Thanks to the people who replied.
I have since received a replacement for the original drive. I had to go back to Grenada from Martinique to collect it after I had left, assuming it was irretrievably lost in post. I installed it and it works without any problems so far (only 115 miles of continuous use).
I now have four drives on the boat. The draught is significantly increased because of it. I'm worried about getting into shallow water ports. I must send the non-functioning ones back to Lewmar.
I have decided to go up to Antigua and, if the new drive continues to function well, cross back to the eastern side of the Atlantic on the strength of this and the spare (which screeches).
When I took out the screeching spare drive to put in the new one, I found that the pinion had slipped on the shaft. This may have been the source of the screeching but I'm not sure. This despite my using loctite on the two grub screws when I installed it.
The whole pinion design is a very bad one. The shaft has a male spline which fits into a female spline in the end of the drive. This is held with a single axial central screw. This can't work long term as the spline is a slide fit and will have some play, which will end up either torquing up the screw until it breaks or loosening it until it no longer touches. When I took out the first pilot, I found the screw was loose. I check it every couple of days now.
The pinion is a slide fit on the short shaft and is prevented from rotating by a key. The pinion is prevented from sliding along the shaft by two radial grub screws. The grub screws come loose. When I took out the first pilot, both grub screws were also loose. These are more difficult to check being practically inaccessible via the trap in the side of the console.
I talked to the owner of a Bavaria 38 Ocean (a model I've never seen before) parked beside me in Grenada. He has a Lewmar drive and it has been in the boat for 15 years without problem. According to the guy at Lewmar, the design was changed in 2009. I assume that, because the old drive was so reliable, Lewmar realised there was some scope to take cost out of it.
When I re-installed the drive, I re-installed the relay (correctly wired this time; Garmin had incorrectly wired the power supply to the motor leads from the ECU). This is a backstop in case the clutch coil in the new drive short circuits like the old one. I also have a suspicion that, because the ECU is so far from the battery, the voltage drop is enough that the ECU is not supplying enough current to the clutch to engage properly.
I cannot get a clear reply whether this relay is required or not. According to Lewmar,the answer is no. According to the Garmin guys in Malta, the answer is yes, but it doesn't appear in any official Garmin notices that I have seen. The sheet which comes with it says that it is to be fitted only when the Lewmar drive is coupled with a Raymarine pilot.
My advice to Karl is;
- Check that your Lewmar drive is not an old version (at least Issue G for the Mamba alone or Issue B for the whole drive unit with the bracket and the pinion). If not get Lewmar to swap it for one.
- I assume that, as you are using a Raymarine computer, you have fitted the relay. Is this true?
- Check the resistance of the clutch coil from time to time. It should be around 6.2 ohms. On my failed pilot, it was 3,2 which caused the Garmin ECU to cut out with a clutch fault. Unfortunately, you need to take the covers under the cockpit off to do this. I have heard of Lewmar drives blowing fuses. This is certainly due to this short circuit.
- Check the torque on the screw holding the short pinion shaft onto the drive and the two grub screws holding the pinion on the shaft.
The critical point appears to be around 2000 miles. This may vary depending on whether the pilot is used in a hot or cold climate. If the clutch coishort circuitl problem is caused by the insulation melting, this could be a factor.
Let me know how you get on!
Sandy Herbert
