Isn't that the same principle that makes a hovercraft and Erkanoplan work (although less extreme).

As an premise for further development and research that is a tenable position even though it is not the obvious one to take.





This is just nonsense. A planing hull also needs more power in order to travel faster, in fact you totally misapply the word power here. It is physically possible (and actually does happen in some cases) were the driving force descreases when travelling faster but the required power rises. This is because "POWER" is the product of "driving force" and "speed". If the speed increases more then driving force decreases then you get into this situation. Several dinghies that transition from displacement sailing to planing actually go through such a situation. So I propose that we'll only using the driving force and no longer the concept of power.

With respect to "forced mode" We must be careful to not read more into a given word then there is too it.




Or is may just be that long slender hulls on a lightweight platform in forced mode lead to lower drag at 20-30 knots speeds then a planing hull of similar length.


Wouter

this thread all seems a bit pointless ,

why not look at powerboat catamarans that allready exist and find the answer, feking fast !!!!, surely these big bouys and smaller ones can give an idea of what can be done if you strap enough hp onto two hulls ,(the thread started with engines) yon funny looking sailing cat above hulls dont look too unsimilar to those on the smaller powerboats .

its intresting to note that as far as i know all catamaran HP racing (motor )cats use planing hulls . and are probably more akin to low flying air craft using forced air under the bridge deck to provide lift .

Nigel Irens has developped high speed wave piercing muultihulls for long distance stuff (trying to keep up with orma 60s who are under sail ) haven't heard of any on smaller fomula racing cats though , would by struggle at corners <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />


PS I always find stuffing the luff exstension down the mast after hoisting effective and helps sail shape at the bottom of sail , though I don't think I'm alone in this tinking <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

I don't think so and I'll explain why.

With the Hovercraft and Ekranoplan the air cushion has a higher pressure as the surrounding medium. As such it is more akin to planing. This earlier 20th century CARGO ship has a air pocket that was at the same pressure as its surroundings. Basically the first derive lift from a dynamically created difference in pressure above and below the craft while this cargo ship was still fully in displacement mode. In fact that cargo ship design would also work if the trench was fully closed off and there were no pumps. The pumps were only there to keep the trench filled when air is lost due to rolling of the ship and other leaks.

Basically the Hovercraft and Ekranoplan completely dependent on the aircushion in order to remain levitated while this cargo ship could even work when the trench was filled with water. In the latter case it would just have more hull drug. So with the cargoship it was just a means to lower skin friction drag and nothing more. And that is why it could carry lots of cargo.

But yes, there are also strong similarities, all four (incl. planing) aim to put as little surface area into contact with the much denser water as possible in order to lower overall drag.

Wouter

That is just the question isn't it.

Powerboat cats are all designed the plane

Sailboat cats (like ORMA 60's) are designed to sail in forced displacement mode.

Only exception the latter rule is the Yves Parlier "seaplane" catamaran "Médiatis Région Aquitaine"

This cat has been pushed hard for 4 years now and not proven to be a winner.

Also of interest is this little bit of info as contained in a press release :




Source : http://www.ybw.com/auto/newsdesk/20040104160707ywnews.html

So indeed it is not a black and white situation. With each design you need to look at the specs and operating point to determine which of the two (or three) paths available is the best. For racing sail powered catamaran the paths most favoured are forced mode displacement and indeed foiling (L'hydropthere, longshot, Techiques Avancee).

A while ago I had discussed planing hulls with some A-cat designer and he replied that they had tried during the 80's to make it work, but failed to beat the normal hull designs. One issue was to keep the hull planing smoothly. Typically the boat would drop off the plane when heeling or pitching due to a gust. This could well be one of the more important reasons why powerboats are all planing designs were sailing cats aren't. It is easy to keep a powerboat "flat" or tilted at an optimal angle.

Wouter

An interesting thing about our Hobie 18 powerboat is that because it is NOT a planing boat, it is able to accelerate to its top speed very rapidly. Makes it better for pulling water skiers, for instance, because you don't have to wait for the boat to get on a plane. (Obviously, the ultimate top speed will not be as high as for a planing boat with the same amount of power.)

Maybe the same thing is true of planing multihull sailboats that it takes more power (and wind) to get them up on a plane in the first place.

Like Richard Roake's Hardcore 16, which seemed to be a dog in light air (compared to displacement cats), but very fast when the wind picked up and it could get up on a plane. Sort of like a sailboard, I guess.

Has anyone ever tried injecting air around the hull(s) of a catamaran when approaching top speed to create cavitation? What would be the probable result?

Power based boats are generally using the tunnel to create lift and less friction. Again, I think this is not realistic regarding sailing beach cats.

Well this is exactly what I am interested in Mary.
My experiment is in the size of the boat to the crew weight also.
My boat is almost as fast as the full rigged two up boat in light so is not exactly a dog but it is aimed at heavy air.
Are there any photos of the Hurricane as I can find none on google.

Are you being serious?, That is a phenomenal boat. It is the fastest catamaran ever sailed solo in 24 hours, no other solo catamaran even comes close to that boat.

Gareth

I think this is what some animals do to allow them to swim faster, a while ago I saw a piece on Discovery about a Blue Marlin who ejected some type of oily fluid to lessen waterresistance.
Also there is a powerboat that is based on dolphin skin.
More info here: http://www.physorg.com/news68812337.html

A while ago I had discussed planing hulls with some A-cat designer and he replied that they had tried during the 80's to make it work, but failed to beat the normal hull designs. One issue was to keep the hull planing smoothly. Typically the boat would drop off the plane when heeling or pitching due to a gust. This could well be one of the more important reasons why powerboats are all planing designs were sailing cats aren't. It is easy to keep a powerboat "flat" or tilted at an optimal angle.

