ARTICLE 3 – Blade Dimensions and Shapes
The oar is a lever of the 2nd order. [Ed - Oh dear, sorry about this but if you want lots more then go here]. The boat is levered forward by the oars pivoting against the forward thole pins, but there is ALSO a 2nd turning point about 50cm from the tip of the blade which moves up and down the blade/shaft during the stroke cycle as obviously the boat is moving forward at the same time that the oar is moving backwards (and sideways – the blade moves in an arc). Any area of blade inside this 2nd turning point during the stroke will be “backwatering” to a greater or lesser degree throughout part of the stroke, especially if the arc from the middle to the finish is more than 37 degrees (more on this later). Part of the logic behind blade shape development has been to try to limit this backwatering effect to the shaft and not the blade.
Let’s take a brief look at the changing shapes and dimensions of blades over the years….
“Needle” Shape – These have been identified from the early 1900’s onwards. They were 32” (81cms) long, but with narrower tips and with the widest point further up from the tip. This was the first development from the “traditional” blade, was a reduction of the tip width and a slight increase in the width point at about a 1/3rd of the way up from the tip. This was in order to move the centre of pressure inboard from the tip and also so that, when the blade was placed in at the catch, more of the lower edge touched the water at the same time. About 100 years later physics and aeronautics takes centre stage….
“Spade” Shape – These were introduced in the late 1950s, and were revolutionary at the time. Basically the blade length was shortened by about 30%, and the width was substantially increased. This compressed shape was designed to ensure that most of the blade length fell outside the secondary turning point so that the ‘back-watering’ effect was more on the shaft. Spade blades were 20”(50cms) long and about 10”(26cms) wide. At that time they were found to be too unwieldy in strong winds, especially headwinds, and the density of the blade area created so much impact on the catch that not even the best rowers in the world could cope with them.
(image, red dot shows approximate size and position of the centre of pressure of the blade)
“Macon” Shape – These were a compromise development from the Spade blade, and we first used at the 1959 European Championships in Macon, France. The blade length was increased slightly (60cms), compared with the Spade, so that the width could be reduced to 20cm-22cms. Also, the widest point was moved further up the blade, away from the tip, to reduce the gearing further. In international competition (sliding seat) they lasted about 35 years, and were not superseded until 1992. The basic Macon shape is still used at club level today, and particularly for recreational and fixed-seat rowing. In gigs and other fixed seat rowing small Macons are taking over from the Traditional and Needle shaped blades.
“Tulip” Shape – This is a modification of the basic Macon shape. The widest point, and therefore the centre of pressure, is moved further up the blade away from the tip by more than half its length, ie., 30-35cms from the tip. The Tulip version of the Macon may be more suitable for less strong crews (ladies & juniors) because with this shape the gearing will be easier than the Macon for a given total blade area.
“Hatchet” or “Cleaver” Shape – This shape was first used at the 1992 Olympic Rowing Regatta, as a result of several years of experimentation thanks to the introduction of man-made moulded composite fibre-glass blades, rather than wood. The logic was to increase the overall blade area giving even more impact at the catch and reducing the “tearing” or “slip” of the blade through the water. But again, this effectively increased the gearing. Most crews at the 1992 Games had two sets of oars – Macons and Hatchets but finally virtually all of the top crews chose the new blades! Was it all psychological?
Unfortunately there has never really been any objective comparisons between Macons and Hatchets, but the Hatchets are now used exclusively in sliding-seating rowing at international level. It should however be noted that by the 1996 Olympic Games, whilst the Hatchets were being used by all crews, the outboard oar lengths had been reduced by around 6-8cms. In other words, the mechanical system had been made so efficient, that the athletes became the weakest link in the mechanical chain and they couldn’t really cope with them. The increased blade area made the gearing too hard, and back injuries were rife. There is a finite limit to the mechanical gearing that any athlete can cope with, and as a result the “big” blade area was maintained, but the outboard oar length was reduced!
