On Saturday afternoon, 8th March, six WBA members enjoyed a very informative couple of hours with Peter Saggers at his shed at Sheldon. Peter is building a 45 foot cruising sailing boat.
The construction method is cold moulded, triple planked. The first skin is longitudinal, 16 mm thick, the second skin is diagonal at approx right angles to the slope of the bow, 8 mm thick, and the third skin at right angles to the second, also 8 mm thick. Planks are generally about 150 wide. At the time of our visit, most of the first skin was in place and partly faired.
Peter described his method to us.
For the first skin, planks are tapered in width. This is to avoid building up stress in the plank by having to contend with edge set. Place the first plank (a parallel sided board) at the sheer. Measure up (say) 5 full plank widths at the frame of maximum girth and temporarily fix a straight edged plank at that point, laying naturally on the frames. The natural lay will cause it to slope closer to the sheer plank at each end. Measure the separation at each frame and divide by 5 (i.e. the number of planks in the first lift). Use those dimensions to set out and pre cut planks (no edge bevel). All planks will then lie naturally on the frames with minimum stress and twist.
Peter has a bench set up for pre-cutting planks. It has the outer edge dead straight, and has cross pieces set out at spacing to match the frame spacing. A fairing batten is set up on the crosspieces using the dimensions calculated above plus the off set from the power saw blade to the edge guide. All ten planks (5 a side) are then cut using a hand held power saw and the same set-up.
The following are other notes of Peter’s methods.
Scarfing – Peter uses a docking saw to get a 10:1 bevel, cut with the plank on edge and held in a suitable jig. Planks are laid out and scarfed in a stack. Each scarf is aligned by feel (to confirm that there is the correct overlap), then held together (to stop slipping apart with 2 panel pins, not driven fully home and with the heads snipped off. The stack is clamped and cured. After curing, panel pins are removed. Peter uses epoxy for scarfs but could use resorcinol. He uses epoxy because the boat is to be clear finished internally, and resorcinol stains the timber. The first skin is also edge glued with epoxy.
The second skin is face and edge glued with resorcinol, stapled with ss staples (left in) and temporary screws where necessary to maintain a close fit for good clamping pressure. He then fairs perfectly at the end of the second skin, finishing with a long board.
The third skin is face and edge glued with resorcinol and ss staples, aligned with the grain of the timber, and set slightly below the surface. Wipe over with metho to bring up the grain before final fairing.
You will recall the various methods we have been shown to spile and then fit the diagonal planks on the little boat we have partly cold moulded at the Museum. Peter carries out this task with elegant simplicity. He uses a router to directly cut the diagonal planks without separately spiling. A router is set up with 2 pins on the face to act as a guide. The line of the pins is slightly outside the diameter of the cutter. Call the distance between the line of the guide pins to the opposite face of the cutter D. The pins project slightly less than the thickness of the material used for the diagonal planking. Each diagonal plank has one straight face and one face cut to fit against its neighbor. Lay the new plank naturally on the mould, such that its maximum distance from the straight edge of the previous plank is D (this can be quickly established by using a spacer block), and temporarily hold it in position. Place the router pins against the existing plank and run the router the full length of the new plank, cutting a face which is exactly parallel to the existing plank edge. Remove the temporary fixings from the new plank and slide it up to the existing plank. One cut, dead accurate, right first time – brilliant.
Other suggestions from Peter:
• Use machines as much as possible.
• Use jigs to reduce repetitive work and setting out.
• In internal fit-out, use a small number of standard radii in curves for openings, etc. They can be cut with the router mounted on a base board with holes for pins at the appropriate radii. This simplifies forming the opening and also prefabricating trim for the opening.
• Use a square pad and square sheet of sandpaper (approx 300 x300 for the scale of his boat) in an angle grinder for bulk fairing – it does not cut in at the edges as a circular pad and paper will. (Final accurate fairing is done with a long board.)
• When building in strip plank, after completing the lay up of the hull, bog but don’t fair in the inverted position. Turn the hull and complete the internal structural fitting out, then turn the hull again and fair externally. If faired before internal fitout, minor unfairness will appear in the external fairing as a result of the internal fitout.
• Glues – Peter uses resorcinol wherever he can, but it needs a close fit and clamping pressure. He uses epoxy elsewhere. Can become allergic to epoxy over a time. E.g. uses resorcinol to laminate the floors.
Peter’s general lesson on boat building: “The objective of today’s work is to make tomorrow’s work as easy as possible” i.e. plan ahead, do accurate work so that future work is not made more difficult.