TO TANK OR NOT TO TANK...

THAT IS THE QUESTION

Article for Dufour Yacht Owners Association by Peter S. Wonson

The majority of boat owners nowadays are acutely aware of existing and potential legislation regarding Waste or  Blackwater holding tanks.  In most Mediterranean countries it is now a mandatory requirement to have one fitted – not yet in Britain, but it is coming as sure as the sun will rise.  The requirement is that the tank has sufficient capacity for the amount of berths on board regardless of the amount of crew.  That is to say, if you have a 6 berth vessel for instance, your tank must be able to cope with that amount even though there are only two of you on board.

 

'' Your company has been recommended on the Dufour Association web forum....''

For a standard hand-pump head the rule of thumb calculation is 7-8 litres per berth per day.  Electric macerator or centrifugal units use less flushing water so potentially increase your holding capacity two-fold and more.

“What system is best?” I hear you cry.  The variation is huge, but the two most common are (a) Divert to tank or sea when required.  This has a deck pump-out (which most authorities like to see) and an on-board pump-out facility.  This can be a hand operated or electric diaphragm pump.  A macerator pump will not do as these are not continuously rated and will let you down when you need it most!  This system requires a second diverter valve or in-line lever valve.  The seacock must be lever type – a Blakes valve would have to be changed as these do not have sufficient flow capacity. (b) Keeping to the K.I.S.S. principal, if you can mount the bottom of the tank above sea level then a gravity system is the most satisfactory option. Everything goes into the tank and your sole control is the seacock. No fuss and very simple.  Open when at sea or to empty the tank, and closed when in use as a holding tank.  Again with a deck pump-out which we would always design above the outlet so if, or when, it becomes blocked a gentle rodding usually solves the problem.  The downside is that the vessel must be hauled out and the seacock must be changed to a 2” version.

In all holding systems a level indicator is a must because when it is full  the only way it can go is up and out of the vent, with the resulting chaos !!  All our tanks and installations adhere to ISO 8099 and CE Standrds, which means that the system will work with no smell!  All tanks are strongly and rigidly constructed from un-corrodable 10mm H.D.P.E. to any profile with an access hatch for maintenance.  The system needs to be rinsed out either with sea-water, or preferably fresh-water, as often as possible – say once every fourth fill or so using our newly developed holding tank treatment and descaler.  This prevents the tank going anaerobic, clogging, and the dreaded limescale.  I have broken into old pipework that has barely 15mm centre clearance on a 38mm pipe.  Curiously, somehow they still work, but apart from transferring unpleasant odour it puts huge stress on any in-line pump, thereby reducing its working life.  The pipe we use is not cheap, but it is guaranteed for a minimum of 5yrs.  I have returned after 15yrs to replace a failed component and the tube is still clear and holding back odour.

Standard sanitation pipe is half the price but will only last 1-3 years.  The cheapest is not always the most economical. 

Bladder tanks are never a good idea because they will start to smell severely 6-12 months down the line, which is the reason we will not install one of these.

First Marine Services have been in partnership with TEK TANKS, the industry leaders for almost 10yrs and we can design, build and install a system to suit you because through experience we  know what works and what doesn’t.
 
We can do as little or as much as you require.  Supply and fit or supply only for your own installation.  We are only at the end of a ‘phone 01420 23351 or 077 6666 4515 or e-mail if you prefer, peter@first-marine.co.uk   or see us at www.first-marine.co.uk