center board V dagerboard?

[ozsmithy]

Hi all, a couple of questions from a novice sailor
I made my ozracer about a year ago and have had it out about twenty times, still awesome fun!
I have bought Perttu's plans for the ocean explorer because I'm getting the itch to build anouther one
Then I found the thread on the mk3 and am wondering about foils and how they work.
Does it make a difference to the sailing ability and performance if the foil is in the center or offset like the mk3?
What difference does the length of the centerboard make to how it sails? I really damaged mine about the forth time out and wound up cutting it down, so now my rudder is the centerboard and the cutdown one is my rudder. It is about 150mm shorter than the orginal rudder and I never really noticed a difference, initialy I was very worried that it would tip over easier but even in very strong winds it has never happened (40 km is the max I have gone out in)
For sailing pro's out there, how do ozracers compare with other small sailing boats performance wise? I realise something like a moth is going to fly but for small sailing dingies that you dont have to hike to much and can stay dry in.
After reading through Perttu's awesome plans I went outside and tried something I had never done and lay down in my duck, I had never tried as at 6'2" I just assumed i would not fit !! to my surprise i can actualy lie down fully! ( it's a bit lumpy) so now I'm thinking that it may be worth while to change to the foil being in the side pod?

[BradLH]

The cut down board and rudder may be contributing to the tacking problem you mentioned in your other post. You may be trying to compensate for the reduced rudder area by pushing the tiller further across which could be causing the rudder to stall.

How does the Puddle Duck compare to other small boats performance wise? They're dog slow but a PDR that's set up well does surprisingly well in handling and stability comparisons.

[PAR]

I'm glad I'm not the one that said it, but Brad is right, the PDR is a bit of a pig, though in skilled hands, you can get one to scoot (relatively) along pretty good. It's a concrete mixing tub with a sail, so you pretty much get what it looks like. It handles well because it's a board boat and small, sort of like comparing a Mini Cooper to a Bentley. The Mini can make a mockery of a Bentley in a tight parking lot, but that's about it.

Off center appendages do cause the boat to have an "advantaged" and "disadvantaged" tack. This simply means you'll have better pointing ability when the boat has the board immersed the deepest, which ever tack that happens to be. How much of a difference? Well folks that drive PDR's probably wouldn't notice, unless they had considerable sailing skill.

A have a few designs with offset boards, but I try hard to not offset it by much. I have 18' (4.87 m) boat with 9" (228 mm) offset centerboard to port, placing it under a cabinet and the aft end of the V berth. I did this so the interior of the boat didn't have a centerboard case intruding into the space. I have another 15' (4.57 m) design with a 4" offset centerboard. This is so the board clears the keel batten, greatly simplifying the build and further protecting the slot from rock jams in beachings and grounds.

If you want to move your board over, go for it. Unless racing against particularly cut throat PDR's you'll probably never notice the difference, plus you can lay down.

[davlafont]

Off center appendages do cause the boat to have an "advantaged" and "disadvantaged" tack. This simply means you'll have better pointing ability when the boat has the board immersed the deepest, which ever tack that happens to be.

Would it also be safe to add "all things being equal"? In other words, the disadvantage assumes your hull is heeled at its optimum angle to put the foils to their maximum effect, right? If that's the case, I would think these PDRs (OzR) are best sailed as flat as possible, which acts to minimize the depth difference on the two tacks. That's a far cry from the difference on a curved hull fitted with a leeboard.

[ozsmithy]

Thanks for the replies, I think I'll do it I have been getting a bit reved up to build a ocean explorer but saw some PD's where they had mounted a small popup tent on top for over night cover

[Boatmik]

but Brad is right, the PDR is a bit of a pig.

?????

Howdy PAR

I know I am pulling your comment way out of its original context ... but it is the kind of thing that people read and remember.

Maybe it also is a difference in OZ/English parlance. "Pig" normally means that a boat is difficult to sail in our neck of the woods.

Your context implies that you mean it has a limited top speed - which I would agree with completely. But it jams up pretty tight against the high threes and mid four knots and it takes a great deal to slow it down much from there.

The Oz variant has burned much more fancy boats off upwind in real racing and keeps going in rough conditions longer than most.

I would also very much disagree with the "skilled sailor" comment. The boat has huge stability - and carries the sail area well at least in the professionally designed variants of the type which have the right foils and helm balance.

Nothing can be further from the truth in terms of handling. Almost no piggishness even for beginning sailors who can jump in the first time and really sail. The boat is also responsive .. so it teaches people quickly. You do the right thing and there is immediate and obvious acceleration.

And very experienced racing sailors have been completely surprised and delighted about the performance and also that the boat FEELS absolutely like a well sorted out racing boat.

Which is exactly what the Oz Racer (formerly the OZ PDRacer mk2) is.That's up to national level sailors in the A-class cats and the local 16ft skiffs.

