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I was originally approached by a Sydney company called Shearwater Marine to draw up a Hire-and-Drive picnic boat for Sydney Harbour. The idea was for a boat that could be built quickly in series production with a minimum of tooling. It had to look cute compared to the opposition - companies hiring out aluminium dinghies with 6hp outboards.
The first Shearwater Marine boat
floating in Elizabeth Bay, Sydney harbour.
Later the idea was to be expanded into a fleet of around 50 boats operating out of different hire businesses up and down the east coast on the plentiful rivers, lakes and estuaries.
Shearwater Marine (Richard and Ken) would take care of the maintenance and repair by the simple expedient of having a couple of extra boats up their sleeves (so to speak) so that when routine maintenance came up for one of the boats up the coast they would simply roll up with a replacement boat on a trailer and swap them over, the other to be refurbished in their factory.
For me as a designer it was another "get rich quick" scheme** - design one boat then get the royalty each time another boat was built - 50 boats times, say $200 each - looks quite good on paper.
** (yes, Another - see the story at the bottom of the Eureka Canoe page: "The boat that almost made us our fortune.")
Well, we succeeded on all grounds. The boat went together quickly because of the prefabrication method with all major components made up on the flat (drawing right), looked quite handsome, behaved quite well in the water, but the problem was the labour involved in painting all that surface area.
Despite the fact the boat was relatively clean and simple the labour estimates for the finishing made the whole project uneconomic - painting one boat was fine - but another 49+ could drive you nuts!!!
It is a bit of a general lesson really - if someone says that a particular boat will take only 6 hours to build, or that their construction method takes half the time of someone else's design then they are quite possibly not including the painting!
Hull Design and Seakeeping:
As is probably obvious to knowledgeable readers the hullform and building method is a derivative of sharpie building methods - in particular those developed by American genius Phil Bolger.
His "State" class rivercruisers (named Tennessee, Idaho, Wyoming etc) are very light displacement and quite narrow, with beam to length at around 1:5.
Flexible interior - click this link for one Alternative Interior Layout (html)
The narrowness is essential to prevent the flat bottom from pounding. One of the great experiences of my life was when the first Tennessee was launched in Adelaide I sat up on the bow watching fascinated while going into a short, sharp Murray River chop - the bow did not pitch in the slightest, cutting each wave in turn. Not a hint of pounding.
Such a dry comfortable ride in a short chop makes the boat a perfect
Murray River Rambler. Boats with more beam and wider entries as the bow will tend to bounce around a lot more, kick more spray up and pound and wallow when heading into waves.
Excellent behaviour for when the waves are close together, even if they are quite tall.
But in circumstances when the wavelength is longer than the boat the boat will travel up the face then launch itself into midair and land with an enormous slam when the flat bottom meets the water. But in their natural environment of rivers, lakes and estuaries the hullform works very nicely indeed.
With the Dayboat/Launch its length of 23ft (7m) would necessitate a beam of less than 5ft (1.5m) which would make the boat somewhat unstable and one of the design criteria was for a central table with seating around (Picnic Boat). The solution (which I was a bit hesitant about at first) was to effectively have the bow of a longer boat but cut it off at the stern. As you can see from the plan view above the boat is all bow.
Boats that are "all bow" often have reputations as wild steerers in a following sea. The stern has so much volume that when a wave comes up from behind it floats up suddenly which tends to thrust the bow deep into the back of the wave in front.
This is the secret of the nice rough water handling of narrow sterned boats - neither the bow nor the stern overpowers the other so the boat remains in balance in rough sea conditions.
My thought was that Sydney Harbour can get choppy at times, but the waves are generally quite closely spaced so both scenarios of either going up the faces and launching into midair or burying the bow were fairly unlikely.
There are many possible options. The original is shown in the drawing above, The cuddy cabin was for lockable storage and a porta potti, which is a great thing to have aboard a picnic boat! A few nice wines or beers and ...
"Pop&I", built by a father and son team some distance up the Murray River, was changed considerably, moving the outboard from a well to just in front of the transom. It has a settee/double berth in the aft end of the cabin and seating on the starboard side has been replaced with a galley (really a cupboard with a flat top a spirit stove can sit on top of and a cutout for a bucket as a sink). The canopy has been run through to the stern and up to the back of the foredeck. A windscreen has been fitted.
The do's and don'ts of the interior include
1/ You can't go up any higher
2/ The cabin has to be light.
3/ The seats, galley etc has to be bonded to the sides of the boat - the interior components support the sides of the hull.
With the 9.9hp six knots is about top speed, though there are some pics of Pop&I whizzing along a bit faster than that when floating light just after first launch. But that is not the purpose of these boats - keep the speed down, save fuel and have a comfortable ride (the faster you go the more it will pound as the boat will lift and present more of the flat bottom to the waves.)
We would probably recommend a 4-stroke outboard because of the slower speed and greater weight. One of the high thrust models would work very well.
For its use as a Hire and Drive vessel, the dayboat had to be put into Survey. I was quite worried that anything this unconventional would have trouble getting past the powers-that-be.
Of particular concern was the criterion that the boat not capsize with the whole six (6) of its crew standing on one edge of the boat. Once I worked out the centre of gravity of the whole shebang I fed it into the computer and quickly found the boat was just short of enough stability. So a lead shoe of 200kg was added to the drawing, which was enough to make her pass.
Richard decided that he wasn't going to fit the lead unless absolutely necessary so when the boat was finished it was whacked in the water and the Survey blokes called in. Four of them arrived on the appointed day in matching spotless white overalls. They jumped aboard and started filling out checklists and the like. Richard asked them what they thought of the stability for six. Reply was "Six, mate ... she'll handle Eight easy".
So much for my hours of working out the weight for each component of the boat so I could locate the height and longitudinal position of the centre of gravity!
Several have been launched and their owners are quite happy with them. Not a bad machine at all (if I do say so myself).
Materials list for Dayboat/Launch (PDF File)
One Alternative Interior Layout (html)