Gearing of oars

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Gearing of oars

Post by topherdawson on Thu Dec 01, 2016 10:12 pm

1   The standard definition of gearing is the number you get when you divide the outboard by the inboard. Outboard is the oar length outside the boat, i.e. from the tip of the blade to the centre of the pivot. Inboard is the rest, i.e. from the pivot to the end of the handle.

2   Gearing is meant to define the leverage which the rower is working at. High gearing means hard pulling for the rower but high speed for the boat. Low gearing means easy pulling but a slower boat. A strong crew in good conditions might want a high gear but a weaker crew in adverse conditions might want a lower one.

3   It seems natural that for a particular boat, crew and conditions, there is a gearing which is neither too high nor too low, but just suits the crew and allows them to make the boat go as well as possible. In the skiff this seems to be between 2.7 and 3. For reasons I will go into later I think with optimum oars the gearing should be 3.(opinions?)

4   Many skiffs have multiple holes or notches which define different gears for different crews and conditions. The pin and plate system can not have holes closer than about 100mm without weakening the plate, and in a 4.5m oar this makes a very big step in gearing. In my opinion (comments please) the gears we need are in the range of 2.7 to 3. On a 4.5m oar the inboard at a gearing of 3 is 4.5/(3+1)= 1.125. At 2.9 it is 4.5/(2.9+1)=1.154. At 2.8 it is 4.5/(2.8+1)=1.184. These are steps of about 30mm, too small for pin and plate.

5 Some boats like gigs have no restraint to prevent the oars moving in or out. This does allow the rower to vary the gearing as they like but it also means that they cannot pull the oar handle straight back when they pull, as this makes the oar slide outwards. To prevent this the rower has to pull in an arc, a lot to the side at start and finish, which is pretty hard on the spine and also unnecessarily tiring. (opinion)

6   The conventional measure of gearing ignores for simplicity the fact that the rower's pull acts between their hands and so is 150 or 200mm in from the end of the handle. The force between the blade and the water acts near the geometric centre of the blade, which with long narrow sea blades can be up to 500mm from the end. If blades get shorter and wider, as they have in sliding seat boats and gigs, the centre of effort of the blade moves nearer the end of the oar, so the effective gearing also goes up. To keep it the same, the outboard needs to be reduced.

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Re: Gearing of oars

Post by Don Currie on Sun Dec 04, 2016 7:44 am

I met Finlay Robertson in NZ in February. He's a pretty clever rooster, and he has two definitions for gearing - extreme gearing, which is as you describe things above, but which, once again as you say, doesn't deal with different blade shapes very well. So Finlay uses a second definition, being True Gearing, which bases the outboard measurement on the distance from the lock to the centre of the blade. (ie True Gearing will always be less then Extreme Gearing) I'd be happy for the forum to adopt those two terms. I'm too dumb to be able to accurately work out the geometric centre of some shapes, but as far as I know, if you make a template of the shape of your blade, then it will balance at the centre. Perhaps Finlay could add useful comment?

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Re: Gearing of oars

Post by topherdawson on Sun Dec 04, 2016 6:58 pm

Hi Don,

Finlay puts his finger on an important point but in fact there is more to it. He points out that the blade force acts not at the end of the blade, but in the middle somewhere. The centroid (centre of area, centre of gravity of a cardboard cutout) is a pretty good approximation.

But the hands of the rower don't act at the extreme end of the handle either. Measuring my hands, a point halfway between them is about 150mm in from the end of the handle.

The sliding seat governing body FISA measure gearing just using outboard/inboard, and this is not always more than the true gearing.

To take your 4.5m oars with 1154mm inboard as an example, and assume the blade is say 600mm long so the centre will be 300mm in. The FISA gearing is (4500-1154)/1154 = 2.899. The True gearing would be (4500-1154-300)/(1154-150) = 3.034. For this reason I propose we use the term "FISA gearing" for the simpler calculation rather than "extreme gearing".

