Hello Arto, and thanks for the welcome.
To answer your first question I need your definition of over balanced.
Heavy or light depends on your sailing philosophy. To me having to hold tiller to weather or to lee to stay on desired sailing course is under balanced. Most traditional semi modern sailing craft I have sailed are like this from beach cats to dinghys 420, coronodoo 14s. prindle 18 2s , cal 20, cal 34 Even my Bolger Micro every boat I have ever experienced sailing on and having a chance at the helm has had this same sort of problem. I hated the constant tendering of the tiller wondering and correcting and holding till at a certain aoa to maintain course. My first proa showed me that that's not necessary. my second proa I only need to steer to a course desired and set the tillers back to neutral straight ahead not holding aoa to maintain any course. Large movements are heavy small movements are light.
Second question yes the sail can be sheeted from the rear only. On certain angles sailed to wind or as (apparent wind increases) meaning windward work the efficiency of sail can be improved to create less drag at higher apparent wind speeds by controlling fore end of boom / sheeting from the front of sail. The higher the apparent wind the higher angle of attack you can get with sail by decreasing trailing edge drag the camber will hold its place due to the apparent wind force. It is a small window but once you capture its like lighting in a bottle. By sheeting front of sail you are atomatically sheet out trailing edge . Unlike traditional sail craft where your sheet back half of sail in at high aoa and trying to adjust twist. The traditional method just seem unatural.
The whole JR with camber at center chord was just a step in the direction of the hybrid dyna or wind sail that I'm still finishing. Similar to the solid wind on my models
Rob Denny inspired flat bottom proa called square harry if your south of the equator and slam tacker if your north of it.
http://www.youtube.com/watch?v=OzqXqDlDwTI
Watch sail sheeting to get an idea of description above. Sail has a 10 % set/rigid camber at center chord, pivoting entire sail leading edge always (as close to the wind) as possible for best performace to according to boat speed which predicts apparent wind speed. Sail will draw high to windward at speed with leading edge seemingly straight into the wind untill boat speed is slowed.
Capturing the apparent wind bubble just a different technique maybe!?
Todd
--- In harryproa@yahoogroups.com.au, Arto Hakkarainen <ahakkara@...> wrote:
>
> Hi Todd,
>
> Welcome back. Your tests and videos have been very thought provoking. Keep them coming please.
>
> Two questions though.
>
> 1) The linked rudder system seems to work well. How heavy/light the steering is? And is it over balanced as the theory would suggest?
>
> 2) If you have the sail attached to the mast from the middle can the sail be sheeted with aft sheet only? Or does it need something on the fore part also? Is that dependent on the wind angle or angle of attck to the sail? I mean if the sailing lower helps the situation could it be that the sail is partly stalled at some angles? My own preference is still to have CoE aft of mast to make it automatically depower but I would love to see better solutions.
>
> Arto
>
> --- On Tue, 6/8/10, bitme1234 <bitme1234@...> wrote:
>
>
> From: bitme1234 <bitme1234@...>
> Subject: [harryproa] Re: Predicting performance?
> To: harryproa@yahoogroups.com.au
> Date: Tuesday, June 8, 2010, 4:34 AM
>
>
>
>
>
>
>
>
> I guess what I'm saying is if camber is preset either by curved battens or put into cloth at mid chord or sail shape is symetrical shape fore and aft(flat cut). Wouldn't the pivot point at yard play a crucial roll in twist of sail. Put halyard attachment 1/4 length from lead edge or even closer and you will see the leech open way up even with a low leading edge angle to the wind. Do you see where I'm coming from?
>
> In beginning of clip look at sail shape and then for a foreline coming off front of boom. I'm holding leading sheet angle with front hand foreline. The trailing edge has no excessive twist or pressure with a very light sheet load.
> http://www.youtube.com/watch?v=VnkRpblVD6E
>
> In this clip look at in at about 2:00 Look how far forward sail is set on mast. I'm grabbing front boom and holding it to set AOA look at what happens when I let go while still retaining same sheet angle at trailing edge sail starts to oscillate. Sheet angle from trailing edge is to high for center chord camber and mid pivoting point on yard. Sail pressures fore and aft or becoming equal and unstable Ease out trailing edge sheet and sail a lower course. Or grab or sheet leading edge and sail a higher course.
> http://www.youtube.com/watch?v=fa8tLZ2rbVs&feature=channel
>
> It might just boil down to a different sail design with a different way in which to control that sail design to achieve same goal of what is already known. But with an added benifit of having a more centered COE from a single sail. I think of it more kite like sailing, sailing of front lines vs back lines most of the time with a preadjusted foil shape already set in sail.
>
> Todd
>
> --- In harryproa@yahoogroups.com.au, "robert" <cateran1949@> wrote:
> >
> > Really glad to hear from you. A very good point abut having the yard mid point of the boom.
> > --- In harryproa@yahoogroups.com.au, "bitme1234" <bitme1234@> wrote:
> > >
> > > I'm back .....
> > >
> > > Cause I really wanted to post to this.
