3D Printing Group

I saw your discussion and first thought I had was...naaaaa, whom would do that?

Than I run a quick serch online

To my surprise some people did, mostly for RC model aiplanes, but the base principle is the same, unfortunatelly the ones I found cost a few bucks to download, but I guess is worthed.

You download one that looks pretty solid design, print it, put it together and try to understand what you can modify to match your needs.

Than jump on your CAD program (if you have none just download FreeCad

from the link above, than go Youtube to see the various tutorials, some actually start with how to install it, how to open a page, make a body, select a plane an start a sketch, if you never ever used CAD programs, others are at the level where you extrude/pad/etc, in the most bizzare ways, spirals, et)

And in a couple of weekends of work I bet you are going to hav e your first print out of your first work.

In order to print it sturdy, go see totorials on printer setup and slicer setup on printing fire guns and model airplanes, those prints must withstand huge impact moments, especially a gun when it fires real ammo, I guess your propeller might need such strenght too.

After a few more re design (best ideas come always after you use your print a few days in real life) you are going to have a good enough product to be happy with, product you can give away on various platforms, here included, or sell on others, for more people to print it.

Or you could pay me 1500USD to do all this for you, yep, when I work on a contract basys I ask to be paid regular rates.

David, I think your going to find that all this is a trade off. An increase in pitch is going to be more load and therefore more current draw. your Kayak is probably going to only work as a displacement hull and therefore is going to have a limit on it's speed based upon it waterline length. 5 mph is probably about all you will get with a Kayak under 13' or so... see below

https://www.boats.com/reviews/crunching-numbers-hull-speed-boat-length/#:~:text=As%20a%20very%20general%20rule,%3D%201.34%20x%20%E2%88%9ALWL).

so, unless you add a ridiculous amount of power and hence energy to get your Kayak on plane, you simply won't get much more top speed out of it. I would look at what you current draw is with the current prop and see if you even remotely have enough battery to carry a larger load for the time you need to be on the water.

If your current draw is nominal then you can maybe prop up to get slightly more performance and still have enough battery to get you back to shore. The trolling motor mfg. should have prop options avaliable for you to try at a much lower cost than creating a variable pitch set up from scratch. Just my Opinion though.

Thanks Mark Ayers

Well Mark, you just spoiled a good one here.

I am sure David would of gotten to the exact same conclusions by himself within a couple of years by usig my way, but in the menawhile he would of also become at least decent if not good at CAD design, 3D printer and slicers settings, might of strived to improve his printer so he can mitigate variables, etc.

Nw he won't do any of this. Blimey.

Sorry, just did not want him to waste a lot of time... Physics is just not real forgiving, and I happen to know a little about boats and hull design.

it would be cool to have a kayak that could do 30-40mph, but it would have to get up on plane and then your talking wave runner...

Although, the old wet bike design, I thought was totally fascinating!

now, he still may want to work on the variable pitch prop for efficiency.

And then he could minimize the current draw and stay out longer.

:)

David

If you are still interested there are about 1500 propeller designs on this site. If you search the library for controllable propellers you will get about 4 results, One of the models is an animation of how the mechanism works, as well there are 3 designs for you to have a look at to get some ideas. Instead of designing a variable pitch propeller what you are really looking for is to what they call propping an engine or motor. Basically you change propellers of varying pitch and diameter until you get the best performance. Piranha Propellers out of Illinois I believe build Flexible propellers for a lot of applications. Once you have the hub the blades are relatively cheap.( no I don't work for nor do they pay me. If it is possible to temporarily change the design of the kayak lets say adding steps on the hull and introducing air into the void created by said step you may be able to get the kayak up on plane. Or just put a bigger motor on it.... LOL

Regards

Scott

Also, you could 3d print several propeller options and try those!

ABS or Nylon would be a great material.

Thanks for all the great feedback. It sounds like I may not be able to get the performance I was looking for with a variable pitch prop. My thinking was I could pull out of the hole with a lower pitch and increase it as I gained speed but as pointed out, the power requirements are too great. Oh well, I am going to print a couple files so I can understand the design better. Thanks again mates.

Hole shots are determined by the amount of the motor you have in the water,, The balance to that is porposing (nose of the boat pops up and down) I am sure that on this site there are enough smart people who can help you along the way. show people you are serious and run some experiments. Publish your findings here and you can enlist some to be sure as an at least you could spark an interest in your project.

Scott

I got you a treat:

here is somebody that explains well all the concept of kayac propulsion and limitations and how to overcome it a bit

Dude is a scietist, but hands on he also builds things to demonstrate, at minute 46 onwards he actually shows a way to put a better propeller, but the kayac limitations itself will come into your way short after ypu try to raise the speed.

To go higher speed you need a hydrofoil underneath

If a 30lb of thrust electric trolling motor will push a medium heavy kayak at 3.1mph and a 55lb motor still only gets up to 3.1 then a proper prop on the 55lb might increase speed and performance without the load limit concerns, right? Or, am I missing a few factors? It seems the 55lb with a little more aggressive pitch prop would move it quicker with a minimal concern for heat, load and such. I know I ramble but, does anyone have the quick answer?

Would R/C plane props be a smart place to look for several differently pitched props. Who would be smart about such things?

Airplane props would be terrible in water! They are designed for a substantuly less dense media.