- Low centre of gravity
- Excellent fuel economy
- Quiet runner
- Layout works well for fishing and diving
- Performs well in rough conditions
- Lock-up cabin
It’s been more than 10 years since Surtees Boats last offered an inboard sterndrive option, so Undercover is quite a big deal for the Whakatane boatbuilder, as well as for Mercury New Zealand, who supplied the 230hp Mercruiser TDi.
Undercover’s owner is Nick Gill, a local builder, who turned to his brother-in-law Mark Cosgrove, owner of Mercury Bay Marine, when it came to setting up his custom Surtees 750 Game Fisher. Mark owns a Surtees 6.1 Bar Crusher.
Nick hadn’t owned a Surtees boat before, but he’d liked what he found while fishing and diving from mates’ boats. Initially he was thinking about something in the 7m range, but once he began putting his wish list together, decided the bigger 750 would better suit his needs. But he was adamant it should diesel powered…
Although Mercury Bay Marine is not a Surtees dealer, Mark is very familiar with the brand, and as a Mercury dealer has plenty of experience with Mercury’s Mercruiser TDi engines. Mark was happy to manage the project, working closely with Surtees and Grant Allen, Sales Application Manager at Mercury.
Fitting a sterndrive necessitated a total re-design of the 750’s transom, plus a whole lot of extra structure under the floor, including 10mm plate girders and dedicated engine bearers. The hull is 6mm thick and the sides and decks are 4mm.
This boat was custom-built, but the lessons learned will carry over to subsequent sterndrive installations, of which Surtees and Mercury hope there will be many. The engine box will also accept V6 petrol engines.
Nick not only sought Mark’s advice when choosing his dream boat, he relied on his technical skills to fit the engine and engineer the vessel’s various systems. Mark also has experience installing Mercruiser TDi sterndrives for manufacturers like Stabicraft.
When we joined the boat in Whitianga, Grant had just finished final engine checks and noted that the temperature inside the engine box on a very hot January day was only two degrees higher than ambient, indicating the engine was getting plenty of fresh air.
Getting the air flow right was just one of the challenges for the Surtees team; they’ve done well to design the ventilation so that sufficient air gets into and out of the engine box, without allowing water ingress.
The two-tier engine box is a modest size too, so it’s easy to work around with good transom access either side. The front section makes a comfortable seat or handy work surface with built-in rod storage; neoprene Deck Grip, also glued to the coamings, softens its aluminium surfaces and provides grip in the wet.
The sterndrive’s installation is tidy with excellent access to engine service points at the front and the ECU tucked safely away out of the elements in a dry locker against the cabin bulkhead on the starboard side.
Batteries – engine and house – are stored in a transom locker which is also a ventilation channel for the engine box. The transom on the port side features a live bait tank and a drop-in door for access to the full-width swim platform and T-bar-style boarding ladder. A high-volume 3700gph bilge pump in a sump drains any water from the cockpit.
Grant and Mark are completely happy with the way the Mercruiser TDi performs: Nick had already clocked up 50 hours, going out 16 times in a month, so any teething issues were well-sorted by the time we stepped aboard.
Cheap to run
Undercover’s role includes boating with a young family, fishing and diving “with the boys” and game fishing – Nick is a keen to put a marlin or two aboard his new boat this season, so she had to be offshore-capable.
The boat carries 300 litres of diesel in her underfloor fuel tank and initial testing indicates she uses around 100 litres in a full day of game fishing, including long runs to and from the fishing grounds.
“She’s very efficient and cheap to run,” says Nick, who wanted diesel power for that reason, despite a higher upfront cost compared to petrol alternatives. He also reckons the inboard lowers the vessel’s centre of gravity, complementing the 750’s already impressive handling.
“l’ve had her out in the rough a couple of times now, and she just punches straight through.”
Nick keeps the boat in a Sea Pen outside his home on Whitianga Waterways, though he also has a trailer. Undercover has a lock-up cabin for security, not only on the Waterways, but also for road trips when the crew might spend the night aboard the trailered boat.
