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I don't know, it seems like poor engineering form to design without a good idea of the specifications I need to design too. If my output really is 100W, I want to confirm that first somehow before spending time, money, and effort building something that may end up completely not right for what I want to do.

I'm trying my best not to sound presumptuous and stubborn. I may be overestimating my ability, but its not out of ego, its out of the best guess I think I can make based on all the research I've ever done on the subject over the last 4 or 5 years. Just settling for "this is average, so you're probably here" doesn't sit comfortably with me, because it seems just as arbitrary as the wattage on the bike.

There's also the issue that I'm not intending to design for matathon races, but rather short exercise sessions of 30-60 minutes, high intensity, highly anerobic sprints in cycling terms. The 300W I claimed the bike told me for my 30min max is not an every day effort, its a once a week at most, best day, highly motivated effort. My sustained heart rate when doing this reaches the 85% level for my age (I'm 28), which is about 178bpm. When I'm done, I'm literally done. Couldn't do another pedal done. Like, rubber legs staggering around done.

For an hour, I hypothesize the bike may tell me I could sustain 200W. It would still be a lot anerobic, so I don't know how long I could go past that, or if I would even make it an hour. I've never actually tested it. I know I use the 200W setting for my cooldown, and as the rest phase when I'm doing intervals (actually I've upped the rest phase to the 250W setting just recently, and the sprint phase to the 400W setting). If I was planning for a marathon type pure aerobic race, I wouldn't think of planning for more than 150W (according to what the bike tells me). When I have my easy days and pedal at the 200W level, my heart rate sits at about 145-150 bpm, I barely break a sweat, and I feel like I'm not even working. I usually give up on having an easy day and start upping the resistance about 10min in or so, when I feel like I'm cheating myself by taking it too easy.

Another data point I have is comparison to other guys who use the same bikes I do. One guy is probably 15 years older than me, cycles regularly (rides to work often in the summer even), and distance runs as well. The other is my age, lifts and runs mostly, but hops on the bike occasionally. When they would ride next to me, I would notice that my wattage resistance setting is consistently about double what they use. So does that mean that I'm just average or below and these 2 people who work out and train regularly (one specifically for cycling) and are visually more fit than me are way below average, or could it be possible that they are working at traditional average levels and my output really is double that?

Finally, I know that over the years I've been training, when I started out I could not sustain 200W (bike level) for 30min. I would have to take stops, and sometimes lower the resistance a couple clicks. Now my max is the 300W setting, with no breaks. I've improved by 100W, according to the bike. I've been trying to find any information I can about true power vs what exercise bikes say, and everyone seems to agree that most are inaccurate compared to reality. But, people do seem to agree that they are consistent with respect to themselves - that is, if the number is going up, you're certainly improving. So then the question is, if the absolute wattage of a stationary bike is inaccurate but consistent, is the delta between the 200W and 300W resistance setting equal to a 100W improvement, or is that unreliable as well? If I've improved by 100W, certainly I didn't start at 0W, so I should expect to output something more than 100w now right?

So, taking into account all that information, and not just the number on the bike, leads me to believe the numbers the bike tells me might not be that far off. Maybe they're a bit optimistic by 50-100W max, but I don't think I should just ignore them completely and go with some arbitrary average just because anecdotally all stationary bikes are inaccurate.

I'm really trying not to be "that guy" who just randomly shows up in a thread full of guys who've been doing this for years and pretends to know it all. Believe me when I tell you I've been reading along with this thread for years and I know you guys know what you're talking about and I respect that. What prompted me to finally post here was hoping to find a way to finally pin down what my output really is. If I had 100% confidence in the numbers, I probably have gathered enough knowledge to start building something by now. But I need to confirm my output, figure out what prop I should go with and account for drivetrain losses so I'm generating the power I want to at the RPM I like spinning at, so I know how much power is actually pushing the boat, and then I can finally use Michlet to help me figure out the optimal shape of the hull for that power. The OCD engineer in me wants to build an optimal machine. If I didn't care about optimizing, I'd just build something and keep adjusting the prop/gear ratio until I found the percieved effort level I wanted.

Actually maybe that is the way to go. Maybe I should just play around with michlet first and figure out the differences between an optimized 100W hull for my weight, and an optimized 300W hull for my weight, and see how the 2 optimized hulls compare with each other at the same speeds. If there really isn't much significant difference, maybe I just build something in that ballpark and then play around with the prop and gear ratio until I find the perceived effort level I want. Maybe ultimately it'll be easier to use a GPS to calculate my speed and use the michlet speed/resistance correlation to confirm the power I must be providing to reach that speed?


Tom, I have not seen the wavebike, but I kinda have a Rick Willoughby style craft in mind, long, narrow monohull with outriggers just above or skimming the water for stability. I'm more comfortable peddling in a recumbant position position anyways.



Sorry for the lengthy and probably rude sounding response.

