For those with outboard conversion ambitions, I have at least 2 different size outboard props that could be experimented with.
One is the twin to the one I use on The Reach Of Tide: a brass 12x12x3" that has been adapted to work on Tohatsu M25B shear-pin drive outboard.
The other is a 14x12x2 (?) brass prop (not balanced) also adapted to work on the Tohatsu.
I also have 2 pitches of 9.9" diameter Tohatsu props.
Image of one of my 12x12x3" props (with PropGuard on my outboard) can be seen here: www.evalbum.com/492
-Myles
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
Sent: Friday, December 25, 2015 5:46 AM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Props for EP
King: That's a great idea. After you finish experimenting, maybe you could pass along your props to group members who are interested in testing them and contributing to some sort of database.
--Bob Moriarty
Ox 1976 C&C 33
LOA: 32.87' / 10.02m
LWL: 26.42' / 8.05m
Displacement: 9800 lbs./ 4445 kgs.
Batteries: 4 X Northstar 210 FT Blue+
Motor: Motenergy ME 1114 Rev A
Controller: Sevcon Gen 4 275 Amp
Current Prop: 2-blade fixed 16X10X1
(original - came w/A4)
Jax, FL USA
On Friday, December 25, 2015 1:21 AM, king_of_neworleans <no_reply@yahoogroups.com> wrote:
Thanks for that, James. It brought a lot of stuff together. I just converted to electric a year and a half ago and I am still running the original 2 blade willow leaf folding sailboat prop which is a real dog of a prop for electric, but money is way tighter for me than most guys here so a LOT of things that I should do or should have done, get put off. I was thinking about increasing my reduction ratio and mounting the biggest 4 blade prop with the widest blades that I could find that would give me decent hull clearance, but I am also thinking it would be really cool to experiment with more blade tip trail and more cupping. So what I really want to try, simply isnt available and certainly isnt available in varying degrees and if it were I would not be able to afford an endless stream of props to try. Modeling software just doesnt do a good job of presenting real world performance comparisons for what we are talking about here; as everyone knows it is mostly all about infernal combustion engine props.
Last week I built a 3D printer from a Chinese kit of parts. 3D printing is not something you just open up the box and DO. It takes a while to tweak all the parameters and techniques. But I am hoping to be proficient enough in a year or so to make an ABS prop, which will greatly improve the practicality of experimenting with different prop geometries. There are some hurdles to overcome. First of all, good solid prints are SLOW to make. Second, ABS is much more difficult to work with than PLA plastic, and PLA simply isn't strong enough. Even ABS will have enough flex that it will not perform exactly like a duplicate in bronze. I figure printing hub, blades, and cap (print area is only 8x8x7 so I have to take a modular approach) for a 4 or 5 blade prop will take about 3 weeks. The good thing is once a print is started, it doesnt require much attention from me and I can just leave it go for a couple of days while it is making a part. I can probably extend the Y axis of the print bed but doing both Y and X axis would be extremely difficult, so printing a one piece prop is not going to happen. Anyway, I thought printing a prop would allow a lot more tweaking and serve as a prototype for casting in bronze or aluminum, and I was wondering if anybody else has done this.
I may take baby steps first, by printing a prop for a 36lb thrust trolling motor I just bought to electrify my pirogue. I will be bypassing the crude and inefficient built in speed control, with a PWM controller, and using a 48v 20ah LiFePO4 e-bike battery pack to power it. The cheapie plastic 2 blade prop looks like a good candidate for an upgrade and I may do some experimenting along these lines with this, first, and scale up the final design for a starting point for a boat prop. All this will cost me is a few rolls of filament, and a diver to pull the original prop which has been on there for 38 years. I should be able to manage okay for myself, after pulling the old one.
I am not really considering using an ABS prop as a permanent replacement... it simply wont hold up to long and hard use, I dont think, and blades will maybe have to be thicker than bronze and the root of the blade will certainly have to be overbuilt. But it would maybe make the experimentation process more feasible and deliver a finished design that ought to work for a cast/machined metal prop. At the very least, I end up with a nicer plastic prop for my trolling motor, and that one I can probably print as a one-piece.
So does this sound like a good idea?
Posted by: "Myles Twete" <matwete@comcast.net>
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