Almost all FISA boats use wide short cleaver blades and with these the blades are all very similar at about 550mm long. As long as they all look similar they can compare gearings with the simpler FISA gearing formula.

With St Ayles the huge variety of blade lengths means that we need to calculate true gearing, and I will do that in the spreadsheet collating existing oar stats. I propose the formula

True gearing = (oar length - inboard - half of the blade length)/(inboard - 150mm)

To take another example our 4572mm hollow oars have a FISA gearing of 3, so their inboards are 1143mm. (4572-1143)/1143 = 3.
Their blades are 840mm long so the true gearing is
(4572-1143-0.5*840)/(1143-150) = 3.03, hardly any different.

If we were to adopt shorter blades, say 630mm, the FISA gearing would stay the same but the True gearing would become
(4572-1143-0.5*630)/(1143-150) = 3.14 so the oars would need to be 105mm shorter to feel the same gear.

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Re: Gearing of oars

Post by Rory Cowan on Mon Dec 05, 2016 3:00 pm

The gearing arguent could turn out to be one of those endlessly rotating arguments.  For young fit rowers in their twenties and early thirties I can agree that  a gearing of around 3 may be optimal, however the reality is that many of our crews on Arran have a cumulative age of getting on for 260years  (excluding the cox) and getting pensioners to row 30/min at a gearing of 3 is a big ask!!  I am looking for an oar with a good 'feel' and what we are effectively doing here is to find a way of defining that 'feel' and putting a number on it.  It is all the things we have hitherto mentioned such as weight of the oar, balance of the oar, the blade size, the angle it is presented to the water, the handle thickness, the finish of the handle (yes that makes a difference as well) slop in the pin or oarlock, the flexibility of the shaft, the flexibility at extremes of the shaft etc etc.  In fact what we really need is a dual approach - one which gives the numbers which we are all addressing here and now and another more subtle rather like the test pilot's Cooper Harper rating scale which we use in test flying.  The C-H rating scale goes a long way to defining the qualitative feel of the system and that is what we are grappling with here.  For example we might be concerned with how an oar behaves in a seaway with a quartering sea - we are concerned with the rolling of the boat, the ability to lift the oar clear of the water, to get the oar cleanly into the water at the catch and take it out at the end of the stroke, we are concerned with the feel of the loom as it moves through the stroke and the ability to vary the stroke rate into and out of wind and sea.  So we get ourselves a table of these attributes and go and row the conditions taking care to consider each aspect in the context of the test - and then we give each attribute a mark out of 10.  Then you go and do it with another set of oars - it can be a long and slow process however it is a good step forward from the numbers we can generate in the first instance as this is a means of comparing the relative importance of those numbers ie the meaning of those numbers.  It might seem long winded but it is tried and tested in an imprecise flight test world where handling qualities need to be defined.

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Re: Gearing of oars

Post by topherdawson on Mon Dec 05, 2016 4:35 pm

Hi Rory,

I'm guessing you must have had something to do with testing aircraft? It's a glimpse into a different world.

If people like the feel of an oar setup it is likely to be a good one, and one of the problems we have is that they find it difficult often to describe what they do and don't like. Stiffness is one such, and it makes a lot of difference to the weight of the oar how stiff you need to make it.

Another problem is that people get used to something even if it's terrible, and may not like an improvement even if it is an improvement.

As to your elderly rowers on Arran, I'm 63 and I row with the 60+ men in our club. Our combined crew age must be about 255. We've just been out in perfect conditions and rowed for 20 minutes over about 3km. We were rowing at 22 strokes per minute at a gearing of 3. Our oars have a lower gear of 2.8 which is 50mm away, which we use for weaker crews or rowing against a strong wind.

Totally agree that we need to try any new oar in lots of different conditions, and take a set round regattas so people can try them.

But I'm concerned that heavy unbalanced oars and handle clashes are making some clubs row at gearings which are much lower than optimal.

Can you make a draft shopping list of what a good oar feels like, so that we will know it when we find it?

