Subject: Re: [harryproa] Re: Build trailerable as a test?
From: "Gardner Pomper" <>
Date: 5/27/2008, 10:18 PM


Ok, on a smaller, simpler boat would be a good place for me to throw some approximate numbers around and find out where my misconceptions are with proa design and displacement. If you know the relevant dimensions for the Elementarry, maybe you can toss them in.

I will make gross approximations for hull shape and volume calculations, but I think the end result should be in the ballpark. I will assume that the ww hul has a semicircular bottom, maximum waterline beam of 2'. Top view of the hull has parallel sides the middle 1/3 of its length, then straight to a point on either end. With a 1' draft and a 15' length, I get a displacement of about 16 cubic feet, or 1000 pounds.

For the leeward hull, I will assume 25' length, 1' maximum beam, center 1/3 is parallel and tapers to a point on either end. With just a 6' radius, for a 1' draft the underwater cross-section would be U shaped. Again with the fuzzy calcs, I get a displacement of 23.5 cubic feet, or 1500 pounds.

I just did these calcs with a pencil, sketching on paper, so maybe I am totally off, but those displacements seem high enough. My reasoning is that the ww hull really just has to support itself and its payload and the lw hull needs to support the entire boat.

The length to beam ratio (7.5:1) is poor for the windward, but I thought that was ok in a proa. The lw hull is a respectable 25:1.

How do these number compare to the actual Elementarry?

I was figuring "canoe" style seating with 2.5' spacing, with feet on the hull floor, and sitting on the beams and crosspieces between would allow for 5 seats. It might be fun to have spinning barstool type seats on top of each crosspiece, to make it easy for passengers to face forward.

Ok, that's it... I am braced.. hit me with a dose of reality :D

- Gardner

On Tue, May 27, 2008 at 9:39 PM, Robert <> wrote:

To carry that weight on something the size of Elementarry and still go
OK unloaded, You'd have to have a flare above the unloaded waterline
of about 50% extra on the width of the hulls and need a about 50%
extra on the the freeboard. Though El could probably handle the
weight as is, but the trampoline would be skimming the water. For the
lw hull, you don't want to make the bows any fatter as they would slow
the boat down when you are sailing fast with only a couple on board,
so any flare has to start just forward of the beam and a fair bit
above the resting waterline. This would add to the windage when
lightly loaded, but this can't be helped It would not be fast when
loaded but would be OK; at displacement speeds similar to a sea kayak.
I think it would probably be a bit heavy for a tender, and you would
have to design a place for it on board the big one. You'd also want to
collapse it to 4'-5'. To get it up on the roof is possible, but it
won't be a cinch to get it up. It may be possible to use the boom as a
gantry to get it up there. It would add just a tad to the windage.
To allow sailing with all on board. You could not push it too hard
unless you designed the beams for a massive righting moment. which
would add to the weight, though I suppose the mast would flex enough
to take off the strain, or you could only expand it on one of the
telescoping section. With that many aboard, you could get them all on
bicycle cranks and develop more power than a small electric drive ;<0
or more seriously , set yourself up with a couple of mirage drives.

A una rig centred in the lw hull can drive the boat oK as there is a
rudder hanging off the back crossbeam to provide leeway resistance far
enough back.
I reckon it is doable , but you would have to design the big boat to
accommodate it, including the winching gear to get it on board. It
would certainly be a lot safer getting around than most tenders.
--- In, "Gardner Pomper" <gardner@...>

> Ok, let me switch tracks here. I was originally thinking of
something like
> the Elementarry design. One of my thoughts is that the liveaboard
proas are
> so long, that perhaps it would be possible to use Elementarry, or
> like that as a sailing tender, with a Torqeedo electric outboard for
> you don't want to sail. It would have to be able to carry 6-800
pounds of
> passengers without swamping, but it doesn't have to have great sailing
> characteristics when fully loaded.
> I don't find any specs on payload for the Elementarry. Also, would
it be
> possible to mount it in a cradle on the roof of the cruising proa?
> I have tried to keep my ideas at least moderately sane, so please
forgive me
> if I have gone too wacky with this one.
> - Gardner
> On Tue, May 27, 2008 at 11:57 AM, Gardner Pomper <gardner@...>

