Trans RINA, Vol 152, Part A4, Intl J Maritime Eng, Oct-Dec 2010


broken water”7 published in October 1855 in the Journal “The Life-boat” leaves no doubt about the fear for broaching-to and the dexterity required for avoiding it [25]:


“On the second point, running before a broken sea, an equal variety of management is observable, as practised on the coast, yet all alike intended to meet the one great risk of “broaching-to”, which nearly all agree in considering to be the greatest danger to which a boat can be exposed, and to be that which calls for the most skill and management to obviate it.”


The magnitude of the problem on the English coast is then stated:


“We have been rather prolix in our account of the phenomenon of


broaching-to, because it is a very


interesting one, which it is important should be understood in order to arrive at the proper management and to obviate its disastrous effects, which have been more fatal to the lives and property of boatmen on our coasts


whatever.”


A detailed discussion follows about operational practices for avoiding broaching-to and also some remarkable thoughts about its cause. The extract below is particularly noteworthy because it describes a practice exercised by oarsmen for mitigating the wave effect: by increasing the drag as the boat was experiencing extra thrust owed to the longitudinal component of wave’s


down-slope


pressure; and, by speeding up while on the up-slope (this helps to avoid being caught in the types of behaviour that we would characterise today as “nonlinear surging” and “surf-riding”8 [26]):


“As before observed, the greater number of skilful boatmen on the coast are in the habit of checking a boat's way through the water or of backing her against a heavy sea on its approach. Their practice is to stop the boat's way by backing their oars until the crest of the wave has struck the boat's stem and passed her midship part, then to give way again, running in on the back of that wave, as far as they may be able to, then watching for the approach of the next, and repeating the same operation until they arrive at the beach, being careful, by steering with oars at the quarter or stern to keep the boat as far as


7 According to the Merriam-Webster Dictionary: “surf – date 1685 - is the swell of the sea which breaks upon the shore; and the foam, splash, and sound of breaking waves.”


8 Surf-riding is a peculiar condition of ship operation corresponding to her capturing between two wave crests in following/quartering seas; i.e. the ship is forced to travel with speed equal to wave’s celerity. Nonlinear surging on the other hand is, the asymmetric oscillation of a ship in her longitudinal direction, where she spends more time near wave crests and passes quickly for the troughs – it represents forerunner of surf- riding.


“Another expedient is to tow a pig of ballast, or a basket, or other instrument, which by its weight or hold on the water has the effect of a drag on the rear end of the boat, and prevents its being beat to leeward by the sea, thus keeping her end on to it. On the coast of Norfolk the following ingenious plan is commonly practised. The boatmen there employ an instrument


for


“The steering with an oar on each quarter is another expedient, employed to prevent broaching-to, as when running, a boat will not answer her helm on being overtaken by a sea.”


than those proceeding from any other cause Then we are introduced to the practice of using


“drogues”, apparently the evolved technology of hawsers or ropes that we had found to be discussed in 18th century’s literature. Drogues were (and still are) valuable aids for keeping the course and for avoiding broaching-to (as well as for avoiding “bow diving”9; as comes out later, bow diving was seen by some as connected with broaching-to):


possible, end on to the direction in which the sea is running. It must be here observed, that this management is so far varied according to the character of the boat; that in cobles, and other square sterned boats which have their bows better formed for meeting a sea than their sterns are, their position is reversed before entering the broken water, and they are taken in stern foremost and bow outwards, but the same principle being acted on rowing back to meet each heavy wave instead of running from it. In a sailing boat this principle can only be so far acted on as to diminish the boat's speed through water by taking her in under a very educed amount of sail, which is commonly one and by towing weights or instruments lade for the purpose.”


Another use of the oars, for maintaining the course, is also considered:


the above


purpose called a “drogue”; it is a conical shaped canvas bag, of the form of a common candle extinguisher, about 2 feet diameter at the base or mouth of the bag, and 6 feet long, having a small opening at the other end or apex of the cone. When running before a heavy sea in broken water, the drogue is thrown over from the stern, and towed by a stout rope with the large end foremost, when it instantly fills, and from the resistance it opposes to the water, holds


the stern back and prevents the boat's


broaching-to: as soon as the danger is past the large tow rope is let go, and the drogue then towed with the smaller end foremost by a small line attached to that end, it then immediately collapses is emptied of water and offers but little resistance.”


9 Bow diving is a phenomenon where a ship, while running somehow faster than the waves, nails her bow into a steep wave’s up-slope. Ships with fine lines, and thus low buoyancy, in the bow area are prone to


resistance to forward motion, experienced by a bow diving ship, causes her slowing down and her possible capsize under the effect of the next wave.


©2010: The Royal Institution of Naval Architects A-167


this. The large increase of


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