-The prismatic coefficient is the proportion of the hull that would
fit into a prism The prism can have any cross section. Therefore you
need to (roughly) take the cross section sectional area at the centre
multiply it by the prismatic coefficient and the length. I don't think
you included the difference between the cross sectional area and a
rectangle.
'Prismatic Coefficient. The longitudinal prismatic coefficient (CP) is
the ratio of the immersed volume to the volume of a prism with length
equal to the ship�
section:
where
If length between perpendiculars and length on the waterline are equal
(as they are for Navy ships), the prismatic coefficient is equal to
the block coefficient divided by the midships section coefficient. The
prismatic coefficient thus indicates the longitudinal distribution of
the underwater volume of a ship�
draft, and displacement, a low (fine) CP indicates a hull with fine
ends. A large (full) value for CP indicates a hull with relatively
full ends. For this reason, the prismatic coefficient is sometimes
called the longitudinal coefficient.
The vertical prismatic coefficient (CVP) is the ratio of the immersed
hull volume to the volume of a prism having a length equal to the
ship�
>From what I have observed, The boats seem to need a minimum 12:1 for
the ww hull, a minimum 17: 1 for the lw hull, preferably a ratio of a
bout 2/3 ww/lw, the cross section of the lw hull closer to a rectangle
with moderate radiuse corners and slight curvature on the bottom ( I
have read some theoretical argument that it reduces wave resistance
going for this shape, a slightly parabolic cross section for the ww to
make use of the unweighting as the speed increases to bring the ratio
up, and about half the lw hull length for the overall width. With a
heavier cruising ww hull the width should maybe be a bit less.
I have used a pole a couple of ways for raising tall object. If the
object is reasonable light, I merely brace the pole to stand
vertically, lash a pully on top and haul the tall section up. If the
tall object is much heavier one end than the other, then you don't
need a tall pole. If it is more even in weight distribution you will
have to have a longer pole and/or lash some weight near the bottom.
The other method for heavier sections I have used such as hauling up
radio masts, is to set up guys to keep the bits from wobbling
sideways, and using what is sometimes called a 'Gin' pole, where a
pole of about 1/3 the height is place vertically at the same base as
the mast to transfer a horizontal pull to one with a bit of lift.
A hinged socket would make it easy to drop in, but you would need
some sort of device for lifting it back out again and balance it to
the point where you could walk it back down again. This can be simply
grunt and a collar with a loose footed tripod to take up the slack
I think you are right that a single piece crossbeam could not do the
job. I think Rob mentioned a two piece crossbeam and I am not sure of
the bury, but the loads on the ww end are a fair bit less than at the
lw end
Robert
-- In harryproa@yahoogrou
>
> Rob, great reply, as usual. Now the onslaught of questions.
>
> Prismatic coefficient (I have been embarrased to ask, but since you
mention
> it), I must be using it wrong.
>
> 15' * 1.5' * (8.5/12)' = 15.93 cubic feet * 0.77 = 12.27 cubic feet
* 62.4
> lbs/cubic foot = 765 lbs displacement. Where did I go wrong?
>
> What is your guideline on relative sizes of the hulls. This looks
like you
> are building the shortest ww hull that can handle the weight, then
you put
> on a lw hull that is as long as possible. Extrapolating from your
numbers, I
> guess you want at least 10:1 length to beam for ww and a draft of
1/2 beam
> (so the underwater cross section is roughly semi-circular?
skinnie-ness
> (wrong word?) is based on full-up whole vessel weight, with a ratio
of 20:1
> or better??? Is there a rule of thumb relating the lengths of the ww
and lw
> hull? In Visionarry and the charter, it seems to be ww length + 10
feet. In
> this it is 15' ww and 40' lw.
>
> My biggest concern with the trailering is stepping the mast;
particularly by
> myself. I had a 25' trailerable tri, which I never used because it
took 4-8
> hours to set up or tear down. But raising the mast was the easiest part,
> using the hinge at the mast step and all the rigging to hoist it up. I
> picture myself standing on top of the trailer trying to pick up a
175lb mast
> that is 40' long and wave it around until I can stick it in a hole. I am
> sure that is not what you have in mind, since you mentioned some
sort of a
> pole, but I am not understanding how it can be done. I was thinking
maybe a
> hinged sleeve at the mast hole opening that I slid the mast into,
with a lip
> on the other side of the hole? Then stand on top of the trailering
vehicle
> with a long stick to push the mast upright? Sounds difficult.
>
> I had a question about the telescoping. You mentioned that the boat
could
> trailer at 8'6", fit in a slip at 12' and sail at 20', all with a single
> telescoping beam. I would think that for an 8'6" width, the
theoretical max
> beam would be 2*8'6" = 17', which would leave no overlap for
strength. How
> are you doing that?
>
> On the layout for my version, you say "Yours will have the cockpit
in this
> area." I don't know which area you mean. From "front" to "back" is the
> layout: galley, bunk, cockpit, bunk, toilet? Deck hatches between
galley and
> bunk and between head and bunk? Refering to questions in the first
> paragraph, if the lw hull has to be 40', is there any real downside to
> making the ww hull 20' or even 25? If the hulls are to be made from
2 flat
> panels each, it would seem to be a minimal increase in cost and
labor and
> would make things easier to fit.
>
> I really appreciate the resin infusion tips. I am unfamiliar with
some of
> your terms. What do you mean by "shade cloth"? Something you would
make an
> awning out of? Sunbrella, or similar (dense weave, heavy, almost like
> canvas)? Is "window sealant" like caulk?
