Mean machine

The Cobra 750 HD may look, from a distance, like the standard Cobra 7.5 upon which it is based. It is, though, a very different beast indeed.
Fitted with a seriously powerful 260hp Mercruiser Alpha One inboard engine with outdrive, the 750 HD is a mean machine. At more than £17,000 for a basic boat, rising to more than £20,000 with optional extras, the 750 HD is not your everyday diving taxi. But for a well-funded group intent on long-distance trips, it could make sense.
The hull is deep-V for its whole length, yet managing to ride high on minimum wetted area without recourse to the perils which can accompany a planing pad at the boat's heel. This efficiency is partly due to the underwater shape and is much enhanced by chunky, long spray rails. Cobra hulls have been around for enough time now to have acquired a good reputation for strength and speed.
Similarly, the tubes are unique to the design. They run forward as a straight line to a point opposite the console, then converge in a wide curve. This creates some useful room forward, not to mention a workmanlike, buoyant-looking bow.
The tubes' asymmetrical rear cones are particular to Cobra. They slope sharply down, with a flattish bottom section to give more support at rest and a sharper lift prior to planing, when they ride clear of the water. Though a complex piece of 'rubber' technology, it appears to work well.
Tubes are made in-house or - as in the case of my test boat - bought from Henshaw. In both cases, construction is of neoprene/Hypalon. It is in the area of engine choice and installation that the company's experience of constructing successful ski boats and racing boats with inboard engines has been of immense value. The problem of getting rid of exhaust gases without creating back pressure has been addressed properly, as has the need to get sufficient air flow over the engine.
When you lift the engine bay lid, you are struck by the large size of the 5.7-litre, 8-cylinder Mercruiser, fed by four carburettors and developing 260hp. Arguably, Mercruiser is the most experienced manufacturer of such units. The company has done huge amounts of research into anti-corrosion treatments and integral power steering, among other things. When an engine installation costs nearly £10,000 of the boat's total price, you do expect excellent electronics and mechanics.
Not all RIBs could handle this amount of heavy metal, but due attention has been paid to the Cobra's build. The GRP hull is strengthened by rigidity-giving fore and aft stringers, made from single-piece timbers, glassed up heavily and extending to form transom bracing knees. Out on the water, the big yellow RIB proved a thoroughbred. It got on to the plane with nonchalant ease and kept a crew of three up there at about 30 knots on a throttle opened some 60 per cent.
We were unable to measure top speed, but an informed guess puts it at over 40 knots, and probably over 30 knots when loaded with six divers and their gear.
The test boat, built for Menorca's S'Algar Watersports and Dive Centre, now carries 10 to 15 divers on a regular basis.
The weight of the boat and engine combination works to advantage, encouraging the hull to cut through the tops of waves rather than rearing up and slamming back in.
If you do fly off a crest, the trim stays pretty level and the full-length deep-V hull takes away most of the shock of re-entry. The power surplus enables you to overcome inertia if a nasty one slows you right down, or to get yourself out of trouble with currents and other vessels.
On the subject of fuel consumption, Picton Boats maintain that the Mercruiser inboard is more economical than a large 2-stroke outboard of comparable power.
At quick-cruising speeds, they say, the Mercruiser will consume 5 to 6 gallons an hour, where a 200hp outboard would consume at least 1 gallon more.
Back in harbour, manoeuvring in close confines is easier than one might expect. We wondered if, with its rear weight bias and slightly stern-down, bow-up attitude at rest, the boat would be blown off easily at the bow by a gusty wind.
This was not the case, there being enough boat in the water to give a firm bite and stiff control.
Turning between some marina pontoons, the 7.5m hull was easy to manoeuvre, helped by the fine sensitivity which is always an attribute of a powerful, multi-cylinder engine.
Picton and Cobra have combined their expertise to put together a robust boat, sporty yet versatile enough for inshore and offshore diving. And you can, of course, take 'offshore' to mean 'cross-Channel'.

Specification includes inboard fuel tank, two-man console with steering, Treadmaster non-slip, external lifelines and grab handles. A range of options is available. As tested, the boat cost £20,562.