Prior art small boats for river, lake and coastal transportation, general carriage, military utility and recreational purposes, are generally wooden structures, metallic structures, concrete structures, and fiber glass structures. In addition, a powerless mini yacht has been made of plastic.
There are many disadvantages of the above stated boats, and they include the following.
1. Wooden boats: are mostly for general utility purposes with complicated and cumbersome manufacturing technology, are easily damaged and are subjected to rotting because of a very strong water absorption.
2. Ferrous metal ships: are limited to larger type marine transportation vehicles having a hull made of large specific weight material. After being used for a longer period of time, repeated depositions and suspensions, such as aquatics shells, adhere onto the hull surface below the water line and erosion and etching of the metal occur.
3. Non-ferrous metal boats: have a high manufacturing cost and a poor antishock capability, are easily eroded and are incapable of being popularly used.
4. Concrete boats: have hull made of specific weight material that can be easily damaged and fractured and have a poor antishock or ability to withstand shock. They are also heavy and are generally not very practical.
5. Glass fibre boats: have a hull of high specific weight material that is easily damaged; they can become easily dilapidated or delaminated and fractured; they have a poor antishock capability; and they are especially difficult to be maintained and repaired. Because of a complicated manufacturing technology, they have a high manufacturing cost, similar to an aluminum reinforced sandwich boat (refer to U.S. Pat. No. 4,365,580 and also Soviet Union Patent 43764).
6. Powerless mini plastic yacht: manufactured by conventional rotational forming technology with a single kind of plastic material for the hull and shaped with a cope and dray mold. They have the simplest construction and utilize plates having the same thickness; they have poor rigidity and are made without a cavity, hold or cellar, port and cabin. In general they are merely used as rowing mini yachts that can hold a load of no more than 200 kilograms.
In the United States, there is an all-plastic boat made of reinforced soft plastics, but merely made from a reinforced concave mold, which needs to be reinforced by metal structural members and beams and has but an extremely simple and small hull (refer to U.S. Pat. No. 4,495,884 and U.S. Pat. No. 4,741,284). Also in the United States, there is another process for preparing an all-plastic boat using a rigid mold wherein resin-soaked glass fibre cloth is multi-laminated on a preformed mold or a stack mold. Alternatively, resinous as well as glass fibre cloth can be successively coated in steps and then allowed to solidify. However, this process is uneconomical, and requires a lot of time and energy, and further it is not very well mechanized. See for example, U.S. Pat. Nos. 4,495,884, 4,365,580, 4,913,944 and 4,247,279 incorporated herein by reference.
In U.S. Pat. No. 4,247,279 there is disclosed a rotational molding system in which a pair of large boat molds carried on separate carriages are alternately heated in a double open-ended oven having opposing cantilevered side sections for receiving concentric drive arrangements. The molds may be driven about two perpendicular axes in a rocking or full rotational motion. The mold is charged with a ground plastic powder, as the mold rotates in the presence of heat, the powder melts and sticks to the interior of the mold. After being solidified, the hull is released off from the mold. However, such a small boat has a simple construction without cellar, cavity, cabin and port, and has a maximum loading of 200 kilograms, as mentioned above.
U.S. Pat. No. 4,913,944 discloses a rotational molding method for making a laminated boat by successively releasing charges of particulate plastics in the mold cavity.
Further, Japan Patent 49-35067 discloses a process for manufacturing synthesized resin boat using a cope and dray mold for a single step or once-for-all hull forming and molding. However, between two separate plates there is used an expansion bag into which foaming resinous liquid is injected. The hull size is much constrained by the expansion bag, the hull construction cannot be too complicated, and it is difficult to carry out the injection.
There are also other Japan, Russian and German patents concerning plastic or glass fibre boat reinforced by metallic members; however, they are not all-plastic, nor made in a single step and they have a maximum load capacity of 200 kilograms.
Substantial improvements are needed to address the problems, disadvantages and drawbacks of the boat manufacturing discussed above.