Ja valgplakater er fint materiale til mange projekter:) kan ikke lige se hvilken kandidat der fik æren som tip-loss-preventer hahah

We measured just once (7 km/h) when both (2x80kg) were onboard, so that was significantly slower than top speed. would guess 10-11 km/h was top speed. And regarding power usage the papers on the topic says about 15 % of total power is to drive the rotor, the other 85% is the wind - so well invested energy..

@@stigantonnielsen the trick is to use a wind turbine to get that 15% energy. maybe a Twisted Savonius Wind Turbine www.saltireserver.com/gx/vawt/PDFs/Board.pdf

HAHA, Yeah we should have painted some pattern to show the rotation clearly! Next time...

The rotation speed would need to be multiple times the windspeed to have the most effect, so a direct wind powered rotation is not so easy, requires at least some transmission and of course sufficent wind power in the first place. However, the problem is that in order to change direction for the boat (or when wind direction changes), the rotational direction also needs to be changes. That complicates things a bit mechanically if it was directly windpowered. So just having a battery that powers the motor is definitely a much easier solution.

С гребным винтом быстрее

Litterature suggest that the area of a sail equivalent to a cylindrical rotorsail is the diameter of the rotor x 4. Yes, inflatable rotorsail is interesting since the shape of an inflatable naturally converges to round. Maybe you already saw my video with a model scale inflatable rotorsail and this indeed holds the potential to be reefed easily.

One of the reasons rotor sails is not more adopted is the limited lift to drag. Sails can achieve much higher L/D coefficients.

Like a reversed propeller, with drag.

The video where we are testing the first version of the rotor shows a little more explanation.. kzfaq.info/get/bejne/gM5xn7p5uMveaWQ.html But in short, the cylinder rotates, driven by a motor. The wind passing by the cylinder flows around say two sides of the cylinder. On one side of the cylinder the surface moves same direction as the wind causing the wind to pass faster, whereas the other side surface moves against the wind direction causing more friction and slower flow. The faster flow means lower pressure which in turn means lift on the cylinder. The principle is referred to as 'Flettner rotor' and 'Magnus effect' if you would like to search for more info.

The max possible for the motor at this setup is 1000 RPM which is fast for this large a body.. but a rotor sail achieves good results at surface speed 3 times the wind passing the rotor. At a wind speed of 7 m/s and a circumference of 0,91m it is 23 rounds/sec which is 1380 rpm..so maybe not quite fast enough for the gusts that day..

@@stigantonnielsen There is an advantage of the decrease when a gust occurs. Points on the drag coefficient curve 0.0 1.2 ratio 1.2 at 1 ratio lowest 0.7 4 ratio 2.5 goes flat at about 5 around 3.5 this is for a Reynolds number 16000 for all the data and 32000 for the first three ratios at the higher Reynolds. the spinning cylinder lift coefficient about a 4 ratio at about 8.5 and for the higher RE ratio of 5 at a coef of 11. A sail will continue to create lift if it is not stalled which it would be for a gust as a ratio of the square of the velocity. Same square applies to the cylinder but the ratio decrease which lowers the coefficient as the square increases.

The spinning rotor compresses air in the region towards the rear of the boat.

This is using what is referred to as the Magus effect. The cylinder is spinning and air that moves past it (wind) very near it's surface will be slowed down on one side (the side moving against the wind) and sped up on the other side (the side moving with the wind - if the surface of the cylinder is moving faster than the wind). Air that is moving faster is at a lower pressure than air with the same properties moving slower. This produces a net force on the cylinder. If you imagine the wind coming from the starboard (right side looking forward) and the cylinder turning counter clockwise, the net force will push the boat forward. If course, as the boat gains velocity, the apparent wind direction will change - you still have to know how to sail.

Think like doing a back spin on a tennis ball.

De hecho se aprovecha el viento, y hay bastantes estudios sobre el tema, puedes buscarlo como efecto Flettner, para darte un ejemplo es lo que da la curvatura a una pelota en un tiro libre, la.ventaja de esto es la economía que produce para mover una embarcación, menos energía, ya se están usando en algunos barcos, para economizar combustible

@@raulramirez6074 obrigado pela atenção!