The other technical development of the Hatchet was a change of the shape of the blade so that about 2/3rd of the area is below the shaft alignment, and 1/3rd is above. Also, the angle of the lower edge is designed to exactly pick up the water along the whole lower edge at the catch, thus enabling the blade to be covered more quickly and efficiently. See the blade shapes diagrams for comparison.
So what can we learn from all these blade shapes for Gig Oars?
It is likely that, in gig rowing, the huge weight of the boat, compared to sliding seat fine shells, points us towards a blade area that remains significantly smaller than the Hatchet blade area and area density. In addition, the asymmetric Hatchet shape would be of no benefit for rowing in rough seas and long West Country “rollers”, and these blades need oars with “D” shaped leathers. Further, because the gunwhales of gigs are much higher above the water than sliding seat shells, the shorter outboard oar lengths necessary with Hatchets would also be inappropriate since a shorter outboard length means that the shaft and handle would have to be at a much steeper angle to the water, making the inboard harder to row with.
The future for Gig blade shapes is more likely to be towards the Macon, but with a smaller area than for sliding seat rowing, depending of course on the power of a given gig crew.
(Image shows effect of blade shape at the catch on the contact point with the water)
We could argue that, despite CPGA Rule 22, current gig oars are hardly of “traditional shape” if “traditional” is taken to mean the 19th century working heyday of gigs. However since we have now progressed this far it is unlikely we will return to the very long blade shapes prevalent in gig rowing up to the 1970s, although they are still used by many crews today.
Future Developments in Oars?
The skills that go into making high-performance wooden oars may one day pass, and it is increasingly difficult to get good quality wood. With further growth of the sport, and the need to at least standardise or reduce costs for clubs, a simple carbon-fibre reinforced oar, with several sizes of Macon blade shapes, could one day be specified. This would provide standardised, low cost, low maintenance, yet robust oars, which would be available ‘off the shelf’.
Croker Oars of Australia make a version of just such an oar for surf boat rowing. Since carbon fibre reinforced (CFR) oars have been around since the late 1970s, they could now be considered as the “traditional” oar in the rowing world!
It’s interesting that in the 2010 London Great River Race with 300+ traditional fixed seat boats taking part, many were using CFR plastic oars.
To measure blade curvature, place a straight edge along the back of the shaft of the blade, so that it is protruding just beyond the tip (see photo). Then measure the distance between the tip of the blade and the inside of your straight edge…
Standard curvature on a Macon blade is 85mm. In principle the greater the curvature, the greater efficiency at the catch, and conversely the harder it is to release at the extraction. Greater curvature means that at the catch the end of the blade will be more perpendicular to the keel of the boat, but at the finish it will be more parallel to the keel and therefore ineffective! (See diagram below). With a big curvature you can collect a lot of water resistance on the blade catch, but at the release there is a tendency for the curvature to hold onto the collected resistance. From the exaggerated diagram you can see that with an overlong angle at the finish the curvature of the blade is virtually “dragging water” as the boat moves forward fast.
In addition, if the finish is not accelerated this inefficiency will be even more pronounced. The curvature of the blade is therefore a compromise. Ideally at the catch you may want more curvature, but at the release you need less.
In terms of technique, when you get to the point where you cannot accelerate the blade further, it is time to release it neatly and quickly, rather than the 1980s and 1990s gig technique of slowing the hands right down at the finish – a technique that results in the blades being ‘towed’ out of the water by the speed of the boat, slowing the boat down.
If there is too little curvature on the blade, the resistance of the water will be less because the “puddle” will tend to slip outwards off the end of the tip of the blade at the catch.
The many gig oars and blades which we measured showed a large range of curvatures from as little as 50mm (relatively flat) up to 77mm. Note that they were all less than the sliding seat standard curvature of 85mm. It’s likely, again related to the large all up weight of a gig, that less curvature than a sliding seat blade will be optimal so as not to increase the mechanical efficiency at the catch too much.
