A Few Thoughts on Outdrives

Here are a few thoughts on Outdrives:

If you are going to keep your boat in the water, don't buy one with outdrives! Outdrives are great for a lot of reasons but storing them in the water, especially salt water, leads to a potentially huge maintenance nightmare. Corrosion and marine growth are disastrous to an outdrive.

 I just got back from looking at a boat whose outdrive was being kept in the water. The outdrive was covered in barnacles and oysters, the tilt seals were shot, the trim position senders were shot, the case was a mess of corrosion pits and the baffles were dry rot cracked. The outdrive had been serviced and painted 10 months ago. You could see where the diver had scraped barnacles off the surface of the drive during the monthly cleaning, however, because of all the angles on the  drive you can also see where the antifoulant paint was scraped off. No diver will be able to clean up inside of the drive and that's where the barnacles and oysters do most of their damage since they grow up against the bellows and will then cut into the bellows when the boat is used. The drive had been bottom painted with the same stuff used on the hull and the cuprous oxide in the paint set up a corrosion reaction with the aluminum in the drive housing leaving pitting all over the drive housing, especially eating away at the collar behind the prop. The zinc probably went away in the first couple of months and nobody caught it. Then what bottom paint was left failed, the inside of the outdrive loaded up with barnacles and the "leak while running" he was telling me about was probably from a cut, in the bellows. To top it all off,when the seal behind the prop needs to be changed or anything else on outdrive has to be serviced the cost of labor to get it done is going to go up, maybe wayyyy up, depending on how much extra corrosion the mechanic has to fight. Stainless bolts in aluminum housings (what holds that outdrive together) react badly with each other, especially when left submerged in salt water.

This was an extreme case but all this damage is easily preventable: don't store a boat with  outdrives in the water! It's worth your time or money to either trailer it or pay for an in/out service dry storage.

 If you must store it in the water here are a couple of things you can do:

The outdrive must be bottom painted. There are several companies that make antifoulant paint specially formulated to not react with the aluminum of the outdrive casing. These paints are good but never as effective as what can be used on the hull of the boat. One solution is to paint the outdrive with a barrier coat first. Then you can use regular bottom paint for better antifoulant properties. When painting, thin some of the paint and use a Pre-val sprayer and make sure you get paint up inside all the crevices around and on the bellows. Apply multiple coats on the outer casing where a diver is going to do the most damage while scraping growth off in hopes that the diver won't inadvertently scrape all the paint back off. Paint the rams with the outdrive in the fully down position. You do not want to get paint on any portion of the shaft that slides up into the tilt rams.

On the outdrive I mentioned above his tilt ram seals were blown out and was no longer able to tilt the drive. After talking to him I determined he always left the boat with the drive tilted up because his slip was shallow at a moon tide and the drives would bump bottom. What happens is the barnacle and other growth form on the exposed portion of the trim rams and every time he would take the boat out (lowering the drives first) the "dirty" exposed section of the trim rams shaft would slide past the seal and wreck that rubber seal. Leave the outdrives in their full down position! If the slip is too shallow then get another slip or turn the boat around! Servicing those seals requires the boat to be hauled out and usually requires replacement of the end caps at minimum. If any pieces of grit manage to score the shaft then that too must be replaced or the damaged area on the shaft will continually eat seals up. When those seals blow out they will dump hydraulic fluid into the water which is not good for marine life and can cause a hefty fine to be imposed, not to mention your trim will no longer work.