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Spinning in Circles
http://www.hobie.com/forums/viewtopic.php?f=26&t=36540		 Page 1 of 2
Author:  Tom Kirkman [ Sun Jul 03, 2011 11:18 am ]
Post subject:  Spinning in Circles
Took the new Revolution out on the water today for a maiden voyage. Learned something very interesting, and somewhat odd.

First, with the standard Mirage Drive fins it was easy to get 5MPH, but you really had to move those things. Easy cruising was about 2.5MPH - you could do that for hours if you wanted.

The ST Turbo fins could get 6.8MPH with hard pumping and some good effort. But what was really nice was the easy cruising speed of 3.8MPH which I could keep up for hours. Very slow cadence, easy to do. Tremendous for a long cross county cruise.

Now here’s the odd thing. I wanted to see how the Revolution would paddle. I removed the Mirage Drive and retracted the rudder. Paddling resulted in a pretty swift speed, but the instant you stopped paddling, the boat would turn sharply to the right and make a complete, tight circle. My buddy also tried this and got the same result. Any time you paddled and then tried to get a little glide from your stroke, the kayak would wheel to the right and turn a complete, tight circle.

Interestingly, if you use the Mirage Drive and retract the rudder, the boat will spin to the left and turn circles in that direction.

So I’m guessing the hull is designed in such a way so that it naturally wants to turn right in order to counteract whatever torque the Mirage Drive is creating to the left.

The odd thing, is that looking at the hull there is nothing to indicate that it would do anything other than glide straight ahead while paddling. But it won’t - it simply turns right and turns tight little circles. So my hope that it would turn out to be a great boat for all uses - including paddling, has been for naught. It will not travel in a straight line unless you seriously adjust your stroke or use the rudder to counteract the boat's natural tendency to go sharp right.

Has anyone else paddled their Revolution and noticed this same tendency?
Author:  SteveLIBS [ Sun Jul 03, 2011 12:57 pm ]
Post subject:  Re: Spinning in Circles
I don't have a revo, but if it's not shaped to turn like that - could it possibly be weighted somehow to turn like that?
Author:  Tom Kirkman [ Sun Jul 03, 2011 2:25 pm ]
Post subject:  Re: Spinning in Circles
We couldn't find any weight or anything else that would make it wheel so sharply. It did so under so much force that I initially thought the rudder had flipped down and was set at far right position. It wasn't, however. The hull simply wants to wheel hard to the right. So far, in fact, you can get out of the boat and just give it a forward shove and it will spin a circle and end up just a few feet from where you're standing.

I don't think it's an accident - although I see nothing about the hull shape that would cause this, I feel sure Hobie engineered the hull to do this in order to counteract the tendency of the Mirage Drive to make it turn hard left. The rudder might not be able to effectively steer the craft otherwise.
Author:  CurtnAz [ Sun Jul 03, 2011 6:06 pm ]
Post subject:  Re: Spinning in Circles
Maybe it's a safety measure. If you happened to fall out, the boat would flip around and come back to you :D
Author:  Tom Kirkman [ Sun Jul 03, 2011 6:14 pm ]
Post subject:  Re: Spinning in Circles
It certainly would, but I think it was designed this way for a different reason. Just not sure what it was.

I'm already working on a new rudder that would allow me to use the boat, with paddle, on shallow rivers where the Mirage Drive can't be utilized. It will require some type of rudder or skeg to keep the boat moving fairly straight.
Author:  Roadrunner [ Sun Jul 03, 2011 9:42 pm ]
Post subject:  Re: Spinning in Circles
Most Hobie Mirage Drive hulls are directionally unstable when going forward. Your boat should spin in either direction, once the motion is initiated. Hull performance and handling with Drive and rudder are design elements; rudderless tracking is not. The bow has skeg-like properties which "trip" the boat so to speak, while the skegless stern is free to slide around (without the rudder). The forward position of the drag-inducing drivewell exacerbates the problem. If you want to go straight without your rudder, your boat should track much better backwards. You'll notice the Revo's paddling equivalent (Quest) has some small but significant changes to the hull and is considered a very good paddler. But alas, it doesn't pedal at all!

Put your rudder down. If you want less rudder, use a hack saw -- they modify nicely. Better to adapt your paddling style IMO. 8)
Author:  Tom Kirkman [ Mon Jul 04, 2011 4:14 am ]
Post subject:  Re: Spinning in Circles
Thanks, this is what I was thinking after paddling the boat - it's not an accident.
Author:  Spinfisherbob [ Mon Jul 11, 2011 8:15 pm ]
Post subject:  Re: Spinning in Circles
It is very easy to lean to one side or the other to turn a Kayak, surfboard or a power boat. I surmise that few of us sit exactly on center, even a rod holder on one side would be enough to explain this phenomena...no worry
Author:  Tom Kirkman [ Tue Jul 12, 2011 8:03 pm ]
Post subject:  Re: Spinning in Circles
Oh no - we're not talking about a tendency to track to one side. I'm talking about a hard about to starboard. A quick and full circle.
Author:  CurtnAz [ Wed Jul 13, 2011 11:25 pm ]
Post subject:  Re: Spinning in Circles
Did ya see that Hobie unveiled a new, shorter, faster than the outback, Revolution :D Being intended for smaller lake access, etc; I wonder if it would turn....
Author:  Spinfisherbob [ Sat Jul 16, 2011 5:56 pm ]
Post subject:  Re: Spinning in Circles
Tom Kirkman wrote:
Oh no - we're not talking about a tendency to track to one side. I'm talking about a hard about to starboard. A quick and full circle.


It is possible it warp a Kayak by hanging it in a warm garage for extended periods. Leaning it end up in a corner might over time and temperature changes might also give it a "set" that produce your hard trun,,,,,,,,,,,, How do you store it?
Author:  Roadrunner [ Sat Jul 16, 2011 7:00 pm ]
Post subject:  Re: Spinning in Circles
Spinfisherbob wrote:
Leaning it end up in a corner might over time and temperature changes might also give it a "set" that produce your hard trun,,,,,,,,,,,, How do you store it?
No, it's in the design. Borrow a Revo and you'll see what Tom's talking about. This may or may not happen with your Outback -- different hull concept. :wink:
Author:  Spinfisherbob [ Sun Jul 17, 2011 5:01 pm ]
Post subject:  Re: Spinning in Circles
Roadrunner wrote:
Spinfisherbob wrote:
Leaning it end up in a corner might over time and temperature changes might also give it a "set" that produce your hard trun,,,,,,,,,,,, How do you store it?
No, it's in the design. Borrow a Revo and you'll see what Tom's talking about. This may or may not happen with your Outback -- different hull concept. :wink:


Cool, just posting my 1 1/2 cents....learning new things never ends....will try a Revo when I get the chance.
Author:  Tom Kirkman [ Sun Jul 17, 2011 5:13 pm ]
Post subject:  Re: Spinning in Circles
It's a brand new boat - straight as an arrow.
Author:  Spinfisherbob [ Sun Jul 17, 2011 7:10 pm ]
Post subject:  Re: Spinning in Circles
Gotcha....as a boat builder for Viking Yachts, Ocean Yachts and Bimini Marine we were very careful about a freshly molded hull...throughout the building process. During water testing, even with all the care that was taken, some boats had trim problems. That's my history...I believe you guys when you tell me the Revo is balanced so close that when power is taken off abruptly ....it spins. I was just looking at the spinning as a one off unique phenomena. Learning never ends :D
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