Good post.

--------------------------------------------
On Mon, 28/5/18, '.' eruttan@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:

Subject: Re: [harryproa] Re: extruded polystyrene core questions
To: harryproa@yahoogroups.com.au
Received: Monday, 28 May, 2018, 2:19 AM


 













|    You are operating on the premise that we are
comparing a short ply hull with a long ultra light weight
composite one. 



You are putting words in my mouth.

My point is a longer hull can be lighter, and a shorter hull
can be heavier.. You have not shown an error in that
thought, nor recognized the truth of it.



| A longer hull inherently has more material in it if it is
to have useful volume.



If these are your premise, than they are yours. They are
not everyone's. There are many proas that have very
fine lee hulls that have very useful internal volumes. If
you cannot imagine a use for this volume , that's fine,
others already have.



| The most efficient layout structurally and in terms of
surface for usable volume is the most compact.



A harryproa is less compact and more efficient, lighter and
has a more voluminous interior. You should question your
premise.



| The finness ratio necessary for a multihull of any kind
to be efficient generally dictates that the forward end at
least if not the aft end also are of limited value other
than displacement and storage of light weight items.



'Generally' does not apply to the specific. And we
are talking specific boats, and at least one of these boats
violates this generality for great profit.



|     The idea that a 40' proa will be equivalent of
less in weight, cost, and time to build than a 30 foot cat,
both boats having equal usable internal volume is in my
opinion unrealistic.



How do we go from opinion to knowing? All it takes is facts
and thinking. Perhaps you are right. Perhaps a 40'
foot will not work. How about a 50'?



Or better yet, have a conversation with Rob. I mean you
have been rather kind to detail your SOR, in rather detailed
fashion. He might be able to whip something up.



|Materials and weight tend to increase with the cube of the
length on a boat.



Only if you assume similar compact structure. Check your
premise.



|  The estimate of a 25% savings in weight between plywood
and foam sandwich without compromising structural integrity
seems to approach reality IF the boat is designed
specifically to get the max weight savings by utilizing the
material to the best advantage.



Perhaps. I can't speak to it, as I do not have the
facts at my disposal. I can speak to the fact that, for any
given payload, Robs designs beat that 25% estimate all the
time.



| The fact remains that I simply do not want a 40' boat
as a single hander, or as a builder.



Then I retract everything I have said. I cannot and will
not persuade you into any given thing. Especially one you
have now declared you do not want..



I thought we were discussing the criteria, parameters, and
ideas, of boat design selection and having fun doing it. It
seems you thought I was badgering you into something you do
not want. No harm, no fowl. I'll stop now.



| I'm somewhat open minded, but the fact remains that
the boat I want to build is a 30' cat, and I do not see
anybody swaying me on this in the foreseeable future.



You are truly blessed if you know what you want.
Congratulations!



|     The idea of doing a flat development and merely
folding flexible corners may be feasible in some situations,
but it clearly is not in this case.



What is clear to you is not clear to me. As I said, I may
be getting this wrong. I do often.



| Anybody with the most basic sense of geometry can see
this. The stuff of fantasy.



I cannot speak to other peoples sense and fantasy. I have
enough trouble with my own. But here is a source for my
thoughts.



http://harryproa.com/?p=726



"The ww hull was originally to be built in moulds, but
is now a very tricky, owner (Steinar) designed flat panel
build, although looking at it, you would never
know."



Take a look at the pics. That's how I want to build a
boat. Having loki help me with seems legit.



| What I see as the most realistic build system is to build
a three dimensional mold of an entire hull side on it's
side on the floor or a table using temporary formers,
stringers, and flat sheet material with a suitable gloss
surface, the intersecting corners being radiused, and sanded
smooth, as well as the joints, and any fasteners. The
entire thing coated with a mold release, and the layers of
the sandwich added and infused ........... no small
undertaking.  The knuckle.... thanks, that was the word
that I was looking for..... and half the bottom, more or
less lock in the contour. 

| Each mold would make two hull sides, and the formers
would be reversed to make the other mold.  The bottom could
be made in halves as part of the two hull sides, or made
flat, and added later, resulting in two full length seams
instead of one.   I like the one seam, as it would be
covered by the 6" sacrificial wood beaching keel I
envision.   Not all beaches are sandy and rock free.



