Planing Catamaran!

This video illustrates a planing cat better than anything I've yet seen:
http://www.youtube.com/watch?v=JbOr46fV4n0&feature=related

the story:
http://www.mckeewildthings.com/Wet and Wild Fluid Dynamics.htm

 

I would have smacked him in the head for driving near my dogs like a tool.

Cat looks like a bit of fun though.
J

 

Very cool. Looks like he could use some battens in that sail.

 

Planing Cats!

It seems to me that the boat was very impressive for its era-the eighties. I can't help but think what could be done now with new materials. I did the one below in that same time frame. Some friends and I have figured out that it could be built today at about 1/3rd the weight it had then.

 

that's nothing. my 500 kg jarcat 7 will plane if you apply 50kt wind to the beam.

 

Aero Skimmer

This thing has planing hulls and a tilting wing rig: http://www.youtube.com/watch?v=7Y8x9JOVwog&feature=related

 

Palm Beach, Northern Beaches, Sydney, Oz --> old stomping ground when windsurfers had teak booms. LOL nice footage, never saw that thing, ever!

 

I saw windsurfers using that type of rig, great for jumping!

 

Notice how the You tube caption says that "We received an Australian design award"?

I was the guy who sailed it for the panel when they were judging it for the award. I said that it was probably not worthy of a design award, as the performance claims were greatly overstated. It was okay when planing on a reach, but slow in other conditions (ie light winds or chop, or going upwind). I can clearly recall the Design Award panel saying that they did not want to discourage those who sought the award, so they gave the boat the nod.

I don't think that (as claimed) the boat failed to sell because people didn't understand the concept. Cat sailors are NOT ******, fools or idiots. They don't go for planing cats because planing cats are, all round, considerably slower than non-planing cats. Sure, the Itzacat throws spray around, but that isn't a sign of all-round speed - look at the incredibly efficient low-fuss motion of an A Class cat or lowrider Moth which throw almost no spray but
go incredibly well.

Basic (and very well tested) hydrodynamics teaches us that the drag of a planing surface is inversely proportional to the width of the stagnation point. Cat hulls (even Itza Cat hulls) are skinny, therefore they have a narrow stagnation point, therefore they lack efficiency when planing, therefore for cats a skinny displacement hull is a better all-round proposition. It's been well known for decades and has been proven numerous times.

It did tack well, although not as well as a Laser as claimed.

 

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CT, the video shows the boat going real well-looks like a lot of fun-didn't you have any fun? http://www.youtube.com/watch?v=JbOr46fV4n0&feature=related
He did say "Laser"-but he also said "skiff"- big difference-but close enough for jazz? His claim to outpace a Hobie 16 doesn't sound outlandish at all-my Kona Kat would as well-80 sq.ft. vs 216 ; asymetrical hulls vs planing hulls in winds 10 knots and up reaching.
I think your obituary on planing cat hulls is premature. Steps can increase the aspect ratio of the planing surface making it considerably more efficient and some step designs use a very small step-lots of room for experimentation.

 

A round a course, give me a well sailed 16 any day over that thing.... no way IMO

 

Doug - I know there is only a low chance of resolving the doubt as Kona Kats are pretty uncommon these days but I highly doubt your claim that it could outpace a Hobie 16. If single hulled craft (ie windsurfer one design) from that vintage couldn't outpace a hobie then how could twice the plastic, increased windage, that same rig and the same righting moment go faster? It doesn't make sense to me.

 

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Windsurfers of the early eighties would definitely outpace a Hobie in the right conditions. So did the Kona Kat on a reach-but not around a course.
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Hobie 16 1975 B Class 16.9 knots
Windsurfer 1977 19.1 knots
Windsurfer 1981 24.75 knots
Windsurfer(womens) 1981 21 knots

 

That 1981 record of 24.75 knots was Jurgen Honschied on a surfboard - not a surfboard-style windsurfer, but a real surfboard fitted with a mast base and footstraps. As a 2.28m 5kg sinker-style board of 26L volume, it is much faster than a longboard (around 3.7m, 16-21kg and 190-260L) in speed record conditions and its performance is not comparable. Similarly, Jaap Van Der Rest's 1980 windsurfer record of 24.45 was also set on a 7kg shortboard that also cannot be compared to something as a large as a longboard windsurfer or an Itza Cat.

Down here the '80s update of the original Windsurfer One Design (same hull, retracting centreboard, better rig) is the most popular windsurfer racing class nationally and its titles attract 40-57 sailors including multiple Olympians. There is no way such a board can pace a Hobie 16 except perhaps in the most extreme conditions. The best speed I know of is a peak of 25.4 knots (achieved by the national champ in extreme conditions and verified by one of the world's top 10 GPS speedsailors, who hit his own Formula board peak of 31 knots the same day) which may be faster than a Hobie 16, but 99.99999999999% of the time the H16 is much quicker, as indicated by its yardstick being some 38% faster.

Did I have fun on the Itzacat, Doug? Not particularly. It planed okay but it had issues. But what I objected to was the way the Youtube caption insults cat sailors by claiming that they did not buy the boat because they did not understand the concept. The planing cat concept is an old one, dating (IIRC) from the '60s. There were boats as big as 60' built around the concept here, and that failed to do what it was supposed to do.

Insulting people because they 'couldn't understand the concept' means opening up yourself to those who want to clear the record, IMHO.

Interestingly, the Youtube caption says that the boat sold to science teachers and those who 'understood the concept'. I wonder how many science teachers are familiar with stagnation points, Savitsky and other facets of planing? And if they were so satisfied with the boat, how come we don't see lots of them sailing and beating conventional cats?

 

CT,

Do you remember 'Big Bandicoot'? That planed didn't it? Or is my memory shot? How did that go?