This Mangawhai-based Senator SL1170 is the largest Senator pontoon boat to date and the first recreational vessel in the world to be fitted with Sealegs’ heavy-duty SL100 all-wheel-drive amphibious system.
Neville, the new Senator’s owner, lives beside the Mangawhai estuary and enjoys riparian access from his front lawn. Neville and partner Anne love fishing, so that’s what this vessel will be used for, spending time around the Hen and Chickens and Mokohinau Islands. Usually they’ll take day trips, but the boat is fully-kitted for overnight expeditions and longer.
Motorsport enthusiast Neville is a bit of a speed merchant. It’s no surprise, then, that his new boat has a pair of Yamaha 350hp V8 outboards bolted to the transom – had they been available when the boat was being built, he says may well have opted for Yamaha’s new 425hp engines. As it is, the smaller V8s give the SL1170 a top speed of almost 40 knots. During initial testing out of Napier, the boat touched 39 knots with seven people aboard.
That’s an impressive number when you consider the hull carries the weight of another engine, 100 litres of hydraulic oil, hydraulic pumps, rams, wheels and legs, as well as 756 litres of fuel – plus all the usual equipment such a highly-specced vessel comes with. Add to the mix heavy-duty construction and the extra structure required to support terrestrial operation, and it’s not surprising the boat weighs well over six tonnes.
To see this ‘amphibious craft,’ as Sealegs likes to term vessels equipped with its patented technology, parked up on Neville’s front lawn is to be impressed. It is big, and far taller standing on its legs than it would be sitting in the water or on a trailer. It’s only when you stand beside it that you get a true idea of its scale.
Its sheer size poses some problems, like getting in and out of it and seeing where you are driving. While the SL1170 can be made to ‘kneel’ by raising its hydraulic ‘sea legs’ until the hull rests on the ground, it’s still a bit of a climb to get aboard. Neville sometimes loads and unloads the vessel by driving it alongside the raised deck in front of his house, but the clever folk at Senator have come up with a more practical solution for day-to-day use.
A door cut into the starboard side hinges down and a pull-out ladder extends almost to the ground, so there’s no need to kneel the vessel. Raising and lowering the door is simple, using an ingenious system of cables and jam-cleats.
The SL1170 was an important project for Senator Boats, explained Grant Simmonds, managing director of the Napier-based boat builder: “Not only is this the biggest pontoon vessel we have built so far [Senator Boats custom builds larger conventional monohull designs], it’s also our first amphibious vessel, so there was quite a lot to learn.”
The team at Senator Boats worked closely with Neville and Sealegs’ engineers to ensure the new vessel met the exacting manufacturing specification for the SL100 amphibious system. The technology is still very new, with only two other SL100-equipped vessels in service so far, both commercial operations in Australia (plus a military vessel in the US fitted with the prototype System 100), though there are more in build.
“The engineering was an interesting challenge because the boat needed a lot of extra structure to support its weight on land. Cutting a door in the boat’s side, right through the rigid pontoon structure, meant adding further strengthening to compensate, and we also wanted the wheels to stow completely clear of the water when not in use,” said Grant.
This is a heavily-built boat. The hull bottom and transom are constructed from 8mm aluminium plate with the rest of the vessel a mix of 6mm, 5mm and 4mm plate. Compared to a conventional Senator pontoon boat, the SL1170 has extra longitudinal runners with shorter spaces between crossmembers – “we went bigger on everything,” says Grant.
Perhaps the biggest challenge for both Senator and Sealegs was Neville’s insistence on a flush cockpit sole – no engine box. Sealegs’ SL100 uses a petrol or diesel engine, in this case a two-litre, four-cylinder Toyota-derived petrol unit, to drive the hydraulics for terrestrial propulsion. It is supplied as a unit on a frame, complete with engine box, ready to drop into the boat and bolt down.
The decision to mount the engine under the floor necessitated some clever thinking from both parties, but especially the engineering brains at Senator.
Finding room for the engine and its associated hydraulics was only part of the challenge: the engine had to breathe and run cool enough at operating speeds. Roger Young and Dean Harrison at Senator Boats, working with Sealegs, solved all the engineering challenges, using electric fans to force ducted air into the engine compartment and over the radiator and dumping the hot air through transom vents. It works a treat, with the engine running at an optimum temperature of 80-degrees C.
The lessons learned from this build will certainly help Sealegs with future SL100 installations.
The upshot of an underfloor installation is a massive, uncompromised SeaDek-covered cockpit. Fishing facilities include two baits stations, one either side of the cockpit (four rod holders apiece), a live bait tank in the middle of the transom, 12V outlets in the corners, an electric pot-hauler on the starboard side aft. Washdowns either side of the cockpit keep things clean.
