Human Powered Boat - Feel free to criticise - I need the help

So, int he quest for the perfect human powered touring boat, I've been playing with Kayak Foundry and FreeShip, and have come up with this. It started as a standard kayak and has obviously been pulled and pushed around a bit.

But because I know nothing about boat design I've gone down the route of drawing up something that looks nice - who knows if it works though?

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The aim is to build it out of 3mm PVC sheet heat formed round formers which themselves are slid onto a box section aluminium spine (which provides structure for seat and pedal mounting). The empty hull will then be decked in the same PVC and filled with expanding foam. The superstructure is then made out of 1mm clear PVC again heat formed, but supported on a simple tubular structure, very lightweight, and surprisingly solid in a bendy kind of a way. Windows will be part of this form, and delineated simply by being masked off before painting. All pretty untried as far as boat building's concerned, but tried and tested in two home built velomobiles.

I've not yet modelled the different parts of the canopy, but I'm thinking a large "targa" roof piece which will lift off, and which is held in place simply with flexible magnetic strip.

Oh and usage - inland waterways - Brittany has plenty of canal, almost all of which is very little used, is very calm, and if the worst comes to the worst, shallow enough to stand up in - but put it this way, it's not going to be ocean going.

Of course one glance at the FreeShip model and someone might point out the huge flaw. So feel free, it doesn't have to be the fastest thing on the water, but it'd be nice to know it'll work.

 

Looks pretty hot, no doubt about that
I took the liberty of checking her out in Michlet. The input file I used is attached along with a plot of the resistance. Note that the hull power losses (product of drag and speed) at 3 m/s (~6 kts) total around 180 watts in calm water. But perhaps of greater interest is that skin friction is fairly high, although wave-making drag is small- this means you might get some benefit from a shape with less surface area for the same displacement, even if it does have higher wave drag. An HPV needs a lot of hullform optimization to get the most out of very limited power; if you haven't tried Michlet yet it can prove pretty useful in this sort of craft.
Stability might prove a bit twitchy, although you do seem to be used to kayaks.

 

Just curious... How is it human powered?

 

Alex
You could expect to do 9kph in it (120W at the pedals, 100W on the hull). This is very good for the displacement and beam. The stability will be more than adequate provided you stow the heavy bits low down including your backside.

You could improve performance a little but I suspect it would come at the cost of stability. I think what you have is reasonable. You could optimise using Michlet/Godzilla but I think you are close given the stability constraint.

Mounting from the water's edge will be a bit difficult unless you make a side door. You need to be able to put your bum in first and then swing the legs around like a normal kayak. If you only have a top hatch you will need something to balance against while you board.

I will be very interested in your building effort. It sounds quite practical and robust. Did you know that you can do the sheet development using FreeShip.

Rick

 

Alex
I did notice something a bit odd when I loaded the boat file into Freeship. It does not use the convention of the stern at zero. Hence the Michlet export file is reversed. So the above figure of 9kph is for going backwards. You could expect a bit better going forward so that it is even better.

Looking at the wave drag in Matt's chart indicates he did not bother to turn the model around either so that data is for reverse. That is why there is noticeable wave drag throughout the range.

This is a slick hull. Would be easier for the rest of us if you turned the Freeship model around. I have never tried to do this before.

A great job. I think it is a winner at this stage.

Rick

 

I knew a guy who had such a concept HPV once. All enclosed, made of fiberglass. Great idea, don't flip it over.
Would be vy warm on a warm day, so ventilation (powered fan from pedal shaft, etc., would help.
Nice concept. Stability pods might be a good idea too, a pair of struts with floats to stabilize when standing, getting in and out, and (using one) self righting. A little vehicle like that could also maybe make use of the fabled mono-prop, an unbalanced low speed propeller with one blade. Theoretically, the most efficient propeller, but limited to low speed, low power applications.

alan

 

Alan
The monoprop will definitely work. Any high efficiency 2-bladed prop on an inclined shaft works as a mono prop. Each blade goes through a high forward thrust and slight reverse thrust during a rev. I have bent shafts under the bending forces involved. It also made me aware of the importance of running the shaft horizontal to avoid vibration. A low slip prop operates at an AoA of 2 to 3 degrees (including any foil camber) so if the shaft is inclined at 4 degrees you get very high forward thrust one side and slight reverse thrust the other side - much worse than a single blade run on a horizontal shaft.

The attavhed picture shows an 8mm aluminium shaft I have operated up to 700W pushing me over 9kts. It operates completely unsupported at the outboard end. A very effective way to reduce drag and maximise prop efficiency by letting it track in line with flow. I have video of it in a turn - it is amazing to see how it follows the flow.

