FISHING BOAT DESIGNS: 1. FLAT BOTTOM BOATS

By Arne Fredrik Haug
Fishing Vessels and Engineering Branch

FOOD AND AGRICULTURE ORGANIZATIONS OF THE UNITED NATIONS, Rome, 1974

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CONTENTS

- INTRODUCTION 
- BUILDING PROCEDURE
- SELECTION OF TIMBER  
- SELECTION OF FASTENINGS
- TABLE 1  
- DRAWINGS

• 4.90m Flat Bottom Boat  
• 5.10m Flat Bottom Canoe  
• 5.40m Flat Bottom Boat  
• 5.94m Flat Bottom Boat  
• 6.80m Flat Bottom Canoe
• 8.23m Flat Bottom Boat
• 8.43m Transport Boat
• 11.25m Transport Boat

INTRODUCTION

THE PURPOSE OF THIS PUBLICATION is to present some basic designs of boats that are simple to construct, for use. in small-scale, non-industrial fisheries. All the designs shown here are of the flat bottom type; that is: the bottom is flat when seen in the transverse direction, while lengthwise there is a slight curvature. In the majority of the present designs, the shape Is simplified to the extent that the sides are built up with parallel planks and the rocker of the bottom is determined simply by the curvature and the flare of the side planks, so no building jig is necessary.

THE EASE OF CONSTRUCTION of flat bottom boats, because of the simple, straight-lined frames and the uncomplicated planking, is considered to be their main advantages, realizing also that this normally makes them the least expensive of all planked wooden boats.

THE SHALLOW DRAUGHT is an important feature for many purposes like navigation on shallow rivers and lakes or in swamp areas or close to the shore. For beach landing operations, it means that the boat can be kept afloat until it actually touches the beach, and because of its flat bottom it rests firmly on the ground after hauling up.

GOOD TRANSVERSE STABILITY when compared with round bilge or V-bottom boats with the same weight and overall beam is another advantage of flat bottom boats. This means that they give a stable working platform for fishing operations.

BIG FLOOR SPACE INSIDE THE BOAT is a valuable asset for certain fishing operations like gillnetting or pot fishing where a working position standing near the side is normal; this is another easily possible, favourable feature of the flat bottom boat configuration.

THE ADAPTABILITY FOR SERIES PRODUCTION is high, utilizing simple moulds and templates; series production is possible with a small labour force. In one country in Africa, the system of kit production in a central place with good access to suitable timber, and assembly in the different fishing villages, has been introduced with great success.

EXPERIENCED BOATBUILDERS are not necessary for the construction of flat bottom boats since the amount of difficult boatbuilding work is reduced to a minimum. Knowledge of general carpentry is required, supplemented with a few weeks training in this particular type of construction.

STANDARD SIZES OF TIMBER can be used throughout in the majority of the designs presented. The requisite timbers can be obtained directly from the timber store or saw mill without spiling or other difficult adjustments of the edges being required. Since standard timber sizes are different in different countries and strength and stiffness are not the same for all boatbuilding timbers, the specifications given should be taken more as guidelines than as strict instructions.

THE MAIN US ADVANTAGES of flat bottom boats are their general tendency to slamming in waves, resulting in discomfort, and requiring speed reduction, and the tendency to side- drift in wind aid waves, due to lack of a deep keel. These features restrict the area of use for these boats to protected waters, inland waterways and some lakes. Spray and water that enter the boat can also be quite uncomfortable, since there are no bilges where this water can be collected and easily bailed or pumped out.

THE BOAT DESIGNS presented here are suitable where low cost, or ease of construction are all important factors and where a somewhat reduced seaworthiness or seakindliness, can be accepted, or where extreme shallow draft requirements are an over-riding consideration.


THE SIMPLEST VERSIONS of flat bottom boat a have cross laid bottom planks nailed directly to the sides, and the lower side planks on each side are increased in thickness to take the nails without splitting The f ramps are mainly necessary to hold out the sides during construction, because the main transverse strength comes from the cross-laid bottom planks The bottom planks have to be held together by longitudinal bottom stiffeners and the side planks by vertical side stiffeners (intermediate side frames) A slight bending of the bottom planks when crossing waves can be tolerated as long as it does not affect watertight ness. Except for MLW-6, which is built over a jig f when one or several boats only are to be built the construction procedure is as follows!

1. Select timber and fastenings according to specifications on drawings (see Chapters 3 and 4 regarding selection of timber and fastenings).

2. Make templates for frames and transom.

3 Prefabricate frames, transom and stem complete with bevels.

4. Join lower side planks to obtain the required length using butt blocks on the inside. Nark position of all main frames and intermediate frames.

5. Assemble the lower side planks, frames, stem and transom on the ground or on a flat floor* When this is done the shape of the boat is given.

6. Fasten side stiffeners to lower side planks and complete side planking.

7. Turn the boat over, check the bevel on the lower side planks for a perfect fit with the bottom planks. Start planking the bottom from the stem, working toward the stem* Apply a strand of cotton and bitumastic compound in the joint between the sides and the bottom. If the bottom planking is made of a timber that swells and shrinks considerably it is necessary to leave a gap, the thickness of a hacksaw blade between the planks. Never fit the bottom planks tight if they are made of pine or similar timber since the bottom planks will buckle as they swell. With most stable tropical hardwoods, however, the bottom planks can be fitted tight on the inside with a small out gauge for caulking the outside*

9. Apply wood preservative on all surfaces. A strand of cotton is driven into the seams with a proper caulking iron and not a screwdriver, chisel or putty knife. The seam is finally rendered watertight by filling the joint with bitumastic compound.

10, Painting the outside of the bottom with bitumastic paint is the best and cheapest way. The sides can be painted but application of wood preservation will give a better and cheaper protection to the timber against rot.


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