Subject: [harryproa] Re: rudder frame desgn
From: "Tim Barker" <clairebarker5@bigpond.com.au>
Date: 4/11/2008, 6:58 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

---Hi Rob
I assume this will be the system used on the livaboard, good thing im
actually keen on tiller steering, although im sure wheel can be
worked out.
Cheers Tim In harryproa@yahoogroups.com.au, "Rob Denney"
<harryproa@...> wrote:
>
> G'day,
>
> I agree, it is fascinating.
>
> Your analysis is correct, but what allows it to work is 2 sheer pins
> which hold the rudder down. One above the height of the beam
(visible
> in the last picture in the Files) and one at the level of the bottom
> of the beam. They are not actually sheer pins, but sheer plates, in
> as much as they will only break in one direction, away from the
beam.
> When it is the bow rudder and it hits something, the top pin lets go
> and the rudder with bearings attached, kicks up around the bottom
> pin. When it is the stern rudder, the bottom pin lets go and the
> rudder kicks up around the top pin. The flanges on the fea model
have
> been lengthened fore and aft to support the rudderand bearings all
> the way to horizontal, in both directions.
>
> Jim,
> The pins are strong enough to hold the rudder shaft, but it is the
> extended flanges which keep it at right angles to the beam. The
> bearings never leave the flanges, so there is no need to flare the
> flanges for re entry.
>
> This system is better than anything else we have tried so far. The
> thing I like most about it is that it is all compression loads over
> short distances, which are easy to resist. The rudder shaft sees
> bending loads, but we have a pretty reliable technique for very
strong
> carbon shafts, so I am not worried about this.
>
> Next is the details. The bearings (pvc drainpipe is not up to
scratch
> on Elementarry, suspect UMPWE would not do it either. Blind Date is
> using a stronger, tougher plastic, rated for the loads. Worse case
> scenario is we need ball or roller bearing shafts, but these are
> easily made, or bought. Steering is also tricky. Tiller and
> extension is not trouble, but wheel steering is a bit more of a
> challenge. BD is using a rack and pinion, another boat a spur gear.
> The charter boat will have conventional rope and quadrants, both
> rudders linked to a single wheel.
>
> Blind Date's rudders are vertically liftable reducing the draft to
the
> same as the ww hull.
>
> John Wright,
>
> Attachments to posts are a problem, please put them in the files or
> photos section. Ta.
>
> regards,
>
> Rob
>
>
>
> On Thu, Apr 10, 2008 at 11:18 PM, jhargrovewright2
> <jhargrovewright2@...> wrote:
> >
> >
> >
> >
> >
> >
> > Mr. Denney,
> > I am fascinated.....with the finite element analysis image.
> > Impressive and colorful.
> > Can you elaborate a little for us laymen. This is the bracket
that
> > attaches to the beam that holds the rudder shaft which will fit
in
> > the channel, vertically? This assembly replaces the fabrication
> > shown in the other pictures in that folder? Is there a picture of
> > the pivot pin (point) that allow the rudder to swing up. And
last,
> > what holds the rudder down?
> > Thanks,
> > John
> > --- In harryproa@yahoogroups.com.au, "Rob Denney" <harryproa@>
> > wrote:
> >
> >
> > >
> > > G'day,
> > >
> > > I have just uploaded a finite element analysis (fea) of the
beam
> > > mounted rudder supports for Blind Date to the "Rough beam
rudders &
> > > fea of rudder supports" file in the Files section. The picture
> > shows
> > > the loads and exaggerated deflection of the rudder box with 7
tonnes
> > > load on the rudder, which is what we ended up designing it for.
> > This
> > > is more than double the weight of the boat, so we are pretty
> > confident
> > > that this part won't break. The test rudder shaft took 15 tons
so we
> > > are pretty confident about that as well. Now just have to sort
> > out
> > > all the details.
> > >
> > > The other pictures in the file are the test version on my
> > elementarry.
> > > Rough, but so far nothing has broken.
> > >
> > > All engineering from now on will be done with fea. Costs more,
but
> > > gives a much better result, plus I like looking at the pretty
> > > pictures. ;-)
> > >
> > > There will be some more pictures of Blind Dates rudders on the
web
> > > update, which unfortunately can't happen until I get a
password from
> > > the web host, which comes by surface mail, for some reason.
> > >
> > > regards,
> > >
> > > Rob
> > >
> >
> >
>

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