Sail with New Freebooters

by Mike K-H

Quebec in five days’ time

Yesterday 27 June 2008 at 09:45 local time, the French sail training ship Belém left Halifax, Nova Scotia and the statue of Samuel Cunard. Low visibility and head winds dictated the choice of the shorter Canso canal route rather than sailing via the 60 mile longer Cabot Strait to reach Quebec by her scheduled date of 2 July.

Belem took on the necessary pilot at 18:00hrs. I wonder how many square-rigged sailing ships he encounters each year.

Reverse Osmosis - gone are the days of fresh water shortages.

Belém carries 20 tons of fresh water, and produces 3 tons from seawater each day, using a reverse osmosis plant. I don’t know the particular brand or model, but I found details of a typical marine system by Stromme (the smallest they make) with the same capacity.

It’s amazingly compact (1200 X 650 x 900mm - about the size of a domestic kitchen sink & cupboard unit), and requires a 3Kw electrical supply. That’s about 5 or 6 horsepower, allowing for losses - a tiny fraction of what her three generatotrs will supply for other purposes.

What’s reverse osmosis?

A process essential to all living things, for a start. If you separate a container full of a solvent such as water from another full of a solution such as salt water by a membrane with holes so tiny that the water molecules can pass through but the salt ions can’t, pure water will pass into the salt solution.

If the tanks are closed, the pressure in the salt water will increase until it is sufficient to stop any more water passing through the membrane. If you use a pump to further increase the pressure in the salt water tank, you can force pure water out of the salt water tank into the pure water tank, thus extracting pure water from a tank full of salt water - that’s reverse osmosis.

Of course, doing this will increase the saltiness of the water in the salt water tank, so a fresh water production system has to have a way of extracting extra-salty brine and introducing new seawater. The new fresh water also needs to be aerated and acidified a bit. Pure water is yucky to drink - have you ever tasted the stuff in battery top-up bottles?