9½' Dinghy

Design Number 230

This design was done for a firm planning to rotomold the boats in plastic. Rotomolding is a specialized method of construction. It involves the creation of a metal form of both the outside and inside shape of the boat. Inside these forms are dumped pellets of the special plastic. The form is heated while it is being rotated in two axes at the same time. The heat melts the plastic and it forms itself into the shape of the mold. Most of the boat fenders we see, often made as net floats, are made this way.

I spent quite a lot of time thinking about how the mold was to be built of steel. I came to be increasingly concerned about the work involved in trying to recreate the sweeping shapes of traditional lapstrake wooden plank layout in steel. I felt it would be much too complex a project.

The result of this cogitation was to try the idea of making the laplines all straight lines on the body plan view. This looked good on the drawings, and the work involved in building the molds should be considerably reduced. The layout is much simpler, and the offsets are just given along the laps, as if they were diagonals.

The wooden lapstrake construction shown on the plans is a good way to build the boat. The simplified lap layout and lofting will make fitting the planks much easier and thus quicker.

If a sailing version is desired, I'd use the rig and parts off the 9' Pacific Peapod design.

Length overall9'-6"2.90 m
Length datum waterline8'-3"2.51 m
Beam4'-6"1.37 m
Draft0'-7"/2'-6"0.18/0.76 m
Freeboard:Forward1'-7"0.48 m
Least1'-0"0.30 m
Aft1'-2 3/80.36 m
Estimated structural weight90 lbs.41 kg.
Displacement, to DWL260 lbs.118 kg.
Displacement-length ratio207 
Sail area58 sq. ft.5.39 m2
Sail area-displacement ratio22.78 
Prismatic coefficient.586 
Pounds per inch immersion110 
Entrance half-angle29° 

Note: The displacement numbers are calculated to the arbitrarily chosen DWL.
The calculated ratios of displacement-length and sail area-displacement will vary widely depending on the loading of the vessel.

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