Undercover is very well-equipped, from the usual range of Surtees options – removable rod rack and dive bottle storage, a retractable canvas cockpit awning for shade, transom bait station, clip-on cockpit seating, washdown and a freshwater cockpit shower – to LED lighting, a Marinco spotlight and Lone Star drum winch on the bow.
Nick has fitted an inverter: the cooker is electric, there is a 100-litre electric hot water cylinder and the fridge runs off 12 or 240 volts. A pull-out pantry is a cool feature.
The electronics are high spec as well and include radar and a top-shelf Panoptix 1kW single frequency transducer for the fishfinder module. A bracket-mounted 15-inch Garmin GPS Map XSV multi-function display takes pride of place on the dashboard, with the usual suite of Mercury Smartcraft gauges, assorted switch panels and controls for the anchor winch, spotlight and Bennett trim tabs filling the helm console.
A Garmin VHF radio and Fusion stereo head unit are flush-mounted in the overhead console; speakers are situated inside hardtop and in the cockpit, with the Fusion sub-woofer mounted in the helm seat base. There are 12V and USB outlets on the dashboard.
Taking in the sights
It was a hot day in Whitianga, so we were grateful to be underway, making a decent sort of run down the coast and taking in some of Coromandel’s stunning scenery. First stop was Cathedral Cove, which was alive with tourists, tour boats and snorkellers enjoying the clear water and wonderful beaches.
Hardtops are great when the weather cuts up, but it can be pretty warm inside on a sunny day. Fortunately, the Surtees 750 Game Fisher has plenty of ventilation options, including sliding side windows, cavity windows in the rear bulkhead, bi-fold rear doors and an opening front windscreen. Like other Surtees models, the 750 has a huge forward hatch.
We cruised along at 26 knots, flying over a residual swell with some wind chop on top. Engine noise was well-suppressed and barely noticeable inside the hardtop with the Sea Mac doors and windows closed and the Mercruiser TDi provides the 750 with some serious urge and great tractability through the rev range. Top speed is around 34 knots.
There was enough ripple on the water to occasionally send salt spray over the cabin – with fine entries and deep vee hulls, Surtees boats ride very nicely, but can be wet in some conditions. Exalto wipers kept the windscreens clear.
The helm position is comfortable. Deluxe seats feature bolsters for back support when standing and the hardtop interior is well-endowed with handholds. With the infill squabs in place, the forward berth is huge and there’s a toilet under the squabs. Additional fixed seating is provided by the rear-facing cockpit lockers, sheltered by the hardtop’s rear bulkhead and roof overhang.
As usual, the Surtees ride quality impressed, and if anything, Undercover with its engine mass down low, felt even more securely planted in the water than most. She certainly cut through the chop with minimal fuss, burning just 23 litres per hour at 23 knots.
With a deadrise of 20° at the transom, trim tabs are mandatory in any sort of crosswind and to compensate for shifting bodies or unbalanced payloads. Adjusting the trim tabs during our extended run ensured the most comfortable and efficient ride. Steering is hydraulic.
Like all Surtees boats, Undercover features a flooding ballast chamber, which comes into its own when the boat is at rest. With the gate in the open position, the chamber fills with 530 litres of water, stabilising the hull. Once the boat moves ahead and climbs onto the plane, the chamber empties again.
If some extra weight low down in the hull is desired – in rough conditions for instance – the gate can be closed to retain the water in the chamber. It’s a well-proven and effective system.
Our next stop was Aurora Caves, which we explored, checking out the amazing fish life inside. Taking advantage of the backdrop and the shelter offered by the high cliffs, we launched the drone and made a few passes for the camera boat.
The run back to Whitianga was just as pleasant as the run out had been. Nick parked the boat at home in the Sea Pen, where he told us how much he had enjoyed the whole project, praising Surtees Boats, Mercury Marine and Mark Cosgrove and his team at Mercury Bay Marine. He made special mention of his wife Hollie, without whose support this project would never have grown legs.
“I love the ride and the layout – it’s a proper fishing boat – and I love how stable it is at rest. I’m also satisfied everything about the boat has been done right: the engineering, the build and the design. Everyone involved has been great and I couldn’t be happier with the outcome.”
Now Nick just wants to take his family and friends fishing.