G'day,
No trouble being patient with armchair critics,
particularly when they come up with good ideas, or even bad ideas that make us
think.
We are well into the design of a 4m proa on which
we will be trying a couple of relatively radical new rudder ideas. The 4m
is the test bed and tender for a very interesting 18m which we will be
building, but looks like it may work as a car toppable single hander or 2 kids
boat as well. Pics soon.
regards,
Rob
----- Original Message -----
Sent: Sunday, January 15, 2006 8:01
PM
Subject: [harryproa] Re: harryproa rudder
fastening stiffness issue?
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
> > > >
> >
>
> > >
> > >
> > >
> >
>
> > >
> > >
> > >
----------------------------------------------------------------
----
>
> ----------
> > > Yahoo! Groups Links
> >
>
> > > a.. To visit your group on the
web, go to:
> > > http://au.groups.yahoo.com/group/harryproa/
>
> >
> >
> b.. To unsubscribe from this group, send an email
to:
> > >
harryproa-unsubscribe@yahoogroups.com.au
> >
>
> > >
c.. Your use of Yahoo! Groups is subject to the Yahoo!
Terms of
>
> Service.
> > >
> >
> >
> >
>
>
> >
> >
------------------------------------------------------------------
------
>
> *Yahoo! Groups Links*
> >
> > *
To visit your group on the web, go to:
>
> http://au.groups.yahoo.com/group/harryproa/
>
>
>
> * To unsubscribe from this group, send an email
to:
> >
harryproa-unsubscribe@yahoogroups.com.au
>
>
<mailto:harryproa-unsubscribe@yahoogroups.com.au?
subject=Unsubscribe>
>
>
>
> * Your use of Yahoo! Groups is subject to the
Yahoo! Terms of
> > Service
<http://au.docs.yahoo.com/info/terms/>.
>
>
> >
>
Yahoo! Groups Links