[MHml] Friction in lines and blocks

Mon Dec 10 15:00:38 EST 2007

G'day,

Much easier to use the lee hull, which is already there than to add
the complexity and windage of the struts.  Two beams will not do it
unless there is something stopping them moving up and down.

regards,

Rob

On Dec 7, 2007 10:13 PM, sysfx <sysfx at yahoo.com> wrote:
>
> Rob,
>
> Good morning,
>
> I've been observing the work of a group developing a 12ft entry cat for kids
> with a self standing mast and sleeved sail. One of the designers
> demonstrated that the use of two solid struts to support the mast at about
> boom level (google "Hobie Bravo" to see it) almost cancels compression on
> the main beam (=lighter structure), greatly reduces mast flexion (= lighter
> mast) and, since the struts' forces on the structure are mostly horizontal
> and outward, the tramp tension helps cancel them (=lighter structure).
>
> A cat is certainly different from a proa, but after seeing a similar strut
> system in Sailrocket (speed record attempt proa) and remembering having seen
> them in older proas, I thought the same principle might be interesting for
> your boat.
>
> All the best,
> Luiz Schechter
>
> ----- Original Message ----
> From: Rob Denney <harryproa at gmail.com>
> To: Informed discussion of multihull issues <multihulls at steamradio.com>
> Sent: Thursday, December 6, 2007 11:03:50 PM
> Subject: Re: [MHml] Friction in lines and blocks
>
> G'day,
> If Roy's cruising cat with a stayed mast is the dark side, then this is a
> comment from way beyond the dark side ;-)
>
> On the unstayed masts on harryproas which do not have ballestron rigs, such
> as my 15m solo boat, the wing mast is round where it goes through the deck.
> This round is continued up 300mm/12" from the deck.  The boom fits on this
> part of the mast, in plastic bearings.  The boom can rotate independantly of
> the mast but cannot move vertically.  ie, it is self vanging.  Leech control
> is done with a multi purchase block along the top of the boom.  Angle of
> incidence of the rig is controlled by a 3:1 line from the cockpit to the end
> of the boom.  This line sees less load than a traveller line as there is no
> traveller friction to overcome.
>
> Much cheaper than the systems mentioned above as most of it can be built,
> rather than bought.  Probably lighter as well as there is no traveller,
> winches or huge blocks required.  Whether the deep boom is a plus or a minus
> I am not sure, but suspect it does not make much difference.
>
> Won't work on most boats, but is great on unstayed masts.
>
> regards,
>
> Rob
>
> regards,
>
> rob
>
>
> On Dec 7, 2007 5:56 AM, Roy Mills < rsirfj at shaw.ca> wrote:
>
> >
> >
> > ----- Original Message -----
> > From: "Claas van der Linde" < Claas.vanderLinde at gmx.ch>
> > To: "Informed discussion of multihull issues" <multihulls at steamradio.com>
> > Sent: Thursday, December 06, 2007 9:56 AM
> > Subject: Re: [MHml] Friction in lines and blocks
> >
> >
> >
> > > Ross writes:
> > > >In carbon the boom will save more than that - so overall a positive
> > > >saving of weight.
> > >
> > > That's the right attitude. On our boat modifications, replacements or
> > > repairs are only allowed if they result in an overall weight saving.
> >
> >
> >        A comment from the "Dark side", having seen little which has not
> > been from the racing types.  My main sheet is an 8 to one set up as per
> > Tennant's diagram. lead through a clutch and passing by a Lewmar 24 2
> speed
> > none selftailer. The Traveller is a 12 foot length of Harken track and
> > positioned by a 3 to one tackle, also passing through a clutch located
> > alongside the main sheet clutch,and passing close by the same winch. All
> > blocks are the 3 inch Harken Big boat ball bearing jobs. TYpically I do
> not
> > need the winch to tighten the mainsheet as much as I want for the 490
> square
> > foot main provided I can get both hands on the sheet, if I can't, then the
> > winch comes in handy. I sometimes do need the winch for the traveller, but
> a
> > lesson learned a few years ago helps a lot to minimise that too. I had
> > turned a mark from a broad reach to a beat, the traveller was well down,
> the
> > main sheet tight. I tried to wind in the traveller without easing the main
> > and ended up breaking one of the traveller blocks, which at the time was
> not
> > a 3inch Harken. So I learned to dump the main sheet, haul in the traveller
> > hand over hand, then haul in the mainsheet similarly. May not be up to
> > racing speed but it always seems to work fine.  One thing I have in common
> > with earlier posters is that when the main sheet is tight the traveller
> will
> > not ease, despite the ball bearing car, until I have eased the main, and
> as
> > they have found it does not require much of an easing to let the traveller
> > move down, then the main can be hardened again. The traveller will move
> over
> > the full length of the track because the two double blocks on the boom are
> > spaced about 18inches apart, something you might think about Ross.
> >
> >        I don't hand hold the sheets, relying upon the fact that the main
> > and traveller clutches are close by the tiller in each cockpit and the
> sheet
> > tails are stuffed, not coiled, into tail bags so should run freely.  Like
> > Martin I launder the sheets each winter, though I had not thought to use
> > fabric softener. Unlike Claas I do not restrict modifications to weight
> > savers only, the 550 pounds it cost me to fit the sitting headroom 8
> seater
> > cabin is worth every ounce, and more.
> >
> >
> >
> >
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