Thread: OZ vs Kiwi

This is a photo taken Saturday in moderate to heavy wind.

I wonder out loud how transferable that info is with your aluminum (aluminium? Why not?) spars. I have quite a bit of flex with my tapered wooden spars which throw some draft or some flatness into the sail without resorting to retying the sail to the spars. The only thing I change is the outhaul tension on the boom to change the draft of mine, but I am using the heavyweight polytarp (12x12 weave, 7 oz perhaps?). Downhaul tension really loads up the spars in my case. I am using a 6:1 boom vang from my Geary 18 for the downhaul.
How much flex do you get from your yard and boom? They look quite, um, robust!

Rick Landreville.

Rick,

I don't know how the aluminum would compare to wood since with wood there is a wide range of stiffness depending on species, grain spacing, grain orientation, and other variables. The yard I'm using has the same dimensions and alloy that Needlespar uses for the Keyhaven scow, which also uses a balanced lug. The yard is robust but I can easily get enough bow in it to flatten the head with the 8:1 downhaul I'm using.

Your 7oz polytarp is more than twice the weight of the 3.1oz I'm using. I think the heavy weight tarp was a major factor in the "90 sf balanced lug sails don't work well in light air" speculation.

I can change the draft in the head using the downhaul but I wanted a little extra for the light air conditions that were forecast, and fortunately the forecast was right for a change. Using the zip ties I could have quickly changed back to my original setup.

Another thing I've done that I didn't mention is put an eye strap on the yard to run the throat to yard lashing through. It seemed that when I would apply downhaul tension the head would slide down the yard and flatten out before there was much bow in the yard.

I'm still experimenting and looking for the optimum setup so I'm not sure what I'm doing is exactly right, but it seemed to work well last weekend.

I'm looking forward to hearing what Mik has to say after looking at the photos I posted

Brad

Originally Posted by BradLH

Rick,


Your 7oz polytarp is more than twice the weight of the 3.1oz I'm using. I think the heavy weight tarp was a major factor in the "90 sf balanced lug sails don't work well in light air" speculation.

Brad

Hi Brad,
The PDRacer World Championships were a light air event this year. 0-5 kmh, masthead flag hanging limp most of the time, and my boat outperformed all the other boats in those conditions. The only flaw was an inablility to tack to port in very light air (like where it was so light you had to wet your cheek with water to feel which direction the wind was coming from). I do not believe there is any light air issue with that much canvas hanging off the spars. I would chalk most of that up to people that are either impatient, or inexperienced. I can't imagine trying to sail with only 45 square feet like some of the others had in those conditions.
Boat and sail setup are crucial when the winds are light or if its really blowing hard. Most folks do not trust themselves to make adjustments and there are very few people with experience with a four sided sail to offer an opinion.
Most of the sailing club crowd don't beleive a lug sail can perform well, until they see one set up right. Even then, they think that if there was a more contemporary rig on it, it would be faster still...

Rick.

Rick,

This is the discussion I was referring to: Yahoo! Groups

Brad

Brad;

I think I replied later on in another thread.
Yahoo! Groups

Rick.

Howdy,

My feeling about this is that the OZ plans lead to the putting together of a very good package. Everything is not too far away from how someone would turn up to a national champs in one of the more competitive racing classes - that's where my head was at when we worked through everything from the plan to the rigging setup - it takes decades of lessons from competitive sailing into account.

That is within the constraint of the cheap materials and polytarp sail of course - even though the materials are everyday - and the sail cloth and cutting is relatively crude - the actual detail is quite highly refined - four masts and four sails for the sprit - and the lug was just great from the first one.

The plans cover all that stuff - so that if someone follows the plan they end up with a very sophisticated and optimised boat.

Something that can be raced in a championship next day (almost).

It is hard for someone without the background to put something together that will work this well.

The other side is Brad has also tricked the boat up with a vang and some other adjustments to make it faster still. As you all know I always struggle a bit with the complexity issue - but everyone else seems to decide what they want pretty easily - simple or sophisticated. No probs!

And the practice counts for a lot too. Before the worlds that they won I think rick in Canada and Shawn in the USA spent way more time out on the water than anyone else.

Put with a good boat it is a very effective mix!!!

MIK

I am almost out of battery - so will comment on the sail shots later.

MIK

A video of brad sailing his OZ derived PDR.

[ame=http://www.youtube.com/watch?v=B3f7n1IWozg]YouTube - PDRacer #431 at Lake Eufaula Oklahoma[/ame]

Hi Brad

Your rig looks very nice indeed, and interests me because I am experimenting with a stiff alu yard on my GIS.

There's just one small thing that you could try which will help with the over-tension along the head. Currently your throat is lashed to the yard below the throat. This has the unwanted effect of increasing the tension of the head along the yard as you apply more downhaul, and makes getting the correct tension up there almost impossible.

Moving the attachment point to above the throat will stop the downhaul tension migrating up the length of the yard so that you can set the head tension correctly via the cord at the peak of the yard. This will allow you to get more power from the sail up top, especially in lighter airs.

Keyhavenpotter advocates this and I've found that this small change made a big difference to my sail.

Let me know what you think
Attachment 150106

Woodeneye,

Yes, the diagonal or tension lashing you're pointing out would go slack when downhaul was applied, before I put the eyestrap on the vertical throat to yard lashing. I've thought about a diagonal lashing like you've described and may put one on. A diagonal in both directions and the eyestrap would eliminate any of the movement of the throat up or down the yard.

Thanks,
Brad

Originally Posted by pdr311

Brad;

I think I replied later on in another thread.
Yahoo! Groups

Rick.

Rick,

I read your post, good stuff.

My rig is stiff enough that I don't have what Bethwaite calls the self adjusting or automatic rig. Mik has designed that into his rigs with the tapered yard and mast that will flex and depower in a gust..

When I get a gust the yard may flex a bit and the head twists off some but I usually either need to hike hard or ease the sheet to keep the boat flat. In moderate to heavy gusty conditions my yard is usually bowed near maximum and the head flattened quite a bit with the downhaul on pretty hard so there isn't much room for the rig to self adjust anyway.

During my build there was some discussion about the GIS yard possibly being a bit too flexible so I decided to go with something a little stiffer than the tapered yard and I like the way it works.

When I built my OZ I was planning to do some serious racing so I added extra controls and used the aluminum mast and spars but I'm not recommending anyone else do what I did. Like Mik says it does add expense and complexity. 99.9% of the OZ builders will be very satisfied with the boat if they build it exactly as he designed it.

Brad

Originally Posted by Boatmik

A video of brad sailing his OZ derived PDR.

You'll notice my form isn't great and I'm not keeping the boat flat but it's because I'm trying to conserve energy Some in the group logged 10 GPS miles on that beat.

It still amazes me that a 4'x8' box with a plastic tarp hanging on a pole can perform that well.

Brad

Originally Posted by BradLH

Woodeneye,

Yes, the diagonal or tension lashing you're pointing out would go slack when downhaul was applied, before I put the eyestrap on the vertical throat to yard lashing. I've thought about a diagonal lashing like you've described and may put one on. A diagonal in both directions and the eyestrap would eliminate any of the movement of the throat up or down the yard.

Thanks,
Brad

Good one Brad, I'm interested to hear your thoughts on the results.

I enjoyed the video. It always amazes me to see a box moving so well in a bit of a chop! Somehow I don't think my beer-trained tummy muscles could survive a 10 mile beat though.