The power plant’s moved inboard on the latest offering from AMF, so Lindsay Wright went along to see how it handled a bumpy day on the Whanganui River bar.

At first glance, the new Pro-Sport 660 looks like the hundreds of other AMF vessels in use around the country. The latest Pro-Sport, fresh out of the factory, has the same striking red, white and blue graphic on the hull, the same pleasing sheerline and nuggety go-anywhere appearance.

Length on deck is 6.1m, supplemented by a short bowsprit and broad duck board at the transom to afford ease of access for divers, skiers or swimmers. Beam is a generous 2.45m.

But the big difference rests inside the compact white box hinged to the deck at the aft end of the cockpit. This boat is AMF’s first diesel stern drive and the box houses a 2.4 litre, D3-160 DP Volvo five cylinder diesel. The Volvo develops 163 crankshaft horsepower (121.5kW) at 4000 rpm, using common rail fuel injection, twin overhead camshafts, four valves per cylinder, turbocharger and aftercooler. The Electronic Vessel Control (EVC) system helps keep tabs on the onboard systems and engine readings.

Fresh water cooling, via heat exchanger, is standard and a stainless exhaust elbow takes care of corrosion problems in that area. The power reaches the water via a Duoprop stern leg swinging stainless steel props. Accessibility to filters and pumps is good after the snug fitting engine box is removed and AMF managing director, Brian Collings, says Volvo was consulted to make sure that adequate fresh air would reach the hard working little diesel through the side vents in the box and vents under the coaming aft.

So how does it line up against an outboard? According to Volvo, the D3-160 and leg tips the scales at 330kg (dry weight). For the sake of comparison, a 175 horsepower two stroke outboard weighs about 220kg and a 200hp Mercury Verado, 294kg. Because the inboard diesel is lower in the boat and a metre or so further forward, it did not require any changes to the standard Pro-Sport 660 hull, says Collings. The 220-litre fuel tank supplied with the outboard models, was reduced to 145 litres for the frugal diesel, a further weight saving, but Collings says future diesel boats will carry 180 litres in the integral underfloor tanks.

Two welded aluminium pods were added to the 660’s transom some years ago to compensate for the extra weight of the new generation four stroke outboards and these stay for the sterndrive models.

Each underfloor fuel tank is a piece of work in itself. Made from 5mm plating with baffles about 250mm apart, the tanks are fitted with an expansion chamber; filler, vent and two pickups to help reduce blowback or leakage in hot weather. The tops are made from aluminium treadplate, fully welded. After pressure testing they are welded in place as an integral part of the cockpit deck.

Any boat test should begin at the factory. Seven workers at AMF’s riverside plant in Wanganui turn out about 45 boats a year. Each boat begins with a 75mm by 10mm aluminium keel bar. The 6mm bottom plating is fully welded to each side of the bar and another 6mm wear strip fully welded over the top of that.

The topsides are of 4mm plate, with angle aluminium capping on the chines. The topside plate extends beyond the edges of the 5mm transom, Collings explains. "Our thinking there was, if a boat hits something solid in the water, it would be much less likely to rip the transom off if the side plating covered the transom edges."

After manufacture, the hulls are filled with water and the underwater buoyancy chambers pressurized with air to check for pinholes in the welding, then they are given a coating of Nyalic for protection and gloss appearance.

Nothing is left to chance with the AMF boats. The design and construction criteria come directly from Colling’s years of experience boating, fishing, diving and as rescue craft skipper across the Whanganui bar and on the wild West coast. Structural uprights are given welded doubler plates to spread the load where they meet the hull and meaty 6mm thick box section is used for rub rails and internal framing.

"It does make them a bit heavier," Collings admits, "but the idea is to make a boat that will last forever…..the sort of boat you feel safe taking your family out in." All AMF boats come with a six year recreational, or two year commercial, hull warranty and, in the 19 years they’ve been building them, Collings says there has yet to be a claim.

The Pro-Sport 660 weighs in at 2150kgs on the standard Voyager dual axle trailer and slides easily off into the coffee-coloured water of the Whanganui River. Rain in the hill country hinterland has sent a roiling freshet down the river and an incoming SW wind kicks it into a fair chop as throttle is applied. The Volvo supplies constant power from well down in the rev range with a distinct turbocharger whistle kicking in at about 2400 rpm.

The weight certainly helps but this boat eats the river chop and there’s hardly any need to use the aluminium pipe hand holds scattered liberally where they’re needed around the cockpit. Framework for the black fabric Targa top is a sturdy internal roll bar structure, added by Collings after he’d seen pictures of other boat’s hardtops and Targas flattened by the weight of water.

The tinted 6mm strengthened glass windscreen is raked at just the right angle to deflect the slipstream over the top and it feels secure sitting in the two upholstered plastic bucket seats mounted on their solid aluminium posts.

