[Rhodes22-list] Mast Crane (was Lou Moore)

[Peter Thorn]

Roger,

I certainly will try it.  It sounds great!

Where did you acquire your 12" mast crane?   Do you recall Loos settings for
forwards, uppers and aft shrouds?

With only 4 cord/inches upper mast bend, my guess is the greatest benefit is
headsail luff sag adjustment.   If you can obtain enough tension to keep a
150 Genoa close to zero cord/inches in a blow, you must be putting  400-500
pounds on the headstay.   R22 construction looks like it would take that.
Stan builds 'em beefy.

Thinking out loud - 1) built the rig first, 2) measure/verify the
"reasonable mast bend" above the spreaders, 3) send numbers to sailmaker.
Can you think of anything else?

Best,

PT


> Peter,
>
> With the forestay cable buried inside of the roller furling foil &
> impossible to get at with a Loo's Tension gage, I've never measured the
> forestay tension.  I have some calculated theoretical values; but, they
> would only apply to my particular boat & masthead geometry & wouldn't be
of
> much use to anyone else.  When you refer to "chord-inches, I presume you
> mean the maximum perpendicular distance from the chord to the radius of
> curvature?  Assuming my definition of chord-inch agrees with yours, with
the
> range of adjustments on Dynamic Equilibrium as currently configured, over
> the 333-5/8 inch length of the forestay, I can adjust the chord-inch value
> from nearly 0 to about 6 inches.  The aluminum extrusions on the headsail
> foils won't sag too much more than that without causing bearing and
furling
> problems.
>
> On my current fully battened mainsail, I went fairly conservative on the
> amount of mast bend the mainsail can respond to.  It is currently cut to
> respond to only about 2 chord-inches, mostly above the spreaders.  The
mast
> curvature actually trails off asymptotically to 0 below the spreaders
> because of stretch in the lower sides stays and the differential fore/aft
> static load I put on the lower side stays.  The forward lower side stays
are
> adjusted tighter than the rear lower side stays to facilitate mast
bending.
> I think the amount of mast bend could be increased to about 4 cord-inches
> without any trouble.  When the time comes to replace this mainsail, that's
> the spec I plan to ask for.  With the current aluminum mast extrusion,
> trying for more bend than about 4 cord-inches is asking for trouble in my
> engineering judgement.  The aluminum extrusion might experience fatigue
> failure (especially in a salt water environment) and the loads on the
> forestay & backstays would start to get a little high for the hull
structure
> and chain plates.
>
> As you probably already know, you bend the mast to straighten the
forestay,
> thereby reducing headstay sag plus flatten the mainsail shape.  Both
actions
> depower the rig for heavy air.  Yes, depowering the rig with the backstay
> adjuster is much faster than any other method because it takes care of
both
> sails at the same time.  I have my backstay adjuster setup with a Harken
144
> swivel cam base with 150 cam-matic cleat, 082 single bullet block, & 071
> stand-up spring mounted on the aft starboard gunnel.  The swiveling arm
cam
> base & cam-matic cleat on the end of the arm allows me to reach the
backstay
> adjuster from virtually any helm position.  The backstay adjuster line is
> marked with calibration marks for quick, reproducible tension adjustments.
> I used the big Harken 144 swivel cam base because this unit is mounted
right
> by where people come aboard over the transom from the boarding ladder.
The
> 144 is sufficiently stout that you can stand on the swiveling arm without
> damaging it.  I've been sailing with this backstay adjuster setup since
> 1988.  It's been absolutely bulletproof so far.
>
> Try it - You'll like it a whole bunch!
>
> Roger Pihlaja
> S/V Dynamic Equilibrium
>
>
> ----- Original Message -----
> From: "Peter Thorn" <pthorn at nc.rr.com>
> To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> Sent: Thursday, March 18, 2004 10:44 AM
> Subject: Re: [Rhodes22-list] Mast Crane (was Lou Moore)
>
>
> > Roger,
> >
> > Thanks for the detailed explanation.  I am the child of an ME, but not
one
> > myself.  All my engineering is pants seat.  I'll add "eccentric loading"
> to
> > my sailing jargon vocabulary.
> >
> > So, how much tension can you add to your forestay by adjusting your
> > backstay?  Can the 12" crane actually put more tension on forestay than
> std
> > crane can?  We all know a light beam straight entry points much better.
> >
> > And, will your Harken furler track allow the forestay to sag and power
up
> > (for light air)?
> >
> > For any boat with sail reduction capacity, mast bending might be a bit
> > unnecessary - but  non-the-less interesting.  After all, one can bend
the
> > mast probably quicker than any other de-powering technique.  During a
race
> > it wouldn't distract from more important things (like paying attention
to
> > the wind) nearly as much as furling would.  How much mast bend (say by
> > "cord/inches") can you induce in Dynamic Equilibrium's mast above the
> > spreaders?
> >
