Header Tank To Eliminate Saildrive Salt Water Intrusion

[ballvalve]

I read that viton seals are only needed for hotter temperatures and I cant see something that has so much water cooling it continuously will ever get to any significant heat. I used the stainless springs from the old seals on the new outer seals, but I guess O rings would also work well.

[RaymondR]

If one goes the header tank route should one consider reversing the seal to keep the oil in rather than the water out?


Years ago I considered getting rid of the cutlass bearing and prop shaft gland and replacing them with opposed tapered roller bearings in an oil filled stern tube with a header tank to keep the seals pressure activated. It was doable and I found a couple of boat owners who had done it successfully however I gave up the idea when they warned me that it did cause noise from transmitted vibration from the prop. Had I implemented it I would have set the seals to keep the oil in rather than water out.

[Chris dCB]

Originally Posted by Privilege

Do these tanks have an overflow outlet? If they are completely sealed they might not work as suggested. The idea as I understand it is that as the oil cools and contracts it creates a vaccum which helps the sea water to enter. A hole drilled in the cap would alleviate the problem.

Good find though. I think I'll order two also.

The mini-moto fuel tank that I used has a cap vent. I pushed on a length of 8mm plastic pipe and used a tywrap to form a coil. That way the tank is always at atmospheric pressure. If the oil heats up it can expand into the tank but there is always a 1-2ft head of oil to ensure that no seawater comes into the gearbox.

[tunnelvision]

Originally Posted by tunnelvision

I just ordered 2 of these to do my sail drives. Dorman - 603-001 - Universal

These worked perfectly with a small hole drilled in the cap. Now I can see at a glance if the oil level is correct.

[double u]

...now i've got myself the Judd-Racing hose-adapter, a hose & a little container from a hydraulic motorcycle clutch - & I read in the Volvo manual to never ever overfill the saildrive with too much oil...what to do?

[billknny]

Originally Posted by timbenner

Sometime ago I saw a really cool saildrive modification on this site that I'm considering doing. I am hoping to get some good input or reasoning as to why I shouldn't do it, before I do. Hopefully the guy that thought of it and posted it, will tell us how it worked out in the long run.

Next to regularly cleaning the raw water intake channels in the saildrive, the next worst thing is when the lower seals fail and sea water mixes in with the oil. Necessitating immediately hauling the boat to replace the seals.

I saw a blog here a few years ago where someone installed a radiator overflow plastic tank just above the water line and ran a hose from the tank to a male hose fitting that replaced the dip stick on top of the saildrive unit. The head pressure from the 90 weight oil in the overflow tank, mounted just above the water line would STOP the seawater from intruding into the failed seal and conversely send 90 weight oil out, before the seawater came in. Given the viscosity of the oil, very little if any would ever leak out, but will block the seawater from EVER coming in.

Seems like a "No Drainer" to me and very inexpensive to do. Much less money than one haul of the boat for an emergency seal replacement.

Comments????

I don't have a saildrive, but the Amel "C" drive unit on my boat is of a similar, though much more robust design, oil filled, with a lipseal on the prop shaft.

For 30 years Amel has been building these with the kind of header tank you describe. I can 100%, absolutely, assure you it will NOT prevent the incursion of water into the oil when the seals fail--even with 4 feet of oil above the waterline.

The way to prevent emergency haulouts is to replace the seals on schedule, and replace them with great attention to detail on the correct procedure.

[motion30]

MerCruiser does the same thing as standard equipment on their outdrives

[Privilege]

The reason that you shouldn’t over-fill the saildrive is because it is air tight and when the oil gets warm it expands causing too much pressure on the seals. If you use an additional tank which is vented, then the oil can expand all it likes and it won’t cause a pressure problem in the drive.

Billk, how can you 100% be sure it won’t work. If two liquids are separated by a seal and the seal develops a tiny leak, the liquid which is under the higher pressure will pass the seal. It’s physics.

[a64pilot]

Originally Posted by Privilege

The reason that you shouldn’t over-fill the saildrive is because it is air tight and when the oil gets warm it expands causing too much pressure on the seals. If you use an additional tank which is vented, then the oil can expand all it likes and it won’t cause a pressure problem in the drive.

Billk, how can you 100% be sure it won’t work. If two liquids are separated by a seal and the seal develops a tiny leak, the liquid which is under the higher pressure will pass the seal. It’s physics.

I don’t have a sail drive, but I was wondering if they were sealed or not.
Coming from a 4X4 background, sealing drive systems was given up long ago as when the warm component was placed in Cool water, it formed a vacuum, and of course pulled water in.
If you have ever had a trailer Boat, it’s likely you had bearing buddies, they work because they keep the grease under slight pressure, and a vacuum won’t form and water won’t be pulled in.

The old US Military M38 Jeep we had as a kid, the mechanical fuel pump was dual chambered, one side pumped fuel, the other side pumped air to pressurize the transmission, differentials and transfer case, just slightly, not much pressure.

There is a lot of precedence of slightly pressurizing mechanical components that are under water.

Of course, I really don’t know much of anything about Sail drives, I’ll be the first to admit that, and I’d be surprised if they were sealed and not vented.

