Torqeedo propeller problem

[Peter Taylor]

On Saturday I set off at 5am from the jetty only to find that the propeller didn't rotate much when placed in the water rather than the air! With the throttle open the motor revs went up but the watts went down - just like a model boat when the propeller falls off. In danger of being swept into a bridge I ended up anchored on a mud bank. I had all the spares needed on the boat, but I didn't have the no.17 socket spanner you use to fit them, so when the tide went out I waded through the mud and walked home to get it! I managed to tighten the nut enough to use the motor to get home (there was little wind that day).

I've since pulled it apart. With the locking nut off, removing the propeller was still a struggle and in the end I used a hammer to tap it off the shaft. The photo shows what I found (left side!). Both spring washers were badly corroded with the inner one broken into three pieces. The only part of the shear pin still present was the length protected inside the motor shaft (compare the old and new lengths). The two ends of the pin were missing which is a mystery since there is no way they could get out from under the propeller; they definitely did not drop out as I took it apart. Possibly the corroded inner washer had ground the shear pin down to dust - it seems unlikely since the two shouldn't be in contact. However if they are, then the spinning propeller might well create an effective grinder!

The motor was bought in autumn 2012 and has had quite a bit of use, always in sea water. Torqeedo say you should wash it down each time with fresh water but it's hard to see how you can rinse out the inside of the propeller. I suggest carrying spares (and the no.17 socket) and regular inspection. If you really want to, you can read more of my muddy adventures on my new web site "seatern.org.uk"!

[Graham W]

Blimey!  That shouldn't happen - thanks for the warning.  There is a clue that similar things may have befallen other Torqeedo users in the past as Torqeedo has a whole page on various kinds of corrosion on their website http://www.torqeedo.com/uk/technology/background-information-on-corrosion   I have only the haziest understanding of differential voltages but I wonder if this is a warning not to charge the motor at 32v when the propeller is in the water.  Are you going to ask Torqeedo for a diagnosis?

Perhaps the coffee grinder effect was the reason why you were only getting 4 knots from your motor?

[Peter Taylor]

I wonder if this is a warning not to charge the motor at 32v when the propeller is in the water.

I don't think charging the battery is a problem since I'd be amazed if the lithium battery management system does not isolate the motor from the recharging voltage. Also my 12v system is not earthed to the sea. The real question for Torqeedo would be whether the spring washers are actually marine grade stainless as implied by their web page. That they tell you to wash it down with fresh water rather contradicts what they say on their page about corrosion. Unfortunately my past experience of dealing with Torqeedo suggests life is too short to bother with questioning them!

Perhaps the coffee grinder effect was the reason why you were only getting 4 knots from your motor?

On a calm day I'll do a test and see, I did wonder if the noise it was making before had changed over time!  However I have to admit that the motor was not quite vertical before - I forgot to adjust it when I transferred it from my Seafly. It needed adjusting by "one hole" which could make a difference to the power. The other factor might be that I've got the propeller that 5cm nearer the surface so the motor will fit the well.  I've been assuming that that will not be a cavitation problem because the motor is below a boat rather than a free surface, but that's only a guess.

I must admit I'm beginning to wonder about buying a petrol outboard!

Cheers,
Peter

[Graham W]

I read somewhere that because Torqeedo motors were originally developed for freshwater lakes, corrosion from saltwater on earlier models (401/801) was a painful learning experience for the company. Matt has said on occasion that if he wasn't running Swallow Boats, he would be tempted to go into competition with Torqeedo.

I'll schedule replacement of the shear pin and washers (£7.50 for the set) as an annual maintenance task. I can only find A2 equivalents to the Torqeedo washers on the web, not A4, so you may be right about the type of steel they are made from.

I have a used Suzuki DF2.5 for sale!  Given how critical I have been about it in the past and despite Jonathan's remedy for the flat spot, I don't feel that I can ask a great deal for it.