Well build how you like and feel comfortable. Obviously I
prefer the geometrically nonsensical technique.



|     The second alternative of course is to just build 3
long flat panels for each side of each hull, plus the bottom
and have full length seams.  A far simpler method, but far
more finishing labor.... at least 6 seams in each hull, plus
the seams for attaching the coach roof bridge deck, and
bridge deck cabin, etc........... 



I cannot speak to either technique. I know this Intelligent
Infusion seems pretty great to me. Perhaps another reader
will be along to advise.



|"idiotic infusion"???

|

|    Speaking of "flat development", developing
a hull shape and formers that is compatible with flat sheet
construction, is an interesting challenge.    I've
always had great respect for people who design smooth shapes
in three dimensions, and that respect is much greater than
it was just a few days ago ;-)



Well, if you map the curve of the delta in your thinking, it
seems to point to some premise shattering.



Rob and Steiner are the guys for making flat sheets into
boats.



|     Your arguments for the Harry Proa are falling on
deaf ears ;-)



You misunderstand. I was not arguing for you to build a
harry proa. I was asking you to explain why, using your
criteria, a harryproa does not fit your needs better. You
were kind enough to answer. Thank you.



Perhaps a subtle difference to you. A huge one to me.



And, I ask these questions because I do not know why a
harryproa does not fit my needs better. Perhaps you have
thought of something I missed. But it appears not.



I do not much care what I build. My restrictions are
strictly practical not unquestionable.



|    As far as carrying sail outboard, a reach beam
reach is about the only point of sail where the main portion
of the sail would be carried outboard.

|

| In ideal sailing conditions there is no chance of a wave
catching a wave, but conditions are often less than
ideal.   I would want to be able to shunt if I had a rig
like Robs Aero Rig, or the junk. rig I'm planning to
use, on a single mast in one hull so that I could sail with
the long end of the boom over the boat.  



If anyone is reading this who has any direct knowledge, or
feels if they can speak to the topic, can you address it?



Let me think this through. If a sail is full, it must be to
the lee of the mast, right? (Ignoring DDW sail as a
parachute situations.)



If, on a harryproa the mast is in the lee hull and the sail
is to the lee of the mast, the sail is over the water for
most points of sail, right?



Afaik, on a harryproa, if the sail is over the boat, your
lee hull is to windward, which is obvious derp. I mean with
the schooner rig or una rig. The balestrom/Aero rig are a
different thing. Even then, the aft half of the rig is over
water all the time, I think.



Perhaps the split rig junk (on a harryproa) is more like the
Aerorig/Balestrom, in that the fore sail is over the boat
and the aft is over the water?



| I will have a low aspect ratio rig & relatively short
mast, which means that the sail will be fairly square, and
the boom long.... about as long as I can get away with and
still be able to sheet with a decent angle.    My idea is
to sheet through a traveling block from the two outboard aft
corners of the boat.   As there is no need for down
pressure as on a Bermuda rig, this can all be fairly light,
and travel from one corner to the other via a line rather
than a track.



Ah. Interesting. Why not a taller mast? And a better
aspect ratio?



|     I've been toying with the idea of completely
reversing the sail.  As the mast on a junk rig is not the
leading edge of the sail, and in

|fact on the Aerojunk is not involved at all, I don't
see a lot of reason why the head sail needs to the the
smaller portion.    Sheeting loads would be double if
sheeted to the short ends of the battens, but that's not
a bad thing and still far less than on a bermuda rig where
there is zero balance area, and tension is needed to shape
the sail.



