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It doesn't have two right angle drives, it uses a belt on the stern too. The belt on the stern is not faired, so I think, that it is impossible to reach 8mph with that drive.

On my racing sailboat, I once tried a new dagger (I think this is the right translation, we call it sword) which was not in its final shape already and it bound the boat to 4kt. After sanding it to NACA 2412 form, the speed increased to 8kt at the same wind speed. With this unfaired belt with more than 3cm space within I wonder it is driving at more than walking speed at all.

 

You're right, I didn't look at this close up of the rear unit which shows the exposed rear belt. I wonder what happens if you get a bit of weed caught in that?

Overall it's still going to have fairly high losses, though, as there are a lot of moving parts sapping power along the way.

 

Probably the losses increase with use, especially in saltwater. I'm wondering what happens if corrosive soup seeps in between the long flex shaft fibers and housing. Unlikely the shaft is 100% stainless metal with submersible seals. Any seepage might turn into a binding gunk with time?

P.

 

Makes me wonder why they didn't just go for a simple small chain drive in a tube. I tried this a couple of years ago and managed to get a pretty low loss drive inside a 1.25" diameter stainless tube. The tube could have been faired pretty easily, to reduce drag, plus I was planning on running the chain in an oil bath, to get around the potential water ingress and corrosion problems.

 

Jeremy
How many teeth dose your chain drive have? The smallest I can get is a 14 tooth gear, I tried making one but couldn't keep the water out. Also was a lot bulkier than yours.

Glen
Just seen your post, am making new outriggers for this boat. 2400mm long 100mm beam and 120mm deep.

Ian

 

Ian, it was the smallest chain I could find, 6mm pitch (slightly smaller than US #25 chain) and the sprockets were 10 tooth. I bought the chain and sprockets from here: http://www.technobotsonline.com/sprockets-and-chain/steel-sprockets/tbot-6mm-steel-sprockets.html and could have used either an 8 or 9 tooth sprocket if I'd needed to get the diameter down a bit more. The reason I didn't use it was only because it was a bit noisy. I experimented with slipping some PTFE strips down inside the tube, which helped a bit, but I couldn't come up with an easy way to fix them in place. Also, the oil tended to spray out from the chain and make a mess of the electric motor - with hindsight I should have come up with a better way of redirecting sprayed oil down into the tube.

Overall it was a pretty good way of getting drive down a narrow leg and I reckon it could have been engineered to work just fine.

 

Hi everyone.

I've stalked this thread for years, always fantasizing about when I'd have the means to build one of these amazing machines.

Suppose that time was now, what is the best way to get started, some of the decisions I'll have to make, and the general process from conceptualization to execution to the lake? Do you guys mostly just build stuff and see how it works now, or do you still try to optimize the hull/prop/drivetrain to the "motor" specs and maximize performance?

I know Rick W did a lot optimizing stuff, but I also know he hasn't been around here in a long time.

Thanks!

 

Welcome Rhinox. What would be your application? Rivers? Lakes? Offshore? Is it windy? Big chop? or is it mostly flat water? solo? tandem? camping? fishing?

 

Primarily Lake Erie, near Cleveland. Sometimes it can be very windy and choppy, but i'd only go out on the relatively calm days. Primarily for fitness/recreation, but I'd probably do some fishing from it from time to time. Primarily short trips 30-60 min of pedaling, but from time to time I might be in the mood to pedal for 2-4 hours. Someday i might attempt a trip out to put-in-bay island. It'd be solo, but I'm a big guy so think tandem displacement but a solo motor. I can do 300W output continuous for 30min max right now. For 1-2 hours, i could probably do 200W continuous. Just want something that goes as fast as i can go for my displacement and power so I can push myself to go faster and farther and longer overtime, and occasionally I might drop a fishing line over the side.

 

How are you measuring your output Rhinox, and what do you weigh?

-Tom

 

Theres a pair of recumbant exercise bikes at my work fitness center I've been using for the past few years. Theres an exercise mode option that lets me set a constant resistance in watts.

I'm 6'5" and currently 375lbs

 

I suspected that. Unfortunately, they're not very accurate. Could be yours are, but I doubt it. You could try contacting the manufacturer for clarification but the usual human output is 100 - 150 watts sustained depending on your level of fitness.

You're a big fella, good for you. You'll want to design with that in mind. Usually, a lot of effort is put into designing for efficiency as our power output is so humble.

Have a read of this thread from the beginning asking questions along the way. Check out human powered everything on Google and youtube, you'll learn a ton!

-Tom

 

I've actually read most of this thread already, though i've probably missed the last year or so. Done a fair bit of research around the web too. I'm an engineer, so i have a natural tendancy towards wanting to learn and understand everthing that interests me

As for my output, eh i work with what i got. My results are consistentt with a different machine i used to use a few years ago. Do you know a more accurate way to confirm my output? I know what the average is said to be, but i also know highly trained cyclists can sustain 400W. I know i'm no where near that, but i've been cycling for probably 5 years now, both on the road and stationary bike. I figure at my size its better for my knees than running (i did run xc for my college team mostly just for exercise not to compete, but i had got myself about 100lbs less than i am now at that point). I also read an article or something a long time ago aboutt how my weight actually helps me produce more wattage output because i can get more weight behind the pedaling, thought iforget the exact details why. I also know tthe exercise bike flywheel provides a benefit i won't have on a ppb. And my output at the pedal will not equal the outputt at tthe prop. But i do expet to be above average, and my output is for 30-60 minutes which i understand is a sprint in ppb terms - sustained is usually output for an indefinite time > an hour, pure aerobic and no anerobic, right? So i'd be designing for a higher output than i would if i had long distance many hour racing in mind.

All stuff i need to work out so i can find a realistic point to design too. I can use michlet/godzilla, but like all eng software the output is only as accurate as the inputs. I know basics like long and slender hull is most efficient as well as larger/slower prop for better efficiency (and lake erie should allow me to use as large a prop as reasonably possible)

 

Exercise bikes are usually hopelessly inaccurate, I'm afraid. Cyclists use calibrated power measurement systems for training and these tend to be pretty good, but they are expensive (and it's that cost that is a good indicator as to just how hopeless gym equipment is at measuring power).

The very best cyclists in the world can sustain maybe 400 W for maybe an hour, going absolutely flat out. Most mere mortals struggle to sustain over 100 W, in fact non-regular cyclists rarely get even this high, 80 W would be more typical. I've been a cyclist for many years, but know that I can't sustain more than 120 W, even that is a struggle as I hit my aerobic limit after a few minutes at that power level.

Earlier in this thread there is some useful information from Rick Willoughby on his power output. He's a pretty fit, regular pedaller who has undertaken a fair bit of "engine calibration". I seem to recall that he can sustain around 120 to 150 W, but he's significantly above average, as he trains pretty regularly and does the equivalent of pedal boat marathon races.

Your best bet would be to design for a power of about 100 W, as that's fairly typical for a reasonably fit individual. Don't forget that this is input power - you will lose maybe 30% of that in the drive train and prop so end up with maybe 70 W to propel the boat.

 

Sad but true big guy. Jeremy and Rick W know what they are talking about. Heed there advice and you"ll have a happier outcome craft wise (and fitness wise too!). Exercise machines are notoriously inaccurate.

A bigger prop would be of benefit but there is of course a point of diminishing returns.

Have you seen the Wavebike? It's another approach that uses a steerable, midship canard that's pretty cool if upright seating interests you.

-Tom