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Tanking rainwater - at anchor


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What is the issue?
Completely clean fresh water can be hard to come by in the tropics. This is particularly the case if you do not have an osmotic watermaker aboard, or choose to do without the attached cost and regular maintenance, and you are cruising in remote areas.

Why address this?
Fresh water is a necessity for life aboard a vessel. Being forced to go to streams in remote parts is far from ideal in tropical islands. Animals are prevalent on most islands now and their droppings wash into the streams and rivers causing unhealthy levels of bacteria. Also some municipal water is unsafe.

Where water is safe and available you may often be required to ferry it back and forth to the boat via the tender. This means you must row the jerry cans ashore and carry them to the water source. To get a large quantity of water may take an entire morning of hard slog in as often as not very high temperatures.

Finding sources of easily accessible fresh water is highly beneficial.


How to address this?
There is usually plenty of water around the trade-wind zones, high islands or atolls in the tropics, and the trick is to build catchment systems to tank as much rainwater as possible when the opportunity presents itself.

The simplest, zero effort, approach is to trap foredeck rainwater run off at the deck-filler side. When the rain comes, depending upon how heavy the shower is, allow an appropriate period for it to wash off all the salt and debris that has built. Once this first wash off is completed, throw a wet towel on the deck to act as a damn behind the deck-filler and remove the plug. The following rain should then flow directly into the fresh water tank.

We found this such a useful approach that we set in place a permanent damn by laying down several layers of sealant behind the deck-filler. I would not recommend this as it caused a salt build up in normal seagoing conditions where it trapped seawater and evaporation just caused salt built up. The easy approach of simply laying down a towel as an occasional dam was in fact the best.

With a little more effort you can convert your awning into a water-catching system. Practically all cruising yachts have a sun awning that can be very easily adapted to catch water. Each awing is designed to fit a specific vessel, but most will turn into an excellent water catcher by having a simple method of unhooking the awning’s apex and dropped it down plus a sewn in plastic funnel and short hose lead of the lowest point when inverted. This then creates an instant water catchment area to collect water with a hose fitting ready to direct all the water into the main tank or jerry cans.

The problem with big awnings as water catchers is that tropical downpours are often accompanied by squalls. In these conditions large awnings flap madly and may need to be stowed. A well fixed awning largely gets around this problem - durable awning material along with multiple fixing points, plus copious short ties fixing it down along the lifelines and coachroof handrails. Another approach is to have smaller dedicated awning especially to catch rain.

Finally filling your tanks this way is daunting at first. It took me some time to get to grips with this as I was concerned that I would get my wash-off timing wrong and take some salt into the main tanks. What I would suggest is experiment for a while with the process. You can use your test runs for bathing water or washing clothes – remember it is not washing but the rinsing, which takes a lot of water in this case. Trap the water in buckets and jerry cans for these purposes. If you have not got the capacity you may be able to do laundry by plugging up the cockpit drains. Then bucket after bucket can be dipped into this for rinsing out and poured over the side. Another approach is to use an upright-stowed dinghy if you thoroughly clean it out. Then when you are comfortable with the approach and quality of the drinking water, direct it into your main tanks.



With thanks to:
Michael Harpur, Yacht Obsession.

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