27 Aluminum Boat Care Tips—Part 2

The shaft and hull should be electrically isolated.

Carrying on from Part 1...

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Dick Stevenson

Hi John,
I was not till I came to suggestion 13 that I realized how pertinent your article was to boat owners who do not have aluminum boats as there are a lot of aluminum masts and booms out there.
Alchemy was 2+ years old and a fresh water boat when I bought it and within a couple of years I had pulled all fixtures on the mast and had Duralac-ed or Never Seize-ed them. Some of them machine screws were already hard-ish to remove, even in that short period of with favorable conditions. I, of course, missed a few and at a later date (5-6 years later), they needed an impact driver activated with 3-pound sledge hammer to remove and most times the fastener was not re-usable.
I have since suggested to every new boat buyer I know to remove and TefGel (preferred now) all ss to aluminum connections ASAP. Interestingly, those owners who have done so and gotten back to me all report no dis-similar metals protection for the connections on these brand-new often high-end vessels.
Used boat owners should do the same. It would be an item I would check when buying a new boat. It would tell a number of things: the depth of maintenance for sure, but also, I would consider spars where the fixtures are un-removable with regular hand tools as damaged. I would direct a surveyor to check this and might try to parley this into a price reduction, especially if the spars are in need of painting or other immediate attention.
My best, Dick Stevenson, s/v Alchemy

Matt

It’s generally wise to assume that on anything aluminum that comes into your possession – whether new or used, and whether it’s a $10 or a $1,000,000 item – whomever last put it together will not have coated the fasteners properly. Even if it’s brand new, the guys who built it probably either don’t know why Tef-Gel is important, or it wasn’t in the spec, or they were in a rush and omitted it. Just budget the time to back them all out and coat them properly.

And I agree with Dick’s recommendation to try backing out fasteners that
thread into aluminum, and to consider the item damaged if they’re seized or corroding, before buying.

Aluminum is a great material, for many reasons. It just requires a different set of construction and maintenance rules than other materials do.

Dick Stevenson

Hi John,
Agreed. I would not wish anyone to stay at the dock or the boatyard doing a non-essential job like that. That said, many PITA jobs lend themselves to being done out cruising as long as one borrows the head-set espoused by the Hippocratic Oath of “doing-no-harm”. There can be lots of “down time” where you can go after a few fasteners at a time. Another similar PITA job that can be done sporadically and pays big benefits down the road is doing wiring and plumbing schematics. For those who stop cruising for the winter, these projects can be excellent winter projects.
My best, Dick Stevenson, s/v Alchemy

Chris Hopkins

John

Having brought a 20 year old Ovni 2 years ago l am reading your articles with keen interest. You have confirmed one change l am about to do as the prop shaft bronze packing gland is earthed to the hull. Did not think that was correct so thanks for the very clear clarification.

Effendi did not have a leakage meter at time of purchased. After researching l ended up getting the SeaBis mainly because l could buy it locally in Australia. Yes the website is poor and vague. But unit works well and shows the slightest fault of which Effendi had several which l have solved. Still need to isolate the engine, windlass and bow thruster which all have negative leaks. Though these all have both postive and negative isolation switches when not in use so only a concern when in use.

In regards to isolating the engine. I have a Yanmar 4JH4-TE and the pressure and temp senders are single pin so negative is through the engine. I have contacted Yanmar and they don’t make 2 pin senders. As such any advise on isolating the engine with single pin senders

Thanks Chris

Chris Hopkins

John

I am thinking isolating the engine from the hull only works until you open the seacock as the salt water then completes a circuit. I have plastic seacocks which electrically isolate the engines raw water from the sea when closed. I see this as I have battery isolating switches from both positive and negative. When I close the engines negative switch I get a caution warning on the SeaBis. Then when I open the seacock the warning goes to critical. With the engine off, I can leave the seacock open and open the negative switch and the SeaBis returns to normal.

Thanks for the lead on the VDO senders. Looking in the Yanmar manual it appears they use VDO senders. So I am hoping if I can get the VDO PN off the senders then I should be able to get the 2 pin equivalent. I like the idea of having a negative bus. That would be the solution wiring the new negatives for the senders. Then instead of having a heavy-duty starter solenoid in the negative lead. I would put a battery isolating switch between the starter and the negative bus. I could then simply turn it off after starting. This is following the mantra of “keep it simple”. It seems a workable solution to me. Though what am I missing?

