FWD Drive (forward facing drive) Volvo Penta

[savage fro]

I have a Volvo Penta FWD drive (forward facing drive), for a surf boat, that is only 4 years old, but it has a leak. There is much corrosion / erosion inside, so the dealer told me I need to replace the entire lower unit, costing over $10K. But, this boat has been used maybe 8 to 10 times per year, roughly, less than half in saltwater, always flushed and cleaned at the docks after any saltwater use, and is stored either in a garage or on a driveway, not in the water. This seems crazy. I have attached a photo. Does anyone know how this could happen in such a short time? Is the design maybe a problem for this unique FWD drive in saltwater?

 

[Scott Danforth]

Have you kept up with anode service?

 

[savage fro]

Yes, the anodes are good. The Volvo Penta dealer has been unable to explain exactly what happened, or why this would happen so soon under these conditions.

 

[BRICH1260]

That is very unusual for a relatively new unit. What anodes are on the drive. You mention both salt and fresh use, each have a different preference of material. You will need to replace as you seals are compromised given the loss of material. You might look to finding a used/rebuilt that could save you a little bit of cash.

 

[Lou C]

With these units I recall reading that the upper drive unit is the same for both the regular & forward drives and if the replacement Fwd lower unit is too expensive maybe you can find a cheaper used conventional SXA lower. That level of corrosion is extreme for a unit that new, & not left in salt water. My 1988 OMC Cobra has been in salt water 20 seasons (6 months in a mooring) & has nothing like that. Might be a bad batch of aluminum.

 

[Horigan]

Being a surf boat, he can't go with an aft facing prop.

OP, Once the issue is resolved (rebuilt, new), you need to use an aluminum anode given you're in both salt and fresh water. You also need to make sure you have a good electrical bond between the anode and the drive, and change them at least yearly.

 

[savage fro]

If I go with a forward-facing prop, I lose the surf feature. The anodes look very good, and always have. I wonder if the saltwater can't drain properly because of the FWD design, when on the trailer? Has anybody heard of others with FWD drive problems?

 

[Lou C]

The only thing that makes sense is either the wrong anodes, or a lack of bonding wires, but even so that much corrosion on a 4 year old drive not stored in the water makes me think bad batch of aluminum. Here's mine. 34 years old and used in salt water & moored in salt water for 20 years. Anodes changed every year and all bonding wires intact....

 

[savage fro]

Wow, that is amazing. Yours looks so much worse than mine on the outside, but I bet way better on the inside. Here is mine showing the outside. It looks almost new on the outside! I would prefer yours.

 

[Lou C]

That’s what salt water drives look like after being painted with anti fouling paint 20x and never dripping the old stuff off lol!

 

[Horigan]

If the anodes "look very good" and the drive is corroding, then either the anodes are the incorrect material, and/or, they are not bonded electrically to the drive, thus not providing any protection. Not sure how yours attach to your drive, but I always use new star lock washers, sand the drive where the anode bolts to it, and apply dielectric grease to that joint so it maintains an electrical bond. Once installed, use a multimeter to confirm good conductivity between the anode and the drive.

 

[Scott06]

Yes, the anodes are good. The Volvo Penta dealer has been unable to explain exactly what happened, or why this would happen so soon under these conditions.

I would push him to see if this could be warrantied, no way that should be corroded that bad At this point. There was another poster who had similar issue with a vp duo prop but he noticed this at year one , yiu may be able to search and find his thread.
was this visible when removing props previouly?

 

[Lou C]

That looks like what used to happen to early Mercruiser Bravo 3s even in fresh water. I think the cure was more anodes…
Also keep in mind the effect of two stainless steel props in causing galvanic corrosion. I agree with another poster in that if the anodes look good but the drive is corroding something is really wrong. Either they are not active enough for the water you’re in, not making good enough contact or missing bonding wires. Every season when I pull the boat out after 6 months in salt water the anodes do show corrosion (not totally gone but surface corrosion evenly spread) and the drive looks like it always has. The only place where I had corrosion is in the ends of the trim rams and this is because in certain years my mooring spot was so shallow that I had to leave it tilted up with the ends out of the water. The Cobra doesn’t have anodes on the trim Ram rods like the Merc drives do. So now I make sure that the ends are below the surface of the water. Looking into fitting some anodes to the rods in the future.

 

[dingbat]

Guessing you had water get trapped (under a seal?) that went anoxic.

At that point aluminum goes plop, plop, fizz, fizz in a hurry