Oboy now we're having fun!
Re: Biplane rig on a foiled cat: This is referring to Icarus II, sailed at Weymouth Raceweek in 1980-1984. Icarus II had 2 lengthened Tornado hulls of about 25 ft. and 2 Tornado masts (which broke regularly) when powered up at 28-29+ knots. It did well in Weymouth but less well in Brest where the waves were lumpier. The book is called "Icarus: the boat that flies", by James Grogono, pub 1987. Other speed rigs are shown, including Icarus I, Mayfly, and the mastless Tornado that went very fast but then tried to go to heaven - really- using a stack of power kites: no wonder her name was "Jacob's Ladder". I am not making this up. Another similar neat book is "FAsterFAster" by David Pelly. Lots of work is exhibited and documented fairly well in these books. Chemists know that it is prudent to examine the literature carefully before doing anything more than cheap "paper chemistry". I am not making this up either!
See other documentation thru links at "International Hydrofoiling Society" www.foils.com

I have been distance racing on a nacra 6.0with the gps in Track mode for the last couple years and done a batch of speed testing. My best tracks are about 13.2 knots Upwind in ~ 20 knots true (flat water) Note that this is not VMG.
I am also a footer by habit.
Broad reaching under main and jib ~22 knots with a large crew

down wind with the spinnaker ~22 knots My observation is this is usualy as fast as you go with a chute. Your vmg goes up with windspeed because you just keep sailing lower

Last year at the Around Newport race My highest GPS reading was 24.8 knots. This was going dead downwind in about 30 knots true windspeed with the chute up. The boat felt like it was planing for a while. My crew and I were sitting on the rear beam with the jib over on the wrong side trying to figure out how the hell to take the spinnaker down without imploding. I remember the bows were clear of the water. Wave height was less then 1 meter.

On the other hand, I measured 52.2Knots on my DN iceboat going downwind in ~22 knots windspeed. To me this is scary fast.

I figure from practical observation a Nacra 6.0 can go ~20-22 knots reliably without crashing and burning as long as it is windy enought that you can twist the sails off and move the center of effort down lower.

Sail fast,
Take Chances.

Eric

Will I don't understand your comment ?? Was it meant for me ?
BTW did you get my second e-mail w/more pics ?

Marc

6076.11549 feet in a nautical mile.
5280 feet in a mile.
1.15 miles in a nautical mile.
0.869 nautical miles in a mile

Eric, your statement:'My crew and I were sitting on the rear beam with the jib over on the wrong side trying to figure out how the hell to take the spinnaker down without imploding.'......

had me LOL here at work, and brings back many a high sphincter tone memory of a situation like this.

Todd,

Maybe remembering the trip we took after installing the I-20 snuffer and chute on your 6.0??? Was a great trip, but a little on the cold side.... Thank god for the counter weight of the crew Huh!!!!

Take care,

Hey Eric, I often wonder how fast we were going on the last race of the windy day at Perf. Nationals last year. My feel is that it was not faster than 20kts.

The fastest I've ever gone as measured by GPS was 23mph/20.4kts. This is a speed while I was actually looking at the GPS. I've received higher max speeds up to 35mph. I don't believe the max speed because of the fact that the GPS is swinging around and probably just caught it right for a second to come up with the max. I maxed out at 23mph on a Hobie 20 on a reach in flat water. If I had more weight on the wire the speed would have been more. I was basically limited by counter weight and beam length. I feel that a Tornado should be able to go a bit faster. I don't believe 30kts but sustained bursts to 27kts is probably attainable on a Tornado. A SC22 would even be faster.

Just had to chime in after reading all of this. Oh yeah and when going upwind in 20knts I've looked down at my GPS and it consistently reads about 10mph even though I think I'm going faster.

Mike Hill
H20 #791

Hi All ,

Accurate Speed measurement is really quit easy,

Just ask the skipper and divide the figure by 2, same goes for Wind speed.

Hey Marc,

Yes, I was saying that what you said were "fighting words". Yeah, I got the pics! I like the shape! When are you going to finish one and take me out on it?!?!?! Really looking forward to the all carbon version!

I wrote an email to you, but Hotmail had a little problem just as I was about to send it. Didn't have time to rewrite it. Should have time to answer your questions some time soon.

All the speeds I stated were seen on the GPS by me. It was pretty steady in it's speed readings. It was a Garmin Etrex Ledged w/WAAS. Believe me though... when it hit those speeds, it wasn't for long... usually followed by a rapid deceleration.

I wanted to download the tracks, but the contacts on the back had become so corroded over the two weeks of the W1k.

