I SEE TALL SHIPS

In my romantic imagination, I see tall ships once again breasting the long ocean swells, fuelling their passage with trade winds and leaving scant traces of their passing; an echo of the clippers of yore.

Romantic? Yes, but also practical and possible!

Under prime conditions, windpowered commercial vessels crossed the oceans at speeds approaching those of many modern vessels today. More than 100 years ago, Cutty Sark travelled from England to Australia repeatedly averaging, 12 knots and sometimes peaking 14 knots in a 24-hour period. (Some of the big American clippers averaged over 18 knots on a day’s run.) Re-rigged, she voyaged to China and loaded tea for English palates, averaging similar speeds. The wind is still there, so perhaps we need to re-rig our logic and thinking for the voyage forward? ‘It has been calculated that the

Cutty Sark’s sail plan was capable of producing a drive of some 3 000 hp. As a comparison, a modern coastal merchantman of similar size … would need a 1 000 hp diesel engine and be capable of some 12 knots…’ (Patrick Brophy, Hamlyn, 1974)

It is postulated that, given that wind power still exists and is the only real constant in this equation, more efficient collection of this power, and transfer of said power to the water with more technically advanced motors and propulsion trains – together with a re-rigged mindset – means a return to wind propulsion is possible, at great cost saving and almost total elimination of exhaust pollution (and its various knock-on effects).

Rather than harnessing direct power for driving a hull, Rotosail suggests the generation of power that charges battery banks which, in turn, (in a controlled and variable form) power electric motors that drive more conventional power-

transmissions similar to dieselelectric trains and some large vehicles. This serves to allow ‘reefing’, or complete ‘ furling’, of the rotor in adverse conditions, while motive power is maintained from previously stored wind-power.

Similarly, during periods of light airs or doldrums, previously stored wind-power may be ‘ borrowed’ for continued drive. This minimises or obviates the possibility of being windless on lee shores and in other dangerous storm conditions. In the harbour, generation and storing of power can continue 24/7 although the ship is at rest. Standby dieselpowered chargers would also be available as a last resort.

The tall ships that I see are not topped by a row of tall trees of snowy billowing canvas, but by a ‘ farm’ of tall Rotosail VAWT’S (Popular Mechanics, Feb. 2017) on the bridging deck of a shallowdraft catamaran hull. With the Rotosail capability of both vertical and radial automated control, the hoisting and reefing of sails is simple. There’s no need for swarms of topmen led by the shrill command of a bosun’s pipe.

It is not suggested that wind is the complete solution, but rather a positive hybrid contributory expedient. Power requirements other than for propulsion could vary enormously; a cruise liner, for example would require enormous additional auxiliary power and would certainly need solar and/or mechanical booster generation.

A very positive aspect would be the expansion of containerisation to small, shallow ports presently serviced only by break-bulk cargoes. The shallow draft and inherent stability of the catamaran would allow containers to be carried in and on both hulls, and loaded or unloaded by a travelling gantry on each side, with a horizontally extendable boom. Differential buoyancy during cargo handling could be compensated by automated water ballasting to maintain trim.

I do not expect to see any of this happening in my lifetime, but can hope my descendants might also see tall ships … not in their romantic imaginings, but in glorious reality. KEITH HONEYMAN Wow, Keith, that took a lot of research for me to fully understand. I’m not a maritime man myself, so I don’t have an intimate knowledge of the pros and cons of various propulsion methods, but I do believe that under the right conditions, the sail is the most efficient way of moving a vessel over water. Well, a sail and a hydrofoil. Outboard motors are already working at a deficit by having to overcome the water forces before they get going.

Either way, this sounds like a good plan, but the batteries may get a bit heavy (and pricey). – Lindsey SINGLE-LEVER WATER TAPS This is a neat, compact design that controls the flow of water available for showers, basins and baths with a single lever. But the inherent problems of this design are:

1. When the lever is in the neutral position and the tap is opened, a mixture of cold and hot water is received, even if only cold water is required. Depending on the distance to your geyser, it takes a long time to get hot water in that position. Therefore, both water and energy are wasted, as the amount of water out of the hot system that was cold is replaced with cold water into the geyser and has to be heated. It is better practice to turn the lever to the hot or cold side as required, before opening the tap.

2. The tap is a ball-valve design, and opens and closes rapidly with little movement of the lever. Closing a fully opened tap rapidly causes a hydraulic shock in the water pipes, straining their joints and resulting in detrimental movement.

3. The latest gas hot-water heaters depend on a pressure drop in the hot-water system to ignite the gas, which heats the water. With the single-lever tap, if opened fully, the water pressure drops, the gas in the heater ignites and hot water is produced, which soon gets too hot for a shower. Cold water then has to be added. With the single-lever tap, cold water alone cannot be added without throttling down the hot water, which causes the hot water pressure to rise, putting out the flame in the heater – somewhat irritating when standing under a nice warm shower that suddenly goes cold.

A partial remedy to this problem is to set the water flow through the gas heater to max, and throttle the gas flow down to obtain the ideal shower-temperature water with the tap lever on max hot. (Your wife will soon complain that the water is now too cold to wash the dishes.) ERIC VENTER Hi Eric, I’ve never thought of my shower tap that much before, so thanks for that. And all of this optimising to then ruin the ratios with an aerator or, even worse, a low-f low shower head? – Lindsey In our August issue, we published a shortlist of candidates for the Popular Mechanics Inventor of the Year at the Innovation Summit 2018 Inventor’s Garage. Unfortunately, a few contestants have since dropped out of the competition for various reasons, forcing us to amend the list. We’ll keep you posted.

See you at the Innovation Summit.