Sunday, January 8, 2017

Argie 15 Seat Framing

Kevin Agee is doing a great job of the Argie 15 that he is building for us. Since my last post he has been completing the epoxy coatings on the inside of the hull and completing the framing for the seats.

The framing for the transverse seats at bow, stern and midships is fairly simple. The plywood panels have timbers glued to them that serve as landings for the seat tops. The stiffeners under the seats are simply slotted or half-jointed and glued into those landing timbers and finished with the top surfaces flush.
Framing of aft seat.
 How to frame the side seats seems to be the part of the project that prompts the most questions on forums. There are various ways to go about this but the method used by Kevin seems to have worked well, so others may like to follow his method.

The difficulty of this work stems from the fact that the seats have curvature both on plan and vertically. The seat front runs parallel to the seat landing stringer at mid-height of the hull side panel, so that stringer sets the shape in all directions. In the photo below, the lengths of string running across the boat serve to define the exact level for the seat stiffeners at the various points along the stringer.
Side seat stiffeners slotted and glued into the inner face of the hull side stringer. The strings define the correct alignment for each stiffener.
Joint of stiffener with side stringer, showing how the string is retained at each stiffener. It is a continuous length of string that runs back-and-forth across the boat, which allows it to be easily tensioned. Each stiffener is numbered to ensure that it is glued back into the correct slot.
Another view of the main cockpit with the string guide and seat stiffeners.

The side seat stiffeners were cut to exact length and angle before gluing them in. The correct angle to cut off the inboard end can be measured at the intersection with the hull, it will be the same at both ends. If you prefer, you can cut the stiffeners slightly over-length and trim later. To do this, wait for the epoxy of the joints to the side stringer to be fully cured, then remove the screws that hold the guide string. Lay the seat top in place and mark each stiffener at the inner edge of the seat top. That will give you both the length and the angle to cut.

The intersections of the stiffeners with the longitudinal cleat that will join the seat front and top to each other is done with a halved-joint. The top half of the stiffener is cut away for the width of the cleat and the cleat has a slot cut into it of the same depth and the width of the stiffener. Then the stiffener ends are all glued into their respective slots at the same time that the cleat is glued in place.
Longitudinal cleat glued to seat stiffeners with halved joints.
Halved joint, with end of stiffener notched and glued into cleat. The screw is temporary and will be removed once the glue has cured.
While this work has been going on, Kevin has also been preparing the seat fronts for fitting. Installing a curved sheet of plywood like this is simpler if the plywood has curvature pre-set into it. He clamped the seat fronts on the work bench to hold them down at the middle, with the ends lifted on spacers. After a few days in that shape, it will become the natural curve for that piece. That will help the unsupported bottom edge to follow the same curve as the top, instead of having a natural tendency to stay straight at the bottom while being curved at the top.
Seat fronts clamped to the work bench with the ends lifted to pre-bend the sheet. He has also applied the epoxy coatings while pre-bent, which will help to hold it to the curve. 
More info on this an our other designs can be found on our main website or our mobile website.