-
The most that could occur is that hte top of a wave was clipped. If
travelling downwind pushed to its limit then it would stabilise the
boat and very slightly reduce its tendency to leap off the top of a
wave. If I could realistically have such a brake I would regard it as
a safety feature. At any other point of sailing I can't imagine an
issue.(Possibly my lack of imagination) Overall I'd much prefer a
chance of the rear support pulling down than the forward support
pulling down. Considering the amount of surface area invoved it is
probably a nonissue.
Having the steep conocsections would reduce the tendancy to plane
either up or down, but at the expense of extra drag.
Robert
-- In harryproa@yahoogroups.com.au, Mike Crawford <jmichael@g...>
wrote:
>
>
> For or a daysailer, any scooping effect at the aft end would not
> matter. But if I were cruising and ran into seas high enough to
push
> the boat to its limits, I'd be a bit worried about anything that
could
> dig either end in at the wrong moment. It could be a non-issue,
but I
> tend to be conservative when not flying a hull.
>
> Good point about the loading on the rudder. It might not be
> important, but then, why risk it? Considering that the current
supports
> are almost fine on their own, a steep cone/pyramid fairing would
> probably be more than enough.
>
>
> - Mike
>
>
>
> Robert wrote:
>
> > G'day,
> > Myself I like the idea of a conical or even a pyramidal support
under
> > the bottom support and possibly above the top support but I am not
> > sure I would like anything in between because of possible
hydraulic
> > wedging creating extra shocks to the rudders. Don't know if this
is a
> > valid objection but it makes me slightly uneasy and probably
wouldn't
> > be a problem with steep cones just providing extra stiffness.
> > Had'nt considered the torsional effect of angled supports. Still
> > can't see that scooping by the rear rudder supports can be
> > detrimental when considering the natural inclination of the rig
is to
> > push the bows down and the stern up.
> > Not only does Rob and Mark have the guts and honesty to put it out
> > there but they are extraordinarily patient with armchair critics
like
> > myself.
> > Robert--- In harryproa@yahoogroups.com.au, "J. Michael Crawford"
> > <jmichael@g...> wrote:
> > >
> > >
> > > I think the stiffness of a thicker section in the rudder
supports
> > is a
> > > good idea -- extended beating in a heavy seaway could put a lot
of
> > > repeated bending moment, shear, and torsion on a brace that
doesn't
> > have
> > > much area over which to distribute it.
> > >
> > > I'm uneasy about an angled foil section, though, for the same
> > reasons
> > > Rob mentioned. Most of the time a rear scoop would not be an
> > issue, but
> > > there are times it could be dangerous, and those are the times
that
> > > worry me. I also like the idea of simpler forces in
perpendicular
> > > planes. An angled foil taking wave action could put a lot of
> > stress on
> > > a structure that doesn't extend symmetrically to the leeward
side
> > of the
> > > hull. Of course, a flat brace could also do that.
> > >
> > > I'd keep the basic idea of a thicker attachment and vary it a
bit
> > > (apologies if I'm repeating):
> > >
> > > a) Fair the top of each top support and the bottom of each
> > bottom
> > > support into a shallow cone shape with the apex right on the
hull,
> > maybe
> > > five or ten cm high at the thickest point in the center. This
will
> > > spread the load way out, help with the bending moment due to
> > slamming,
> > > and also shed a bit of water at the same time. With a foam
center
> > and
> > > carbon skin this would not be very heavy. The downside is that
it
> > might
> > > make it more difficult to get in between the brackets, but since
> > they're
> > > already fixed, I'm not sure this is an issue.
> > >
> > > b) Create hollow box with a rounded triangular shape to
connect
> > the
> > > inside top support to the inside bottom support. It wouldn't
be as
> > > sleek as the current empty space between the supports, but then
> > there's
> > > normally nothing hitting that space, and if water were slamming
> > into the
> > > hull there, the system would be better off with the box
support.
> > The
> > > benefit would be uniting the top and bottom brackets into a
single
> > > system that turns most forces into shear, tension, or
compression.
