Practical: Seating
Sick and tired of having an aching back? Bob Couper solves the problem of the lack of back support on many boats with this handy $46 do-it-yourself transportable backrest-cum seat.
I find sitting in the cockpit of Spindrift for long periods hard on the back because of the lack of back support. However, while travelling down the Murray I met Canadian physiotherapist Steve Fletcher on his boat, Water Hen. He'd made a backrest-cum-cockpit seat so he could sit with a better posture and reduce potential back problems.
The backrest consisted of two pieces of ply joined by hinges. The back flap was padded with foam, covered with vinyl and supported upright by the cockpit coaming. The bottom flap was slipped under the cockpit cushion to keep the backrest in position. Alternatively it could be used with a loose cushion and supported against another surface such as a stanchion. Steve had made a loose cushion in a wedge shape specifically for this purpose.
The measurements given below should fit most people. However, you might need to vary them slightly to suit your particular body size or seating position.
Then cut a ply strip 70 x 350mm and glue it to the underside of the bottom flap across the hinge edge to thicken and strengthen it. This also allows you to recess the hinge fixings to prevent damage to any surface the seat is placed on and slightly slopes the seat forward to encourage the correct pelvic tilt.
Next join the flaps together with the two reversed offset angle hinges. For extra strength use bolts instead of screws. The offset hinges allow space for the nuts.
Disassemble the pieces, round off the corners of the flaps and edges, sand smooth and give both flaps at least two coats of varnish.
Although you could use a straight rectangular block of dense foam to pad the back, it is better to shape it into a curve that fits your back contour. The correct contour is one that gives the maximum projection just above the small of your back. Note that the foam covers only the top third of the back flap.
To make the foam easier to shape, cut the foam slab into slices with an electric bread knife. Then cut each one to the correct contour and then glue them together with contact adhesive. You can buy the latter in a pressure can that allows you to spray the adhesive on, making this job easy.
If you haven't got reasonable sewing skills, get a local upholsterer or motor trimmer to mark out, cut and sew together some vinyl to cover the foam padding. It looks best if you use three panels (two end ones and the main piece) rather than just wrapping around a single piece.
Then it's just a matter of stapling it all onto the back panel. First staple the bottom edge of the vinyl upside down as shown.
Then swing the foam and vinyl up into position (this will hide the bottom edge staples) and staple the other edges around the back of the seat. Alternatively fix the padding onto a separate piece of thin ply and use top ties or Velcro strips to fix this latter panel to the main flap.
Using offset hinges allows the seat to fold flatter for storage. Note the non-slip material attached under the seat with silicone sealant to stop the seat slipping.
Top tip
Spray the inside of the vinyl and top of the foam with contact adhesive before assembling to keep the vinyl following the shape of the foam.
Positioning and proportions of the contoured foam padding.
What you'll need to buy:
You will probably find much of what's wanted in your scrap bin. But if you need to buy anything, here's what you'll need:
* One piece of 900 x 450 x 9mm plywood (marine or exterior grade), $13
* One pair of 63mm (21/2 inch) reverse-angle brass or SS butt hinges, $6
* 12 20mm (3/4 inch) x 4.74mm (3/16 inch) round head bolts each with two washers and a nut, $6
* Varnish, $5
* One piece of non-slip cloth, 380 x 100mm, $1
* Silicone sealant, $1
* One piece vinyl cloth 700 x 400mm, $1
* Foam block (dense grade) 380 x 300 x 30mm, $5
* Spray adhesive, $8
Total: $46
