That's it! I think the Planecat is the Richard Roque design -- it was a 16-footer, wasn't it? I I couldn't think of the name earlier. And Randy Smyth won the Worrell 1000 on the bigger Roque design back in the 1980's, just edging out Roy Seaman on the Nacra 6.0, which Seaman designed for the Worrell. If this is wrong, let me know. I got this info from Rick. Randy expressed his opinion at the time about the Roque design vis-a-vis the Nacra 6.0, but I am not going to repeat it, because I don't want to misstate somebody else's opinions.
Beauti Luiz
beautifull tri -
The question most have would be how efficent or effective are the forward angled boards -foils - they look great
-Did they provide not only tracking -verticle lift ,-but horizontal lift on the hull ,-what is the ideal heel angle of these while sailing .
Are the anams 100 buoyant ,-that is like the 60s can you fly on one hull , or does the design reply on the lift of the angled boards and center hull remaining in the water .
Thanks
Carl
I haven't read this thoroughly (I'm in the middle of my work day), but this article seems to explain some of the physics:
http:/
FWIW, if I take the hull speed formula from the Annapolis Book of Seamanship and apply it to my Prindle, which I think is 16 feet at the water line, I get:
Maximum Hull Speed = 1.34 * LWL1/2
= 5.67 knots
I can go a lot faster than that with both hulls in the water in pure displacement mode. You don't have to lift a hull to exceed this kind of speed. The Annapolis Book of Seamanship says that the normal hull speed limitations do not apply to catamarans. I think that catamarans normally are displacement boats, even when flying a hull, but the oversimplification normally used for dinghy's just ain't applicable when analyzing the way our favorite displacement boats work.
I found some other interesting links that I need to read in more depth. Here's one on optimizing hull shape for drag and other characteristics:
http:/
Ah well, back to work ;->
Jonathan
Unfortunately, the 1.34 "constant" is true for monohulls with a fineness ratio of about 3:1 or 4:1 (J/24 is ~2.8:1, based on ~22' waterline length:8'6" beam) but not for typically much finer multihulls. The beam of each hull on your Prindle is less than 2', which combined with a waterline length of 16', leads to a "constant" more like 3 or 4. Thus theoretical top speed under sail is more like the high teens. I know the speed record, under controlled conditions, for the Hobie 16 is 26.7 mph (or is it knots? I'm not sure) but anyway much much faster than the 1.34 constant would suggest. Naturally, more fineness leads to a higher constant.
sail fast
The simple truth is that Froude's law doesn't predict the maximum boat speed for lightweight boats with slender hulls. It is therefor nonsense to continue using that law in a fashion that is was never intended to be used.
Froude's law only correlates a rise in drag (wave making) to a specific speed at which the bow wave and stern wave length equal hull length, nothing more. In Heavy boats this wave system is so big that it prevents the boat from going faster. With ligtweight boats with slender hulls is only results in a bumb in the drag plot or an increase in overall drag.
Wouter
I`m not sure you can apply Froude`s law to a small light displacement catamaran - we may sail displacement boats that might not plane, but it`s not sensible to apply a law that was written based on observations of heavy dispacement boats.
Further to this, if you take the length to width ratio of the average beach cat with a rounded hull-shape ie symetric hulls, you will find a ratio of about 12,5 : 1. If you take this and multiply it by say 2metres you get 25metres - A keelboat of 25metre
length with a 2metre beam would have to lug a large lump of lead around to keep the mast pointing skyward, or would need a few hundred crew out on trapeze ! That`s why cats are faster than mono`s. So next time you sail faster than Froude`s law
says you should be able to, just smile ! Life`s a bit faster on a cat.
Carl,
It is beautiful, indeed - I expect mine to look even better due to some small details.
Answering your questions:
The Bruce Foils (inclined daggerboards) provide vertical and lateral lift, like those of the Open 60s. The only difference is that in the Catri the foils are designed to lift up to 90% of the boat's displacement, while in the latest Open 60s they are designed to lift about 20% (Aldis Eglajs' estimate).
The ideal angle of heel is small. The best atitude for speed is with the ama sinking 10% of the total displacement, the foils supporting the remaining 90% and the mainhull skimming the surface.
The floats' volume is about 110% of the displacement aided by up to 90% lift provided by the foils in high speed, totalling 200% "flotation".
In short: it flies two hulls, but goes faster flying low.
When the mainhull flies higher, the rudder's foil is raised and stops lifting, so the mainhull automatically returns to the ideal atitude. This is (part of) the stabilization system patented by the designer.
With less wind, the speed is smaller and the float can sustain 110% of the displacement - but then it is sharing the weight with the mainhull. Conclusion: the foils' lift enable the floats to be smaller (= lighter + less windage).
Sorry for writing too much - I just can't stop...
Cheers,
The boat I sailed on was a Planecat 18. It had square looking flat hulls. It was a dealer or factory demo. It was cold and only 3 people showed up.I was the only person willing to go sailing a second time.
My impressions of the boat were; slow in light air, fast but hard to control in medium air and weird things happened (it popped off plane or tried to spin) when it started to fly a hull (that's when the Hobie 16 passed us). With experience you would get used to it's quirks and anticipate what it was going to do but, there was nothing about it that inspired me to want to try.
Cats are displacement boats. That law is not general, and it is wrong to apply it to beach cats.
Beach cats sail through the water pushing it aside, therefore it is proper to say that they sail in displacement mode and they can be properly called displacement boats..
Cheers,
I heard about Carl Roberts planing cat but sadly never saw it. Carl's experiences with a cat's behavior when planing help visualize the problems of speed, lift and control. This may be a triangle- you can have any 2 of the 3!
It's tempting to think about dropping a planing surface under or in between the hulls when you are going fast already, but how does one get such a rig to sit back on this surface while planing at speed? Besides the force in the sails wants to blow everything sideways. Hydrofoil sailboats have the same sideforce to deal with: It looks as if vertical fins above or below the foils are necessary to deal with the wind pressure, converting it to forward motion. This is not so simple.... even when you have lifted both (light) hulls out of the water already! It makes you breathe hard and grin a lot, tho. 8^)
I think my initial post was unclear.
The following resource does not use the 1.34 constant, and seems to go into some depth about the actual factors used to calculate drag for catamarans:
http:/
After citing that resource - and I can't vouch for it's accuracy, but I can say that it looks detailed and careful - I then attempted to say that a straightforward application of the hull speed formula using the 1.34 constant - which is NOT advocated in the URL above - would give very low speeds indeed for my boat.
Jonathan