> > As always, I enjoy your posts.
> >
> > PT
> >
> >
> >
> > > Peter,
> > >
> > > Michael is talking about Dynamic Equilibrium's masthead.  I have my
> double
> > > backstay attachment point moved aft about 6 inches in order to allow
the
> > > double backstays to clear the roach of my fully battened mainsail.
> > >
> > > Mast bend is highly dependent upon how you setup the tension in the
> > standing
> > > rigging.  I believe there is there is a standing rigging tuning
> procedure
> > on
> > > the FAQ page.
> > >
> > > However, if you modify the masthead geometry, like on my boat, the
mast
> > > operates a little bit differently than standard.  The mast can be
> modeled
> > as
> > > a column statically loaded by the standing rigging in compression + a
> > > cantilever beam point loaded at the masthead.  The standard masthead
> > > geometry loads the upper end of the mast pretty symetrically.
However,
> > when
> > > you move the double backstay attachment point aft, you are introducing
a
> > > factor called "eccentricity" (e) into the column loading.  Basically,
> > think
> > > of e as the amount by which the compression force vector is moved off
> the
> > > neutral axis of the column.  i.e. when e = 0, the compression load is
> > > applied right down the neutral axis of the column & you have pure
column
> > > buckling.  As e is increased, the deflection of the column under the
> load
> > > behaves like a combination of column buckling + bending of a
cantilever
> > beam
> > > point loaded on the free end.  This cantilever beam bending from the
> > > eccentricity is in addition to the cantilever beam bending induced by
> the
> > > standing rigging.  As far as inducing mast bend, it's the total
> cantilever
> > > beam deflection we are interested in because it's reproducible &
> > > controllable.  Column buckling is sort of an on/off catastrophic kind
of
> > > failure - i.e. virtually no bend up to some critical load & then, BAM!
> > > buckled mast.
> > >
> > > You might not think that mast bend is possible in a masthead rig.
> > However,
> > > you have to think about the behavior of the mast in a 3-D world.  As
the
> > > mast is bent, the height of the masthead off the deck is also reduced.
> > > Although the forestay length attached to the front of the masthead
> doesn't
> > > change, because the masthead drops down as well as moving aft, the
mast
> > can
> > > still assume a bent shape.  This bent shape can be fine tuned by
> adjusting
> > > the tension of the 4 lower sidestays, which collectively restrain the
> mast
> > > from moving from side-to-side as well as fore-aft at about the
midpoint.
> > > The standard double backstay tension adjuster with the standard
masthead
> > > geometry is also capable of bending the mast.  However, because e is a
> > very
> > > small value with the standard masthead geometry, the required backstay
> > > tension to achieve a given amount of mast bend is much higher, which
> > > compression loads the mast closer to the critical column buckling
load.
> > >
> > > Note, this discussion is only applicable for the standard rig.  Never
> bend
> > > an IMF mainsail mast.
> > >
> > > Roger Pihlaja
> > > S/V Dynamic Equilibrium
> > >
> > >
> > > ----- Original Message -----
> > > From: "Peter Thorn" <pthorn at nc.rr.com>
> > > To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> > > Sent: Thursday, March 18, 2004 3:27 AM
> > > Subject: [Rhodes22-list] Mast Crane (was Lou Moore)
> > >
> > >
> > > > Michael et al,
> > > >
> > > > 12" mast crane?  Very interesting idea..  Would the forestay tension
> > boost
> > > > with that much leverage?  Or just create mastbend above the
spreaders?
> > > Has
> > > > anyone, in the life of the universe, ever created upper mast bend
with
> a
> > > std
> > > > rig?   (You were probably thinking about clearing a big roach).
> > > >
> > > > Afterthought- Does a Harken forestay furler have a soft track?  If
its
> > > hard
> > > > metal, can you somehow belly the Genoa entry for light air?
> > > >
> > > > PT
> > > >
> > > > PS - Go fasts are fun, but I'd trade them for a favorable shift.
> > > >
> > > >
> > > > > well now, I think I have to switch sides this year, full-batted
main
> > > sail
> > > > with a 12 inch crane are the way to go, single line
> > > > > reefing and a soild boom vang, but IMF is more convent.
> > > > >
> > > > > MJM
> > > > >
> > > >
> > > > > >
> > > > > > __________________________________________________
> > > > > > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > > > > >
> > > > > >
> > > > >
> > > > > __________________________________________________
> > > > > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > > >
> > > > __________________________________________________
> > > > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > > >
> > > >
> > >
> > >
> > > __________________________________________________
> > > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> >
> > __________________________________________________
> > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> >
> >
>
>
> __________________________________________________
> Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list