Promise you Paul ... it is completely surprising ... and it has changed my thinking a lot about design. Get the foils REALLY right and the rig dynamics right and you have a very high level of efficiency.

With the centreboard question ... I think you can probably lose about 100mm off the centreboard length without much issue at all. It might make the boat a little slower in rough water upwind. The next design iteration was going to see a narrower board of the same length to reduce wetted surface.

So some performance will be lost.

Boats will sail with leeboards quite fine. But the location is a compromise.

The basic problem is that designers work out the location of the foil from working out the location of the centre of the sail. But this is done on a flat piece of paper. However the real situation is that the forces from the sail are three dimensional. They go from near the centre of the sail with most of the force sideways ... but also a little forward. it has to be this way or the boat won't move forward!

However if you project this line of force relative to a leeboard .. the line will be ahead of the leeboard on one tack and behind it on the other. This means on one tack you will have extra weather helm and on the other extra lee helm.

But with a centreboard it is symmetrical.

One of the PDRs had a mast and sail on both sides with a leeboard. The boat was unsteerable when the mast was on the opposite side to the leeboard and fine to sail when they were on the same side. Because this three dimensional effect gets bigger with the bigger lateral distance between the foil and the mast.

That everything is really close to being perfect in terms of lining up is what makes the OZ easier to sail.

One thing that might make it harder to tack is the location of the sail relative to the mast for the lug. or not enough downhaul on either rig.

HOpe this helps!
Michael

[PAR]

A pig in this country means slow, sorry for the confusion. Slow is a relative term for an 8' boat and you're right she does surprisingly well in some areas. I also agree she's an easy boat to sail, particularly with her initial stability and generally forgiving nature. I've never seen a heads up, but I'd imagine she'd fair well against an El Toro, Sabot or Holdfast, though it might be more interesting to see a PDR against a Flipper, National 10 or Zoom8. As a sail trainer, you could do a lot worse then PDR, particularly with the investment aspect.

I know you have a soft spot for the PDR Mik, but I was wasn't intentionally picking on it, so much as I think the amount of materials used in one, could be applied to a faster, slightly longer boat. Of course, this might limit it's usefulness to some owners. I have to admit to not a lot of time in a PDR and the time I've had, has been in less then well assembled examples. I did manage to get some level of "ability" of one, with some tuning, but I couldn't help but notice the broad expanses of materials, that could have been stretched into a 10'er with better potential, maybe a 12'er, knowing getting wet and hiking to keep her up, would be the only options. I guess I'm spoiled, because I have a 15' 6" (4.72 m) boat that easily does low teens in moderate winds, with mid to high teens (MPH) in gusty winds. It's hard to go from a 14 - 15 knot boat to a 3 knot boat and still be objective, so please accept my apologies.

[ozsmithy]

Hi thanks for all the information Mik where I was thinking of moving the board to was inside of the inner line of the top so about 300mm side ways, so I could lay flat through the middle as I would love to explore between the gold coast and brisbane and the idea of sleeping in the boat at anchor is cool I saw the mk3 forum and it got me thinking, as to what diffence it makes. I still learning to understand how the different forces work and try to sail pretty flat.

example, when close hauled does it make a difference that the block for the sheet that slides accross striing at the back of the boat is out to the side? I have experimented pulling it back to the center but it seems best about 3/4 of the way across for pointing to wind.
I am going to make a new set of boards soon, as i am using my rudder as a center board and my old board as the rudder has had about 250mm cut off after a bad day with a rock. so I am a lot shorter than your plans at the mo.

The reason I got thinking about a chinese lug was reefing in or trying to drop the sail and set anchor in any sort of a breese gives me the hebby gebbies, this may relate to my sail balance as I have tried to practise 'heave to' and cant make my duck do it, it just wants to fly.

I have to add about the stability when you are learning to sail, the duck is fantastic, where I sail on the gold coast broadwater I often have lots of big boats, 40' cruisers ect powering past at 20-30Knots and a big chunk of fun is surfing around on their wake!

In the past I had my lug set up with lazy jacks, one to make it easy to get out off the beach and two to try and have something to drop the sail into. last time out I got rid of the lazy jacks and put in a couple of extra gromets in the luff and leach, I have run small lines from the reef points through the gromets to small blocks at the ends of the boom and back to jamers in the middle of the boom on the top and this worked much better for reefing and unreefing, and droping the sail down onto the hull when stopping seemed better to, less blowing around

[Boatmik]

A pig in this country means slow, sorry for the confusion.

It's hard to go from a 14 - 15 knot boat to a 3 knot boat and still be objective, so please accept my apologies.

None necessary Paul!

Just different terminology/slang! And your discussion always adds a great deal of info!

Cheers
MIK