I'm sometimes slightly suspicious about a range of boats produced by an engine company for the simple reason one wonders what the chief motivation has been behind such a decision. Is it simply a means to sell more engines or is it genuinely the case that the company desires to launch a valid and worthwhile boat to compliment what is already, in some cases, largely an over subscribed market. Coming up with a product that succeeds in fulfilling the latter is no easy matter. For ultimately, of course, the public are going to decide and in a competitive market place there have to be clearly discernable reasons why one boat or boat/engine package is preferable to another.

It has been several years now since the first Tohatsu RIB rolled off the production line, or to be more precise, sprung from the virgin mold. The ‘One Design’ RIBs the company has been marketing over the course of the last two years have sold well. The boats have shown themselves to be deigned by people with an understanding of what is required by those who wish to use a RIB for what it was originally intended for - multi-purpose offshore use. They fulfill this wide ranging function well and therefore can be seen leaping round the RIB racing circuit, traversing the Solent as commuting vehicles, port hopping the Westcountry or being used as Yacht Club tenders. The Tohatsu range offers a straightforward approach to design in an effort to moderate the pricing structure of each of the 4 models now available from 6.1m to 7.5 in length. Though the company brochure speaks of optional seating and console designs, the general thinking behind the One Design concept is standardization throughout the range.

Not surprisingly, these RIBs are powered by OBMs bearing the same name. Though dated in appearance and the technology they use, these engines have nonetheless served their masters well. No doubt in response to the very large strides forward made by the ‘opposition parties’, ie. Marine Power and OMC, Tohatsu as can be seen elsewhere in this same issue, have now begun powering these boats with their latest and finest. But that’s not all, the introduction of diesel power is a big jump for the boat manufacturing arm of the company and gives them a product which can be marketed to yet another sector. The Yanmar 230 is one of a range of engines from probably the most prolific diesel manufacturer in the world. Distributed by E.P. Barrus Ltd. here in the U.K. these engines have been widely used by RIB owners and with much success.

Fitting a diesel engine to a RIB is no simple matter - if it is to be done correctly that is. Engine mounts, location of electrics, including starter motor, waterproofed housing and suitable venting of the engine compartment, are all paramount issues which need to be addressed with expert knowledge. Knowledge that must be based upon the peculiarities associated with RIBs as opposed to other powered craft. This is for the reason RIBs, given their level of sea keeping, are generally driven much harder than other forms of craft. Furthermore, these boats enter hostile waters more frequently than their contemporaries, hence, swamping and extreme hull stresses are more likely to be experienced. The RIB and its power unit therefore need to be built and installed with such trials in mind.

Taking this subject a little further from the point of view of its relevance to the Tohatsu 7.5m, it is true to say that diesel RIBs potentially are more vulnerable than their outboard powered counterparts. The reasons for this could fill a feature length article, but essentially, avoiding water contact with the engine and its electrics must be ensured at all cost. This means closed transoms or engine housings that span the full beam of the boat as well as the issues surrounding engine-housing ventilation and adequate scuppers are vital aspects to take into consideration well before the vessel even leaves the draftsman’s board.

Tohatsu’s new diesel RIB went through quite a lengthy prototype stage with engine housing modifications etc. being made prior to the new model being sold on the open market. These development ‘mods’ included the engine housing vents being built as rearward facing structures set behind the seating pods of a critical height above that of the sponsons themselves. Thus if a heavy sea swamped the boat the air intakes would be above the water level. The housing itself is neatly styled with attractive curvatures and sits central to the deck with good external clearance either side of the unit. It also features a closable vent to its top section which is a good idea. When the ‘sprung loaded’ lid is lifted it reveals a small GRP lip to which the lid closes securely down over. Though the latter presents a rubber edging to the deck face I would hardly describe it as watertight. Internal bailing though consists of no less than two bilges, whilst on deck, a further two 3 inch trunked scuppers take care of any shipped seawater. Though not ideal, in the sense a top mounting is by far the best, the Yanmar 4LH-STE’s starter motor has been positioned half way up the body of the engine as opposed to being located on its underside. The latter of course would be fatal not only from an access point of view but also with regard to the obvious conflicts involving water and electrics.

As regards this engine’s performance, though featuring an intercooled turbocharger, the 230 hp takes an age to pull the boat up onto the plane. It is in fact so pronounced, that on my first attempt behind the wheel, I thought the engine was suffering from some kind of automatic shut down problem. It did however eventually pick its skirts up, and with the RPM counter showing a little under 3300, the boat began to feel more like a RIB and less like a tug. In fact, when fully underway and over the ‘hump’, the feel of the boat and the responsiveness of the Yanmar felt really good. With a steady ride, sure-footedness in the chop and a useful degree of power when once the prop was fully swinging – the boat felt very useful indeed. However, in addition to simply the annoyance of poor lower end acceleration, the potential problems of trying to drive this boat in a heavy sea could be serious. In difficult conditions there is no substitute for power, without it a RIB becomes vulnerable. Without quick responsive acceleration, the boat will simply not be able to negotiate big seas at low speeds or react to dictating situations quickly. Helming could form a repetitive cycle of (a) falling off the plane or (b) inappropriately charging off with the bit between its teeth just at the wrong moment. To be fair, the counter rotating stainless 30 inch prop to the Bravo 3 leg might have been a little much, a lesser pitch might be better suited therefore in assisting the revs to pick up sooner.

Whilst the hull in past trials certainly proved itself well matched to outboard power it is nonetheless of narrow design for a diesel RIB. Big, heavy diesel engines need plenty of beamy buoyancy aft to ensure the stern doesn’t dig in. I’m afraid at low speeds, the boat did tend to ‘drag its bum’ somewhat, adopting an exaggerated bow up attitude in the process. It is possible trim tabs may help to correct this tendency but of course the problem shouldn’t really have to be corrected in the first place.

Further to the matter of the boat’s fit out. It was well finish, attractively styled and of practical design. The main helm console has benefited from a few refinements and additions that make it superior to the earlier models. The positioning of the instrumentation was excellent with nothing being to cramped or out of reach. A good sized locker to the main face and a useful, tidy looking forward seat built into the front section of the unit were also good features. The left handed wheel/throttle position worked well too with the steering system proving very smooth and responsive. The overall layout of the boat of course holds true to the classic offshore RIB school of design, especially so with the inclusion of the jockey seats, which in the case of this 7.5m, consist of just two positioned side by side. I would just say, that in general, I don’t like seat back rests of this type. In order to properly support the lumber region, a fully padded panel as opposed to a small ‘pad’ is required. It also looks as though the upholsterer ran out of gas too – as if he skimped on the job. I know it isn’t the case of course - but it just appears that way to my mind. Otherwise, these seats and their bases are good. All other features, such as the stainless steel work and sponson construction etc. are sound and well finished. Overall therefore, apart from the low-end performance problems, this new Tohatsu 7.5 is a likeable boat with many good attributes.

Specification

Price as seen £28,000 plus VAT

Tohatsu Marine Ltd. Portmore, Lymington, Hants, U.K. SO41 5RF

Builder
TOHATSU MARINE LTD
Portmore, Lymington, Hampshire UK

Tel. +44 (0) 1590 670787
Fax +44 (0) 1590 670520