Saturday, August 1, 2009

Swimming Uphill

For years, we have been aware that our pool has an uphill & a downhill.

It is noticeably more difficult swimming west-east than east-west & takes about one extra stroke.
This is surprising, as the circulating water enters on the west side & exits on the east side.
Compared with the pool cross-section, the water flow must be about negligible anyway.

A test confirmed that the anomaly is only present with the circulating pump on.
A further test showed that sizeable objects (full plastic jerrycan) floating just flush with the surface to avoid wind influence, move quite clearly east-west, wherever they start.
I concluded that there must be a relatively rapid circulating current, west-east at the bottom & east-west at the top, due to the jet effect of the water from the pump, which comes via 2 orientable nozzles in the west wall, both pointing moderately downwards.
So I thought I would see what happened if I set the nozzles more horizontal.

While fiddling about, I played with pointing them up, which gives a noisy fountain effect.
Less steeply up, gives a visible swirly current on the surface.
Angling that swirly surface towards the side wall of the pool, produces a significant current along the edge of the pool.
That immediately washes all floating insects, leaves etc rapidly along the pool & into the skimmers at the east end.
The difference in cleanliness of the pool surface is radical & stays that way as anything floating on the surface drifts towards either the north or south wall then gets swept to the skimmers.

Pity it took me 10 years to discover that.

The uphill/downhill effect is reduced too.

Parting thot: "Crystallizing my feelings about the game, I find that squash is less frustrating than golf, less fickle than tennis. It is easier than badminton, cheaper than polo. It is better exercise than bowls, quicker than cricket, less boring than jogging, drier than swimming, safer than hang gliding." - John Hopkins

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