Saildrives?

[tuskie]

Originally Posted by dennisail

My SD20s have 1500 hours and the seals have worn grooves into the shafts. I was able to linish most of it away.

For grooved or worn prop shafts that pre-maturely wear oil seals the invention from heaven is the "Speedy-sleeve". Well actually from SKF, not heaven!

SKF SPEEDI-SLEEVE

These are very thin, ultra hard faced stainless steel bands that are precision engineered to be driven over shafts to replace the worn section where the seal runs on. You must very carefully measure the shaft diameter and order the correct size Speedy-sleeve. They come with the correct installation drift and are doubly secured with Loctite and can save heaps of $ compared with new shafts. The sealing surface is actually smoother and harder than the new shaft.

I have used them on inboard and outboard prop shafts, as well as automotive axle hubs and gearbox shafts.

I'm glad to see that you are successfully giving the old Crowther a new lease on life, and doing it for less money than some "experts" predicted. Cheers.

[DotDun]

Originally Posted by ggray

Venting as you describe would probably be better than the original setup, but could get messy if the oil is pushed out. This seems to happen in cold weather. But you will still have less pressure inside the saildrive than the water pressure outside against the seals. With the header tank, in effect, the saildrive will be vented, plus by having the tank maybe a foot above the waterline, there will be slightly more pressure inside than out.

I have been using this system for about 10 years now I guess.

I'm not doubting the header tank solution works, just wondering if that extreme is required.

Of course, the real solution is new prop shafts!

I don't understand how cold weather expands the oil, interesting characteristic.

::note to self - Stay in warm weather ::

[ggray]

Not saying cold weather expands the oil, but the aluminum housing certainly contracts more than the steel parts inside, and perhaps the oil as well.

I experienced this "overflow" of the oil several times before my modification, and this was the only explanation I could think of.

[DotDun]

Originally Posted by ggray

Not saying cold weather expands the oil, but the aluminum housing certainly contracts more than the steel parts inside, and perhaps the oil as well.

I experienced this "overflow" of the oil several times before my modification, and this was the only explanation I could think of.

I haven't experienced any leak/overflow using just a vent hole. I do keep the oil level towards the bottom of the range as shown on the dip stick. I opened the fill and watched the oil flow while the engine is running and the pump keeps a nice bath of oil on the top (horizontal) gears, but I still maintain the oil level within recommendations.

New prop shafts in my future.

[Andrew Troup]

@ggray: The differential contraction of alu with respect to oil (and steel) is not sufficient, I would stake my fortune (ha!) on it, to create a perceptible pressure rise in a sternleg, even if the bottom end was topped up so it was completely air-free before sealing.

I don't pretend to have an explanation, but possibly the air INSIDE the saildrive was warmer, and/or the barometric pressure lower, when you cracked the filler plug open? Or the level rose due to water leaking in?

If it was indeed due to cold, but experienced while the unit was running: could it be a viscosity effect, whereby the oil was being churned from beneath, and the viscosity allowed that churning to raise the level in some locations and lower it in others?

I personally like the sound of a header tank. One more think to think about in consideration of an inversion, but in principle sounds to me like a good idea, particularly for a long distance voyager, with sail drive(s).

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In respect of inversion, broadening the scope to engine lube oil: does anybody know in detail how lifeboat engines, rated for running during and after inversion, manage the oil issues? Yanmar talk vaguely about "oil mist separators", but there must be some breather technology which lets air in and out (or, more pedantically but perhaps importantly: allows for volume changes).

The only things I've so far thought of which seem to me might work have been

a) Some sort of porous plastic breather, where the pores were too small for oil molecules - or even Gore-Tex™ (although that seems on the face of it like overkill, I guess it would exclude water - but it would, I imagine, be inclined to clog over time with oil droplets, let alone liquid oil contact)

b) A gravity and/or buoyancy operated shutoff (the latter brings to mind a kid's snorkel with pingpong ball)

c) Some sort of header/expansion tank, draining back to the sump.

d) A neoprene or similar bag or balloon, whose interior breathes to the atmosphere (like the "Pronal" bags, used for hydraulic oil tanks in very humid industrial settings)

I'm not sure how to handle the blow-by emissions line back to the air intake, in any or all of these

Anybody have experience with any of these, or able to cast some light in my darkness?

