Oars, part 4. Blade dimensions for each seat.

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Oar and Blade Dimensions for each seat :

Why do the 6 Oars for a Cornish Pilot Gig vary in length by around 15cms (6”) and sometimes by as much as 20cms (8”)?

Rowing boats without outriggers will obviously have a variation in the width of the boat at each seat position, with the widest being around the middle, and the narrowest being towards the tapering ends of the boat.  This means that if each rower is to have the same amount of oar handle in front of him to pull on, the inboard lengths of the oars will have to vary to accommodate the width of the boat.  This is one reason for the variance in the overall length of each oar.

The second reason is that because the boat widths and inboards vary, this means that the outboard lengths will need to be different as well, in order to maintain the same gearing ratios for each rower in the crew.

Spread Variation per Seat :

In the picture below it is clearly obvious that the width of the boat at each of the six rowing positions is different.  Assuming for the moment that each rower is sitting as close to his gunwhale as possible,  this means that the spread for each of the six positions will be different.

The measurement from the rowing thole pin directly across the width of the boat perpendicular to the forward thole pin is called the Span. In sliding seat rowing the spread is half the span, and is from the pin to the centreline of the boat. In gig rowing the spread will be from the thole pin to the centreline of the cushion. Since this is variable (dependent on where rowers place their cushions) we don’t have these dimensions but the table below is sufficient to make the point.

In a typical gig the Measurements for Span and Spread in each Position are as follows:

Position Span

(pin to pin)

Spread

(to centreline of boat)

Spread

(to Centre line of Cushion)

6 1275 mm 638 mm 638 mm Plus??
5 1370 mm 685 mm 685 mm Plus??
4 1410 mm 705 mm 705 mm Plus??
3 1390 mm 695 mm 695 mm Plus??
2 1343 mm 671 mm 671 mm Plus??
1 1230 mm 615 mm 615 mm Plus??

We can see clearly from the table above that the inboard oar length will have to be longer or shorter depending on the width of the boat and the relative spread to centre of cushion.

If we look at the column for Span we can see that the bow (#1) seat is the narrowest, followed by stroke (#6), then #2, then #5, then #3 and finally #4.  Therefore all six oars will need to be different lengths to accommodate the different widths of the boat, or sitting positions of the athletes.

In the days when gig oars were much longer, this was partly due to much longer inboard lengths and there was a standardisation of the inboard lengths which was 3” (75mm) shorter than the opposite gunwhale.  Logic would suggest that, whilst inboards are now shorter, they should still be of a standardised length relative to the width of the boat.   Our measurements however, showed no such correlation.

Also, in days gone by, all 6 oars were of different lengths, yet over the past 15 years it seems that many sets of oars have been ordered with the middle 4 oars the same length and only the bow and stroke oars a different length. All things being equal this means that in such sets, the #2 and #5 seats are being given harder gearings than #3 and #4!

The less the spread dimension, (Thole pin:Centre of Cushion), the harder will be the gearing because the ratio of spread to outboard will be greater. It is therefore very clear that the inboard oar lengths should be different in all 6 seats to accommodate the 6 different spreads.

In addition, and this is where it gets even more complicated, the shorter an inboard oar length, the shorter will need to be the outboard oar length if the same gearing ratio is required throughout the boat.

In simple terms therefore the bow seat, which has the narrowest spread, will need the shortest inboard but also the shortest outboard.  Conversely the #4 seat with the largest spread will need the longest inboard and also the longest outboard. This is why each oar length should be different from each other both inboard and outboard.

In practical terms, since an individual athlete can adjust their point of oar leverage on the leather, in or out a few cms, and since the difference in boat width only varies by a couple of cms, it is more than acceptable to have the oar lengths the same for the middle pair (#3 & #4).  Equally, you can have the same oar lengths for #2 and #5, since again the difference in boat widths between these two seats is only 30mm.  However, the difference between #3/#4 and #2/#5 is too much for these 4 oars to be the same overall lengths, since there is a range of 70mm difference in the width of the boat for these four seats.  We therefore recommend that you should order the #2/#5 oars slightly shorter lengths than the #4/#3 oars.  In addition, only the bow and stroke seat oars will be different again and different from each other.

Overlap :

This is a reminder from past articles, but is relevant to choosing the inboard length of oar.  We have already mentioned that currently a lot of inboard oar lengths are too short and this is why athletes row their handles past the side of their body at the finish and/or row with their hands very close together on the oar handle, and with their shoulders hunched inwards. Equally we have just mentioned that with the old traditional oars (pre 1980s) the inboard lengths were set at “3 inches short of the gunwhale at each seat”. Whilst this is probably too long for today’s technique, at least the inboard length of each oar was exactly standardised in accordance with the width of the boat at each seat.

