Subject: Re: [harryproa] Re: SA/D and Bruce number calculator
From: Doug Haines
Date: 4/24/2009, 2:28 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au



i didn't think of the fact that you can't self tack a jib sheeted aft of the mast.
so it's a manual release and haul around mast to other side?

--- On Fri, 24/4/09, Robert <cateran1949@yahoo.co.uk> wrote:

From: Robert <cateran1949@yahoo.co.uk>
Subject: [harryproa] Re: SA/D and Bruce number calculator
To: harryproa@yahoogroups.com.au
Date: Friday, 24 April, 2009, 3:03 PM

-
A taller wing mast might be more comfortable than the present system as it would be more inclined to have a low resistance damped feather when reefed, especially if damping material such as polypropylene is used in construction. Provide motion is damped, weight aloft can actually improve the motion as it gives greater angular inertia. A wing mast would also be stiffer fore and aft, enabling better forestay tension control and greater ability to hang extras off it
I reckon about 15-20% more mast height with a tapered wingmast would be plenty for 'Rare Bird'. The boat sails quite well enough for a cruiser as it is.
I tend to go with the screecher off an extension of the boom rather than off the lee bow as it brings the tack round more to catch the wind and allows the shunting to proceed relatively normally. The changing sides of the screecher no more difficult than on any multi rig, and it keeps the forces more compact. The stay would not have to be changed during the shunt, but you would need to be aware of back winding dangers and have the stay fused.
-- In harryproa@yahoogrou ps.com.au, Rob Denney <harryproa@. ..> wrote:
>
> Yes and no. The boat will probably steer ok, but the rig balance may
> be stuffed. All the ideas suggested so far are worth a try. I like
> the higher mast as there is more air up there, especially in under 6
> knots when the wind is laminar. Issues with weight and windage when
> reefed, which is why I am looking at telescoping, although with an
> unstayed mast, i am not entirely convinced it is worth the effort
> unless there are bridges, trailers etc involved.
>
> I also like a screecher off an extension of the jib boom, sheeted to a
> track off the side of the main boom. May have to rig a brace to the
> front of the jib boom to trim it, but in light air, not a big deal.
> Tried this with a spinnaker once, worked ok, but there was not a lot
> of breeze. The main problem with light air sails is that you put
> them up in 5 knots of breeze, the boat accelerates to 5+ and they see
> near enough 10 knots apparent. Things start to get seriously loaded.
> Get a puff to 10 knots and they either break or have to be very heavy.
>
> regards,
>
> Rob
>
>
>
> On Thu, Apr 23, 2009 at 11:01 PM, Gardner Pomper <gardner@... > wrote:
> >
> >
> > I was thinking that with a ballestron rig, you eliminate the point of
> > sail factor, because you trim your sheets for an apparent wind
> > direction and then just rotate the mast to keep the sails at that
> > angle to the wind.
> >
> > Anyway, is the end result of all this that one can have a large, light
> > air headsail without killing the balance?
> >
> > Deferring to the expert,
> >
> > - Gardner
> >
> > On Thu, Apr 23, 2009 at 10:55 AM, Rob Denney <harryproa@. ..> wrote:
> >>
> >>
> >> G'day,
> >>
> >> No, it's not. The geometric centre of the sail is what is
> >> traditionally used, but it is an approximation, not the centre of
> >> effort. The coe moves around a fair bit depending on the point of
> >> sail, mast size and shape, sail shape and wind strength (especially
> >> with unstayed rigs, big roaches and jibs on unstayed masts). For
> >> getting started after sheeting on a big roached (probably oversheeted
> >> as the sheeting is set for higher apparent when the boat is moving)
> >> mainsail on an easy rig it can be 75% or more aft. If the mast is
> >> big diameter, with the topping lift strapped on hard to make the jib
> >> work well and the top of the main flag, coe can move ahead of the
> >> mast.
> >>
> >> regards,
> >> Rob
> >>
> >> On Thu, Apr 23, 2009 at 9:48 PM, Gardner Pomper <gardner@... >
> >> wrote:
> >>>
> >>>
> >>> I can calculate the center of gravity of a triangle, just by adding
> >>> the x coordinates and dividing by 3; then do the same with the y
> >>> coordinates. Is that they same as the center of effort?
> >>>
> >>> - Gardner
> >>>
> >>> On Thu, Apr 23, 2009 at 9:45 AM, barrie lyall <protocomposite@ ...>
> >>> wrote:
> >>>>
> >>>>
> >>>> Re Cof E, Simple one, if I remember correctly or correct me if i am
> >>>> wrong.
> >>>> Make a paper scaled pattern of the sail and find the centre balance
> >>>> point
> >>>> with a pin.
> >>>>
> >>>> --- On Thu, 4/23/09, Mike Crawford <jmichael@.. .> wrote:
> >>>>
> >>>> From: Mike Crawford <jmichael@.. .>
> >>>> Subject: Re: [harryproa] SA/D and Bruce number calculator
> >>>> To: harryproa@yahoogrou ps.com.au
> >>>> Date: Thursday, April 23, 2009, 9:17 PM
> >>>>
> >>>> <<Have you happened to run across any info on how to calculate the
> >>>> center
> >>>> of
> >>>> effort of a sail?>>
> >>>>
> >>>>   (off-group) Nope.  I don't think I'll bother going that far.  I'll
> >>>> give
> >>>> Rob the specs I want and let him and the engineer help with the details.
> >>>>
> >>>>        - Mike
> >>>>
> >>>>
> >>>> Gardner Pomper wrote:
> >>>>
> >>>> Hi,
> >>>>
> >>>> Thanks! That's cool!
> >>>>
> >>>> Have you happened to run across any info on how to calculate the
> >>>> center of effort of a sail? I have also been thinking about sailplans
> >>>> and am trying to figure how much headsail I can have before putting
> >>>> the COE too far forward for the ballestron rig to weathercock.
> >>>>
> >>>> - Gardner
> >>>>
> >>>>
> >>>>
> >>>
> >>
> >>
> >
>


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