by Eric Coleman

One of the attractions of the “tub” type of dinghy to those who like to reduce risks to a minimum is its ability to look after the crew when they make a mistake. It is true, of course, that a sailing canoe with watertight hatches is even more foolproof because although they capsize easily, they can be righted without difficulty; nevertheless, such boats and similar craft offer only a primitive standard of comfort and most of us take little pleasure in being tough if hardship can be avoided.

One type of mistake is to be caught broadside by a wave, the action being as follows: -

The particles of water in a wave oscillate backwards and forwards as well as up and down as shown in diagram (1).

When a wave becomes very steep, the top portion receives additional thrust from the upsurge of particles moving to windward in the trough - diagram (2). This increases the momentum of the top portion and an overhang is formed which is unstable and collapses. The greatest force is delivered by a wave if it strikes an object just as it is about to break.

When a dinghy is struck broadside with the plate down, the movement of water under the hull drags the plate to windward and the top portion of the wave pushes the hull to leeward. These two forces add together to form a capsizing moment. If the plate is in the up position, the tendency is for the hull to be pushed bodily sideways and the chances of a capsize are greatly reduced.

In my own case I was sailing on a reach with the plate half down and I was struck broadside by a wave of about 5 feet in height which was on the point of breaking - (2). I only had time to lean backwards (I was sitting on the side deck using the toe straps) and free the mainsheet in order to try and keep on an even keel. The boat resisted the impact of the wave, which passed clean over the leeward gun’l - (3). This has happened on two previous occasions when waves have been encountered in this manner.

On another occasion I was running close reefed with the plate right up. Wishing to gybe I found it difficult to haul in the mainsheet so leant backwards away from the boom to get a good purchase. Suddenly the boom came over and I fell into the leeward bilge so the boat broached to. I think that only the "tub" type of boat would have withstood this example of mishandling.