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Re: Gearing of oars

Post by Rory Cowan on Mon Dec 05, 2016 6:37 pm

Hi Topher,
Yes I will, but to go back to C-H - it is a good tool that we can use - just because it is wrapped up in sexy flight test jargon is no reason not to use it.  It's not difficult, anyone can make use of it and it can help each and every one of us to reach a reason as to why we find one oar better than another or maybe even unusable.  Of course there will be some who soldier on whatever they are given, bit at least here is a tool that can enable someone who uses an oar to describe what is good about it, what is not so good and what they may like to change.  It is no different to using, say an axe and asking yourself how to define 'heft'.  It is all to do with the balance, the weight and the ease with which you can use it / swing it - or not and relate that to the use.  For example if you are felling a tree with an axe it is rather a different job to cutting kindling with the same toy.  You relate the tool to the task.  The tool is the same, but the task and the user define what the good features are for the purpose.  Back to the oar.  We need to define what we want the oar to do and from that work out and define the features that will enable us to achieve that. It will be quite interesting to isolate and define the necessary features.

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Re: Gearing of oars

Post by topherdawson on Mon Dec 05, 2016 6:51 pm

I guess what I was saying was, how can we use Cooper-Harper to assess an oar? It does from what you say look at the border between the human and the implement, and that is infinitely complex because each human is different physically and also in their experience and learning.

Can we list the situations in which we use the oar, and define what makes it good or bad to use? I'd say the unbalanced handle force and the stiffness of the shaft and the way the blade grabs or slides through the water define the feel of the oar, plus maybe the polar moment of inertia.

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Re: Gearing of oars

Post by John Irvine on Wed Dec 07, 2016 6:45 pm

I hope the outcome will be that it's up to each club to select the gearing that suits them. The question that arises on gearing is whether we should be allowed to use the plastic collars used by sliding seat crews, which would allow gearing to be adjusted for different crews and different conditions.

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Re: Gearing of oars

Post by topherdawson on Wed Dec 07, 2016 7:15 pm

It seems sensible to me to have some way to vary gearing to suit crews and conditions. One way would be to use your system with effectively a button, and pad out the button with removable C-shaped "clams" so the oar is moved inboard by the thickness of the clams.

Possible gearings could be 2.7, 2.85 and 3.

This system would allow the oars to be easily pulled in but the downside is that the oar needs constant outwards pressure to prevent it drifting inwards.

An alternative system would be multiple notches or holes. If the notches were in a plate glued to the underside of the oar then to slide the oar into the boat one would need to raise the oar 20mm or so. This is easy if you don't try to lift the whole oar, but just raise the handle and let the blade float.

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Re: Gearing of oars

Post by topherdawson on Wed Dec 14, 2016 7:43 pm

This post is from a Word document sent to me by Sandy Pratt of the Ayle of Quinte Skiff Club in Canada:

Length
Please consider the following table which reports the Ayle of Quinte Skiff Club’s experience since we launched our first skiff in 2013
Oar Outboard Length Speed ¾ Pressure Speed Maximum Pressure
Concept 2 Carbon Fibre 8’ 11 ½ “ 4.1 knots 4.7 knots momentary
First set wooden oars 10’ 4” 4.8 knots 5.0 in bursts
Second set wooden oars 10’ 11” 5.2 knots sustained over 1 mile

These speeds were in fresh water with 60+ aged rowers. Note theoretical top speed of a St. Ayles Skiff is 5.8 knots (1.34 x square root of 19’ = 5.8 knots).

Conclusion: Skiff speed varies directly with outboard oar length
I therefore feel that any move to shorter oars fleet-wide would be a retrograde step, though I must say that my opinion is not universal within the Ayle of Quinte skiff club. I acknowledge that shorter oars can be compensated for by higher stroke rate, but I refer to the Japanese experience in the ’36 Olympics recounted in “The Boys in the Boat”. Small men, short oars, stroke rate 50/minute: faded after the first 1000 metres. Further a remark from the Coigach oar maker to the effect that whenever he encountered another team with short oars he would not have to worry about them on the race course.

