Inception 

About 5 years ago I embarked on my latest boating adventure, building the boat I always wanted to have. I've always been a boater. I used to drive a boat on Lake Eildon while my father and his friend tolled for trout in the freezing cold at age 6, made my first fiberglass canoe at 12 whilst at school, then an 8ft single seater hydroplane at 16. My father always had boats, a 10 ft tinnie, then a 20ft half cabin later on. When I grew up (a hard thing to say as a jet boater really). I bought my own tinnie, then a nice 18ft fiberglass half cabin which did me proud for a while.

Interest in Waterjets

I became interested in jet boating the day I accidentally overheard while driving, and subsequently stopped to see some jet sprint boats run around a paddock in Melton in Victoria. I've also always built engines, and being interested in classic horsepower I was naturally lured by the jet sprint action. After some time, I did some investigation around jet pumps and their application to recreational boating. I spoke to people at Hamilton Jet, Scott and also Doen Waterjets. The concept of picking up a mass of water, hurtling it backwards into thin air and letting the words of Isaac Newton's Third Law of physics explain why a boat would move forward still excites me to this day in fact every time I go boating. 

The Specification

Having been involved in boating for about 30 years by this stage the list was long;

  • Large enough to carry the family without compromise
  • Trailerable (so less than 3 tonne including trailer and fuel)
  • Power in reserve, and plenty…
  • Shallow draft
  • Suitable for fishing, skiing and other water sports
  • Well thought out’ - layout, features
  • Excellent performance  

Initial Thinking 

So the research started once again with renewed enthusiasm. In summary, the decision was made to build a custom alloy boat, traditional American push-rod V8 power and of course, the jet pump. The most important thing to do was to get the Doen and Plate Alloy teams together to talk about the general approach. I learned a lot about the perspectives of design from both parties what was needed for effective jet pump operation, and what was needed from a hull perspective.

 Hull Design

 

The boat I built together with a company from Melbourne, Plate Alloy Australia, run by John Pontifex. I had spoken to a few boat builders, even took a trip to Tasmanian to meet with one in person before settling with John's company. I chose Plate Alloy Australia mainly due to their interest in the project - a first of a kind for them at the time. The design and modelling work was done by Catran Galema, an enthusiastic marine architect who took a particular interest reaching out to his contacts around the world for advice. Mike Postma who has been with John for quite some time also brings to the company a wealth of boat building and engineering experience. 

John also runs boat building courses whereby ten or so people make a boat from scratch – well worth the time and money if you are contemplating building a boat, and they sell quality well priced welding equipment for the 'do-it-your-selfer'. I must say that working with Plate Alloy Australia is very rewarding and we remain in contact. They are simply a bunch of engineers, that don't compromise on quality, have enormous experience and provide services to the Australian market at sensible costs. Website /www.platealloy.com


 

Hull design is an absolute art. Every time I take the boat out I take comfort that it's a very dry boat, cuts through waves like a knife. The dead rise on my boat is only 14 deg at the transom making for incredible stability while at rest. The main thing I grasped is that commercial boats are all about compromise. How can you buy a boat that can have various accessories added to it, or have outboard power from say 90 to 250 hp and be well balanced? The answer is you can't. 


The front of the boat essentially provides the 'knife', the rear the greatest 'lift'. Finding the balance point for where these two functions are optimal can only be achieved with every factor considered. It should also be noted that building the boat from scratch resulted in a stronger construction without adding excessive weight as a consequence. Spread throughout the design is 3, 4, 5, 6, 8, 10 and 12 mm thick aluminium. A team of three spent nearly 5 weeks welding the pieces together to make the hull. 

Fit Out

 
So a factor in the hull design was the weight of everything I planned to put in the boat, from the 150m of anchor chain at the front to the cast iron mass of a big block, and everything in between from inbuilt fish tackle boxes, bait wells, seats, dashboard gauges - everything. So before the design was actually completed, I had purchased everything that was to go in the boat and supplied all the dimensions, positioning and weight of every item. This proved to be so important, not just to give the boat the right balance, bow up angle, wetted surface area etc, but for adding in all the fit-out items due to the CNC router that cut the plate making all the right provisions. Plate Alloy Australia use nothing but the finest 5083 grade marine alloy, difficult at times to work with but with the strength almost of that as mild steel.   

 


Finally, everything on board is in its place, the electronics, seating (with seat belts), bait box and live wells, bait board, rod holders, toilet, carpet all look like they were put together a package because they were. The swim platform and loads of grab rails and bollards and large bow rail make for a safe boat.

