Kite propoulsed trimaran - open project

Discussion in 'Multihulls' started by macsnail, Dec 8, 2016.

  1. macsnail
    Joined: Mar 2016
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    macsnail New Member

    I am working since a longer time on a development of a kite propulsed trimaran. Recently we have performed some tests to estimate what performances can be reached when boat-kiting. I would be pleased with any comments and hints You all may have with this respect. Please see details on essepcially under "news". :)
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  2. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    Hi and welcome to the forum. I am interested in kite sailing large boats. Eliminating the expensive and tall rig could be a good thing. However I am yet to be convinced a kite is going to be safe, easy and cheap to use. The kite would not add much if any heeling moment like a regular rig and reduce the dynamic displacement instead of increasing like most rigs do. So a hull designed for this would be more efficient. IE a trimaran will not need 200% displacement floats and tiny ones would probably be good enough (notwithstanding wave capsize).

    All your vid seems to show is something just about anyone could do which is connecting up a normal kiteboarding kite to a small monohull in light wind so the lines are not ripped apart.

    Issues I see are:

    How do you raise and lower a kite large enough for a live aboard cruiser safely?
    How long will it take to do this?
    How do you account for various wind speeds? A new kite for each wind speed?
    Do you have concerns about running the kite/lines over if it falls in front of the the boat for various reasons?
    Do you need active kite sine-ing? If so how will it be done.

    Thanks, Dennis.
  3. DennisRB
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    DennisRB Senior Member

    I have just found the data you have recorded. Thanks for making this public. :)

    You compare a 15m kite to the normal 21m rig usually fitted to the boat. Its interesting that between 120-155 degrees without signing the kite is equal to the normal rig but much worse on most other angles. However with sineing it beats the regular rig considerably from 115 deg and deeper. Sailing higher than 115 its about 15% slower.

    So depending on the angled sailed it appears the kite needs to be around the same size or a bit smaller than the regular sail area. Thats a huge kite for a normal cruising catamaran. I can't see how this would be handled, but would love to see a solution.

    Try getting your hands on an old tandem paraglider (foil kite). They are up to about 45m2. Launching and retrieving would be interesting.
  4. macsnail
    Joined: Mar 2016
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    macsnail New Member

    Hi Dennis,

    Indeed You are fully right. The questions You are rising above are in most of the cases topics that need to be addressed.:idea:

    In the part 2 of my report (free available at "downloads") I tried to describe our general observations. In the part 3 all the measurements we performed are also assessed. I started the project as an OPEN PROJECT so all data will be public as well as anyone interested is also freely invited to join :). I can also supply raw data if someone would like to analyse any further :).

    A 15m² kite that we used, was simply dropped into the water and as soon as it drifted away to span the lines a typical water start was then easy. Similarly for the landing. The method is simple but possible for a relatively small kite. Moreover You always get it wet back on board :(.

    For the moment I do not have a better idea for the start. It will probably remain a delicate issue.

    You ask about the setting time. It is not very long. I assume all the hardware remains fitted to the boat (lines at the mast step). You need just to pump the kite and make sure the lines are not tangled. With lines on drums - further foreseen steps the untangling issue shall go smoother. Then You won't even need 5 minutes from the decision till "kite in the air".

    The kite size - yes, I think abt. 3 different kites (size) for different wind conditions would be a good figure. However one shall always be careful with too much. The kite gets the power multiplied by a factor of up to 10 when flying quickly in the power zone... Here a very efficient safety de-power / release is a must.

    Thank You for the idea with the foil kites. Indeed this is to be tested. For a foil kite i still need to find a way to start it from the boat.... Anyone have an idea???? ;).

    I would be glad for any input / comment to the project ;)
  5. DennisRB
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    DennisRB Senior Member

    That would not be easy. But not much about this idea is once you move up from regular kiteboarding size kites. The boat should be designed for it. IMO the best hull configuration for a kite boat is a stabilised monohull as they have the least drag but are still stable. I think the humble outrigger configuration is best for the following reasons.

    1: Only one small hull needs to be built so its easier, cheaper and more practical use of space.

    2: The large area between the main hull and the outrigger would be a good area to work with kites unlike the small areas between a trimaran main hull and each float.

    3: It has the least drag of all hull shapes for a given displacement (which still has stability). The tri form stabilised monohull is also very low drag but look at all the threads around the net. The smaller ones all seem to report handling issues due to the small beam between the large hull and small floats in various sea states. The outrigger would handle more like a cat with a wide beam between the main hull and the float. It seems a waste to build a regular trimaran style hull spacing, size and displacement when a kite boat has next to no heeling moment. But if you can get one for cheap which is highly likely as they are not worth much it would be a good doner hull.
  6. village idiot
    Joined: Dec 2009
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    village idiot Junior Member

    Looking at this thread with some interest.
    I have been sailing boats / sail boards / land yachts for the last 40 years , have been a very active kite boarder for the past 10 years . Have had a great deal of experience with both inflatable and foil kites.

