Wednesday, 11 June 2014

Swim Like a Ship - Article by Barry Young

Barry Young is not only one of our most enthusiastic master swimmers, current holder of several FINA Masters world records, he was also a senior lecturer at the New Zealand Maritime School with over thirty five years experience in teaching ship stability, propulsion and ship stress. In these two articles he points out the remarkable similarities between ships and swimmers as they both try to move through the water as efficiently as possible.

1. Shape:

Ship: Long, narrow ships are easier to move through the water than short, wide ships. The boat in the photo
has been specifically shaped to slide through the water easily. The centre hull is 12 meters long and only 1 meter wide. It uses only a half a litre of diesel fuel per nautical mile and is capable of travelling 2400 miles without refuelling.

Swimmer: There is not too much we can do to change the shape of our bodies but it is a fact that most of the world’s fastest swimmers are tall and slim. Weren’t those speed suits great? They definitely changed our shape. I always felt that Master Swimmers gained a greater advantage from them because they squeezed our lumps, bumps and wrinkles into a more lean, efficient hydrodynamic shape. Whenever I put mine on I felt like Superman – capable of slicing through the water without a ripple! You could particularly feel the difference with dive-starts and turns. The suits were an aberration and had to go, but they were great while they lasted! Wetsuits have a similar effect and, in addition, their buoyancy further reduces drag by lifting you upwards.

Conclusion: In all strokes we should be keeping our body as long as possible. Stretching out during the glide part of the stroke will make you more efficient. Rolling from side to side in freestyle and backstroke is good because your body offers less resistance when on its side than when flat on your front or back.

2. Interaction:

Ship: Whenever a moving ship gets too close to another object – like the sea bed, a canal bank or another ship – it experiences drag which slows it down. This is known as ‘interaction’. Apart from slowing down, a ship in shallow water also sinks lower in the water, which means that more of the ship is under water creating more drag. This effect is known as ‘squat’. In addition, the size of the ship’s bow wave and stern wave increase in shallow water which means less of her power is available for propulsion - see ‘wave making’ later.

There is one situation in which interaction can increase the speed of a ship, this happens when one ship closely follows directly behind another. In this situation both ships go faster.

Swimmer: Most of us have worked out that deep pools are faster than shallow pools. The shallower the pool the more drag you experience, this is why Olympic pools are so deep. Swimming close to the lane ropes or the wall also causes drag. In an open water swim it is possible to get a little help by drafting close behind one or more swimmers – which is why drafting is not permitted in some open water races.

Conclusion: The best place to be is in the centre of your lane. During starts and turns, remain half way between the pool bottom and the surface for as long as possible. In this position you are as far as possible from drag creating surfaces.

3. Propeller:

Ship: In the 19th century. when most ships were propelled with paddle wheels, there was a lot of discussion
and argument about the efficiency of paddle wheels as compared with the modern screw propeller. So two identical ships were built with identical engines, RATTLER on the left had a screw propeller and ELECTO on the right had two paddle wheels. The two ships were tied stern to stern as shown in the picture and a tug-of-war followed. The RATTLER won. It towed the paddle wheeler backwards all round the harbour. This proved beyond doubt that the propeller is more efficient than the paddle wheel.

Swimmer: For many years swimmers thought of their hands as paddles pulling straight back through the water. We now know that the hands are much more efficient when used like propeller blades. We achieve this, when swimming freestyle and butterfly, by moving each hand in an “s” shaped curve as it pulls backwards through the water. This is a three stage sculling motion. At the front of each stroke the hand starts the “s” by moving outwards, away from the body’s centreline. Then it moves inwards under the body, then finally outwards again to complete the “s” at the end of the stroke past the hip. In each of the 3 parts of the ”s”, the hand is slicing sideways through the water like a propeller blade. The angle (or pitch) of the hand changes each time the direction changes from outwards to inwards and then to outwards again. In backstroke, the “s” is there too, but the 3 parts are downward, upward and downward, ending under the hip. In breast stroke, the “s” is reduced to 2 parts, outward and inward, making it more of a diamond shaped stroke than an “s”.