 

One way to check your true power output would be to see if you can find some really good local cyclists who have accurate power meters on their training rigs and ask if they'll let you do some sustained power runs. The bike gear tends to be reasonably good, and gives the figures that are usually quoted for good athletes. It may well be that if you've been training for a fair time you have upped your power to the 200 to 250 W level, but that is around the sort of average power that a good road racer cycles at competitively for an hour or two.

When it comes to the power needed to make a boat move it's heavily dependent on the speed you want to go, the wetted area of the hull, the displacement and the waterline length. My big, fairly fat and heavy, just over 17 ft long, two seat electric boat will cruise all day at 4 mph (our inland waterway speed limit) on around 75 W, but to get to 6 mph I'd need to up the power to about 180 to 200 W. If I were to change the hull design by increasing the waterline length and trying to reduce the wetted area a bit I could get that power for 6 mph down a fair bit, I'm sure.

 

That was a lengthy dissertation but you made your point. It sounds like you'll want to be contacting a university with a good Human Performance lab and paying for an output evaluation. I know Calgary has one but I'm sure you can find on in southern Ontario.
I have an extensive background in the fitness industry and can asure you that you would benefit more from less intensive workouts. I know, it's hard to believe and completely counterintuitive but it's true. You would benefit hugely however from progressive resistance training in combination with moderate aerobic exercise. Once a weight room regime is established, one benefits from both aerobic and anerobic at the same time while getting the maximum return for effort. Some of the lowest % body fat athletes I've worked with train this way.
The reason you out perform those other guys in your gym is specificity. You train a lot on that particular bike and it sounds like they don't.
You may want to consider the wattage differences you quote as a percentage difference rather than a wattage difference, this would validate the improvements more accurately.
I'll be curious to see how differently your test results compare to what's been suggested here for design wattages. I believe they will be within acceptable tolerences.
Your prop design should reflect your performance expectations. You'll end up with a slightly less efficient prop at moderate exercise levels but still have reasonable efficiency at your higher output targets. JavaProp is brilliant for this type of design work.
I do hope you'll receive my comments in the positive vain in which they are intended.
I by no means want to take any wind out of your sails.

All the power to you.

What ever floats your boat.

-Tom

P.S. What cadence are you most comfortable at?
I am a Mechanical Engineering Technologist.
Are you a Civil Engineer?

 

Rhinox; engineering types like you (and me) and many others on this thread, are often smitten with the desire to gather reliable data. Why not build a pedal driven dynomometer. It could be as simple as a Prony brake or a little less simple with an automotive type generator/alternator. In either case you could use your skills and knowledge to calibrate the machine accurately.

You may find it difficult to get the boat performance that you'd like, simply because of basic stuff like power to weight ratio. It would be interesting to plot human power output against boat velocity as a function of displacement. I'll bet that has been done already by some of our more technically inclined participants.

 

Rhinox,

You can build to your power to weight ratio with fantastic results.

-Tom

 

That picture confused me for a while. I really thought that you were using the
top of a small car as a cabin, and complaining you couldn't move fast.

It's a fine looking boat and I apologise for my uncharitable thoughts.

 

OK 2 posts coming up so I don't make another single huge 1.

I thought of another way of looking at it. I just finished today's workout. I set the resistance to 250W. I held it constant for 30min. I kept checking my heart rate (by counting my pulse) and found I averaged 141bpm. Felt pretty comfortable, I probably could have kept going a little while longer, but 30min on the bike is my usual tues/thurs workout.


I used the following equation from livestrong.com to calculate calories burned based on my heart rate, weight, and age:

For men: [(-55.0969 + (.6309 x heart rate in beats per minute) + (.1988 x weight in kilograms) + (.2017 x age)] / 4.184

Based on the formula, I get a result of 17.64 kcal/min, for a total workout burn of 530kcal. Not too shabby. The conversion from kcal/min to watts is 1kcal/min = 69.73W (1W = .01433 kcal/min). When I convert 17.64 kcal/min to watts, it tells me my body is burning 1230 watts. Energy burned is not energy generated though. I'm having a hard time finding the source for the biomechanical efficiency of cycling output vs stored food intake, but I seem to remember it being something like 20%.

1230 watts burned times 20% efficiency = 246 watts generated.

If all the above is correct then that at least somewhat confirms that my stationary bike's wattage is pretty close to accurate, but I guess it could be a coincidence. Thoughts?

Also, any thoughts on the difference between spinning a stationary bike flywheel vs. peddling a ppb? I figure without the flywheel, I'd lose a bit of energy, as I think the analogy to peddling a ppb is like trying to ride a bike on sand. I think I remember that conversation somewhere in this thread.

 

Jeremy,

I don't know if I know anyone THAT into cycling around here. Besides, those racing bikes would probably moan quite a bit with someone of my size on them.

As for the hull, yeah speed detemines power. I don't have a speed limit though, so I figured I'd be doing some itrating with michlet - Pick a speed I think is close, optimize the hull, check the resistance, rinse and repeat until I find an optimized hull at a speed that predicts a resistance close to my output minus predicted losses (drivetrain, wind resistance, etc.)

