Crazyhorse 47 Posted October 24, 2018 Share Posted October 24, 2018 Any suggestions appreciated. We run a zinc collar on our prop shaft. If we don't the prop leaches out, had it happen years ago. Last year we noticed fizzing around the admiralty pattern and advised to treat it with vinegar then dry it out and then use everdure. Hasn't worked. The prop shaft is isolated from the engine /gear box via a flexi coupling so the gland will be too. I am thinking I need to have a earth strap from the gland to the engine? I know too many zincs and earthing skin fittings etc on timber boats is not advisable so where to from Here? The photo shows the buildup of salts. Quote Link to post Share on other sites
Island Time 1,235 Posted October 24, 2018 Share Posted October 24, 2018 Most boats run a brush on the shaft, and both it and the gland connect to ground.... Quote Link to post Share on other sites
Priscilla II 392 Posted October 24, 2018 Share Posted October 24, 2018 Earth bonding straps just create a circuit on wooden boats so are a no no. https://waitematawoodys.com/2015/05/15/electrochemical-damage-to-wood-the-marine-version-of-leaky-homes/ Also it is well worth checking neighbouring moored vessels as I have experienced fizzing and suspected the source was from a nearby launch who had alarming amounts of electrolysis in both stern gear and props. Quote Link to post Share on other sites
Crazyhorse 47 Posted October 25, 2018 Author Share Posted October 25, 2018 Trying to track down Noel here as he might know? Bloody annoying after spending hours last year cleaning it up and treating it. We don't more Pris' but yep, have heard the horror stories! Friends from Canada ("Barefoot") refuse to berth next to steel boats, we are wood probably how we met them. Their boat is alloy. We do have an old anode under the shaft log. It's been there since 2002 and is not earthed to anything yet over time has slowly eaten away...remove it? Quote Link to post Share on other sites
Crazyhorse 47 Posted October 25, 2018 Author Share Posted October 25, 2018 That should have been "moor"...(fat fingers..). Quote Link to post Share on other sites
Island Time 1,235 Posted October 25, 2018 Share Posted October 25, 2018 Do you have an isolating transformer? Or galvanic isolator? If no shore power, no problem without, but if you use shore power then you should have protection. If you have either of these devices, another vessel cannot effect you - there is no circuit. Wooden boats can be subject to stray current corrosion, same as any. If there is no bonding system each peice of immersed metal needs an anode. Quote Link to post Share on other sites
Crazyhorse 47 Posted October 25, 2018 Author Share Posted October 25, 2018 Do you have an isolating transformer? Or galvanic isolator? If no shore power, no problem without, but if you use shore power then you should have protection. If you have either of these devices, another vessel cannot effect you - there is no circuit. Wooden boats can be subject to stray current corrosion, same as any. If there is no bonding system each peice of immersed metal needs an anode. Thanks Matt. Caught up with Noel, "yep I know the problem and not much you can do". Seems there is a reaction between the kauri and the bronze glad. It should have been seated in years ago using lots of lead paint (didn't know you could still get it!?). He said keep squirting white vinegar at it, could last years then at some point pull it out, cut out the effected wood and scarf in a new piece. We do have 240v when plugged in at a marina but there is no earthing as we use extension lead powering a junction box, no hard wired mains. Seems its more than simple electrolysis? The kauri doesn't like the salt water on the bronze producing an alkaline? Noel said no way earth anything in the water on a timber boat so thats out. After spending the day rebuilding our old MV-2 morse, I'm feeling a bit gutted.... Quote Link to post Share on other sites
Island Time 1,235 Posted October 25, 2018 Share Posted October 25, 2018 OK, lets get a couple of points straight. Bonding IS NOT EARTHING. Bonding simply ensures that all the metal objects in contact with the water are at the same potential - zero volts. There is a good description of that here http://newboatbuilders.com/pages/electricity14.html - saves me doing it again. 2nd, what you have is corrosion - again, a good description here http://newboatbuilders.com/pages/corrosion.html possibly woodburning or fastner corrosion - follow the links to that from those pages if your keen... Many timber vessels are already (unintentionally) bonded. There is no electrical isolation from shaft to gearbox to engine, so the main parts are connected. Quote Link to post Share on other sites
Crazyhorse 47 Posted October 25, 2018 Author Share Posted October 25, 2018 Zero volts...earth. Quote Link to post Share on other sites
