Yes, we should ignore S7. It is unusable without the STW data. I'm not sure what went wrong but we did have trouble with the instruments and had to re-solder all the connections at one point.

Anonymous wrote:

We did some more tests on Amiina in July and the CSV files are attached. The numbering starts with P3 and S3 to follow on from the files that David recorded. I have included David's files again and added the May date to their file name for clarity.

There are a set of files recorded on a very windy day when we were heavily reefed which are labelled accordingly.

I was hoping to do some more testing in the Falmouth area this month but other things have intervened so it hasn't happened - yet.

OK Alan. Got the files. Thanks.

I'll work up Amiina first since it'll be a new boat for me then Weaverbird wingsail ending with Weaverbird wing vs single-ply comparison.

rslef

Anonymous wrote:

David wrote:

Weaverbird is in Poole Harbour, and this morning we managed a few runs on Amiina with the performance measuring equipment rigged. The data is yet to be processed. 

This afternoon, we sailed Weaverbird (wing sail) and Amiina (split junk) together, assessing relative pointing angles and speed. On all points of sail, our speeds were equal. Amiina is a little shorter, so Weaverbird should have been faster by about 3.5%, but since Weaverbird cannot raise the outboard whereas Amiina can, and Weaverbird has twin keels whereas Amiina has a fin keel, I think this would account for it.

However, the noticeable difference was that Weaverbird was able to point appreciably higher, by about 3 -5 degrees, while sailing as fast.

Edward disagrees, says the pointing difference was 2 - 2.5 degrees!

I did two runs on each tack on Weaverbird this morning. CSV files for both boats are attached.

Was there any more CSV file data collected this summer? I'll try working up the data if this is all that was collected.

rself

Rob,

I expressed myself unclearly. What I meant, was that my range of Johanna-style sails can be set with a balance between 12 and 17% (with respect to mast), or even 10 to 17% on the sails with higher aspect ratio. The position of the slingpoint sets the final limit for the sail balance (we don't want it to touch the mast.). If you want to increase to 20-22% balance, then the yard angle must be reduced. However, changing from the present 10% to 16-17% should make a big difference to the helms balance.

On the first two trips with Ingeborg, in 2016, the sail was set with about 12% balance. To trim away most of the weather helm, I increased the balance to 15-16%, by both lengthening the  standing tack parrel, TP (in harbour, before next trip), and then using the yard hauling parrel, YHP, to bring the halyard’s slingpoint closer to the mast.

I don’t have a running TP, so I can only shift the top of the sail back and forth under way by playing with the YHP and the tack hauling parrel, THP. I generally don’t bother. To remove the last bit of weather helm on Ingeborg, I would have needed to lengthen the batten parrels and maybe even the fore batten pockets. I haven’t bothered. I need to reef in the middle of F4 and then the weather helm is reduced.

I have been pondering the idea of making another sail for Ingeborg, very similar to the one I have, but with the camber increased from 8 to 10%. Any armchair speculations about the outcome of such a change is useless; only full-scale sailing will do. In case I go ahead and do it, I will reduce the batten length from 4.90m to 4.75m, and the batten parrels will be made long enough to allow a full 17% balance.

Clear as mud, right?

Arne

PS: Now I looked up your boat in your album. By measuring with a yardstick on the screen, it appears to me that your sail is already setting with 17% balance. How is your rudder? Could it be improved by simply gluing on an endplate?

I find the shown pointing angles, 32-36°, to be good, but not spectacular. Only on my present boat have I fitted a simple wind-direction indicator. This has the vanes set at 32° from the centreline. I find that I can quite easily sail this close with my plain, single-ply, cambered panel sail.  My guess is therefore that the big, dominating gain in performance has been achieved by going from a flat to a cambered sail. The extra step up to Split JR or wing JR will only produce fine, subtle improvements, if any at all.

(.. My present boat, the IF Ingeborg, is special. Her slim hull and big keel make very little leeway, so she is actually closer-winded than any boat I have owned before...)

As for keeping my boats in the groove when close-hauled; I find that quite easy, as that groove is fairly wide, and the luff of the sail and telltales at the leach are easy to read.

My motives for choosing a Split  JR would therefore be others than performance to windward:

·         The sheet forces of a SJR are clearly lighter than on a sail with lower balance in it, like mine (12-17%). That would be useful, in particular when day-sailing and racing with lots of manoeuvring.

·         Helms balance stays better when reaching and running, so no need to modify the rudder or arrange with adjustable sail balance.

·         The squared-out SJR sail should also have better clearance to the sea than my wide low-balance sails.

·         Its batten parrels cum downhauls appear to also act as active fan-up preventers. Good!

·         In some cases, the high-balance sail would let one step the mast further aft, which may better suit the deck layout and interior. In other cases a low-balance sail fits better.

·         The SJR could even be made by an amateur like me.

The Wing JR would never be my choice, simply because my ambition level with respect to VMG to windward  -  and my skills with GRP or epoxy  -  are not high enough. I rather choose a close-winded hull where the outboard’s leg can be swung up.

Anyway, good luck!
Arne