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DESIGNING THE OzRacer.

Although I think it's fair to say I coerced him, or maybe even bludgeoned him into working with me on the first PDRacers we built, I asked to write some stuff about how the design for the OzRacer came together as a result of those rather heady weeks.

POTENTIAL

In March 2006 Peter started showing me the pictures of the PDRacers being built overseas - I really liked the diversity of approaches from all the designer/builders - I am still awestruck by the Spanish Galleon version complete with cannon! But at the same time very few seemed to be achieving anything like the sailing potential of the boat.

What sold me on the idea was boat #2 built by Ken Abrahams. Clearly Ken has a fair bit of a sailing background - the boat just "looks right" and it seems to move along quite nicely. Also it was the first PDRacer I saw that had some elements of a really excellent design approach - the curves of the cockpit coaming, the neat and efficient rig, the clear timber finish, the graphic on the side - it all just comes together.

That's what makes an inspiring boat. Seeing boat #2 was when I actually started to be interested - even excited about the humble Puddle Duck Racer.

DESIGN
a holistic process

Get it right and the boat, the water and wind and the sailor become one.

Look at the videos of how the OZ PDRacer and OzRacers sail - and see how the boat fits the water and how the sailor fits the boat (that's me sailing it by the way) - how it sails turns, accelerates

This idea/feeling then extends out to the design of each of the components, how I can make them easy to construct, as light as possible, what materials are best.

A big part at this stage is to work out what I can get rid of from the design. Every piece that can be removed is money and labour saved by the builder. Every expensive component that can be removed without losing function is a gain in dollars

That's sort of what I see at the beginning - even before I start putting the boat down on paper or the laptop - how it all fits together into one fluid thing. If I don't get that feeling - I'm just not interested.

IS SAILING EXPENSIVE?

Most people think that sailing is expensive - but is it true?

Sailors of conventional boats are obsessed by high-tech (expensive) solutions. The result is that many types of sailing boats that were meant to be cheap and simple now cost many thousands of dollars.

The Manly Junior was designed in Australia to be a boat a family could build over the winter to have sailing for summer. Originally designed to cost a few hundred dollars they now retail at $A7800 and the use of timber is banned. Boats for adults can be much more expensive. Often the cost is totally out of proportion to their function.

The sad thing about the Manly Junior (and all all its ilk) is that they were good boats to begin with, and didn't need expensive construction methods and expensive equipment chucked into the mix. You can see more information about that here.

New competitive boats for people to get into sailing should be available for less than $1000. Maybe less than a few hundred dollars (like our boats) if they were to use some of our strategies.

Peter and I have a background in sailing fast boats - so have high expectations of the way any boat should go and should feel to the sailor. We were not going to be satisfied with a tub that couldn't sail out of its own way.

The question was how much performance would it be possible to get out of a boat costing not much. The answer - Quite a lot .

For a boat to be fun to design and build it needs to push some boundaries. Pushing boundaries implies some sort of risk.

The areas where we were taking a bit of a chance with the OZ PDRacer were bigger sails and lightweight construction. Both of these are traditionally the forte of Australian and New Zealand small boat design. It should also be noted that given the cost of the boat, rectifying any discrepancy was never going to be a big problem either. The OzRacer plans reflect the experience we gained with those experiments.

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BALANCING THE RIG

The bigger sail did mean that the centreboard had to be located well towards the back of the boat - lots of people said this wouldn't work - to the point that I started to doubt myself! But if it all went "pear shaped" I could always rip it out and move it to a more sensible position - it is just more woodwork. In the end there was no problem - centreboards can go a long way back.

I also hedged the risk of the rig being unbalanced by setting up the mast so it could be raked (tilted back and forward) to move the centre of the sail back if required. This would also give us the ability to trial different sailing rigs.

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SIMPLICATE, THEN ADD LIGHTNESS

That was the philosophy of Colin Chapman, the founder of Lotus Cars, and it holds true for PDRacers as well.

Once again - if you build an OzRacer using my plan and guidelines you will end up with a light but incredibly strong boat, good simple technology!

The way we chose to do it is completely unoriginal on my part - the credit has to go to decades of experience of Australian and New Zealand boat designers and builders.

Most of our indigenous sailing dinghies built in the most highly evolved wooden construction weighed around 10lbs per foot of length (15kg/m). European and American classes tended to be around double that. Australian wooden boats do this without sacrificing durability despite winds being predominantly much stronger than they are in those countries.

The trick is to maximise the stiffness and strength of the structure without increasing the complication of the boats;"simplicating". The lightness reduces the amount of material that has to be purchased saving money, at the same time as increasing performance, and actually reducing some of the resultant structural loads.

Modern epoxy construction allows careful set-up of the intersections of the different plywood planes so that the major loads can be carried in the plywood rather than the timber frames in more traditional construction. Typical weights using these methods seem to be around the 8lb per foot mark. My 15ft 6in Goat Island Skiff is similar construction and comes out at 126lbs (57kg) without any fancy structure or by using thin ply (it is all 6mm).

This equates to 8lbs per foot using very conservative construction. These are not ultra-lightweight "disposables".

We were pretty happy when our first PDRacer hulls came out around 55lbs before epoxy and varnish/paint and fittings were added. About 7.5lbs per foot.

Straight out of the box and using a relatively heavy hardwood construction ply, and pine framing.

There is nothing secret about these types of structures. If you take a cardboard box and open the top it is very floppy - not a good structure at all. But if it is closed up and taped along all the edges it becomes hugely rigid.