Crazyhorse 47 Posted October 25, 2018 Author Share Posted October 25, 2018 OK, lets call it NEUTRAL. NO electrical potential be that positive, neutral or negative potential in relation to all other conductors. Quote Link to post Share on other sites
Priscilla II 392 Posted October 25, 2018 Share Posted October 25, 2018 CH ,Noel is most correct as usual. Try attaching a voltmeter to the stern gland and ground. You may well be surprised. Busy little dissimilar metal convention going on in that part of your yacht. Stainless shaft with zinc anode and bronze stuffing box with prop attached to cast iron or alloy gearbox / engine.all held together with timber permanently immersed in salt water. You can bore a few shallow holes around the gland to syringe in the vinegar to assist with penetration. Quote Link to post Share on other sites
Crazyhorse 47 Posted October 25, 2018 Author Share Posted October 25, 2018 I don't know what the prop shaft tube is made out of so that could be the issue. She is glassed over so no timbers exposed to the sea. The fizzing gland is not connected to the prop shaft, I've checked with a multimeter and the prop shaft is totally isolated from anything else. The cutlass is non conductive but there could (should?) be another top bearing. Either way, I can't see how stray electrical currents could be the answer when seawater is the only conductor? Noel said he has seen this before, apparently the timber sets up its own reaction with the bronze fitting when there is salt water getting in. Our hiscock valve sits on a bronze skin fitting....guess whats getting replaced next! Thanks for all the help guys. Next year will rip it all out, replace the shaft log tube etc. Quote Link to post Share on other sites
waikiore 399 Posted October 25, 2018 Share Posted October 25, 2018 SS shaft, Bronze prop, copper stern tube, ally or iron in engine/gearbox, Bronze or gunmetal gland -there is already quite a mix. A bronze gland in kauri will not react at all without outside influences. You are right easiest way to put it to bed-next year put an epoxy stern tube in with a shaft seal as you have -prop speed the prop and you will see a big reduction in potential. Quote Link to post Share on other sites
Crazyhorse 47 Posted October 26, 2018 Author Share Posted October 26, 2018 True but only if electrically connected as in touching each other or attached to a common conductor. My multimeter shows 100% resistance between prop shaft, gland and engine. Dissimilar metals immerced in a conductive solution require some kind of return path for the electrons otherwise nothing will happen other than oxidisation which is what I think Noel was talking about. Quote Link to post Share on other sites
Priscilla II 392 Posted October 26, 2018 Share Posted October 26, 2018 Need to add to the underwater party copper in your anti foul and hull fastenings if applicable along with red lead primer. Quote Link to post Share on other sites
Crazyhorse 47 Posted October 26, 2018 Author Share Posted October 26, 2018 Need to add to the underwater party copper in your anti foul and hull fastenings if applicable along with red lead primer. Why copper? We use carbolene anyway (tried that vivid stuff, failed) which has copper in it. Not sure how the antifoul would change things? Noel did say sealing it all with lead primer is the way to go obviously after removing everything so there is only the timber shaft log with a big hole in it! Quote Link to post Share on other sites
Priscilla II 392 Posted October 26, 2018 Share Posted October 26, 2018 Just pointing out all of the multitude of variables of differentiating materials that lurk in that portion of ones vessel. Bloody heaps. Quote Link to post Share on other sites
Crazyhorse 47 Posted October 26, 2018 Author Share Posted October 26, 2018 Yep, you are dead right. The issue for electrolysis is that you need a earth return to create an electrical potential so allowing electrons to flow. So we are not talking dissimilar metals and as such galvanic response but a chemical reaction? It would seem salt water turns caustic when in contact with bronze and timber!!!?. Buggard if I know, but seems to be the only answer to our fizzing gland. Quote Link to post Share on other sites
harrytom 642 Posted October 26, 2018 Share Posted October 26, 2018 Just a thought,you have a dripless stern gland??When vessel in water the gland fills with water so the s/s shaft and bronze gland holding the shaft in place,there is your connection. ss+ bronze+water Quote Link to post Share on other sites
Crazyhorse 47 Posted October 26, 2018 Author Share Posted October 26, 2018 Just a thought,you have a dripless stern gland??When vessel in water the gland fills with water so the s/s shaft and bronze gland holding the shaft in place,there is your connection. ss+ bronze+water How are they conductively connected? Quote Link to post Share on other sites
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