|Subject: [harryproa] Re: Pro vs bi-rig cat?|
|From: Mike Crawford |
|Date: 4/3/2008, 8:06 PM|
You were clear about the biplane rig; I just didn't catch that part until after I hit "send". Nor did I catch the typos.
I don't think that anyone would argue that you can't create a fast lightweight cat with unstayed masts. The Radical Bay 8000 is a great example of a biplane cat that performs well.
I've toyed with the idea myself, perhaps using Skimmer Catamaran hulls to get a head start in construction ( http://www.skimmerc
Using the Skimmer hulls, you could create a sweet, fast, easily-handled freestanding biplane-rigged open-decked cat with several double beds (but not queens) for under $100,000. You could also put a cabin on the bridge deck, but that would involve a lot more construction time.
However, I personally care about a few things that a bridgedeck cat isn't going to provide:
- Shuntability in low wind. I'd probably sail the proa as a tacking proa, without shunting, at least half the time. We often have days on end with six knot winds in the summer, and there's a six-mile upwind series of short tacks to get out to open water. On days like that, it would be nice to just tack back and forth by turning the wheel. But I still want to be able to shunt for those really light wind days when a 40' cat isn't going to want to come about through the wind. Our current catamaran is 27 feet, and there are days with so little wind that I have to tack by gybing instead of coming about. Shunting would make the light winds a non issue, and would save me from losing the upwind distance that a gybe would cost.
- Shuntability in big winds. I'd also want to be able to shunt downwind on those really big wind days so I can avoid gybing.
- Accommodations free of structure. There are no daggerboard trunks or masts in the accommodations area which is quite nice, and adds a lot of freedom.
- Performance. Since I'm not looking for a liveaboard boat, performance is of top concern. In this case, the longer waterline of the proa, combined with the greater righting moment (achieved by keeping the weight in the ww hull) both help the performance.
- Stability. The longer waterline and rockerless hull will help with pitching. While a big cat with a rockerless hull will have all sorts of problems coming about, especially in light wind, the harryproas can still turn nicely because of the shorter ww hull and the two high-aspect opposing rudders several meters apart.
- Demountability. I'd like to store the boat on our property instead of paying $3,000 per year to a boatyard. The Harryproas without the extended saloons can all be demounted and transported over roads.
- Safety. As mentioned earlier.
Again, you can create a great boat with the catamaran platform. If the items above are not at the top of your priority list, there may be no reason to go with a proa instead of a cat. The boats simply do different things.
If you do go forward with a biplane-rigged cat, and post designs in a catamaran or multihull forum, I'd love to see what you come up with.
Thanks for the reply. I guess I wasn't clear enough in what I was
asking. I am not talking about a "regular" cat. I mean a bi-rig cat,
where there is a freestanding mast in each hull, just like the harrys
have in the leeward hull. Then there is no stress anywhere on the
bridgedeck, no rigging, no strengthening of the hulls. Just like the
harryproas, the cat can be built VERY light.
The bi-rig cats I have seen on the web all have dual mains, but I
would think you could have the same balleston rig as the harry's,
although it would have to have a higher aspect ratio to keep the booms
from hitting each other when perpendicular to the hulls.
I guess my question boils down to, if a cat can be built as light as a
harry (due to the rig), and the displacement is the same from 2 45'
hulls, instead of 1 40' hull and 1 60' hull, is the proa still going
to be faster? They would have the same payload capacity, so that evens
out the "liveaboard" issue. It seems to me that Rob has mostly been
successful because of the rig. Even the reefing seems to be a function
of the rotating, unstayed mast.
Of course, I am assuming that removed of the rigging, and with proper
motivation, you can build a cat and a proa with the same displacement
I can see some advantages in being able to go directly backwards, but
there are also advantages in being able to have engines and rudders
set for a single, forward direction. That seems to be pretty much even
on both sides.
--- In harryproa@yahoogrou
ps.com.au, Mike Crawford <jmichael@.. .> wrote:
> You're right about what you can do with a cat, and that if you
> reinforce a bridgedeck cabin enough, you can also get the benefit of a
> freestanding rig.
> In many ways, there are no inherent advantages of a proa. It all
> really depends upon what you want to do with your time on the water.
> If you want to carry as much weight as possible for the least
> investment, a cat might be a good solution. If that is the main
> criterion, I'd suggest looking at a Wharram Tiki 38 or 46 (
com). It will be difficult to find a tougher,
> boat that can be build for less money. They are also beautiful,
> provided one likes their lines. Of course, I'm a big Wharram fan, so I
> am biased.
> Where a proa start to shine is sailing quickly and safely. The big
> two reasons to get a proa for me are:
> a) Performance per dollar, as well as performance per unit of weight.