Balance

There has been a reasonable demand for a better balanced oar. I know that you consider my maximum inboard length of 55” to be excessive but please consider that this virtually eliminates clashes and that it enables good balance if oars are left at full 2 ½ square inboard of the pivot, assuming a 15” handle

Cost

Longer oars demand a stiffer material to avoid excessive flexing, both fore and aft and up and down. Douglas Fir with a modulus of elasticity of 1.95 offers the most likely answer to this problem. You in Scotland have the advantage of locally grown Douglas Fir. Ours comes from the West Coast and is thus expensive and hard to get. This makes it hard for us to get under the 50 pound material cost.

Thank you for your consideration of these points.

Sandy Pratt
Ayle of Quinte Skiff Club

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Re: Gearing of oars

Post by Ian Mills on Thu Dec 15, 2016 9:42 am

In Defence of Light Gearing:

I agree with John that we should all be free to decide what gearing to use.

I do not agree that 1:3 is optimal at all.   (Sorry!)
Here in Crail we use something like I:2.6 and we might even try lower than that this year.

Slidy seat boats at top Olympic level use about 1:3 but their boats are much lighter and travel much faster than ours at a much higher rating.
The St Ayles is a heavy boat and the majority of crews will not be performing at their physical best at a gearing of 1:3 in my opinion.
Perhaps strongly built blokes (yes – that's you Topher!) may be fine with1:3, but for the rest of us, a lighter gearing is more appropriate.

A greater force can be applied to the pin (ie the Boat) with an easier gearing. (Simple lever physics.)
This is particularly the case for weaker crews and if rowing into a headwind which can otherwise stop the boat if over geared.
If a greater force can be applied to the pin the boat accelerates!
(Force = Mass x Acceleration)
It is the speed of movement of the load (The Pin, and hence the boat) of our lever (The Oar) which is important – not how far it travels per stroke.
i.e. You can still row at 20spm with a low gearing – You have a faster drive and can enjoy the longer recovery phase. (Let the boat run!)

A fit and dynamic lightweight crew can be competitive against a bigger stronger crew, even into a head wind – but not if over geared.

Injuries – there is considerable strain on the body pulling the St Ayles – especially at the catch. If injuries are to be prevented then the ability to have a lower gearing should be encouraged please. Especially among lightweight crews – male or female.  

There are a couple of us in Crail who have historic lower back problems but still managed to win medals at the Worlds. This would not have been possible without a low gearing (1:2.6), especially into the headwind on the return leg!

Long Strokes - A lower gearing encourages a long stroke. It is easier to maintain stroke length into a head wind or when fatigued if you are not over geared.

Acceleration – a crew which is rowing at a lower gear is more able to increase the rating and hence boat speed at the end of a race compared to a crew of similar strength/fitness which is over geared.

Adjustability of gearing – it is important to be able to tweak gearing to suit the crew and conditions in increments that make small differences. Our system allows the use of packers (18 mm ply) to make adjustments, plus the whole block can be moved bigger amounts if necessary.
The current proposal is weighted towards stronger crews and has adjustments which are too large in my opinion.
However, as long as clubs can make informed decisions about gearing and are able to alter it to suit, then all will be well!

Ian

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Re: Gearing of oars

Post by topherdawson on Thu Dec 15, 2016 10:20 am

Hi Ian,

I'm aware that a gearing of 3 is at the top end of the current range, and also that Crail got a lot more medals than us! It makes sense to provide a range of gearings which covers the present gearings used by clubs, and it well might need to go down to 2.6 if people want that, or even 2.5.

In Ullapool our oars have two gears, at 3 and at 2.8. We do use the 2.8 when going to windward with womens or mixed crews, and I have tried to encourage mens crews to try the lower gear in racing but they don't want to do so. I can't force them.

To some extent we are all used to our own systems and don't want to change. All we can do is provide an easy way to experiment with different gears, and to do that we need to agree what values the gearing should be.

