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We are frequently asked if a design can be built in some other material than that noted. Any of our plans intended for planking with sheet material are designed to be a segment of a cylinder or a cone called “conendric” development. This usually means sections of the hull will be straight lines or convex. Sheet material cannot be bent into a convex section without goring or forming. Thus, theoretically plywood, aluminum and steel are interchangeable in a design based solely on the premise that the planking can be bent to shape without distortion. Obviously the construction is entirely different and details are not furnished in the plans for building in all three materials except in very limited cases.

 The big problem is the wide difference in the weight of the three materials as illustrated in the table below. The practical thickness limitation for welding aluminum is usually considered 1/8” and that for steel is 10 gauge. Steel boat designs are impractical for smaller planing hulls, they will simply weigh too much when weight is a function of speed. As an example, a typical 25′ steel hull will weigh about 2000 pounds more than the aluminum counterpart.

If you do consider switching materials, review the chart below. Remember these are the weights per square foot of the planking material, the interior structure will also be proportionately heavier. Some logic will make it apparent that switching smaller designs from plywood to steel is ill advised. 

 

                        THICKNESS                          WEIGHT PER SQ/ FT.

               INCHES         Millimeters     PW          ALUM        STEEL

fractions  decimals

1/8”             .125”           3.2 mm       .49 lbs.       1.75 lbs.     *        

3/16”           .188”           4.8 mm       .63 lbs.       2.60 lbs.     7.65 lbs.              

¼”               .250”           6.4 mm       .80 lbs.       3.46 lbs.     10.20 lbs.

5/16”           .313”           7.9 mm       1.00 lbs.     4.33 lbs.     12.75 lbs.

3/8”             .375”           9.5 mm       1.13 lbs.     5.18 lbs.     15.30 lbs.

½”               .50”             12.7 mm     1.53 lbs.     6.91 lbs.     20.40 lbs.

5/8”             .625”           15.9 mm     1.88 lbs.     9.00 lbs.     25.50 lbs.

¾”               .750”           19.1 mm     2.23 lbs.     10.58 lbs.   30.60 lbs.

1”                1.00”           25.4 mm     3.23 lbs.     14.16 lbs.   40.8 lbs.    

10 gauge steel is .135” thick and weighs 5.63 lbs./sq. ft.                              

Note: Weights are approximate and will vary with alloy.

Glen-L has many designs available for aluminum and steel in our online catalog.

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