Cutting of solid wood is reduced when the design is for a plywood hull too. Plywood frames eat up plywood quickly as well because of the vast amount of waste while solid wood wastes very little. Thickness of gussets can also be thicker to compensate for using a box store grade of plywood without much of a cost penalty (they sell 2 x 4 ft pieces so you don't have to buy a whole sheet. Plywood works well for gussets however- much better than solid wood where splitting is a problem with short pieces of solid wood. Solid wood usually can be had for a fraction of the cost of quality plywood. Solid wood can be fir or yellow pine or some harder cedars (like spanish cedar) for reasonably light weight frames. There's several approaches you can take, to incorporate all plywood framing, but you should adjust the scantlings to accommodate the physical properties of the new material choices, if you expect similar strength and stiffness figures for a given weight.Ĭost is another issue. Or reducing frame spacing and using similar molded and sided dimensions with an extra stringer or two tossed in, to compensate for stiffness loses. It's actually lighter and stronger this way, than tripling the spacing, doubling the frame thickness and quadrupling (or considerably more) the molded dimension on a plywood frame.įrom a practical stand point and given the same weight, spacing and approximate thickness at each frame station, the depth of an equivalent plywood frame will be at least 60% more (given sided dimension reductions for weight), so a 1x4 solid wood frame converted to plywood will be at least 6 1/2" deep, which robs usable interior volume, which can be precious in small craft.Īgain you can move the numbers around to help a bit, such as leaving the spacing the same, accepting a weight penalty and reducing the molded dimension a bit to gain reasonable interior volume. This is precisely why you see dainty little hardwood frames on relatively close centers in some traditional build types. The only time this get rivaled is with particularly dense hardwoods, though with these you can use even thinner molded and sided dimensions, because of the great torsional stiffness of solid hardwood stock. This is because for the same frame spacing, you can use smaller, both molded and sided dimensions, then the same strength and stiffness physical qualities, if built entirely from plywood, plus the edge fastening advantages of solid lumber. A hard chine build with relatively straight sided frames, will be lighter and stronger using solid wood futtocks with plywood gussets or lapped and pinned joints. The real concern is the considerable difference in longitudinal strength and stiffness. I spec plywood ring frames frequently on may designs. It's not that plywood frames can't be used, but that their good and bad points need to be considered in the scantlings. Edge fastening is an issue, but tabbing and epoxy can solve this on some build types.
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