The SL1170’s transom lockers are given over to hydraulic hoses, pipes, batteries and switchboards, most of them to do with the AWD system. The gas locker is under the two-person bench seat against the shower bulkhead on the port side, with another seat and outside sink unit against the cabin bulkhead on the starboard side.
A large separate shower and head opens off the cockpit. The toilet is raised off the floor slightly so it’s at a more comfortable height and the interior is the only part of the boat to be painted – the rest is vinyl wrapped.
Rollo’s Marine in Hamilton completed the boat’s fit-out, including electronics, Narva cockpit floodlights, foredeck light bars and LED lighting throughout. The MFD is Garmin, a 16-inch unit with sophisticated sonar modules, two transducers and Radar, as well as the ability to display camera feeds.
Trim tabs are Zipwake Interceptors, which operate manually or automatically, and the sound system is Fusion. A Maxwell windlass deploys the Sarca anchor with anchor locker access behind the lifejacket locker in the fore-cabin bulkhead.
Powerful bilge pumps, by Bilge Systems Ltd in Napier, are specific to this vessel. Bilge Systems’ pumps are compact and easy to install into tight areas. As here, their electric drive motor can be be located away from the bilge area above the waterline, eliminating the number-one cause of pump failure – drowned motors.
The SL1170 has a fully-enclosed cabin with all the comforts of a launch, including a comprehensive galley. Two sliding side windows per side feature tinted glass and the three-pane, raked windscreen has three wipers with washers. Ceiling vents, including for the shower compartment, aid airflow.
The lined cabin impresses with its size and headroom; the ceiling is well-served by hand rails. A simple teak table can accommodate four people: two in the bench seat against the bulkhead, one on the swing-out stool and one in the luxury helm seat on the port side, which swivels around to address the table.
The forward cabin is equally spacious and similarly endowed with headroom and handholds. It’s configured with two comfortable extra-wide v-berths (no infill squab). The only people likely to stay in the boat overnight are Neville and Anne. At their age, says Neville, they can manage without a double berth for a night or two.
Describing how a Sealegs-equipped vessel performs is in two parts: on land and at sea.
On land, the SL1170 is governed to a maximum speed of 9kph. Its operation will be familiar to anyone who has used a Sealegs amphibian before, including the simple engine and hydraulic controls, though they are particularly well-laid out in this vessel.
What most strikes you from inside the cabin is your height above the ground. At Neville’s place you are staring into the trees – from the helm, it’s impossible to see the ground immediately in front of you. Consequently, the wide angle, day-night bow camera is essential. The picture is displayed on the 16-inch Garmin MFD, without which, safely operating the SL1170 on land would be impossible.
This is a long vessel, so the turning circle is wide. Fortunately, so is Neville’s front lawn. Driving the boat down into the estuary was as easy as you like and Neville says he can use the boat at any state of the tide.
Once afloat and with the wheels stowed in the up position, the SL1170 is like any other large cabin boat to operate. The controls are all electronic and this vessel features SeaStar’s Optimus EPS (electronic power steering) adjustable electronic helm for sportscar-type steering.
I particularly like the vessel’s wrap-around helm console. It is Neville’s design and has a distinct automotive feel. Everything falls very nicely to hand, the bank of rocker switches on the port side being a good example.
“I didn’t want to be hunting around for anything, so everything’s easy to see and easy to reach,” he says.
Neville was happy to throw the big Senator around once we cleared Mangawhai Heads, carving high-speed turns and showing off the big Yamahas’ torque in the hole shots. There was plenty of wind and the sea became lumpier the further out we went, but the Senator hardly noticed the bumps. Like Senator’s other pontoon boats, the SL1170 has a soft ride – Neville’s previous boat was also Senator and its ride quality was one of the main reasons he went back to the company for his new boat.
As already mentioned, top-end performance is a respectable – we saw 37 knots fully-loaded – but when Neville heads out to the Mokes, a more realistic cruising speed is likely to be 25 knots. At that speed, with the V8s spinning at 4,500rpm and the doors closed, it’s quiet and comfortable inside the cabin.
From the helm, it’s clear this is a big, heavy boat: it certainly feels substantial as it punches through the waves. Since it carries a lot of its weight low down – engine and hydrapak, as well as fuel and holding tanks are located below floor level – it handles well in a seaway and is very stable at rest, too. The helm seat with its fold-down armrests and bolster delivers comfort and security.
Neville’s SL1170 is a great example of what two innovative New Zealand companies can achieve. Sealegs’ new SL100 system is an impressive piece of kit, suitable for vessels up to 7.5 tonnes, and the feature-packed 12m Senator it is driving is equally impressive.
With this SL1170 Neville and Anne should enjoy many years fishing the waters of Bream Bay and beyond, while for Senator and Sealegs this could be the first of many similar vessels.