Rivercraft 375 Sprint

The longest tributary of the South Island's Buller River, the Maruia presents some special challenges to jet-boaters. Paul Smith climbed into a Rivercraft 375 Sprint to tackle one of the river's most demanding sections - 21 years after first running it.

Rivercraft 375 Sprint
Rivercraft 375 Sprint
The Maruia River forms in the southwest Spenser Range and runs west for some 29 kilometers as far as Springs Junction on the western side of the Lewis Pass. This upper section of the river is generally too shallow to be boated by any craft other than the smallest of rafts or canoes, but rumour has it that jet boats have been used in flood conditions. A good flow is required even for jet boats to reach the Maruia Springs Hotel (and hot pools) and this is generally considered to be the upper limit for jet boating.

From Springs Junction, the river turns north, flowing some 32km across the river flats of the Maruia valley where it is joined by the Warwick River. From this confluence, the Maruia River flows away from the main road around the western side of Mount Rutland through beautiful, dense beech forest before joining the road again flowing 5km to Paenga.

In this section, the river narrows down through a rocky gorge and there are a number of steep rapids between Deer Creek and Coffee Creek. Between the rapids are lengthy sections of quiet flowing pools intermingled with rock gardens. From Paenga, the river flows quietly north for another 11km to the Maruia Falls that are some 10 metres in height having been created by the Murchison Earthquake of 1929. Below the falls, the river flows quietly to its junction with the Buller River.

Designed as a low-powered but nimble, entry-level jet sprint craft, the Rivercraft 375 is 3.75 metres in length with a reasonably narrow chine beam of 1.52 metres. It's definitely a two-person boat. Constructed of marine grade 5083 alloy, the hull and deck are fully welded to form a strong but lightweight (125kg) monocoque. The delta keel section is formed in 6mm plate to which the 4mm outer bottoms are welded. The transom is 3mm while the deck and topsides are formed from 2mm plate.

Two full length box section bearers provide rigidity while the cockpit floor and footbrace is formed from alloy treadplate welded to the bearers. The underwater profile of the hull is characterized by wide turned down chines to provide lift and to deflect spray down and away from the hull, while three planing strakes either side of the keel provide lateral adhesion. The hull is a variable deadrise design culminating in 18 degrees at the transom.

The engine is a Nissan SR20 - a two-litre, all alloy, in-line four-cylinder design with DOHC and four valve per cylinder technology which is rated at approximately 100kW. It's been marinised by Rivercraft Marine and is controlled by a Microtech electronic control module. A Scott SJ510 single stage waterjet was selected with a 19 degree three bladed impeller which discharges through a large 118mm nozzle.

The Nissan will pull 5200rpm at Wide Open Throttle and is well-matched to the Scott waterjet. The whole of the engine compartment is protected by a strong alloy cover that is upholstered to match the seats. There is plenty of storage available either side of the engine.

Having used the little boat a number of times on the braided lower sections of the Waimakariri River over the summer, I was confident that with judicious use of the throttle and helm, the Rivercraft 375 Sprint was up to the task of navigating the treacherous rapids of the Maruia.

Although we (me and 15-year old son Etha) were the first to arrive at the agreed rendezvous point of Springs Junction, it wasn't long until the other members of the expedition showed up: John Watson of Christchurch had Dennis Gottimeyer as his crew in John's extended Hartz Explorer boat which is powered by a new Generation 3 LQ9 Chevrolet six-litre V8 through a 8.5" 2 stage Scott Jet - easily the most potent boat in the bunch.

Brendan Hannah with his crewman Cliff Attwood both of Christchurch, know the Maruia area well having spent many hours hunting and fishing there. Brendan's 4.1 metre Rivercraft hull is powered by a 170 Volvo through a Hamilton 2 stage waterjet.

Owen Cassidy of Christchurch had his 4.6 metre Rivercraft boat InXS which is powered by a 302ci Ford V8 through a Hamilton 3 stage waterjet. Owen had Licoln Deardon of Riverton with him as navigator.

Ted Sagar of Christchurch is the owner of Rivercraft Marine who knows each of the boats well - with the exception of John's Explorer - having built them all. His crew for the day was Craig Johnson, also from Riverton. Ted had his four-metre "boulder basher" adventure boat which, like Brendan's boat, has a very flat deadrise hull for optimum shallow water capability. The boat is powered by a two-litre Opel/Holden Camira engine through a Hamilton two-stage waterjet.

