Pedal Powered Boats

@jdrower:
The Lakerunner was surely one of the best HPB, but Yamaha decided after building 5 prototypes not to go into production.

 

Question to everyone

I would like to build a shaft drive going through the hull, but there are two parameters I don´t have the expertise how to dimension:

Question 1:
Which diameter stainless steel rod (hollow/full) do I need for a mean torque of 4Nm? Can I take an 8mm with 1mm wall thickness?

Question 2:
If this shaft runs through a 12mm hollow shaft going through the hull with 1mm wall thickness, how many Teflon bearings do I need to support the inner shaft? All 0.5m?

Thank you in advance for all help

 

Flex shaft stiffness

Initially I used a 1/4" solid stainless steel drive shaft, 8' long with 1:5.3 gear ratio. I measured its compliance at 4.42 Nm/Rad. At low to medium power that shaft worked OK. At high power (sprinting) the shaft was very springy. If I increased the shaft diameter to 5/16" the stiffness would increase by (5/4)^4, a factor of 2.44x to 10.8 Nm/Rad which would be sufficient for cruising and maybe OK for sprinting. I measured my carbon fiber drive shaft at 19.9 Nm/Rad. It feels very solid even when I am sprinting.

Dave

 

Thanks Coach Dave!

My plan is a modular drive system. The first module would be a two stage gear with a HTD belt 100:22 and a second stage with 4:1, totaling in 18:1. This module can either drive a direct shaft or a Z-drive twistable for about +-30°.

According to my calculations, a 16" APC prop has about 90% efficiency, but in reality will be at 87% due to false Reynolds and so on.
A 8" custom prop would run at 1200rpm and still have 84%.
Designed for 1600rpm it has really good weed shedding running at 83%

60rpm at crank will get 150W
90rpm at crank will get 550W

550W is needed for a 5.5m monohull driving at 5m/s (18km/h, or 10kt)

Andreas

 

Flex shaft stiffness

Andreas,

The information you provided on your proposed gearing gives me a better idea on your approach. When I am sprinting with a gear ratio of 5.3:1 and a shaft compliance of 19.9 Nm/Rad on the carbon fiber shaft (i.e., 105 for the product of the two) the shaft feels very solid. With the same gear ratio and the 1/4" stainless steel shaft's compliance of 4.42 Nm/Rad (i.e., 23 for the product) the shaft feels rubbery (springy) and limits how much power I can deliver to the propellor. So my experience is the gear ratio x compliance product should be about 100 or more for sprinting on a pedal powered boat.

Let's compare configurations: I measured my 1/4" x 8' solid ss shaft at 4.42 Nm/Rad compliance. Scale it up from 1/4" to 8mm (8/6.35)^4 = 2.52 so the compliance would be 11.1 Nm/Rad. The gear ratio x compliance product would be 18 x 11.1 = 200 so it should feel very solid. Now instead of the 8mm solid ss shaft consider a hollow one with 1mm wall thickness. Its compliance is less (8^4-6^4)/8^4 = 68.4% of the 11.1 Nm/rad which is 7.59 Nm/Rad. The gear ratio x compliance product would be 18 x 7.59 = 137 which should also feel very solid. If your shaft length is different than 8' then scale the numbers accordingly.

Dave

 

Nautibike

I was searching the web and can across the Nautibike which is a typical small pedaled cat. of about 3 m lg. This is quite well engineered but the interesting thing is a very large propeller about .55 m diameter. I could see no reason for this and wondered if they were attempting to use a surface piercing prop.

Dennis

 

No, a bigger wheel is better for efficency and works better with human power production erognomics.

 

Nautibike

The prop looks large and robust - for a rental boat it needs to be fairly rugged so it won't require frequent repairs. Their belt drive system limits the gear ratio which favors a large prop running at low RPM. The large prop prevents operation in shallow water and has quite a bit of drag. Keeping the same prop pitch while reducing its diameter would allow operating in shallower water and reduce the prop's drag. A prop diameter of about 0.46 m would probably provide enough thrust for this catamaran. For a lower drag hull like a long slender stabilized monohull less thrust is required so a 0.33 m prop diameter would be sufficient with a higher gear ratio. Some folks are using even smaller props with good results on low drag hulls.

Dave

 

http://nautibik.o2switch.net/nautibike/en/index.html
here's a link

 

I have also experimented with a belt drive, but I am using a two staged gearing at the moment, as the maximum ratio you can get with one stage is around 1:5. This means, that the prop has a speed of below 300rpm leading to a prop with an advancement ratio of 1.4 (advancement vs diameter). In order to keep high thrust at blade angles over 45° (--> advancement ratio 1) they had to keep the blade area big.

By doing so, the efficiency goes down from >90% to 84%, which my 0.2m prop has too (but for twice the speed )

By the way, where did you find a picture of the prop? I couldn´t find one.

 

Prop look like RC type:

http://www.nautibike.fr/water-bike_nautibike_pictures.html#.Ui-EGH_nKSo

Fourth picture down. Not a surface piercing from what I can tell...

One stage, high gear ratios can be done with a planetary, but I don't know if these are available in the HPB range.

P

 

OK, I have to revise my statement after seeing the picture.


The prop has around 90% efficiency and is fully submerged. It is a 16" RC prop, just branded with their name.


Together with this short and wide hulls, the efficiency of the prop seems just to be worthless. You can go at 8kph at very high efficiency

 

Lakerunner on ebay

There's a Lake runner on ebay - bidding ended just 2 days ago, and it didn't meet its reserve of 1250 USD.

 

Bid-Ask illustrates the lack of a market for rare, one of a kind, top notch pedal boats. Often a loss leader for manufacturers. Even top notch 'foils and Greg's Within designed by Rick W. couldn't catch a decent bid last I saw. I would be on my own as regards parts and repairs and have to use very often to justify the storage and depreciation..

Porta

 

Hello,
my name is Achim, living in Germany near by the saar-cole-canal.
This winter I want to start my hpb projekt and hope to get some advices from here.
The hpb is for french canals and rivers , for daytours, week-end trips and one long distance tour next summer, not for sprint, but with good performance, as I hope.

It is a catamaran 4.6 - 4.8 m lomg, max hull width is 25 – 30cm, the hulls in two parts for transportation and storing, made of ply, foamed out with 2 compenent pu foam. The displacement will be about 180 – 200 kg each, enough for me, camping gear, bike and bike hanger + reserve for my long trip.
There are some big floodgates where I can not go in., the boat will be tranported on the bike hanger. The hanger ist just two wheels and an axle put through two hull halfs.

Woa +120cm (don't know yet) any idea ?
Beams are fixed with lashings to the hulls, as I prefere it to be flexible.
One rudder in stern plus dipping rudder in front for good steering.

I tend to chain to right angle gearbox to shaft drive, what allows me going backwards.
The prop can be lifted up with the shaft for weed cleaning and beaching.

Prefered frequency is 60 to 70 rpm ---- normaly I count in bpm -beats pm

Is the 1:4 ratio the right way to play with by using a APC 16x16 ?
How thick has the shaft to be ?
Does it needs bearings beween gear box and the support of the prop ?
The shaft will be 200 – 250 cm.
Or better to use a flex shaft ?

All comments and advices are very very welcome !

Achim