[MHml] Bi plane rigs.

[Rob Denney]

G'day,

The theory is that you can carry much more sail upwind for less weight and
windage aloft, and let the rig flex to depower automatically.  The upwind
savings may or may not offset the downwind losses.  As most unstayed rigs
are for cruisers, and most racers are rule limited, this has yet to be
tested in a serious race boat campaign, although it nearly was with Team
Phillips.

There are weight and drag savings from not having to carry the sprit and all
it's rigging.  If the overall boat is light enough, there are significant
weight savings from not needing the extra sails (weigh them when they are
wet) and rigging, nor the crew required to handle them.  This leads to a
smaller (not shorter), lighter, more easily pushed boat, which means less
sail area is required.  Taken to the extremes this approach results in some
quite astonishing weight, windage and cost savings.    For example, I have
started building (ww hull half done)  a 15m/50' harryproa for the solo
TransPac in 2008.   It will weigh less than 600 kgs/1,330 lbs in racing
trim, 40% of which is me, safety gear, food and water.  It has less frontal
area than a 15m mono rig and rigging, and will cost less than
$Aus20,000/$US15,000 in materials (all carbon), plus the same again if I
paid someone to build it.

Also, there is no reason why an unstayed mast cannot carry extras.  The mast
is designed around the maximum capsize load, not the sail area.  For me,
though, an Outleader kite makes much more sense.

regards,

Rob


----- Original Message ----- 
From: "Bill Gibbs" <billg at gibbsCAM.com>
To: "'Informed discussion of multihull issues'" <multihulls at steamradio.com>
Sent: Monday, September 04, 2006 4:02 AM
Subject: Re: [MHml] Bi plane rigs.


> I am intrigued by stayless bi-plan rigs and boats like the Schionning
> Radical Bay 8000.  If you get the power to weight ratio up to
Afterburner's
> level, you solve the AWA problem as we never sail below an AWA of 70
> degrees.  Dandy didn't get fast enough.  The next problem is the AWS
> problem.  AWS diminishes as you fall off from close hauled, which normal
> boats compensate for with ever larger headsails, jib to screacher to
> spinnaker. Or in Afterburner's case, 2 jibs, 2 screachers, and 2
spinnakers.
> Cat boat style uni-rigs don't seem to address this issue.  For sailing
deep
> a biplane cat seems the ultimate kite launching vessel.
>
> Bill
> Afterburner
>
> -----Original Message-----
> From: multihulls-bounces at steamradio.com
> [mailto:multihulls-bounces at steamradio.com] On Behalf Of Roy Mills
> Sent: Sunday, September 03, 2006 11:45 AM
> To: multihulls at steamradio.com
> Subject: [MHml] Bi plane rigs.
>
> Snip
>
> He tried a bi plane rig on  his cat "Dandy" with a 23 foot LWL and
> discontinued it after 2 years and 2000 miles. He initially tried it
because
> Lock said " the drag of the rig is not as important as the actual force
> produced. Water drag and aerodynamic drag of the vessel itself are of a
high
> order and the parasitic drag of rigging wire etc is relatively small"  I
can
> go along with that but his comment is "Lock, I wish you had been right".
> Lock had sent him a drawing of a
> 28 by 23 foot day sailing biplane cat,( that is extremely wide- a C Class
> cat is 25 by 14) thought to be like an ice boat so it was fast enough to
> always bring the apparent wind forward of the beam. "Dandy"
> would not do that. On a reach the leeward sail flopped about. It had
virtues
> he said.  It tacked faster than any other cat he ever sailed ( which
was/is
> one of my concerns) and he said that it pointed very high but was not fast
> to windward. It would tack through 60 degrees but speed was low, when
> bearing off to tack through 90 the VMG was still not good.
>
> This seems not to be current experience with biplanes. Is it the
> advent of unstayed masts that has made the difference, or larger sails in
> proportion to the boat, or hull forms more suited to speed than cruising,
or
> all three, or more changes that have escaped me?
>
> Comments please.
>
> Roy Mills
>
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