Although our gears have a step of 0.18 between them I can't say it's such a huge step I'd want another in between. It amounts to 50mm of movement of the oar and I think 40mm is about the smallest movement we can accommodate with multiple steps, which is a change of about 0.16 in gearing.

Your 18mm spacers do offer the chance to reduce gearing at will, but not to increase it. Your current gearings are at the low end of the range and ours are at the high end. Perhaps we both need to supply rowers with the means to find out what really suits them, over the range in which most clubs row?

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Re: Gearing of oars

Post by topherdawson on Thu Dec 15, 2016 10:28 am



Longer oars demand a stiffer material to avoid excessive flexing, both fore and aft and up and down.  Douglas Fir with a modulus of elasticity of 1.95 offers the most likely answer to this problem.  You in Scotland have the advantage of locally grown Douglas Fir.  Ours comes from the West Coast and is thus expensive and hard to get.  This makes it hard for us to get under the 50 pound material cost.

Thank you for your consideration of these points.

Sandy Pratt
Ayle of Quinte Skiff Club


Hi Sandy,
Although Douglas is a stiff timber it is also a lot denser that Western Red Cedar and so for a given weight needs to be less bulky.

A solid shaft of a lower density timber will be stiffer than Douglas because the fibres are further from the neutral axis. The only way round this is to make the oar hollow, and thus move the Douglas out to be further from the neutral axis without adding weight.

Also the Douglas we use for oars comes from Canada! Scots grown Douglas in nice wood but not clear enough.




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Gearing vs Blade size

Post by Rory Cowan on Thu Dec 15, 2016 1:53 pm

It seems to me that for competitive crews, gearing is self regulating - high gearing for the fitter / younger crew and lower gearing for the less fit / older crew.  There is merit in changing down a gear to go into wind and up a gear to go downwind - however since efficiency falls off quickly at the limits of high and low gear with the force of the oar becoming too high at low stroke rates and a high stroke rate does not give the rower time to develop a suitable force for long enough.  Ergo we are likely to end up around the 2.6 to 3.2 mark to suit most crews so perhaps regulating the gearing is unnecessary.  Having said that the combination of gearing and blade size will also make a difference since a small blade on a high geared oar will slip more than a larger blade thus effectively reducing the resistant force perceived by the rower.  So we can't really get away from the interrelationship between blade size and gearing.  The most useful we can set out to do here is to give good guidance as to blade size and gearing as a starting point.  There will never be a perfect combination for all conditions and it will be a bit like choosing sails for a particular sailing race dependant upon wind conditions.  Should we therefore be looking to limit the number of different sets of oars we take to a regatta or limit the number of bolt on combinations we can take.

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Re: Gearing of oars

Post by topherdawson on Thu Dec 15, 2016 2:44 pm

Hi Rory,

I think we should aim at a specified length for each oar, maybe 1, 2, and 3 all the same and 4 shorter, plus a blade of fixed design and size, plus a specified oarlock system, plus say three gears at fixed notches. Currently looking like 3 for the top gear, and I'm negotiating with Ian Mills of Crail for bottom gear.

Long story short, we are aiming for an oar new clubs can make which is comfortable to row with, has a variety of gears, does not clash, and is the same for everyone. With the let-out clause that clubs can go on using their own oars but not have curved blades, i.e. under the existing rules.

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Re: Gearing of oars

Post by Finlay Robertson on Wed Dec 21, 2016 7:04 pm

Another thing worth noting is that not everyone puts their hands in the same place; there are obviously going to be variations between individuals, and I wonder whether anyone has noticed widespread tendencies within specific clubs?

The practice of putting both hands at the extreme inboard end of the handle (something we in North Berwick used to call 'grunting' - long story!) strikes me as being reasonably widespread (though we discourage it), and such clubs/persons are effectively rowing at a significantly lower gearing than those with hands spread. If any clubs teach this technique as a matter of course, the calculated gearing needs to be amended to reflect this. Topher's suggestion of deducting 150mm from the inboard for calculating gearing works only if we are all rowing the same way.

