Rave V Foiling Trimaran.

[mcm]

That windward sail canted to leeward could add some downward force and increase the RM a bit.
And perhaps that leeward sail that's canted to windward could add some opposing lift on the lee side and also increase the RM a bit.
I'm thinking of the canted rig on sail-rocket.

But how are these amas going to react with these forces acting through them instead of the main hull ?
Are they going to be competing with each other and difficult to balance ?
Will they increase the torsional loads on the beams ?
Any opinions ?

 

[Doug Lord]

Rave V

Here is a presentation made by Larry Knauer at Foiling Week-detailed and very interesting. Thanks to Brian Eiland for the video!
https://www.youtube.com/watch?t=228&v=JD5-shtZalY

 

[brian eiland]

I think it is pretty neat that the foils are all 'within' the beam of the vessel, and that they can be completed retracted up.

They appear to be pretty convinced that those 'sonic tubes' will eliminate a lot of the drag loses around the converging foil tips of the "V' formation,....and the tip of the rudder blade in lieu of a T foil tip.

 

[Doug Lord]

Rave V

Frankly, I hope he's right about the "sonic tubes" but I'm not convinced.

 

[lucdekeyser]

His explanation sounded quite cogent. I presume the same principles are at work with tunnel fins.

 

[Doug Halsey]

In the video, from ~14:00 to ~15:00, he talks about the importance of Reynolds numbers (Rn) & how this boat's Rn is similar to what's found on transonic aircraft. He uses that to justify the selection of a supercritical airfoil section for the foil. He says that Rn at 20 knots is between 20 & 25 million. Later he gives the maximum foil chord as 1 foot.

Here's my calculation (in English units):
Using Speed = 20 knots * 1.688 (ft/sec)/knot = 33.76 ft/sec
Chord = 1 ft
Kinematic Viscosity (water at 15Deg C.) = 1.23/10^5 ft^2/sec
Rn = Speed * Chord / Kinematic Viscosity = 2.7 million

Did somebody get a decimal place wrong?

 

[Doug Lord]

Rave

Doug, what is your opinion of the "sonic tubes"?

PS- good catch in your post above-I completely missed it.

 

[Skyak]

In the video, from ~14:00 to ~15:00, he talks about the importance of Reynolds numbers (Rn) & how this boat's Rn is similar to what's found on transonic aircraft. He uses that to justify the selection of a supercritical airfoil section for the foil. He says that Rn at 20 knots is between 20 & 25 million. Later he gives the maximum foil chord as 1 foot.

Here's my calculation (in English units):
Using Speed = 20 knots * 1.688 (ft/sec)/knot = 33.76 ft/sec
Chord = 1 ft
Kinematic Viscosity (water at 15Deg C.) = 1.23/10^5 ft^2/sec
Rn = Speed * Chord / Kinematic Viscosity = 2.7 million

Did somebody get a decimal place wrong?

I did it in metric, 10C water and get 2.4 million for 20Knot, 3.6M for 30kn.

So adjusting for temp. I agree with you. There is a formula for pipes but again it is still an order of magnitude off.

I was very intrigued by the video. He sounds like he knows what he is talking about. The one thing I can not get past is the high lift he talks about getting from the tube -I can't help thinking that you need to sweep a wider section of water at that speed to get the force he needs -conservation of momentum. His comment about high Re made me think he might be onto something I never learned because I don't pay attention to 'supercritical' -they just don't apply to small sailboats.

This seems like something we could test with a piece of PVC tube held out of a car window at 70.

 

[Doug Halsey]

Before seeing this, I wasn't familiar with anything called a "sonic tube." However, it seems to be similar to what I know as a "ring-wing," which does have smaller induced drag than a planar surface with the same lift & span. Of course, it also has more wetted area & I haven't done any calculations comparing the totals if you added the induced drag & the viscous drag. But if his calculations are based on a Reynolds number that is an order of magnitude too high, then he might have reached an incorrect conclusion.

The apex of a V foil is a messy area, though & I don't want to speculate how its drag would be affected by adding this device.