The boats were quickly launched and we elected to let the faster boats go first and settled in behind Ted's boat. A couple of minutes after getting away I noticed the engine coolant temperature gauge had moved right across to 230 degrees from it's usual 180. Fearing I had picked up a stone which may be partially blocking the cooling intake from the jet, I eased off the throttle and lifted the engine hatch to check hoses and the sandtrap.

It was a relief to see the discharge tap on the sandtrap had been knocked open, presumably when I was loading the portable gas cooker, which allowed most of the cooling water to discharge overboard before reaching the engine! Closing the tap saw the temperature gauge quickly resume its usual position.

The first section of river was quiet, but we soon came upon the first "riffle" shortly after passing the confluence of Pea Soup Creek. The rapid was taken without stopping although I was happy to negotiate the white water very slowly in order to get a gauge on how the little boat would handle the aeration. In theory we may have been at a slight disadvantage with our relatively modest power and single stage jet, but in practice, the little boat acquitted itself well.

Once past Coffee Creek the rapids come thick and fast. Although fresh rainfall had been through a couple of days earlier, the river flow had quickly dropped to its usual low levels and the larger rapids involved steep climbs around massive boulders and rocks with foaming white water cascading all about us.

As my confidence grew, I began to appreciate just how good the Rivercraft 375 Sprint was in these types of boating conditions. The deeper deadrise kept the jet unit intake well primed while the precise and nimble handling allowed us to skirt around most of the obstructions with ease. The short length of the boat meant however, that it was wise to approach the larger standing waves as slowly as possible to avoid taking one over the front.

We found we were able to keep up with the other boats in the quieter water by cruising at 4000rpm, yet in the rapids we could make our traverse comfortably with around 3200rpm on the clock. There were a couple of occasions when the jet lost grip momentarily in the worst of the aerated white water, but it quickly recovered without hindering the boat's upstream progress in any way.

After an hour's boating we arrived at Dallow's Flat. Situated just upstream of one of the bigger rapids in the river, the grassy clearing made an excellent lunch stop providing an opportunity for the boys to regroup and recount their experiences of the trip so far. The weather had improved markedly and we enjoyed our lunch beneath blue skies, little wind and the magical music of the bush.

All too soon it was time to move on up river in the sure knowledge that although we had successfully navigated some sizable rapids already, the most challenging ones were still ahead of us. By this time my confidence in the capability of the Rivercraft 375 Sprint to handle the white water had increased to the point where I was relaxed in the knowledge that we could skirt around almost any obstacle such was the precision and accuracy available. Any problems encountered in this regard would clearly be driver related.

We had only been underway for a short time before we rounded a sharp corner and a very steep, very aerated rapid came into view. I have to confess to swallowing a lump in my throat at the sight of it. However, the larger, more powerful boats had already got through it and were waiting for us, although out of our sight, above. We watched Brendon edge his way up and around rubbing on a couple of obstacles as he did so. Ted followed with much the same result.

As we edged our way slowly up the rapid, we lost grip a couple of times for only an instant, but I preferred the slow approach being mindful that it would be very easy to drop the bow into the back of a large wave given that we were in such a short boat. Apart from gently nudging a couple rounded boulders with the chine, our traverse of the rapid was pain free and our excitement at the top spilled out.

This was how I remembered my first uprun of the Maruia more than 20 years before - but then I had a 308 Holden V8 and Hamilton 3 stage jet with which to power up through the white water. This time, the excitement emanated from having to be technically adept and I was really enjoying the experience in the Rivercraft 375.

In between the larger rapids we came across a number of rock gardens that we had to carefully pick our way through. In these conditions the nimbleness of the little boat was a decided advantage. All too soon we found the river beginning to open out and we left the confines of the gorge with its exciting rapids behind us. Some 45 minutes after having left Dallow's Flat we reached the weir just below the Boundary Road bridge.

I had no recollection of a weir from my first trip up the Maruia and had been confused when the other guys had mentioned it repeatedly. I had boated right up to the bridge near Springs Junction in 1984 and I was certain there was no weir then. Happily my brain had not been addled with rum afterall as Peter Brooker advised me that the weir had been constructed in 1987. One thing was certain, there was no way the weir could be boated in the flow available to us this day, although I suspect that Ted was sorely tempted.

Specifications: Rivercraft 375 Sprint
(price as reviewed $28,000.00)
LOA: 3.75m
Beam: 1.65m
Beam (Chine): 1.52m
Deadrise: 18 degrees @ transom
Construction: 5083 marine alloy
Engine: 100kW Nissan SR20, two-litre, four-cylinder, DOHC/16v
Waterjet: Scott SJ510, single stage, axial flow
Nozzle: 118mm
Towing Weight: 480kg

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