If the spread is measured to the centreline of the cushion, (or a line up the centre of the athlete’s body), inboard overlap is the amount by which the oar handle overlaps this centreline when the oar is at 90 degrees to the boat.  Your inboard oar length therefore comprises Spread + Overlap.  The spread accounts for the width of the boat to the centre of your seat, and the overlap is the extra that you need to have some oar handle in front of you to sit behind and pull on!  Ideally you should be holding the handle with one hand either side of the centre line of your cushion, ie., one hand either side of your spread measurement.

The amount of overlap you need will depend on the position in the boat and upon the length of trunk, and/or sitting height of the athlete. A simple guide to finding optimum overlap is to sit the athlete at the finish of the stroke (say, leaning back at 45 degrees, although he/she may have gone further back than that during the draw phase and come up again) and making sure that in this position the end of the oar handle is in line with the sternum or centreline of the ribcage.

In the picture below, the “leaning in” frame is optimum, whilst the “past” or “out” frames show an inboard (and overlap) that is too short and is being rowed past the side of the body.

Currently most inboard oar lengths, (and overlaps), are still too short and we would therefore recommend that, if in doubt, order your inboard dimension 1 or 2cms longer. If any are then too long, you can always trim a cm or so off the end.

Many women’s crews have already demonstrated that you can row more efficiently with longer inboard lengths (and overlaps), because when they are rowing with men’s oars they will naturally pull their leathers inboard by 5-10cms to make their gearings easier and by doing so they increase the length of the inboard and the overlap to a more effective length.

Inboard and Outboard Oar Lengths in relation to Spread :

We have measured the span (width of boat) and spread (width to centre of cushion) on a number of gigs and they are all fairly similar, and of course they should be identical. We have also looked at inboard oar lengths for each seat in relation to the span and/or spread for each seat, and currently there is absolutely no gearing correlation at all!

Equally we have tried to analyse the inboard to outboard oar ratios for oars in each seat and again, there is no clear gearing correlation although there is a slight trend. We therefore cannot give any specific recommendations except based on the empirical evidence of current sets of oars.

In principle however, the ratio of spread to outboard, and/or inboard to outboard should be the same throughout the boat assuming all the athletes to be of equal power (More on different athletes later).

Gearing :

Gearing therefore depends on the ratio between the outboard length of the oar and the spread. Remember that in sliding seat boats, where the rowers sit centrally, the spread is from the centre line of the boat to the rowing pin.  In boats where the rowers sit off-centre, the spread is from the centre line of the athlete (Centre line of the cushion) to the thole pin.  For the purpose of this discussion, we will assume that the rower is rowing exactly on the middle of the oar sleeve, so the outboard will be from the centre of the sleeve.

In general where the boat width is greater, and the inboard is longer, then the outboards will also have to be longer, and vice versa in order to maintain the same gearing ratio throughout the boat.  A very simple rule of thumb is a ratio of from 1:3 to 1:2.5 between the spread and the outboard oar lengths.  The oars and spreads that we have measured show a slight relationship to this range, but when you look at specific sets of oars, the relative ratios for each position appear to be random at present!  This is clearly an area which requires further experimentation.

It may be that the coach specifically wants some members of the crew to be on easier or harder gearings, rather than the whole crew being on the same gearing which is what should be intended initially.  However, this opens yet another ‘can of worms’ which is better left for a future time when at least some gearing logic has been applied to each given seat within the whole crew.

Stroke Arc :

In sliding seat rowing using a pin and swivel there is no fixed limit to the arc angles at the catch and release, and indeed these can be controlled by altering the spread.  However in fixed pin boats the arc angle at the catch and finish are restricted by the width between each pair of thole pins, and also by the angle of each pair to the central line of the keel.  The space between each pair should be identical and should be 4” (10cms), but the angle of each pair to the centre line varies.  This can be seen clearly from the gig diagram below.  We will therefore assume that a given rower can row from virtually locked pins at the catch to virtually locked pins at the release, so the total arc angles will be the same in each seat.  However, in shorter athletes, perhaps with shorter arms as well, the arc at the catch and release may simply be limited by the length of reach of the athlete concerned.

In this case the athlete may choose to move their cushion in towards the centre line of the boat in order to be able to row a bigger arc within the limits of the thole pins. This would reduce their spread and have the effect of increasing the gearing, but since the crucial part of fixed seat rowing is to get the biggest arc at the catch as possible, then this may be beneficial. However, no athlete should move their cushions in to the extent that they restrict the reach forward of the athlete behind them.

