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hydrofoil at max speed limit

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edt
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Re: hydrofoil at max speed limit

Postby edt » Thu Dec 07, 2017 5:21 pm

Lots of theoretical arguments. What we need are kiters to head to Luderitz and try their hydrofoils on that channel. Has to be one of the scariest things you can do on a kite. Until then we can argue back and forth on the physics and not get anywhere.

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Re: hydrofoil at max speed limit

Postby Foil » Thu Dec 07, 2017 6:03 pm

edt wrote:
Thu Dec 07, 2017 5:21 pm
Lots of theoretical arguments. What we need are kiters to head to Luderitz and try their hydrofoils on that channel. Has to be one of the scariest things you can do on a kite. Until then we can argue back and forth on the physics and not get anywhere.
I don't think it's deep enough :D

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Re: hydrofoil at max speed limit

Postby plummet » Thu Dec 07, 2017 6:39 pm

Foil wrote:
Thu Dec 07, 2017 6:03 pm
edt wrote:
Thu Dec 07, 2017 5:21 pm
Lots of theoretical arguments. What we need are kiters to head to Luderitz and try their hydrofoils on that channel. Has to be one of the scariest things you can do on a kite. Until then we can argue back and forth on the physics and not get anywhere.
I don't think it's deep enough :D
Why do you need a channel? Find some flat chop with 40+ knots and as long at the mast height is longer than the chop your good to go for a speed run.

Now what would a speed hydrofoil look like? have any been made?

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Re: hydrofoil at max speed limit

Postby revhed » Thu Dec 07, 2017 7:19 pm

For sure most good speed places for "on H20" boards will not be deep enough for hydrofoils.
They like to be in as little chop as possible and due to high wind this means close to shore line.
But,
Here (France) as the fastest pilot lives, as well as many others, they are looking for more and more speed, MANY protos being built, tested as I type.
As noted I feel shorter STRUTS, smaller wings, stabs and young brave pilots will be looking to do dedicated speed runs.
Mark my words, 50 knots is not out of the question, in a few years.
R H

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Re: hydrofoil at max speed limit

Postby edt » Thu Dec 07, 2017 7:31 pm

They are dredging to 1 or 2 meters deep now. they used to only make the channel 10 cm or so deep but there were problems getting their record recognized so now they make the channel a lot deeper. If you have done speed runs on a hydrofoil you know it's much easier to prevent ventilation on flat water. Chop provides a problem that sometimes your mast can get ventilated at high speed. I mean it's the same for hydrofoils and sailboats, flat water is faster. Look at the sailrocket they found the flattest water possible even tho they were on hydrofoils. I am pretty sure the center of the luderitz channel is deep enough for a 1.5m hydrofoil, just don't go near the edges.

New records on hydrofoils are coming. It scares me just to think about it.

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Re: hydrofoil at max speed limit

Postby revhed » Thu Dec 07, 2017 7:37 pm

edt wrote:
Thu Dec 07, 2017 7:31 pm
they used to only make the channel 10 cm or so deep but there were problems getting their record recognized
Why?
R H

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Re: hydrofoil at max speed limit

Postby edt » Thu Dec 07, 2017 7:46 pm

This came out in 2008 right after the very first luderitz records when the channel was just a couple of cm deep. Now they had tried to make it you know exactly 50cm but the way they dug that channel it's very crude so it might be 50cm in some places 10cm in others and 100cm in some places. So they decided just to make it deep enough so that there wouldn't be any controversy so right now it's 1 or 2 meters deep which is enough for the speed hydrofoils that the french are building which for some reason I guess use a shorter mast than usual. By the way digging the trench this deep has indeed made the kiters slower than they otherwise would be so it has had an effect. The very first records at luderitz were in fact taking advantage of this "shallow water effect" to reduce friction.

* * * *


Explanatory notes on the WSSR Newsletter No 155..

There has been much debate about the attempting of sailing records in very shallow water. The controversy has only recently come to light because up until now the need for skegs on windsurfers made water depth self-limiting. However the high speeds being claimed by kite surfers has circumvented this as although they need to "edge" their boards somewhat to generate lift, at 50 knots and at deep wind angles, the edge doesn't run very deep. There was a real concern that unless some sensible ruling was brought in, a world record claim using water only as a lubricant was a possibility. For example, creating a record course by covering a large car park with a plastic sheet and then wetting it to a few mm depth. There was a general feeling that this stretched the aim of breaking records on "water" too far.

