Argo 600

A dichotomy exists in the world of jetboat design. On one hand there are parameters governing boats used in fast-flowing, usually shallow water; and on the other, parameters for boats used in deep water and coastal sea conditions. The Argo 600, writes Paul Smith, fits both.

Argo 600
Argo 600
Over the years designers have attempted to "bridge the gap" by creating a boat with the broadest possible appeal. Given the lower propulsive efficiencies of early jet boats compared with contemporary technology, hulls intended for river boating had minimal deadrise (up to 10 degrees at the transom) and wide flat bottom sections (usually monohedron) to provide plenty of lift at low speed. Consequently, they exhibit a harsh ride in choppy water and tend to slide around and through corners.

The development of "deep vee" hulls for planing "blue water" powerboats resulted in improved rough water ride and greater directional ability. The trade-off, particularly in a jetboat, is that deep vee hulls draw more water, especially at low to medium speeds. However, as propulsive efficiencies improved, boat speeds increased which led to a demand for better handling hulls.

Over the last decade there has been a proliferation of variable deadrise monohulls which have additional buoyancy and stability courtesy of pontoons from the bow down each of the topsides – either in solid alloy construction, inflatable bags or closed cell foam.

The combination of variable deadrise hulls with solid alloy pontoons has not been widely accepted by the jet boating fraternity for river use, but a few manufacturers of these boats have installed waterjets for general deep water work while retaining the advantages of shallow draught and positive handling in surf and bar conditions.

Napier-based engineering company Argonautica Limited recently introduced its Argo 600 to the market, and it encompasses many of the design features discussed – variable deadrise monohull, solid alloy pontoons and waterjet propelled. It is Argonautica's answer to the quest for a multipurpose boat which can navigate certain inland waterways as well as being equally at home in the "blue water".

Construction & Design
Constructed entirely of marine grade aluminium alloy the Argo 600's delta keel section is folded from 10mm plate while the outer bottoms are 6mm. The topsides, for'cabin and transom are all 4mm, while the pontoons are 3mm.

The hull is reinforced with four, full-length alloy bearers while rigidity athwartships is enhanced with three bulkheads – one in front of the engine, another across the for'cabin access and a for'd bulkhead in the front of the cabin which also forms the anchor locker.

The cockpit sole is fully welded to the main bearers, forming sealed chambers either side which extend from the transom for'd to the middle bulkhead. Each of the pontoons has three sealed chambers. A 200-litre fuel tank is located under the cockpit floor amidships between the engine bearers just for'd of the engine.

Engineering on the Argo 600 appears to be to a high standard, with the heavy duty construction almost to the point of overkill. This boat is no lightweight and should be capable of withstanding severe treatment and/or conditions.

Argonautica commissioned Paul Vickers from Primal Design in Hamilton to draw up the boat. It also sought technical input from Scott Jet Ltd in Geraldine in respect of optimizing the design and construction for waterjet propulsion.

The general lines of the Argo 600 are pleasing and while pontoon boats are not usually described as pretty, the Argo 600 deserves better than just being described as functional. The delta keel tapers for'd to a vee bottom with the deadrise decreasing from 28 degrees back to 22 degrees when measured at the transom.

There are two planing strakes either side of the delta keel. These extend from the transom for'd to about half way along the length of the keel. The strakes are designed to provide lift and lateral adhesion, while the bow sections remain clean to smooth out the ride.

The chines are heavily turned down and are separate to the pontoons which sit 50mm above the chines at the transom. When the boat is at rest the pontoons sit nicely on the water surface to provide stability but are clear of the water when the boat is planing.

There are air intakes either side of the cabin that direct fresh air via 100mm tubes to the enclosed engine compartment.

At the bow, the Argo 600 has a short bowsprit with a stainless steel fairlead. Access to the bow for anchoring duties is via a Weaver hatch in the cabin, although a Maxwell helm actuated capstan is due to be fitted. The cabin itself has two full length vee berths with storage under. For'd there is a raised platform which assists in hatch access, but this could also be used for mounting a marine toilet facility if required. The cabin is fully lined and given the absence of a full bulkhead to port, access is very easy.

The bi-level helmstation is located against the cabin bulkhead to starboard. Across the top is the "Faria" engine instrumentation encompassing the tachometer, gauges for oil pressure, engine coolant temperature, volts and fuel. Below the instruments is a parcel shelf with upstands and beneath this the steering consol housing flush mounted Eagle Intellimap GPS/Plotter and Eagle Seafinder sounder and fishfinder.

Passenger accommodation is well provided for in the Argo 600. There are two, adjustable pedestal-mounted bucket seats in front, with benches and padded backrests attached to the inside coaming. The flat-topped engine cover also has a removable upholstered panel on top that can accommodate up to another four bodies, enabling the Argo 600 to seat up to 10 persons.

The cockpit coamings each have two stainless steel rod holders and a solid stainless steel bollard. The flat transom has a non-slip strip across the top and although there is no provision for a transom door as such, access to the boarding platform is also easy.

The platform itself deserves special mention in that it is nicely blended into the rear of the hull, but more importantly, is of such a size as to be extremely practical. At 1.5 metres across the beam of the boat and some 600mm deep, the platform has extensive non-slip panels as well as a SoPac hatch for access to the waterjet, driveshaft, hydraulic pump, sandtrap etc.

Power & Propulsion
Even though the deep vee hull form is optimized for rough water use, the rugged construction and waterjet propulsion allows the Argo 600 to operate on many of the inland waterways accessible by jet boat. Furthermore, waterjet propulsion provides a greater margin for error when traversing tidal river bars in addition to superior propulsive efficiency in aerated water.

