Welcome to the world of aluminum - as another former wood boat owner, I think you'll appreciate the advantages while you probably appreciated the 'classic lines' that make our boats popular with 'woodies'.

It sounds like the area you are writing about probably had a weak spot in the barrier coat. One of the ongoing debates on aluminum is this: if the hull has no paint whatsoever, charges are dissipated over such a broad area that they may lose most of the damaging effects. When the hull is painted, any small unprotected areas take the full hit and corrosion at those points is much greater.

We're in salty water on the Chesapeake Bay, so we have a professionally applied (by EPA license) barrier coat, then bottom paint. There are a lot of Marinettes on the bay and somehow they're still afloat. Fresh water is a lot less worrisome. Of course, never, ever, use any paint with copper anti-fouling, you'll create a great battery and the copper will win over aluminum every time.

As to the pitting, our boats have 3/16" hulls with 1/8" elsewhere, and some degree of loss is engineered in. A certain amount of pitting has occurred with most, if not all Marinettes to some degree. You'll get plenty of much better informed replies than this, but for my money, unless the pitting is really deep, get the barrier coat FULLY applied after blasting or sanding clean and you'll get many more years of pleasure out of your new boat. The key is, absolutely EVERY minute spot of below water hull must be coated, with no room for error. Use more than one coat, to ensure that what you missed the first time will get covered by subsequent coats.

Also, continue to follow all of the chatter on this site about our Capac monitoring system and galvanic isolators. Make sure you, your marina and your neighbors' boats do not have any leaking charges and you'll be fine.

You did not mention your sacrificial anodes. If they're okay, that could be good or bad. Ask the seller when they were last replaced. If they look good after any great length of time in the water they are probably not connected galvanically to the hull, so once again, the hull is the battery and your 'zincs' are nice ornaments. If they are badly corroded, replace them before you splash the boat. Marinette has the complete set of correct anodes available. Make darn sure you've abraded the points where the bolts pass through and use lock nuts that will dig into the aluminum when the bolts a drawn down.

As to getting through a season, that's a judgment call, but again, in fresh water you're probably okay. You could really hedge your bets if you did not plug in to shore power, but if so, you'd better make sure you run often enough to keep the batteries topped off. We have a 32' Sedan, with half the open cockpit you have and a camper cover that keeps it dry when at the dock, Therefore, very little trouble with water in the bilge. If yours has good covers, consider it, but listen to the folks who are going to jump in behind me on this one!

Enjoy your new boat, send some photos...

Dang, one more question...I keep reading about mag guppy...what is it?

Roger,
Thank you! Boat is currently at National Marine in Peo Hts, but seriously looking at Wharf Harbor. Pretty sure that's where I will end up IF I don't get cold feet on this boat!
Rick

Rick...repeating my favorite buyer sermon: get a professional survey! From a no-nonsense guy YOU hire and who has absolutely no connection to seller or broker. Surveyors vary in experience with aluminum boats so vet one who has appraised Marinettes before and is familiars with their pros and cons. There are definite corrosion issues with this otherwise nice boat and that's a #1 strike against it. But they can be remedied. You say the shaft zincs have wear. Wear on zincs is a good thing. Better they than the boat. But shafts should be isolated and for the most part the shaft zincs shouldn't be needed therefore and should show little or no wear. There is a quick, simple (in the water) test for shaft isolation and one was posted on the board very recently. Do it.

The survey will cost you 300 to 500 well spent bucks.

Rick, thanks for the photos, they help us all.

First, let's talk "zincs" vs "anodes", or more specifically, "sacrificial anodes". We usually refer to ours as zincs maybe because it's easier to say, but that is a misnomer, since the whole idea is to attach a less noble metal to the boat's more noble metal(s) so the less noble one will be sacrificed over time just as the plates inside a battery are eventually sacrificed while it produces a charge. On a steel, wood or glass boat, zinc is fine, because it is less noble than brass through hulls or stainless fasteners and shafts.

Our aluminum/magnesium hulls are LESS noble than zinc or any of the above metals, so if we put so called standard zincs on our boats we'd be adding to any problems that may exist. So, we use special anodes that are less noble than the aluminum/magnesium hull. As I said yesterday, Marinette has full sets available for our boats and they ship pretty quickly.

Others will chime in, but the anodes on your rudders don't look familiar to me. I'm wondering if someone just picked up zincs at the boat store? Also, the long strip on your keel looks to be virtually new. If it's bonded properly to the hull and if it's the proprietary anode designed for our alloy, it should be showing a lot of wear - unless it's new, which the seller should be able to tell you.