> > This
> > > should be a lot easier to resist than the bending moment. Even
if
> > this
> > > were only to extend halfway out to the edge of the supports,
they
> > should
> > > be able to resist a lot more bending moment, and the system
would
> > be a
> > > bit sleeker.
> > >
> > > c) a + b. Fair the top and bottom outside brackets, connect
the
> > > inside brackets with a smoothed box structure. Really strong,
kind
> > of
> > > clunky.
> > >
> > > d) a * b. Another combo. Make short conical fairings on the
> > top and
> > > bottom outer supports, and much taller conical fairings in
between
> > the
> > > inner supports. That's stiffer than a and much sleeker than b.
> > Waves
> > > pass through and forces are greatly reduced.
> > >
> > > Any of the above mean that the foil, kick-up, or pintles will
> > need to
> > > give before the brackets do, but that probably goes without
saying..
> > >
> > > ---
> > >
> > > Also, kudos to Rob for having the guts to debate this all out
in
> > the
> > > open, even inviting additional debate from detractors on the
> > proa_file
> > > group, and yet still answer design critiques patiently. Most
> > people
> > > would either hide the ups and downs, get grumpy when anyone
doubts
> > them,
> > > or both.
> > >
> > > It's also great to see a patient, iterative approach.
There's no
> > way
> > > you'll ever think of everything ahead of time, and it's not
always
> > wise
> > > to try. It's more valuable to create a good solution, try it in
> > the
> > > real world, see what works and what doesn't, and then make a
much
> > more
> > > informed design choice based upon experience. More is usually
> > learned
> > > from failure than from success.
> > >
> > > - Mike
> > >
> > >
> > > Robert wrote:
> > >
> > > > G'day,
> > > > You're right I do mean the rudder supports, but I can't agree
with
> > > > your arguments in dismissing the idea
> > > > (a) They could be left where they are and keep that extra
lever
> > arm
> > > > (b)Not necessarily a bad thing but it would probably remain
out of
> > > > the water according to my reading your pics. It wouldnt
> > necessarily
> > > > make a rooster tail
> > > > (c) don't see that necessarily follows. The supports would
have a
> > > > thicker cross section and allow the top surface where the
pintle
> > > > emerges to be near horizontal
> > > > regards,
> > > > robert
> > > > --- In harryproa@yahoogroups.com.au, "Rob Denney" <proa@i...>
> > wrote:
> > > > >
> > > > > G'day,
> > > > >
> > > > > I assume by braces, you mean the horizontal rudder
supports? If
> > > > so, I would keep them horizontal. a) they have now been moved
> > clear
> > > > of the water, b) the aft one would act as a scoop and c) they
put
> > the
> > > > rudder pintles in bending rather than shear, which is much
easier
> > to
> > > > resist.
> > > > >
> > > > > regards,
> > > > >
> > > > > rob ----- Original Message -----
> > > > > From: Robert
> > > > > To: harryproa@yahoogroups.com.au
> > > > > Sent: Tuesday, January 10, 2006 10:20 AM
> > > > > Subject: [harryproa] Re: harryproa rudder fastening
stiffness
> > > > issue?
> > > > >
> > > > >
> > > > > Thanks Mark and Rob for detailed replies.
> > > > > I was considering making the braces in a foil cross
section
> > set
> > > > about
> > > > > 15-20 degrees attack for the forward facing rudder. This
would
> > > > > provide stiffenning as well as a bit of lift. Possibly
> > vetilate
> > > > them
> > > > > in case of severeely depressing the bows. makes sense to
put
> > the
> > > > big
> > > > > quadrant under the floor. When I look at just about any
other
> > > > foil
> > > > > arrangement in other boats they are all vulnerable.
Breking
> > waves
> > > > > from behind can put enormous strains on the rudders of
most
> > > > boats.
> > > > > overall your present design looks pretty good and they
> > obvoiously
> > > > > work.