The most difficult load to absorb in the boat is twisting (torsion) - as the mast tries to turn the boat over and the crew resists by sitting on the side of the boat to keep the whole shebang level. It happens that torsion is the very thing that our closed boxes are best at dealing with.

So we placed three closed boxes in the boat - the front buoyancy tank and the two rear tanks. These sections of the boat just won't deflect (twist or bend much) even with quite extreme loads.

There is about 3 ft (900mm) of boat length between the two lots of tanks which is more subject to twisting and other deflections - but we have linked the sets of boxes with quite a wide side deck and also the centrecase support structure - which is also in that less supported area. With the boat on dry land Peter and I were able to stand on opposite corners of the boat - no visible deflection at all.
 

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PLYWOOD THICKNESS

This structure allows us to use much thinner plywood - up to a third the thickness of some of the existing PDRs. In the end we outsmarted ourselves a little - the ply we chose 4mm (5/32") was fine for everything except the bottom of the boat. Peter, who is a bit heavier and doesn't have my catlike agility <grin> put his foot through the bottom of one of the boats.

(NOTE: in fairness to the big boofhead bloke who is 6'3" and weighs around 200 lbs, the ply we used was a brittle hardwood construction ply with major defects - see "materials". We decided that a more conservative approach would minimise risk and leave substantial reserves for inexperienced builders.)

So we had to remove the bottom and replace it using 6mm (1/4") ply. It took each of the boats off the water for a day - the silly thing is if we had spent another $10 on plywood at the beginning we would have had no problems at all (but we wanted to see how light we could go).

We expect the weight of the OzRacers to be achieved with economical plywood - even exterior grade softwood plywood.
 

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FOILS
Centreboards and Rudders

Racing sailors spend big money on foils. They are the most important component after the mast/sail combination.

Years ago I used to make my own centreboards and rudder blades by eye. These seemed to work quite OK, with me finishing in the middle of the local fleet of NS14s.

There was a lot of information around at the time that a really good set of foils could save an NS14 around 4 minutes round the race course.

Professional foils were accurately shaped to NACA sections - the same airfoil shape as used on many aircraft and finished to a high polish. When I had saved my money the new foils made the boat completely different.

Not only was my boat faster, but much easier to sail - it would go where it was pointed, tack and gybe smoothly and accelerate much faster. Suddenly I was up near the top of the fleet in my racing and having more fun sailing that ever before.

So with the OzRacer foils we used a special airfoil section and we provide you with a simple template so you can make an accurate shape.

The actual shape was one developed a few years ago by Australian Aerodynamicist Neill Pollock and cuts quite a lot of the labour complexity out of shaping the foils.

Take a bit of time getting the shape and the finish smooth and your they will be close to equal to the best that money can buy.

The materials for the centreboard and rudder can be quite basic and cheap. We used finger jointed junk pine strips about 30mm (1 1/4 wide). Most of the load is carried in the layer of fibreglass that goes around the outside.
 

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RIGGING

Sailors of conventional boats have a huge addiction to using large amounts of expensive equipment. They also like to make every aspect of their boat adjustable.

This adds a huge cost component to the boats with a thousand dollars or so being sunk into fancy bits.

Thirty years ago the same boats were well known as good, fun racing boats and they didn't have anything like the same amount of gear.

The Cost of Mechanical Advantage

One of the most important adjustments in high performance boats is the stay tension - the tension in the wires that hold the mast up.

Let me tell you just how much this one adjustment costs on senior racing boat like a Sharpie, International 14 or 505. (prices accurate 2006)

1 ball bearing triple block (ie pulley) each side - $90 = $180
1 ball bearing triple block with becket $95 = $190
Two single ball bearing blocks $25 = $50
Double ball bearing block with becket $45
Single side mount block = $25
Two single blocks $25 = $50
Two carbon cam cleats $42 = $84
Spectra or Dynex rope to make it all work = $55
Miscellaneous screws, bolts, tangs, washers saddles = $80


Don't worry about the jargon - just think of your wallet. We have a total of $759. And there are another 6 or 7 major systems.

Three decades ago these same boats didn't put the same priority on these items and the racing didn't suffer in the slightest.
 

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The silly thing is most of the simple boats for beginners have gone (or are going) the same way. One person changes their boat in the direction of more complexity - which makes the boat very marginally faster - so everyone else has to get the same bits so that they can all go at the same speed as each other.

A nautical "Arms Race".

For our OzRacers we ended up using three blocks (pulleys) - TOTAL. Under our rules they are not allowed to be ball bearing blocks so are cheaper, lighter and stronger plain sheaves.

Our tiller extension universal joint is a bit of rope going through holes in the extension and the tiller. (Don't worry about the jargon - the plans just show you where to drill the holes and where to tie the knots). Saves another $15.

A lot of the ropes are simply fitted through holes in the hull and spars - eliminating many specialist fittings and the screws and bolts usually needed.

The OzRacer as a Package

The aim of racing boats is to make them as automatic to sail as possible - so you don't have to adjust things all the time. But they achieve it by having a huge amount of adjustment so they can move things around until they find the points where the boat responds automatically.

Peter and I have used all our combined racing and construction knowledge to wring every last bit of expense out of the OzRacer. At the same time we have used some of the developments of racing boats to make the boat respond automatically to the wind so the sailors can enjoy the ride without getting too concerned with tensioning bits of rope - if they are all about right everything will work fine.


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