The 'mag guppies' you've read about are our version of the zincs you can buy at the boat store that are cast in the shape of a fish. The 'fish' is at one end of a wire rope with a clamp at the other. You simply clamp it to a metal part topside, usually a rail, drop the guppy in the water and it serves as an extra zinc added to what you already have. Once again, for a Marinette or any aluminum hulled boat, zinc is too noble, so Marinette sells 'magnesium guppies' for this same purpose - I'll note here, only in fresh water which we all know is your case.

If your boat, your neighbor's boat and your marina are all wired properly and if your boat has the proper sacrificial anodes, extras like the mag guppy should be unnecessary. It's great if you travel to an unknown marina, you can drop one or two in the water, just in case.

Joel's right, find a qualified surveyor or walk away. How about the Chicago area? You're about 200 miles from a major shipping area with plenty of metal hulled craft. Have you talked with your insurance company? How about Boat US? When we got ours surveyed several years ago, we got recommendations from Boat US and hired someone from Annapolis, MD to come down to Virginia for the day and it was money well spent. He worked for a marine architect and was very clear that the only reason they do surveys is to keep building their own database on what does and doesn't work long run. He cost us $500, spent 8 full hours with us, then had to go back to Annapolis and write his report and send it with photos attached - I still refer to it 7 years later.

You were asking about reparing the area in question aft of the bow. Only someone with experience with alluminum hulls can determine the extent of the damage. I am NOT making any recommendations that is a call you have to make.

If you decide the damage does not put you or your boat at risk... here is a possible fix.

1. Clean area completely down to bare metal with SS brush.
2. Immediately etch the area with primer wash.
3. cover area with epoxy filler (not polyester!) This needs to be done shortly after area is etched.
4. smooth out and let cure.
5. Apply at least two coats of barrier coat. (this step is often omitted when using epoxy filler)
6. Apply min. of two coats of bottom paint.

Looking at your photos... I appears that you have more than enough anode protection on your rudder. They may not have continuity with the hull. Your rudders should be isolated from the hull so the anodes will only protect the rudders. Your keel strip looks good.. again make sure it is making solid contact with the hull.
It is best to remove them when you haul out clean and install to insure contact. The mag guppy is handy in fresh water. If you start loosing protection you can supplement with the guppy. I keep my boat in the water for three seasons and usually after 2.5 seasons.. my numbers are falling due to growth on anodes but mostly due to loss of continuity. If you also want to reduce the load on your hull anodes the guppy will help.
Be careful not to OVERPROTECT voltage should not go above -l.05 mv. Also your numbers will tend to be a lower in fresh vs. brakish or salt water.

Simple rule if your anodes are not pitting and disolving then they are NOT bonded to the hull!

Since this is an older vessel check to see if you have a Galvanic Isolator install on your AC ground assuming you have shore power. This keeps stray DC current from comming in through the AC ground. DC current is what causes corrsion. AC current will only slightly but is DEADLY!
I prefer Galvanic Transformer vs Isolator but they are very heavy and expensive! Most our boats were factory installed with an Isolator.

Here is a link to a great site for mag. guppies, and other anodes including the proper strip anodes for our big M's.
John Althouse is an excellent source for the hull and rudder anodes.


http://www.boatzincs.com/grouper.html

safe boating,
dave

Hi Dick,

The "Goo" is from the the ultra sound I had done on the boat on Friday afternoon. You're right about the NADA but frankly, it is very low. Add the fresh engines, generator, radar....not a bad deal EXCEPT for the hull. I think I finally talked my self out of it. After further conversations on here and with fellow boaters, I don't think the anodes are of the right type, or not bonded correctly to the hull. There is enough corrosionto make me pause. I seriously doubt it would pass a survey, so it would need to be fixed and surveyed after for insurance purposes. I would like to thank everyone here for the great help and advice. Some times common sense must prevail.

Rick:
Ask the surveyor to check the 12v DC wiring inside the boat near the pitts. There should be a bilge pump, shower sump pump and maybe a toilet solenoid in that area depending on the year and model. Make sure the wires are well insulated and not discharging current into the water in the bilge. There is also a through-hull for the head and/or A/C pump that could be brass or bronze and not properly isolated from the hull. Also ask him to confirm that the cutlass bearings are non-metalic. Brass or bronze will cause your hull to pit near the shafts.

You are on the right track. Every boat has some issues. The fresh engines, genset and radar should make the boat worth more. Just be prepared to not find any source of the pitts. It could have been caused by a faulty charger from the next slip over or a faulty bilge pump switch that was replaced.

The collective knowledge and experience of the members on this site (and Jeff's repair site) is amazing. No matter what the issue is, someone has dealt with it before and can give you advice that will save you time and lots of money. Good Luck!

p.s. send me a PM and I will e-mail a copy of the capac meter manual. It will answer a lot of questions about the meter and the causes of galvanic corrosion.