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Hull speed vs. max speed
http://www.hobie.com/au/en/forums/viewtopic.php?f=11&t=3864		 Page 1 of 1
Author:  Roadrunner [ Wed Jun 14, 2006 12:09 am ]
Post subject:  Hull speed vs. max speed
It's interesting to look at Hobie's different hull designs and see how they develop speed.

The older generation Mirage Tandem has a waterline length (LWL) of about 13.5 feet for a "hull speed" of 5.7 MPH. In the picture below, OffRoad and some deadweight are pushing it pretty close to their max of 6.8 MPH, beyond which it refused to go. It exceeded its hull speed with the help of a couple of pair of Turbofins but, as you can see, it is stuck in its own "wave trap".
Image

The Adventure uses a different hull design and is more successful at avoiding the issue. With a LWL of about 15.5 feet, the "hull speed" is 6.1 MPH. With only 40% of the power used to drive the tandem (one set of standard fins), it can top 7 MPH; with a set of Turbofins, it can do at least 7.8 MPH and not look like it's stuck. As pictured below, The Adventure is running close to its hull speed. Notice how little water it's pushing!
Image

Aside from a small turbulance behind the rudder, you'd hardly notice it was moving.

It would seem that Hobie's newer generation hulls are opening up the speed envelope, and the Turbo fins are able to exploit it quite effectively.
Author:  Rnykster [ Thu Jul 20, 2006 10:55 am ]
Post subject:  Re: Hull speed vs. max speed
Roadrunner wrote:
It's interesting to look at Hobie's different hull designs and see how they develop speed.
Hi Roadrunner. I've experimented with the speed between the Adventure and the Outback and have found that the Cruise speed is about 0.5-1 mile per hour more in the Adventure than it is Outback. When it comes to top speed for 10-20 minute bursts, used in conjunction paddling, there is not much difference in the top speeds. I assume it is due to there being much less surface area due to the shorter Outback. Due to the small turning radius, a much more stable ride, and drier ride from the Outback, if I ever decide to buy another Mirage, it'll be a Outback instead of the Adventure.
Author:  johannes [ Thu Sep 07, 2006 4:51 am ]
Post subject:  Re: Hull speed vs. max speed
Last Saturday I finally had my first test ride with a Hobie Mirage drive in the lagoon of Venice (click here for a short video clip; requires DivX decoder). A great experience! I was really impressed by the build quality, all the well thought out details, and speed and capacity of the Adventure in particular.

However, I'm puzzled by the top speeds I see posted in various locations. How hard I tried, I never managed to go faster than 9.9 km/h (6.2 mph) which is slightly above hull speed but significantly less than the speeds others claim (without Turbo Fins).

I think I can discard not being in shape because I go cycling often and, for instance, the day afterwards I went on a cycling tour of more than 112 km (70 miles), just to give you an idea.

Does it make a difference how much stuff you carry with you? I had a tent and other camping equipment as well as the sail kit with me.

Or do I simply have to find out the best seating position, pedaling speed and so on?

It looks like I have to go for more test rides...
Author:  Roadrunner [ Thu Sep 07, 2006 9:19 am ]
Post subject: 
Hi Johannes and welcome to the forum.

Yes, weight makes a difference. First, more weight makes more hull displacement. Given the same hull, more displacement makes a larger "wave trap" the hull has to overcome as it approaching "hull speed". Second, more weight means more surface area in the water, meaning more "skin friction".

Finally, horsepower requirements increase much faster than speed. In other words, it takes almost twice the horsepower to go from 6 to 6.5 mph. The standard fins can't provide the required power to achieve the higher speeds. If you want more power (and your legs can deliver it), you need the Turbos.

What Hobie model do you have? That makes a huge difference. 8)
Author:  kepnutz [ Fri Sep 08, 2006 1:01 pm ]
Post subject:  6.8...6.8...6.8...6.8
Been out on full bore sprints with two different fellow endurance cyclists in my tandem mounted with turbo fins, on flat water, with no wind and have not been able to push past 6.8 (gps) yet ! When I was a road bike racer I would hit 40mph in flat ground sprints in training and races over and over but never saw a 40.2 :x I could have bought bigger gears and tried that way but 40mph usually did the trick :wink: It seems you are correct Roadie, the power required to go just a little bit faster must go up exponentially to see even a marginal gain in speed. Twice as hard for half the gain then four times as hard for half of that etc etc till you hit the wall. :twisted: To go just point two miles an hour faster and make it an even 7mph has not happenend yet. :cry: I will try again and let you know if we ever make it. :wink:
-kepnutz-
Author:  thebaker [ Tue Sep 12, 2006 5:18 pm ]
Post subject: 
Welcome to the forum Johannes.

Interesting discussions regarding the Adventure and speeds people see. I don't own a Hobie Kayak (I am working very hard trying to save up for one and can't wait to get one) but I did take an Adventure for a test ride a few weeks back. I posted my review titles "Still Grinning Ear To Ear".

After reading comments to this post, I had to go out and check my hand held GPS last night. I checked it against my bicycle speedometer which I know is quite accurate. It was nearly dead nuts on compared to my bike speedo. I checked it at 4 mph to 15 mph and it is very close all the way through that range.

So with my experience, I gotta stick to the speeds I listed in my write up. I have never had a chance to pedal with turbo fins so take this comment with a grain of salt. But I feel the standard fins can generate quite a bit of forward thrust. In my mind, it's like a being in a lower gear on a bike. You really wouldn't be limited on top speed unless the gear is low to the point that your legs just can't crank out any higher RPM. On the Mirage Drive I found it possible to pedal at a high enough cadence to provide enough thrust for the speeds I saw.
I did two full out blasts on the lake with one being 7.4 mph and the second being 7.9-8.0. They were in opposite directions and I was with the wind on the second so I'm estimating calm water/no wind equivalent of 7.7. I know these seem high and I'm certainly no super human but that's what I saw.

The Adventure hauls the mail in my experience no matter how you cut it.

Because I haven't bought a single yet, I'm curious what people estimate the sustainable, cruising speed difference is between the Adventure and the Revolution.

I'm interested in long distance rides so speed is important. The dry factor does sound very apealing on the Revo. Tough, tough, tough decisions. My first yak will more than likely be a tandem though so it really doesn't matter for now.

Happy kayaking!
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