Chris

JCFlander

Hello Chris,

You might have there a mounting bracket where oil pressure switch and sender are installed, that is mounted on rubber pads and fed by a short hose – ie. pressure sensors are not necessarily directly screwed on engine block.
I was lucky to insulate one 6-cyl yanmar engine by just cutting the metal braid on oil hose, so that it didn’t earth the sensor mounting bracket anymore.
There was some reason why we had trouble sourcing suitable insulated pressure sensors, so that bracket insulation was necessary then. But 2-wire temp sensors were easy to find at the time.
Last thing to add was insulated alternator and earthing solenoid for starter motor, and Voilà – insulated Yanmarin.
We did use Bluesea ML 7701 heavy-duty thing for solenoid , but on hindsight, it was a bit overkill. Regular heavy-duty automotive solenoid would have been fine.
It seems that 2-wire pressure senders are readily available now. I cannot remember what was the problem on 2014, perhaps there was a temporary shortage. Here’s one supplier: http://www.gauge-shop.com.au/catalogue/14-products-by-brand/5-vdo/52-senders-switchestransducers-adapters/74-temperature-senders-a-switches

Chris Hopkins

John

I figured I was missing something, opening the seacock complete the other half of the circuit. I also see my logic of using a switch to isolate the starter is flawed. I was thinking that as I have to enter to cabin to turn on the negative switch I would also turn on the starter switch at the same time, then turn if off after starting. Though once I have isolated the engine from the hull I will be able to keep the engine positive and negative isolator switch on at all time while under way. So a big safety plus and a good reason to spend the time and money in isolating the engine. So thanks for helping me to clarify the logic. And thanks for the advice on trouble shooting on land. It is very timely as Effendi will be lifted out next week.

JCFlander

Thanks for the information on how you isolated and the source for senders. And I see they are in Australia so a bonus.

Chris

JCFlander

I’m a bit surprised that you got what I meant 🙂 I really need to wait before posting, I seem to have a tendency to encrypt myself with plain words… :d
Anyway, I managed to find two pictures of the thing:
– First: mounting bracket. And yes, this was Yanmar gray before blasting. From left to right, lo press switch, press sender, and starter solenoid (which is optional).
http://aijaa.com/pBLZdg
– Then, oil hose, on “as mutilated” state. Doesn’t win prices, but wins a day…
http://aijaa.com/aqjkCq
HTH, Cheers.

David Bricknell

Our new Ovni 395 is currently being made at Alubat for launch in May 2018. Very useful, interesting and pertinent article. Going to have a busy summer refining the commissioning!
Thanks for sharing your thoughts. Looking forward to Part-3.

Dave

Not all aluminum is created equally.

https://www.proboat.com/2014/11/jade-resurrected/

Svein Lamark

Hi Chris! Like you I have Yanmar 4JH (whithout any Turbo). It has done 10 000 hours and is fine. Normally this engine will do 22 000 hours. The electric system is not good and made for cars. The starter and its panel is the main problem. I have tried to improve it, but that is difficult. Several oil engineers have given me their solution: They build a stainless steel sink anode box on the hot water pipe line system of the Yanmar. The hot water of the Yanmar is connected to a heating system with floor heating, hot water tapping tank, oil heater for water, electric heating and a 10 000 W truck heater. The sink anode is in this system. The sink must be checked regularly. This is not a perfect solution, but much better than nothing at all.
The perfect solution is of course to have no electricity on the engine and start it by compressed air. I have a Callesen built to expedition standard this way. It has made 130 000 hours and is fine.
To John: Using plywood as isolation material seems a bit original to me: Most ship yards I know use nylon plates. The do not lead electricity and if wet by salt water, they expande a little and their by prevent any leak. Their life time is endless.

Svein Lamark

Hi John, I had a talk with Christian Jonsson on this matter sa few years ago. Christian is a boat builder in Denmark and has worked with many expedition ships with success. He showed me several 10 years old marine plywood parts used as insolation plates. The plywood was originally of the highest quality. After 10 years they where all soft in the corners. Christian said that humidity will attac the marine plywood and especially in the corners. After 10years use they should be changed. Christian advised me to use nylon instead of plywood. I use nylon. Nylon has no such problem and has an undefined life time. Checking the plates when out sailing is something I do not do. It is done when at home again. That is why a do not like amateur solutions. They can lead you into trouble. I also advocate starting a diesel without electricity and use the simple way by compressed air. Almost any commercial engine is started this way because of several good reasons.

Dick Stevenson

Hi Svein,
I enjoy your contributions. I guess I knew about diesels being started by compressed air, but I never think about all the different variations of doing things and it is good to be reminded.
Thanks, Dick

Paul

I’m looking forward to Part 3, where we’ll get some ideas on why we should want aluminum boats. After reading Parts 1 and 2, I’m filled with more than a little panic — because I already have an aluminum boat. Of course, all of us with such boats should be mindful of the main ideas, and John gives us much practical detail that is hard to get elsewhere. While I let the Valium go to work to help me recover from John’s reminders, I have a question and an observation.

My question is this: Would any of this matter for a boat with a dry exhaust system? That’s what I’ve got: no seawater circulating into the hull to cool the engine (the coolant circulates in a “keel cooler,” which is actually the skeg). Now, if understand where electrons are flowing, this means that such a boat would not have the problem of dissimilar metals inside the engine posing a corrosion threat to the hull. Have I got that right? Now, there are other potential pathways between engine and the sea. If the engine (and every last wire attached to it directly or indirectly) isn’t completely isolated, I guess that having a dry exhaust/keel cooler is no panacea. What are the advantages of such a system (with respect to hull corrosion)? (I’ve mentioned some other advantages of such a system, unrelated to corrosion, in replies to other articles.)

My observation is this: I want perfection. John’s boat seems to be as near as one can get to that realistically. But it does make me wonder what the zincs are for. If I interpret John’s approach, the zincs are a tertiary backup system to rely on when all else fails. That’s one approach. But I wonder if that’s effectively missing out on the benefits of zincs. They are “sacrificial anodes” after all. The idea is that the zincs are part of the “circuit” of dissimilar metals. If the zincs are working as intended, they will protect more noble/cathodic metals in the circuit, including aluminum (the hull). If so, isn’t seeking perfection — which is very costly indeed if you start pricing up all the ways to do it, and very costly in time, too — bordering on extreme and, beyond a certain point, unnecessary IF one has properly installed zincs? I’m not at all suggesting that we should not aim for perfection — I lose sleep about this stuff, so I worry about it all the time. However, a zinc is a zinc. It’s there for boat’s that aren’t perfect (which I guess is nearly all boats). Most folks seem to replace zincs annually, with some noticeable-but-not-extreme erosion. That ought to be doing all of the work of protecting the hull, takes little time, and isn’t very costly in the big scheme of things (but good-quality zincs ain’t cheap; cheap zincs are, well, cheap). Naturally, if a zinc wastes away hugely in a year (and maybe if not at all), there’s a problem that needs to be sorted. But if the zinc erodes, say, by a quarter, should I be losing sleep and pricing an isolated ground alternator, etc.?

Paul

Many thanks John. What I don’t quite understand is to what extent engine coolant might act as an “electrolyte” of sorts. I think it might NOT do that, with nitrite in the coolant being an aluminum protectant of some sort. If so, even though the coolant is in contact with the hull, it ought not be a problem (but I could be totally wrong about this). The electrical system was built on top of the sprayed foam, so it’s isolated from the hull (assuming no shorts, of course). However, the engine is not isolated from the sea: it connects to the sea via the prop shaft, which itself is nominally isolated from the hull on the shaft bearing. I don’t know to what extent this might threaten the engine, but it has gone a decade like this. If there’s a problem, it’s a slow-acting one. Assuming the engine is still isolated (I’ll do checks when I get back to the boat in March), the hull should be OK. I guess all of this makes me moderately worried about this issue, leaving a small surplus of worry to apply to other things (there are so many things to worry about that I need to spread the worry rather thinly on each item!).

I guess one thing for aluminum-boat lovers to consider is whether a keel-cooler system might help out with the overall project of isolation. If my understanding is correct, it’s a positive in this respect.

Paul

Thanks again John. Regarding isolating the shaft, now that’s a tricky one. I wonder if anyone else reading this has a system similar to mine. I have a direct connection between shaft and transmission. I’m concerned that if I were to install a Drivesaver there might be a disaster if the Drivesaver were to disintegrate, which is what it’s supposed to do (if I understand its function correctly). The consequence could be the prop hitting the rudder (because my boat’s single rudder is directly behind the prop).

Do you carry a spare Drivesaver in case it fails? I assume that you do.

Charles L Starke

Hi Paul & John
I put a zinc on the drive shaft inside the boat as it exits the boat (and the boat is fiberglass). This limits the loss of the shaft.
I like the idea of the drivesaver. Thanks!
Best wishes,
Charles
Charles L Starke MD
s/v Dawnpiper

Paul

Thanks Charles. Indeed, on my previous boat (a Pacific Seacraft) I put a couple of beefy hose clamps on the shaft forward of the shaft seal to keep the shaft inside the boat in extremis. I don’t know why I didn’t remember that when replying to John previously.

I have been digging around online (for what it’s worth) to learn more about Drivesaver-type devices. There’s at least one other on the market that is designed to keep the shaft connected to the gearbox if the plastic bit fails as designed. Just going on this (and not having any experience at all with the quality of these things), I would be inclined to go with something like that instead of a “Drivesaver” brand per se. (Paradoxically, all of the instructions for these devices describe how to ADD a grounding strap between engine and shaft. Of course the metal boat owner wouldn’t need or want to do that.)

Paul

Thanks John. Regarding the shaft collar and PYI, they also sell the alternative to the Drivesaver I mentioned previously.

I will install one of the flexible couplers unless there’s an obstacle. It’s just a matter of finding one that will fit (my gearbox is commercial grade so less common). It’ll put the prop closer to the rudder, but I doubt the effect will be significantly adverse. One thing I cannot work out (revealing my ignorance) is what the shear key on the shaft is meant to do. I always thought that the key was there to shear away, thus protecting the engine-gearbox from a stopped shaft due to prop strike, etc. But I think I have this all wrong.

What I like about these couplers is that they (in principle) provide some vibration absorption in addition to isolating the shaft — that is, they do three things: isolate, absorb a bit of vibration and disintegrate if needed. (I say “if needed” because I once met a sailor who had one of these things fail in the Med, possibly due to incorrect bolt tension. He needed to get a tow because there was no wind.)

Charles L Starke

Hi John
Is it easy and worthwhile to install a flexible shaft coupling on my engine without the need for electrical isolation (Fibreglass Trintella 47)? Is it a job I can do myself?
PYI and DriveSaver both have models. Is one better or recommended over the other? PYI looks much more substantial than Drivesaver. Thanks.

http://www.pyiinc.com/flexible-shaft-couplings.html

Bruntons has one that serves as a drive thrust bearing and coupling:

http://www.bruntonspropellers.com/sigmadrive/

Best wishes,
Charles
Charles L Starke MD
s/v Dawnpiper

Paul

Hi Charles. I have nearly the same questions — which means I cannot answer them from any experience, but I can share my thoughts. Like you, I came to the conclusion (from reading online only) that the PYI-marketed coupling appears to be more substantial. It seems to also have the advantage of (in principle) hanging on to the shaft if it fails, whereas the Drivesaver would require another method to hang on to the shaft. As for isolation, if you don’t want that, the PYI device has an optional connection.

I didn’t know about the Brunton’s device. Now that looks great in principle (and very costly?). Depending on space behind your prop, it might require shortening the shaft (not a do-it-yourself job, unless you have a lathe et al.). From the look of it on their website, it does not appear to provide any isolation. Otherwise it looks cool — but maybe too cool? All I can think about is how long it is likely to last, and what happens when it fails, or whether it’s designed to fail (like the polymer flexible couplings).

I would like to have a way to reconnect the shaft directly to the engine if (when?) the coupling fails. With the polymer couplings, I think this could be done “easily” while the boat is in the water (but it would require fiddling with the shaft seal so that water doesn’t flood in when the shaft is moved forward for recoupling to the transmission). Carrying a spare is an obvious option, but it’d be nice to be able to do a direct connection in extreme circumstances.

That’s my thinking so far. Right now, I’m inclined toward the PYI first, Drivesaver second. I’d like to hear more about actual experience with these couplings.

Best,
Paul

Paul

If I understand the Bruntons product that Charles is referring to, it can be used like a Drivesaver (one unit) or like an Aquadrive (more than one unit plus a thrust bearing). If I understand John’s system, the Drivesaver isn’t doing nearly as much work as it would in a system without an Aquadrive. It might not be experiencing any stress at all apart from that arising from rotation — none fore-aft or (what’s the word?) wobbling due to slight misalignment. If I’m right, John’s Drivesaver ought to last forever because it has a very easy job to do — it’s not being asked to do nearly what it was designed to do. If I’m right, its longevity may not be indicative of the potential longevity of an installation in which the Drivesaver connects the transmission directly to a prop shaft and thus gets all the stresses in all different directions. It’s that taking of multiple stresses, in addition to isolation, that is the potential value of such a device. And I guess the inclination of the device to fail so as to protect the drive train is useful, too.

I would wager that John’s Drivesaver has helped to protect his Aquadrive, and vice-versa, from stresses. But going this way has its own challenges, as John implies. (I think I mentioned in another reply a Drivesaver disaster on an aluminum sailboat. Getting the installation just right, and the bolts torqued precisely, seems to be vital to success.)

Wouter Bod

Hi John,
Concerning your #15 and #16; why should the voltage of the shaft be at least 0.03V lower than that of the hull? Thank you for your help!
Kind regards,

Wouter

Wouter Bod

Hi John,
I always had between -1.11 and -1.04 voltage on the hull and between -0.93 and -0.99 on the propshaft. The last time I measured I got -0.51 on the propshaft (the hull was at -1.11). I dried out the boat to check the zinc anode on the prop. Took it of and made sure it was properly back on again and making good surface contact. But I am still getting the -0.51V reading. Any thoughts? Regards, Wouter

Wouter Bod

Hi John,

My bad! I was measuring from the metal ring of the pss shaft seal instead of the shaft! Got -1.00V on the shaft, 0.10 less than the hull. Apologies for wasting your time!

Ruslan

Hi John, I was told that aluminum boats cannot be docked near to steel boats for a long time and if that happens you need to find another spot. It’s ok for a short time, but for a full season, it will be a problem. How true is this?
Also I have a marina with corrugated metal walls all around it, below boardwalks, rusting away. Do you think it is safe to keep aluminum boat in such an environment?

Ruslan

Got it. Thank you John.

Dick Stevenson

Hi John and Rusian,
Am I correct in saying that once a boat is plugged in to shore power, the boat are no longer isolated?
My best, Dick

Ruslan

When I was checking out Boreal, it had big isolation transformer to prevent that from happening. There are also small ones that ppl sell for GRP boats.

Dick Stevenson

Ahh, yes, forgot about those. Thanks, Dick

David B

My 6 month old Ovni395 was fitted with a MasterVolt isolation transformer by the boat yard Alubat.

Marc Dacey

Out of curiosity, may I ask which model? We have a 40 foot steel yacht and the relatively compact Mastervolt GI 3.5 model seems well-matched to a 30 A/120 VAC boat accepting a 30 A service (although I can take 60 A, we never do). It’s this model: https://www.fisheriessupply.com/mastervolt-isolation-transformer-88000355
Thanks.

David B

Marc
Alubat fitted the GI 3.5 along with a MasterVolt combi inverter/charger and other interfaces. My only input was to specificy MasterVolt and Alubat decided on the detailed spec. Alubat probably have more accumulated knowledge of wiring metal boats than anyone else. We have only had the boat 6 months and anode wear seems “normal” although we are not heavy users of shore power (D400 and solar keeps up with requirements). I periodically test the hull potential with a test silver-carbide anode and it reads -1000mV (in the non-fizz zone) in the marina but drops to -800mV (fizz!) at anchor or on a mooring chain which I have not got my head around yet; anyway, that is nothing to do with transformer. Hope that helps.

Marc Dacey

Very much so! Thanks for the field-testing information. We will have largely a similar setup. I concur the fizz zone reading is a bit puzzling, unless there’s some impresssive underwater power cable near your mooring. The silver test rig is on my purchase list as I’ve confirmed to my own satisfaction that the end of the dock finger where we are at is not a particular problem. I need to go from freshwater magnesium anodes to zinc for the trip to Nova Scotia next summer. Good luck with your Ovni…they are beautiful boats.

David B

Thanks John and all points noted. I have been putting the -800mV readings down to the proximity of a mooring/anchor chaim or local conditions; currently they are -1000mV in our long term marina. I will check the isolation transformer as you describe and continue monitoring readings; still on a learning curve. BTW, would aluminum anodes work on an aluminium hull?

David

Wayne Berge

Hello John,
This is my first comment on your site. Great site! These three articles on care of aluminum boats are worth much more than a year’s subscription.

I would just like to make a couple comments about the SeaBis leak detector. I recently purchased one and athough recommended to connect permanently and to be left on at all times, I installed a two-pole switch to enable me to turn it off/on at my discretion as it leaks almost 0.1 mA on both + and – when turned on. I have solar panels and am using a good PWM charge controller but whenever the batteries reach the preset “float” setting of the charge controller, the SeaBis unit starts flashing it’s red AC alarm light as well as the green + and green – normal lights. I have done a lot of testing with another controller, changing float settings and even without a controller (direct to batteries) to pin down the cause. The seller doesn’t fully agree but doesn’t dispute my conclusion either that the SeaBis unit is recognizing a slight pulsating DC current as AC. Not a big issue but false warnings can be concerning if one is not aware of the reason. Just wanted to pass that on as I see someone else in these comments using one as well.

Klaas Hartmann

I’m in the process of repowering my aluminium yacht, and have found your material very helpful, many thanks!

I’m planning on using a Python Drive which will enable me to achieve a slightly better alignment with existing engine bed and hopefully have the side benefit of reduced vibrations.

The conundrum I’m facing at the moment is achieving electrical isolation of the shaft from the engine (I have an alu yacht). The Drivesaver suggestion you’ve made is neat — but very expensive, about $400USD including shipping for our situation! I was wondering if you have any other ideas of achieving this isolation at lower cost? R&D flex couplings are much cheaper, but have been warned that this may provide too much flex in the system. I imagine the coating systems used to achieve isolation in flanged piping systems would be compromised by the strong forces on the bolts in this application. Although, ultimately, I might try that (at near zero cost) and if it fails rely on carefully keeping the engine isolated from DC neg.

Any thoughts?

Klaas Hartmann

Hi John,

Thanks for your quick reply. I thought as much. In 3000 hours of motoring we haven’t fouled anything dramatically so I consider it fairly low risk (except now that I’ve said that it’s bound to happen). For our setup, and with shipping, the python drive is $1030USD and the drive saver $410USD… So it’s a substantial extra cost. An R&D flex coupling would be $165USD, but I’ve been warned against that…

I enjoy reading all the advice on your website and have obtained lots of good tips. However for many of your articles I have to see your advice through the lens of my own budget and prioritise the most important aspects!

Cheers,
klaas

Garry Crothers

John,
I read somewhere that there is an ABYC requirement that the shaft must be grounded. Can you comment on this. I have recently checked with the ohm meter and see that the shaft on my OVNI 435 is not isolated from the hull. These boats normally come with MAXPROP propellors and are notorious for eating up anodes.
I’m considering fitting a drivesaver or RandD coupling

Garry Crothers

John,
I agree totally with your analysis, I hadn’t done the test with a half cell, just the ohm meter, but I’d expected to get a few ohms showing up if it was just seawater. I’ll investigate further when I get my new half cell. I’ve been using a bit of silver wire dipped in bleach, not great.. How’s that for a cheapskate.
Re the ABYC ruling about connecting the shaft to the hull, I can’t find the link to where I’d read it, and was wondering if this was one of those situations like floating DC where you and Steve agree to disagre. Also I’ve since found more specific Abyc regulation saying that metal hulled boats should indeed be shaft isolated, presumably the original post was talking about non metal hulls.. I’ll investigate more on how my Ovni was built, but I’m thinking about a Drivesaver install would be a start to help with my excessive (to my limited mind) anode consumption.
Am I correct in thinking that on a aluminium hull the prop anode is to protect the hull/shaft tube. But on a non metal hull the anode is to protect the prop itself?