Thread: Mystery Oz PDR prototype

Will send bob. Rick, you haven't lived until you have seen Bob wield a dutch oven! MIK

Well, gosh, that's quite a build-up... good thing Rick isn't going to be at Paulina Lake. I wouldn't want to disappoint his expectations!

By the way, this year, in addition to the Dutch oven desserts I will be experimenting with baking bread in the Dutch oven. Should be fun.

Well I looked it up, and Paulina Lake is 10 hour and 20 minutes drive from my house. Almost do-able.

I raced my MkIII against a few other Puddleducks today. Got a neat picture of the boats beside a turn of the century 300 foot long sternwheeler. The little 8 foot boats sure look small beside that behemoth!

Oh yeah, I won too.

Rick Landreville

Any feeling for the speed of the Mk3 Vs the Mk2

Originally Posted by Boatmik

Any feeling for the speed of the Mk3 Vs the Mk2

If there is any difference, I cannot detect it. If anything, the Mk3 is faster for me because there is more room, I can adjust trim on the boat easier because I do not have to pre-plan where I am going to put my feet. Also, sail handling is easier because the leftover cordage isn't easily hung up in all the framing as what would happen with the Mk2. I have placed the 'bad tack' of the sail against the 'good tack' of the leeboard location, so they kinda cancel whatever 5% loss of effeciency there might have been between the two. On my GPS I hit 13 kmh a couple of times yesterday and outpointed a Catalina 27, much to the amazement of the captain! All in all, a pretty nice little boat.

Rick Landreville

Thanks for that Rick.

I think you would only truly know if sailing against a Mk2 with an equally good sailor.

But what this does is show that the boat does feel right on the water and has some other small advantages that make the boat nicer to handle.

I will bet my bottom dollar that the Mk2 is faster around a racecourse, mostly because it is a bit lighter (less panel area) and the centre located centreboard.

Some of the PDRs with biplane rigs - a mast on each side of the boat - found that when sailed in a highly asymmetric mode - mast on the opposite side to leeboard - that the boat was just about uncontrollable.

The reason is that it would go from strong weather helm on one tack to strong lee helm on the other. That's because the force from the sail is slighlty forward as well as sideways. One one tack that arrow from the centre of the sail goes in front of the leeboard and on the other tack behind the leeboard.

This shows that there is a clear inefficiency from an asymmetric leeboard setup (leeboard on one side only), but if the lateral distance between the mast and the centreboard/leeboard is not too great then it is not too bad.

Centreboard and mast near to inline is more ideal. Wherever they are placed across the width of a boat.

Best wishes
Michael

Hi MIK;

I wonder out loud how much of the CLR (center of lateral resistance) is actually taken up by the absolutely massive rudder blade on the Mk2 and Mk3 Oz Racers. Because of this, I conjecture that the slight assymetry of the daggerboard is less of a factor than it would be in a boat with a narrow rudder blade. If the CE (center of effort) of the sail was anywhere near correct on the good tack, the bad tack would be compensated for by the wide rudder blade picking up some of the load as far as side-slip is concerned. I offer this observation from my experience of losing the bungee cord that holds the rudder down and the boat wanted to head up into the wind no matter what I did with balancing the boat with my weight, or trimming the sail. I could sail my old Mirror 16 without the rudder fairly easily, yet found it almost impossible with my Oz boat.
Also, my own experience with the bi-plane PDR makes me think that it was the long narrow rudder was not helping balance the sail at all, and could have been a more positive experience had I had used your foils (and not as a leeboard either).
I still have that 2 meter wide PDR with the biplane rig. Maybe I should rework the boat to give it a fair test of the theory.

Rick Landreville.

Howdy Rick,

Carrying some of the lateral load on the rudderblade is generally good practice. But you don't want to go past having the tiller at about 2 or three degrees to the centreline.

More than about that and there is starting to be serious drag from the rudderblade ... which is exactly where the drag from an asymmetrical or other out of balance setup will come from ... the rudderblade.