Your boat looks very nice. when I first glanced at the thumbnail, I thought you had a cabin or canopy, then for a second a contemplated why there was a car in your boat. THEN I realized, perspective

edit: I see I wasn't the only one who thought that haha

Tom,

I definitely appreciate your comments. There's a lot more to my workouts than just riding the bike. I already do resistance training 3x per week. I sort of do a modified riptoe starting strength 3x5. Mostly I'm doing upper body though as I don't have access to a power rack anymore. I'm not trying to gain muscle now, just maintain muscle mass while I lose weight. I'm down 20lbs in 2012 so far, actually. I do a little bit of cycling every day - tues and thurs are my long days where I go for 30min, MWF I go for 15-20 minutes and I do intervals, not quite HIIT level though. I usually rest 2 days on the weekend, though I might get in a walk or 2 with the wife and dog. Might not be the most ideal program, but its something I can stay motivated to sustain, and at this stage of my life thats a lot better than just sitting around. I have no real goal in mind other than being able to ride roller coasters again. I know I'm never going to be ripped or have abs

edit: forgot to mention, I'm a mechanical engineer. I work for a company that designs and builds pumps, and most of my work currently is FEA stress analysis stuff.

edit2: I usually pedal somewhere in the 75-90 rpm range, depending on resistance. Today, I was around a pretty consistent 82-83rpm according to the bike. Usually, the higher the resistance, the faster I have to pedal, too slow and my legs burn out way too quickly then I'm done.

messabout,

Thats not a bad idea actually. Could be as simple as putting a sprocket on the alternator and attaching the chain from my bike to it.

I realize my weight has me at a disadvantage, thats why I wanna build the best craft I can for my weight. My output might be higher than average, but compared to racing cyclists my power to weight is like 1.2-1.7 watt/kg, where as racers are 3-4 minimum. I wouldn't even be close to competive. As for boating, I don't expect to be even close to the performance of a Rick Willoughby or anyone who races these things competitively, just because it'll take so much more power to push my heavier displacement craft through the water.

 

I saw the same thing at first glance, Leo.

That Jeremy is a character, I think he was having us on!

-Tom

 

The Prony brake idea is a good one - it's a pretty foolproof way to get reasonably good power measurements. It's not rocket science to knock one up, either, although you'd need a flywheel to smooth out the torque and an assistant to adjust the brake to keep the lever arm level at the given load. The simplest one I've seen is this one: http://www.youtube.com/watch?v=9Wi51Kf8bzA which could give pretty good results if you can keep a steady cadence and have a big flywheel on the crank.

 

75 - 90 is fantastic for what your ambitions and expectations are.

I think a Rick W boat would be ideal for you, it's just going to be larger.

I would consider the greatest gain in sizing to be in the freeboard department so that if your weight does drop (not saying it should), you wont have lost much hull efficiency.

It would also increase it's resale value, something that should always be considered when investing in a boat of any kind.

-Tom

 

Rhinox
You have to start somewhere and your first boat is always a bit of trial and error. The parameters that will restrict you are transport, storage and where you are using it. Transport is how big a boat can you fit on your roofrack/trailer, where are you going to store it. Launching the boat off a beach or from a pier and if the waterways have a lot of weed. The ideal boat is not always practical otherwise you would see a lot of skinny 10m long boats.

Ian

 

Rhinox,

I missed your post #1387.

The efficiency number I recall for human output is 10 - 15% but it's just an academic recollection so I have no reference to back it up.

I think bodyweight may be skewing your formula a little.

-Tom

 

How much do you trust wikipedia numbers? http://en.wikipedia.org/wiki/Muscle#Efficiency

Its the only reference I was able to find. I don't know how to account for my bodyweight skewing the formula, or how much "a little" is. I found another set of calculators at shapesense.com. The age/weight/HR calculator seems to be using the same formula, but they have another equation that is age/weight/HR/VO2max based. But I added another layer of estimation because I had to estimate my VO2max based on my resting heart rate. The site claims the method is more accurate if you exactly know your VO2max (which I don't), but with my estimated VO2max number it predicted even higher calorie burn than the age/weight/HR method. :shrug:

Ian,
Yeah lots of considerations for sure, but I'll have to start somewhere. Might as well start with the ideal, and work out what's practical from there once I decide what compromises I'd need to make.

 

Well, I can tell you mine was measured when I was 24 at 59ml/kg/min O2 uptake which, according to their chart, was one point off elite athlete. At the time I was a mediocre marathon runner and weighed about 165. Again, a university human performance lab could provide you with this information with good accuracy, but I don't think it necessary.

How about this for an idea. If you change your weight number to say 225, how does that affect the output number? Is the difference reasonable or does it lack logic?

As far as trusting wiki numbers it all depends on the wiki source which is usually traceable.

-Tom