Maxwell 430 and 151A Jet boat

A pair of jet boats manufactured by Methven's Maxwell Boats & Motors combines rugged construction with impressive speed and agility. Paul Smith used the rivers and gorges of the South Island to investigate their performance.

Maxwell 430 and 151A Jet boat
Maxwell 430 and 151A Jet boat
The Maxwell 430 and 151A hulls are fabricated from marine grade aluminium alloy. The keel plate is formed from 10mm 5083 alloy, though either 8mm or 12 mm thicknesses can be specified depending upon the intended use of the boat. The outer bottoms of the hull(s) is from 5mm as are the for'd bow sections, while the topsides are from 2.5mm alloy and the transom 3mm.

Two full-length engine bearers (folded from 6mm alloy) are welded to the hull. Two longitudinal runners located between the engine bearers and the chines provide further bracing and floorboard support, while a stiffener is located athwartships for'd.

The Maxwell 430 and 151A utilise a moulded GRP topdeck bonded to the alloy hull. A tinted Perspex windscreen with powder-coated handrail completes the standard hull/deck/screen assembly. The cockpit sole is painted plywood that is screwed through to the bearers and, in the case of each of the boats in this review, has been carpeted over.

For many years, jet boat hull design centred on a monohedron hull form: where the deadrise remains constant over the length of the keel line. In recent years, variable deadrise hull forms have become popular. A deeper deadrise for'd tapers back to a lesser deadrise at the transom in an effort to provide a softer ride in choppy water and to provide better directional capability, by encouraging the boat steer from a point further for'd on the keel line.

In reality, the best compromise is where the deadrise remains constant over a distance of around half the overall boat length for'd of the transom before increasing a little at the bow sections. This is the strategy adopted by Brian Maxwell in his hulls: a moderate deadrise of 17 degrees at the transom is carried for'd 2.4m before deepening to 20 degrees.

A delta keel section provides lift aft and locates the waterjet intake and grille. Either side of the keel is three planing strakes to provide additional lift and lateral adhesion. The Maxwell 151A is the larger of the two boats (LOA 4.6m and 1.78m beam). The 430 shares the same hull profile, but is restricted in length to 4.35m and beam by 100mm. Most of the length has been taken from the bow area, resulting in a considerably shorter foredeck with a loss of only 100mm in the overall length of the cockpit.

The layouts of both the 151A and 430 are similar and reflect the status quo in the majority of recreational jet boats. Two front bucket seats are mounted on alloy bases with dry storage under. In keeping with standard jet boat practice, the helm is mounted to port. Behind the front bucket seats is a forward facing extended bucket in the 430, which provides sufficient bum space for two adults or three smaller children at a pinch, while still allowing access to the secure storage lockers either side of the engine compartment.

The 151A utilises a full width extended bucket rear seat, which can easily accommodate three adults. The rear seats in each boat sit atop the alloy fuel tank. The 151A has a fully enclosed engine compartment with walk around access right to the rear of the cockpit - better for fishing and/or waterskiing retrieval.

The helms of both models are the same, with the instrumentation housed in a curving binnacle directly in front of the driver. The steering wheel and boss is centrally mounted, while the forward/reverse controller is mounted in the port coaming.

I found the central instruments were obscured by the steering wheel in both boats, and the flush-mounted "Sportline" wheel in the 430 was mounted too low for comfort for my taller-than-average frame. The wheel in the 151A, however, was mounted on an extended column and at a comfortable angle, but it still obscured those central and important engine coolant temperature and oil pressure gauges.

A boarding step is incorporated into the dashboard and a spacious glove compartment occupies the dash immediately ahead of the front passenger. In both of these boats the throttles are actuated by the progressive and smooth Morse foot pedals.

The cockpits in each boat were fully lined and the soles were clothed in marine carpet. The 430 also had a full-length side pocket along each side of the cockpit for storage of paddles, weed rakes and suchlike. The upholstery in each boat was nicely finished and complemented the colour schemes of the boats nicely.

Power and propulsion
The Maxwell 430 had been fitted with a four-litre Toyota/Lexus V8 engine. Its all-alloy construction and contemporary technical specification (four cam, 32-valve) combined with electronic fuel and ignition management appeals to many.

The engine was coupled to a Hamilton 773 waterjet - a three-stage axial flow pump with a great reputation for durability and aerated water performance. Although Hamilton Jet has long since discontinued production of the 770 series, a number of companies in the US continue to manufacture clones of this solid workhorse.

The impellers in the 773 waterjet have been re-pitched to suit the power and torque characteristics of the Toyota V8, with maximum engine speed restricted to 4700rpm (some 700 short of where maximum rated engine power of 260hp is delivered). Nevertheless, performance of is more than sufficient for general-purpose jet boating, while fuel economy at cruising speeds is excellent.

