<<I am hoping someone here might take pitty on my fence riding
and give me something definitive that tips the scale either way for
good>>
Given your criteria, combined with your design, I'm not sure you'll
find any definitive reasons to go with one option versus the other.
There are a number of good reasons to go with rigs in the leeward hull,
but if your goal of an 8.5' trailer width is a fixed one, the reasons
to go leeward might not be showstoppers.
I also think that the design is a masterpiece of ingenuity, and have
a hard time arguing against keeping
all the steering components in the same hull.
That said, I'd still like to comment on the rudders, and then get
your thoughts on wracking forces and sail handling. I know I brought
this up before, but I didn't catch a response. Not that you need to
provide a response -- I'm just interested in what you have to say.
Rudders.
I love the idea of losing leeway prevention as you progressively fly
a hull -- I'm a fan of using the windward daggerboard in catamarans for
the same reason. I'm not as much a fan of losing steering ability as
the hull rises. As long as you sail conservatively, and have someone
who can dump your sheets, the pros might equal the cons. Or outweigh
them if you stick with keeping everything in the windward hull (which
would obviously radically simplify your steering setup for a
trailerable proa).
Keeping the whole steering system in the same hull is wonderful. I'm
having a hard time coming up with a steering system that allows me to
collapse the boat on the water while still maintaining steerage.
Stopping the spray could also be useful. One downside, though, could
be more difficult access to the rudders and steering system if a
problem were to develop.
Twisting/wracking forces.
I agree that the windward hull design would be very strong in terms
of bending moment, particularly with the masts transferring loads
directly into the beams. However, there are huge fore/aft loads on the
sails and the leeward bows that will need to be translated through the
beams into the opposite hulls. The leeward rig, which has all its
major
fore/aft sailing and rig forces in line, should make for a design that
requires less structure and perhaps less engineering.
Sail handling.
I'm still not quite sure how you'll safely handle the sails in a big
wind and sea when it's time to reef, or take care of a blown sheet or
jammed
halyard. That windward hull has beautiful lines, but not much in the
way of protected area to stand on while the boat is pitching. With the
rig in the leeward hull, you have the leeward hull to leeward, and the
trampolines/deck to windward. Wings would largely eliminate this
issue, but I'll personally be going with sails.
---
For me, the choice of a single tall leeward rig comes down to how my
wife and I
sail. 90% of what we do will be daysailing, typically in the light
summer winds, with several miles of short-tacking against a sea breeze
before we hit open water.
Thus, I'd go with the tallest rig I can fit in the ICW, in order to
take advantage of wind aloft, even if the water is a mirror. I'm not
so concerned with hitting 20 knots in big wind as I am being able to do
5 knots in almost no wind. That's why the height matters, even if it
has a
higher COE than a schooner rig.
If the boat does suffer a knockdown, it would likely be from a sudden
gust when most or all of the sail is up, while traveling at low or
reasonable speeds. Such as if a friend has the helm while we're
ghosting along, and we pass between islands and catch a big burst of
air that he or she didn't plan on. Your point of the mast not
necessarily helping at 20 knots is a good one, but at 5 knots, it's
much more likely to help. As you said, any chance at all is at least
something.
Finally, a few hours of shunting a schooner rig up the channel could
get old pretty quickly. Having one rig means half the work. Unless
the boat tacks in very light wind, which is something I wouldn't be
willing to bet on before building. If someone else does it first, I'll
be most grateful.
None of these criteria matter the same way if you're cruising, so the
ideal live/cruise/trailerable boat might not necessarily be the ideal
daysail/cruise/trailerable boat.
- Mike
On 7/26/2010 7:17 PM, Dennis Cox wrote:
Hey Mike, et al.
I have the greatest respect for Robert's HarryProa. I am
certainly not implying any superiority of the Atlantic design. In
fact, most of the reasons are not performance related. Also, its
interrelated with the steering leeway resistance issue. I am hoping
someone here might take pitty on my fence riding and give me something
definitive that tips the scale either way for good... but hear me out,
because these are the things that am pushing me toward the Atlantic.
