front rowing system for canoe

Since it hasn't been mentioned yet, I just wanted to mention the existence of "Reelfoot lake oarlocks". They are used to navigate the cypress choked oxbow lake in the NW corner of Tennessee. Haven't been there in many years, but they were on all the rental boats. A google search didn't turn up much, unfortunately. Maybe someone with more persistence can dredge something up.

 

Magnus,

In the right application I would like steel, but not aluminum because its hardness lets it retain the designed shape better. Except where it rusts in a water enviornment, or when the mating surface needs to be as hard or harder - typically means heavier. Aluminum wears rapidly in metal to metal contact unless the pressures are very low.

Happily, Delrin/ acetal has good (not great) frictional properties, is relatively stiff, and relatively light weight. So it holds its shape well in a wear situation, I suppose that is why typical sailboat pulleys are made from it.

Urethane on the other hand is classified as an elastomer, no matter what grade you have, and deflects a lot for a similar load. That works great when you want a tire - roller blade wheel/tire, etc., but no so great when you want enough stiffness to keep you load mechanism working without deflecting - which usually costs you lost energy. Not something I'd want in a rowing mechanism. We really don't need a shock absorbing mechanism in a row boat, at least I don't.

Enough, just try the urethane wheels and let me know how it worked. Didn't for me, but I might not be very clever.

Marc

 

Delrin cam followers are available. You can probably find plastic rollers for sliding doors and windows in a hardware store and smaller ones around 1" used for kitchen drawers: they won't last as long as cam followers but they would be cheap, easier to get and OK for a proof-of-principle prototype.

 

Magnus,

I see I didn't read over the message above very well.

Steel works great in a mechanism, except for corrosion and my desire not to make a swiss watch precission.

Aluminum wears too quickly.

Sorry for the poor wording.

Marc

 

Ancient Kayaker (aka turkey dancer?)

The typical rollers are polyethelene. Better get a big one so they don't distort and stop the test. Just not very stiff, sort of like the urethane. Just think about the load on a screen door, not as much as even close to what a modest person can generate.

If you just want to see the mechanism move, I agree with you completely. If you want to use it, at least use nylon - not as good as Delrin for friction, but it probably won't bind up if it is at least a fair size (not screen door rollers).

Again, talk's cheap (mine I mean). Please let me know how it goes.

Marc

 

Actually the cheap 1" ones I have look like nylon. I put four under each of the the storage boxes in the crawl space so I can roll them out easily for access; those boxes are loaded quite heavily. They have been there for years and the rollers haven't taken a set.

The ones under the old sliding patio door (which weighed a ton) also looked and felt like nylon. They worked for at least 35 years during which time I lubricated them just once when I replaced one a few years ago - it had seized and worn a flat. The door was replaced last year but still moved easily and smoothly = although not as smooth as the new one. Whatever those things are made of, they seem pretty tough and I think they'll last long enough to verify a design.

 

I used acetal (delrin) rollers on the foot carriage of my bow facing rower; two on top and one on the bottom. they are about 30mm in diameter and have sealed 608 (skateboard) bearings. They are holding up fairly well; they show some surface flaking riding on an anodized square alloy tube, which shows no wear.

I finally bought a GPS and got my craft out of storage to do some speed trials. I also took 14 pounds of hardware off, added a basic seat, footbrace and a carbon elbow paddle to compare speeds. I was about 1.5 knots slower with a paddle in relatively short sprints, I will do more testing. It was sure a delight to throw 30 pounds up on the car instead of 44, and you have to love the simplicity of the paddled craft

 

Magnus,

Do you have a picture, I'm interested.

Sounds like my rear facing sliding rigger carriage.

Marc

 

Phil, google Reelfoot Boats instead of "oars"

http://www.reelfoot.com/bow_facing_oars_1.htm

They look like the double jointed system, with an ability to stow the oars along the gunnels and thus out of the way.

 

I cannot get a picture to load tonight. I introduced the boat to the forum on page 58 of "designing a fast rowboat" thread. I was a bit off topic I discovered after reading the entire thread: it is at 80 pages now and covers traditional rowing mostly. There is a picture there, and you can get some detail if you zoom

 

Jim, here's the link your image -

http://www.boatdesign.net/forums/attachments/boat-design/49698d1289625027-designing-fast-rowboat-rowing.jpg

 

Thank you Terry, I am handier in the shop than at the keyboard

 

Here is a model of dual straight tracks w/sliding seat(4' stroke) dimensions

The tracks and the cross piece on the 10ft oar are all 76inches.

The rectangle sitting in the boat is 4ft by 2ft outside to outside and is for reference.

The close up shows the problem of a collision between the tracks and oar if the oar is dipped.


Now I'm thinking of going back to the curved track, and use a cylindrical track like the Japanese guy.

His wheels solve the oar dipping problem. Instead of concave wheels I might use side-by-side skate wheels and maybe some lube on the wheel to pipe contact.



It might be easy to curve a metal cylinder similar to how they bend electrical conduit: by inserting a flexible object(coiled spring) slightly smaller than the inner diameter so the pipe can't fold. In this application there would be no need to removed the object so maybe a dowel cut into short sections would work. Maybe with epoxy, too. Stuff a bunch of wet epoxy coated wooden dowels, bend and let cure for extra strength.

Then a couple of bends(like the Japanese guy's) to make the tracks connect head-on amidships so they brace each other.

 

The overall length of the two straight segments is unfortunate; the length of the curved-track comes out to half plus the carriage length for the same rowing geometry.

That can be avoided by inclining the outboard ends of the tracks down like the curved-track system by the Japanese guy. The center of the carriage where the oars attach will remain at constant height. But I don't think the straight-track system is the way to go.

I think multiple wheels around the pipe instead of each concave wheel would reduce friction and bearing stress.

A plumber, some machine shops or one of the guys who do custom exhaust pipe systems would probably do it for you cheaply.

 

something a little different

Feel free to continue this train of thought, but I thought I'd post something a little different that I'm thinking of experimenting with. It's similar to Rontillas system, but somewhat simpler. I'm not an engineer, but it seems to me that with something like this you get a good range of paddle movement while limiting body movement. A metal spring helps lift the oars out of the water on the return.


What do you think?

(I used gickr.com to make the animation)