The Sea Sprint 5.7m RIB (left) is the first offering to the sport diving world from Lowestoft boat builders Crompton Marine
By John Bantin
Crompton Marine are commercial boat builders, originally boat dealers, who went into production when they discovered that the boats they sold did not meet their own high standards.
Based at Lowestoft, on the Suffolk coast, they are surrounded by expertise in the building of boats for the offshore oil industry.
Initially, I was sceptical of their claim to be building a truly original dive boat, as there are now so many RIBs on the market; but I went to Lowestoft to find out for myself.
Crompton Marine had enlisted the help of one of their customers in demonstrating the Sea Sprint, their offering to the diving world. Mark 'Dog' Phillips was a fast rescue craft instructor at North Sea Training Services, an organisation which teaches rescue techniques to bodies like the DTI, Fisheries Protection and oil companies.
What is the difference between boats built for commercial use and those built for the leisure industry? Commercial boats are designed to a function rather than to a price. They are no good as tools for a job if they break easily. These boats must be brought up to the unforgiving legs of oil platforms and the hulls of larger vessels, often in conditions which would have made the leisure user turn back long before. They must survive repeated craning aboard and, worse, dropping back into an angry sea.
'Dog' told me that he thought the Crompton Marine vessel was up to the build standard of far more exotically priced commercial craft like the Atlantic 21. Neil, of Crompton Marine, had piloted the very first Atlantic 21 employed in the North Sea oil industry more than 20 years before.
I looked at the way they laid up their hulls. I was impressed at the immense strength that seemed to be designed in - for example, the triangular box section to which the tubes are bonded rather than the more normal thin flange of glass fibre.
I tried the 5.7m Sea Sprint with 'Dog' driving for the photography. He didn't approve of driving irresponsibly, but I managed to get him to give me some more dramatic boat-handling than he was inclined to. He explained his enthusiasm for the deep-V hull with its 60-degree dead rise - what Crompton Marine call their 'deltaconic' planing curve - and the concave chine and spray rails which run the full length. The spray rails give the transom end of the hull an unusual saw-tooth look.
The hull incorporates two large, watertight compartments which run the full length, again imparting tremendous rigidity and inherent buoyancy. Between these is space for an inbuilt 270-litre fuel tank. I found that all this translated into an immaculately dry ride in what was a rather nasty short chop outside Lowestoft harbour. Without any weight on board, the boat sat high on its hull, the tubes contributing little to its sea-keeping abilities. In fact they rarely seemed to touch the water. Its deep-V hull entered oncoming waves with no tendency to deviate off course, giving it tremendous directional stability and, in tight turns, a lateral grip on the water which was only limited by one's ability to stay with the boat!
Conditions were so bouncy that there were times, when I was driving, that I had difficulty keeping tight hold of the throttle control without suddenly slamming it shut and bringing the boat to an instant halt. With only two people in the boat, it was so lively over the waves that for once I found myself wishing I had a boat loaded with divers. I certainly had no doubt it would adequately and safely take the six fully equipped divers, plus cox, suggested by Neil, if not a few more.
Neil also said that in calm water, with the 115hp Evinrude fitted, this boat was good for more than 60mph. I resisted the temptation to try. The suggested hp range is 60-130hp. With only two passengers 60hp would have been more than enough. 'Dog' said it was the fastest hull design he'd experienced.
Bruised but remarkably dry, we headed back in, where I took time to examine the hardware more fully. The Sea Sprint 5.7m has a beam of 2.55m and a weight of 525kg. Its 48cm diameter military spec 1500gsm Hypalon tubes have three air compartments. These meet at the bow, which is naturally strengthened by an inbuilt chain locker. This is rather more substantial than any chain-locker normally fitted in RIBs, and provides a handy pulpit to stand on when pulling the anchor in. It's watertight, and the massive buoyancy it provides makes it almost impossible to dig the nose under by over-enthusiastic coxing in a following sea.
The decking is totally sealed, and there is a well at the stern (useful for positioning an electrical pump), drained by two large elephant-trunk bailers. The decking will take up to 1200kgs of load.
Fuel tanks can be underfloor, or built in to the console, or both. Commercial rescue boats can also have the option of an underfloor stretcher space for a casualty. This area, ahead of the two-seater console, can be utilised in the dive boat version to store diving cylinders - a rather nice way to transport such items during long voyages. It keeps the centre of gravity of the boat low and saves problems with such heavy items becoming 'live'. There's a similar storage space below the deck at the rear.
The console itself is equally robust, with a back rest and grab rail which felt as if they were screwed on with more than just a few self-tappers. Holding on determinedly, when 'Dog' was driving, at no time did I feel that any part was going to come away in my hand. It had a locker both at the front and under the seat, in addition to space for the plastic 80-litre primary fuel tank.
Because the tubes are so high above the waterline, one feels secure and deep within the vessel. The non-slip floor helps with this feeling of security. The aft deck is more than 1.5m wide.
It's sometimes hard to find your way around the price structuring of RIBs, because there are often so many add-ons and options. The package price of 9950 for the Sea Sprint, complete with 90hp Evinrude outboard motor, indicates to me that these commercial boats, in fully-fitted-for-use mode, are as competitively priced as any others available and aimed squarely at the leisure market.
Options include the additional under-deck fuel tanks (up to 270-litres), self-righting gear, wrap around bucket seats, and under deck stretcher facilities.
Last word from 'Dog' Phillips: "You might make a big mistake, but this boat always pulls out safe and dry."