Non Performance Reasons
These are reasons that have to do with the trailerable aspect or
for me personally. They have nothing to do with one design
being superior to the other.
- When on the trailer, the first thing, I'd step the masts on the
windward hull. As you suggested, I was thinking of a relatively small
"crane" based on the cheap car engine hoists. Once up, these can be
used in conjunction with the boats winches to lift the windward hull up
and over and down.
- I've been watching a lot of Rick Willoughby's comments. If I
keep the leeward hull simple (without) mast and leeway
prevention structure, I can make it quite cheap. The one I'm making
now should come in complete for less than $2000 and somewhere around
800 pounds if I don't get sloppy. The point being, I could very easily
make a second one using the squared off sheet hulls that Rick's
research suggests may have a superior performance edge. It may go for
less than a $1000. IOWs, I can play Mr. Potato Man.
- The lee hull is lighter - for getting off the trailer and
moving it around.
Structural
IMO
and for a schooner rig, one design has no significant advantage over
the other.
-
In a
HarryProa or an Atlantic Sloop the mast loads have to be
transferred from the mast base to the cross beams by torquing
the hull. In an Atlantic this would make things far more difficult.
It fully justifies Robert's statment about being able to make the
unstressed HarryProa windward hull far lighter than the Atlantic. It
would be clearly lighter. However, in a HarryProa or Atlantic Schooner
there is no torque in the hulls. If the masts are mated to the cross
beams all moments from the masts can be directly transferred into cross
beams. My contention is that both hulls could be made lighter in a
schooner rig and frankly there would be no advantage of one over the
other (that I can imagine yet).
-
The
largest moment in the beams of a HarryProa (and thus largest cross
section of the beam) is at the base of the leeward hull. In an
Atlantic, the largest moment in the beams is at the base of the
windward hull. It is helped out by a significant structure... the
bridge deck. The beam (in an Atlantic) as it goes into the lee hulls
has nearly no moment... just shear. It can be much smaller and thus
offer less resistance to waves and submerging.
-
I
hear what has been said about leaning the mast out and keep the boat
from going past 70 degrees. I can easily see that in Robert's smaller
designs. I'm having a little trouble with it for a 10,000 lb boat.
Mast tend to come away in roll overs. It is said any mast that
doesn't... is way over built and way too heavy. In my minds eye, a
boat traveling 20+ knots and has flipped at a rate that the helm
couldn't save must have significant angular velocity. When the mast
and sail slaps the water, IT will come to a dead stop while the linear
and angular inertia of the rest of the boat (27 feet up in the air) is
certainly going to continue... result (I believe) is a snapped mast and
flipping of the hulls. Arguably, the HarryProa having a little chance
is better than no chance at all with an Atlantic.
-
Fluid
Dyanmics
Out
of my comfort zone, but...
-
I
guess the heeling moment does get larger with an Atlantic when flying,
but only as a result of exposing the bottom of the hull in addition to
the sail forces, while a HarryProa windward hull shields the sail
somewhat. But in this size of a boat, I don't really thing exposing my
bottom is really in the game plan... unless I've unloaded all the soft
personnel and am racing. And even then, I wouldn't be flying... just
kissing.
-
The
main one that drove me toward a Harry Proa is the significant decrease
in COE by lowering the base of the masts to the lee hull. At first
this was clear cut. HOWEVER, strangely enough, if I go to wings or
oversize wing masts (still debating that one also) the heeling moment
is far less than a sail. My calculations show I can not get the
lard-ass, windward hull up so I can get to the 25+ knots Michlet says
the lee hull could do if unburdened. So in this strange case, its
better to put the masts up on the windward hulls to actually encourage
heeling. Yes, I know, I could put larger wings/sails on the leeward
hull, but that adds to the trailering issues.
-
If I
put the rudders under the mast bases (on the windward hull) all that
splashing and spray as seen on the all the videos, is under the
bridgedeck and we have a cleaner view from the bridgedeck overlooking
the lee hull.
-
With the
rudders on the windward side, flying the hull reduces leeway prevention
and thus lets it slide.
I
think that's all, but I'll bring up more, when they hit me. HELP!
Stop the voices.
Dennis