Darryl,
I saw this thread once and concluded SEP.

How could you see the thread and recognize it as such then? The math used here is very powerful though.

If you needed more weight while getting up to speed you could have a scoop to fill a bladder on the tramp just by putting a pipe facing forward which would force water into the bladder then you could let it out when you slowed down. You'd need good baffles in the bladder or the cat would roll over when you turned.
regards

Warbird: Do you have any GPS tracks from any of these 20-25kts sessions?
I am really interested in how those runs where built up because 25kts is a lot of speed (especially without a spi),
I have done 28kts on my windsurfer and cant image doing that on a "simple" beachcat.


(btw. I found 1 of your bookname suggestions a little disturbing, and its spelled "Mein" not "Mien". http://www.learntospell.com

Those books and articles are part of the 20% that got it (mostly) right.


Wouter

Forget about adding weight to the rear of the boats or any piping boys. Just add T-foils to your rudders and give then a downward angle of attack and watch those baby's provide many kg of downforce much like a F1 race car when the boat speed picks up.

But what the hell do I know right ?

Wouter

The boat has only been out twice since I changed the rig etc for speed runs.
It has not been out in more than 15 knot winds and has not travelled faster than that in its new guise.
I have sailed the boat at twenty with its high rig and they are known as an extremely fast reaching cat. Well faster than an H 16 for example.
The spinny is not my option at these speeds nor is it needed. There is heaps of power enough in 25/30 knot winds in this rig and indeed it may not need the jib.
I am happy with the results so far and so I have just ordered new sails for it from Whirlwind and as I set the boat up and run it I will prvide GPS tracks etc. The 25 knots over a measured distance is my aim. It has not been achieved so I may well fall flat on my face with these ideas.

But, obvously, I do not think so.

I understand that cats are racing up and down wind courses with no reaching.
Something about reaching being a parade.
Perhaps if we got them to go fast enough on a reach it might be worth it again.

Nice rig change on the PT. PTs go like stink off the breeze when it is fresh, especially for a 14 footer. I would watch those loads on that tiny front beam though.

Build a 18 or 20 foot version with 10 foot beams (cut and shut 2 old PTs for some fun even), reduce the rig size and dont be affraid to run it flat and I am sure you will get some impresive speed out of it.

As for no kite, a cat will sail the quickest on a 2 sail reach without kite due to less drag. Kite does not make you go faster..... Just increases VMG down wind.

Your eyes deceive you. That'a a Tiger Shark and it's already 18'.

Going faster than hull speed without planing is called "forced mode" and cats are doing that any time they have their transoms depressed but not submerged, indicating that they are making a longer hole in the water than their hull length, and they are sailing 'up' out of this hole. Conventional lead mines don't have the power:weight to start climbing out of the hole the way cats do, and 'hull speed' is the point at which one enters forced mode.

--Glenn

Spot on Glenn !

Wouter

As stated this is a foam core 18' version of the Pater Tiger and it is already a fast boat...I am not widening the boat as this will induce pitch not lessen it.
It would give me more righting moment with two "weights" strung out the side but this would push the lee hull down into the water more creating drag and the whole idea is to eliminate as much drag as possible by having the boat plane rather than be 'force moded".
The boat feels like a far less stressed platform than say the Taipan or the Nacra and that has a direct affect on my attitude in that it "feels" a lot safer at speed.

Who says that the drag associated to "forced mode displacement" is higher then the drag incurred by planing ?

Or if you will, are Tornado catamarans faster or slower then 18 foot skiffs while carrying less sail area ?

Without some dependable data we're all (me incl.) just guessing here and that isn't science.

Wouter

I am going to go out on a limb here Wouter and say that a hull of equal dimension, shape etc being forced through water has more drag than that same hull planing over the top of the water.

That is why that hull traveling through water needs more power to make it travel....hence the word "force" in the description "force moded".

In regards to the T traveling faster than the skiff it may be that the huge rig and wings and extra crew etc of the skiff create MORE DRAG via windage than the T.

Really, is that why we always rake the I20 crazy back for distance races and when we thing we're going to have big weather? Hu?... I never knew

[sarcasm off]

moving the weight and the CE aft helps survivability in big air.

Sorry Warbird but subjectively "observed reasoning" without empirical testing will invariably lead a person to incorrect conclusions, particularly when applying “low” speed hydrodynamics with aerodynamics interacting on an object at the boundary layer between the two – it is just not as simple as it “may” seem without applying the correct maths AND actual objective testing any/all theoretical results.
(Slightly off subject but question for Wouter – are you by any chance familiar with the “theory” and the maths that is being applied to research being conducted into “hyper-cavitation” for submerged “missiles” (formally called torpedoes) at present by the military?)

what about the 1 where the torpedo forces out steam? from it's skin so that it effectively eliminates almost all of the skin drag! kind of like air hockey i guess

cut from the bbc webpage
"The new missile, called Hoot, or Whale, could be deployed on Iranian ships in the oil-rich area, which is home to the US 5th Fleet.

No warship can escape from this missile because of its high speed

It is said to travel at 360km/h (233mph), three to four times faster than most conventional torpedos."

Don't be sorry Darryl, I understand what you are saying but we are not talking "missile science" here as I think (without checking google) the weapons you're are talking about are trying to create a "cushion" of air around the submerged projectile so the hydro drag does not exist and the missiles can travel mach 2 under water.
This science has been worked on by the Russians for two decades and they "may or may not" have it.
Like the scram jet engine it might finally come to fruition but not in an obvious way for the beach cat back yard.
So a truly erroneous avenue for what I am doing which is simply setting up a beach cat that planes easily and is predictable sailing above 20 knots.
In that area, as I suggest to Wouter I think a planing hull will go faster , easier than a submerged, wave piercing hull. I think that because I think the planing hull wil have less drag than the semi-submerged hull.
I am happy to be wrong about that and I will provide results here.

I spent a lot of time around science when working in the Auckland Museum. What I observed was that science bends and scientists are often have to back track. When they do they cover their butts by pretending they really knew what the problem was all along and just had to find some "empirical proof".
Science has its drawbacks as sometimes it is about what you don't know you don't know like Einstein not believing in the expanding universe theory and fighting until he died against it even the genius can be wrong.

You never got back to me about the foiled rudders by the way.

Not that it helps when you try to apply the results back to sailing, but since an engines thrust is likely below the center of drag you shouldn't be speed limited by the bows pitching down.

It would be better to have Jacob's Ladder problem, controlling lift.
http://www.cobrakite.com/jaclad.html

John

I'm aware of it and have read some articles on it but I'm not familiar enough with it to be knowledgeable about the math and physics applied.

But I always did feel that it bore strong resemblence with a ship hull design of the earlier 20th century. Here a normal but rather box like cargo ship hull had wide trenche all along its keelline that was filled with air and kept under pressure. This meant that a very large portion of the "wetted area" wias in fact between this aircushion and the water which lead to a lower drag overall. This idea was tested by never fully persued.

Wouter