When i first started sailing (NACRAs), an old-timer told me to pull my daggerboards halfway up when reaching. He said it would help me from being pushed over by a big puff, because the hulls would "slide" a little sideways, instead of the sailplan being pushed over the top of the boards. I've felt this happen, has anyone else? Although it's hard to call it planing, it certainly isn't displacement....

From what I understand this is to prevent what is called board planing. Powerful boards will create to much lift and help the boat rotate into a capsize.

Mike

Hello,

Ventilo claims that there new 'zip'o' 16 foot cat plains!?
It has a flat bottom and a wave piercing shape
see pics

Good concept Luiz

Looking forward to seeing the tri sailing .

There is a great book titled --Curious Yachting Inventions -
which took a look back at various nautical applications of ideas from the 1800s on .
Did a patent search once on a rig concept I had ,--as you look through old volumes and micro film photos and diagrams of other concept inventions in catagory it is AMAZING -and sometimes humorous ,--
It makes great reading ,--someone should write one on --Curious multihull Design concepts ,--
They could place my angle rig concept in there somewhere .

-Though thinking of it --it did get a very negative write up in a now long defunked magazine ,--calling it a Rube Goldberg contraption ,-which was an old newspaper funnies comic on making inventions to accomplish simple tasks in the most complex way possible ,--it was a mean spirited commentary on someone like many before experimenting with concepts .
-{ gee wonder why the mag. went out of biz} --

good life lessons early on ,-not too much phases me now, no one should allow other small minded people to with negative derogatory comment ,-public humiliation etc ,--its nothing ,--people like Edison had thousands of failures before finding solutions that worked ,-from the knowledge gained in each was able to make fantastic connections of concepts and ideas . We all need to take a page from his book and be persistent and patient with such things of life ,-and each other too !

Have fun
Carl

Carl,

No doubt the "flapcat" would work. The question is how much would be eaten from the downwind advantage by the lower upwind speed due to the additional weight in that position and, most important, if the additional cost and work are worth it.

My Catri 27 will still take some time. The molds took more time to build then expected, the construction is technically more sophisticated then I expected and I demand perfection (as expected...). But the boat is finally being laminated now.

The second Catri 27 made in the US is performing well in its first trials: sustained 27 knots with almost 20 of wind, under main and jib only. It seems that it will easily surpass 30. The performance is more or less matching that of an Open 60 in equal conditions.

The designer refuses to make any prediction about the top speed, so I guess I'll have to wait to test it myself...

(Before anyone steps in to say that the ARC 30 tops 35, remember that the tri carries an engine, folding gear, a head and other amenities)

In case you want to see the boat in action, I am attaching a photo of the first US Catri sailing in San Francisco.

Cheers,
Luiz

"Success is the ability to move from one failure to the next without a loss of enthusiasm."

[color:"#666666"] Winston Churchill [/color]

From what little I understand SOP (Seat Of Pants, for Mary):

Think about hull shapes.
An assymmetric cat doesn't work unless it 'bites' the water. Even on a heel, you've got quite a bit of 'v' hanging below. If you didn't, the boat would merely be pushed off sideways, with nothing to stop it, well, except the rudders. Thass displacement if ever it was.

Other designs involve fine bows with hemicircular sterns. Now in the case of these boats, it's a matter of the WWW factors and speed. At lower boatspeed, windspeed, rougher water (either/or) you're gonna want to sail the boat bows down, or in displacement mode, which as it turns out is most of the time. But if it's flat, or blowing stink, or you're really 'sheeting in and maxing out', you'll set the boat more towards its sterns and begin to plane to some degree.

Looking at the newer designs, the Inters in particular, are designed more as a planing boat, with rather flat bottoms. But regardless, when you're going slow, cats are displacement, and depending on the hull design, as you go faster, they begin to plane.

So the answer, to me, is...
BOTH.
Depends on the hull design and WWW factors.

sea ya
tami

all planing hulls displace at lower speeds.

catman,

I used to have a Laser, and when I'd sail it in heavy air, reaching and running off wind, as it planed, if I forgot and left the board down, Wow, over I went, it wasn't the wind, it was the lift on the daggarboard when the hull planed! Always let me know when I left it down! I'm sure many have experienced and know this.

I wouldn't say any of our current cats plane. They "lift at speed and reduce the amount of hull dragging in the water.

I sailed on supposed planning cat, the Planecat. On a smooth lake, it traveled through the water they way little fish do when a big fish is chasing them. It was noisy, it bounced, and it wouldn't track. To top it off we were outrun by a Hobie 16.

Opposite to this was a homebuilt 18 sq. It had very deep, very narrow hulls, with lots and lots of rocker. The idea was it had a great fineness ratio so it had a high theoretical top speed. The theory was as speed build, the leeward hull would lift, reduce drag, and go faster.

It was a nice boat to sail, smooth, good tracking and an OK boat to tack as long as your weight was aft. Actually it reminds me of the new Ventilo 16 with narrower, deeper hulls.

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://members.xoom.virgilio.it/mfcatamaran/hull.html

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://www.basiliscus.com/CaseStudy/geometry.html

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^)