therefore you need to put on the largest pitch propeller you can, with the optimum blade area ratio that can fit onto your boat. 4 bladed propellers are also a good option as they will move more water at lower rpm.
you then need to gear the electric motor to the propeller. This is where you have two choices. You can gear the motor at full rpm to be at the continuous rating of the motor, or you can gear the motor at the full rpm to the intermittent rating of the motor.
If you gear for the continuous rating of the motor, then the motor will run cool at all times, and you will have a higher continuous speed for the boat. This is the approach I usually take with gearing a motor.
If you choose to gear to the intermittent rating of the motor, then the motor will make more spontaneous power. IN this case, It is imperative to have a torque cutback when the motor reaches a certain temperature to prevent the motor from overheating. We usually cutback torque by 10 percent for every 1 degree over the maximum temp setting of the motor.
A marriage occurs in a drivetrain between the motor, the controller, the gearbox, the propeller and the related cooling system(s). The gearbox and the propeller determine the power that the motor is required to develop at any given rpm. The motor and the controller develop the power accordingly.
Each drivetrain has a rating of power over time.. Its up to the owner to choose the interval that they want to develop, for both continuous and intermittent power levels.
If the propeller is very efficient (because it has high pitch, and optimum blade area ratio), then the system has to develop less power for any given speed - you will have a higher top speed, and you get a boost in both continuous and intermittent power levels.
Variable pitch propellers allow you to run at any speed and vary the pitch to the heat of the motor. With diesel, it is to the exhaust gas temperature.
Feathering propellers that are adjustable allow you to trim the propeller to the heat of the motor (AC currents ) Some feathering propellers can be run in reverse for regen and will typically be better for regen as the blades are flatter and reverse can be pitched right out. The Autostream propeller is on my wish list for my boat..
Have fun with this, as it is an iterative solution, and if you get it right the first time, then you are doing really well. Its best to find another comparative boat with the same motor and find out what other people are doing. The good news is the gear ratio allows you to choose whatever personality you want for your boat, and can be adjusted for any propeller / motor / controller combination. If you get it right, you get better range, or top speed, or in some cases both.
James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
On Oct 2, 2018, at 3:03 PM, michpop@gmail.com [electricboats] wrote:
In designing the system for our Roberts 29 I'm trying to wrap my head around the propeller options
I find it hard țo get answers to the following questions
1. General considerations in propeller choice given the lower rpm and higher torque
2. Optimum features of a regen prop in general
3. I assume a fixed pitch propeller can be used for both propulsion and regen. It would just require switching the polarity when switching to regen.
Is that correct?
4. I noted the high speeds required for serious regen.
We are moored most of the time in a 2 knot tidal current. Is there a way țo trickle charge over long periods?
Thanks for your thoughts
Mitch
__._,_.___
Posted by: James Lambden <james@electroprop.com>
| Reply via web post | • | Reply to sender | • | Reply to group | • | Start a New Topic | • | Messages in this topic (3) |
Have you tried the highest rated email app?
With 4.5 stars in iTunes, the Yahoo Mail app is the highest rated email app on the market. What are you waiting for? Now you can access all your inboxes (Gmail, Outlook, AOL and more) in one place. Never delete an email again with 1000GB of free cloud storage.
SPONSORED LINKS
.
__,_._,___
No comments:
Post a Comment