Re: [Amel Yacht Owners] Re: Distributed vs. Conventional Electrical Systems

James Alton

Bill Kinney,

   Thanks for doing the testing and providing the results.  I knew that the SM bow thruster was more powerful than the earlier Amel bow thrusters but the upgrade in power is far more than I realized.    From your measurements,  if my math is correct, 420 x 24.1 = 10,122 watts/ 750 = almost 13.5 HP electric as compared to the unit on my boat having around 1.6 HP.  In the case of your voltage measurement, can I assume that the 24.1 volts being measured at the battery terminals rather than the thruster motor terminals?  

   I have never seen a 500 AMP or larger DC breaker so perhaps the lack of availability is this is the reason Amel did not install that form of protection?  Clearly the system has worked well for a lot of boats over a long period of time, but the fuses you mentioned do seem like a good idea in case a short ever developed.

   With the SM motor rated for 6.3 KW and actually being hit with 10KW+ I can now understand the reason that it is important on the SM to limit the burst time to 30 seconds to control motor heating.   With the thruster on my Maramu, a run of 2 minutes results in very very minor heating  (Maybe a 10C rise at most)  but then a thruster is generally only needed for short bursts so I think that the path Amel took to push the motor harder for a short duration was a good choice.  I am wondering if it might be possible for me to increase the power on my thruster by changing to to a different motor?  A doubling in power would be nice to have for higher winds,  perhaps someone else has already looked into this?      The lower unit of the thruster shares many of the same parts with the SM based on the bow thruster items I have ordered so far from Maude and I think even turns the same size prop as some of the SM's.  

   Would you know  (or anyone else reading this)  if the Santorin uses 12 or 24V on it’s bow thruster?


James Alton
SV Sueno,  Maramu #220

On Oct 18, 2017, at 8:52 PM, greatketch@... [amelyachtowners] <amelyachtowners@...> wrote:


The SM does not have any factory installed protection for the bow thruster circuit.  On my boat the fuses on the battery terminals have a total rated load of 500 Amps, which is reasonable based on the ampacity of the wire used, and has never blown while in use.

And... since I am on the boat, rather than calculating, or looking up, or guessing...  I figured a bit of measurement is in order.  With fully charged batteries (and charger off) using the Magnetronic Amp meter to measure the current draw, and my Smartguage to simultaneously display voltage,  here is what I find:

The bow thruster draws 420 Amps at 24.1 volts.  That's where it stabilized after about 5 seconds.  That's with the boat tied tightly in a slip, so any movement of the hull would (slightly) reduce the load on the prop.

It figures...  almost exactly splitting the difference between what Amel has in the manual, and what the motor nameplate says.  If it matters, this motor was just professionally overhauled last year with new brushes, windings, etc.

Bill Kinney
SM160, Harmonie
Back Creek Annapolis, MD

---In amelyachtowners@..., wrote :

Bill Kinney,

   Good point about the voltage drop. I measured mine as dropping from 13.5 (charger was on so this was not an accurate test) to about 11.75 after a 5 second burst. 

   Does the SM have a breaker for the bow thruster and if so can you tell me the amperage?   I guess that the 6.3KW rating doesn’t tell us much since we don’t know how loaded the motor is.  

   Also, can someone tell me about how much free play is normal for a bow thruster?  I can rock the prop on my thruster back and forth about 3/16” without any resistance as measured from the tips of the blades.  The output shaft does not seem to have any play in it’s bearing so I assume that what I am feeling is the gear lash plus any play in the shaft to motor splines.

James Alton
SV Sueno,  Maramu #220

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