> wrote:
> > Hi,
> >
> > Ok, I can tell by the responses that it won't be a small boat :( I was
> > hoping for something smaller than the design that is taking shape.
> > that looks to be not true, let me fall back to that one, and drop
the weight
> > requirements and the 6 passenger (we will only invite people on a
nice day
> > for a few hours. They can sit on the trampolines (there can be
> > right?) Then we can design for crew weight of 600lbs, and seating
for 3-4.
> >
> > I notice that you are not using the ballestron right. I am flouting my
> > ingorance here, but how can you go upwind with a mast centered for
and aft
> > and no headsail?
> >
> > I was also thinking of a 3-4' flat panel, hinged at the floor, to
give some
> > sort of walkway outside the cockpit. Fold it down once the beam is
> >
> > Is the sail loose footed? The charter proa talks about the boom
and mast
> > being one piece, but it would seem to make it too wide for trailering.
> >
> > Since you have basics worked out on that trailer sailor, do you
have an
> > estimate of work hours for an "average" finish? I know you have
> > 1400 for the charter proa hull (by professionals, I am sure).
> >
> > There looks to be a single bunk "forward" also. Is that true, or
is that
> > the galley? What are the bunk dimensions?
> >
> >
> >
> >
> > On Tue, May 27, 2008 at 11:38 AM, Rob Denney <harryproa@...> wrote:
> >
> >> G'day,
> >>
> >>
> >> On Tue, May 27, 2008 at 11:00 PM, gardnerpomper

> >> wrote:
> >> > Hi,
> >> >
> >> > Some sort of liveaboard harryproa seems like my next cruising
boat. I
> >> > am interested in both sampling the experience, and finding out if I
> >> > have the fortitude to build one. I have seen messages about a
> >> > trailerable design and I have some questions specific to using
it to
> >> > "try out" the home build/proa idea.
> >> >
> >> > Requirements:
> >> > 1) trailerable as other specs (8'6" trailer width,
> >> easy
> >> ><1000lbs with trailer (negotiable))
> >> Difficult, negotiations can start when i have done some drawings.
> >> > 2) build method as similar to proposed charter boat as
possible, since
> >> > that is identified as simplest for larger boats
> >> > fast and easy on/off the trailer. this would be a daysailer,
driving 2
> >> > hours to the water, set it up, sail for a few hours, break it down,
> >> > trailer it 2 hours home.
> >> Easy
> >> > 3) I am heavy (300lbs), so the crew weight (3 of us) would be about
> >> > 550lbs. We would like to be able to invite another 2 adults and a
> >> > child and still sail it well, so total crew weight could be 900
> >> Difficult, I will see what the minimum size is to do this. How much
> >> extra for food and safety gear?
> >> > 4) Enclosed head
> >> easy
> >> > 5) sail without getting wet
> >> easy
> >> > 6) camping propane stove
> >> > 7) comfy seats and table to eat at
> >> Can this be outside, under a removable bimini with roll down sides?
> >> Otherwise, it is a bit ticky for 6 people.
> >> > 8) standing headroom (fold down bimini ok)
> >> easy
> >> > 9) rain protected
> >> easy
> >> > 10) will never be INTENTIONALLY sailed in > 20 kts
> >> Yeah, right!
> >> > 11) ballestron rig
> >> easy
> >> >
> >> > I won't be racing, but I will want performance comparable to
what we
> >> > have heard from Rare Bird and the charter proa design (i.e.
> >> > up to 15 knots). I *don't* want to fly a hull!! (I'm timid)
> >> Timid is good, but it will be a sizableboat to do this with 6
people on
> >> board.
> >> >
> >> > Questions:
> >> > 1) What would plan cost be?
> >> TBA when i see what is involved. Probably $Aus3,000, as it is going
> >> to be a one off. You get 10% off any future plans sold to the
> >> design until the next one is sailing. After that it is as per the
> >> Goodwill Fee on Part of the plans
> >> price wil be deducted from the big boat fee.
> >> 2) would plans include info on resin infusion and building a table,
> >> > etc, etc? Or at least point me to such info?
> >> yes. As much information as you need on anything in the plans.
> >> > 2) Estimated build time (novice.. experienced with
> >> > even some with carbon mat as reinforement, but never built a
boat). If
> >> > you prefer, you can supply "average estimated build" and I will
put in
> >> > my own "idiot factor" multiplier
> >> TBA, but mostly it will depend on the level of finish inside and
> >> outside that you require.
> >> > 3) Would it be close to the "trailer sailer" layout jpg I see
> >> > in the forums?
> >> Not if you want a cockpit for 6, which will replace the bunks
> >> >What are hull lengths?
> >> Long! What is the longest you can build, trailer and handle on
the ramp?
> >> > 4) When could I start? I have a building available this
> >> > but it is not heated
> >> Tomorrow, building the table. You won't get all the plans
> >> immediately, but i will keep ahead of your progress. Pay for half the
> >> plans up front, the rest before the last drawings arrive.
> >> > 5) material cost? availablity?
> >> Not a huge amount, probably less than the resale value of the boat.
> >> Can get it from your local supplier, apart from the carbon for the
> >> mast, boom, rudders and beams which I will supply from Texas.
> >> >
> >> > BTW, I live in Pennsylvania (US).
> >> No problem ;-)
> >>
> >> > Thanks,
> >> > - Gardner
> >>
> >> My pleasure,
> >>
> >> Rob
> >> >
> >> >
> >>
> >>
> >
> >

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