At 11:39 AM 7/06/2010, you wrote:
>New to the group
>Has anyone ever put an electric motor onto a jet drive system.
>I have been working on this project for the past couple months, it
>has two jet drives systems attached to a small 16 ft boat. not quite
>sure how to do the math on what size motor is needed to get the boat
>up on plain.
>I am also thinking of starting a video tutorial on the progress of
>this project.
>after this small project I got my eye on doing a 32ft Trojan sport
>fisher, anyone do anything like this?
>
>Thanks
>
>James A Gaudino sr.
G'day James, James here!
I worked with the Australian Maritime College as they built their
"greenliner" electric boat, powered by a Doen jet. Now, planing needs
a lot of horsepower, in a light boat. This has two effects - it makes
your waller much lighter, and doesn't give you a lot of range.
First, do you know how much power it takes to plane your hull?
Unfortunately, you need to know, or at least have a very good idea,
unless you can afford to try, change, try again. You say you're not
sure of the maths for what it takes to get it up on the plane,
unfortunately it usually isn't so much maths as experimental. What
engines were in it? What do similar hulls use for engines? If you
know the power of a similar hull (or borrow an outboard to try) then
from that you can work back to an equivalent electric power.
OK, now you know how much power, you can convert that back into
batteries: for example, a Thunder-Sky 100Ah lithium cell (3kg, 6.6lb)
will give about 200amps for half an hour at about 3.2 volts, about
640 watts, so you can plug that back into power calculation. For
example, if your hull needs 20kW to plane, then you'll need about 30
batteries putting another 90kg into your hull to give you 30 min of
planing range. At this point you don't care about how many batteries
of what size, since you could use half as many batteries of twice the
amp-hour capacity for the same power, and weight.
Of course, now you need to find a motor and controller capable of
doing 20kW (or whatever you need to have). For example
http://www.evparts.com/products/street-vehicle/motors--dot/48-to-96-volt-street-vehicle-motors/mt5615.htm
is 15hp continuous, 50hp peak at up to 80 volts. Adds 130lb or so to your boat.
OK, now you know weight of batteries and controller. Will your boat
get up on the plane with that much weight in it? It will? good. Our
30 100-amp-hour Thunder-Sky batteries are a bit high in voltage for
this controller, so better to drop to 22 batteries, 120 or 160 amp-hour.
Next you'll need to maximise efficiency. I watched an AMC final-year
engineering student do this, he *doubled* the operating duration of
the boat. Map the motor efficiency, get the jet impeller efficiency
curve, and belt-reduce or increase so that the curves lay alongside each other.
So that motor & controller combo will set you back $4500, Batteries
(160Ah x 22) $4200, battery management system probably another $800,
Charger maybe another $600 or so. About $10,000. Is that the sort of
budget you were expecting?
Hope this helps
Regards
[Technik] James
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