Oars ~ Notes and Plans
Two very important pieces of advice for new builders of St Ayles skiffs: Firstly the oars shown on the original plan have proven not to be a particularly good design for the type of rowing that the skiffs are used for and secondly don’t leave building your oars until the last minute. There is nothing as frustrating as a finished skiff and no finished oars to row it with. The oar building can be delegated to a small team or individual and done away from the place that the skiff is being built.
Topher Dawson, Treasurer of SCRA and builder with “Ulla” syndicate and Ullapool High School has updated the Oar page originally published here in 2010 and now writes:
This is a complicated and contentious subject, much debated in pubs around the coast. The St Ayles Skiff is rowed by four rowers, one rower per seat and one oar per rower. The Fair Isle skiff on which the hull is based was not rowed in this manner and it turns out that if the rowers sit in the centreline of the boat they tend to hit each other in the back with the handles of their oars.
I would recommend making a set of the 11ft Ullapool oars first (plan below), because they are cheap, easy to make and light to
row with. Ullapool have had them for years and won many races with them. They are close to optimal for light crews so your women
crews will not complain about the oars being too heavy. Others may recommend longer ones like the Coigach ones or the longer hollow Ullapool ones, or later you might want to design your own. Plywood blades are lighter than timber ones, and easier to make.
To understand the solutions to the clashing problem it is first necessary to explain oar gearing. For any rowing situation (boat, rower, weather) there will be a comfortable gearing where the rower feels they are making progress but the pull is not too hard. As the
oar is slid outwards from the boat, the length of oar inside the boat (inboard) gets less and the length outside (outboard) gets more. It
gets harder and harder to row but the boat goes further and further with each stroke. This can be likened to a high gear on a bike, fast
on a flat road but hard on hills.
Doing the opposite, sliding the oar inwards, makes it much easier to pull the oar but the boat goes less far with each stroke. This is like a
hill climbing gear on a bike. Boats don’t climb hills but they do row against the wind or with a weaker crew. Thus it can be useful to
“change gear” by moving the point on the oar where it pivots at the gunwale. The “gearing” of an oar is a number made by dividing the
outboard by the inboard.
In St Ayles skiff clubs the gearing people have ended up with varies between about 2.8 and 3. The gearing you choose will affect how
long your inboard is and thus whether you have a clashing problem. There are two ways to avoid rowers clashing with each other. The
first is to make short oars which allow rowers to sit away from the centreline, staggered towards their thole pins. The longest oars you
can do this with are about 11ft long, depending on how wide the rowers are and how accurate their timing. Short oars are lighter, cheaper and can all be the same length.
Long oars allow the rowers to sit away from their thole pins and thus avoid clashes. The stroke oar has to be shorter, 11 to 13 feet
because the stroke rower sits with his or her feet constrained in the narrow centre of the stern of the boat. If the handle of the oar is
long enough to be much off to one side, it strains the stroke’s back. The number 2 and 3 rowers are on wider seats and so their oars can
be longer, 15 to 16 feet. The bow oar tends to be shorter again, 12 to 14ft, because the boat is narrower there.
Long oars seem to be slightly more successful in racing, at least with strong crews, but short oars have won many medals. The
longer oars are heavier and to make them as light as possible takes care.
The measurement rules specify timber only for the oars. The blades must not be spooned, i.e. concave, and must be symmetrical about the centreline, i.e. not cleavers/ choppers
Lightness is an advantage, and making a light strong oar takes thought.
Standard oars you can buy:
Port Seton started with standard Plastimo pine dinghy oars, which have round section shafts and flat blades. These are readily
available up to 10ft long for about £45 each. Port Seton screwed stainless eyes to them, which fitted over stainless thole pins (which are not in fact allowed under the measurement rules), and had a lot of success with them. They were light and easy to row at a fast stroke rate. Ultimately the screws weakened them at the point of maximum stress and they tended to break.
Other oars available to purchase are Admiralty pattern, round section shaft with a long straight blade. They cost about £180 each for a 12ft spruce one, (Collars) but you can get them up to 17ft if you want. Suttons also make hollow spruce oars with ash backs, and make most of the Cornish gig oars. These are between 11 and 13ft long, and cost about £260 each. They gig oars are spoon blades which are not allowed in the Skiff, but I am sure Suttons would make you flat blades if asked nicely.
