I wouldn't say I'm neglecting the slot effect; perhaps I'm just
de-prioritzing it.
If you want to race short-handed with a light air monster, the una
has some advantages to a standard bermuda:
a) For a given sail area, the top is noticeably further from the
water, up where there's actually wind. 1+1 may equal 3 when there's
wind, but when the only breeze is far above the water, the slot
effect won't do much for you.
b) The whole sail depowers when you let out on the mainsheet.
That's nice if you're short handed -- trying to dump a main and a
highly-loaded genoa, gracefully, while steering in response to gusts
and obstacles, can be a challenge.
c) Between sail twist and mast bending, the whole rig has some
built-in gust response, allowing you to carry significantly more
sail area with significantly less running about. In essence, you
can have "too much" sail up, and yet still keep going without
capsizing. I'm not sure if the jib on an easyrig will depower in a
gust as efficiently as the mainsail in an una, particularly because
the twist effect is not the same.
d) Fewer strings to pull for fine-tuning. If you have a full
crew, it's easier (and fun) to set the jib track and sheet tension
just right, work with the vang, mainsheet, and outhaul, and get all
the shapes just so. If you're short-handed or solo, there's a lot
to be said for having only one sail. With a rigid boom, the
mainsheet controls the sail angle, and the outhaul location and
tension control shape.
The una will have a higher center of effort. You'll probably have
to reef more often, though some of that need will be offset by the
bendy mast, and also by the ability to let the boom completely out
(no shrouds in the way) during a gust.
None of this is to say I that want an una rig, though. I like
them, but I also really like the idea of a semi-balanced sail with
more area down low. I also particularly like the idea of not having
to grind a winch in each tack. Since I have to do a lot of
short-tacking to get out to open water where I am, this colors my
view of rigs. If I could count on being on a single tack for
minutes or hours at a time, I'd probably think differently.
I have a catamaran where I have to tension my forestay with the
mainsheet (8:1, though many with this boat have gone to 12:1 or even
32:1 on a fine-adjuster). It would be more convenient to have a
backstay, but then I'd lose all that wonderful sail roach. So
loading up the sail works for me.
- Mike
bjarthur123 wrote:
i think both of you are neglecting the huge performance value of the slot between the jib and main. the accelerated flow from the jib onto the back of the main is a HUGE benefit. 1+1=3. it's like a third sail.
i'm not completely familiar with all the boats out there, but are their any open development classes with no restriction on sail area for which a una rig is preferred to a bermudan? my impression is no. i infer that the reason is because for a given righting moment the most efficient sail plan is a bermudan rig. i've read that A-cats only have unas b/c of a restriction on total area. am i wrong on this?
that being said i'm on the fence about una vs. balestron for a proa. the saggy jib really bothers me. one fix is to get a high-modulus sail and crank on the outhaul. hobie cats and farrier tris both have rotating masts and hence loose stays and tension the forestay with LOTS of mainsheet. should work on a harryproa too i think.
but then the mast would have to be heavier because of the compression. and you've got the weight of the fore boom as well. i really don't know where the optimum lies here. and then there's the rudder issue!!
wetas have no boom or traveller and sail down wind just fine without. has anyone considered skipping it on a una rigged proa as well? could purposely go aback to drop it on the nets when taking it down...
ben
--- In harryproa@yahoogroups.com.au, Mike Crawford <mcrawf@...> wrote:
> Personally, I wouldn't say that the lee helm with one rudder is a mark
> against the easyrig. If you put an una rig on a proa that has a
> tendency to luff into the wind, the additional weather helm would make
> it luff more. Neither rig is perfect.
>
> In the end, it's a matter of preference.
>
> The una rig will have a higher aspect ratio and taller mast than an
> easyrig with the same sail area. However, it will also have higher
> sheet loads, and jibes will take some skill. You also get the option of
> sailing with a single foil, at least on the smaller proas. If you want
> to race, don't mind the higher sheet loads, and prefer to have the mast
> waaay up there (more sail where it counts when there's no wind), it's
> perfect.
>
> If you want to cruise, there's a lot to be said for the lower sheet
> loads and graceful jibes of a semi-balanced rig. You'll also have a
> lower bare pole if the wind really starts to howl and you can't get out
> of the way, and the center of effort will also be lower. As for the jib
> tension, it's not perfect, but that's not the end of the world. Cut the
> jib for the right shape with a certain amount of sag in the stay and it
> will still be efficient.
>
> If you want to both cruise and race, it's a toss-up. That tall una
> will be faster, but require more effort. How lazy are you? I'm
> personally pretty lazy 75% of the time that I'm sailing, so that colors
> my rig preferences.
--- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@...> wrote:
> My thinking exactly. Hope to get round the shortcomings by telescoping
> the rig and raking the mast forward so the centre of rotation is just
> ahead of the coe, same as the ballestron. Gybes aren't (or shouldn't be) a
> problem on a harry.