Symmetric spinnaker, subtle differences in design

[Channel Sailor]

I have two spinnakers that came with my yacht the newer one which I use all the time, except once when I hoisted the much older one just to see if it was OK. But it was not up for long. At a glance I think one is possibly very slightly larger and may have a deeper belly to it. My question is, if I can find space to spread the two of them out or even suspend them, what am I looking for to understand if they have different uses? In particular which one would perform better if set shy.

Reason for asking is I want master setting a spinnaker on a reach and how close to the wind it will go. So I need to understand if I have a sail that will do it in the first place, before I waste time only to later find out I need a new sail anyway.

 

[lw395]

It's the flying shape that matters, you won't see that spread out on the lawn.

I'd suggest putting the two kites up in turn and maybe taking some photos.
A flatter sail will go closer to the wind, but there are no magic angles, the angle you can carry a certain kite to will vary with windstrength.
Very often is possibler to carry a kite on a tight-ish reach, but it won't do you any good, just heels the boat and stretches the kite.

What cuts are the kites?
A simple horizontal or radial head is likely to go less close than a star cut. But that may not be a reliable guide.

 

[flaming]

Depth and size of shoulders is the key. A broad shouldered deep kite will run well but not reach. A relatively triangular kite will reach much better but is giving up area on a run.

 

[Channel Sailor]

Useful, thank you. One of the spinnakers I think does have quite noticeable broad shoulders, the one I use mostly and it does not seem to set all that easily on a reach, so far. I will look more closely. Noted the point about setting shy can stretch the sail, as I have already noticed in a good sailing wind the dramatic increase in apparent wind and heeling which when wind is too far fwd the sail (and rig) gets a hammering.

 

[Foolish Muse]

From my singlehanded tips book regarding a deeper spinnaker versus a flat spinnaker, specifically in regards to what would be designed for a singlehanded sailor:
I contacted Rick McBride with Leitch and McBride Custom Sailmakers in Sidney, British Columbia. Rick explained the differences between a stable and a flat spinnaker. The skipper should keep in mind that all spinnakers act like a wing, with air flow from the luff to the leech, even when sailing deep downwind.
A stable spinnaker is designed to be used with minimal attention to sail trim. It will fly even as the apparent wind oscillates back and forth in normal conditions. A flat spinnaker, in contrast, requires constant trimming or will collapse. A stable spinnaker has greater cord depth. This allows the boat to sail higher or lower without the sail stalling. It also has a more elliptical leech, allowing the luff to fold over on itself without collapsing. A flat sail will collapse if the leading edge folds over at all.
Like the wings in a jet airplane, a flat spinnaker is faster but is more prone to stalling or collapsing than a stable spinnaker designed for singlehanding. This tradeoff between speed and stability depends on how much the skipper is able to work the sheets over hours at a time. The accompanying drawings are highly exaggerated. In reality a stable spinnaker has a cord depth only a few percent greater than a flat chute.

 

[Kerenza]

airflow is not always luff to leach, simple example here though there are more technical papers.
https://www.sailingworld.com/symmetric-spinnaker-flow-control

 

[Steve The Seagull]

To tell the difference in spinnakers on the floor you look at the half width vs foot length.

Approximately a reaching spinnaker will have a half width less than the foot while a running spinnaker will have a half width bigger than the foot.

To find the half width take the head down to each clew and mark halfway on each leech and then measure across.


http://www.sailing.org/tools/documents/ERS20172020UpdatedPrintVersion-[20912].pdf Measurments found on page 35.

 

[lw395]

Or look at the angle the leeches make at the head.
A wide head = big angle