One factor that drives a lot of us is cost. At the time that I wanted to go bigger with my prop, I couldn't see spending hundreds of dollars on a new prop that might not deliver or might deliver performance that just didn't justify the cost. Add to this the fact that most of my boating was short trips with little range anyway, it really was a luxury to even consider going to a more efficient, larger diameter prop. Still, I went that direction and bought at least 5 different props and tried at least 3. Since my drive is via an old 25HP Tohatsu outboard lower unit, I've been constrained to using its small diameter shaft hole and having to use a sheer pin drive. Used or surplus propellers out there that are larger diameter and of the shapes & pitches we'd like generally aren't designed for higher speed outboards and use conical tapered key-fittings vs what is used on outboards. My first prop I tried was a higher pitch Tohatsu prop---was able to get the speed up higher, but it wasn't any more efficient. After deciding to go larger, I modified my lower unit to allow swinging up to a 14" diameter prop. At some point I got a 14", used 2-blade brass prop on Ebay for a good price. With that in hand, I had a friend machine a brass insert that allowed attaching this prop to my outboard shaft. While it was pretty clear that the larger diameter prop was a bit more efficient, it had 2 flaws: insufficient blade area due to only 2 blades and secondly, the prop shaft hole we ended up with was not aligned well enough---vibration levels were just unacceptable. At some point I bought a pair of good used 12x12x3 brass propellers on Ebay. We again created inserts for these, but this time we were careful to ensure proper alignment. I've been using one of these 2 props now for perhaps 8 years now (?) and have been pretty happy with it. While I'm sure there's an optimum out there that is something like a 14x11x4 prop, what I have now is pretty darn efficient and its size along with the 12-S lithium pack voltage (31-48v) causes the motor to hit about 10kw at full throttle---ETEK motor is rated at 8kw.
In retrospect, about the only thing I wish I'd done differently is to come up with a conical insert for these props that is quickly adaptable to a new prop instead of being press-fit and glued in place. Had I done that, I'd probably be swinging a 14x11 prop now.
Anyway, if someone out there needs to spin a 12x12x3 prop on a standard Tohatsu outboard shaft someday, I have a spare they can try or perhaps buy from me. Also still have that 14xNx2 prop that is good to experiment with.
-Myles Twete, Portland, Or.
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
Sent: Wednesday, December 16, 2015 9:53 AM
To: 'Sdolan' sdolan@scannersllc.com [electricboats]
Subject: [Electric Boats] Props for EP
Since many of us who have converted to EP are limited to which prop parameters can be changed. For example the original 3 bladed prop I'm using is 16 inches in diameter has a 14 inch pinch. Like many others I can not increase the diameter but, could change the pitch or number of blades
It is working well but, I don't know if I could do better. Think there is a real need for a program geared to EP systems to find the best prop parameters for each boat with EP. Sounds like a great engineering grad project. :)
Sent from on board BIANKA
http://biankablog.blogspot.com
From: 'Sdolan' sdolan@scannersllc.com [electricboats] Sent: Wednesday, December 16, 2015 10:11 AM To: electricboats@yahoogroups.com Reply To: electricboats@yahoogroups.com Subject: RE: [Electric Boats] Electra Glide Data and updates |
I'm checking with the Prop Designer for more info but I think they only did a balance on the ones used not make them from scratch.
www.wildcatprops.com in Chesapeake, VA
I have little info on the props but the boat is being hauled out in a few weeks and I'll see if the Yard can give me some visual data on the props themselves. I'm no were near knowledgeable on props but think it's deserving of my attention if there is improvements to be made in performance.
Steve in Solomons MD
Lagoon 410 SE
Was this an industrial electric boat solution for the prop ?
Whats the pitch, please ?
Just to confirm, 18" X 1100 RPM prop rpm.
Any data re: efficiency / speed ?
The 18" "sounds good" to me.
The 18" prop has over double the area of a 10" prop, circa 10 hp usable power.
Thus, with a lower pitch, perhaps near 4-5", it might be significantly more efficient.
1100 rpm seems a bit high, to me, perhaps ??
Just looked online, and a 20Hp ICE drive recommended about
10.4" prop, 6.1 pitch, for 20 Hp motor
(30 feet, 5 ft beam, 5000 lbs, 5500 rpm, 2:1 transmission, just to try this).
It states 5 Hp used for speed of 6 knots.
https://www.vicprop.com/displacement_size.php?action=calculate
On 16/12/2015 15:06, 'Sdolan' sdolan@scannersllc.com [electricboats] wrote:
The Props are 18" 3 blade (No damage) connected to the motors with a straight shaft.
Batteries
--
-hanermo (cnc designs)
Posted by: "Myles Twete" <matwete@comcast.net>
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