> > > > > Robert
> > > > >
> > > > >
> > > > >
> > > > > --- In harryproa@yahoogroups.com.au, "Mark Stephens"
> > > > <stephens@o...>
> > > > > wrote:
> > > > > >
> > > > > > I really wouldn't be concerned about the rudder
brackets and
> > > > > quadrants from a vulnerability to waves point of view.
However
> > > > the
> > > > > loads they see from leeway prevention are huge. For the
last
> > few
> > > > > months, prior to the first sail, I had been concerned
about
> > their
> > > > > ability to withstand these loads and was tempted to take
them
> > off
> > > > and
> > > > > beef them up. I decided to leave them for a number of
reasons:
> > > > Better
> > > > > to test them gently and see where the cracks develop, we
may
> > need
> > > > to
> > > > > adjust the rake angle which would also requires a rebuild,
> > there
> > > > was
> > > > > plenty of other things to get on with. As it happened a
shear
> > pin
> > > > > broke which put enormous twisting loads into the case
causing
> > > > > breakage. I fixed this quickly to get us sailing again.
You
> > can
> > > > see
> > > > > the repairs in the photos and video.
> > > > > >
> > > > > > On return from the second sail we noticed some hairline
> > cracks
> > > > on
> > > > > the unrepaired rudder case which I have since repaired,
again
> > > > just
> > > > > strengthening it enough to go sailing again. Rather than
> > > > completely
> > > > > rebuilding the rudder cases I am interested in keeping the
> > > > variables
> > > > > to a minimum.
> > > > > >
> > > > > > The triangular brackets that attach the rudders to the
hulls
> > > > are
> > > > > remarkably strong. They may look a bit flimsy but there
are 4
> > per
> > > > > rudder with plenty of carbon and glass and are well
> > triangulated.
> > > > > There are more upwards loads than expected so a 45 deg
brace
> > will
> > > > be
> > > > > put in from the bottom pivot bearing to the hull. When the
> > first
> > > > > rudder broke from the shear pin shearing it caused the top
> > > > bracket to
> > > > > bend up about 120 degs. When I detached the broken case
and
> > > > quadrant
> > > > > it sprang back into position without damage. I just had to
> > > > replace
> > > > > the composite pivot bearings.
> > > > > >
> > > > > > The rudders were always going to be the major challenge
for
> > us.
> > > > > Consider that they have to rotate 240 degs., raise up and
> > down 2
> > > > > metres, break away if hit (but not under enormous sailing
> > loads)
> > > > and
> > > > > be balanced under all points of sail. Also keep in mind
they
> > are
> > > > > dagger boards, resisting all the sail loads, as well as
> > rudders
> > > > which
> > > > > have to operate in two directions. The bottom bracket
> > probably is
> > > > too
> > > > > close to the water. I have raised this by 100mm for Blind
Date
> > > > and
> > > > > subsequent boats.
> > > > > >
> > > > > > Considering the above I think we have a pretty good
rudder
> > > > design
> > > > > once it has been strengthened. We are considering other
> > > > approaches,
> > > > > such as beam hung rudders, but so far this is the most
> > workable.
> > > > I am
> > > > > considering replacing the large quadrant wheel with a
small
> > one
> > > > and
> > > > > getting the 'gearing' from a large quadrant under the
cockpit
> > > > floor.
> > > > > >
> > > > > > The slow progress must be frustrating for all of you
who are
> > > > > watching this from afar. Now the boat is sailing, repairs
or
> > > > > improvements and indeed sailing have to be done in 'play
> > time' of
> > > > > which there is little at this time of year. Harryproa has
just
> > > > landed
> > > > > a very nice contract for 100 carbon fibre masts for GPS
> > aerials
> > > > on
> > > > > container terminal forklifts. These have to be completed
by
> > the
> > > > end
> > > > > of January so we will be very busy next month.
> > > > > >
> > > > > > A big thank you to Luke for the pictures, video and
report.
