More on oars

Ok. How long should an oar be?

I don't have the plans yet to see what they recommend, but it shouldn't be so hard to work out.  Looking around there seem to be three rules that come up repeatedly...

• half the beam times four.
• half the beam times three plus six inches
• Half the beam plus 2 inches times 25 over 7.

These three give significantly different results. The first is simple and gives the longest answer. It perhaps suits the advice, take a long oar and keep cutting it back until you are happy.

The second gives a much shorter oar. To my eye too short except perhaps for boats like yacht tenders with a short length compared to the beam.

The third seems to originate from  Shaw and Tenney and gives something in the middle and a figure with some professional credence. Using this for Tammie Norrie gives an answer a tad over eight foot six.

The long rule gives just under nine feet and the short rule only about seven (!).

An interesting approach was from boat designer John Welsford. He calculates back from wanted boat speed to find what oar length he needs...  Always curious I reverse engineered the method in excel to make a prediction of boat speed. With conservative numbers for cadence rate  and the length of a stroke, and including changing the gearing by moving the oar in or out a little I get a range of 2.1 to 2.9 knots. Up to 3,5 with a more energetic cadence.  Plausible if unverified...