Pedal Powered Boats

I've just taken 'Fangle' apart for painting. I spent as long messing around with the seat bases as I did with the rest of the build. And still not great. With a couple of late nights, we might get into the local lake at the weekend - with a bit of a family gathering along - nothing like a little pressure!

 

I can offer some useful information here - maybe I have already stated it.

I have never managed to be satisfied with any boat on the first outing. Some have been terribly disappointing. It is primarily a learning experience that has a lot of anticipation. It marks a different phase of the work. Typically second outing results in better performance but only after correcting niggling issues.

I am looking forward to the photos.

A GPS is a very handy piece of equipment to guage performance and subsequent improvements. I have three portable ones and there is a fixed one in wife's car. They are everywhere now days and cost very little. If you are into exercise and engine calibration then the Garmin Edge are brilliant little units.

Rick

 

TT
Greg just posted his GPS distance - 245.164km. So now wait to get it officially recognised.

The number of comments suggests quite a few watching his progress. Advances interest in pedal powered boats and their real potential as a means of getting about on water. Still a long way off being an Olympic event though.

Rick

 

I've already stated that pedal-powered boats could become as popular on the water as fancy bicycles are on land. Many people enjoy the exercise, the quiet, the slower pace. But mention pedal boats and most people think of those kids' toys. It's guys like Greg, and you and Geno, and a couple small firms now moving from Model T to Model A models that will make them practical and acceptable and eventually available. I think that in ten years we'll be seeing them everywhere.

 

less than ten years...

Congratulations again to Greg and Rick... I would say (and hope) less than ten years, times are ripe. But look at collective distributed innovation, this will be the gateway to innovation this time.
Giuseppe

 

Fangle lake trials

I got my pedal boat fangle into the water today, and I am very, very pleased. It is a conversion of Dart 18 hulls, with the addition of a deck in place of the trampoline, and two seacycle drive units with 16" seacycle props, and Trice recumbent bike seats. It packs up well on the trailer, and assembles and breaks down readily. As predicted, trim is slightly down forward, about 40mm at the prow, with two adults only, but the upward aspect of the deck disguises this, and it allows for passengers and gear on the deck. The boat tracks beautifully, but is also very manoueverable under rudders. It is also very manoeverable under power alone, just requiring more communication between the two engines! This gives us the possibility of cruising with no rudders in the water, only putting them down when a lot of fiddly manouvering is necessary. The only downside of this would be the fact that the more powerful engine, Paul, would have to ease off to match my weaker pedalling, to allow us to track straight. I have no idea whether the reduced drag of those large rudders out of the water (which could be used to correct the power differential) would compensate for Paul not being able to max out.
The lake trials revealed some snagging: The seat bases and attachments of the seat to the base needs work. The straps round the front spar to provide hand holds to pull against when pedalling hard would help.
There was a slight tendancy for the hulls to creep apart - my deck panels don't tie the hulls together the way the trampoline would have.
The pedals could do with being a couple of inches higher, and nearer the back of the boat, to allow shorter legged engines to perform. This will mean rather more fiddley engineering of the beams.
The trial was hindered by a lack of understanding of the country park staff: A meathead in the rescue RIB came hairing after us at about 25 knots, yelling that we were "classed as a pedalo, and had to stay within the pedalo area" - though there was no evidence of any pedalos, and that meant access to about an eighth of the water area. I also hit an underwater something while pedalling hard, which has bent and stressed the ABS? propeller, and seems to have damaged the drive unit internally - it clonks on the power stroke now under load, and starts to bind if pushed hard. I shall have to see if I can get it apart.
Anyway, the leisurely, pedal all day pace you can see Paul and his wife Fiona not getting out of breath at is 3.8 knots, according to the elderly GPS, and we hit 5.3knots in a burst, until I knackered the prop and drive. So, teething troubles, but overall, I'm delighted with what promises to be a very controllable, manouverable, versatile and reasonably quick boat.

The wmv movie is about 1min 45seconds long, and under 4mb.

 

TT
Nice to see Fangle on the water. Where did the name come from?

Actually the trim looks good. Hard to tell it is bow down.

The performance is below what I calculated but it is early days. You would certainly get benefit from removing the rudders. You only need one at most.

I will be interested in what you find with the damaged drive leg.

Need to do some engine calibration and get some data on the power level. Do you have any idea of the cadence for a particular speed? You can get this off a good video clip by counting frames for say 10 revs at a known speed. The Garmin edge 305 is a great unit if you want to get serious with engine/boat data. It helps quantify benefits of any changes - guess it depends on what you want to do.

I look forward to your next report.