Wouter [/quote]

I have certainly experienced this affect. I have presumed it was because I have cut the rig down to almost a masthead and I was overreacting to hull lift. It has helped to make much smaller adjustments in mainsheet. But when it does drop it feels like time has stopped.
Ideally I am trying to keep both hulls in the water and this is a learning curve also as I only want outright speed and am spending no time on general performance. The boat is so far much easier to keep on an even keel than say my Hydra which has less sail area and is heavier.

Warbird: From where are you doing your speed sessions?
I have spent some time in the BoI (Opua/Pahia area) but dont remember are places with flat enough water or high enough winds (then again, it was a few years ago).

I forgot another exception. Yellow pages and Macquary Innovation. These are planing contraptions for an all out speed record. But they are very different to a normal catamaran and mostly in the sense that they are very wide and don't have long hulls at all. Yellow pages and the other have three hulls which are all pretty small and the leeward ones are in line with a significant gap of water between them. These will remain "flat" very well due to this overall configuration, but makes it very different to a normal cat like the Tiger Shark.

Wouter

We must not forgot another things as well. The way a hull rides the waves and chop. Typically wind powered craft need alot of wind to propel them to high speeds and such conditions have a very strong correlation to a pretty uneven watersurface.

It would not be the first time that a sailing catamaran outpaces a powerboat in a blow because planing in such conditions is very violant. This also leads to the question of how the rig will behaved when it is shaken about very violantly because of the planing surfaces trying to follow confused seas.

Actually I have this experience with landyachts. Sometimes the beach is not flat but has small wave sand structure. It is very hard to keep the sail drawing in such conditions. Even so much that it pays alot to just take a much longer route around such an area, simply because of the ability to reach much higher speeds when the craft and rig operating in a smooth manner due to traveling on a smooth surface.

Of course waterskiing stops with even a very little wave like disturbance of the water surface.

Wouter

And still, it doesn't hold the outright record for 24 hour solo run.

Actually there are 3 forced mode displacement boats and skippers that in front of it in the record listing. One of these being a 60ft tri. Note how "Médiatis Région Aquitaine" is a 60 ft cat build to the same rules as the 60 foot tris.

Basically, you statement is only "true" because you choose to include the condition that any challenger must be a "solo catamaran". If you had used ""solo multihull" then your statement would not even have been in the least bit "truthful".

Situation is very much the same for fully crewed 24 hour records even in the 60ft or shorter class.

Nice try, but definately a smoke and mirrors kind of counter argument.


Wouter

If you meant to refer to the Hardcore, I cannot find any pictures of it, either.

The only time we ever saw it was when I think they had two of them at a Red Lobster Regatta in Sanford, FL back in the late 1980's or early 1990's(?) Excellent sailors were sailing both of them (one an Australian, and I can't remember his name, I think maybe it was Brett Dryland?)

Anyway, they did not do well, and after that debut, nothing was heard about them. The Hardcore is still listed in the Portsmouth ratings for old boats, but it obviously had a provisional rating, since it never raced enough to get any good data.

Randy Smyth won the Worrell 1000 one year on another Roake planing design, but he said it was a pretty rough ride. Rick saw him from shore and said the boat was skipping across the waves like a sailboard, but perfectly level, while the other boats were going up and down over the waves.

Warbird,

Overall width may really help you here also.

It could be an idea to just remove the trapeze and make the boat wider and only hike off it.

If you are really after planing then have the luff hull take part of the planing. This will make the platform very rigid in its side to side attitude and allowing you to keep optimal planing angle better.

Again this assumes that you can get proper planing to work at all.

Wouter

after almost 6 months of winter snow out at the lake this week i finally got my nacra 5.2 back in the (cold) water, surrounding volcanoes still covered in snow

today had the most breeze and as i had the gps on board i tried to better my previous top speed of 16knots, set the end of last year

still a noob and without a proper trap harness i've been making do with an old windsurfer harness and just sliding my butt off the side of the hull. all winter i've been reading "catamaran racing for the 90's" so was sitting just behind the dagger to reduce transom drag

winds picked up, aimed for the reach and off we went, played the main to keep the windward hull just kissing, wind blew a little more, speed picked up another level, leeward hull starts kicking up big spray and suddenly the whole platform starts tipping forward! leeward nose almost completely under and i slide back to the rear beam as fast as i can

everything pretty stable in that position and a couple of minutes we are across the lake and out of the main breeze

gps says top speed 15.5knots and later trackpoint data downloaded to show the points either side

23/04/2008 12:46:07 0.2 nm 0:00:41 14 kt 98° true
23/04/2008 12:46:48 0.1 nm 0:00:29 15 kt 109° true
23/04/2008 12:47:17 0.2 nm 0:01:01 13 kt 113° true

looks like it isn't going to be easy for me to get much quicker. going to need a proper trap harness, foot straps, nonslip tape, more time on the water and slightly bigger balls;o)

another plug for GPSaction replay, very cool cranking the speed up and watching the boat zip around the track with each section colored according to speed, pic attached

I hadn't heard of the Hardcore before and also haven't found anything on google. If RetiredGeek is around maybe he can share some history.

However while poking around on google, I did find the following, which might also be of interest (as a historical note).