Fishing Craft Technology (1+1)

Unit 4 - Boat building materials and construction of boat

4.6. Construction of wooden boat

1) Requirements for wooden boat construction
During construction of wooden boat the following plans are required
(i) The construction plan:
This will give the details of the plan, section and profile also relevant structural details.
(ii) Lines plan:
The lines plan is a geometric description of the hull. The sheer, body plan and half breadth plan are collectively called the LINES PLAN. This plan also gives an idea about the water lines, buttock lines, diagonals and sheer line and also showing the shape of the boat at each station with diagonals.
(iii) The table of offsets:
This is a table draws up by the designer so that the plans can be used off without inaccurate scaling of the line plan. All these lines are used to make a complete picture of the shape of a boat which the designer wishes the builder to reproduce. To assist the builder to draw the shape of a boat in full scale size, all measurements necessary to draw the various lines are gathered together in a table called the offset table. In order to obtain a fair and true shape of hull for building purpose, a full scale drawing of a boat is drawn on the boat construction yard, which is called as mold lofting. For mould lofting, offset table is necessary. This table will show the value of keel, water lines, deck, sheer from the half breadth line of boat and keel, deck and sheer from heights above from the base line for making easy drawings. The measurements on the table are normally expressed in feet, inches and sixteenths eg. Half breadth at LWL on station 6, 8 ft 6¼ in would be appear as 8-6-4.
(iv) The sail and spar plan:
This plan is to enable these parts to be made
(v) The specification:
This is a complete schedule of all the materials etc., to be used in the construction of the boat.

2) Wooden boat construction
The following are the different stages of boat construction

i) Mould lofting:
This is the process of transferring the plans or blue prints into full-size interpretation on a floor or services of boards. These boards are usually painted matt black to provide a good contrast with the chalked lines. Laying out the plans to full size enables accurate patters and templates to be made; it also shows up any discrepancy in lines thus enabling the loft man to fair there off. The first step in boat building is making the mould lofting which is the full scale drawing of construction profile and plan view and drawn in floor of construction yard. This helps the builder to see the pre view details of construction before setting up the hull.

ii)Building stocks
Building stocks are the group of members arranged to provide the seating arrangement of the backbone assembly. These members should have enough strength to bare the load of the boat and its structural members and to serve till the complete construction is over.

Generally good quality, hard wood timbers are used for making the building stocks. The size normally varies from 20 to 30 cms in width, 35 to 65 mm in thick and more than 1 to 2 m in length depending upon the type of boat to be constructed. Initially at one end of the stock, a slot to the size of the keel is being cut and in the other end is made to sharp to enable the builder to drive it on the ground. This type of stocks can be erected at any uneven ground with loose soil. These stocks are driven on the ground to the maximum possible by leaving enough height from the ground to the keel.
During the setting of the building stocks all the stocks are made ready and positioned on the ground. Since, the ground is uneven, a base line is extended by means of a string or a twine tied, at both ends of the perpendiculars erected on either ends of the boat length. This line can be checked by means of a spirit level. As per the rake indicated in the lines plan, a second line is extended from the base line to indicate the keel line. At this stage the builder can drive the stocks in their respective positions by maintaining the rake of the keel.

Preparation of mould :
Moulds or station templates are made from cheap timber about 25 to 35 mm thick and 15 to 20 cm wide. The finished shape of each mould can be got from the body plan drawn to full scale on the mould loft. Making the mould is to make a wooden pattern or shape that fits this outline. The best way to do this is to make the mould with different pieces of timber marked 1,2,3,3,4, etc., using the body plan on the lofting platform and assemble the pieces as shown in the sketch.
The opposite piece of timber should be exactly the same shape that 1,2 and 3 are the same shape of either side of the mould. The top stay (cross piece) No.4 will hold the top of the mould together at its correct widths No.5 is another cross piece of batten which helps to strengthen the mould and it is parallel to No.4 piece. No.6 is another strengthening piece at the bottom of the mould and must be placed on the same side of the mould as No.4 &5. The different piece of the mould can be nailed or screwed together and it is important that the finished mould should be true in shape and made.

In the lofting platform, the body plan or the section lines are drawn including the thickness of hull plank. Hence, before starting to prepare the mould it is necessary that the plank thickness should be deducted. The thickness of the planking is given in the specification. The thickness is taken in a pair of dividers and arcs are drawn on each station line. All these arcs are joined together by using a batten and pencil and thus the line drawn parallel to the body plan. This is the outline for the preparation of the mould. This is done for the transom board also. The centerline of the boat should be marked on the top cross pieces which is half the width of the boat at whatever position the mould is designed. Each mould should be properly numbered. The waterline, the deck at side, and the sheer are marked on either side of the mould. In the body plan on the lofting platform only half widths of the body from the centerline are given. While passing templates or mould they are made for the half section, which has already been drawn on the platform (after deducting the plank thickness.

Mounting the mould on backbone
The moulds can now be mounted on the backbone of the boat. The position of each mould is marked as sections in the lines drawing has been transferred to the mould loft and in turn. The positions are already marked on the top of the hog keel and properly numbered while preparing the backbone assembly. The edge of the mould is placed exactly on this mark in such a way that all the moulds at the aft of midship with the back edge on the mark and the forward of midship are placed with front edge on the mark. The position of the uprights can be fixed at this stage. The cross pieces and battens are made to the upright so that the upright is 25mm above and behind the mark for moulds, aft of midship and about 25mm above the front mark of the forward moulds. Thus the bottom can be fixed. All uprights are erected and the moulds are nailed or bolted to the uprights.




