Re: [electricboats] What if...? Hybrid conversion for Trawler???

Your "What if". Is a little smaller then my cabin cruiser style boat.  If the hull is Semi-displacement it is technically a Cabin Cruiser, not a Trawler which would be full displacement.  Marketing people be dammed. 

 I average about 4 knots at 4 kW.  13 ton 41 foot Semi-Displacement boat.   After the charger loses, Your generator will get about 6 kW to push the boat.  The extra 2 kw will not buy you much more speed. Maybe 4.5 or 4.6 knots .  You can see my running watt to knot at my travel blog http://www.deny.org  before I did the jump from Carrabelle I had very encrusted props which where costing me about 2 knots.  After the Jump to Tampa, is more typical of my power draw. 

2 10 kw motors per side will do the job,  I have 20 kw per side and never use the top half.  For those props you will need a metric ton of reduction, I started out with 22x22 props and was still over propped with 5:1 reduction.  You will need at least 6:1 or 8:1 reduction or smaller props.  

You will most likely need to parallel two 3 kw chargers to get 6 kw of charging.  As finding A 6 kw charger is not easy.  I just have 3600 watts of charging right now, and am thinking of getting a second 3 kw charger to have a higher no battery travel speed.  Which in my case is mostly pointless as 95% of my travel is from solar or batteries. 

 

If those speed are what you want, quite slow boating can be fun. 

James Sizemore

On Feb 7, 2020, at 8:07 PM, john via Groups.Io <oak_box=yahoo.com@groups.io> wrote:



The following scenario is a "what ifffff" for a "trawler" class cruising boat.

These boats are generally powered by old diesel engines - typically 120-275HP each (twin engines).

If the diesel engines died for whatever reason, could I replace them with some kind of electric motors, and run the electric motors from the still working generator?   I'd still be burning some kind of fuel, but I'd be rid of two large diesel engines (that I might not be able to get repaired).

Here are the specs for the boat:

Length:  38'

Beam:  13.6'

Draft:  3.6'

Weight:  21,000 pounds

Semi-displacement hull.

Props:  2, bronze, 24"x26"

Gear ratio (if the transmission was kept) - 2.5

Hull speed for the boat should be about 9.5mph

Here are the readings that were taken during a survey of the boat (RPM's for both motors):

700 RPM              3.3MPH

1000 RPM            5.6MPH

1500 RPM            7.5MPH

2000 RPM            8.8MPH

2500 RPM            9.25MPH

The current generator on the boat was a 7.6KW.

If I wanted to be able to attain a max speed of 7.5MPH, at about 1500RPM for each motor, with 24"x26" props, how big would the electric motors need to be?

Can I drive each motor on 3KW or less?

Can this be done practically??

Thanks,

John