I'm more concerned with what it will do to the stability of the boat. A visual at 18:15 in the presentation says that at high speeds, 80% of the lift comes from the sonic tube & not the V. I have my doubts about that, but if true, it would be similar to adding an extra submerged foil below the V, so the lift wouldn't change much when more of the V comes out of the water. Sort of defeating the purpose of a surface-piercing foil, in my view.

He is correct that theoretical flowspeeds are higher at the apex of a V foil than at the midspan of a planar foil having the same lift and span. And they will be higher still if the V foil is flying too high & has an even smaller span. He's also correct that this can lead to cavitation at lower speeds than we would normally expect. (I have some GoPro footage that I think shows one of Broomstick's foils cavitating at only slightly over 20 knots. I'll edit a short clip of it & post it when I get a chance.)

 

[Doug Halsey]

I have some GoPro footage that I think shows one of Broomstick's foils cavitating at only slightly over 20 knots. I'll edit a short clip of it & post it when I get a chance.

I'm going to post this video in a new thread in the Hydrodynamics & Aerodynamics subforum, since there might be some people who would be interested & wouldn't see it here.

 

[Doug Lord]

Rave V

Well, the boat has been launched: http://www.sanduskyregister.com/Government/2015/11/04/Sandusky-produced-sailboat-hits-the-water.html

More here: http://www.windrider.com/blog/rave-v-in-the-water-102515/

 

[Skip JayR]

hm.... on first moment, just as spontaneously feedback I'd have to say: It does not look sexy. As the pilot looks like being sandwiched between the central hull walls. Is it the proto-type ??? Windrider should pimp the hulls with a "happy & cool" airbrush. The dark "military grey" main hull does not promise "performance". - And the logo in the sails isnt very attractive, too.

For now it looks very boring. And I'd expect at least a 2-seater (version), too.

Let's see what the videos will show.

 

[Doug Lord]

Rave V

Rave V sailing video:
https://www.youtube.com/watch?v=Zf2jTj1kwhE


Rave V tow testing:
https://www.youtube.com/watch?v=OVpXz_maoio

 

[Doug Lord]

Rave V

From the newsletter: http://www.windrider.com/blog/rave-v-ongoing-on-water-testing/

What we learned and the tweaks we are making:

1. With the twisting in the akas we need more torsional rigidity. We will switching from 2.5in tubes and going to a custom D profile. This D profile will still allow us to telescope the amas in and out, but will provide more stiffness.

2. The rudder foil was too small, but the tubes on the main foils are just right. We will be going back to the original design of a 6in tube on the rudder foil, but keeping the 4in tube on the V-foils.

3. Sail plan was aggressive. We found that with the 26ft masts and the sails, we had too much sail area. The boat sailed better when we reefed the sails. We will be decreasing the mast length from 26ft to 23ft and decreasing the sail area.

4. The RAVE V is fastest on a close reach. Unlike the WR17, the RAVE V is fastest when sailing closer to the wind. The other interesting thing to note here is that it points about 15degrees higher than the WR17

5. Freeboard of the mainhull is too much. We will be removing between 4 and 6in of freeboard from the production boat. This will give us better clearance over the water, helping to reduce the effects of hitting waves.

6. Lowering the mainhull side V foil. To get the boat out of the water sooner and allow it to ride higher over the water, we will be lowering the main hull connection point of the main V foils. This will put about 10 more inches of foil into the water right off the bat.

7. Fixed angle of attack on the rudder. Our prototype has an adjustable rudder, but we have found that about 6degrees of angle of attack on the rudder is about perfect for all conditions. For simplicity we are looking at keeping it a fixed position instead of having it adjustable. This will mean that while sailing, you won't ever have to touch the foils, the only thing you will need to do is trim the sails and steer the boat.

 

[Skip JayR]

come on guys.... point 3 is not amusing:

3. Sail plan was aggressive. We found that with the 26ft masts and the sails, we had too much sail area. The boat sailed better when we reefed the sails. We will be decreasing the mast length from 26ft to 23ft and decreasing the sail area.

Why not overlet it to the people to sail "smoothly" with a reef, and then have the option to sail an overpowerd boat with fully sails size ? That would give much more fun.