s.w.a.t.h. kiteboat - is this possible?

[captiankeyboard]

hello

i am thinking about designing the boat attached

my knowledge is limited and i cant work out

1 - the pulling force of kites

2 - the drag of the bulb keel

just to begin with.

i would love for more knowledgable members to point out

the limits of such a design.

it would be for deep water so draft is not that important.

thanks

[Munter]

It looks like the purpose of the moveable weight is to keep the bulb and fin upright. Why is this so? Most "hull-less" designs I've seen combining a kite with a hydrofoil (they go by the name hapa I think) work with the strut inline with the pull of a kite so that no moveable ballast system is required. You've effectively got the kite at the top of a mast and your ballast is there to keep the mast upright. With a kite this is no longer necessary.

One problem with a vertical strut like that without some form of foil perpendicular at the base of the strut is that it would tend to get lifted out of the water whenever the kite powered up. The low change in bouyancy that would result would mean it would be lifted up very easily.

Have a look at the following link which shows the more conventional arrangement.

http://escento.com/html/ks2000.html

There are a few other hapa links out on the internet but I can't find them at the moment.

[Guest625101138]

It is difficult to get something like this to be stable. The majority of the drag occurs on the bulb under water while the thrust is well above the surface. This tends to tip it over. Your balance weight would likely have limited ability to right it. If it is heavy then it will simply float balance weight down. You need some sort of hull at the surface to give it a stable reference.

The attached photo shows a submerged buoyancy craft that is stable in operation providing you do not accelerate too fast. Looks fine on paper. Trouble was it took me 2 hours to work out how to mount it and I got dunked numerous times trying. What I did learn is that you need to have the submerged bit about 3D under the surface to effectively eliminate wave drag.

I can give you design parameters for drag and thrust so you can determine likely performance.

The optimum shape is an elliptical nose and parabolic tail with a fineness ratio around 8. My submerged part is about 7ft long and 1ft diameter.

For it to work you probably need a lot of buoyancy in the keel portion. The kite will tend to lift as well so the thing will travel higher when under way.

You need to do a full force equilibrium on the thing to see if it is stable.

Rick W.

[water addict]

What is the purpose of the vessel? Are you intending to carry cargo, weapons, or people?

[captiankeyboard]

thanks for the replies

i want to design the boat to carry one person for coastal sailing in the widest range of sea states.

i dont want a hydrofoil because of the sudden loss of lift and hence speed.

i would rather a swath type craft with a contant waterline.

draft no more than 6 meters.

i want it to be fast

You've effectively got the kite at the top of a mast and your ballast is there to keep the mast upright. With a kite this(movable counter weight) is no longer necessary.

munter would this mean that the boat without the counter weight would operate at a list or upright? and what would limit the list if there is one? etc length of submerged keel, weight of ballast in bulb, foil section of keel, power of kite etc.

i would rather not have the counter weight and keep it as simple as possible.

The majority of the drag occurs on the bulb under water while the thrust is well above the surface. This tends to tip it over

.

Rick i thought this might be a problem. i did a basic calculation of the horizontal foil tailing the bulbat speed and the force i got was massive and thought this would stabalize pitch? rick could you also send me the drag and thrust parameters thanks janderson22_1@hotmail.com

One problem with a vertical strut like that without some form of foil perpendicular at the base of the strut is that it would tend to get lifted out of the water whenever the kite powered up

i also thought the upward pull of the kite would easily dislodge the bulb.

would it be better to attach a perpendicular foil to the base of the keel? would this also stabalize pitch when powered up? is this idea limited because of the underwater volume needed to achieve bouyany?

everyone welcomed to responed as i really need to know if this is possible before i invest alot of time gaining the knowledge to figure out it isn't

thanks

[TheUnlogicalOne]

I have no real information to add, but I saw this video some time ago. It is a similar set up, although not quite the same. It uses foils with control surfaces to counteract the forces from the kite.

