100% RE driven: across the Atlantic Ocean in less than a week

[renvistec.com]

Traveling across the Atlantic Ocean on a yacht purely powered by renewable energy sources, mainly wind, should be possible in less than a week!

According to the concept, such a yacht would be powered

a) primarily by kites achieving high speed (planing) mode at strong winds,
b) additionally by electric engines supplied by (solar modules / generator charged) batteries, if there's no or little wind.

For a), kite control technology (e.g. as used by SkySails*-*Home en ) would be necessary.

You find all details at: Kite yacht

I would like to get your opinion about the concept and my draft calculation. (Feel free to download the .html, open it with e.g. Excel and play around on your own).

Any feedback will be highly appreciated!

Thanks and regards,
Hans-Peter

[Cloxxki]

Very cool race idea.

Not large enough kites, you say? Have you seen the kites used on massive ocean freighters? Those are used to cut down fuel consumption by up to 20%.

Kite assisted vessels are not a new idea. You vessels may want to aim a bit quicker than the 40kph or so of freighter.
Also, I already believed freighters could "do" the Atlantic in 5 days. 40kph, 24h/day, it adds up. Actually, it multiplies :-)

[jibbguy]

Fascinating concept, but it's more limited than it at first looks

You will be subject to worse problems than the old "square-riggers" had, in regards to vessel & wind direction ("pointing up into the wind"). I am strongly suspecting that the kite cannot trail behind the beam (travel more than 90 degrees to the vessel's direction), or it will try to push the vessel "backwards".

A modern "fore-and-aft" sail works more as a wing, imparting aerodynamic "Lift".. That is how it can impart forward motion when heading into the wind (not directly into it actually; but up to about 30 to 40 degrees off of the wind depending on the rig and boat). In the case of the kite, it is a simple mechanical force load that is put on the cable (no different than being towed by another boat), and the "wing" aerodynamics that allows operation into the wind is missing.

So the direction of the wind in relation to the vessel is greatly more important here than with a standard "Marconi-rigged" sailboat.

In fact the actual "angle of attack" to successfully use the kite would be less than "90 degrees to the beam"; since the forward speed of the vessel must be vectored with the wind speed to come up with the actual maximum angle to the wind that will be allowed.

So instead of being able to use it in an arc of "180 degrees" (port beam to starboard beam), with a wind of say 16 knots and a hull speed of say 8 knots, the angle of allowed travel would be approx. "120 degrees".

Unlike a modern sailboat, which under certain conditions can sail up about 10 to 15% FASTER than the wind, a kite system will never allow speeds exceeding the wind.

However on the other hand, the ship-sized unit claims "5 times the power of a standard sail". So when the wind happens to be "going your way", it is very effective and powerful

[renvistec.com]

modified idea

...
I am strongly suspecting that the kite cannot trail behind the beam (travel more than 90 degrees to the vessel's direction), or it will try to push the vessel "backwards".
...

Yes, of course, the kite must be be before the beam on the lee side to push the ship forward.

...Unlike a modern sailboat, which under certain conditions can sail up about 10 to 15% FASTER than the wind, a kite system will never allow speeds exceeding the wind.
...

O.k., as I did not consider this, it seems to me that we should leave the concept with a (large) vessel moving at planing speed. Thus we're restricted to displacement mode cruising (unless for very small units, like kitesurfboards).

Let's modify the idea a little bit: the kite is flying close to the vessel's zenith - before the beam to ensure forward motion, controled in a way that it's only a little bit on the lee side. This means the kite also works as a wing with an aerodynamic lift, mainly like that of a plane, i.e. towards the zenith.

The vessel then will move with the major part of the hull above the water -actually, at powerful winds, only the centerboard and the rudder will be in the water.

Thus I assume kite powered motion forward should be possible even with a wind angle of more than 120 degrees. Shouldn't almost 180 degrees be usable that way, if we additionally engage electric engines (propellers) at wind angles
- between 0 and 30 degrees,
- between 150 and 180?

[jibbguy]

Yeah, that was my thought too at first and why i mentioned the limitation of wind speed; as many new prototype designs of catamarans are now using Hydrofoils to eliminate Hull Speed restrictions and so go even faster. However, this works on a big Cat mainly because of the fairly traditional sail plan that can allow them to reach speeds of 30 Knots in a 25 knot wind

Remember that with a "Hobie Cat" or similar catamaran, when you are going the highest possible speed you will be very close-hauled into the wind because of the boat speed vs. wind vector; and the "wing" effects that happen at this angle to the wind is the only thing that allows hulls speeds greater than wind speeds. Lol and if in a Hobie, you WILL be getting wet

In order to plane up on the hydrofoil pylons, a high wind indeed would be needed for the 'chute (+25 knots). And as we know, high winds are always accompanied by high waves in open ocean, which are the enemy of hydrofoils; they cannot be effectively used in rough seas from what i have read about them (i guess this is the major reason the US Navy gave up on them).

Although on a protected bay or inland lake (with maybe less than 4 foot of chop), it would make a pretty cool sight to see a hydrofoil powered by a 'chute on very windy days. However, this brings up another issue, that of Control: We can always let the sheets go in a sailboat and head into the wind (or even "heave to"), and thus slow down fairly quickly (hehehe, but there are no "brakes" on a boat, as newbie owners find out all the time ). With this rig, there may need to be a quick-release mechanism for emergencies (otherwise the stress of suddenly turning sharply may break the cable or ring bolt that holds it, or cause some other havoc like a huge sudden heel and even a capsize)... And then there would be the problem of later recovering the 'chute as the thing is likely to then fly away

I would have to disagree about using it a little on the leeward bow to create "lift", there is no way i can think of to make this thing have any aerodynamic effect on the boat's hull similar to a traditional fore-and-aft sail... Like i said before, the imparted force will appear to always work like another boat towing you. I thought about using multiple "control lines" from either side of the 'chute mounted at various points on the deck, but this would just seem to divide the pull force, the result simply being the sum little different than having one force point... However this may need looking into further as a control method for collapsing the 'chute for slowing down quickly.

But i like the concept a lot as a really cool sport "super spinnaker" that when the conditions are right, can be deployed as a tremendous and exhilarating booster for speed. I agree stepped planing hulls like power boats will be required to best utilize it in smaller vessels; because as i am sure you know but many here may not, boats are always limited by their designed "hull speed" and exponentially greater power is needed to exceed that inherent hull speed... So adding it to a traditional monohull sailboat design with a hull speed of "8 knots" will not help much above that 8 knots, only stress the hell out of the ring bolt holding it

But living in a tourist area (FL Keys), and often seeing several incarnations of 'chutes & kites being used with tourist rentals & excursions ("Para Skiing" off a power boat, Kite Boarding, even powered ultra-light aircraft using them), i can imagine a catamaran sail boat maybe 16' long with seats for two, that uses the kite principal, and also has a sail or motor for going upwind. Tourists love "cool" stuff like that, and $100 an hour is not usual for such thrills The advantage over the others types is, less athleticism & skill would be needed and a guy and his wife or GF can do it together without risking life & limb