dimensions notation on boat plans

[sierrasmith71]

I have a set of plans for a 18'.8' Mackinaw sailboat and it has several unknown (at least to me) notations of components sizes:

for example: Floors. W. Oak S. 1" M. 4 1/2" .. I understand the Floor and W.oak, but what does the S. and M. indicate? Measuring, with an architect's scale, from the plans shows the width of the floor to be 1" and the maximum height to be 4.5" .


David Garrison

[dmg]

David

The S means "sided", which translates to thickness. The M means "molded", which translates to width.

The text that came with the plan set should tell you if any of the wood parts can be made from lumberyard stock, example-your floors cannot be gotten out of 1 x 6 as the sided dimension would only be 3/4".

Dave

[Jon Etheredge]

Start with the "molded" dimension...

Imagine a point in the center of the boat, i.e. centered fore and aft AND side to side. Now draw a line from that imaginary point through the piece you are considering. The dimension along this line is the "molded" dimension.

The other dimension is the "sided" dimension.

Some examples:

1) At the stem, the fore and aft dimension will be the molded dimension and the side to side dimension will be the siding.

2) If you are looking at a floor timber then the fore and aft dimension will be the sided dimension and the up and down dimension will be the molded dimension. On your plans, the "thickness" of the floor timber will be the sided dimension.

3) A steam bent frame will have the molded dimension running side to side (or up and down) and the siding will be fore and aft.

Equating thickness and siding is not always correct because most people think of "thickness" as referring to the smaller dimension. A small canoe might have steam bent frames that measure 1/4" x 3/4" with the 3/4" dimension layed against the planking. Most folks would say the frames have a thickness of 1/4" but this is actually the molded dimension. Naval architects use this molded/sided nomenclature just because it eliminates this ambiguity that can result from terms like thickness, width, etc.

[Nicholas Carey]

I find it easier to think of the molded dimension being that dimension lying perpindicular to the surface of the mold on which the boat is built (or alternatively, to the skin of the boat). The sided dimension is that dimension lying parallel to the skin or surface of the mold.