    As mentioned there are definite pros and cons for both types of kites. To get something efficient and well developed performance and safety wise , you would have to go with a well known kite brand , someone who has put in the development and research.

    pros / cons

    Inflatables are safer when it comes to dropping them in the drink , they float as long as there is air in the bladder , a foil kite will be ok if relaunched fairly quickly , my experience if it in the drink more than about 10 mins , you have a massive sea anchor on your hands , if this happens on a boat that would pretty much be the end of that kite . Imagine a double skinned spinnaker , with cells inside full of water .

    The down side of the inflatables is that they need to be pumped up manually , the foil kite will self inflate , another issue with the inflatable kites is the reliability of the bladders , they are fairly robust in a kite surfing application , but when it comes to heavy yachts , not sure on the longevity of these , they need to be constructed light so the kite will fly, if a bladderer was to burst the kite won't fly , you would have to be very carefull moving it around on the deck and setting and packing up . If it was to drag across a shackle or a horn cleat , it would be finished,

    A down side to the foil kites are the dozens of lines they require for the bridals to support the kite, inflatable kites have minimal or no complicated bridals . Thesebridals are a nightmare when working with the kite on the deck and launching and landing ,

    Both have similar power and depower , foil kites are a bit more efficient , inflatables a little more user friendly.

    Not sure how to successfully launch and retrieve either a inflato or foil kite off a boat , you would need some type of mast ( maybe telescopic ) to raise to centre leading edge of the kite up , and once in position pay it out with some sort of winch system out on its 4 lines. And the opposite to retrieve.

    My choice would be a foil kite , because of the ease of inflation and the questionable reliability of the bladder system.
    Flysurfer are probably the leader in foil kite development , they make a 21 or 24m kite off the shelf , they also make a single skin foil kite , used mainly for snow kiting , if you could work out how to keep this out of the water this would be ideal .

    Other issue with a kite over a conventional rig is that the kite requires constant input , the conventional sails you can set them , cleat them off and go about your business , a kite needs someone flying it the whole time , some of the big ships which use kite as a fuel saver , have computers which automatically fly the kite.

    For a cruising boat your talking a hell of a lot of stuffing around .

    The application I can see these kites being used is like the big ships which use them . I can invisage and big power cat , like the ones you see fairly commonly getting around 35-50 footing ,the kite could be used for longer passages with favourable wind direction and strength to reduce fuel consumption .
    Another use could be for racing boats ect , if you were to break a mast or something , you could set one of these to help get you home.
    They take up bigger all room and are light.

    The application for an everyday sail replacing a conventional rig is a fair way off I think.
  7. rob denney
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    rob denney Senior Member

    I have been playing with kites on boats for a while. The biggest is 400 sqm on a 20m/66' monohull see attached. Adding a kite board kite to a boat is simple, particularly if you beach launch and reach back and forth. see

    Going bigger, kite management becomes an issue. The best kites are Peter Lynn kites. Self inflating with only 4 lines and auto zenithing. Release the bar and they fly stably overhead. Shorten one of the front lines and they fly stably on the edge of the window out to one side. This makes it possible to launch and retrieve them without needing a line winch. Attach the lines ~2/3rds of the kite width apart, hold up the middle of the kite and it will fill and fly stably. Ease the front lines and make sure the rear ones are loose. When it gets to full height, fly it as normal. Launch time is as quick as you can ease the lines without them going loose. The stronger the wind, the quicker it goes up. Lowering it is as quick as you can pull in 2 light-moderately loaded lines. A large deflate flap makes final recovery easy.

    Pump up kites have structural and aerodynamic issues above about 50 sqm, ram air can be as big as you like.

    Launching or retrieving any large kite from the water will be hard work. Took 8 of us half an hour when we dropped the big kite in the tide. Keeping the lines tidy is essential, but easy with large captive winches that do not carry flying loads. A reasonably competent flier will rarely if ever get a kite wet.

    Boat size kites fly in the stronger winds above 50m. They can be sine waved at speeds up to 4 times the wind strength, which is ~16 times the power. Consequently, one smallish kite can cover the entire wind range, if you are prepared to actively fly it. Accidentally sine waving a large kite will pull the fittings out of the boat unless some fuses are installed. These are easier to install with a PL kite. Sine waving is pretty simple, but as yet, not automatic, although everybody is working on this.

    The best boat type is a proa (double ended, same as a twin tip board) as tacking a kite can easily lead to serious sailing backwards problems. The kite attachment can be moved fore and aft for steering balance. A rudder is still required.

    The most advanced kite boat guys by far are Don Montague and Peter Lynn's Kite Cat. The kite pilot in the video is about (next week) to launch a 15m ocean capable kite powered proa which could also raise the bar.

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  8. Tiny Turnip
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    Tiny Turnip Senior Member

    This guy seems to me to have something rather good worked out. The attitude of the craft is perhaps a little tail down, and seems to dig in and churn up a lot of wake, but the kite forces counteracted by the foil is pretty neat.

  9. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Thanks TT-that's really cool-very clever idea for developing lateral resistance!
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