There is much anecdotal evidence about the positive effects on speed by the shallow water effect and certain published study including the effect on fast ferries when entering shallow water and using the effect to "unstick" seaplanes. However in order to obtain some hard data, the Council commissioned the Wolfson Unit of Southampton to prepare a paper on the specific subject.

Their conclusion of this detailed study was that the drag of a planing board is reduced when the water depth is less than the beam of the board, with a possible reduction of 50% in very shallow water of less than half the beam of the board. A water depth of 50cm would be deep enough to avoid shallow water effects.

It was agreed by Council that to introduce a ruling which would require the width of a board to be measured in order to establish the water depth would be impracticable and thus an overall 50cms depth has been introduced, as follows:

"Record claims will not be ratified when, in the opinion of the WSSR Commissioner, the minimum water depth over the whole course is below 50 cms"

It is believed that this depth of water negates the "shallow water drag reducing effect" but does not disadvantage the usage of existing courses that are protected and relatively free from current and waves.

John Reed.
Secretary to the WSSR Council

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Re: hydrofoil at max speed limit

Postby Foil » Thu Dec 07, 2017 8:18 pm

We need a much wider, a much deeper trench

Image

Image

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edt
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Re: hydrofoil at max speed limit

Postby edt » Thu Dec 07, 2017 8:39 pm

tks foil. Looks like it's only deep where the speed record is being done that's not enough has to be deep in the runoff too or you have some spectacular crashes. I have a feeling if they knew foilers were going to use it, they would deepen it a bit. Does it have to be any wider?

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Re: hydrofoil at max speed limit

Postby revhed » Fri Dec 08, 2017 8:28 am

edt wrote:
Thu Dec 07, 2017 7:46 pm
This came out in 2008 right after the very first luderitz records when the channel was just a couple of cm deep. Now they had tried to make it you know exactly 50cm but the way they dug that channel it's very crude so it might be 50cm in some places 10cm in others and 100cm in some places. So they decided just to make it deep enough so that there wouldn't be any controversy so right now it's 1 or 2 meters deep which is enough for the speed hydrofoils that the french are building which for some reason I guess use a shorter mast than usual. By the way digging the trench this deep has indeed made the kiters slower than they otherwise would be so it has had an effect. The very first records at luderitz were in fact taking advantage of this "shallow water effect" to reduce friction.

* * * *


Explanatory notes on the WSSR Newsletter No 155..

There has been much debate about the attempting of sailing records in very shallow water. The controversy has only recently come to light because up until now the need for skegs on windsurfers made water depth self-limiting. However the high speeds being claimed by kite surfers has circumvented this as although they need to "edge" their boards somewhat to generate lift, at 50 knots and at deep wind angles, the edge doesn't run very deep. There was a real concern that unless some sensible ruling was brought in, a world record claim using water only as a lubricant was a possibility. For example, creating a record course by covering a large car park with a plastic sheet and then wetting it to a few mm depth. There was a general feeling that this stretched the aim of breaking records on "water" too far.

There is much anecdotal evidence about the positive effects on speed by the shallow water effect and certain published study including the effect on fast ferries when entering shallow water and using the effect to "unstick" seaplanes. However in order to obtain some hard data, the Council commissioned the Wolfson Unit of Southampton to prepare a paper on the specific subject.

Their conclusion of this detailed study was that the drag of a planing board is reduced when the water depth is less than the beam of the board, with a possible reduction of 50% in very shallow water of less than half the beam of the board. A water depth of 50cm would be deep enough to avoid shallow water effects.

It was agreed by Council that to introduce a ruling which would require the width of a board to be measured in order to establish the water depth would be impracticable and thus an overall 50cms depth has been introduced, as follows:

"Record claims will not be ratified when, in the opinion of the WSSR Commissioner, the minimum water depth over the whole course is below 50 cms"

It is believed that this depth of water negates the "shallow water drag reducing effect" but does not disadvantage the usage of existing courses that are protected and relatively free from current and waves.

John Reed.
Secretary to the WSSR Council
:thumb:
WOW, this will be VERY hard to prove where I live one of , if not the first speed courses in he world as kite boarders often come very close to shore.
Not a prob for Foil boards!
R H


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