2.2 Boat plans
2.3 Mould loft floor
2.4 The grid
2.5 Laying off profile and plan view
2.6 Battens, splines and straight edges
2.7 Body plan
2.8 Additional information gathered
2.9 Transom projection
2.10 Patterns - general
2.11 Camber pattern
The lofting requirements and techniques for a ferrocement hull do not differ in any great way from those needed for other materials. Because it is easier to alter a pencil line than a section of steel once frames have been made, great attention should be paid to accuracy of measurements and fairness of line to reduce any errors to a minimum which, in turn, reduces rectification cost and provides a fair shape to the frames onto which the hull reinforcement is applied.
There are many publications available written on the art of lofting to which the reader may refer. This chapter will provide a reminder to those already familiar with lofting but not familiar with ferrocement construction.
A complete set of plans for the construction of a fishing boat will probably vary from one designer to another, but should include at least the following drawings for a ferrocement fishing boat:
1. Lines plan and offset tableand as many other details as requested by the builder from the designer, viz: deck gear fabrication details, fuel, water and electrics schematics, exhaust system, nozzle details, propeller details, and accommodation details. Usually, the drawings may be read in conjunction with a detailed specification drawn up by the designer which will normally cover all principal characteristics, scantlings, material specifications, machinery requirements, electrics, deck gear, ventilation, cathodic protection, painting and safety equipment.
2. Hull construction profile and plan
3. Hull section/frame detail
4. General ferrocement reinforcement details
5. General arrangement profile and plan
6. Sterngear and liner tube details
7. Rudder gear and liner tube details
8. Fuel tank(s) construction details
9. Water tank(s) construction details
10. Deck construction
11. Superstructure profile plan and details
12. Fish hold construction details
13. Hydrostatics and Stability curves
Lofting cannot begin unless a good level platform has been prepared to ideally accommodate the full length and depth of both the profile and plan half breadth allowing an additional 600-1000 mm each way. It makes it easier, particularly if the lofting area is to be used frequently, to lay either hardboard or plywood sheets onto the lofting surface first and paint the boards with white emulsion or similar before laying any lines.
Hardboard sheets should first be soaked on the underside with water and allowed to dry before painting and fixing into position. This will help prevent the sheets from distorting once laid.
The sheets are pinned at their joints allowing for easy removal and subsequent re-use if required.
At the same time sufficient boards should be prepared for the subsequent laying off of the body plan, which will ultimately be the final frame making shapes of the hull at the location dictated by the design. The number of boards required will depend on whether a full frame or half frame drawing is required for frame fabrication, or indeed whether the production schedule calls for two frames to be made at the same time.
The first stage after the lofting platform has been prepared is to lay the grid for the profile and plan of the hull. The designer will have indicated his stations spacing (which ideally in the case of ferrocement construction should also be the frame locations) coupled with the spacing of water lines and buttock lines (ref. Fig. No. 1).
Figure 1. Lines plan
On the profile view the designer's offset table, coupled with any useful measurements given on the lines plan, are used to lay off the underside of the keel, stern, sheer, rabbet, deck at side, knuckle (if indicated), buttocks and profile of the backbone and transom.
The offset table measurements will usually be given in millims to the outside of the hull, and either measured +/- from the DWL or LWL (datum water line or load water line) or a vertical measurement from the baseline (ref. Fig. No. 2). Additional fore and aft measurements for the landing points of the lines should also be indicated on the lines plan by the designer, but invariably these points need to be picked up during lofting.
Figure 2. Table of offset related to lines plan
On the half breadth plan, similarly, measurements are taken from the designer's offset table and laid off for the sheer, deck at side knuckle point (if indicated), water lines, and diagonals. The designer should provide (sometimes he does not) measurements for finishing points for all the lines that fall between stations on the lines plan where they run into the half breadth of the rabbet at the stern and the half breadth of the keel, and centre line, at the aft end.
All the lines as they are laid are checked for fairness, and half the skill in lofting is in the choice of either easing an irregular measurement, in or out, up or down, whilst keeping the changes moving in a particular manner, at the same time remembering what has been done on previous lines checked, without drastically altering the designer's intentions as regards shape. The fairness of each line is 'in the eye of the beholder' and ultimately is in direct proportion to the skill of the loftsman and designer.
At this point perhaps a note about splines, or battens, and straight edges would be advisable. A fair line is better represented by choosing a spline of adequate length for the full extent of the line to be drawn, and thickness and width near to the maximum non-breaking dimension to suit the curve being drawn. The splines or battens should have a long straight grain which should not split when bent. For the sheer line and other long easy curves, a size of 40 x 40 and 50 x 15 mm will be enough. For the plan view lines, a size of 25 x 10 mm and 20 x 20 mm will be useful. For the frame/station lines, battens or splines of 10 x 10 mm or a little heavier or lighter will give a fair line. Teak was always a good material to use for this purpose, but as long lengths of teak are now nearly a thing of the past, one needs to experiment with whatever is available prior to the final laying of the lines.
