Claude L'Honnen wrote:

Richard Brooksby wrote:Marchaj shows a *great* increase of lift from an elliptical sail for some upwind angles, especially with lower AR. [Aero-Hydrodynamics of Sailing, fig 2.140.]

I am new to JRA and joined to get sound advices about my own project of conversion to junk rig. I then read the different posts to be personnaly "instructed".

Welcome to the JRA! I hope your project is going well.

However if my opinion may be useful, I would say  your reference to Aero-Hydrodynamics of Sailing, fig 2.140 seems irrelevant.

The higher the AR, the higher the driving force of the sail; the lower the AR, the higher the drag coefficient as shown by this Drag of a sail diagram (probably coming from the very same book).

Your diagram only says a sail has a better lift if rounded or elliptic.

You'd better check before cutting the sail !

Yes, the diagram you link is also from Marchaj, and is not many pages away.

I was responding to the discussion in this thread about whether to bother with an elliptical sail, or whether to use the rectangular plan of Poppy or Amiina. So I am not sure why measurement of that difference would be irrelevant.

Marchaj also discusses AR in great detail. But it is not always a choice. For my boat, extending the mast is probably unwise. It is not a very stiff boat. Instead I plan to increase my sail area (for light downwind) with a lower AR sail. Marchaj's tests show that an elliptical tip is even more effective for low AR.

Also, the diagram you linked shows greater lift for a low AR gaff rig at apparent angles greater than 30°, so it is not as clear cut.

I hope I have understood you correctly.

I expect to be cutting several sails and sail parts, but this is not a thread about my sails. That's over here

Arne Kverneland wrote:

Chris’ proposed rig is looking good, for sure, but...

frankly, if I were to make a split JR, I would aim for a planform very close to that of Slieve’s Poppy. It may not look as elegant as this elliptical planform, but the Poppy rig has three advantages:

·         Many identical panels makes the lofting and sewing job a lot easier.

From my personal the point of view I suspect “a lot” is more like “a bit”.

·         A sail, which is wider higher up, adds sail area, and a generous sail area is very useful for downwind sailing, something we do a lot of the time.

Again, for my plans, I'll be dramatically increasing total sail area, and am more interested in achieving a balance of performance downwind and up. Marchaj shows a *great* increase of lift from an elliptical sail for some upwind angles, especially with lower AR. [Aero-Hydrodynamics of Sailing, fig 2.140.]

·         The vertical leech prevents the sheetlets from getting caught by the batten ends or under the boom, when tacking or gybing.

I think extending the batten ends, and if necessary running a line vertically between the ends, should take care of that, as long as the sheeting angle is OK.

Boring arguments, maybe, but that is how I am wired:

“Easy handling beats performance,
and
 performance beats fancy looks”...

Me again...

Well, most of us are involved with junks for easy handling, but all comparisons must be quantitative. How *much* performance to trade against how *much* handling?

I'd add something before all of these. Aren't we all here to have fun with our boats? To easily forgotten. Chris said he'll have fun making a more interesting sail, and I'm with him on that!

Apologies for bizarre formatting. Impossible to fix on my phone with awful forum software.

I'm afraid I missed this thread, but have just been directed to it by Chris Galliene after he was mentioned in a reply to my post The Spitfire junk.

I'll link that here out of interest and start reading through the whole thing. I'm certainly considering splits by the way, along with everything else.

Chris Gallienne wrote:

I shall attempt to sand down the bottom of the mast by the required 0.3mm (plus a bit?) and join the sections using slow-cure epoxy as a lubricant/adhesive.

Chris

I managed to do this, back in my National 12 dinghy racing days, to add a 1 3/4in diameter topmast to a 2in x 1/8in wall mast tube. I think you're going to find it very hard work on a 5 1/2in mast.

OK, armed with inside and outside joint calipers and a digital vernier, I have tried accurately to measure the mast and extension tube. I measured the ID of the extension tube at 3 points roughly 60 degrees apart at each end. The mast I measured in two orthogonal places at 3 positions along the four-foot section which has to go into the extension. Here are the results in terms of mean and standard deviation for each set of measurements:

	Mast	Ext
Mean	139.82	139.52
Std. Dev.	0.041	0.534

This is interesting. The variability in the freshly-milled extension tube was quite high compared to that of the Needlespar mast, which has been knocking around in China Girl for the best part of 30 years, and was near-zero. I knew that Needlepar roll the taper into the top sections of their masts, and roll the joints of the three sections. Either they are buying in tube with much better tolerances than mine, or they're rolling the whole mast to get it dead straight.

The upshot is, not only was I using my insert to 'straighten' the cross-section of the extension tube, but apparently to increase its mean diameter by some 0.3mm! No wonder it took a lot of pressure to insert it!

I shall attempt to sand down the bottom of the mast by the required 0.3mm (plus a bit?) and join the sections using slow-cure epoxy as a lubricant/adhesive.

Chris

Edit: The site linked by Phil below gives tolerances only for outside diameters of round tube. The tolerances for ID are probably wider. Nevertheless, the variability in the ID for my tube are within those OD tolerances, so the tube I've bought seems to be quite acceptable in those terms.