If there is a bit of a balance problem there ... with a touch of weather helm on one tack - which gives the rudder some weather helm to deal with - which gives you lift. But on the other tack things are reversed with lee helm and the angle of the rudder blade lifting in the wrong direction.

With the Mk3 and most single leeboard PDRs there is not too much of a performance disruption - I would guess around the 5% you guessed at or in that range. But where the mast is on one side and the leeboard on the other the angles required from the rudder create so much drag and also in Dave Grey's case made the boat uncontrollable - that is showing the forces are too big for the rudder to deal with.

A classic example of the two leeboard boat with a central mast are catamarans. They need the hull centreboards a fair bit further forward than a monohull. Usually the reason given is that it is because of the offcentre drag of the leeward hull. That might be so ... but a much neater example is that the line of action of the centre of effort of the sail being a slightly forward vector requires the centreboards to be on that line to retain the correct amount of weather helm.

As so clearly demonstrated in a biplane PDR using only one rig.

MIK

Hi MIK;

I can't really call the Mk3 a leeboard boat, when the daggerboard is only 300mm or so off centre. Perhaps that is why I am not really noticing much difference between my Mk2 and the Mk3. It would be nice to race head-to-head against another, but they are scarce up in these parts.
I am finding it easier to sail because of the extra cockpit room and lack of framing to get in the way. I can tack faster, and retrim the boat easier, which I believe make the boat faster in the long run. If racing against some hotshot dinghy racer in a Mk2 might be a different story, but if that hotshot weighed 5kg more than I did, the weight would be the same. So we might be talking about a 5% increase in performance on one tack, and perhaps only when going upwind. Over most courses, this would maybe work out to 1% of the entire race. I like my chances.
Oh, by the way, I named the boat "Controversy" for all the grief I have had with the Puddleduck establishment.

Rick Landreville.

The name made me laugh out loud!

I was just going through the leeboard stuff because we haven't talked about it here for a while and the puddleduck experience with the biplane rig explains so many things where the explanations are so unsatisfactory.

Bolger said that with off centre masts and foils that "boats don't notice the difference" - whereas we now know more than that.

We also have an explanation for the performance drop - which didn't exist before - it was just speculation - now this one is proved.

Also it cleans up the explanation of why multihull outrigger centreboards have to be somewhat further forward and acts as a guide for design.

Not bad for a bunch of homebuilt boats being built by people of differing abilities!

Also while having a hunch that having the leeboard near the side of the boat causes a lot of inefficiency (drag from the different waterflows around the hull and the foil interfering - the risk of ventilation reducing the foil efficiency) making me want to keep it away from the Chine ... having this data meant I wanted to keep it well away.

To give the least asymmetry possible.

MIK

Hi MIK;

If you liked the name of my Oz Mk3, you will love the name of my new Oz Goose! Details and pictures to follow soon.

I am glad to help you sort through some of the assymetry problems, even if I don't fully understand how what I did helped.

One more week until the Puddleduck World Championships up in Summerland B.C., I am hopeful that I can further put the screws to to the 'establishment' by winning or placing well with my Mk3. I might even let em measure it to prove it is close enough to be still called class legal.

I am off to build a new lug sail for that race. Any tips on how to make it a tad bigger on the same spars? The winds can be very light this time of year up there.

Rick Landreville.

Originally Posted by pdr311

...I might even let em measure it to prove it is close enough to be still called class legal...

Do the MkIII's lines fall within the tolerances of the class pattern? (Sorry if that was stated earlier in the thread; I did read the whole thing but I can't say I understood all of what's been written because I had not yet read the PDR rules).

That would be a great outcome. Might that push MIK over the edge and into producing plans? No definitive reply required good sir; I'm only hoping aloud rhetorically.

I would seriously consider building a MkIII as part of my GIS strategic approval campaign (yes, I'm married). The MkIII's design is simplified enough beyond the already simple OZ PDR that I can get over my ambivalence/dislike of PDRs. This picture really does it for me:

I'll admit that I'm actually quite ignorant regarding the details of any of the PDR designs, including the Oz, except for what pics I've seen. But this thread really illustrates how little cutting and gluing there is in this design. While I'm still trying to convince myself that I could possibly convince my bride that I should be able to build a Goat, this is clearly a no brainer. I've built storage sheds more complex.

