In the real world / non racing, I'm
not sure that flat bottom versus round bottom, versus deep V is
very important. The V bottom has a significant advantage in
build time, but how much of the time spent building a multihull is
spent on the hull itself... probably far less than 10%?
Ironically the biggest most dramatic parts of any construction
project are the ones that consume by far the least time. The V
bottom clearly works well with infused full hull panels, leaving
only the single seam down the keel, and the seams at the deck /
cabin / bridge deck. The V bottom offers an inherently stiffer
contact point when beaching. Richard Woods cedar strip chined
hulls or their equivalent in foam sandwich are considerably more
labor intensive.... and to what end?? Bernd Kohler's flat bottom
hulls offer several advantages including the possibility of using
the boat bottom as the sole.... though he does use a bilge and
sole a few inches above the bottom. There would be some
attraction of simply gluing down several layers of ordinary
construction XPS foam, and glassing it over and calling it good
enough, both from the standpoint of simplicity, and of flotation,
and puncture resistance, not to mention stiffening for beaching.
The flat bottom means 2 more panels to infuse, and two more full
length seams. The flat bottom means more displacement per inch of
draft initially........ ultimately less draft for the boat...
which means more safety margin in coral strewn seas, but people
ALWAYS push the limits.... I'm liable to beach my boat, and sail
into thin water (carefully) to get away from the crowd in a
backwater where I have the area to myself, while a guy with a
monohull with a deep fin keel is going to be extremely chary of
shallow water.
Looking at the HP drawings, I long
ago came to the conclusion that the layout simply did not serve
my purposes well. I would want stand up space in the opposite
hull. My intent with a catamaran is to have the galley starboard
center, and my workshop / workbench port center. Master berth
aft of the shop, and head aft of the galley, and only one forward
berth. My "home" will be on the bridge deck. I'll sleep in a
recliner there... as I have for many years. The HP designs
concentrate everything closely together in the windward hull... of
necessity, and make little use of the leeward hull...... I would
want a cabin in the leeward hull for my workspace. Unlike most
folks, I have to work with my hands, I have to build things,
invent things, and fix things. Some folks need toys.... I need
tools, it's hardwired into my very soul. My conclusion has been
that it would take a 50' HP to give me what I want. Distribution
of spaces is as important as total volume in many ways. The
large amount of open deck is attractive.... some of the time. On
a cat I would have a bimini over the cockpit, as my skin does not
tolerate sun very well. I wear long pants and long sleeve shirts
and a hat year round.....shade matters at high sun angles.
Morning, evening, and winter, it's not a problem.
I've obviously frustrated some
people by not stating the why's for my size criteria.... let them
be frustrated. The 30' price point in marinas is hardly relevant
to a multihull because of it's huge beam, and the fact that they
are comfortable anchored out, which is still legal in many places
that are not Spanish administered, or the sensitive marine areas
off Northern Australia, and in Hawaii. More and more countries
are trying to force boats into marinas or onto moorings for no
other reason than to generate revenue for local businesses. In
reality the upward spiral of larger and heavier is a not
insignificant consideration. Cost is an ongoing issue, not just
an initial build consideration. Bigger boats mean bigger heavier
taller more expensive everything. Boats have been justifiably
been described as a hole in the water into which one throws
money. I remember one wag describing the sport of sailing
(racing) as equivalent to standing under a cold salt water shower
shredding hundred dollar bills and throwing the shreds into the
wind.... or something of the sort. For some people bigger is
better... for me the reverse is true. The foundations of my 30'
LOA criteria are mostly eroded since I have gravitated into the
multihull camp, with only one remaining compelling (to me), but
even if that didn't exist, avoidance of that insidious upward
spiral is reason in itself. I need a boat I can afford to own
and maintain, preferably mostly with my own hands. Some version
of the junk rig will be on it, probably based on Paul McKay's
Aerojunk, in low aspect ratio largely rectangular. I've toyed
with ideas for a "compound yard" that could be peaked up well
above the mast both fore and aft of it to get more sail up higher
without having a taller mast as well as using a carbon fiber wind
surfer mast as a sort of gunter.
I would love to sail (on) an HP,
but there are none I know of in my area........ I would travel to
the Puget Sound or SF Bay area next summer to sail on one if that
opportunity presented itself. The Atlantic Coast, Europe, Oz, or
Nz are pretty much out at this point. The issue of tacking
versus shunting looms large to me, as I've never sailed a proa,
and as I've said before, it seems that tacking makes sense in a
narrow waterway if it can be done efficiently... The junk rig
makes tacking effortless, and the HP rudder system it seems to me
could bring a light multihull through a tack extremely quickly
before it loses way.