[ggray]

They are sealed/unvented.

However, with the sail drive immersed in the water, I can't think the innards get as hot as a transmission or whatnot out of the water. And they are already immersed so there is no change in heat transfer capability.

But with so little air space, aluminum housing (high expansion co-efficient), water outside the seals, it's asking for trouble IMO.

[Privilege]

Originally Posted by a64pilot

I’d be surprised if they were sealed and not vented.

I agree...I'm surprised too but everything that I see on mine tells me that they are sealed to the outside world. I've enclosed a couple of photos I found online.

I too am happy to admit that I am no mechanic and would love to hear the opinion of someone more experienced than I, but it seems obvious to me that this design creates two problems...
1) Cooling oil will contract creating a vacuum (if only minutely) in a sealed unit. If your seals are not perfect, it will suck salt water in.
2) Even without a vacuum, as the entire unit is below sea level, the outside salt water is at a higher pressure (again minutely), which, if the seals are not perfect, will allow water in.

A header tank seems to be an easy fix for both of these problems and allows easy visual inspection of oil levels.
[ATTACH][/ATTACH]

[billknny]

Originally Posted by Privilege

Billk, how can you 100% be sure it won’t work. If two liquids are separated by a seal and the seal develops a tiny leak, the liquid which is under the higher pressure will pass the seal. It’s physics.

Privilege,

First, it is important to note that I am NOT saying a head tank is a bad idea. In general it is a good one. As for it being a good idea on a saildrive or not, I will leave to the manufacturer. What I am saying is that the claim a oil head tank will prevent all water intrusion all the time is not accurate.

What you say about physics is true enough, and applies in the static situation, when the shaft is not moving. Unfortunately the physics is more complex than simple pressure gradient when things start moving. The rotating shaft generates pressure dynamics that are more complex that the static analysis would indicate.

A lip seal actually is designed to "pump" a (tiny!) bit. They definitely have a front and a back side. A typical prop seal is "two faced". The outer lip "pumps" water out, and the inner lip "pumps" oil back in. Once the outer seal fails, the inner seal "pumps" water into the oil. And the outer seal is almost always the one to fail first.

Now I grant you that if the pressure gradient is high enough you will blow oil out, but you will not get that with a head tank on a sailboat. Don't forget that oil is lighter than water. To generate a positive pressure at the bottom of the drive, you will need a head tank significantly above the water line. You'll need your head tank to be about a foot above the waterline just to get to zero pressure difference. In the real world, any positive pressure you think you are generating is trivial. A few inches of water pressure at best.

The reason I can be 100% sure it will not work, is I have seen water come into such a system (where the header tank is 22 Inches above the static waterline) and cause the oil to turn into mousse. In fact, enough water can come in to overflow the oil head tank. Unfortunately the oil and water have not read the same physics textbooks.

[Chris dCB]

Just a quick follow-up note... When I bought my boat (4 years ago) the saildrive was full of mayonnaise. There were two seals in the leg, facing in opposite directions; nevertheless, the repeated changes in internal pressure had clearly resulted in seawater being drawn into the leg.


Fortunately, the shaft was not too badly worn but I replaced the two seals and, as a precaution, packed the space between them with marine grease. I then installed the header tank solution. At the latest haul-out I drew off the oil and replaced it (probably unnecessarily). The drawn off oil was completely clear.


You have to make your own decision on this, but I have had no reason to regret installing the header tank and would recommend the modification to anyone with a saildrive.

[Christmas Beetle]

I purchased a 22 year old Grainger (cat) with 2 x 22 year old SD10s (originally Selva Marine Italy and subsequently bought out by SF) 3 years ago and it came with header tanks, breathers etc. I understand the conversion to header tanks occurred over 15 years ago. Due to accessibility to the original dip stick etc I am so glad I have the header tanks etc. Over 15 years sounds like a good system. And from the aspect of sealed systems that consistently get hot and then cold including car transmissions, the concept of a sealed system just doesn’t make sense to me.

[pmar]

Hello, today i found out that oil in my 130S Volvo penta saildrive is looking like milk, probably I've made already around 30h on it which is scary but everything seems to work well, I immidetly pumped out the oil 3 times, and filled new, to get rid of the water, I am planing to do so at least 2 more times until oil will be clear. It will take some time until i will be able to take boat out of the water, but I am planning to mount external oil tank hopefullty to prevent getting more water into oil until i fix the problem.
I have around 60cm of space above waterline to do so, which should be enough to pressurize system with olny mass of oil. Neverthless idea to me is new, I just found this topic when i've been looking for solution to mitigate the issue, so i would humbly ask for Your support.

Could You tell me if i understood the idea correcly:
Im mounting some over flow tank like this one (ideally with vent): https://www.aircraftspruce.com/catal.../reservoir.php around 60cm (20 inches) above waterline. then connect it with some oil hose to cap fitted in place of oil dipstick (like this https://www.juddracing.com/products/...-breather.html) and overflow whole system with oil (of course i will leave like half of installed tank empty to give oil possibility to expand) and that's it?
If I am correct, could You tell me how big the overflow tank should be?

Thanks, pmar