An investigation, by instrument and direct observation, into hull sea-keeping ability at high speed in rough water and the resultant fatigue experienced by man and machinery 50' Thames class prototype and 52' Arun Mk, II off GuernseyHOW WILL a hull driven at speed by high-powered engines respond to the impact of rough seas? How easy will she be to handle? What will be the strain on her propeller shafts? How great will be the physical stresses imposed on her crew? These were just some of the questions, vital to lifeboat design, to which answers were being sought by the RNLI technical staff together with BSRA (British Ship Research Association) in trials held off Guernsey in mid-March; trials embracing both recorded scientific measurement and human experience and observation.

The trials, organised with the invaluable help of Captain J. C. Allez, Harbour Master and RNLI Honorary Secretary of St Peter Port, took the form of a comparison between two of our latest self-righting lifeboats, comparable in overall length but entirely different in design concept. One was St Peter Port's own new lifeboat, Sir William Arnold, the second in the 52' Arun class (52-02) whose hull form was designed by Allen McLachlan, of G. L.

Watson, Glasgow; she is a broadbeamed (17') wooden boat with flared bow sections, wide decks, broad stern and a spacious wheelhouse. The other was the prototype of the 50' Thames class (50-001), a development by the RNLI design office of the 44' US Coast Guard cutter; built of steel, she is a narrower-beamed boat (14'), with straighter bow sections and tug-type tumblehome, a smaller wheelhouse and an entirely different approach to general arrangement.

Arun (52-01) has been subjected to extensive and vigorous testing. She has been sailed over 12,000 miles, in allweathers, round the British Isles and up the coast of Europe from as far south as Spain to the waters of Norway in the north. She has also spent some months on station. So, at Guernsey, for the prototype Thames hull there was the advantage of direct comparison with a hull already well proven.

To obtain measured values of motion in rough water, both lifeboats were fitted by a team from BSRA, led by Christopher Lamb, with instruments which would give a continuous and accurately-timed analogue chart record of: (i) Pitch and roll.

(ii) The torque, or twist, on each propeller shaft together with the rpm at which the engines were running.

(iii) The athwartship accelerations experienced by the boat and hence the human body at three different parts of the boat: bow, stern and, most important, the coxswain's position at the wheel, (iv) The vertical accelerations experienced at bow and stern.

That was one side of the story.

Equally important was the personal assessment made by every man aboard the two boats, and here the RNLI was greatly indebted to the St Peter Port crew for a wealth of willing and able assistance. With great enthusiasm they took a full part with the RNLI base crew in all the operations afloat (and, once the boats were berthed, had the lifeboat hut kettle boiling hospitably in record time, so that the day's experiences could be talked over in comfort).

During the period of the trial a reserve boat replaced Sir William Arnold on station for normal duty.The two crews manned the boats turn and turn about, so that direct comparisons could be made, and there was much that could be learnt from the critical experience of such seamen. In overall command of the operation was Captain Roy Harding, trials officer, RNLI. He coxswained first one boat and then the other, backed by the base crew, Bill Dent, Ian Johnson and John Ashford, together with George Moore from Littlehampton ILB station. John Petit, Lloyd de Mouilpied and Bill Ogier, of St Peter Port, each took it in turn to coxswain the opposite boat, backed up by Eric Pattimore, Chick Robilliard and Ron Munson. Representing the RNLI technical staff, and acting as co-ordinators, were Syminton Macdonald, chief staff officer (technical), and Stuart Welford, research and development officer; like everyone else they changed from boat to boat each time out.

Each of the trial runs (six in all) was round an octagonal course. The first leg was into a head sea; the next with the sea on the starboard bow; then on the starboard beam; starboard quarter; dead astern; port quarter; port beam and finally port bow. Before the start of each run, and also halfway round the course, anemometer readings of wind speed were taken on both boats and the wind direction noted; at the same time a wave-rider buoy was lowered overboard from Sir William Arnold, for the measurement of wave height.

Once the wave-rider buoy had been recovered, the run began. The two boats, in constant VHP communication so that recordings could be synchronised, set off on parallel courses about 100 yards apart at the fastest speed of the slower boat, about 17 knots. Thus, as far as was possible, each boat was experiencing the same conditions at the same moment and BSRA's instruments were making a permanent recording of their performance.

While in the after cabin of each lifeboat sensitive pens kept their ceaseless scientific chronicle, the crews at their stations were keeping their records, too.

For each leg, the time of start, ship's heading and duration of run were noted, as well as Decca fixes at start and finish.

At the end of every leg the observations of both coxswains were recorded; these included ease of steering, course variation, amount of spray and their own general comfort at the wheel. To round off the picture, every other member of the two crews was asked to write down, once again at the end of each leg, his position in the boat, whether he had been standing or sitting and his degree of comfort (or, for that matter, discomfort); handholds, vision, ventilation, all passed under review.

In four days of trials the weather, bright with spring sunshine, was most co-operative, giving a range of wind speed and wave height wide enough to provide good basic working data. Five runs were made off the south of the island in winds ranging from 10 to 25 knots and in confused seas with wave heights from 7' to 14'; and one run was made off the north of the island in a rolling swell with a wave height of 14'.

The last of the runs off the south of the island was made at half speed to broaden the range of variables and also for comparison with readings taken from model experiments in rough water.

Recordings were also made during calm water runs to provide a basis from which the rough water data of the two boats could be compared.

One way and another, a mass of information was accumulated which is now being analysed by BSRA and the technical department of the RNLI at Poole. It will probably be some time before a final pattern takes shape. From these results, not only will greater knowledge of the two boats tested be gained, but also invaluable data will be built up for reference in future design work. And, who knows, some new line of thought, completely unexpected, may perhaps emerge from the general pattern; that is, after all, one of the most exciting rewards of research. J.D..