The 212.5mm diameter two-stage Scott Jet provides excellent acceleration and good load carrying capability as well as high resistance to cavitation. The "Salt Water" version of the jet features cast stainless steel impellers and numerous zinc anodes.

Of particular importance to this application was the adjustable trim nozzle option which enables the boat's fore and aft trim attitude to be tailored to suit prevailing water conditions or to enhance acceleration of the boat on to the plane with a heavy payload.

Although the Scott Jet trim nozzle and the forward/reverse control actuation is usually electric, the designers have opted for an electric over hydraulic actuation system for both functions which proved exceptionally easy and convenient to use.

Big waterjets require plenty of grunt to drive them, and to deliver the desired performance levels, a large capacity petrol V8 engine was appropriate. Wasp Marine, a marine engine package designer and supplier based at Lake Tekapo, recently developed a new package based on the Generation 3 Chevrolet 6.0 litre LQ9 engine.

While similar to the all alloy 5.7 litre LS1 engine, the LQ9 has a cast iron cylinder block, alloy cylinder heads and other castings, plus a state of the art plastic inlet manifold. Engine management utilizes every OEM engine sensor and is governed by a Motec M800 ECU resulting in smooth, efficient power delivery.

The engine produces 392hp at 5245rpm and peak torque of 426lb-ft is developed at quite a high 4400rpm. However, the flat torque curve shows that more than 360lb-ft of torque is available from 2000rpm. The whole marinised package weighs 285kg thereby providing a pretty fair power to weight ratio.

The engine operates on a closed circuit heat exchanger cooling system with anti corrosion inhibitors.

Performance & Handling
We only had a couple of hours to play with the Argo 600 so we elected to forego braided river testing in favour of evaluating the boat's salt water performance. We were able to conduct our speed trials on Brooklands Lagoon which, although being salt water, was glassy calm.

I suspect the Argo 600 would record fractionally higher speeds with a little chop on the water surface to "release" the hull and the speeds recorded are also free of any current influence. The boat had three passengers aboard, and carried approximately 100 litres of fuel. The nozzle trim was optimized to ensure the best boat speed at each engine speed interval. Since the boat required a minimum of 3000rpm to make the transition to plane from displacement, but would comfortably hold a clean plane at 3000rpm, we took this as our base-line measurement.

Engine Speed Boat Speed
3000rpm 14.5 knots
3500rpm 27 knots
4000rpm 33 knots
4600rpm (WOT) 40.5 knots

We noted from the power curve that at Wide Open Throttle, the waterjet was absorbing just over 360hp.

On heading out across the Waimakariri river bar we passed a number of jet-skiers playing in the swells, powering their machines skywards off cresting waves. In the Argo 600 we took a more conservative approach picking our way out with the tacho showing 3000rpm. The pontoons certainly provided plenty of lift for'd and deflected the water down and away from the boat. Our traverse proved safe and predictably "boring" compared to the jet-skiers who were obviously having a ball.

Once out into Pegasus Bay where a moderate swell was running against a strengthening wind out of the southwest, the Argo 600 gave up a comparatively smooth ride. Although a little windblown spray was picked up across the windscreen, it was nothing to get upset about. We found the boat performed best in these conditions with the nozzle in the full up position, keeping the bow up and most of the spray behind us.

Similarly, in a following seaway, with the nozzle up, the boat surfed down the back of the swells tracking straight and true showing no tendency to broach or knife off line. We set our course back across the bar and the Argo 600's good manners inspired confidence as we powered up the back of a large cresting wave riding it in until it dissipated into a boiling, frothing mass. A touch more throttle and we powered through on to the back of the next wave with no sign of cavitation from the Scott Jet and plenty of power in reserve.

Back in the calm water of the river estuary we noticed the boat's tendency to bank through a hard turn in either direction in typical deep vee fashion, and occasionally, air could be ingested into the jet. This could be mitigated with judicious use of the trim control. From a standing start, the Argo 600 was punched up on to the plane by the LQ9/Scott Jet combination demonstrating plenty of acceleration for towing skiers, water toys, wakeboards and such like.

The Argo 600 is certainly a powerfully-constructed and nicely-finished boat. The example in this review is the first off the production line and had just nine hours on the hour clock. It was kitted out for comfortable recreational boating but could easily be specified in more basic form as a hard out fishing machine with fewer seats, a rocket launcher, bimini cover and unlined cockpit sole.

The boat was supplied on a galvanized steel, multi roller, tandem axle braked trailer which made launching and retrieval a breeze. At 1250kg dry (boat only) and around 1800kg trailerable weight, the Argo 600 is a substantial six metre boat. On the water it feels very much like a solid GRP boat rather than a "tinnie" and that's a good thing. Standout features for me are the large boarding platform and the smooth performance of the engine and waterjet.

Is it all things to all people? Probably not, but the Argo 600 certainly has plenty of versatility and capability. Argonautica has made a great job of this its first production boat. I think it deserves commercial success.

Argo 600 Specifications
($100,000 inc. GST as reviewed)
Hull: Deep-vee mono with pontoons
Construction: Marine grade alloy
LOA: 6.0m
Beam: 2.45m
Deadrise: Variable, 22 degrees @ transom
Engine: Wasp Marine Chevrolet 6.0 litreV8, multipoint EFI
Output: 392hp @ 5200rpm
Waterjet: Scott Jet, 8.5", 2 stage 'Salt Water' Series
Price: From $84,000 inc. GST (basic fisherman's model)

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