If, at the catch, you do hit the body of the person in front of you, then the person being hit must move further out towards the side of the boat.

Arc Angles for each Position in the Boat:

You can see from the diagram above that the gunwhales of a gig do not run parallel to the centreline of the keel except in the #4 and possibly the #3 seats. In the bow the rowing pin is closer to the centreline of the boat than the aft pin which allows the bow and #2 seats particularly to row an angle of a few degrees more at the catch, but conversely a few degrees less at the release.

In the stern, the stroke rowing thole pin is further away from the centreline of the keel than the aft pin which reduces the angle at the catch by a few degrees and increases the angle at the finish.

Measuring the actual angles achievable is extremely difficult to do accurately and these angles will be influenced by the thickness of the shaft underneath the oar sleeve, the thickness of the leather, the thickness of the lacing, and ultimately the exact distance between each thole pin in a pair.  Whilst the space between each pair of thole pins should be the same (4” – 10cms), it may increase due to wear on the thole pins.  In principle, the wider the space between the thole pins, and/or the narrower the oar at the leather, the larger will be the possible stroke arc.  For example with worn tholepins there might be an extra degree or two available if you can risk them not breaking!  Equally, ladies oars may be thinner than men’s underneath the sleeve, as they don’t need to be so stiff!

The diagram above shows the actual measurements of a gig which show quite clearly that the bow position offers the biggest angle at the catch (51 degrees) and the shortest angle at the release (44 degrees) and conversely the stroke seat offers the shortest at the catch (41 degrees) and the longest at the release (51 degrees).

You can also see that in the 3 and 4 seats the angles at both ends are similar because at these points in the boat the gunwhales run more parallel to the centreline.

The different arc angles at the catch offered at each of the seats does also affect the overall gearing at each position in that the larger the angle at the catch the harder the gearing, but also  the more efficient will be the catch if the athlete can cope with it.

The main difference between fixed seat and sliding seat rowing in terms of the effectiveness of the body to lever the oar (move the boat) is that in fixed seat rowing, because of the lack of a sliding seat with which to use the full range of the leg muscles, there is less efficiency from the 90 degree point (orthogonal) to the release.

In all forms of rowing the most effective part of the stroke is from the catch to the orthogonal, for both mechanical and bio-mechanical reasons, but in fixed seat rowing the angles from the orthogonal to the release are much more difficult to accelerate through since by then you are left with only the weak arm muscles in this latter part of the stroke.   Biomechanically you are therefore in a weaker position than the same part of the arc in sliding-seat rowing.

In fixed seat rowing it is therefore vitally important that every precious degree of arc angle at the catch is used, and used effectively. Many gig rowers can achieve the body reach required, but actually fail to place the blade in the water at this maximum reach point due to lack of accuracy in placing the oar in the water with the hands. Hopefully, in the future, we will try and write a few short articles on efficient fixed seat rowing technique and we will address these technical implications then.

Suffice to say that in Gigs the 51 degree maximum achievable in the bow seat is still not optimal and in Olympic rowing they are using up to 60 degrees angle at the catch! This makes the point that we should always be looking for the absolute maximum propulsive length of stroke at the Catch.

Conversely, we also know (absolute fact) that the optimum arc angle for the release is 37 degrees from the orthogonal. By referring to the chart above you can see that in gigs it is possible to row up to 51 degrees at the release (stroke seat), which is 14 degrees well in excess of the optimum. To row up to 50 degrees at the release does require the rower to row the handle past the side of the body. In addition, it is simply not possible to accelerate the blade from the orthogonal to the finish if rowing past the body.  With an under-hand grip for the outside hand, this also involves changing the grip from under to over-hand as the handle passes the body and is extracted already on the half-feather! As this happens the outside arm cannot possibly be accelerating the blade, and also because the blade is already half-feathered and still under the water!

Mechanically, it  has already been stated that more than 37 degrees is not only ineffective, but actually has a negative effect on the speed of the boat as the boat is literally towing the blades out of the inside of the puddles at the release and they are acting as a brakes.

In fixed seat rowing you should accelerate from the catch and keep accelerating until the oar handle comes into the ribs. When you cannot accelerate any further then it is time to release the blade.

In summary, we are trying to achieve maximum arc angles at the catch and acceleration of the blade through to 37 degrees past the orthogonal and no more.  If you cannot continue to accelerate the blade, and/or have gone past 37 degrees, then it is time for a quick and clean extraction.  No doubt this is controversial, but food for thought!!

In concluding this section you will need to specify your Overall, Inboard and Outboard lengths of oars according to each seat/position in the boat.  This may also include variations in the dimensions of the Blades as well.  All this can be done using the sample Oar Specification Chart included in
Article – 3.