Straight edges are initially required for laying the grid lines but as they are invariably used later in setting up the frames and helping to check level lines generally throughout construction, a mixture of sizes are required. Two straight edges the length of which exceeds the maximum breadth of the hull by 150 mm are needed, 150 mm wide and 18-25 mm thick. Other smaller general purpose straight edges will also be used.
Once all the profile and half breadth lines have been laid, the revised measurements are noted on a new offset table No. 2. Attention can now be turned to the body plan for the first time. The body plan boards are laid and a grid as depicted on the designer's lines plan drawn with all the water lines, buttock lines, diagonals and centre line of the boat marked off as shown.
Initially, fixed points of both half breadth and height (+/- DWL or from baseline), for the sheer, deck line, knuckle line, underside of keel and intersection of frames on centre line or rabbet line are marked in. Using the revised offset table No. 2 each frame can be plotted by marking the half breadths along the water lines, the heights +/- DWL on the buttock locations and distance from the centre line down each diagonal.
Using suitably sized battens/splines, the frame lines are drawn. Visually one can check to see if the curves have met all the measurement locations, as well as whether the frame lines are in 'sympathy' with each other. By easing the frame lines and retaking the measurements one can fill in a further revised offset table No. 3 and recheck that the changes on the plan and profile views fair in.
By now the errors should be minimal and the number of measurements requiring minor modification are nominal. The body plan frame lines are rechecked and if the body plan, profile and plan views coincide on all the measurements taken, one can now say that the measurements are faired and a final offset table may be filled in and kept as a record for future use, especially if the frame making boards are damaged or not stored properly.
At this stage, the designer should be advised of the changes to the original offset table measurements.
Whilst laying off the lines, many additional measurements that may not only be useful to the builder but also to the designer, may be included in the final offset table. The majority of errors are in the 0-12 mm category and this sort of difference is expected when the original lines plan is to a scale of 1:20. Many designers will have greater errors than this, hence the reason for full-scale lofting out.
Additional information has been picked up, the AP (aft point) being an example. This can help by providing fairing points for the splines aft of where a line may actually finish, as well as providing a pattern to check out the transom shape and fairing in of the frames at the setting up stage. Additional information has been included for the deck at side measurement also the crown of the deck, which are useful check measurements when proceeding with the construction, particularly if a ferrocement beamshelf is to be included in the construction.
The transom of the boat may or may not be vertical. If it is vertical, the measurements will be the same as the AP. 4 However, if the transom is raked, it will need to have its expanded shape drawn. The centre line of the transom shown on the profile plan, becomes the centre line of the half breadth view of the expanded transom. Each water line is drawn at right angles to the centre line which increases the distance between the water lines in accordance to the rake of the transom (ref. Fig. No. 3).
Figure 3. Transom expansion
The buttock lines are drawn in parallel to the transom centre line and spaced as required by the design. The expanded transom intersection points on the buttock lines is made by squaring from the transom centre line and buttock intersection on the profile view, to where they cross the vertical buttock lines in the expanded view.
The half breadth measurements for each water line are picked up by squaring the water line intersection to the rake of the transom on the profile view down to where the intersection is made with the water lines in the plan view. The resultant measurement between the transom centre line and water line intersection for each water line will give the half breadth measurement required for transfer to the expanded view.
Once all the points have been marked onto the expanded view a batten can be used to fair in the marks and the resultant shape is a view of half the expanded transom. The full transom shape can then be drawn out on a patterning material and can be used for making any number of transoms for that design. It should be remembered that the shape drawn will be the aft side of the transom.
Generally speaking a small number of patterns are needed for the construction of a ferrocement fishing boat. It is useful whilst the profile shape of the boat is drawn out full sized (and the designer is forward enough with his sterngear and rudder gear requirements), to make up a profile pattern of the backbone shape including marking on it frame locations, the shaft centre line and rudder centre line. If the reinforcement is curved above and below the sterntube, not only will the pattern give the shape accurately to bend the main reinforcing rods to, but will also give a check at the frame setting up stage to ensure that the space between the transom and keel is as it should be, to avoid any later problems in rudder gear fitting or indeed if a nozzle is fitted.
Because it is normal to paint over the lofting area for future use, a pattern of the stem, with water lines, stations and location of main reinforcing bars will be useful. As for all patterns, they should be clearly identified and kept with the frame making boards in a suitable place for any subsequent construction of the same design.
Finally, the pattern that not only helps the hull constructor, but is also used at fitting out, is the beam camber board. The camber board is made from the designer's required camber usually in the region of 15 mm in 300 mm, the actual figure varying with the beam of the boat and the specified amount of crown/crop in the deck. It is useful at times to have a male and female pattern depending on whether the boatbuilder can use the pattern either over or under the reinforcement which may come in the way.
The camber pattern will need to be made from material 18-25 mm thick, a few cm longer than the full breadth of the boat and a little deeper than the maximum crown of the deck.