How does a boat builder determine the dimensions of a plank that is to be formed into a strake?
"Strake" in this context means a skin plank. A strip from stem to stern that can consist of one or more planks. See Image 7.
What successive operations will the boat builder have to perform to achieve the correct dimensions for a plank which, once heat formed or steamed, will become a topside strake that fits?
This example deals with a strake, the sheer strake (see image Strakes below). This strake is fitted to the port side from midships to the stern post. On the port side the sheer strake from the stem to midships has already been fitted. The tools required are present in the workshop.
A stock of oak timber is present in the depot. The strake will be sawn from one of these planks.
We shall first look at the implements, machines and tools required. The successive steps for shaping a strake will then be explained.
In this context, fitting means to match up with the already fitted sheer strake and to match the lines of the boat required by the master boat builder.
Tools, implements and machines for making a plank into a strake which, after steaming or heat forming, will fit on the ribs.
Planks from one tree as they arrive from the sawmill. Shaped plank ready for heat forming into the correct form.
A sufficient number of small laths. These laths will be fitted to the pliable plank at a spacing of approximately every 15 centimetres. In the example shown the pliable plank is five metres long. A quantity of 40 small laths will therefore be more than sufficient for this. The small laths are approximately 20 centimetres long and 2 centimetres wide. These dimensions are related to the size of the future strake and therefore the size of the boat.
The board will be fixed to the ribs using the nails.
The small laths can be attached to the board quickly by using staples.
A thin, very pliable plank
In the example in the photograph on the right a solid timber plank is used however plywood can also be used. It is important that the plank is easily manageable and is very pliable. The thickness of the plank shown is 1.2 centimetres. Plywood of 3 millimetres thickness is sufficient. This plank is also called a board.
The end points of the small laths on the board will be transferred to the plank using a pencil.
This measuring stick will be used to join up the marks made on the plank. This will create a smooth line.
Once the contours have been marked on the plank the strake is sawn from the plank using a chainsaw or circular saw.
Successive operations that will allow a plank to be sawn, which will then take on a suitable shape by heat forming.
Selecting the plank that will subsequently be heat formed into a strake. Oak has been selected in the example.
- Material thickness - This depends on the type of boat, its professional use and future sailing area. The wishes of the client and the client’s financial budget are also determining factors for this. In the example shown the sawing thickness of the planks is 1.6 inches. After working (planing) approximately 1.5 inches will remain. 1 inch = 2.54 centimetres
- Type of timber - The type of timber selected usually depended on the type that was mostly available from stock. In Scandinavian countries a lot of pine was used for boat building because of the extensive pine forests. In the low lands and Great Britain oak was the preferred type of timber which, in addition to its good properties for boat/ship building, was also present in sufficient quantities. Oak is used in the example shown.
- Plank dimensions - The plank has to be selected in such a way that the strake that is to be sawn can be sawn from the centre of the plank. The centremost section must also meet the quality requirements.
- Timber quality - The section of the plank that will form a strake of the skin must not have any defects. Bark, sapwood and knots/burrs can not be worked.
Plank as delivered to the yard from the sawmill. The length is approximately 10 metres
The first section, approximately one and a half metres in length cannot be used in boat building because of a knot. This plank therefore only has a remaining length of eight metres that can be used
The width of the strake is determined by the required number of strakes. In the example there are six strakes between the bottom and the rubbing strake. One broad garboard strake (garboard plank) and five equal strakes until one reaches the rubbing strake.
Determine the bottom line of the strake. This is the subject of "matching" the boat and is covered as a separate skill.
Note: when fitting the strake against the skin the heart side of the plank should be fitted against the outside of the boat. This helps prevent the strakes opening up.