Will R

Frenchie / Mary

Probably you are both right. Frenchie refers to flat water, no current, ideal conditions, design limits; while Mary refers to outright instananeous speed and average course speed.

Note that with waves and current help, any boat can surpass its theoretical speed limit. Also, in a burst the limit may not apply. Suppose a tornado (not the boat, the storm) hits a cat. It will fly at incredible speeds. If the storm carries a person, he will brake man's (women's) natural speed limits too.

That said, the key points to check are:

Instantaneous speed x speed over a given distance
Flat sea x favorable waves
No current x favourable current

Personally, I believe that Frenchie is right - and that wave, current and microbursts may have caused some exceptional records (as Mary pointed out) that do not conflict with the limits.

This all standing for standard beach cats - without foils. With foils, the figures are higher.

Something else - maybe Frenchie is not familiar with the ARC 27 and 30 "beach cats", which easily surpass his calculated figures due to their size and excelent engineering.

In any case, beach cats are the fastest cheapest clean way to sail.

Cheers,

I can't resist putting in my two cents. In the attached photo, the chase boat was reading 35mph on the speedo (30.4kt). Now, I take this with a large grain of salt, BUT, I'm sure we have to be going more than 20kts. I'll have to find out if my new gps is waterproof for this summer. (I thought they were just for avoiding getting lost in the bush)
wishing you all flat water & high winds
AL

Hello to all,

Again HAPPY NEW YEAR 2003 !!!!!!

To Grob... of course, biplane rigs seem theoretically very very interesting, by dividing aerodynamic loads by 2 on each rig, at SAME ASPECT RATIO, you lower the CoE by 20% or more and cracks the induced drag ( in theory ) by 2 also...BUT, practically, things come a little bit tougher...

First, because of Munk's wings stagger theorem, you see interference drags between 2 ( if lateral gap is under 30% rigs span ).

Secondly, broad reaching in light to medium airs could suffer severely when the AWA is near 90° ( acceleration process ) from the "shadow effect" of the windward towards the leeward rig...

Thirdly, structure becomes quite complicated with diagonal internal shrouds, compression connection beam somewhere in the heights, spi attachment mess...shroud limiting course of battens due to crossing backstays... EXCEPT, self-sustained masts strongly set up in carbon dwells inside hulls...that's rather hard to manage.

May be, with new fibers such as Akzo M5, M40J carbon or Boron's Silicates, one day, you could set up the rig so simply that even a Laser will seem you a 505 !!!!

Friendly Yours,
Frenchie

Hello again,

I just forgot,

Take a loook at a fabulous sailing biplane rigs machine on http://marine.bdg.com.au

The aussies are incredible enthousiats...

Frenchie

Frenchie,

"if lateral gap is under 30% rigs span "

I am unsure what you man by the terms lateral gap and rig span.

Does this mean if the distance between the masts is under 30% of the boom length?

Thanks

Gareth

P.S. here is another good looking biplane boat http://www.mko.freesurf.fr/innovoile/historic_e.html

a little late but;
sail mag has a article on this subject in the jan 03 copy

Dear GARETH,

No, the transverse distance between rigs ( gap ) should be at least 30% of the top of the mast height ( 9,3 m on a Tornado ).

Frenchie

I think one of the common misconceptions is that as recreational catsailors, we tend to take the fastest speed reading of our GPS on a given day and indicate that as the potential speed of our catamaran. While I'm no speed demon, I'm sure there have been times when My boat is hurtling upside down through the air that it seems faster than it really is. Notwithstanding that, I think the discrepancy between personal speed experience and the Quoted capabilities of our boats is basically a function of how we measure it.
As performance oriented sailors, we tend to think in terms of our best peak performance, not some averaged time over distance calculation that reflects not peak performance capability but something entirely different, averaged speed over distance. That's not for me. I'd rather tell the story that once I made my cat go 30 than if you averaged out all my true speed while I was racing on my cat. It would include those days with no wind, sailing the drifter, maybe time on the trailer, or number of leaves collected on the tramp over a season on those days I had to work, and that time I was late for a regatta driving 85mph to get to the start line on time. Averaged speed doesn't reflect performance capability. & who really wants to be average anyway?
All that considered, think I'll stick with remembering that time I went the fastest, & yes I was probably upside down and in the air, just for the scientific purpose of trying to eliminate that friction with the water component of the equation.
CARY

Frenchie,

Since you are obviously interested in foils and speed, maybe you would like to know that Aldis Eglajs (the designer of the Catris) also believes that in the future supercavitating foils will be used in the fastest boats.