> Take the Visionarry Sport (
a.com/visionarry). Here's a boat with a .htm
> two queen bunks, a stand-up head and shower, a third single
> and storage in a long row of cabinets and in the lee hull. Okay, none
> of this is revolutionary. But when empty it has a Bruce number higher
> than an empty Formula 40 cat, a boat with no accommodations. That's
> amazing. That it does so with only $50,000 of materials (give or take,
> not including cruising fit-out such as ovens, electronics, etc.) is
> more impressive.
> To get that level of accommodation in a catamaran or trimaran
> with the same level of performance would be quite expensive, and would
> require a much larger boat in terms of total material (and therefore
> higher cost).
> b) Ability to handle various winds with less stress and effort.
> The first trick in handling difficult weather is to reef early
> and often, and that applies to proas as well as to cats and tris. A
> proa has a few unique advantages, though.
> Shunting, rather than coming about or gybing, can be done
> gracefully in any wind. In light winds, you can tack a proa out of a
> crowded harbor in winds that would never allow a catamaran to come
> about. In heavy winds, shunting can be less stressful than coming
> about, and is definitely far safer than gybing.
> You can also stop at any time, and reverse direction if needed,
> in order to pick up a man overboard. Or, if the weather is really bad,
> you can turn around with a controlled shunt instead of trying to plan a
> 270 degree turn in between steep wave faces.
> The Harryproas have other advantages that come from Rob's work with
> unstayed masts. Having the accommodations completely free of mast
> supports and daggerboard trunks is quite nice.
> Not having to carry tens of thousands of dollars of rigging and parts
> is equally beneficial, especially since 50 extra parts (wires, swages,
> chainplates, turnbuckles etc.) means 50 extra points of risk for a
> dismasting failure. It's really difficult to determine if there's
> crevice corrosion or stress fractures in stainless wire and fittings,
> and if you intend to sail a boat for long periods of time, there's a
> to be said about doing away with the rigging.
> The flexible masts are also great at reducing stress on the boat, as
> well as avoiding capsizing in big gusts.
> With kick-up rudders and no daggerboard trunks to fail, the
> are also great if you happen to hit a sand bar or whale. Underwater
> collisions that would sink other boats would simply require
> the rudder and re-fastening its case.
> There's also the chance, especially with a schooner rig, that the
> hollow carbon masts would have enough flotation to keep the boat from
> capsizing past 90 degrees in a knockdown, and then allow the boat to be
> righted. I'm not aware of any other multihull with queen-sized beds
> that can even dream of doing this.
> A schooner rig would also be pretty easy to sail even if both rudders
> somehow failed. The twin sails, combined with the ability to shunt,
> would allow maneuvering in most winds without any steering device at
> all. Sailing a catamaran without a steering device can be near
> impossible in low winds (can't come about without a rudder), and pretty
> scary in high winds.
> This is not to say that the proa is better for living aboard. It's
> just that the proa has unique advantages in the areas just mentioned.
> In the end, many sailors will look at a proa and decide that it's
> awfully small for its length. What? You only get that for 15 meters?
> Why, a 15 meter catamaran would have huge amounts of space, and could
> carry tons of cargo! True.
> But that's also the point: the proa can provide a long waterline
> length for a given investment of money and materials, and therefore eke
> out more performance per dollar and hour spent building (assuming you
> don't overload it).
> - Mike
> gardner.pomper wrote:
> > After following the discussions on the advantage of proas, and playing
> > around with a layout for a liveaboard version, along with very limited
> > info about the upcoming charter version of the harryproa, I realized
> > that I seem to be missing some basic points.
> > The proa has an advantage because all the stresses are concentrated in
> > a small portion of one hull. That seems to be mostly due to the
> > ballestron (sp?) rig.
> > Weight and cost can be kept down by keeping accomadations out of the
> > hulls and putting them on a bigger bridgedeck. That would apply to
> > cats too.
> > So, I am wondering, if you design a bi-rig cat with a freestanding
> > ballestron rig in each hull and just put everything up on the
> > bridgedeck, wouldnt that work pretty much as well as the proa concept?
> > It would seem that the weight would be about the same.
> > Things would be different; you would have 2 identical hulls to build,
> > somewhere near the average of the ww and lw hull sizes. That should be
> > easier. You only have to sail in one direction, which would make the
> > rudder and wheel designs easier. You could mount inboard diesel
> > engines, which would be handy for liveaboard crusing, so you can
> > travel when there is no wind. You do need 2 masts, and they would have
> > to have shorter booms, so they don't run into each other.
> > Can someone give me a clearer picture of the inherent advantages of a
> > proa? (not compared to cruising fat cats, but for a liveaboard couple,
> > wanting a small level of comfort)
> > Thanks