T or F? Mirage drive vs paddle kayak speed relative to length...

Didn't know know how to keep it short enough.

The question is do you lose less speed as you get shorter on a mirage drive yak vs a paddle yak?

I.e.  if I bought the shortst mirage drive kayak (sport?) how much better could I keep up with say an outback vs if I used my nine ft mini x.  I know it's kind of a "it depends" answer but generally speaking.  Seems like a lighter kayak might go faster even f it's shorter with a mirage drive...but that seems to go against conventional wisdom. 

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It's more affected with hull shape for the Hobies, then length.  In my opinion slowest to fastest would be:

Sport
Outback
Revo 11
Revo 13
Addy

The sport and outback have very similar hulls, and they aren't fast hulls.

My sailboat racing friends always told me longer is faster, but,

This guy: http://www.kudzucraft.com/articles/longboatmyth.php thinks that, at normal speeds, a shorter kayak takes less effort to push thru the water - its only at very high speeds the longer kayaks shine.  I'm assuming he compared the same hull widths.  Who knows if weight is a factor, but shorter kayaks are generally lighter.

  I agree with Lee's assessment that hull design, along with strength, is more important than length for us mere mortals.

As an old sailboat racer, I grew up with the saying that the boat speed is directly proportional to length of the waterline of the hull. I also agree that other factors like hull shape certainly has an impact on the speed. When I decided on what Hobie to buy for myself, it was between the Revo 13 and the Outback 12. I came very close to choosing the Revo, because it has the longer waterline and is a very sweet boat. I chose the Outback for it’s stability and it had more room for my stuff and frankly, I never felt my friends that chose the Revo were all that much faster.

I'm also suspicious that the blades on the mirage drive are like inverted sails that propel our kayaks through the water by the contractions of our most powerful leg muscles rather than gusts of wind over huge airfoil-shaped sails, They even have an adjustment screw that tightens the trailing edge on each blade like a sail trimmer tightens or loosens the leech and the luff of a sail, to select between more power or more speed.  Those folks at Hobie are very clever IMHO.

I'm also suspicious that the blades on the mirage drive are like inverted sails that propel our kayaks through the water by the contractions of our most powerful leg muscles rather than gusts of wind over huge airfoil-shaped sails, They even have an adjustment screw that tightens the trailing edge on each blade like a sail trimmer tightens or loosens the leech and the luff of a sail, to select between more power or more speed.  Those folks at Hobie are very clever IMHO.

Well put pops!

I thought hull speed was a function of aspect ratio - length/width. 

The higher the aspect ratio the faster the boat given equal power.

The short answer is yes, but the differences are not linear.  Lee nailed the order of peck

The Sport (at least with my fat behind in it) is WAAAAAY slower than the Outback and I believe that's a function of what demonick said (aspect ratio) It's so short and a wide that you run into your wave at pretty low speeds (3 knots?) l/w 3.89

I have the Adventure as I was looking for something that could paddle and get out of its own way (l/w 6.86) and it does. But at the loss of a fair bit of initial stability. No biggy, you just have to learn to paddle and  straddle it with your legs overboard for rock solid fishing. Standing is not going to happen (not for me at least).

 I thought the Revo should be a good compromise (so does Hobie apparently) and thumbed my nose at the Outback and "lesser" boats. That was until I got out on the ocean with a buddy in an Outback (l/w 4.38). I knew I was going to have to slow down for him.
Ahhhh, no.

His boat with the turbo fins had no trouble at all keeping up with me and with his sailing rudder, he could spin around his length. (The Adventure won't do that without a paddle) Then I made the mistake of borrowing his two Outbacks for a charter and that confirmed all my suspicions. Tons of useable deck space, initial stability of a catamaran, and it scoots along very quickly AND it does not weigh a gigaton (cough <pro angler>cough) so that one normal human being can put it on top of a car at the end of the day. The Outback still does not paddle worth a durn, but it does not have to. Its a pedal boat!

