Oars Power

I have rowed in different guises – as a schoolboy, for my university, in small yacht tenders, including inflatable and small wooden ones, and also in PicoMicroYacht. From the sublime to the …… well I really enjoy PicoMicroYacht.

At each level I have given no real thought the physics of the oars I was using. At school and at university I just accepted the oars we had as being the right ones.

The evolution of competitive rowing  oars:  http://www2.gvsu.edu/ciunganc/History.html

I learned to row competitively using square blades, which even in those days seemed very old fashioned. I then used macon blades for the rest of my school rowing and also my university days.

When PicoMicroYacht came along blade design had moved on, with the ‘cleaver’ blades, I think called ‘hatchet’ when used for sculls. I thought they might more difficult for rowing at sea, but there have been no problems and I now do not even have to feather the blades if the sea is calm, this preserving my wrists.

PicoMicroYacht hatchet sculling oars being put into their rowlocks

In theory, the hatchet blade is more efficient for sculling because of having less drag.

When thinking about the PicoMicroYacht oars, I became curious as to how oar length is chosen. 

Many people are put off rowing because the oars they learn with in small dinghies are small and inefficient – it can be fun but possibly not designed for  adventurous rowing.

Is this fun? Of course it is if you are very small  -
this one of the smallest plans produced by the fantastic Fyne Boat Kits http://www.fyneboatkits.co.uk/kits/

A sleek rowing shell, with the right length blades, glides along almost effortlessly. As the rower tunes into the rhythm of the boat, this gliding sensation is very pleasant.

Rowing boat morphology was developed for speed and pleasure

John Biglin in a Single Scull in 1873 by Thomas Eakins

Of course it is possible put long oars in a very small boat, as in the photographs below. This is the Half Pea, the plans produced by Hannu's boatyard. Half Pea was given long oars, which means that it really does row easily for it's size.

The four foot Half Pea undergoing lake trials: The plans can be obtained from:

 http://hvartial.kapsi.fi/dinghy44/dinghy4.htm

Long oars improve the experience of rowing, but how long should they be?

Before the advent of small boat engines, all rowers tended to have longer blades because they needed the efficiency and power.

It turns out that efficient length is dictated by the required gearing ratio of the oar and the physics of how the oar connects to the rower. 

Apparently, an efficient oar needs a ratio of approximately 2.5-2.7, where the ratio is calculated as the distance from the rowlock to the blade end, divided by the distance from the rowlock to the handle end.  To achieve, this sculling oars are recommended to be approximately 287 cm in length.

Variables used in the calculations regarding the forces in rowing. From https://sanderroosendaal.wordpress.com/2010/07/12/basic-equations-3-oars-and-blades/

This ratio also ensures the oars are sufficiently long, with the oar handles moving more or less in line with the boat direction, as the oar axis rotates around the rowlock. Also, the oars remain more at right angles to the direction of the boat, increasing efficiency as it is pulled through the water.

The higher the ratio, the harder it is to pull, and this suits strong rowers in calm waters. It provides not such good power at low speeds and a high ratio is not suited to slower boats.

I checked my PicoMicroYacht sculling blades and found the ratio was 2.43, at the easy end of the scale – but then PicoMicroYacht moves slowly and has to put up with waves and potentially strong headwinds. The PicoMicroYacht oars are a little shorter than recommended, at 254 cm in length, but they seem to do the job.

PicoMicroYacht going down the Thames with a large orange sponsorship flag

I also started thinking why it is better to overlap the handles of sculling blades when sculling, since this is a more difficult technique.

The Don Valley rowing club shows how to lead with the left hand over the right in the recovery phase when sculling

http://learntorow.wikifoundry.com/page/The+Grip

Handles overlapping at the end of the stroke

Apparently, it enables the sculling handles to move less away from the centreline at the start and end of each stroke. The handles should overlap by four to six inches.

Catching a crab in the middle of a race - the oar gets stuck in the water and can drag the boat over

Some people do not like this technique since it can lead to bashing your hands against the handle of the other oar, which can make you lose control and potentially ‘catch a crab.’

So how much power can you generate through rowing? The answer is surprisingly little, which is why you need a very thin light boat to get up to a high speed.

One metric horsepower is need to lift 75 kilograms by one meter in one second

An old wisdom is that a rower can generate around 0.25 horsepower. A rowing athlete can increase this to about 0.7 horsepower over a standard 2,000 metre course. Not much when you consider that a basic petrol outboard motor produces two horsepower or more.

My little Honda 2.3 is over three times more powerful than an elite oarsman

What would happen if you put a Honda 2.3 engine on the back of PicoMicroYacht? That would be another story.

What 2.3 HP can do for a canoe