Rigging, Leverage Formula and The “M”

Reader Mike writes:

Hi Mike – love your site and your book – one question I can’t seem to find the answer to… What is the “M” value of CII Fat Smoothie sweep oars? Look forward to the answer…

Mike is talking about the leverage formula that I use to keep track of the load of a specific rig. I discuss it in detail in several places, but basically here is the formula:

[(L-I)-B/M]/S

In the equation L= oar length, I= inboard, B= blade length, M is a variable, S is the spread, and B/M togther represent where the center of pressure is on the blade.

Two things of importance here:

1. Measurements are metric
2. Do not use this formula to compare between different blade shapes, just between oars with the same blade shape.

The M that reader Mike refers to helps find the approximate center of the oar. The number that I use is, for rectangle shaped oars (or close to it)  2 (for 1/2 the length of the blade), and 3 (for 1/3 for the length of the blade) for macons. I am not sure what I would use for something like a delta, I would have to measure it first, or talk to the maker.

In this case,  a for CII Fat Smoothie that is 52 centimeters long, the M would be 2.

There is debate as to whether this number, and in fact the formula, have value. I’ve found it to be helpful for me in keep track of things, although I strongly caution again anyone to use it to compare different blade shapes.

What do you use to keep track of your leverage/load?