Rick

 

The gap between predicted and actual was enough for me to check my earlier calculations. I did find an error. The impact is not as dramatic as the scale of the error because of the hull shape. I used pounds instead of kilograms from your original weight estimate.

I have attached the new curve. It still suggest a significant gap. With two reasonably fit men you could expect to hold 100W each in an all-day mode. This should give you about 4.7kts. At a more energetic level then 150W for 30 minutes or so is possible. This should give over 5kts. In an all-out sprint then two men could each get over 500W in a well set up system. This should get Fangle to the 7.5kt mark.

These estimates are based on overall drive/propulsion efficiency of 80% in calm conditions. The allowance for appendage drag is taken up in the overall efficiency. Big rudders and poorly shaped drive leg would make this worse. Thing is, you can isolate the cost of these individually if you have the engine/s calibrated.

Anyhow the boat goes and is not at all shabby in performance or looks. Just have to convince the local authority it is not your typical pedalos.

Rick

 

Rick, thanks. I am arranging a callibration session at the local gym.
I forgot to mention that before damage to the drive leg, which considerably limited the amount of power it was possible to exert on the cranks, we were previously hindered by insufficient resistance in the kick back buttons, so every time we pedalled hard, the units kicked up. I didn't get this correctly adjusted until after the drive leg damage occurred.
Also, we out ran the longest straight course in the 'Pedalo area' very quickly - perhaps 200 metres at most. The gps was struggling to keep up. And in addition to the adult engines, we were carrying another 140lbs of boisterous young boys. Bar testosterone fuelled rescue RIBs, we were still the fastest thing on the lake - outstripping a canadian canoe with three paddling with ease. So, we are looking forward to better things.

 

Oh, I forgot to ask - I am thinking of raising the drive legs a little, to improve the pedalling position, and bring them further back to accommodate shorter legs. Is there a minimum recommended depth of water over the top of the prop?

 

I was very interested to see how linear the speed/power relationship is both below and above 4.5 - 5 knots on your graph, too. I had expected it to be more exponential - presumably the curve will go exponential at much higher speeds?
What makes it change angle at the 4.5 - 5 knot mark?

 

Oh, and Fangle comes from the delightfully translated sales blurb on the package of a cheap toy combine harvester for my boys, which was described as 'All are fangle' as in new fangled. - it means a new thing, something invented for entertainment. And the rhyme with 'mangle' combined with the rotating thresher of the combine harvester rather suggested a slightly sinister pedally action. Fanglewangmangler perhaps?

 

TT
I set my props about 2" below the surface. This is borderline once you get some chop. If I accelerate hard the swirl from the tip vortex will suck air but once moving it is OK.

With your drive leg you need to watch out for wake from the drive leg causing a trench. If the prop is facing forward then this will not be an issue. The bow wave from the hull may cause a trough as well. So the setting is dependent on conditions to some degree. If you can set it so it does not ventilate most of the time then you have found the best position.

The kick in the curve around the 4.7kt mark is where the wave drag starts to develop. The wave drag does not increase much beyond 5.5kts so the viscous drag dominates. If you remember, in my original analysis I pointed out that the boat responds well to extra power for a relatively short hull length.

The Garmin Edge 305 I have can give time resolution down to 1 second so is very good for data collection. It has heart rate and cadence recording included. They are not the cheapest but certainly good value.

You should be able to do some reasonably comprehensive testing by trying things like 1 rudder, no rudders, one drive leg and so on. If you are into the engineering aspects it can be good fun understanding where the power goes.

Rick

 

TT
I was wondering what you are doing about your damaged prop?

It is quite easy to make very good props from stainless flat bar if you can weld. A bit tedious shaping with a hand grinder but not very difficult to get a good profile.

If you want to have a go at this then I can provide details on what to make and how to do it.

Rick

 

Rick- I would like to have a go at this- I do have a 125amp mig, but my welding is pretty Chickensh*t and I've never tried s/s which I understand is pretty techniquey. but I do have an excellent, cheap s/s Shop down the road from me, with laser cnc, so I could get them to make up hub and blade 'blanks', and then get medieval on them with the grinder. the pictures you have posted of your props look beautiful. how critical is the foil profile? its hard to imagine getting this very accurate by hand with the grinder. I remember you saying that the props would be low slip. would that imply that a lot of their effectiveness is from screwing forward through the water and less from lift off the foil?
would the engine calibration inform the prop design significantly? I'm wondering about props designed to an 'average' engine, or tailored - two different props for the different engines?
In the mean time I have straightened the bent prop (not abs on second thoughts) reasonably successfully.