Tom Speers on boatdesign.net has some posts on split rig wig
sails. I don't know how relevant they are to a split
rig junk, but take a look. He suggests the balance point
should be around 20-40 of the total cord length. I imagine
you would want the mast forward of the balance point, but I
know nothing.



|  It might look a bit strange to have a backward sail,



You are building a split rig junk sail, and you are worried
about how it looks? Looks are not the parameter to
optimize, IMHO.



| but realistically if one looks at a masthead Bermuda
rigged boat, in many cases the head sail is larger than the
main.   The wind doesn't care.  The important thing
is that the camber is distributed ideally for max
efficiency.    One big advantage in doing this is that a
tension based automatic sheet release could be used so that
if one was napping below, and was hit by a sudden violent
gust, the sheet would go free in stead of the boat being
knocked down.



Yep. I think I might prefer the inherent dumping of a gust
by the mast proper, via flexing. Or a greater righting
moment. But an automatic sheet release makes sense, but I
don't know how they work. Or how expensive or durable
they are. Do you?











#yiv0864448665 #yiv0864448665 --
#yiv0864448665ygrp-mkp {
border:1px solid #d8d8d8;font-family:Arial;margin:10px
0;padding:0 10px;}

#yiv0864448665 #yiv0864448665ygrp-mkp hr {
border:1px solid #d8d8d8;}

#yiv0864448665 #yiv0864448665ygrp-mkp #yiv0864448665hd {
color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px
0;}

#yiv0864448665 #yiv0864448665ygrp-mkp #yiv0864448665ads {
margin-bottom:10px;}

#yiv0864448665 #yiv0864448665ygrp-mkp .yiv0864448665ad {
padding:0 0;}

#yiv0864448665 #yiv0864448665ygrp-mkp .yiv0864448665ad p {
margin:0;}

#yiv0864448665 #yiv0864448665ygrp-mkp .yiv0864448665ad a {
color:#0000ff;text-decoration:none;}
#yiv0864448665 #yiv0864448665ygrp-sponsor
#yiv0864448665ygrp-lc {
font-family:Arial;}

#yiv0864448665 #yiv0864448665ygrp-sponsor
#yiv0864448665ygrp-lc #yiv0864448665hd {
margin:10px
0px;font-weight:700;font-size:78%;line-height:122%;}

#yiv0864448665 #yiv0864448665ygrp-sponsor
#yiv0864448665ygrp-lc .yiv0864448665ad {
margin-bottom:10px;padding:0 0;}

#yiv0864448665 #yiv0864448665actions {
font-family:Verdana;font-size:11px;padding:10px 0;}

#yiv0864448665 #yiv0864448665activity {
background-color:#e0ecee;float:left;font-family:Verdana;font-size:10px;padding:10px;}

#yiv0864448665 #yiv0864448665activity span {
font-weight:700;}

#yiv0864448665 #yiv0864448665activity span:first-child {
text-transform:uppercase;}

#yiv0864448665 #yiv0864448665activity span a {
color:#5085b6;text-decoration:none;}

#yiv0864448665 #yiv0864448665activity span span {
color:#ff7900;}

#yiv0864448665 #yiv0864448665activity span
.yiv0864448665underline {
text-decoration:underline;}

#yiv0864448665 .yiv0864448665attach {
clear:both;display:table;font-family:Arial;font-size:12px;padding:10px
0;width:400px;}

#yiv0864448665 .yiv0864448665attach div a {
text-decoration:none;}

#yiv0864448665 .yiv0864448665attach img {
border:none;padding-right:5px;}

#yiv0864448665 .yiv0864448665attach label {
display:block;margin-bottom:5px;}

#yiv0864448665 .yiv0864448665attach label a {
text-decoration:none;}

#yiv0864448665 blockquote {
margin:0 0 0 4px;}

#yiv0864448665 .yiv0864448665bold {
font-family:Arial;font-size:13px;font-weight:700;}

#yiv0864448665 .yiv0864448665bold a {
text-decoration:none;}

#yiv0864448665 dd.yiv0864448665last p a {
font-family:Verdana;font-weight:700;}

#yiv0864448665 dd.yiv0864448665last p span {
margin-right:10px;font-family:Verdana;font-weight:700;}

#yiv0864448665 dd.yiv0864448665last p
span.yiv0864448665yshortcuts {
margin-right:0;}

