Mirage drive thrust

Wasn't sure where to ask this so I will start here and take any advise.

Talking with a mate about props etc, as he is thinking (needs a good slap I think) of getting a Native Ultimate propel. The topic of thrust came up as he was trying to tell me they have more thrust (ow my ribs hurt from laughter ) but then when I tried to find any actual info on the thrust of the different Hobie fins and the Propel, I could not actually find anything.

I think I read once the the Propel system also has a range of prop sizes but could not find that either. Anyway, a fool if he gets one, but I am still interested if there are any actual "lbs thrust" info out there so I can rub his nose in it .

A tug of war is the only way to settle this!

_________________
The Wind Is Your Friend...

With a full sheet in 15 knots

Actually I cannot say to much, he has my Adventure at the moment. He has used it before + tested the propel and he still wants a propel. I am sure I had both fins on the mirage last time .

I haven't used the Natives before, but looking at some of the images and having ridden a number of recumbent bikes over the last 5 years, I think I can imagine why he feels the Native has more thrust. It has to do with body position in relationship to the pedals. The Natives appear to have the equivalent of what bent riders refer to as a high bottom bracket. This higher pedal results in a what is called a more closed body position, and this position feels more powerful than a more open, relaxed posture I seem to get in the Hobies. For short, fast sprints, closed positions can be easier for some people to generate power bursts, but most find the position less comfortable over longer hauls. Knee and hip pain are the most common complaints, along with numb toes. These issues tend to result in the bikes with real high bottom brackets and closed positions doing well in sprint competitions, but usually having a harder time keeping up in endurance events. The more familiar "spinning" action of their pedals may also feel more comfortable to him and encourage his belief that the Native has more thrust.

Propellers are certainly a simple mechanism when it comes to transitioning rotational power of an engine into the water. In the case of a peddling person, the mechanics of the power generation are different so I tend to believe that the conversion to rotational motion is probably not as efficient. Of course I don't have any science to back that up, it's just more of an experiential/instinctual opinion. I thought Hobie had some of the science published somewhere, but unfortunately I cannot find the page I remember at the moment. Even if I could pull it up though, I am guessing that while your friend says it is about thrust, it really is more about personal feel, and no amount of science and thrust data will change that "seat of the pants" impression.

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-Dylan

There has been discussion on these forums, but I can refer more easily to a discussion on the http://www.kayakfishingstuff.com site from awhile back.

I like this comment the best:



http://www.kayakfishingstuff.com/community/showthread.php?t=77768&page=4

_________________
Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)

Ah yes that KFS discussion.
Sometimes heated but always interesting!
If my memory serves me correctly Roadrunner hooked up to a spring scale on a dock and pedaled until it broke!
(the spring scale- not the dock, though with the thrust generated from the MD anything is possible! )

Wow, Stringy, you've got quite a memory! In fact, we broke the scale at 75 lb. (verified by the dock master). Here's the start up:


This is what it looked like when we got some water churning:


In a more practical demonstration, here's what some stump-pulling Mirage Drive thrust can do in an actual boat rescue:


Attempting static or low speed thrust like that with a Propel Drive only results in a cavitating prop.

Here's what happened with an early version of the Propel Ultimate 12 on the second sprint:


On the first sprint max speed was about 4.5 MPH (compared to about 7.7 MPH with a Hobie Adventure). In all fairness, hull characteristics can play into boat speed as much or more than thrust output. Nevertheless, Hobie doesn't make a hardshell kayak that sprints that slowly. IMO, the Propel is not in the same league as the Mirage Drive with Turbofins in terms of thrust, efficiency or ease of use.

ELM, I wish your friend good luck with his Native Propel Drive. Some folks just prefer props and/or crank-style pedaling. Native is a reputable company and makes a decent product and has a very comfortable seat, so I'm sure he'll enjoy his ride.

PS: To the best of my knowledge, the Propel unit has only one factory prop. There has been some discussion of having an optional prop. He can look on their forum for the latest info.

Thanks for that, specially Roadrunner, interesting how you actually tested it, here have I been imagining mounting pressure gauges to fin stems and all sorts Dope Ed
I have used a propel and while I agree it is a very well made unit as are there kayaks, it just didn't seem to perform and I found it quite uncomfortable.

Hope this info will sway his judgment.

Speaking of which, he hasn't brought back mine maybe I have and I just found out
Ow well, another happy Hobie customer of sorts .

Better check for well cracks when you get it back.

In case he tries a tractor pull, or tearing cleats off a pier, like roadrunner.

_________________
The Wind Is Your Friend...

For curiosity sakes, don't suppose you tried comparing the standard fins against the turbo's while you were at it Roadrunner?

No, when the scale broke the test was done. But about 4 years ago I compared boat speeds with my Adventure using standard fins, ST fins and Turbofins. Speeds vary slightly, so these represent average speeds.

Three scenarios were used:
1. 40 Cycle Per Minute (CPM) "slow cruise" over a defined course
--std fins....3.0 MPH
--ST fins.....3.5 MPH
--Turbos.....4.5 MPH
comment: Turbos perform better, partly due to efficiency but also due to greater pedaling effort.