Blade Shapes and Dimensions:
In conclusion, you need to provide your oar supplier with the following dimensions:
- Blade length.
- Blade widest point.
- Blade widest point from tip.
- Blade tip width.
- Blade curvature.
Probably, the main disadvantage of the older oars with the long traditional blade shape, is not so much the blade shape, but the very heavy “weight” in the hands, or balance. Current top level crews are clearly experimenting increasingly with the Macon shape and/or the Tulip version of the Macon.
Macon Blade – Shapes and Dimensions (mm): -
It is unlikely that gig rowing blade areas and shapes will vary much outside the dimensions given in the table above.
Note that the main variation between the Macon and the Tulip shapes is that, with the Tulips, the Widest Point is further inboard from the Tip than with the basic Macon. This moves the centre of pressure up the blade and provides an easier gearing. Also note that for the ladies oars the Tip Widths and Curvatures are noticeably less than for the men’s blades.
Whilst the major effect of gearing will be the outboard length of the oar, gearing can also be adjusted by the blade dimensions, particularly how far the Widest Point is up from the Tip, and the Tip Width of the blade. In all cases you would expect that less strong crews would have reduced dimensions compared with stronger crews.
Since the gunwhales are very high in gigs, there is a limit to how much you can reduce the outboard length of the shaft for weaker crews because the shorter it gets, the steeper will be the angle of the handle. This makes it more awkward to row with. Therefore it is suggested that a reduction in the blade area, as mentioned above, would perhaps be preferable to a significant reduction in outboard oar length for less strong crews.
Putting it all together – The specifications you should be submitting to your Oar Supplier:
Over the past 3 articles we have tried to address all the different dimensions you should ideally be providing to your oar supplier, and to explain and rationalise the pros and cons of each dimension and the principles behind them.
However, your supplier will not be interested in all the rationale, just the specific dimensions you want for each blade in your new set. The table you should provide will need to include 6 lines, 1 for each oar in your set!
Whilst all gig measurements have traditionally been given in feet and inches, it is much easier for oar manufacturers if all dimensions are given in metric. It is also more accurate for smaller measurements.
The Table below provides an Example of a 2009 Men’s Stroke Seat Oar (mm):
The Headings are as follows:
Oar – Number & Code
Oar – Overall Length
Oar – Outboard Length – (Measured from Centre of Sleeve)
Oar – Inboard Length – (Measured from Centre of Sleeve)
Oar – Sleeve – (Length & Material – Leather or Plastic) – Table should read – 490mm
Oar – Shaft under Sleeve – (Circumference & Diameter)
Oar – Handle – Length
Oar – Handle – Circumference – (Not on above Table)
Oar – Stiffness
Oar – Balance Point – (Weight in the hands)
Oar – Overall Weight – (Kgs)
Blade – Length
Blade – Width @ Widest Point
Blade – Widest Point – Distance up from Tip
Blade – Tip Width
Blade – Curvature.
Once you receive your new set of oars, don’t forget to measure them first, to ensure that they are exactly what you ordered, but also so that you can monitor any changes in them over time, especially loss of stiffness.
It is likely that you will be specifying different Overall, Inboard and Outboard Dimensions for each of the 6 oars, or perhaps No.3/No.4 the same, No.5/No.2 the same, No.6 different, and No.1 different again.
You may specify the same blade dimensions for all 6 blades, but equally, if you have a known set crew, then you may want different blade dimensions for different rowers in the boat, eg., perhaps a smaller Tip Width and Widest for the No.6 oar, if your stroke is a less powerful rower, or perhaps a larger Tip Width and Widest for your ‘engine room’ rowers if they are bigger and stronger, etc.
Good luck with specifying your next new set of oars!
In the next (final) article on Oar Specifications we will address the rationale for the different oar dimensions for each of the six different positions in the boat. We will also look at oar and blade variations specific to individual rowers, and finally we will identify the ideal type of rower you are looking for, for each position in the boat.
Citations and references -