#yiv0864448665 div.yiv0864448665attach-table div div a {
text-decoration:none;}

#yiv0864448665 div.yiv0864448665attach-table {
width:400px;}

#yiv0864448665 div.yiv0864448665file-title a, #yiv0864448665
div.yiv0864448665file-title a:active, #yiv0864448665
div.yiv0864448665file-title a:hover, #yiv0864448665
div.yiv0864448665file-title a:visited {
text-decoration:none;}

#yiv0864448665 div.yiv0864448665photo-title a,
#yiv0864448665 div.yiv0864448665photo-title a:active,
#yiv0864448665 div.yiv0864448665photo-title a:hover,
#yiv0864448665 div.yiv0864448665photo-title a:visited {
text-decoration:none;}

#yiv0864448665 div#yiv0864448665ygrp-mlmsg
#yiv0864448665ygrp-msg p a span.yiv0864448665yshortcuts {
font-family:Verdana;font-size:10px;font-weight:normal;}

#yiv0864448665 .yiv0864448665green {
color:#628c2a;}

#yiv0864448665 .yiv0864448665MsoNormal {
margin:0 0 0 0;}

#yiv0864448665 o {
font-size:0;}

#yiv0864448665 #yiv0864448665photos div {
float:left;width:72px;}

#yiv0864448665 #yiv0864448665photos div div {
border:1px solid
#666666;min-height:62px;overflow:hidden;width:62px;}

#yiv0864448665 #yiv0864448665photos div label {
color:#666666;font-size:10px;overflow:hidden;text-align:center;white-space:nowrap;width:64px;}

#yiv0864448665 #yiv0864448665reco-category {
font-size:77%;}

#yiv0864448665 #yiv0864448665reco-desc {
font-size:77%;}

#yiv0864448665 .yiv0864448665replbq {
margin:4px;}

#yiv0864448665 #yiv0864448665ygrp-actbar div a:first-child {
margin-right:2px;padding-right:5px;}

#yiv0864448665 #yiv0864448665ygrp-mlmsg {
font-size:13px;font-family:Arial, helvetica, clean,
sans-serif;}

#yiv0864448665 #yiv0864448665ygrp-mlmsg table {
font-size:inherit;font:100%;}

#yiv0864448665 #yiv0864448665ygrp-mlmsg select,
#yiv0864448665 input, #yiv0864448665 textarea {
font:99% Arial, Helvetica, clean, sans-serif;}

#yiv0864448665 #yiv0864448665ygrp-mlmsg pre, #yiv0864448665
code {
font:115% monospace;}

#yiv0864448665 #yiv0864448665ygrp-mlmsg * {
line-height:1.22em;}

#yiv0864448665 #yiv0864448665ygrp-mlmsg #yiv0864448665logo {
padding-bottom:10px;}


#yiv0864448665 #yiv0864448665ygrp-msg p a {
font-family:Verdana;}

#yiv0864448665 #yiv0864448665ygrp-msg
p#yiv0864448665attach-count span {
color:#1E66AE;font-weight:700;}

#yiv0864448665 #yiv0864448665ygrp-reco
#yiv0864448665reco-head {
color:#ff7900;font-weight:700;}

#yiv0864448665 #yiv0864448665ygrp-reco {
margin-bottom:20px;padding:0px;}

#yiv0864448665 #yiv0864448665ygrp-sponsor #yiv0864448665ov
li a {
font-size:130%;text-decoration:none;}

#yiv0864448665 #yiv0864448665ygrp-sponsor #yiv0864448665ov
li {
font-size:77%;list-style-type:square;padding:6px 0;}

#yiv0864448665 #yiv0864448665ygrp-sponsor #yiv0864448665ov
ul {
margin:0;padding:0 0 0 8px;}

#yiv0864448665 #yiv0864448665ygrp-text {
font-family:Georgia;}

#yiv0864448665 #yiv0864448665ygrp-text p {
margin:0 0 1em 0;}

#yiv0864448665 #yiv0864448665ygrp-text tt {
font-size:120%;}

#yiv0864448665 #yiv0864448665ygrp-vital ul li:last-child {
border-right:none !important;
}
#yiv0864448665