> > > > > >
> > > > > > Merry Christmas to everyone,
> > > > > > Mark
> > > > > >
> > > > > >
> > > > > > Mark Stephens
> > > > > > www.harryproa.com
> > > > > > 0431 486814
> > > > > > ----- Original Message -----
> > > > > > From: Robert
> > > > > > To: harryproa@yahoogroups.com.au
> > > > > > Sent: Saturday, December 24, 2005 10:03 AM
> > > > > > Subject: [harryproa] Re: harryproa rudder fastening
> > stiffness
> > > > > issue?
> > > > > >
> > > > > >
> > > > > > Must admit those forward rudders seemed vulnerable.
Don't
> > > > know
> > > > > > exactly how vulnerable as strong composites can be
> > deceiving.
> > > > > > Probably the loads on the rudder blades under sailing
are
> > > > greater
> > > > > > than the loads exerted by waves hitting the supports.
> > Don't
> > > > see
> > > > > mast
> > > > > > stiffness as an especial issues. The boat was
travelling
> > > > pretty
> > > > > well
> > > > > > for the wind strength. Make it too stiff and the shock
> > loads
> > > > on
> > > > > the
> > > > > > bearings would be greater. Running stays would need a
> > > > reddesign
> > > > > of
> > > > > > the rig in terms of loading and sail shape. Possibly
the
> > flex
> > > > > allows
> > > > > > the boat a little movement without effecting the
velocity
> > of
> > > > the
> > > > > top
> > > > > > section of the mastas much?
> > > > > >
> > > > > > Certainly impressive the motion and the speed and
lots
> > of
> > > > nooks
> > > > > and
> > > > > > crannies for the kids to explore.
> > > > > >
> > > > > > Loved it
> > > > > > Robert
> > > > > >
> > > > > > --- In harryproa@yahoogroups.com.au, "dominiquebovey"
> > > > > > <dominiquebovey@y...> wrote:
> > > > > > >
> > > > > > > Hi all,
> > > > > > > after seeing the video I have the feeling of two
> > potential
> > > > > stiffness
> > > > > > > issues on the visionarry and HP in general, the
second
> > is
> > > > > rudder
> > > > > > fixture:
> > > > > > > I sailed in the irish sea lay May on a 28'
monohull, we
> > got
> > > > got
> > > > > > pretty
> > > > > > > rough sees and wether, like Bf 8, wind against
current,
> > 15-
> > > > > 20'waves
> > > > > > (I
> > > > > > > am translating from metric for you anglo-saxon
people ;-
> > )
> > > > where
> > > > > the
> > > > > > > boat fell hardly because the front of the waves was
> > almost
> > > > > > vertical.
> > > > > > > I wonder how the rudders would bear such shocks,
> > especially
> > > > the
> > > > > > front
> > > > > > > one which takes the brint of the hit.
> > > > > > > I am especially worried about the horizontal wheel
which
> > > > could
> > > > > be
> > > > > > > bent/broken by waves? Visionarry is a light boat
which
> > will
> > > > be
> > > > > > > probably very fast with bare mast in 40-50kn of
wind and
> > > > > > correspnding
> > > > > > > sea (european category A), so it'd better be TOUGH!
> > > > > > > And sorry, also the fastening to the hull looks
fragile
> > to
> > > > me,
> > > > > maybe
> > > > > > > it isn't but it looks so.
> > > > > > > I would think of an arrangement similar to the
> > catamarans:
> > > > two
> > > > > > tillers
> > > > > > > with a rod joining them, and sticks. But I agree
that
> > with
> > > > this
> > > > > > you'd
> > > > > > > have problems fitting an autopilot... HAAA
compromise,
> > the
> > > > > basis of
> > > > > > > engineering!
> > > > > > > But maybe this is a solution for an emergency
steering
> > > > system,
> > > > > when
> > > > > > > the cable-based system breaks.
> > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > Yahoo! Groups Links
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > Internal Virus Database is out-of-date.
> > > > > > Checked by AVG Anti-Virus.
> > > > > > Version: 7.0.344 / Virus Database: 267.14.1/206 -
Release
> > > > Date:
> > > > > 16/12/2005
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
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