Keeping my fingers crossed for your success at the Worlds. Actually, I hope you don't blow them all away because that will work against the argument that the boat is no different from others. But I hope you don't suck either because that will work against the MkIII's viability. No pressure or anything...

Originally Posted by davlafont

Do the MkIII's lines fall within the tolerances of the class pattern? (Sorry if that was stated earlier in the thread; I did read the whole thing but I can't say I understood all of what's been written because I had not yet read the PDR rules).

That would be a great outcome. Might that push MIK over the edge and into producing plans? No definitive reply required good sir; I'm only hoping aloud rhetorically.

I would seriously consider building a MkIII as part of my GIS strategic approval campaign (yes, I'm married). The MkIII's design is simplified enough beyond the already simple OZ PDR that I can get over my ambivalence/dislike of PDRs. This picture really does it for me:

I'll admit that I'm actually quite ignorant regarding the details of any of the PDR designs, including the Oz, except for what pics I've seen. But this thread really illustrates how little cutting and gluing there is in this design. While I'm still trying to convince myself that I could possibly convince my bride that I should be able to build a Goat, this is clearly a no brainer. I've built storage sheds more complex.

Keeping my fingers crossed for your success at the Worlds. Actually, I hope you don't blow them all away because that will work against the argument that the boat is no different from others. But I hope you don't suck either because that will work against the MkIII's viability. No pressure or anything...

The Mk3 design is so close to actually meeting the class requirement, that when I measured mine, it did actually did fit within the tolerances (After I sanded the transoms down to raise up the measuring point. Cheating? Nope, just exploiting the rules). If you really wanted to make it comply, copy the measurements for the bottom 10" from the class rules, but build the boat according to MIK's plans. I wouldn't bother.

I should do okay at the Worlds, especially since it looks like there may only be local boats there, and I have not been beat by a local in over two years. I have sailed my boat a lot in that time, and have it pretty much sorted out exactly the way I like it. Most of the local guys like to build better than they like to sail, and the performance shows.

My fear is that they will not recognise the achievement because of the stir that was created this spring in the PDR circles. But that will be their problem and not mine. I would be just as happy promoting an Oz Racer class instead of a PDR class with the hopes that one day in the future the two could merge.

If you message MIK, he will sell you a set of the Mk2 plans, and if you ask nicely, he may even finish up the Mk3 plans for retail sales if there is enough demand. Duckworks in Texas has the Mk2 back up for sale on their site too. He will no longer be supporting or promoting the PDR class at this time.

Rick Landreville.

Hi Davlafont,

Rick pretty well sums it up.

Basically my plans try to show a "state of the art" approach to every aspect of the boatbuilding. But it is kind of hidden.

If the PDRacer class had a "fair" (means smooth curve) for the bottom I would probably still be designing inside the class. But it isn't and I've been told I cannot use the available tolerances to bring it back to a smooth curve. The powers that be also say I can't warn builders of this fact.

I've spent hours trying to make it work on the computer and finally marked it out on some ply and ran through with the right sized batten. Some points are out by 3/8" and others are up and down about a quarter inch. The back end of the boat is not too bad.

Problems are that it makes the boat harder to build, it is crappy methodology and the normal practice with any design is to fair it up first unless you are sure that it is fair. Which my boats always are.

So I guess I am an outlaw or excommunicated.

There is a chance of getting back together with the PDRacers down the track, but wiser heads would have to prevail on that side.

So that's it for now. The OZ Mk2 racer is a separate entity. The Mk3 will eventually be available as a kit in North America - as a kit I don't have to run any risks about it fitting or not fitting the rules ... the kit builder will handle those.

There might be a plan for the Mk3 eventually. But as a plan it won't be a PDRacer ... it just can't be while the current rules and certain other unwritten requirements are in place.

By clicking on my name to the left of this post you can send me an email or a PM (Personal Message) and I can tell you a bit more about the Mk3 plan.

Best wishes

MIK