An understanding of french might help.

http://youtube.com/watch?v=1tEw_mlUh7g

[Guest625101138]

Rather than going into the calculations I will give you some parameters.

Lets say you want to do 20kts and the total weight of the craft and rider is 135kg.

The drag on a single submerged hull will be 27kgf it is 3 or more diameters below the surface and the optimum shape. This is not a lot if going directly down wind and drag and thrust are align. Once reaching the forces go up because you have to resolve into sideways and forward components. They will still be manageable. Maybe need a winch for long hours to easy the pressure.

The problem is you have to get going. The buoyant bulb is always fighting to get to the surface unless you can keep the weight directly above it.

The only way I could see it working is having wide spanning outboard hulls something like I did on the yellow thing above.

Dynamic stability is no use until you have speed. You then need to get very clever with control surfaces.

Another way to reduce stabilising force would be to shift the point of attachment of the kite so it was always in line with the drag. This could be done using a series of control line attachment points around the bulb. Each line will contribute drag though.

The yellow boat was like riding on a big cushion. It did not respond to the surface directly under the seat so there is no doubt swath craft are soft riding. The problem is making them inherently stable.

Given that you will have a huge amount of force available from a kite you could consider say 4 widely spaced submerged hulls. Going to four hulls having 1/4 of the displacement will increase drag to 38kgf but now the boat is inherently stable. You could sit on a pod in the middle that rests just above the surface. Once the kite loads up the thing will lift and you will ride above the surface. The tow point could be moved around by having draw points on each hull. Each hull would be mounted from something like a 150mm chord NACA0020 section. Span may be 10m wide and 20m long. Hulls would be 180mm diameter and 1.4M long.

The drag coefficient for a kite going directly down wind is say 1.1 so you can determine the size of kite. Reaching will depend on the shape. If you want to point at all you need something like a parasail. The lift coefficient for these might get as high as 0.8 but I have not studied them. You could always use a solid foil kite made from CF.

Rick W.

[captiankeyboard]

the unlogical one

L'aile d'eau is it

it just needs a chair on top above the water

would anybody like to explain the design and the control

system seen at around 1:58 on the youtube video

thanks for the help

[water addict]

At least part of the time for coastal sailing, you would likely need to go upwind, or at least close reach. You can't do this, at least very well, with a kite.

[captiankeyboard]

water addict

what angle to the wind would you estimate?

[Guest625101138]

Originally Posted by water addict

At least part of the time for coastal sailing, you would likely need to go upwind, or at least close reach. You can't do this, at least very well, with a kite.

This is convincing evidence they can make effective progress to windward:
http://www.youtube.com/watch?v=f1KQsWDGOI8
No reason why a modern high aspect kite could not go close to what a a fixed sail can achieve.

Rick W.

[Guest625101138]

The quad surfer in the above video is a bit like what I was describing with the four outboard swath hulls. Instead of planning hulls it would have the swath hulls but at much larger spacing. Would be test structurally but not impossible with modern materials.

Having a control line connected to each hull would allow the line of force to be directed in line with the resistance so the thing runs flat.

Rick W

[captiankeyboard]

in relation to L'aile d'uea(mastless boat) found this link

http://en.wikipedia.org/wiki/Paravane_(water_kite)

[eponodyne]

Originally Posted by water addict

At least part of the time for coastal sailing, you would likely need to go upwind, or at least close reach. You can't do this, at least very well, with a kite.

I have no idea why, 12 years into development of kites for boardsports and landsailing, this myth continues to perpetuate. People, please do a little research before you post something that is demonstrably and provably untrue. Please.

I'm not sure the SWATH is the best bet for a kiterig-- and 6M draft? For a coastwise rig? Planning on towing a dinghy?

[captiankeyboard]

a bodyboard actually

the 6 meter draft was just a limit

anyhow i would like to understand how this thing works

http://youtube.com/watch?v=1tEw_mlUh7g

and put a pod with me in it in between the kite in the water and the kite in the sky - only joking but i would like to understand the l'aile d'uea