Time to continue my education:
What are the pros and cons of a unarig vs a normal sloop rig?
–Doug
Doug -
in general - or “Footy” related?
PRO
Easier sheeting - only one mainsheet
Leading edge isn’t backwinded by jib
Full battens provide better foil shape - if rules allow
Boat points higher than with jib
No forestay/jib luff sag
If rotating mast, no need for back stay - mast bend controls luff curve and fullness of sail.
Seems to be able to fully use the sail twist - no interference from jib
Rig can run loose shrouds to allow mast rake back for upwind sialing, and mast flops forward for downwind sailing
CON
Taller (higher aspect ratio) sail needed to have same sail area as a boat with jib
More tipping force than low aspect ratio sails
More difficult to “tune” if not fully battened (leech control)
Needs use of vang to control leech shape
More difficult to sail downwind
Less sail area if mast height is controlled by rules
These are my thoughts based on my big boat multihull experiences - my uni-rig could point well above the cats with main and jib, but was tricky to dial in downwind. Downwind sailing by jib was much easier to read/do than with only a main.
Not sure how much of this would translate to a “Footy” since I have little interest in that class.
Some more PROs amd CONs
PRO
With unstayed mast, easy to let boom forward of athwartships on run, thereby preserving flow over sail (not stalled plate) - but of course you can tack downwind.
Mast bend does not affect forestay tension (possible to avoid with an unstayed Footy rig, but complex).
CON
It’s putting Dick’s point about downwind control slightly differently, but try looking at some photos of a well-sailed Finn or OK dinghy on a run in a blow. The boat is being deliberately heeled to windward to keep the centere of effort over the hull:
http://www.okdinghy.co.uk/gallery/ffsc04/leew3s.jpg
You can’t do that with a Footy (although you can have a balanced una)
Higher cente of effort increases tripping couple.
My (as yet untried) solution is to use two masts -a ‘Dua’ rig!
Dick & Angus,
Very interesting comments. I’m not sure that I entirely agree that the rig needs to be taller & higher aspect in order to achieve the same sail area. That being said, a low aspect single sail can have more issues with balance, especially when running.
The standard cat rig will have a considerable offset of the CE from the boat centerline, causing alot of rudder trim to resist yaw moment, or the need to heel to windward as seen in the OK Dinghy picture. As Angus points out, it is possible to have a more balanced una rig. This can be done by projecting an area in front of the axis of rotation, similar to what is done to acheive a balanced rudder. This is one of the things I like about Brett’s concept (to be seen in the below pictures). The CE offset is much less than if the rotation is at the leading edge of the rig. This has the added benefit of less servo effort needed to change sheeting angle.
- Brett’s design
- Brett’s rig
3)my rig showing sail draft with wing sleave
4 & 5) more profiles
Very interesting rig Bill. Questions.
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Transferring transverse moment from the mast to the pivot looks like an engineering nightmare - or am I just thinking in full scale terms?
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Obviously we have independent adjustment of the camber of the upper part of the sail. Is this used as an adjunct to automatic flattening through mast bend or instead of it?
Latest version of my Una rig weighs in at 10grams complete.
Can be built in 15minutes.
auto depowering is better than in previous versions.
Just have to perfect the ammount of stiffness required for each rig size.
This will vary from boat to boat.
pictures coming soonish.