I have been giving thought to how to instal a holding tank to Calista. Partly driven by requirements for the next trip to the Med (scheduled for 2013 now), and partly to make life easier when dried out on beaches.
So the issues: Most Mediteranean countries require visiting yachts to have and use holding tanks. Discharging efluent or “black water” in the jargon being punishable by heavy fines. It is also difficult when we visit any of those nice places where we dry out, Rock, Solva, Sandyhaven and Tenby being specific places where we dry out on sand, and people can walk around the boat when she is aground. There is also the issue of trailing long distances, when we use Calista as a caravan.
Potential solutions: I have talked to a number of other owners about fitting a chemical toilet into the bows in place of the nowmal marine toilet. I have also fitted holding tanks to a previous boat, of the same size.
Pros and cons: The chemical toilet seems the easiest way to solve the problem. It is particularly useful when on the trailer because there is flushing water as well as somewhere to store the “black water”. However it means lifting the upper section off, and releasing the tank, to carry it through the boat and ashore. There is always the danger of dropping it either inside or on the way down to the ground. I am particularly concerned about how difficult it might be when afloat. I rarely use marinas, and am likely to want to empty it while at sea. That might be difficult to actually do while being thrown around. Having explored the different models available it seems that one with a 10 litre flushing tank and 10 litre holding tank would physically go into the space available. The problem is that to fit it I would have to remove and fill the holes left by the sea cocks. I would have prefered to be able to try it for a year and be able to replace the “Lavac” if I wanted to.
At first sight the holding tank seems more difficult. However there is room for one of at least 45 litres in the bows above and forward of the toilet. That has the advantage that it is above the waterline and should empty by gravity. That removes the need for a second pump. In the last boat I added a second tank low down for flushing water. It filled when the boat was afloat and provided water to flush the toilet when aground. It just needed the inlet hose to enter at the top of the tank and the outlet to the toilet at the bottom so that it stayed full when dried out. It did work. There is room for a reasonably sized tank in front of the toilet, and below the holding tank. This would solve the problems when using drying anchorages, and allow discharge at sea. With a pump out facility it would also be OK on inland waterways. I think that motor homes discharge tanks into a sort of concrete funnel which they drive over. If that is correct then that would work as well – just open the sea cock when over the “funnel” and use a hose to wash it all down afterwards!
I have made some tentative measurements and am starting to plan to make special tanks to fit made from epoxy resin and glass cloth. I was thinking of making the spiggots from the same materials formed around cardboard formers. I think bought tanks wont really fit, and will be expensive. I have some ideas to minimise the plumbing and mount the pump onto the lid of the tank. I thought of incorporating mounting flanges and other details as well. The tanks I made before were made from woven rovings and polyester resin. So I know that lould work.
So the idea would be that the sea water went from the inlet seacock to the inlet tank, then from that tank to the inlet to the toilet. The outlet pipe from the toilet would pass through the holding tank to an elbow on the top where it would enter the pump, and then from the pump into the top of the holding tank. An outlet would go from the bottom of the tank to the outlet seacock. There would be a pump out fitting in the deck with a pipe to the top of the holding tank with an extended spigot ending near the bottom of the tank, over the outlet spigot (so it can be rodded through if needed). A vent would go from the top of the holding tank to the top of the hull side near the bows.
Comments and ideas invited – preferably before I make any decisions!