I have some thoughts for your cost-benefit analysis.

I currently have a flat H-R sail from 1983, straight out of "Practical Junk Rig" and I sail happily in all directions, even though I can't make progress to windward in a F7 on a short chop.

Make no mistake I'm interested in playing with other rigs, but that's because I'll enjoy the construction and experimentation. That's the key part to factor into your analysis.

I'm pretty sure I could achieve everything I want to as fast as I really want to with my current sail.

I certainly wouldn't spend much it anything on a ready-constructed new sail, which tells you something about the value of efficiency to me!

Edits: this site is really not mobile friendly!

Arne Kverneland wrote:

I realise that my Ingeborg will never really fly. With her six metre waterline and with some displacement, she will hardly ever see seven knots. I can live with that. The point with that boat is that she has the roundest polar diagram of any boats I have owned.

Hi Arne--Is the polar plot for IF or Nordic folkboat online some where? I've searched but can't find.

thanks

robert self

VO TO wrote:
I came up with another design that is a cost-effective way to add camber.

I read about wing tail flaps on "Theory of Wing Sections" by Abbott and von Doenhoff. A flat flap 0.2 of the chord in length, with 30-40 degrees of deflection can add quite a bit of coefficient of lift. It is like gurney flaps, but it slides on a hoop.... like the aerojunk rig foresail that slides back and forth on an arc to create camber.

Vo,

did Abbot and von Doenhoff mention anything about increased drag in the process? It would surprise me hugely if a 40 degree flap would not increase the drag as much as the lift.

Arne

Arne Kverneland wrote:

If you are considering making a hotter version of the JR, wing or whatever, I suggest you make a little cost-benefit analysis before you go ahead.

The fairly plain JRs I design, basically Hasler-McLeod sails with camber added in the single ply panels, are most probably not the fastest version of the JRs to windward, but they are still quite good. Therefore, I think it will take serious improvements (read: cost and/or weight and complexity) to achieve as much as 5% increased VMG to windward.  When reaching and running, the gain over a plain, cambered JR will be very moderate indeed. Are you willing to pay for that 5% extra speed to windward, either by shelling out serious money, or by having to work long hours in the workshop to assemble a big number of bits, which well may decide to fall apart a couple of times before you get it right? If yes, then by all means, go ahead  -  but remember:
It is so easy to dream up great, aerodynamically superb rigs in the armchair. It is quite another thing to actually convert the dream into reality.

As said, I go for the ‘second-best’, straight JR with camber. However, it saddens me quite a bit to think of the many people (2/3 of the ‘junkies’?) who are still sailing under inefficient, flat sails. I have owned one such sail, and I most certainly don’t want to own one again.

Arne

 

I came up with another design that is a cost-effective way to add camber.

I read about wing tail flaps on "Theory of Wing Sections" by Abbott and von Doenhoff. A flat flap 0.2 of the chord in length, with 30-40 degrees of deflection can add quite a bit of coefficient of lift. It is like gurney flaps, but it slides on a hoop.... like the aerojunk rig foresail that slides back and forth on an arc to create camber.

It a lot less material than the aerojunk, because the two long wishbones are not needed. The forward 80% of the sail is a regular flat junk rig (or a cambered junk cloth, or 2-ply wingsail section), then the last 20% splits out into a V batten. The arc connects to the V batten ends; looks like a slice-of-pie outline. The 20% panels slides on the arc with rings/grommets. The sheeting attaches to the rings/grommets to steer the flap to deflect and also steers/trims the forward 80% sail.

No gap between the trailing flap and main sail, it's all one sail. The flap may be un-battened to get some curve. No moving parts (except rings sliding on an arc) or joints. 

This cool invention needs a cool name.... I call it the 'Flapper' :-)

David Tyler wrote:

Am I a tweaker or a fiddler? 

You are probably both, David, but don’t worry. The main thing is that you are a doer. You therefore know what it takes to complete a project. Now that you have acquired experience with Weaverbird’s Mk1 version of a wingsail, it will be interesting to read about the results you get when you upgrade the sail to Mk II, with the mast hidden inside a doubled fore-section (..that’s what you are planning, right?...).

My posting below was more a warning to those who want the non plus ultra rig before having upgraded from flat to cambered sails yet.

I may even have done a bit rig fiddling myself, from time to time. I still have a couple of ideas lined up in my head, but for the last years I have spent more energy on debugging my junkrigs  -  getting the sheets, lazyjacks and different parrels right.

I realise that my Ingeborg will never really fly. With her six metre waterline and with some displacement, she will hardly ever see seven knots. I can live with that. The point with that boat is that she has the roundest polar diagram of any boats I have owned.

Annie. I have done some motorsailing in other’s boats and I don’t mind motorsailing if one is a bit short of time. When topping up the tank after these trips, we have found that the sail has cut the diesel-consumption with as much as 50-70%. Quite amazing; the diesel purrs along at a constant 2200rpm and we expect it to have a constant consumption, but that is not the case. If a fuel-flow meter were made visible in the cockpit, we would no doubt be surprised to watch how the reading flies up and down with varying winds. I would therefore encourage boatmen to fit an auxiliary JR on their displacement motor vessels, and thus end up with a greener and safer boat. Graham Cox has written in other postings about how the rig and the engine of his Arion are backing each other up to windward. Personally I neither have a work schedule nor long voyages to do, and Ingeborg is, as said, quite good upwind, so my use of her outboard engine is generally restricted to getting us out of, and sometimes back into the harbour.

Arne