Rick Huckstepp | Issue 66 | April-May 2008 | Blue Water Magazine

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With a newly optioned Yanmar diesel engine, the highly acclaimed Theodore Coastal 720 is a boat gaining even more fans where rough seas and mounting costs need taming. Rick Huckstepp puts the new diesel version to the test.


Trailerboat sport and gamefishing is currently at an all-time high, with excellent access to offshore grounds up and down the east coast of Australia. The reliability and economy offered by the modern-day outboard has been a great contributor to this, along with the easy access to information on how to catch oceanic speedsters, which anyone can source from the Internet or great publications such as this mag.

Diesel engine manufacturers are not resting on their laurels either. While the big-boat industry is getting bigger - and those manufacturers take all but a crumb of the engine business for that sector - small diesel engines for trailerboats are being improved and fitted as the propulsion of choice at an ever increasing rate. Economy with common rail injection systems and a rapid decline in engine weight are proving to boon for all involved. 

Theodore Marine has been manufacturing a Coastal 720 model out of their Port River Marine yard in South Australia since 2005. Nestled in a shed among even bigger sheds and trawlers packed on hardstands, the boats have been trickling into the marketplace. They can be found in various coastal towns, predominantly around SA and Victoria, where rough seas are the norm. Built to 2C survey, they are finding favour among cray and other commercial fishermen looking for manoeuvrability and a boat that won't keep them on the ramp and separated from their catch when things get ugly offshore. 


I tested this boat about three years ago when the prototype hit the water. Since then, the Theodore has had numerous awards and mentions at the AMIF Boat of the Year Awards. That first boat was fitted with a Volvo Penta 285hp engine, which really got it cracking - up around 40 knots.

With the release and fitup of the new Yanmar 6BY 260hp engine, the Theodore has dropped a little in the speed department, but the lousy test-day weather didn't allow us to investigate this thoroughly (and it's only a matter of a few knots. But the real difference is in the ride, with the reduction in engine weight from one engine model to the other being about 168kg. As a result, the marlin board sits much higher above the water, and when backing down there is minimal bulldozing, with the board skiing over the surface rather than burying.

Another plus was the extremely responsive steering of the Bravo III duo-prop leg, which was easy at the helm and positive all the way to full lock on port and starboard, with no difference in torque. 

Much of the bulk of the engine is tucked under the transom bulkhead, With the enginebox lid off, the engine is shrouded over the top and on the front with separate shields to cover belts and pulleys. These may be unskrewed to access the aforementioned for maintenance quite easily. There is ample room down the fore end of the engine to get the arms and spanners in to do the deed. Also easily accessed here is the diesel fuel filter, water strainers, L-cock (for the water pickup), float switches for the bilge pump, water level alarm and deckwash pump.


Fishing-wise, the aft corners provide a good stand-up position. While the enginebox encroaches a little on the cockpit space, it is another good safety barrier when fishing in rough seas. With a cushioned top and grabrail down the centre, you can easily sit down to ride out the rough stuff while hanging on with loaded rod in hand. 

The fascia of this bulkhead is perpendicular to the deck; inside, the cranking batteries are installed and accessed via a small hatch. This hatch is a little too small for easy access for uninhibited maintenance to the batteries which, as many of you will realise, are often ignored if they're too hard to get at. The bottom of this fascia has a pair of vents either side of the enginebox that allow water to get through to the scuppers on the transom. There are big enough for the toes to sit in while you are standing up at the transom.

A good-sized bait rigging station is centrally located over the rear bulkhead and in line with the enginebox. The live bait tank sits squarely beneath the station and is large enough to handle a day's worth of good-sized slimies. As a stand-to rigging station, it would be hard to properly use in its current location and would be more practical if installed on one of the side gunwales - although it would render the rodholders of less use. This is the beauty of buying a boat that may be built to order; you get the boat built to fit around you, the buyer. Personally, I'd like he baitboard on a port or starboard gunwale and a stubby, four-rod rocket launcher on the transom, aft of the lid of the livebait tank. Centrally located near the helm seat in the deck, a wet tank, complete with bilge pump, is an ideal place to thaw baits or stow deadbaits before rigging. The sidepockets sit below high gunwales that contact well up the thighs for good fishing stability. These pockets are voluminous enough to install gaff and boat hook racks if required. A pair of handrails either side are rebated into the inside edge of the coaming, ideally placed for tying off rod safety lanyards.

The seat modules allow for observers to view astern, sitting on padded lids that access stowage inside. The backs of the passenger and helm chairs serve as backrests, and they have swivel bucket seats with forward and aft sliding capability. Although not insulated, these modules would make good iceboxes with the addition of same, As tested, they were large enough for small tackleboxes and trays. The EPIRB and fire extinguisher are rebated into the inside of the wall of these modules.


A wide helm brow is capable of  holding a pair of recessed, medium-sized chart plotters and depth sounders. While there is plenty of room for engine-management instrumentation, should you want to go big in the electronic cabinet department, the flash dash has ample room. 

The hardened glass screen is set at a comfortable height and a person of 170cm should see over the top when standing. Clears fitted to the test boat were 100 percent effective in the squally conditions we experienced. With these removed, by anglers in the tropical zones, there will be plenty of ventilation for anyone under the soft canopy, which is supported by a sturdy stainless steel frame that may be folded back into the cockpit for towing long distances.

We tend to fill dashboards up with all sorts of knick-knacks and tag cards when out on the blue, so a fence of sorts at the aft end of the dash is a nice complement to this area. If you are in the rough there are plenty of grab rails to use - around the windsceen, on the sliding lockable cabin door and on the passenger's side.

Inside the cabin, the looms behind the helm are secreted behind a large, form-fitting, fibreglass shroud (with a quick inspection hatch) that hinges down for access to fuses and the like. The usual stowage is found under the vee-berth seating, along with a portable toilet under an infill central and forward of the leg well. 

In the flat forward bulkhead, a flush mounted hatch gives access to a Stress Free anchor winch, which is loaded with rope and chain, and SARCA ground tackle. While this cabin could sleep two with an infill for the leg well, it is large enough for the serious fishing angler to fix down tackle lockers when the cushions are removed.


I touched on the exceptional steering when going astern in the Theodore. This was the case even when backing down into one-metre chop. Going forward at speeds below planing, the boat is again very positive in the steer. Its sharp deadrise at the forefoot, which extends well aft, gives it a positive tracking wedge to keep it in a straight line with minimum effort. When doing so into steep chop it also makes for a comfortable ride, cutting through the crests of waves rather than slamming into them. The beam on the Theodore runs well forward before cutting away to this varying deadrise. The effect of this design is minimum rock and roll when under way over variable seas, even at an angle, and good stability dead in the water.

Running with the swell and chop the hull doesn't lose its manners, and is again a pleasure to steer. Results from the GPS and tacho ranged from 5.6 knots at 1000rpm and 10 knots at 2000rpm to 36 knots at 4000rpm. The beamy midships of this hull have it planing at about 12 knots. A comfortable cruise speed is around 23 knots  (2500rpm). The manufacturer claims fuel consumption at this latter speed is around 16 litres per hour and 20 litres per hour at 26 knots (3000rpm).

The Theodore gets full marks in the handling department. When Mother Nature gets the case of the sads, you will be glad you weren't caught at sea in anything else. The price tag with a diesel engine might scare a few, but look at the economy, especially if you are doing the miles! If you can't get your head around that, there is always the outboard option, which in this day and age is very good - although not as economical as a modern diesel engine.

Article Blue Water Magazine Issue 66 Apr
Article Blue Water Magazine Issue 66 Apr