>
> when you say "cut the cloth and peel ply", do you mean the
fiberglass cloth?
> or the shade cloth? The order of stacking is glass, peel ply, foam,
glass,
> peel ply?
>
> The plastic conduit (with holes drilled) is layed on top of the
glass? or on
> top of the stack of foam/fiberglass? If on top of the glass, how
does the
> layer of fiberglass on top of the foam ever get infused?
>
> I'll start gathering materials this weekend. I have some West System
epoxy
> resin already. I guess I can experiment with that, but it is high
viscosity.
>
> As always, your help is appreciated.
>
> - Gardner
>
>
> On Wed, May 28, 2008 at 1:19 AM, Rob Denney <harryproa@.
>
> > G'day,
> >
> > Preliminary numbers
> >
> > ww hull 5m/15' long, waterline 450mm/18", draft 220mm/8.5",
> > displacement 640 lbs, prismatic .77. (Use this to allow for the hull
> > shape when you multiply the cross sectional area in the middle of the
> > boat by the length). I would probably go a little longer to cope
> > with your other requirements.
> > lw hull, as long as you can build, trail, afford and handle. The
> > longer it is, the higher the top speed and the drier and more
> > comfortable the motion.
> >
> > The single sail works well on boats with light windward hulls, as the
> > rudder is aft, which makes it balanced. With 600 kgs on a shortish ww
> > hull, the ballestron may be a better bet, although once you know how
> > to shunt, it won't be a problem. With a lot of people on board, and
> > not much boom clearance the ballestron needs to be watched while
> > shunting.
> >
> > There will be trampolines, which will be on side pieces with a hinge
> > in the middle so it can be folded when the boat telescopes. A
> > walkway can do the same.
> >
> > Sail is loose footed (attached only to the outboard end of the boom).
> > On Elementarry, the boom is attached to the mast. It has a sock luff,
> > so this is not a problem. Yours would have slides, so the boom needs
> > to rotate relative to the mast, but not move vertically. Not a big
> > deal. Your boom will indeed be too long to attach permanently. It
> > will be strapped to the bearing on the mast, again, not a big deal.
> >
> > The hours on the charter boat are for the shell. This one could take
> > anywhere from 500-1,000+ hours depending on all the usual stuff, but
> > mostly on the standard of finish required. There are some alignment
> > details to make it telescope smoothly, which could add some time.
> > They are all done before the beams are closed up permanently, so are
> > not difficult, just might take a while.
> >
> > Materials cost? Same as the other trailer sailor, give or take a bit.
> > It is cheaper to import the materials from here. Let me or Raps
> > know if you want to share the shipping costs.
> >
> > Could be a single bunk, or the galley and stowage. The double is
> > 6'x5', the single is 5x3. Yours will have the cockpit in this area.
> > The toilet at one end of the hull and the galley at the other end.
> > Access will be through deck hatches.
> >
> > Re infusion. Derek's workshops are fantastic, Henny at
> > http://www.fram.
> > Houston, but I don't have his web address. By far the best way to
> > learn about it is:
> >
> > Get a vacuum pump from ebay, (old milking pumps, fridge compressors,
> > air con evacuators all work) and a sheet of window glass about 30"
> > square. Buy some clear builders plastic, some window sealant, glass,
> > foam, peel ply and resin, some shade cloth and some 10mm plastic
> > conduit. Drill the smallest holes you can every 4" in the foam and a
> > 1/4" hole every 4" in the middle 18" of 2 pieces of 4' lengths of
> > conduit, cut the cloth and peel ply and lay it on the glass with a 2"
> > border all the way round. Put the shade cloth on the glass and wrap
> > it around the perforated section of the lengths of conduit such that
> > one piece is on one side of the job, the other is on the opposite
> > side. Cut a piece of plastic the same size as the glass and seal it
> > to the glass and around the conduit. Block one end of one piece of
> > conduit and hook the other end up to the vac pump. Block both ends
> > of the other piece. Check for leaks (listening) is the best way.
> > When it is leak free, unseal the ends of the non vacuum conduit and
> > put them in buckets of resin. Prepare to be amazed. When the
> > infusion is complete (look under the glass aswell as on top), seal off
> > the resin conduit and leave it to cure. You now know more about
> > infusion than 95% of the world's boatbuilders. Study and weigh the
> > sample, and let me know what it looks like and what went wrong and I
> > will start lesson 2.
> >
> > Elementarry as a tender? Could do, but without seats, it is not very
> > comfortable. It is also a bit fragile for hauling up beaches and over
> > rocks. The Torqueedo would work, but rowing wouldn't. No sweat on
> > the payload, but it would all be on the trampoline. You would be
> > better off with a conventional dinghy. Loading El on the cabin top
> > for blasting around when you get there has more merit, but the mother
> > ship really should be bigger for this.
> >
> > Let me know what the next step is, or if I have forgotten to reply to
> > anything.
> >
> > regards,
> > Rob
> >
> >
> > On Tue, May 27, 2008 at 11:57 PM, 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. Since
> > > 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
> > trampolines,
> > > 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
> > expanded.
> > >
> > > 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
mentioned
> > > 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
<gardner@...
> > >
> > >> 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 lbs.
> > >> 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.
windspeed
> > >> > 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 http://www.harrypro
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
epoxy/fiberglass,
> > >> > 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
posted
> > >> > 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
summer/fall,
> > >> > 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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