Specification Trends for Different Types of Rowers :

These are probably obvious in that for weaker athletes you would expect an easier gearing; however, we have already seen that there are a variety of ways of easing or stiffening the overall gearing for individuals and/or a whole crew.  We know that the rules do not allow us to adapt the boat in any way, so it all has to be done via the oar specifications.

The main effect on gearing, which we can adjust, is the outboard length of the oar, and also the shape and dimensions of the blade area.

However, as has already been discussed, if you decrease the outboard length of the oar too much, this will mean that to cover the blade fully in the water, the angle of the shaft and handle to the water will be increased.  Since the height of the gunwhales in gigs is significant, the oar shaft angle to the water is already quite steep.  If it is increased more, by a reduction in the outboard length, then the angle of the handle becomes increasing difficult to manage and indeed becomes less and less horizontal to the boat.  If we do reduce the outboard oar length for weaker athletes, these rowers are also likely to be those who sit less tall in the boat, and therefore for whom any further increase in the steepness of the handle could mean that the outside end of the handle is more at shoulder height than at chest height – anyway, too high to pull on efficiently!

It is recommended therefore, that whilst ladies oars or junior oars do need to be shorter outboard than men’s oars, you should try not to decrease the outboard length too much, and instead you should reduce the gearing by reducing the stiffness of the oar and also the blade area and curvature.

If you want to increase the gearing, then the best way to do it is to  increase the outboard length of the oar and this will also have the effect of making the shaft and handle angle to the water (and rower) shallower, which is advantageous.  Equally, to increase gearing in gigs by increasing the blade area too much could result in too hard a gearing specifically at the catch because gigs are heavy boats compared to sliding-seat shells, and the relatively greater impact at the catch of a larger blade area will be significant.

So this rationale suggests that to increase or decrease gearing on the outboard oar length and/or the blade area, you do not simply adjust the measurements in the opposite directions.  Instead, the Table below should provide a Guide:

Order Order

in which to Decrease Gearing
on Outboard & Blade

Order

in which to Increase Gearing
on Outboard & Blade

1 Decrease Outboard Oar Length (Slightly) Increase Outboard Oar Length as main change
2 Decrease Shaft Stiffness Increase Shaft Stiffness (Slightly)
3 Decrease Blade Widest Width Leave Blade Widest the Same
4 Decrease Blade Tip Width Increase Blade Tip Width (Slightly)
5 Decrease Blade Curvature Leave Blade Curvature the Same
6 Move Widest Point further away from Tip Move Widest Point further towards Tip
7 Weight in the Hands (Balance) Should always be Light for weaker athletes Weight in Hands (Balance) Should always be Medium for stronger athletes
NB A little of all of these is better than just a significant Decrease in the Outboard Length An increase in gearing can best be achieved simply by increasing the Outboard Length of the Oar alone, or by small increases to some or all the other dimensions.

Your choice may also depend upon whether it is for a whole set of oars, for one position, or for a particular athlete.

Whilst the above order is more or less the same, there are significant differences in the priorities and these should be noted.

We can also reduce or increase gearing by changing the inboard length, but as we can’t adjust the boat, we clearly need as long an inboard as possible.  Whilst this gives an easier gearing, it has a minor effect compared to changes in the outboard oar length.  What is much more important is that you have as long an inboard oar length as possible, as the more of your pull angle that is directly behind the inboard arc of the handle, the more effective will be your applied force.

We have already mentioned the main disadvantages of too short inboard oar lengths which allow the handle to swing past the side of the body.  In addition, shorter inboards make the balance of the oar heavier.  Ideally the end of the oar handle should be in line with the centre line of your body at the release.  Currently most are too short; however, it should be pointed out that if the inboard oar length is too long, it may restrict your length of reach/arc at the catch, and/or at the release.

Finally, you can alter your gearing by moving your cushion (and your body) slightly inwards, as has already been mentioned, which could increase your stroke arc at the catch, but would also increase your gearing.  However, the bow seat is the only one where you can move your cushion inboard slightly without interfering with other members of the crew.  This scenario is only likely to be relevant to less tall athletes who may be struggling to reach the maximum angles at the catch, since most rowers can already ‘lock pins’ at the catch.

If you move your cushion further out towards the side of the boat, this would make your gearing easier.  This is more likely to be used by very tall athletes who can easily reach the maximum catch angle, and this simply gives them the opportunity to have a fractionally longer inboard length, and also to work ‘within themselves’.

Hopefully this section has given some general trends and ideas for increasing or decreasing gearing for different types of rowers, via oar and blade specifications, and this now leads us into the final Article which will look at matching the athlete to the seat/position.

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