> > >
> > > This is pretty interesting stuff. The thing I found using my own JR is when you set up the halyard to be fixed to the center of yard this alone helps to control twist of sail along with having battens running horizontal on sail? I also have my downhaul almost at center on boom. It seems to me having pressure created from wind in front of mast on sail actually keeps the twist out and a uniformed trailing edge without excessive curvature. When I added the camber to my sail with darts I put the camber at mid chord. This may or may not add to better twist control as well. Found the same to be true on trapezoidal sail the battens and (yard pivot)how far in front of mast the yard is plays a roll in controlling twist. The trap sail is flat cut with flat battens. Or this could be just another obscurity of misinformation?
> > >
> > > Todd
> > >
> > >
> > >
> > >
> > >
> > > --- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@> wrote:
> > > >
> > > A solution
> > > > (not the one used by James, whose sail has a lot of twist) to the sheeting
> > > > angle conundrum may be to put up a backstay and run the sheetlets to pulleys
> > > > tied to it. The sheetlets can then be lead down to the deck and to the
> > > > helmsman. Less drag as you have one big bundle, rather than a bunch of
> > > > little ones, and the pull is horizontal instead of near vertical.
> > > >
> > > >
> > > >
> > > > rob
> > > >
> > > >
> > > > On Sat, May 29, 2010 at 1:56 PM, robert <cateran1949@> wrote:
> > > >
> > > > >
> > > > >
> > > > >
> > > > > I had a good look at the sheeting arrangements. They sheet way back to the
> > > > > stern. This would not really go with the Harryproa configuration of sheeting
> > > > > back to the ww hull. Posssibly sheet back to a pulley midway betweent the
> > > > > two bows. I suspect the hinge would have to be made extra strong to handle
> > > > > the different sheeting arrangements. If the timber wishbones were skinned
> > > > > with some carbon tow, they should handle the extra loads. It would probably
> > > > > be worth it aiming for an optimum leeward shape.
> > > > > I don't particularly like the wrinkles on the ww side. Possibly cutting the
> > > > > sails on the bias could smooth things.
> > > > >
> > > > > I am concerned about the sheeting angles. Hopefully Gardner can sort it out
> > > > > before I commit.
> > > > > regards,
> > > > > Robert
> > > > >
> > > > > --- In harryproa@yahoogroups.com.au <harryproa%40yahoogroups.com.au>, Mike
> > > > > Crawford <jmichael@> wrote:
> > > > > >
> > > > > > Robert,
> > > > > >
> > > > > > << you could get away with rice bags and still have a reasonable shape>>
> > > > > >
> > > > > > Precisely! I'm not sure if it would be a premium racing rig, but
> > > > > > while cruising, it seems to me that the average sail shape, particularly
> > > > > > in light winds, would be superior to a bermuda rig.
> > > > > >
> > > > > > To get the right sail shape with a single skin takes time, in terms of
> > > > > > adjusting leech/outhaul/vang (no vang with fixed boom), and money, in
> > > > > > terms of sail cloth, track, and battens.
> > > > > >
> > > > > > Plus, the battens that work at 40 knots will be to stiff for five
> > > > > > knots, and the battens that work at five knots will be too flexible for
> > > > > > 40. I'm tired of yanking on my boom to get the battens to switch over
> > > > > > in light winds. I like to sail, but I'm not the kind of guy who would
> > > > > > keep three sets of battens on hand in order to have just the right
> > > > > > strength for the day's winds. So I have a medium-stiff set that
> > > > > > functions in all winds, but really isn't good for light or heavy weather.
> > > > > >
> > > > > >
> > > > > > <<The strings need not be a big source of drag with dyneema but one
> > > > > > would need some gloves.>>
> > > > > >
> > > > > > Agreed. Though I'd probably try to use dyneema on all the individual
> > > > > > lines, feeding into a single wider-diameter mainsheet (one shet per bow,
> > > > > > of course) that would be easier to handle and cleat.
> > > > > >
> > > > > >
> > > > > > <<Some people swear by junk rigs and this makes more sense to me than a
> > > > > > straight junk.>>
> > > > > >
> > > > > > Particularly if you want to go upwind. I'll daysail much more often
> > > > > > than I go cruising, so going upwind is a big deal. A friend of mine
> > > > > > says one spends 70% of one's time sailing upwind, and I have to agree.
> > > > > > If I just go out and back for the day, the windward phase is noticeably
> > > > > > slower, and covers a lot more distance, than the leeward phase.
> > > > > >
> > > > > > - Mike
> > > > > >
> > > > > >
> > > > > > On 5/27/2010 7:29 AM, robert wrote:
> > > > > > >
> > > > > > >
> > > > > > > Hi Mike
> > > > > > > I am with you on this rig: you could get away with rice bags and still
> > > > > > > have a reasonable shape; the sheet loads are lighter; it's easily
> > > > > > > reefable; if the top section rotted out, it would be easy to replace
> > > > > > > without wrecking the lines of the sails; there's no sail track to buy
> > > > > > > or jam; and the battens can be low tech. The strings need not be a big
> > > > > > > source of drag with dyneema but one would need some gloves. I will
> > > > > > > have to make up my mind before I start trying to set up for making the
> > > > > > > masts. A simple tapered section makes the most sense and it wouldn't
> > > > > > > need the bearings of a lot of other rigs.
> > > > > > > Apart from not being common I am not sure what the problems with it
> > > > > > > are for a cruising rig. Some people swear by junk rigs and this makes
> > > > > > > more sense to me than a straight junk.
> > > > > > > Robert
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > >
> >
>