Powerplant

For me this was the easy choice, not to go modern with anything fancy, but to build a good solid power-plant. Plenty of power without working hard. Plenty of power in reserve for whatever the challenge. Simple really - Chevrolet Big Block. I used a local engine building company to whom I gave a specification to for a build a base 'short motor'. The marinising and additional work I completed myself.
 
The engine itself has the following main features;

   

Chevrolet Big Block, 511 cu, 10.5:1 compression

Ported cylinder heads, large valves

Mildly aggressive camshaft

MSD marine ignition system

Holley 1050 CFM Marine Dominator carburettor

Edelbrook Dual Plane manifold

IMCO water cooled extractors and 4” S/S exhaust system

Closed cooling system system for engine block and exhaust manifolds

Twin remote oil filters and oil cooler, 3 Litre Oil Accumulator

High output alternator and triple batteries

intelligent batter isolater setup

 

Propulsion

I decided on working with Doen Waterjets for the jet pump, not purely because they were local, but the fact that for Frank Udvary, Mike Madden and the team clearly the focus was on quality engineering. Doen is a very impressive Australian company exporting products to many clients around the world so difficult to do in these times. The (646) 202-7708 pump was the unit we chose, a single axial flow type. It is well engineered to serve in a salt water environment in which it was primarily to be used. This is a very robust 10” waterjet with a special high thrust 6 blade stainless steel impeller and a 6” nozzle. In my application, we were needing to push the best part of two and a half tonnes of boat and passengers, so the larger diameter impeller coupled with large intake grill and chamber provide excellent performance. 

 
The reverse bucket is a large split duct type which is electrically operated. The bucket outlets also angle out to 45 deg. This provides excellent steering at less than 5 knots, by adding some reverse thrust in addition to the majority of forward thrust. Not particularly efficient, but excellent directional control is obtained! The pump has an integral gearbox with many ratios available so we were able to select the correct ratio for the input power I was contemplating ensuring the highest efficiency of both engine and jet pump.

 Performance

I can honestly say I don't want for anything more in a boat. Regardless of what the nature of the boating is the boat does whatever it's asked to do. The weight of this 27ft boat is less than 2.5 tonnes fully fuelled. Despite this, it only takes about 1 second for the BBC to get to full RPM, at which point if you aren't holding on you're no longer seated or standing. Performance is a staggering 45 odd knots at wide open throttle. Whilst it may look odd towing two big 'burly blokes' on single ski's it does it effortlessly –in fact I don't even use full throttle to left them out of the water. Cruise speed of around 25 knots is held with engine RPM of 2600. Acceleration from this speed to 45 knots is remarkable. Planing is achievable at around 11 knots with a few people on board, if I have more than 6 people I can still plane at this speed using the trim tabs. Stopping power is violently fierce which is why I have a 'detent' button on the bucket lever to prevent accidents. Steering is very positive at speeds above 5 knots. I did add some small fins onto the rear of the underside of the hull to assist with tracking in a straight line at full speed.

 

 Final Thoughts

 
During construction, I took one of my friends Greg Cameron down to Plate Alloy Australia as he was interested in having a look at its progression. I recall Greg saying to John at the time, It must be nice to build boats like this? and John replied, No-one has a boat like this!.
 
I didn't realise at that time, how significant this comment was. Every time I park the boat on the street, or go to a boat ramp, or am on the water, without fail people approach me and ask me about it. The questions I'm asked range from the overall design choice, the engine choice and of course the application of the water jet. When I explain to these people the reasons why I went down the path I did, they are genuinely impressed. I've come across people who have always wanted a jet boat, but did not know how to approach it. They also come with stories they have heard from others around how outboard and inboard propulsion is better than the capabilities of a jet pump  often suggesting that I should have just put a 'thumping big outboard or two' on the back instead like everyone else does. 

When I explain how a jet pump works, the performance characteristics, the 'fundamental rawness' of its operation and the handling benefits it seems to make a dent it their initial perspectives

  • Driving the boat onto the trailer with no prop hitting the ramp bottom... 
  • Navigating a shallow bar at 15 knots with around 300hp in reserve and instantly available 
  • Reversing the boat of beach effortlessly... 
  • This boat actually has a reverse that works and even goes sideways...

Yes, it is louder and uses more fuel than most outboards, so what! When I depart from a ramp, I see them standing watching for what comes next. When I open the throttles, even from a distance away - I just know they understand more than they did.