Stavanger, Mon

Graeme
I didn't know that Alert's mast was aluminium. Aluminium combined with slippery
plastic lining in the gaff jaw will ease any friction problem.

Still I would avoid Alert's low and wide sail for offshore work. I would be
afraid of dragging the boom in the water too often. If keeping weight aloft is
critical, I would rather fit a two-masted rig.

Anyway, I don't think we get much closer to the perfect rig while sitting in our
armchairs, and as said, I am not much motivated to try out the CG rig, now that
I have a JR which serves me well. So I think I leave it to you to find out :-)
....

Cheers,
Arne




--- In junkrig@yahoogroups.com, "graeme" <graeme19121984@...> wrote:
>
>
>
> Arne,
>
> cambered panels are a great idea!
>
> Among other things Bolger had great abiding interests both in
speed/performance under sail, and very (but very!) shoal draft craft. A
corollary to shoal draft for monohulls is sail COE and rig mass best sited at
the lowest height possible. This may be why the Chinese Gaff seems usually drawn
with such very low AR, the foot nearly as long as the deck! aluminium pipe mast,
and also with light weight necessarily flexible battens which however also can
be used to induce efficient sail shape, but require sheet loads be in line with
those weak light battens by way of a sheeting staff. Such a rig shape also may
minimise freestanding mast intrusion into accomodation space and facilitate easy
pivoted lowering. I wonder if any much higher aspect ratio may actually entail
compromising the CG advantages?
>
> If a little more weight can be tolerated aloft in heavier battens, if the need
for pressing speed can be less and a reef taken in sooner perhaps, then perhaps
cambered panels are also for the CG as shown for Bolger boats. Are they?
>
>
> --- In junkrig@yahoogroups.com, "Arne Kverneland, Norway" <arkverne@> wrote:
>
> > With the whole sail moved aft of the mast...
> > • ..the bending forces on the mast goes up,
>
> With reference as to gravity only, by way of cantilevering, yes, but as to
applied sail pressure, and also resultant sheeting forces: they're reduced.
>
>
> > • ..the friction of the gaff when hoisting and lowering goes up,
>
> Not reported as an issue -- two halyards like the gaffsail.
>
> > • ..and I bet there will be a shafe problem too at the jaws,
> > at least at the low AR Alert rig.
>
> Do you mean the jaws themselves chafing on the mast, and not sail luff
material in some way? If so, it's not reported, and there's fixes such as
slippery polypropylene fitted to the surface bearing on the aluminium pipe mast.
>
> > The sail of my 29'/3ton sloop Johanna has about the same sail area
> > as Alert, but is controlled with just four running lines; one
> > halyard, sheet, luff hauling parrel and yard hauling parrel.
>
> There's sail area, but there's placement, AR, sheet angle etc. The CG vang
isn't handed once set. The CG has two halyards, as little as one sheet, but
there are "x" reefing batten downhaul lines.
>
> I think the CG would benefit from camber sewn into sail panels in addition to
making higher panels from progressively heavier cloth as is sugested in the 1999
Bolger article. Flexible battens could then be dispensed with, although the
difficulty, such as it is, of tuning flexible CG battens to induce camber in
flat cut cloth is likely an easier process for many than sail fabrication from
correctly shaped cambered panels. The advantages of easier stiff batten
construction thus gained would be added to by their increased weight which may
make the reefing downhaul lines and vang quite unecessary and still allow the
horizontally in line light sheeting force (perhaps this is what Jim Melcher was
halfway trying for on his Alert rig as described).
>
> Graeme
>