Slower than the Revo's and Adventure? Yeah, but just nominally. But its far more efficient than the Sport. Dang near as much usable real estate as the Pro Angler and more than 60 lbs lighter(!), the Outback, in my vaunted opinion*, is the best fishing boat Hobie makes. 






*worth about half of what you paid for it
 

I put turbos on my old sport at ORC and held my own. I put them on here when we got back and have been on the gulf, no sweat except the sport still has no where to put a large fish. Art

For completeness:

length/width

3.89     Hobie Sport
4.38     Hobie Outback
4.74     Hobie Revo 11
5.49     OC Trident 13A
5.86     Hobie Revo 13
6.97     Hobie Adventure

The short answer is yes, but the differences are not linear.  Lee nailed the order of peck

The Sport (at least with my fat behind in it) is WAAAAAY slower than the Outback and I believe that's a function of what demonick said (aspect ratio) It's so short and a wide that you run into your wave at pretty low speeds (3 knots?) l/w 3.89

I have the Adventure as I was looking for something that could paddle and get out of its own way (l/w 6.86) and it does. But at the loss of a fair bit of initial stability. No biggy, you just have to learn to paddle and  straddle it with your legs overboard for rock solid fishing. Standing is not going to happen (not for me at least).

 I thought the Revo should be a good compromise (so does Hobie apparently) and thumbed my nose at the Outback and "lesser" boats. That was until I got out on the ocean with a buddy in an Outback (l/w 4.38). I knew I was going to have to slow down for him.
Ahhhh, no.

His boat with the turbo fins had no trouble at all keeping up with me and with his sailing rudder, he could spin around his length. (The Adventure won't do that without a paddle) Then I made the mistake of borrowing his two Outbacks for a charter and that confirmed all my suspicions. Tons of useable deck space, initial stability of a catamaran, and it scoots along very quickly AND it does not weigh a gigaton (cough <pro angler>cough) so that one normal human being can put it on top of a car at the end of the day. The Outback still does not paddle worth a durn, but it does not have to. Its a pedal boat!

Slower than the Revo's and Adventure? Yeah, but just nominally. But its far more efficient than the Sport. Dang near as much usable real estate as the Pro Angler and more than 60 lbs lighter(!), the Outback, in my vaunted opinion*, is the best fishing boat Hobie makes. 






*worth about half of what you paid for it

From a bias Outback owner I couldn't agree more.

I thought hull speed was a function of aspect ratio - length/width. 

The higher the aspect ratio the faster the boat given equal power.

The ranges you give for your "aspect ratio" calculations for Hobies are quite narrow (and I guess the same can be said  for most kayaks and certainly for the various sailboat classes racing monohulls).  In fact, there are racing handicaps for mathematically determining the winners for different kinds of racing boats, competing in the same race, based on hull configurations.

I liked your calculations for the various Hobie models  and the aspect ratios hovered around the 4's and into the 5's, for the models I was interested it. My guess is that the same can be said for most fishing SOTS.
Now let's assume most of us agree that we like the 33 inch width of the Outback, but we might like a little more speed.  So if we build a Hobie that is the same 33" width, but 2 feet longer the Outback aspect ratio then increases to 5.09 (which is about a 16% faster, if we assume the aspect ratio is linear). That suggests that the simplest and least expensive route to getting more speed is by lengthening the hulls' water line.

    A 14 or 15 foot Outback Hmmmmmm....
 
    I'd like to see that happen.

 

    A 14 or 15 foot Outback Hmmmmmm....
 
    I'd like to see that happen.

But I would hate to have to lift it over my head to car top it.

I feel the outback is MUCH slower the revo. Granted I only spent one day on the outback, but I was unable to keep up with the revo and addys in the group. Another thing I don't like is that the cruising speed is near maximum hull speed. With the Addy a few fast hard kicks and you can add a mph or two more. The outback just bogs down and pushes more water.

On the other hand I've heard the PA 12 is faster than the longer Outback.

The tension screws on the fins are nice but I wish you could actually adjust them far enough to tension the trailing edge.

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The  oasis is as wide as an outback, but with the Revo hull shape, so it's fast and stable, but requires two people.

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