustrates a bottom structure to be attached to the blank of the boat, the combination of these two yielding a rowing boat with a sturdy structure, to which a small outboard motor can also be mounted.

It is obvious to those skilled in the art that the basic idea of the in- vention can be implemented in various ways. The invention and its embodi- ments are thus not restricted to the examples described above but they can vary within the scope of the claims.