Oar Philosophy

 We built a set of oars for the St Ayles Skiff Hoi Larntan during the winter of 2012/13. The following notes may help rowers to understand why they are as they are.

 Length of oar

The original plans for the boat show a 12’ oar and the rowers sitting in the middle of their seats. But, there is an inherent problem with the St Ayles Skiff, because of its length and the distance between the seats. Other rowers have found that there is a tendency for the hands of one rower to collide with the back of the next rower if all sit in the midline of the boat. Other crews have overcome this problem by sitting alternately to port or starboard of the midline. This can be achieved by using oars, which are either longer, or shorter than 12’. With shorter oars, the rower sits toward the side with his kabe/thole pin and vice versa with longer oars.

Having measured the span of the boat at each rowing position and the distance between the seats, we chose to use oars with an inboard length of 33”, being the longest that would not cause collision.

We chose a gearing of 3:1 (outboard length : inboard length), which is almost universal in all types of rowing. The measurements being taken from the tip of the blade to the tholes (outboard length) and from the tholes to the end of the handle (inboard length). This gave an overall length 132” (inboard length (33”) X 4).

Since the span (distance from port thole to starboard thole) is different for each seat, with oars of the same length, the rowers do not sit equidistant from the midline of the boat. This has a consequence on the listing moment of the crew. If all the rowers are of the same weight and all have oars shorter than 12’, there will be a tendency for the boat to list to the side of the bow rower.

This could be compensated for by giving the stroke a shorter oar, thus moving him further away from the midline, but we chose to have all oars of the same length for simplicity and ease of replacement.

Of course all rowers are not the same weight and the listing moment problem can be alleviated to some extent by sitting the lightest rower in bow seat and the heaviest at 2.

Shape of blade

Traditional oars for sea going boats have long narrow blades. These are said to be easier to manage in rough water than wider blades. One of the consequences of a long narrow blade is that the centre of resistance to the water is further from the tip of the blade. This effectively reduces the gearing (see above).

Cornish gigs have now largely abandoned “traditional” pattern blades for modern designs based on those used in fine racing boats. These have been found to be more efficient in normal circumstances.

We have chosen a blade profile similar to one used by junior gig rowers, but without  a “spoon”,  which is not allowed under the rules of the SCRA.

Thole pins and collars.

Different St Ayles Skiff crews have adopted a variety of methods to link the oar to the boat at the gunnel. We have chosen to keep to the English tradition of a leather collar on the loom of the oar, with no button, lying between a pair of tholes.

In fact Hoi Larntan has a sort of hybrid system with the forward pin being replaced by a kabe, but it all works like a pair of thole pins.

This allows rowers to increase or decrease gearing by sliding the oar in or out.

Loom section

We have chosen a square cross section for the portion of the loom, which lies between the thole pins.  This effectively sets the angle of the blade in the water, when the rower pulls against the thole pin and the flat surface of the loom conforms to the face of the thole pin (kabe).  We thought that this would tend to reduce the twisting of the handle in the rower’s hands, which might be a consequence of the wider style of blade if used in rough water. We chose square rather than D section so that the oar could be used on either side of the boat with the stitching to the leathers facing up.

Length of handle

We chose a handle length of 16” as used on gig oars.

Wood

The SCRA bans carbon fibre and other “hi tech” materials from competition. Many high quality wooden oars are made from Sitka Spruce, which is strong and light, but expensive and not readily available locally. We used Douglas Fir, which although strong, is 30% more dense than Spruce (and half the price). Consequently the oars are heavier than they could have been.

Adrian Hodge

11th June 2013

We are in the process of deciding about another set of oars.  it would be really good to have some feedback as to what these should be like.  Adrian and Andy are keen to be sure we have not ignored a fundemental fact and gone off on a tangent!

Please let us know what you think

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2 thoughts on “Oar Philosophy

  1. From the oar builders.
    We found that the oars as originally made were too heavy. We have reduced the quantity of wood in the blades, without reducing there area. We have also reduced the dimensions of the square section, where the loom of the oar rests between the kabes/tholes. This has allowed more to be taken off the looms, thus reducing the outboard weight. The loom dimensions are now 21/4″ square at maximum, reducing to 1 1/2″ x 1 1/4″.

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