Rick W

 

You saying, Rick, that the shaft is whippy, following the blade?
Nice boat, incidentally. What does it weigh? Looks like it goes thru a set of bevel gears off the pedal shaft.
You say you ran almost a horsepower thru it. Was that electric power?

 

Alan
All-up boat weight is 24kg. Hull and outrigger weigh 16kg. Heavier than a standard OC1 but mine has some extra plating to carry the drive frame.

The right angle drive is 2:1 step up and there is a chain step up on the input shaft of 3.75:1 so overall gearing is 7.5:1.

Cruising speed with the 1951 model engine is 10kph and it can max out at 17.8kph. Still to crack 10kts in any of my HPBs but my current objective is long distance cruising efficiency.

Rick W.

 

Alan
Forgot to add that the engine is me. 700W at the limit - maybe 730W on a really good day. These are RMS levels.

The flexible shaft robs a bit on average due to dead spot on the crank at full power but I am not really chasing outright speed. I would use foils if I wanted to go fast at my power limit.

The attached chart shows the speed log for the first day of the annual river race I have started doing. You can see the engine winding down after lunch.

Rick W.

 

Still, pretty good power. How do you do against rowing shells?

 

I've got the '54 model, love to row. What kind of efficiency comparison would you draw between oars and prop? I can see that your gearing must be robbing 15% at least. Doing 5 kts all day in anything that would hit 10 kts is damned good. What if your mechanism could work at 10% better efficiency? I'm guessing you're doing 120 rpm or so on the pedal shaft at somewhat above cruise speed. The prop is then about 900?

 

Alan
The comparison with a rowing shell is not really appropriate. A top rower will push out almost 700W for the 6 minutes it takes to blast down a 2km course. The boats are optimised for this power output. On the other hand rowing shells are not suited to long-distance river events because of the requirement to actually see where you are going and the lower biomechanical efficiency of rowing.

Rowing is competitive with other forms of propulsion for events up to about 1 hour duration in calm water. In rough water or longer events the biomechanical efficiency of pedalling or paddling get the advantage.

My latest boats are faster than the best kayaks over a long distance with equivalent engines. Mainly because of the efficiency I can get from a prop compared with what a kayaker or canoeist can do with a paddle.

Rick W.

 

Alan
I find rowing or paddling tedious compared with pedaling.

The following video will give you a good comparison between rowing and pedaling in choppy conditions:
http://www.youtube.com/watch?v=qrbNiCbzK3s
This is a commercially available pedal boat and not as fast as my best. I now tend to use very low reserve buoyancy so the boat runs flat in chop.

You are much more compact when pedalling and also facing forward. It is a bit like having a 2HP outboard motor that you can crank up or idle just by thinking about it. Really great fun.

My best gearing has measured at 95% efficieny overall and I have made props that are 87% efficient at my cruising speed. So overall about 83% efficient. The numbers for olympic rowers indicate about 70% efficiency and average joe rower about 60%. There is no technique involved in pedalling. You just roll your feet over and only difference between pilots is the power output and level of fitness. It is nice to use "clipless" cycling shoes if you are going to do it for a continuous 8 hours.

Rick W.

 

Thanks guys for all the input, and huge apologies for having it the wrong way round, I guess it's the problem of starting in one program (Kayak Foundry) and exporting to another (Freeship), Kayak Foundry starts you off going right to left, I'll see if I can turn her round somehow.

I'm pleased she'll do 9 kph in reverse though, it means I'll know I can pedal backwards against the flow and stop myself going over the weirs if I have to.

She's always going to be a compromise between stability, comfort, and speed, I was erring on the side of the two former, as I'll be spending a couple of weeks in her crusing the Nantes - Brest Canal which between the first and last lock is 360 kms long. I'll have to work harder at resolving the getting in and out issues though, I might just go for a couple of stabilisers. I'd wondered at one point about a very lightweight "tail fin" with a tear drop shaped top "bulb"split down the centre from front to rear, and hinged at the bottom, so each half can swing down and act as stabilisers. This might also help in a capsize to prevent the whole thing flipping right over. Anyway that's a work in progress.

As Rick knows from the HPB list (yes I am that one) drive has gone through a range of different options. I wondered at one point about centrifugal pumps, then rear props on long shafts, then the "standard" twisted chain, it's yet to be finalised. What I do know it'll have to deal with is being hauled out on a regular basis (as some of the locks are now sealed) and also if I'm feeling courageous the use of some Kayak slides - stainless steel slides about 1m10 wide which drop between 2 and 4 metres down the weirs next to the locks on the canalised river sections. So whatever I come up with has to be foldable, or lift out of the way - able. Ideas are always welcome (although not like my dad's who said "why not just get an outboard?")