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

[Roger Pihlaja]

Peter,

I modified the standard masthead with some aluminum bar stock & a MIG
welder.

Look on the FAQ page for the tension settings.

The way to measure maximum chord inches is to first load up the rig with the
backstays.  Then, run the main halyard down to the base of the mast & tie it
off taut against the slot on the aft face.  Then, using a bosun's chair or a
step ladder to get up high enough on the mast, measure the maximum
chord-inches from the halyard to the slot on the mast.

Note: If all you want to do is eliminate the headstay sag, the standard
backstay adjuster with the standard masthead geometry will do that.  The
only real reason for the crane is to create clearance between the backstays
and the big roach of a fully battened mainsail.  You also need to be a
little conservative re the amount of roach in the mainsail.  Designing in
too much roach will disrupt the balance of the sail plan by shifting the
center of effort (CE) aft, thus causing an excessive amount of weather helm.
Some of this weather helm can be dialed back out by adjusting the static
tilt of the mast such that the mast leans forward slightly, thus moving the
CE of the rig forward.  The static tilt of the mast is adjusted with the
turnbuckle on the forestay or by shortening the forestay cable.

After having installed both a high tech composite genoa on a Harken roller
furler & a fully battened mainsail, I'd say the genoa returns the biggest
performance bang for the buck.  But, the fully battened mainsail looks
totally cool when hoisted & the sail shape is much easier to adjust to
exactly what you want for the prevailing conditions & point of sail.

You will have a choice between sail slugs and a bolt rope on the luff.  I
choose sail slugs & my mainsail almost falls down the mast when the halyard
is released.  Reefing it under load sometimes requires the sail be hauled
down; but, that was true with the partially battened mainsail as well.  You
will have a choice between loose footed & footed using a bolt rope.  I
choose a bolt rope on the foot, mainly because that's what the standard
mainsail had.  I would order the optional zippered shelf which will allow
you to increase the fullness of the lower 1/3 of the mainsail shape for
light air.  You zip up the shelf to flatten the mainsail shape for heavy
air.  After you've paid the big bucks for this fully battened mainsail,
definitely get a leech line & cleat.  The primary function of the leech line
is to stop the trailing edge of the sail from fluttering as the air foil
sheds its trailing vortices.  This fluttering subjects the sailcloth &
stitching in the leech to a lot of high frequency wear cycles, which can
result in premature fatigue failure of the material.  You tighten the leech
line just enough to stop the fluttering.  Thus, the leech line extends the
life of your expensive new sail & is well worth the money up front to have
it installed.  You will have to specify the number of reef points in your
new mainsail.  I originally ordered just 1 set & later had a sailmaker
retrofit a 2nd set.  The next time around, I will order two sets of reef
points.  My 1st reef point reduces the mainsail area by 1/3 and the second
reef point by 2/3 relative to the full mainsail area.

Finally, this new fully battened mainsail will be substantially bulkier when
furled on the boom vs. the standard mainsail.  The chances are, your current
mainsail cover will no longer fit.  I modified my old mainsail cover to fit
the new sail.

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 5:21 PM
Subject: Re: [Rhodes22-list] Mast Crane (was Lou Moore)


> 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
> > > > > >
> > > > >
> > > > > > >
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> > > > > > >
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