2. 60 CPM "fast cruise"
--std fins....4.5 MPH
--ST fins.....5.0 MPH
--Turbos.....5.7 MPH
comment: As speed increases, the gap narrows and hull resistance increases.

3. sprint speed (GPS)
--std fins....6.98 MPH
--ST fins.....7.30 MPH
--turbos.....7.53 MPH
comment: Assuming similar all-out efforts here, speed differences would be largely due to differences in performance efficiencies.

Notes: Different boat models would produce different speeds. The data is not exact, but averaged over multiple runs; variables include fin set-up, Drive condition, water conditions and user interface. Additionally, Turbos and STs have since been improved somewhat due to changes in rubber compounds. Still, this gives a good ballpark comparison. On the sprint test, fin thrust is not linearly proportional to boat speed (progressive increases in speed require ever greater thrust. My guess (based on boat speed differences) is the Turbos are putting out about 65% to 70% more thrust than the standard fins at this speed.(thrust requirements almost double for every 1/2 kt speed increase; also, standard fins start to "mush out" over about 5 to 5.5 MPH as their efficiency diminishes).

This may be a little of topic but I am very interested in these speed definitions. (JUST TURBOFINS!)

"slow cruise" is 4,5 MPH.
I tried to find my own def for "slow cruise" and the result for me is 4,7 MPH wich I can hold for over 3 hours. Then I have to take a leak!

"fast cruise" is 5,7 MPH.
My own def for "fast cruise" and the result for me is 5,2 MPH wich I can hold for over 1 hour. Therefore I still consider it as a "cruise" speed.

"high speed" is not def by you.
My def for "high speed" and the result for me is 6,0 MPH wich I can hold for 5 min and then reach 0,5 Mile.

"sprint speed" is 7,53 MPH.
How long time or what distance is needed by you for determine "sprint speed"? Is that the same as top speed?
For any practical use it can´t just be a few seconds. Or?

best regards
thomas

Thomas, I think everyone else is done with the subject by now so it's probably safe to wander off topic at this point.

You could consider these as speed ranges rather than definitions. More correctly they should be called "40 CPM" cruise and "60 CPM" cruise. To make the tests repeatable, it was desirable to work with a constant cadence. Forty CPM because it felt like a leisurely pace that a typical user might use as a practical matter so this was arbitrarily called a slow cruise. It could have just as easily been 35 or 45 CPM.

Not knowing if the fin performance relationship was constant, I picked a second speed to compare the fins at. It takes a lot of concentration to maintain a specific cadence from run to run, so I used 60 CPM or one cycle per second -- easy to stay on pace with a stop watch. Again it seemed like a reasonable pace to sustain for awhile for somebody who was more in a hurry to arrive at a destination -- hence "fast cruise".

for anyone who cares, all these tests were done with a flying start on a 100 meter course, alternating East and West for a minimum of 4 runs, with any spurious runs being rejected. The results were reasonably constant for any given day.

Sprints consisted of 20 cycles at maximum effort with a running start of over 5 MPH in smooth water, no tide or current, minimal wind, alternating directions. Variartion was about =/- .2 MPH.

For exercise I usually run a "one hour cruise" (also called a "fast cruise") with the objective of going the maximum distance within one hour. In the Adventure with factory Drive (Turbofins), speed ranges between 5.3 MPH and 5.6 MPH; with a modified Drive I usually can get another .1 MPH. So it's a virtual race of sorts. I also like to use this to compare different hulls.

Not being particularly strong, I rely very heavily on Drive and fin tuning to get the most out of my limited resources -- minimum Drive friction and maximum fin efficiency are huge in achieving the most thrust for the effort!

Everybody has their own pace, stroke length, etc. etc., so for most, the useful significance of this data is the comparison of relative performance -- how much difference is there between the fins, and is it worth the cost. For crazy speed demons such as yourself, I think the next step is to experiment with your Drive set-up to make sure it's giving you its full potential.

We're definitely fortunate to have someone like you to document the unique potential of the Mirage Drive over a variety of distances, as shown in your race series:

1km - 0,621miles - 00h-06m-09s - 9,756km/h - 6,062Mph
5km - 3,107miles - 00h-32m-27s - 9,245km/h - 5,745Mph
10km - 6,214miles - 01h-07m-29s - 8,891km/h - 5,525Mph
25km - 15,534miles - 03h-10m-19s - 7,882km/h - 4,897Mph
100km - 62,137miles - 15h-33m-00s - 6,501km/h - 4,039Mph
122,2km - 75,932miles - 24h-00m-00s - 5,092km/h - 3,164Mph

Great stuff!

Thanks for all that info Roadrunner, very informative. Have read many of your posts and they are always very informative.

Mind you, I am sure you must go through Mirage drives like car tire's the miles you do .
I cannot wait for my back to get better, I now want to get the scales out and have a go for myself.

Thanks for a very informative answer!
The method to determine "sprint speed" was the most interesting part. Thas is realy an individuell top speed performance test. For a given hull and person.

And by the way, you are faster than me in the "one-hour" run.

best regards
thomas