On 17 Nov 2006 15:55:01 -0800 CS
) wrote:
I am toying with the idea of driving a bow thruster with a 3 phase AC
motor and wonder if any one else has any experience in this field.

I just finished composing one:
http://qatsi.ath.cx/cgi-bin/foto/438/53.jpg from
http://qatsi.ath.cx/cgi-bin/foto/414/45.jpg and
http://qatsi.ath.cx/cgi-bin/foto/408/76.jpg
The motor is 4kW 400 VAC 2845 rpm, the bowthruster is from a Vetus
95 kgf type, both bought second hand.

I have a genset that is 1 and 3 phase and a sail drive leg already
fitted with a 3 blade 12" kaplan prop - not exactly sure of pitch but
it is BT prop.
Vessel is 22m steel and displacement 65 tons. A friend in similar sized
vessel has a 5.5 kw motor, so I was planning on the same and either a 4
or 6 pole - so 1500 or 1000 rpm. I think that a 5.5 kw AC motor will
have the same end effect as a 10/12HP engine.

5.5 kW is about 7.4 hp, is your friend satisfied with it?

A reversing contactor is the easy part but my queries a

whether to have a braked motor or not and

I would prefer a time delay over a brake.

whether to feed the 3 phase through an AC drive??

Is the most beautiful solution.

I understand that an AC drive can incorporate a braking function, but I
think using a drive may just overcomplicate it all.

If you or someone close is comfortable with a drive, well with a
joystick you have a very smooth control.

I guess that when the motor is switched off, it will stop pretty
quickly with the prop, so a braked motor may not be necessary.

Exactly and that is also why bowthruster suppliers have a time delay
option.

The alternative is to use a DC 24v motor at 200-300A which will turn at
1440 rpm, so much the same power. Powered from battery and with
dedicated battery charger. DC motor is quite expensive option.

AC option will require me to start genset each time, DC option requires
battery and charger. Plenty of other vessels have a small diesel engine
driving BT, so starting genset is not an issue and I do not use the BT
all the time - did not use it for 2 weeks bringing vessel back from
Netherlands to UK along canals.

Best thing is do the math. My frequency controllor cost me a "thank
you", normally the most expensive part, hours on it say enough:
http://qatsi.ath.cx/cgi-bin/foto/438/44.jpg more pictures at
http://qatsi.ath.cx/cgi-bin/cath_pub?7 and other pages.

What happened with the Silette Sonic?

--
Richard
e-mail: vervang/replace invalid door/with NL.net