iii) Setting the backbone assembly:
The back bone consists of the stem, Apron, stem knee, keel hog, dead wood, stern post and/or transom. These parts are shaped and sided before forming together. At first, cut the solid wood from thick wooden log at desired length and lay as a keel over the keel post. Over this, place longitudinally a false keel known as hog keel. Note how the various interlocking timbers are assembled to produce the structure. Particular attention must be given to the fastening of the various components such as knees, horn timber, transom post, stern post. Stop waters should be fitted in all joints that cross rabbet lines (lines where the planking joins the backbone structure). These are round dowels of soft wood, which swell in contact with water to prevent water leaking along the line of the joint. When the rabbet (the cut-out joint into which the planks fit) has been roughed out the backbone structure is set up on convenient foundation blocking ready to receive the frames.
1) Keel: The principal fore and aft component of a vessels framing, located along the centre line of the bottom and connected to the stem and stern frames. Floor or bottom transverses are attached to the keel.
2) Hog keel: It is a false keel or extra keel which is in the upper part of the keel.
3) Stem knee: A triangular piece of wood which connects the stem and the keel.
4) Stern: The aft end of a vessel, the farthest distance part from the bow.
5) Stern knee: A triangular piece of wood which connects the stern and the keel.
6) Transom frame: Transom frame is the part which is connected to the horn timber. Transom planks are fixed in the transom frame.
7) Transom knee: A triangular piece of wood which connects the transom frame and the horn timber.
8) Horn timber: A timber extending aft from the stern post to the transom of a vessel and forming the central support of the stem.
9) Dead wood: It is a member of the backbone assembly connecting the keel with the stern post where the strong back passes over the deadwood, where great strength is required.
10) Shaft log: Shaft log is the member through which the propeller shaft passes.
11) Skeg: The extreme aft part of the keel of a vessel, the portion that supports the rudder post.

Setting up of keel:
It is usual to set the keel up on blocks of suitable building height so that the declivity is correct is so that the bulk heads would be upright and the waterline level in the position the boat is intended to assume when afloat. The top of the stem and stern post or transoms and may be the moulds, if necessary are braced by temporary fixings to a building or other convenient place. The whole backbone structure is carefully checked for being upright with level and plumb line.


iv) Preparation of mould

Setting up of moulds and bulkheads:
Moulds are built up with pieces of soft wood, joined together. Deal is a good material for this purpose. The moulds are to be set up on the keel at the number of station required. They can be held on the keel with a small block or blocks screwed on each side and screwed down. The upper side is held up by braces from any convenient part of the building and then squared up with the keel and plumbed to upright with the centre line.
The actual number of moulds will depend on the shape and type of vessel. If the vessel is to have a number of bulkheads, these can be erected in their finished condition to advantage. The moulds or bulkheads are fitted to the hog. The moulds are usually fixed by a small removable block screwed to the hog. Check each mould carefully for being upright and true.
Setting up of planking:
It is usual for the boat builder to set out the planking by eye using a true flexible batten by marking along the moulds in a fair curve. The planks will be about the same width at the stem but will vary from the gar board strake from fairly wide depending on the shape of the ends of the boat, to narrower in the turn of bilge and widening again on the flatter section of the top sides to the sheer strake. The narrowing of the turn of bilge planking is necessary to prevent distortion of the planks on the sharper curve of the mid-ship section. It is necessary to spend a good deal of time and trouble offering up the batten and sighting through before an acceptable curve is found. The sheer and the whole of the planking must be perfectly proportion for a clincher boat of look good.
The keel and hog are either glued or beaded together and can be fastened with screws, clenched rods or bolted with nuts and bolts. If the keel or hog are long and have a joint, this should be in the form of a scarf preferably of the hooked type and in a keel joint there should be a stop water fitted in the line of the rebate which will be covered by the planking this stop water is often omitted of the joint is glued. The stem having been carefully shaped will now be scarfed to the keel. There are several methods of doing this. This stem knee is now fitted having first been sided. If there is to be an apron a scarf is cut at its upper end. The stem knee is fastened right through the stem, keel and hog scarf with bolts are clenched rods arranged. Dead words are fitted on the top of the keel is good construction. If the boat is to have a stern post it must be scar fed or half jointed to the aft end of the keel. A transom stern is jointed to the keel. This joint may run right through but it will be a neater and better job checked half way through. It is usual to build the wood keel and the structures of the boat direct into the metal keel resting on its blocks.

Template fixation:
The first stage of construction work is to make the templates for all the members from the mould loft. The templates are refer to the pattern of waste wood, arranged over the keel to give the required shape of hull.
Framing:
Frames are either sawn or laminated are then assembled and raised at the correct position on the keel structure. Once the frames are fixed then it should fastened with side planking through copper nail. When clamped in position they are through¬ bolted in place. As the frames are raised they are held in position by wooden battens. At the bow and stern there will be a number of frames that do not cross the keel but have their heels notched into the deadwood or horn timber. These are known as half frames, while the frames that cross the keel are known as square frames. In this case the heels of the frames should be notched into the deadwood, sternpost and horn timber.
Planking:
In very small craft, where for instance the planking runs the full length of the hull, it is possible to mark off and spiel planning like clincher building. If the boat is larger it more usual to steam bends the timbers into the place before planking commences. In the case of sawn or grown frames. These are erected fully beveled and faired.
Setting up of planking:
It is usual for the boat builder to set out the planking by eye using a true flexible batten by marking along the moulds in a fair curve. The planks will be about the same width at the stem but will vary from the gar board strake from fairly wide depending on the shape at the ends of the boat, to narrower on the turn of bilge and widening again on the flatter section of the top sides to the sheer strake. This narrowing of the turn of bilge planking is necessary to prevent distortion of the planks on the sharper curve of the mid ship section. It is necessary to spend a good deal of time and trouble offering up the batten and sighting through before an acceptable curve is found. The sheer and the whole of the planking must be perfectly proportioned for a clincher boat to look good.