Conclusion: At first it can be confusing and frustrating to try to force the hands to follow the “s” shaped curves, changing pitch twice each stroke as described above. Don’t stress about it! Just leave the idea sitting in the back of your mind while swimming. One day it will just happen. “Distance per stroke” drills encourage swimmers to lengthen their stroke and encourage the “s” movement of the hands. Sculling drills with the hands alongside the hips and ‘long dog’ drills also help.

4. Propeller speed:

Ship: Large ocean-going liners and cargo ships which are trying to move across the oceans as efficiently as possible while using the least amount of fuel, travel at a constant speed and have large diameter, slow turning propellers. These propellers are kept submerged at all times. High speed vessels, on the other hand, have smaller, high revving propellers. Some of these “sprint” propellers are only half submerged!

Swimmer: Think of your hands and feet as your ‘propeller blades’. If you are a middle distance or long distance swimmer, efficiency is more important than power. You will be wanting to get the maximum distance from each stroke with the minimum use of energy. A longer, slower stroke and kick will achieve this best. These swimmers need to have an excellent appreciation of “pace”. They are constantly asking themselves the question “can I keep this pace up for the rest of this race?” If they start out too fast, they will get into oxygen debt and be forced to slow down. If they go out too slow, they will not swim a good time.

Sprinters, on the other hand, are putting out maximum power in order to achieve the highest speed for a short period. Stroke rates are high, with little of the “s” shaped stroke mentioned above and the kick is furious. Sprinters are a strange breed – different to the rest of us. I have trained with some of our best sprinters over the years and am always amazed at the way they loaf through the training session until we get to the sprints – then there is no catching them! They only have one speed – flat out - and that is the way it should be. A sprinter who has an appreciation of pace is not really a sprinter.

Conclusion: Most of us sort out fairly early on in our swimming careers whether we are sprinters or distance swimmers – then we concentrate on refining our stroke and pace to best match our chosen distance. Some of us 200/400 meter swimmers occasionally get roped in for a 4 X 50 meter relay and you very quickly realise how much you need to change your stroke to be fast over the shorter distance.

5. Wave making:

Ship: A moving ship creates two sets of wake waves as can be seen in this photograph. First there are the
vee shaped “divergent” waves at the bow and stern, and then there are the “transverse” waves, which follow along behind the ship. Waves waste energy and leave less energy for forward propulsion. An efficient vessel slips through the water making as little fuss as possible, creating the least wake. The faster a ship moves, the larger the waves it creates.

Most large ships have a “bulbous bow” just beneath the surface, as shown in the sketch below. This bulb produces a wave, which is out of phase with and therefore cancels out, the ship’s divergent bow wave. Fuel savings of up to 15% have been claimed.

Submarines, at the same power settings, go faster when fully submerged than when on the surface. This is because, like ships, the wave patterns made when on the surface use up a considerable amount of energy and leave less energy for forward propulsion.

A submarine which is moving just beneath the surface will still make waves on the surface and will not be as fast as one fully submerged.

Swimmer: Some experienced coaches can tell a lot by observing the wake waves made by a swimmer. Efficient swimmers, like efficient ships, leave less of a wake behind them. There is a possibility that a swimmers head acts like a bulbous bow on a ship to cancel out the main wave created by the swimmers shoulders and torso. In order for this to be effective the top of the head would need to be at or just below the surface of the water.

During a dive start or turn, a swimmer just below the surface will still create waves and will experience drag, so it is better to remain well below the surface during the glide and then rapidly rise to the surface to start the arm strokes. The best place to be in a dive-start or turn is mid way between the surface and pool bottom.

Conclusion: Swimmers need to do everything they can to reduce wave making.

6. Skin friction:

Ship: Below the waterline, ships are painted with special paints which are designed to reduce the friction or drag on the hull as it moves through the water.

Swimmer: The speed suits we were allowed to ware for a while were coated with a friction reducing material. Now that these are no longer allowed, all we can do is to remove as much body hair as possible by shaving down before a meet. No serious male swimmer would wear a beard. “Smoothie” wet suits are designed to be as slick as possible.

7. Appendages:

Ship: Appendages are parts of a ship which stick out from the main hull - like the rudder and stabilizing fins. These cause drag so designers go to great lengths to remove them where possible or to streamline any essential appendages.

Swimmer: Our racing goggles are designed so as to have a low profile and to be recessed into our eye sockets as much as possible. Our ears are tucked under our caps to keep them flat.
Barry Young

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