My conclusions remain largely
unchanged, and I'd like to think it has nothing to do with
convention, or closed mindedness, though others might claim
otherwise. I am if anything open minded. Open to new ideas, and
strongly attracted to innovation, and outside the box
thinking..... which is why I'm here at all. Infused foam
sandwich is without a doubt an important part of the final
solution.. a way to stay within my self imposed criteria in every
respect. StruCell puts it within reason financially. I may be
forced to fudge my LOA criteria and give up on my last reason for
adhering to it, but if so it will not be due to outside pressure,
or ridicule, but because I simply cannot make it work...... That
however does not appear to be the case at this point. The
frustrating thing is that I will need to modify or design hulls
from the ground up doing the displacement calculations, etc as I
go. I've been building models from construction board at my
drafting table, and I end up building deep V hulls and trimming
the V off to create a Kohler type hull. (below). I inevitably
begin looking at rounding the bottom a bit using foam and glass,
which could be infused or vacuum bagged.
H.W.
On 3/14/19 4:29 AM, Rob Denney
harryproa@gmail.com [harryproa] wrote:
Great thread, keep it up. A few comments:
Flat bottoms are much easier to build and repair. After fairing, fitting and installing floor bulkheads is the most soul destroying boat building job. They also allow lower headroom, if the hulls are designed right. The weight and windage advantages of these outweighs any small difference in wetted surface/friction drag.
2 (or three) piece sleeved masts for trailering are no problem, and not much harder to build than one piece (the joining sleeve is a cut off piece of one section slit and glued into the adjacent one. The important part of the build is that everything is straight, which is as easy/difficult for short bits as long.My telescoping round mast was probably more work than it was worth (I don't go under bridges or have to tow my boat, which changes the pros and cons), but telescoping wings have some potential. A couple of weeks ago a client was here and we played with attaching sails to masts with hoops, which make telescoping rigs more viable. The results were promising, he will use them on his 18m/60' mono. More exciting is the work Steinar (he is visiting, the ideas are flowing thick and fast) and I have been doing on a telescoping wing mast (60% of the chord) for his boat. Ordered the sail yesterday for a short length of 1/4 scale model. If it works, it has low sheet loads, little or no twist (ie no vertical sheet loads) and no boom. Results and pics next week, maybe.
Reefed sails rarely set as well as unreefed (the sail luff is cut for different mast bend characteristics ) and the drag of the top mast is slow. As Mike says, a bigger issue on a stayed mast than an unstayed one.
A 30' cat will weigh near enough the same as a 40' proa for the same accommodation. The 18m/60' of cat hulls are shorter than the 20m/70' of proa hulls, but the proa hulls are lower and narrower. Therefore the sail area can be the same, although the proa will have much more righting moment. The proa accommodation will be more usable. The proa will be quicker to build (easier hull shapes, only 2 appendages, no unnecessary curves, one simple mould usable for both hulls/decks), faster, safer and more comfortable as it is longer and both sails can be seen without having to turn around. It will also cost more in a marina, but it will have a tender big enough that you can anchor off, motor in and avoid paying altogether.
New Ex 40 drawings are finished, will be on the web page when Steinar stops doodling telescoping wings. ;-). First one is being built in Barcelona.
We have also designed the latest "best ever" rudder mount after 2 weeks of discussion, sketches and finger drawings on the beach. Simpler, lighter and easily mounted on the inside or the outside of the hull. First part of the laminate for an El test version is curing as I type. It works for bidirectional or one way rudder sections (NACA0012).
We spent today working on rudder build methods. I drew every one I had tried or heard of in the sand (about 30m of sketches) and we picked them apart. Came up with something simple and quick.
Had a sail on Kitetik (15m Solitarry, weighs about 500 kgs/1,100 lbs, plus 3 crew) yesterday. 25 sqm/260 sq' (20 sq m projected, which is less than a Tornado cat) leading edge inflatable kite, dirty bottom, 10-15 knots of breeze, 30C air temp, a beautiful day. Top speed 8 knots, pretty poor up wind. For the first time, all the systems worked, so we can now move on to boat improvements and bigger kites, starting with a converted 28 sq m (28 sq m projected) paraglider. .
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Posted by: StoneTool <owly@ttc-cmc.net>
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