He maintains contact with ressearchers of the former soviet union in this area and wants to build an offshore trimaran with supercavitating foilers in the future.

Tom Speer's site is excellent, but his goal is to make a smaller cruising foiler for recreational purposes. He likes speed, but he is not exactly after record breaking speeds.

Cheers,

Now that it is more or less established that Frenchie is right and that the mid twenties (knots) is the benchmark top speed for beach cats, it is time to discuss how to go faster.

In this regards, I can tell you that the second US Catri 27 already sailed at sustained speeds of 27 knots in flat waters and the crew is confident to surpass 30 knots. Actually, there is talk of a Catri 22 surpassing 32 knots in Holland.

If we consider that the Catri is almost a cruising boat, with cabin, head, kitchen, engine and amenities, it is clear that foils are a rather convenient solution for achievieng higher speed in multihulls.

The problems of complexity, poor upwind and low pressure performance of the Trifoiler and Rave are minimized or inexistent in the Catri.

Based on this boat, I expect to see foils used in more beach cats (or beach multihulls) very soon - probably also with planing aids (like flaps), steps and other smart tricks - but certainly with the simplicity of concept of the Catri.

Cheers,

The fact that no more comments are to the contrary doesn't mean that Frenchie is right.

Also it is not very likely to see much development in foiling craft as these designs often lack speed at the lower spectrum of the windspeed range to be all-out regatta winners.

Of course a good regatta boat has the optimal compromise between light wind speed and strong wind spped, it does not necessarily need to have to be fastest in one of each conditions.

What also strikes me as odd is that 27 knots claims made by displacement boats are branded as inaccurate but that a 32 knot by a cruising tri of similar length called catri is presented as dependable.

Very often people forget that foiling is certainly NOT drag free. Unlike planing , foiling is noticably best near its design speed. Catri's trick to overcome this is to have aiding foiling which is basically a displacement craft of which part of the weight is carried by foils. So the catri is a cross between both technologies. However it would be strange that a say 400 kg's cruising tri of 22 feet would outperform a 170 kg tornado of 20 feet because the displacement of the catri is reduced to say 200 kg's by the foils.

Yes the aided foiling system is expected to improve the performance of a given craft when design well, but that is something else than being all-out faster than all others.

And ofcourse the catri system will never become fully foiled as that would make the whole system unstable. The simplicity of the catri system is dependend on the fact that the (lee)hulls are never lifted away from the watersurface. Only then can the tail foils act like arrow stabilizers and keep adjusting the angle of attack of the main foils to an optimal angle. Without it teh system could go into a run away proces and try to put boat on its tail and be alot slower due to massive drag. With systems like these one always need a good margin between normal operation and full foiling to prevent a freak condition from upsetting this balance and pitching the boat.

So to be able to attain higher top speed the design maximum speed with it's maximum foiled weight (say 75%) needs to be as high as possible. Downside of this is that at lower speeds the amount of foiling is reduced thus reduceing gain there. Set the the speed of maximum foiling to low and the top speed is limited by it's limit to not be lifted free of the surface.

And ofcourse there is the cavitation problem. Use a powerful full foil to achieve noticable foiling at low speed and you are sooner limited in top speed by cavitation. Other way around and in light and medium conditions you will hardly notice any improvement and you'll have made a "go fast only in heavy wether boat" = bad regatta boat.

In this respect foiling is alot more difficult to get it right than planing. But than again foiling can be made to less held back by chop and other not flat surfaces. But the compromise system of the catri is not the best foiling system in this respect. The rave system is better in this, but than again this system is full foiling and thus requires more complex control systems.

Now aftyer this neagtive remarks I would like to say that the catri system is a very neat system that I expect to achive great results with a rather system setup. However this does not immediately translate into being a superiour system likely to be incorporated into many different other designs in the near future.

Please lets not forget that displacement system are still the most simple systems, among the least affected system by seastate with a rather good compromise between low and high wind speed velocities. Especially given their light overall weight of today. This last aspects makes sure that sizeable partions of drag are not the direct result of displacements. A sail rig in a airflow of 30 + knots does indeed created alot of drag too and so do the human bodies hanging from the trapeze. Therefor a large reduction is displacement related drag may only result in a far more limited reduction in overall drag and thus limit the speed improvement. And catri/tornado = 32 knots/23 knots = 40 % speed improvement doesn't seem logical in this respect.

But then again I do not have the full picture of the Catri design yet (sail area, mast hight, aspect ratio, etc)

Wouter