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Re: Gearing of oars

Post by Finlay Robertson on Wed Dec 21, 2016 7:49 pm

I think we're talking cross-purposes here! What we call 'grunting' is what No. 2 is doing in this picture - putting both of his hands close together, at the inboard end of the oar. The type of rowing that we encourage is more akin to what Stroke is doing - hands spaced apart. (Ignore No. 1 - he's rowing with a broken oar!)

(I'd also like to note that none of the rowers in the picture is a member of our club - it was taken at a Trades Cup a few years back but does illustrate the issue quite well.)

The point I'm trying to make is that the length of the inboard (or of the handle) isn't necessarily a reliable indicator of gearing - the location(s) on the handle that the rowers are taught to put their hands are also important.

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Re: Gearing of oars

Post by topherdawson on Wed Dec 21, 2016 7:59 pm

Sorry, I did get the wrong end of the stick, or oar handle. Since we can't design the rowers, only the oar, I don't think we need to worry about this. If we provide a range of easily changed gears then what rowers row at is their own business.

Thinking about my own rowing, I do shift my hands around to change the grip and sometimes wrap my outside hand round the end of the oar for a change, which probably changes the gear.

Mark Irvine of Coigach has a theory that the stroke oar needs to be more heavily geared because otherwise the stroke will row at a rating too high for the longer oars at 2 and 3. I see his point but other clubs do not do it, on the whole. I've updated the master spreadsheet with rows of averages for bow and stroke oars by the way.

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Arithmetic of oar gearing

Post by SHUG on Sun Jan 15, 2017 1:23 pm

I think I posted this elsewhere but it is particularly relevant here:
Gearing: From hydrodynamic limits, the maximum speed of a skiff is about 5.5knots or 2.8 metres per second.
The range of movement of the rower’s hands during the Drive is about 1metre.
At 32 strokes per minute the total stroke sequence takes about 1.9 seconds and if that is split evenly between Drive and Recovery (which is debateable) then the time spent in Drive is 0.95 seconds.
This means that the rower’s hand velocity in Drive is 1/0.95 metres per second or 1.05m/s
So to match the boat speed to the hand speed we use the gearing of the oar.
So, the first stab at gearing is: boat speed/hand speed =2.8/1.05= 2.66
Oars are not an efficient means of propulsion and are generally about 80% efficient due to slippage, vortices shedding etc so lets add on 20% to allow for that and this brings the gearing to 3.2. For simplicity lets make that a nice round 3 which is a commonly used gearing.

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Gearing could be just a defined property of an oar.

Post by Rory Cowan on Mon Jan 16, 2017 9:44 am

As one of around 4500 whisky tasters clinging to a rock in the Clyde, looking at Shug's post, it is really rather worse than that as we note that our Drive is significantly shorter than the recovery stroke - maybe we have it wrong, but that is the way it is.  For that reason therefore the effective gearing will be even lower.
That said, does it really matter what the gearing number is or how it is arrived at since all it is, is a means of describing the ratio between the outboard to the inboard oar lengths in the context of what we are likely to perceive as either a hard, comfortable or easy row.  We can dance around defining exactly where we are to measure and so forth, but at the end of the day the rower will put his hands where he finds it best or has been taught, and the gearing number will merely describe one property of the oar he is using. All we have to do is decide exactly where we take the measurements and keep it the same and after that we have a definable and repeatable oar property. As an aside a GPS we carried claims that we managed to make 11.6 kph - that works out at 6.259 kn - but that was down sea with the wind behind.

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Re: Gearing of oars

Post by topherdawson on Mon Jan 16, 2017 10:26 am

Hi Rory,

I've never gone down the route of trying to calculate what the optimum gearing is, rather I think we should leave it to the rowers. For a given set of conditions there will be a gearing which people think is not too high and not too low. By observing what gears clubs use, and providing an adjustment which covers all that range, we can let people please themselves. All we need to do is make the adjustment so easy anyone can do it without tools and during the row.

I'm struggling with the mental picture of 4500 whisky tasters clinging to a rock: are you in Dumbarton?

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