Pedal Powered Boats

If I use a 3 ring front crank combined with the 8 speed internal gear in the back, then I can use 2 of the front rings so I can have a low and high gear range.

The third and outermost ring I can use for the prop drive. I can just slip the chain on the 3rd ring when the bike is mounted on the trailer frame / cataraft frame and then onto the prop drive assembly.

next, what prop drive to use?

 

Nexus hub

Sheldon Brown has info on the hub at http://www.sheldonbrown.com/nexus-mech.html if you are interested in more details. If you use the coaster brake version of the hub it is not compatible with a derailleur. That is not a problem if you get one of the hydraulic disk brake bike models.

Using the third (outer) chainring for prop drive: When a front derailleur is aligned with the center ring of a triple chainring the derailleur's outer plate interferes with a second chain being on the outer chainring. You can swap positions of the middle and outer chainrings to provide enough clearance between the outer chain and the derailleur's outer plate. That makes for a big step between the inner ring (smallest) and middle ring (largest). Compact road double rings are typically 34T and 50T so they can handle a 16 tooth jump.

With planning it looks like what you are trying to do is achievable.

Dave

 

3D-printed prop

Andreas,

Probably the size of the hub is driving the cost. The hub diameter is typically around 8% or 10% of the prop diameter. For my 20" prop the hub is 1.95" diameter. I need lots of thrust at low speed to push my heavy boat along. For faster, lighter, more easily driven boats smaller props can be used. So I am curious how much it would cost to 3D print a 1" diameter hub. If you cut all the dimensions in half the volume goes to one eighth. Is that easy for you to scale from the model you built? That might put the cost per hub into a more interesting range.

Thanks, Dave

 

@Dave:
50% is 104€ for stainless steel and 12,5€ for PA6 (both solid).

@Porta:
The most efficient supershort HPB is not easy to tell, but I am currently building a 2.6m x 0,65m boat with 0.23m draft, which according to tests will go at 10.5kph cruise @150W and weigh much less than 20kg. The building costs are around 500€.

 

Thanks Dave!
so from what my thread over at mtbiker is telling me the Nexus isn't really the choice over there but there are others, I still have some shopping around to do.

about the front derailleur, when in prop drive mode I could have the derailleur positioned to the inside chain ring so there is room not to hit the prop drive chain?

dang, I just thought about how the front derailleur idea might not work, the chain travel distance will change and it's the rear derailleur that takes up the slack so ...... can't use the hi/low range idea in the front, but I can still use the other chain ring for the prop drive. I'll have to select my range using the front and rear sprocket set up initially.

also, I think whatever resistance spinning the rear wheel is will be hidden by the prop resistance in the water? I'm not trying for ultimate efficiency , just ease of operation as my on water distances are short.

I'd use a disc break not the coaster/rolling version if i end up with the nexus. it is supplied with the "fat sand bike" model I'm looking at but there is the option for the disc.

still playing around with the trailer and cataraft frame design .....
I can use the stock hitch but I'm not wanting to use the rest of the trailer.
I like the idea of the rear shock, plus I could remove the whole rear swing arm when I go into the cataraft mode to give the bike rear wheel some room? Hadn't played with this enough to know this yet.

 

about the front derailleur - Yes, you can position the front derailleur so it won't interfere.

The 8 speed internal gear hubs give a 3 to 1 range of gears so it is probably not a problem if you can't shift between front chain rings. Just choose a front chain ring that places the gear range to give you the speed/torque you need.

Dave

 

3D-printed prop

Andreas,

12,5€ for solid PA6 seems worth it to me if I was making a 1" hub or perhaps twice the cost for a 1.25" hub. Not very expensive to get a custom fabricated piece. That would avoid the machining and have the holes properly positioned.

Thank you for letting me know about the 3D printing.

Dave

 

Proper Sub Topic For Propulsion Forum?

This is an extensive thread with lots of solid information. It appears to deal with propelling a boat with human power.

Would it be wise to reclassify this thread and create a new sub topic for the propulsion forum?

Then in this forum we can discuss the best hull form for a human powered lobster boat.

 

Tom
What exactly is a lobster boat?
Number of people, load to carry, speed, open water or sheltered waters?

Ian

 

Hi everyone. I'm a new member with several questions re: pedal power, questions that have not been answered in this thread (I read the whole thing, cover to cover, over the last few days and nights). First I need to familiarize myself. Here's a try at posting a picture.

Nothing.

OK, I can't copy and paste from Flickr, better read the directions. First I'll try to C&P the URL...

http://www.flickr.com/photos/48858202@N05/6528925733/sizes/m/in/set-72157629770540321/

Looks good, I'll post this to see how it comes out.






Ok, let's see if this works. Wish I could just C&P it.

No dice, looks like I missed the "upload" button, will try again.




OK, that's from "My Pictures", Windows XP.

 

Welcome to the forum Gib.
There are two ways to include photos in your post. You can select photos from your local drive by clicking 'Go Advanced' and then 'Manage Attachments' to upload the photos and attach them to your post, or you can use IMG tags to embed a jpg that is already hosted on your website or webspace elsewhere (not a url of an html page but the url of the actual jpg image) into a post. (longer explanation)

 

I don't know how to use the image tags, and I don't see any directions for doing so in "Manage Attachments".

Also, it appears that all of my several posts were run together into one, which makes it a bit confusing I expect. Will this always happen if I post consecutive messages?

 

Here is an explanation of the codes you can use, including IMG tags, within your forum posts.
http://www.boatdesign.net/forums/misc.php?do=bbcode
Note the IMG tags won't actually attach or upload the photo to your post; they will simply include the image pulled from your other website into your post so you should take care that the image isn't removed from the remote site and that you haven't hotlink protected it if you use IMG tags.

(P.S. the sequence of test posts were merged because they appeared to be test posts rather than part of the Pedal Powered Boats discussion.)

 

Well, I don't speak Greek, and that sure is Greek to me, so I'll just stumble onward and make due with what I do know how to do. I guess if I paste images from other websites into "My Pictures" I can move them from there to the reply box easily enough, not that I plan to be doing much of that anyway. Thanks for trying to help though, I appreciate it. I'll post this now, then get to the point in a new post.

 

Gib,

To get image tags to work the image needs to be hosted somewhere on the web, not on you PC (you're Flickr image is already web hosted).

you can either manually wrap tags around the link to the image, or you can use the button in the "Go Advanced" reply option that does it for you.

For example, the Flickr image you linked to earlier really has this URL: http://farm8.staticflickr.com/7004/6528925733_5982440dd9.jpg but if you just add the link then it doesn't appear as an img. To get an image in the middle of your post you have to surround the URL of the image (which must be the actual image, not a web page with the image in it) with "img" tags.

This is what that same link looks like when inserted as an image (just using the letters img and /img either side of the URL, enclosed in square brackets):



You can also just attach uploaded images from your local PC, as you've found already.