Saildrive Finishes

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richardbrennan

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I have just had a new Volvo saildrive installed in my boat which comes with a nice shiny paint finish. The advice from International on antifouling was a coat or two of Primacon followed by two coats of Trilux and that I would need to key the surface first with 180 grade wet and dry. As I was going through this exercise, the mechanic fitting the new engine and drive pointed out that this invalidated the warranty.

Having looked around the yard, I could find no boat that did not have the saildrive leg antifouled; it therefore seems daft to me that the legs are supplied with such a finish, which might look good at the boatshow, but is totally impractical in the real world, or am I missing something?
 
I agree 180 grade sounds a bit coarse. OTOH 400 and above sounds a bit too fine.
 
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richardbrennan said:
I have just had a new Volvo saildrive installed in my boat which comes with a nice shiny paint finish. The advice from International on antifouling was a coat or two of Primacon followed by two coats of Trilux and that I would need to key the surface first with 180 grade wet and dry. As I was going through this exercise, the mechanic fitting the new engine and drive pointed out that this invalidated the warranty.

Having looked around the yard, I could find no boat that did not have the saildrive leg antifouled; it therefore seems daft to me that the legs are supplied with such a finish, which might look good at the boatshow, but is totally impractical in the real world, or am I missing something?
Click to expand...

I'd ask Volvo themselves for advice.

Although from personal experience I can say the factory finish of the saildrive is quite smooth and doesn't give much to grow on.
The problem is however that the clever people of Volvo bolt the drive together with stainless steel bolts. So what happens after a while is that the surface around the bolts corrodes because of the galvanic interference between the bolts and the aluminum.
They should have put some isolation rings under the bolts or so.
So I've just finished the first exchange of the rubber ring and in the process had to repaint the leg. I've used several coats of good quality epoxy-primer for this. Afterwards I've coated the leg and the bolt heads with copper-free antifouling.
The picture shows the leg after I removed all the corrosion.
 
This is what your nice new saildrive leg will look like after a year in the water if don't antifoul it:
Highland-20120323-00228crop.jpg

I put a new saildrive in last April, and on the advice of the yard, didn't paint it. This year it's had 2 coats of epoxy primer and 2 coats of trilux 33.

You'll also see that the prop anode has completely disappeared and the saildrive anode is well gone.
I'm going to fit a galvanic isolator, to see if it helps reduce the corrosion, which is much worse this year than the last 4years. The boat was plugged in to the marina supply all winter (same as before) but it looks like more stray current this year.
 
Ian_Edwards said:
This is what your nice new saildrive leg will look like after a year in the water if don't antifoul it:
Highland-20120323-00228crop.jpg

I put a new saildrive in last April, and on the advice of the yard, didn't paint it. This year it's had 2 coats of epoxy primer and 2 coats of trilux 33.

You'll also see that the prop anode has completely disappeared and the saildrive anode is well gone.
I'm going to fit a galvanic isolator, to see if it helps reduce the corrosion, which is much worse this year than the last 4years. The boat was plugged in to the marina supply all winter (same as before) but it looks like more stray current this year.
Click to expand...

If its a Volvo leg, I thought they were electrically isolated from the engine
 
That's how I understand it as well, but there is salt water path, through the saildrive leg into the heat exchanger, which is bolted to the engine. Assuming that the inside of the leg and the inside of the heat exchanger aren't covered with and insulating coating, then there must be a sea water conductive path between the two?

I might try putting a multi meter between the engine block and the sail drive and see what the electrical resistance between the two is.

I thought I'd try a galvanic isolator .... simple because I don't know what else to do.
 
Ian_Edwards said:
I thought I'd try a galvanic isolator .... simple because I don't know what else to do.
Click to expand...

There's always the Volvo Active Corrosion Protection system; OK, sold as being designed to protect outdrives (there's also a version for IPS drives), but the saildrive isn't a lot different in terms of materials. My outdrive equipped boat has it, the anodes last an embarrasingly long time (and that's not because the drive is corroding) ! It has a reference electrode and an active electrode. If the control unit senses the electrical potential to be in the area that allows corrosion, it applies a correcting potential from the active electrode.
 
Ian, seeing your picture brought to mind the advice I got from Bruntons at the boat show. The guy on their stand said to use some paint/nail varnish round the holes where the bolts go through; this will prolong the zinc round the bolts and keep the anode in place for longer. Looks like what has happened to yours is that the zinc round the retaining bolts has been eaten away and the anode has fallen out - apparantly quite a common occurance. I routinely replace mine every year as it has become insecure rather than 'running out' of zinc; I now await looking at the anode later this year to see how nicking a bit of SWMBO's nail varnish has worked!
 
I rubbed it down in the end very lightly with 240 wet and dry and the Primacon seemed to go on well followed by the Trilux. Having seen Ian's picture, it seems to me that they do need antifouling so my question as to why Volvo or any other manufacturer do not supply them suitably finished for this remains.

As far as anodes are concerned; I have a Volvo folding prop rather than an autoprop which has three seperate anodes which together form a complete ring around the hub. I have not had a problem with the leg anode in the past, there's generally a lot of meat left, but the anodes on the prop certainly struggle to last a season and there's probably only about 25% left when I bring the boat ashore. I do have a galvanic isolator in the system.

This coming season, rather than have a diver do a mid season scrub for me, I might well use the boat lift ar Haslar Marina and change the prop anodes at the same time, even though there ridiculously expensive for three small bits of zinc!
 
My VP saildrive has now done five seasons and has never been antifouled or painted, this was on advice at commissioning of the boat however after the first season I coated it with Propshield, which is a lanolin wax which flows when warmed. I have stripped the original Propshield off this winter and replaced it with fresh, so it lasts four years with some touching up. The VP paint underneath still looks like new. However my boat spends a good part of each season in fresh water.
I am pleased that it was never primed or antifouled.
The anodes on the VP three blade folder are well gone after 6 months and I would not trust them beyond 9, but I have a stone pier near here that I can lean against if I needed to stay in all year, the anodes on the leg last at least five years but I bed the fixing bolts on a liitle silicone sealant so that the erosion is reduced in that area. I always did that with shaft anodes in the past as otherwise the corrosion was more rapid at the fixing bolts, quickly loosening their grip.
 
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