An ideal self-pumper for a dinghy on an exposed mooring, or even for a rather wet cruise.

In the figure marked no. 1, which is a graphic representation, a sort of explosion has just occurred outside the pump whereby all its constituent parts have been pulled out somewhat.

In figure 2, the parts have clicked into place again. The two balls are phosphorbronze balls of ⅜” diameter, which entice the water upwards and then trap it by falling. They may be obtained from the makers of ball-bearings. The three brass plates forming the base are ⅛” thick, measuring 3” by 1”. The two holes on which the balls sit are drilled ¼” and counter-sunk on both sides with an ordinary rose bit.

The hole in the top plate which communicates with the pump barrel is ½” diameter, as are those which should be drilled on a line along the middle plate and opened out with a chisel and file to form the slot. The three plates are riveted together and then sweated all round the edges with solder. This can easily be done by heating on the flame of a Primus and rubbing with flux and a stick of solder.

The two barrels are pieces of brass tube, ½” bore and 2” long. They are over the holes of the top plate. A ring of brass wire is first slipped over the base each tube to give a bolder grip.

A small piece of ¼” tube is soldered over a hole on the side of the delivery barrel, at an angle, to take the rubber tube which conducts the water to its destination. The top of this barrel is closed with a soft wood plug after the ball has been inserted.

The plunger is a piece of brass tube which will just slide easily in the barrel. Its lower end is closed with a piece of brass plate soldered on, the solder being reinforced by a wire ring inside, and filed off flush with the tube. It is drilled for the gudgeon pin, a piece of stout brass wire. Have the plunger too slack rather than too tight in the barrel. If filled with oil occasionally, sufficient will find its way past the gudgeon pin to produce a good suck with quite an easy fit. The wooden connecting rod is a length of ⅜” dowel rod stocked by most ironmongers.

A hole is drilled up it to take the end of the stout brass wire which is hammered flat at the bottom and drilled to an easy fit on the gudgeon pin. A piece of fine brass gauze the size of a penny is soldered below the intake hole to keep foreign matter out of the pump. The post is pine, 2” by 1”. The pump barrel lies in a shallow groove cut in the 1” side and the delivery barrel passes into a hole drilled up the post as shown. The hole is slotted out to allow the small delivery pipe to project, and a brass strap embraces the pump barrel and is screwed to the post to fix the pump firmly in place.

The construction of the spindle carrying the mill and crank will be readily seen from figure 4. The spindle is a piece of brass tube ⅜” in diameter, and revolves in a brass tube ⅜” bore, which is driven tightly into a hole drilled through the post. The middle part of the spindle should be reduced in diameter with a file, leaving a bearing full size for ½” or so at each end. This will reduce friction and allow the oil with which the spindle is filled to escape from the small hole and form a good film. The oil is confined by plugging the ends of the spindle with wood plugs, that at the mill end being left projecting for removal when fresh oil is required. The crank is of ⅛” brass plate drilled for the spindle and sweated on. The crank pin is part of a round-headed brass screw and the hole for it should be drilled ¼” from the centre of the spindle to give the plunger a travel of ½”. The ‘big end’ is of stout brass wire bent into an eye to fit the crank pin easily, and it is slipped over the pin together with its washer before the pin is soldered onto the crank.

Make the connecting rod of such a length that the plunger is well away from the bottom of the pump barrel. The thrust of the mill is taken by a brass wire ring soldered to the spindle just behind the hub.

The mill is of sheet aluminium 1∕16” thick, but iron will do quite well if painted. From the centre describe two circles one 2” and the other 10” in diameter, and draw twelve radials which should be cut down with strong scissors as far as the small circle. The hubs are two discs of elm ½” thick and 2” in diameter, and are screwed together with the mill in between. The hole for the spindle is a good fit to prevent turning the mill on the spindle when at work, and yet loose enough to enable the mill to be pulled off for stowage by taking hold of the front hub. When finished, give each sail a twist so that its outer end makes an angle of about 30º with the plane of the hubs. If left lying about on the boat the mill will get bent, and it is a good thing to fit a peg to the under side of one of the seats the same size as the spindle so that the mill can be pushed up over it for stowage.

In figure 5 is a pump fitted to a 12 ft dinghy. The post is notched out to take the edge of the thwart and fixed by a brass pin which passes through the thwart and a block of wood screwed to the post. Here the end of the rubber tube has a piece of brass tube inserted, and this is pushed into a hole in the capping of the centreboard case. The post is long enough to allow the mill to show clear of the sheet line. In this case too, post and mill are clipped under a thwart for stowage, where they are out of sight and cannot get in the way.

The same method of fixing is used at the stern thwart, with the delivery taken through a hole in the transom.