Oar Design - 8' Douglas Fir

I have worked up this design for 8' oars using solid Douglas Fir from 4x4 stock. I'll post pictures as it progresses.

 

I prefer to laminate two pieces of 1 inch stock. The glue line helps as a visual guide when shaping and the grain structure is more favorable, less prone to split, run out, warp

 

you will need to find some really clear lumber stock, to shed that much wood from a 4x4 and have no flaws would be difficult since you can not inspect the grain until after you have bought it and cut it down. Laminating up smaller stock of clear lumber usually is easier to avoid defects in the grain.

 

Much easier to find spruce around here (Maine). Available in more dimensions, usually cheaper.

 

Some of our more knowledgeable members have shown that a cupped oar blade is less efficent than a flat blade. Some persuasive evidence of that can be found by exploring the videos of various Olympic rowing and paddling events. Intuitively, one would presume the cupped blade to be the way to go. So much for intuition. To make matters even more confusing, competitive oarsmen have taken to using blades that are not symetrical about the shaft.

 

The most efficient paddle blade should be smooth on both surfaces, especially the forward facing surface, and should be high aspect ratio (long and narrow). I would also make it flat, but the cross section would best be a long, thin ellipse shape.

I would also make it symmetrical around the center line, that way you do not have a left and right blade, they would be interchangeable and have no "front" or "back", less chance of using it incorrectly. I think the asymmetry of the racing oars is to try and take advantage of the stronger pull in the downward stroke than on the upward. but for recreational paddling I doubt this is the major consideration.

 

I had a good look at the Douglas Fir 4x4 posts, none were usable.

I will make the looms out of 1x4 select SPF boards, laminating with epoxy with alternating grain on the 3 boards.

The looms will be trapezoidal as suggested here: http://www.gacooarlocks.com/a-superior-oar-shaft.pdf

I ran some deflection calculations, these are definately stiffer than a round section.

 

Stiffness can be good and bad. For everyday use I like an oar with a spring in it. They are less fatiguing for my rowing style.