Aerodynamics of 'overlapped' staysails

[brian eiland]

and then continued after my multiple postings in 2023 ??

That should have read, the postings DID NOT continue after my postings ??

I realize there are difficulties with staying this rig, ...BUT the aerodynamics of it really make sense.

 

[brian eiland]

i'm still surprised that no follow up postings have been added to this interesting discussion of 'overlapped staysails/headsails'

 

[philSweet]

Some somewhere in the intervening time this got added to my collection-

https://www.blur.se/images/The-effects-of-staysails-on-yacht-performance.pdf

 

[brian eiland]

philSweet,
I don't think that study is that applicable to my aftmast arrangement as it largely looks at spinnakers as the A sails, rather the genoas.

 

[brian eiland]

I'm working out the sail suite for a Class 40 under construction, and am wrestling with a problem that seems to bother no one but me.

The problem is that it's common for racers to use multiple headsails in such a way that the leech of the A-sail extends further aft than the leech of the aft-most headsail -- thereby ruining the various 'slot effect' benefits of the inner sails. It doesn't seem sensible aerodynamically.

Since reading Gentry, my (amateur) understanding is that the leech of the trailing sail must extend further aft than the leech of the leading sail, or else the singular foil is compromised. A staysail that is 'buried' by the leech a big A-sail might help a bit with mainsail flow attachment... or might reduce the drag of the mast... but is more likely to simply add drag itself or to generally interfere (particularly if its twist cannot be controlled to match that of the A-sail and main, which is usually the case in the low clew jibs and genoas used on most racers).

Staysails that are 'overlapped' by A-sails don't add upwash, lift, etc.

But no one seems to pay attention to this. Very smart people are violating it everywhere -- on Maxis, VORs, Class 40s...


But so far, I'm only getting blank stares and shrugs from designers. Conventional practice ignores the issue. I just can't figure out why I'm wrong.

Thoughts and/or recommended resources very much appreciated.

I assume you are referring to this article by Gentry, attached

That is one reason I chose the twin headsail arrangement I did on my aftmast rigged cat.

https://www.boatdesign.net/attachments/the_double_head_rig-pdf.191119/

 

[brian eiland]

Not if you configure the slot between the headsail and the staysail the way i did with the aftmast rig,...consistent slot

There is plenty of beam on a multihull to be able to sheet those 2 headsail out to beam of the vessel for broad reaching conditions,...(and for carrying those multiple backstays)