Many of us have made our own oars, some from the plans at 12ft, but these clash. Ulla’s oars started at 13ft 2 inches, heavily made
from Douglas fir, but they clashed. So we went to very long ones, 17ft, by gluing bookshelf wood on to the ends, with the idea of
cutting them down till they worked. Even at 15ft they were heavy and slow. Then we made 11ft oars from cheap B&Q wood (£1.50
each) and 3mm ply blades. They were light (6 pounds) and easy to row with, and the plans for these oars and a number of other
successful oars are linked below. If you like your first set of the 11ft oars you may want to make lighter and more sophisticated
versions. If you use a cedar core faced on the front and back faces with a 10mm thick strip of ash, you can reduce the vertical
thickness from 38mm to 30mm which reduces both the weight and the wind resistance.
Oar timber is usually softwood, but hardwood lifeboat oars have been tried. Sitka spruce is the lightest and most expensive timber.
Douglas fir is harder and heavier, available in the long straight clear lengths we need. Ash is sometimes used for oar backs to resist the
compression on the forward side, or for whole oars in heavy boats. Western Red Cedar is available and makes good lightweight cores.
Plywood can be used for blades, and we (Ulla) have used 3mm ply with good success. Hollow spruce/ash shafts used to be standard in river racing oars before carbon fibre became the norm.
Oars have to resist bending stress, the highest being at the kabe. For this reason oars are usually thickest there. Most working fishing
boats had rectangular section oars and did not feather (rotate the blade parallel to the water on the return stroke) them. Sea oar
blades tend to be long and narrow, and in Irish currachs they are just part of the shaft, 2 inches wide. Some people think narrow
blades have less windage than unfeathered broad blades. The long narrow blades do have the advantage that they are less critical
about how deeply immersed they are, which is good in waves. In the St Ayles Skiff it is not yet clear whether feathering the blade is
worthwhile. It does reduce windage when the oar is out of the water but requires more effort from the rower’s wrists to feather.
Rectangular cross section oars are in fact more efficient in resisting bending stresses, compared with solid circular or oval cross-sections, because more of the timber is at the extreme front and back of the oar, where the stress is. This means they can be made lighter for the same strength, and are obviously easier to make.
Sliding seat racing oars have hollow tubular round section carbon or glass shafts, and although glass and carbon are not allowed in our
class, tubular i.e. hollow oars have been tried and are light and strong. Longer oars have more bending stress and tend to be heavier than short oars. Balance in an oar means that with the weight of the rower’s relaxed forearms and hands resting on the handles, the oar is balanced. The greater weight means that there is more inertia to change direction at each end of the stroke, so longer oars tend to lead to a slower stroke rate. This does not mean the boat is slower, as Coigach have showed.
Oars bend a little when the force is applied, or a lot depending on how flexible they are. Carbon oars are very stiff, but some of us like oars which flex a little. Oars near to breaking tend to feel very “soft” in bending, due to invisible compression failures on the forward face. Making the oar wide in the horizontal direction makes it stiffer and also stronger. This is more efficient than adding wood to the vertical thickness.
The most successful racing clubs use oars with blade area between 900 and 1300 square cm, or 140 to 200 square inches. The traditional blades are long and narrow, made by gluing strips of spruce to either side of the shaft and carefully shaped. A strip of hardwood glued across the tip strengthens them against impact.
Thin plywood (3 to 6mm) makes good light blades which stand up to years of use, and the inevitable dings are easy to repair with epoxy.
Handles: These need to be about 15 inches (380mm) long to take two big hands spaced apart by about one and a half handwidths. Small hands need a diameter of about 35mm and big hands about 45mm. A compromise which is stronger than a circle is an oval with the long dimension fore and aft. Experiment to see what your rowers find comfortable. Smooth handles make less blisters, so round the ends off too. If the change of section where the handle meets the shaft is sudden, cracks can start there so make it gradual.
Whatever system you adopt, make sure that the oar itself is not wearing away, or your valuable wood and work will be wasted. Leather is one way to protect it, but don’t use nails, which rot and weaken the wood. Sew the leather and shrink it on in place. The traditional Scandinavian system is replaceable wear plates of wood. Again, avoid nails or screws which allow water into the wood; glue the plates on and when they need replacing plane them off.
Lubricant is good to reduce wear and friction, and we have had good results with candle wax which is cleaner than tallow.
Please do add to the shared knowledge on this topic by adding comments below.
Some successful oars: