Anodes on aluminum boat and motor?

Hey, Recently I inherited an aluminum boat from my father up in Wisconsin where the boat was manufactured. It is a 16 ft aluminum v hull with a 15hp mercury tiller engine on it. The boat and I both reside in Tampa, FL. The boat lives its dry life outside under cover on a trailer and its wet life in the saltwater for day trips. I rinse the boat, flush the motor and wash the trailer after each use and plan to do a little more preventive things in the future to keep the corrosion at bay.

My question is regarding the anodes. The hull of course does not have any and as far as I can tell neither does the engine. I thought they were to be under or around the cavitation plate but....nothing... I contacted the manufacture and they told me that because they mainly sell the boats in the midwest they don't really deal with this sort of thing. From my research it looks like I need Zinc but my research also has not been able to find out how much and if I need them on the hull and the motor. the inner motor clamp clamps to the wooden transom and the outer is to the painted surface so the engine from what I can see is not directly bonded to the hull. so everything I've read about zinc anodes is that there is "no perfect formula" well no formula at all that I can find. they just say to install them and check back in a year but dont put to many or to few on otherwise you'll be asking for trouble. so I've turned to the experts here for advice.

so do I need to bond the engine to the hull via a bonding strap or is it fine enough just through the battery.

can anyone recommend a starting point on placement, requirements for the anodes.

I appreciate your advice and assistance.

-Mark

 

I say do nothing, but rinse the boat and trailer ... a lot.

If you get saltwater in the bilge; even flood it.

I took my aluminum skiff to salt for a week and it was okay, but took a couple of seasons to get washed off decently.

 

I don't think I'd add an an anode to an often trailered small boat. I'd focus on the after use rinse. One thing to think about we saw a fair bit was bunk rash caused from carpet bunks on trailers. Would trap enough salt apparently to cause problems, usually on seasonally stored boats up north.

A good freshwater rinse should do just fine especially if you keep the water out of the inside.

 

The more modern motors also have a freshwater flush. I think you can make a quick connect and flush the engines to also extend life.

 

You get galvanic corrosion when you have a conductive circuit joining two disparate metals connecting them to ground. The pathway includes an electrolytic like saltwater. Or else the circuit is soon broken as corrosion forces loss of contact.

The more noble metal steals electrons from the less noble metal because the grounded circuit creates an electrical pressure variance where the noble metal loses electrons to ground if it can replace those electrons by stealing them from the less noble metal. The sacrificial anode replaces the lost electrons and also prevents lost electrons by feeding its elections into the low electrical pressure system to relieve the electron vacuum.

So you need three elements to have galvanic corrosion; disparate metals, a conductive connection in an electrolytic, and a pathway to ground (a way to lose electrons from the system).
Bonding your motor to your hull would likely only result in improving the circuit connection to ground by tying in an element that may otherwise have been isolated.

For an aluminum outboard on a trailer, you are best safeguarded by keeping your disparate metals isolated with a coating or otherwise reducing the physical contact. There are no prefect solutions, you're always losing a few electrons here and there, but you can slow it down to a level that will take decades to notice by reducing the exposure to an electrolytic while on the trailer and avoiding direct contact between metals.

The motor itself may benefit from a sacrificial anode if it has steel parts that come in contact with aluminum parts in the water. If you berth her in a marina with a poor dockside electrical system or too close to that steel fishing boat that isn't safeguarded with its own SA.

 

Great, thanks for the reply's. Sounds like it's not very necessary to add anodes.

I went over the boat and all of the hardware is stainless steel. I understand stainless steel is the better option and less likely to cause issues but I read another article about someone who installed nylon washers with his stainless hardware to further isolate the fasteners. not something ill jump on but something i may consider.

as Will mentioned our main concern is galvanic corrosion and aside from the stainless hardware the only other issue would be the prop. it is a painted steel prop. The first thing I was planning on doing was replacing it but I was instantly overwhelmed so i may take a moment to breath before I jump on a new stainless steel prop.

also the trailer has rollers. I love the rollers because I can very easily launch the boat by myself and the boat is so light that I can launch or retrieve it in just about any depth of water and let the rollers do the work. I do my best to clean and grease them but I know its a matter of time before they rot out.

below the waterline is bare aluminum so...... i've read a lot of different opinions on bottom paint. some say leave it bare because it will naturally develop a layer of oxidation that is just as protective and others believe the boat will melt if it looks at salt water without bottom paint. I believe the Coast Guard loves to use bare aluminum boats. good thing I'm far to busy right now to do anything about it.

I do flood the bilge after each use but now I'm thinkin about placing a couple intentional holes in the cover to allow rain water to the bilge and naturally flush it out.

I do have an adapter that attaches to the engine and a garden hose that i use and run the engine for a few mins after each use.

thanks again

-Mark

 

I would avoid covering if possible...sort of..

when I took my boat to salt, it had a fine layer of crud on it until it got well hit by rain

this can lead to other issues like molds and mildews, so done within reason is best

 

Yeah I'm still on the fence about covering it. the boat is from 2005 and my father took care of it with crazy attention to detail aside from him only putting maybe 20 hours or less on it per season ( I would say less).

The last time I took it out, it was under cover for a little over a week and the seats already had mold growing on them, so that is a bit concerning.

but it's a toss up, what's worse the florida sun melting everything inside or the mold eating it up? I originally had built a PVC structure to support the cover and hold it up to avoid collecting rain water but it must have gotten super hot because it completely deformed the pvc.

There are about 50 boats in the storage yard and almost all of them are covered, I'm assuming they have it figured out? but its florida and so many people here just follow and don't ask questions.

The cover does have what I would guess to be exhaust holes but I don't think they're quite sufficient enough. I might make a few more intentional holes to let it breath a little and see what happens.

-Mark