Multiple Gear Boat w/ Propeller

Also an interesting idea, but I think the one with the propeller is easier for me to start with. Just the right angle converter is needed, some sort of shaft and some clever bike mounting in my original project. Plus, when I saw that vintage video of the human powered boats competition, the paddlewheel designs mostly ended up being last, and a boat with two guys and a propeller won.

 

If gears were a good idea in boat propulsion, we would likely see them widely implemented.

As was explained to me a long time ago, operating a motorboat is comparable to driving a car at high rpm and driving uphill wherever you go. There is a huge difference in a bicycle or car coasting down the road vs. a boat pushing through the water. While most modern cars have engines producing well upwards of 100hp, it only takes around 5-10hp to keep the car going down the road - the extra hp is used for acceleration, climbing hills, towing, etc. The boat is always using the majority of its hp to push through the water.

As Rick pointed out, much more application of power generally results in cavitation at the prop.

Perhaps it would be more efficient to modulate the angle of attack of the prop blades (like a helicopter) rather than to fiddle with gears in the driveline.

At the very least, you could play with prop venting as is done in high-performance props (allows air (or exhaust, in the case of outboard engines)to access the prop blade at low rpms to reduce water resistance at low speeds, then becomes nonsignificant once cruising speeds are reached) - this allows for higher-pitched blades than would be possible with a given amount of power.

 

Yes, I've been coming to the realization that gears perhaps aren't very important or needed in a boat from Rick's posts already. However now, the question stands about what right angle converter to use, where to mount it on the bicycle, and what sort of metallic shaft to utilize, and how to utilize it when it goes from the right angle converter to the propeller.


Edit:

I still do think that leaving the gears in place will allow me to use them beneficially. Personally, I am quite an avid fisherman, hence the need to use my big old flat bottom boat. There are close destinations where I could get on a hard gear to pedal for just a few minutes, but to go very fast, and there are long distances I want to go to, where I would select an intermediate gear which would utilize my leg muscles most efficiently so that I could pedal comfortably the whole way there.

 

I have attached the data sheet for the T-081. It is close to ideal. The "T" configuration offers more flexibility as you do not have to worry about the direction of rotation of the prop. You can change rotation by flipping the box. If you look closely at the photos of my boasts you will see they use a "T" type box.

You now need to get a sprocket for the shaft that will accept bike chain.

Building something like this is easier if you have access to some basic workshop capability.

Rick W

 

How exactly will the sprocket be utilized in my setup? Why can't I just use the sprocket from the bike's gear system?

 

The shaft on the bike is fixed. It does not rotate. You need to find a way to get one of the small sprockets from the cassette onto the gearbox. Or buy something like a 12T or 14T sprocket and mount it on the shaft.

The only items of use on the existing drive train are the chainring, bottom bracket and cranks. The rear wheel will need to be removed.

Rick W

 

I have used a MTB 15T sprocket welded to a metal boss and fitted that on a gearbox shaft but I find it easier to buy a standard 14T sprocket and modify it to suit the narrow bike chain.

Rick W

 

Though I see the sprocket isn't really too expensive, I haven't been planning on such a complicated mod. I imagined that I will be leaving the back wheel on for some reason. I guess it should come off, but I have never even tried to disconnect the gears from the back wheel. Can't really imagine how I would mount the bike on its forks and install the sprocket to work together with everything. How can I retain my ability to switch gears in this setup?

 

As you get into it you will see that the bike and the boat do not go well together. By the time the bike frame is set high enough for the cranks to clear the bottom of the boat you will be sitting quite high and the boat will be marginally stable.

The easiest and best set up would be to cut the bottom bracket out of an old frame with about 300 to 400mm of tube on either side. This gets inverted and mounted to a plate that fits in the bottom of the boat. You would get a nice comfy seat to mount on the rear box seat of the boat so you can pedal in a seated position. It would be semi-recumbent.

The gearbox would be low in the hull with a small sealed shaft tube that penetrates the hull. The prop would mount just behind the transom on a springy curved shaft so it can be pulled up for beaching.

I can draw this up if you are interested. This would be a more serviceable set up and make the expense of the gearbox worthwhile. Anything involving the upright riding position of the existing bike frame will be ungainly and bordering on unsafe when in operation.

Gears are an unnecessary complication. Riding on the water is very much akin to riding up a long steady incline that just goes on endlessly. Taking time to change gears means you quickly lose speed and have to start over. Cyclist that take it up soon learn that there is no coasting. Stop spinning and boat soon stops. Glides on somewhat more if the prop freewheels but then no reverse.

I can give you better targetted information if you let me know what workshop facilities you have access to. Things like brazing, welding, milling, turning, drilling, grinding, fibreglassing etc.

Rick W

 

In terms of expectations what speed are you hoping to achieve with this pedal powered boat?

Rick W

 

I am greatly interested in seeing a drawing if you could make one. In regards to speed, the faster the better. The whole point is to have my hands free while moving the boat (as I mentioned I am a fisherman) and the second point is for the fun of it, especially if I can make it work with gears. I don't know what exact speed I am aiming at. If I row at an average of 8mph, (whatever the speed is, I don't know) then I want the propelled boat to go about that speed. If it can't do any faster, it's not much of a problem because I still have my hands free when moving, but if my rowing average is 8mph, then a max of 4mph with the propeller would really be unexceptable.

 

In regards to the workshop facilities, VERY limited. No welding at all. Pretty much drilling I can do, and grinding I guess. Very limited powertools. Actually, the only power tools I have so far are a drill and a saw. Got lots of hand tools, and a friend who has several lots of stuff which I would probably be able to use. But so if you can give more specific directions/instructions, try to treat the situation as a given that I have minimal equipment.

 

You may be able to manage 4mph while rowing. You may get the boat to 5mph with pedalling if it is set up well - bit more if you really put full effort into it. The boat is not a speed demon. Its shape, with typically human power level, condemns it to slow speed.

I will draw it up tonight. Can you give me the hull dimensions; just length beam and height to save me estimating?

The easiest way to assemble it all is with epoxy and glass tape if you cannot weld thin wall steel tubing used on the frames.

Rick W

 

Thanks. Take the dimensions from here: http://www.academy.com/index.php?page=content&target=products/outdoors/marine/boats&start=0&selectedSKU=0141-00124-1032 The boats are serial so mine is most probably the exact same size and shape. It looks 100% the same anyway. Thanks again.

 

I have attached a 3D image of the proposed configuration. I have used a rendering of one of my boxes rather than the Mirpak but they are similar. The Mitrpak is slightly smaller.

This is intended to show how the inverted bike frame would be used. I can describe ways to mount the gearbox that you should be able to achieve. There are some basic parts you need to get. If you have a tight budget it will be worthwhile pricing all the things before you jump in. Also some bits may be hard for you to get. Some things will be best done by connecting to the existing boat and you need to decide how permanent these will be. A hole in the hull will be difficult to patch neatly without welding ability and there may not be a big market for the boat.

I expect you will enjoy it and it certainly leaves hands free. It will attract a lot of attention so you have to be prepared to deal with that.

I have no idea where "yes" is so cannot make meaningful suggestion where you might look for parts.

You should be able to sustain about 4.5mph and hit around 7.5mph at full tilt for a short period. This assumes you are an adult male of average weight and fitness level.

Rick W