Trusting your Thrust

It may have been said before but the B57 has a price to pay for its outstanding sailing performance. This is the placement of the rudder with respect to the propeller. The result is nil propeller wash on the rudder resulting in that you go in the direction the bow is pointing at low speed. Not a big issue, even when reversing you can handle it with the help of the bowthruster.

During this summers (2021) cruise in Italy and Croatia we has lots of friends and family flying in and out to ports resulting in frequent marina visits.  

Artemis has a 24volt MaxPower thruster of the CT125 model. As you can see below it sports dual props and a huge electrical motor drawing 300amperes resulting in 7.2kW or around 11 hp.

Taking into account that it is located in the sail locker, beneath the locker floor, this space in not visited that often. Add that even if you do lift the floorboards, you need to unscrew a wooden box covering it. This sail locker also house the forward blackwater tank. So there is always a slight unpleasant odor in this space. Making it a place you avoid spending your holiday in.

It  began as intermittently as no thruster working

Luckily this was when we had no guests aboard and on the hook in a really nice cove near Dubrovnik.

Here is a closeup of the two power relays, one for each rotation direction, mounted on the beefy motor. The blue cable is negative, the brown positive. You can see how it is attached to one of the relay lugs and with a short busbar connecting it to the second relay. 

Note the severe oxidation on all copper surfaces. It looks worse than it is as the oxidation does not reach beneath the connection why the electrical conductivity is not really affected, the joints are airtight. 

On the right side you can spot the now cleaned up mess of cables with faulty relay removed but retained fuse. The relay was wired so that it was always on, it completely eludes me what its purpose was as it did not function as a control signal isolator. The blade fuse was severely corroded, soon to fail, but the source of malfunction was not this but the fact the the relay was fed up being drawn all the time. You can also see that the relay socket was oxidised too, just moments away from failing.

The relay was removed as it had no function. The power relays had some control wires using 6,2 mm 

flat spade connectors. 

Lower center above is shown the correct type of plugs used. To the left the two power relays with contact surfaces clearly visible. This is normally shielded by a cover.

The fixed lugs on the relays where of course all black too and these got worked with the brass wire brush. Test-pulling the attached wires resulted in separation of wire and plug.

Was I surprised? Not the least, using this type of cheap insulated plugs has no place in a professional installation. The crimping is just simple pressing and does not achieve a gastight connection between the wire and lug. Another failure moments away. New wires where made using tinned cables.

Now everything worked and it felt like a relief knowing that this was not going to fail anytime soon.

An illusion

As we returned to our home port in pitch black night we sneaked quietly in to our mooring along the main pier when we heard a distinctive new sound from the bowthruster. I looked at my brother and we sort of knew from the sound. But our bunks where calling.

Next morning my brother had to know, he slid into the water and in no time confirmed what we knew, the gears in the drive leg where giving up. The grinding sound the night before gave it away.

When the CT125 was installed in 2004 the drive leg was made out of metal. On some models was a small tank with oil in next to the motor. The idea would be that with the oil filled up it would ensure no water would enter the gear housing below the water line. The model on Artemis had not this feature. As it was made of metal is also required to have to change anode. Had that ever been done? Nobody knows. 

The mechanics of the unit looks like this;

The lower part, the one in the water, is the drive leg (part 41). Its is much the same function as your angle grinder.

  

Luckily for us MaxPower has evolved and created a drive leg in composite that can be retrofitted and it is sealed for life.

It was ordered, delivered and with some additional items can replace the old unit. 

Stand by for replacement!