-been thinking of a possible speed hump. Once the bow depresses, the
frontal area and surface area in the bow the increases, increasing
drag and causing further torque to depress the bows. if the weight
can be kept back to prevent the depression in the first pace it may
prevent the spiral. Towing tests may not pick it up unless you towed
from the CoE of the sail
The only other suggestion to partially offset it would be more lower
down bouyancy and less on top as that would reduce surface area and
wave resistance, but that would reduce the leeway prevention of the
bows.
Regards,
Robert
-- In harryproa@yahoogroups.com.au, "Rob Denney" <proa@i...> wrote:
>
> G'day,
>
> Agree it is a bit peculiar. Best I can come up with is the reduced
weight. 31 kgs (including the rudder) is significant on a 130 kg
boat.
>
> COE is near enough the same. The rig(s) are both pretty ordinary,
due to mast stiffness and repairs. The speed hump is an interesting
possibility as I achieve 16 knots pretty effortlessly, and despite
feeling a lot faster, have yet to crack 17 knots. Need to do some
towing tests, but at this speed it gets very difficult to steer and
watch the scales!
>
> Weather and sea conditions are the same.
>
> regards,
>
> rob
> ----- Original Message -----
> From: Robert
> To: harryproa@yahoogroups.com.au
> Sent: Thursday, February 09, 2006 1:55 PM
> Subject: [harryproa] Re: Sunday sail
>
>
> I'm intrigued. Trying to thnk of all the parameters and can't
really
> think of any that make sense.
> Weight. Easy to check by adjusting weight but doesn't seem to be
> sufficient for such a large contrast. Easy to test.
>
> CoE. Should be pretty similar with the una compared with the
> schooner, unless the combination of the two sails brings it
forward.
>
> Efficiency of rig.Possibly the single rig is so much more
eficient
> that it pushes forward so much more than sideways and so reduces
drag
> on the hull ( and I have to eat my words on the UNA/schooner rig
> question)
>
> Hull drag characteristics. There is a hump in the speed drag
> characteristics of the hull.
>
> Something in the conditions such as currents or chop that was
> sufficiently different
>
> Or something else I am not imaginative enough to thnk of.
>
> Curious,
> Robert
>
> --- In harryproa@yahoogroups.com.au, "Rob Denney" <proa@i...>
wrote:
> >
> > G'day,
> >
> > I sailed with both rigs and one rudder, still felt like it was
> pushing a lot more water than with the single rig. Not sure
about
> the rake. The new rudder is raked aft, so may be able to compare.
> >
> > regards,
> >
> > Rob
> > ----- Original Message -----
> > From: Robert
> > To: harryproa@yahoogroups.com.au
> > Sent: Wednesday, February 08, 2006 7:58 AM
> > Subject: [harryproa] Re: Sunday sail
> >
> >
> > Rob,
> > Is it possible that the decreased resistance by lifting the
> forward
> > blade and the raking forward of the rear could contribute to
this?
> > regards,
> > Robert
> >
> >
> > --- In harryproa@yahoogroups.com.au, "Rob Denney" <proa@i...>
> wrote:
> > >
> > > G'day,
> > > Hi Rob
> > >
> > > Did you just use one of the schooner's rigs in a new
central
> hole?
> > > Yes
> > >
> > >
> > > Did you have to restrain the forward rudder or just
ignore it?
> > >
> > > Initially I kept it aligned with the flow (ie restrained
it),
> but
> > it was easier to keep the rear one aligned so I steered with
the
> > front one. Both took a lot of concentration, so I pulled
the
> front
> > one up altogether, which was far easier than either.
> > >
> > > Did you move aft to keep the bow up?
> > >
> > > I sat just forward of the aft beam and the angle between
bow
> and
> > hull bottom popped into view regularly. Sitting in the
middle
> > depressed it, but not by much, probably no more than level.
This
> is
> > illogical, I will check it next time as it is relevant for
the
> > bigger boats where the weight cannot be moved.
> > > regards,
> > >
> > > Rob
> > >
> > >
> > > Regards,
> > >
> > > Col C
> > >
> > >
> > > --- In harryproa@yahoogroups.com.au, "Rob Denney"
<proa@i...>
> > wrote:
> > > >
> > > > G'day,
> > > > Went sailing on Sunday in Elementarry to assess una
rigs vs
> > > schooners. 15 knots of breeze, solo, with 11 sqm/118 sq'
of
> > sail.
> > > This is half a Tornado sail area but the sail itself
probably
> > less
> > > than 75% as effective due to the mast and the set up.
> > > >
> > > > Simply amazing. It is a different boat. Flies over the
> water
> > > rather than trying to force it's way through it.
Steered
> > itself,
> > > the bows were up upwind and top speed was not a lot
different
> to
> > the
> > > schooner rig (16.4 knots max, vs 16.8 with the schooner
in
> > similar
> > > conditions). Followed a Tornado upwind, was pointing as
> high,
> > but
> > > going slower. Quicker than a racing Hobie 16 reaching.
Not
> > many
> > > other boats were sailing. Not much sea, but occasional
large
> > wakes
> > > from powerboats. Handled with aplomb, although wet if
the
> beam
> > hits
> > > the wave top.
> > > >
> > > > I steered using only the aft rudder which was similar
to
> > steering
> > > a conventional boat, the forward location making up for
no
> > > daggerboard, the oversize rudder making up for the lack
of
> lever
> > > arm. Shunting was very easy (a nuisance going to
leeward to
> > lift
> > > and lower the rudders), never got close to getting into
irons
> or
> > > caught aback. Downwind, it just got up and went.
> Occasionally
> > > buried the bow, but did not slow it down. It is now
> definitely
> > a
> > > boat anyone could sail solo and one which I look forward
to
> > teaching
> > > my 4 year old daughter how to sail on. Should also be
able
> to
> > look
> > > at the gps while sailing, rather than only the max speed
at
> the
> > end
> > > of the day.
> > > >
> > > > Interestingly, I only flew a hull once or twice the
whole
> time
> > > (too lazy to get off the windward hull, too amazed by how
> > > comparatively easy it all was to bother with pushing the
> limits),
> > > which suggests that the rig is under utilised, something
> > supported
> > > by looking at it. A new wing mast will help this. I was
> going
> > to
> > > increase the una rig sail area, but think I will go with
the
> same
> > > area, but with a wing mast, maybe forward raked to reduce
> sheet
> > > loads. Also building a single rudder setup so I don't
have
> to
> > raise
> > > and lower them each shunt.
> > > >
> > > > The single rig is quicker to rig and derig; An hour and
a
> half
> > > from arriving at the ramp to sailing, but at least half
of
> this
> > was
> > > one off jobs that needed doing. Also easier to right
after a
> > > capsize and 4 grand cheaper.
> > > >
> > > > I am not a lot wiser about how long boats should be for
a
> given
> > > sail area, but am pretty certain that it is much longer
than
> they
> > > currently are.
> > > >
> > > > I think this was not so much a comparison between
schooner
> and
> > > una, more between lots of sail and less, although 2 is
> definitely
> > > twice the effort of one.
> > > >
> > > > Apologies for cross posting.
> > > >
> > > > regards,
> > > >
> > > > rob
> > > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
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