I don't see any more difficulty in lowering the mast. Either have the tabernacle above the bundled booms, or have the tabernacle below the booms but high enough to so that when the the booms are at right-angles to the boat, there is enough room to clear them.
I have been considering how to make a strong enough hinge with the double boomlets and I think a decent sized pin with judicious carbon with stops like on a door hinge should work, though it may be worth cushioning to avoid shattering in gusty conditions
--- In harryproa@yahoogroups.com.au, "Rudolf vd Brug" <rpvdb@...> wrote:
>
> It seems that the attachment point of the halyard to the yard is important, not only incontroling twist.
> I am busy building a JR on my 10m flat botomed scow. I am using 6m alu. square tubes for battens.
> Hoisting that lot connected by lines keeping it all to the desired shape showed that the attachment point at the yard is pretty much
> decided by the balance of the battens being pulled up following the yard.
> This point is near the middle of the yard. Attaching it more to the front showed twist occuring even without sail between the battens.
> Also the aft end of the battens would hang down untill the front of the yard was pulled down hard.
>
> The JR is to get used to this type of rig, I believe the swing wing could be the best solution for a soft sail.
> A practical problem for me using the swing wing on my boat is the wishbones would prohibit lowering the mast,
> and I have to negotiate a bridge 1.4m high.
>
> Also it seems that small size testing beds like Hariette and Todds boat give different results than larger sizes.
> I remember sailng Rob's boat in Perth left me wondering what problems there could be in sailing a proa.
> It much easier correcting vices by weight shifting or just pulling or pushing something hard enough when things are small.
> At a certain size things have to be balanced to be able to handle them.
> This is no criticism to everyone trying stuff with small boats! That is the only sensible way to try things.
>
> regards,
> Rudolf
>
>
>
>
> ----- Original Message -----
> From: bitme1234
> To: harryproa@yahoogroups.com.au
> Sent: Tuesday, June 08, 2010 3:34 AM
> Subject: [harryproa] Re: Predicting performance?
>
>
>
>
>
> 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
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > >
> >
>