The Maxwell 151A is fitted with a Maxwell remanufactured 350ci (5.7-litre) Chevrolet V8 engine. It has alloy cylinder heads and a camshaft specification to drive the Hamilton Jet HJ212 waterjet fitted with a 2.4kW "Turbo" style impeller. The HJ212 seems to deliver its best performance up to 4500rpm and the engine in the Maxwell 151A turned the jet at 4200rpm at Wide Open Throttle where the jet was absorbing approximately 250hp.

Performance and handling
We drove the 430 on the lower reaches of the Waimakariri River. The weather was fine and calm and the river low and clear - perfect conditions for jet boating. I liked the solid feel of the boat on the water - there was little in the way of water noise and no irritating squeaks or rattles when the boats passed across turbulent water.

The 430 rides a little flat for my liking with the inside strakes cutting water just ahead of the driver's position. While this set up is good for slower speed cruising, especially in shallow braided water, I feel it could suffer from bow steer in aerated white water.

I would hasten to add, however, that while the boat responded instantly to input from the helm almost to the point of being a little twitchy, it did not feel in any way uncontrollable. The engine responded instantly to the throttle and the three-stage jet provided plenty of grip.

One of the most appealing characteristics of the 430 is the way it holds a clean plane at 2400rpm with 22kph showing on the GPS. This makes the boat ideal for exploring tight, twisting, and shallow water. As the figures in the table below confirm, the 430/Toyota V8/773 combination has a reasonable turn of speed, too.

By way of comparison, we also sampled a 430, which was powered by a 4.3-litre Chevrolet V6 engine coupled to a Scott Jet 7.5" diameter two-stage pump. This boat was set up for hunting and fishing trips and was sparse in terms of its fitout.

Although it was noticeably quicker off the mark and more responsive to manoeuvres in the mid-speed range being a bit lighter than the review boat, its top speed of 80kph @ 5000rpm downstream is significantly less than the 773 powered boat, which was turning at 4700rpm at Wide Open Throttle.

Maxwell 430/Toyota V8/773 Upstream (kph) Downstream (kph)
3000rpm 41 50
3500rpm 53 62
4000rpm 65 73
4500rpm 72 81
WOT (4700rpm) 75 86

Maxwell 151A
Our acquaintance with the Maxwell 151A took place at the Rakaia Gorge. River conditions were good, and the boat offered the same solid feel on the water, and a much more comfortable driving position for my long frame. The longer foredeck also gives a more balanced look to the vessel. This balance extends to the ride - the 151A feels as though it slips through the water with more poise than its smaller sibling.

Both boats have great directional ability and neither could be induced to hop or skip even under severe provocation. The HJ212 waterjet is the defining factor separating these two craft. Not only is the 151A considerably quicker off the mark, it is significantly quieter in operation and provides greater grip in the turns holding the boat down on to the water.

After being favourably impressed by the ability of the 430 to hold plane at just 22kph, I was absolutely blown away by the 151A's ability to plane cleanly at just 2000rpm and 17.7kph. In fact, the overwhelming characteristic of the Maxwell 151A's performance was its long-legged feel, making it a superlative cruising machine. The performance figures in the table below should be read in the knowledge that the higher altitude of the Rakaia Gorge has a slightly negative impact on the performance of naturally-aspirated engines.

Maxwell 151A/350 Chev V8 / 212 Upstream (kph) Downstream (kph)
2500rpm 37 54
3000rpm 49.5 63.5
3500rpm 60 74
4000rpm 70 83
WOT (4200rpm) 80 91

When Maxwell Boats & Motors is commissioned to supply a turnkey jet boat, almost every facet of the build is completed in its own workshop, with the noticeable exception of the upholstery. The review boats were supplied on single axle, unbraked, galvanised steel trailers that are tailored to fit each hull. At around $45k for the 151A as reviewed and $40k for the 430 as reviewed, these boats are well built, reasonably priced and offer more than acceptable performance levels and handling ability.

Special thanks to Jeff Parker (151A) and Stuart Russell (430) for making their boats available for this review.

SPECIFICATIONS: Maxwell 430 & 151A Jet Boats
Hull Maxwell 430 Maxwell 151A
Construction Alloy Alloy
Design Brian Maxwell Brian Maxwell
LOA 4350mm 4600mm
Beam O/A 1680mm 1780mm
Beam - Chine 1460mm 1560mm
Deadrise @ transom 17 deg 17 deg
Weight (bare hull only) 225kg 235kg
Engines Toyota 4-litre V8 Chevrolet 5.7 V8
Waterjets Hamilton 773 Hamilton HJ212
Price (as reviewed) $40,000 inc. GST $45,000 inc. GST

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