Subject: Re: [harryproa] Re: First building quote for the 60' Seabattical charter proa
From: "Rob Denney" <>
Date: 5/1/2008, 9:33 AM


Prismatic theoretically is 0.8, but I have no accurate and easy way of
measuring it to be sure. No negative rake on the bow, although there
was when it was first joined. Windward hull has same prismatic but
is fatter. Why should the prismatic make any difference? I have the
materials for a second half, just figuring out what I want to change
and how best to measure the effects. The young girl made the asme
comment as soon as she saw the drawings on the screen. She is getting
a bit irritated with dad continually making excuses about her boat not
being ready yet.



On Thu, May 1, 2008 at 10:04 AM, Robert <> wrote:
> -Congratulations. Looking forwards to the photos. Any idea of the
> prismatic coefficient? Is there a slight negative rake on the stem?
> Theoretically the ww hull should be just as easy if done with slightly
> lower prismatic coefficient.
> three more quarters to go plus a reinforced wind surfer rig and you
> have a small Elementarry for some young girl to take out solo.
> Robert
> -- In, "Rob Denney" <harryproa@...> wrote:
> >
> > G'day,
> >
> > Got the first quote in for the build of the Seabattical charter proa.
> > Ballotta in Peru will build the two hulls, decks and beams, with
> > bulkheads and floors, all LPU painted and joined together for $96,000
> > (all prices US dollars). Ballotta make some of the lowest cost
> > quality cats in the world. Their 14m/46' cat to the same stage is
> > $135,000, their 11.5m/39' cat is $99,000.
> >
> > Materials were priced from the USA and were expensive compared to
> > buying and shipping them from Australia. A saving of $10,000 for the
> > foam option, $16,000 for Polycore, plus whatever time and material
> > savings are available from the new build system (see below).
> >
> > The proa will be easier than the cat to fit out as the windward hull
> > is all on one level and flat. It will be built on the workshop floor,
> > then lifted and bonded to the hull. However, it has 4 double cabins
> > with ensuites, compared to 3 in the cat, so the end result will
> > probably be similar. The 39' cat ready to to sail costs $275,000, the
> > 46'ter $350,000. The 18m/60' proa with the same fit out, (see
> > but a lot more space and
> > performance, will be somewhere between them.
> >
> > Of particular interest is the 46' cat's stayed alloy rig cost of
> > $52,000. We expect to beat this price with 15% more sail area in an
> > unstayed schooner rig. A quote for the complete boat will be
> > available when I finish the drawings, at which stage I will also be
> > looking for feedback on layout etc from list members. Construction
> > should start later this year.
> >
> > The 2.4m/8' long quarter scale model of one half of the charter proa
> > lee hull is completed. The system worked a treat. Took me 90 minutes
> > to mark out (2 measurements every 250mm/10" on the model) and glass
> > each side, and another 30 minutes to join them along the keel line.
> > The gunwhales were then lifted to near vertical and the bows squeezed
> > together. The below water shape was close to what I had drawn, but
> > the bilges were slacker (more Vee'd). As expected, it had 20mm/three
> > quarters of an inch of negative rocker 600mm/24" back from the bow,
> > tapering to nothing in the middle.
> >
> > I rested 25 kgs/55 lbs across the gunwhales above the negative rocker
> > and left it overnight. Next morning, the rocker was straight, the
> > bilges more rounded and when I laid the panels down flat, they were
> > noticably compounded. Glassed the inside in under an hour, then
> > flipped it and glassed the outside in 40 minutes. Profiled the bow
> > and cut the sheer and it was essentially done. It is typically
> > rough, the full size hull will need some supporting (I just sat it on
> > he floor) but fair. The section shapes are very flat U sections (no
> > floors required) and close to what I had drawn, no reason to believe
> > that anything between this and a V could not be achieved. No doubt
> > that Polycore (and presumably foam) can be compounded quickly and
> > accurately for rockerless hulls with vertical stems. The Polycore
> > soaked up 200 gsm of resin per side, a little less than H80 foam
> > (250gsm), but with a much stronger bond. Photos when I find the
> > cable for the camera.
> >
> > Next time I will taper the keel joining glass towards the bow to
> > avoid the hard knuckle I ended up with. If a polystyrene nose piece
> > was included, which I think is an excellent idea, then the shape for
> > the last 200mms or so (which is where any mistakes show up) would not
> > be a worry.
> >
> > The full size panels will be done on a vacuum table. Maybe infused,
> > maybe not as I think it will be quicker overall to bag it twice and
> > have a mould finish on both sides of the panels.
> >
> > regards,
> >
> > Rob
> >

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