The 2.1m vinyl covered bunks in the forecabin can be fitted with an infill for overnighting and the tinted Weaver deck hatch provides plenty of light and ventilation – or access to the standard hands off Lewmar windlass. The hull sides are covered by tasteful blue marine carpet and huge bins provide ample stowage around the sides and under the bunks. The reverse side of the instrument panel has a watertight hatch and the wiring and control cables inside are neatly arranged and fastened.

You either like diesels or you don’t, I suppose, but to me the Volvo’s throaty roar is an ideal complement to the staunch hull that it’s powering…this boat was born to be diesel driven. "I suppose we could fit a petrol inboard if someone really wanted it – but why would you?" Collings pondered.

AMF design developments are driven by the people who use its boats and this shows at the helm. The console houses a rather higgledy-piggledy collection of instrumentation and EVC gauges, but the controls and wheel fall comfortably to hand and the huge carpet covered shelf above the dashboard has a handy lip for retaining all the gear that comes in handy at sea. The test boat is fitted with two M97 Hummingbird fishfinder/GPS/chartplotter displays and there’s room for heaps more electronics.

Lining up between the breakwaters, the diesel AMF sweeps past a group of surfers riding the incoming breakers, before soaring over the first steep brown wave. The boat falls off the hollow back of the swell with a resounding thump and a wall of water shoots out either side but it’s all pretty undramatic.

The lumpy 1.5m ground swell is just enough to make it uncomfortable as we run parallel to the beach at the boat’s chosen 3000 rpm. This is where the Pro-Sport is happiest; Volvo fuel graphs show that it should be using about 15l/ph at those revs and Collings says that it’s doing about 28 mph (24.3 kts/ 45 km/h). The GPS isn’t working due to an antenna glitch and my handheld is in a desk draw at home, so we can’t verify this, but he says top speed is 40 mph (34.8kts/ 64.3 km/h) at 3800 rpm. Fuel consumption at full revs is about 20 l/ph….trolling at 1800 rpm uses about 6l/ph.

Collings suggests we play in the waves but they’re dumping too close inshore for comfort so we try some high speed runs with the swell on the beam, straight into it and from dead astern. Very little spray spatters the wind screen and the Pro-Sport stays remarkably dry though a sheepish Collings admits that he did manage to ship a solid dollop of seawater over the top of the windscreen due to what he calls "turbocharger lag" on the new engine while out trialling the boat earlier.

An electric pump sucks water out of the engine box bilge and two separate sumps either side are also provided with pumps to clear any water that gets on board.

A waterproof hatch to port provides secure and accessible stowage for house and starting batteries and individual battery isolating switches are close at hand under the engine box, along with an easily visible Racor fuel filter/water trap.

AMF builders, and most of their owners, are apt to dangle a line in the water at any opportunity and this is what the Pro-Sport is geared for. The wide gunwale gives plenty of room to perch but there’s also secure toe space underneath and a comfortable rounded edge to lean against while cranking in a big ‘un. There are four rod holders set into the gunwale and another six are set to fish from the standard rocket launcher. The bait boards have a canny ski pole incorporated into them for multi skilled boat folk.

One readily discernible difference over an outboard is that this boat stops on a pinhead when the engine is put astern and those duoprops begin to backwater. Shifting is smooth and positive and the Volvo revs freely throughout the range.

There’s something reassuring about having all the aluminium between yourself and the sloppy brown sea off Wanganui, but Collings explains that a lot of the boat’s ride characteristics come from the design. "There’s an 18.5 degree vee at the transom," he says, "and about 27 degrees under where we’re standing (at the helm seat). You don’t get any pounding or drama. I really like the ride characteristics of catamarans and this boat is about as close as you’ll get to that." The hull form keeps the boat level as she comes out of the hole and the transition to planning trim is barely discernible once the duoprop’s two big stainless steel wheels spin into action.

The Pro-Sport responded to trim changes throughout the speed range and also ran reasonably flat across a steep beam sea.

Back in the river, we tried a few full throttle turns and the Pro-Sport tackled the challenge without any drama, break out or reverse roll. It’s almost like being in a catamaran – the G Forces are all lateral, the hull holds its grip on the water and the boat just turns.

The Pro-Sport diesel would be a great passage maker. One of the 68 optional extras is a long range fuel tank, and other AMFs have frequently made the 97 nautical mile (179.6 km) run from Wanganui to the Marlborough Sounds.

"Yeah, she’ll whip down there no problem at all…just about anywhere you want to go," says Collings confidently.

Specifications AMF Pro-Sport 660 Diesel Sterndrive (Price as tested $123,000)

LOA 6.6m
Length on deck 6.1m
Beam 2.45m
Bottom Plates 6mm
Transom 5mm
Sides 4mm
Shelf and hardtop 3mm
Fuel 180 litres underfloor
Engine D3-160 Volvo diesel 163 hp @ 4000 rpm.
Drive Duoprop stern leg
Steering Hydraulic
Weight 2150kg on trailer with full fuel.

Keep up to date with news from Trade-A-boat or like us on Facebook!