[Jim Cate]

Andrew, I don't know what measures are taken, but a friend of ours pitchpoled a Lightwave catamaran on the Wide Bay bar a few years ago. He was thrown clear, and when he finally swam back to the inverted cat, the engines were still running. AFAIK, they were unharmed by this maltreatment. IIRC, they were (and still are) Yanmars. He did not mention that there was much oil loss, but the overall mess was so severe that it may have seemed trivial. Next time we run into him I'll ask for more details.

Cheers,

Jim

[Thumbs Up]

My somewhat grooved saildrive shaft became leak free for a while when I replaced the seals but an accident with the dinghy tow line must have broken the "outer facing" spring on the outer seal. After that "and changing the oil" I have been cracking the dipstick open every time I shut the engines down. I also leave the key in the engine compartment as a reminder. The inner facing seal seal that keeps the oil in is perfectly capable of keeping seawater out if there is no suction in the saildrive as it cools off. I think that venting the saildrive is the solution to most leaks. I am out the water now and found out that my saildrive boot held up well so I may do it again this way: sprayfoam with 5200 smeared over it then antifoul.

[ggray]

Originally Posted by Andrew Troup

@ggray: The differential contraction of alu with respect to oil (and steel) is not sufficient, I would stake my fortune (ha!) on it, to create a perceptible pressure rise in a sternleg, even if the bottom end was topped up so it was completely air-free before sealing.

I don't pretend to have an explanation, but possibly the air INSIDE the saildrive was warmer, and/or the barometric pressure lower, when you cracked the filler plug open? Or the level rose due to water leaking in?

If it was indeed due to cold, but experienced while the unit was running: could it be a viscosity effect, whereby the oil was being churned from beneath, and the viscosity allowed that churning to raise the level in some locations and lower it in others?

Well, the coefficient of expansion of Al is double, IIRC, that of steel. I didn't do any calculations! Just thought that might be the explanation. Changes in temperature can have major effects. Think about RR rails buckling on hot days.

No water, for sure; not sure when the oil was pushed out, just found a puddle of oil below the filler cap. Engine had probably not been running for a couple of weeks, so was cold.

This had never happened when the engie was running, or on warm weather.

[Andrew Troup]

This is my second attempt at this post.

When I pressed "Submit", the forum software evidently thought I was intending to surrender, and decided I wasn't logged on, and tossed my first submission out the air-lock into cyberspace.

(... even though I had just logged back in after the site came back after a maintenance period, and my name appeared at the top of the same page)

Sigh...

I did a quick calc to make sure my intuition here was not off-beam.

Conveniently, because the coeff for alu is double that for steel, and the latter similar to oil, I was able to do the calc for a steel sternleg containing a fluid with a zero coefficient. The answer should be about the same.

(Alu: 20 millionths linear expansion per deg C; Steel and Oil: 10 millionths)

The volume of a 100mm cubic (1 litre) steel container, for 1 deg C increase, would grow to about 1.00001^3 of the original size, or ~ 1.00003
Hence a volumetric increase of 1.00003 – 1 , or 0.00003 litres

so for a 30 degree C rise, the volumetric increase would be thirty times this, or 0.0009 litres, say 0.001 litres, or one-thousandth of a litre

Which would *roughly* be a level change of one tenth of a millimetre in the original container. (because 100mm level change corresponds to a whole litre)

in US customary units: a change in level of about four one-thousandths of an inch, for a temperature change of about 85 degrees F.

[Andrew Troup]

Here's a line I forgot from my original post, triggered by ggray's
<<Well, the coefficient of expansion of Al is double, IIRC, that of steel. >>:

Hmm - that's exactly right, but we're talking VERY small numbers.

It struck me that an apt comparison would be if the rabid fan of some famous celeb (perhaps, say, one whose small dog travelled in her handbag) claiming that her IQ was "double that of a genuine Barbie doll"

Maybe the forum software supplier has a maintenance staffmember who took exception to that analogy? I'll see if this post also gets the airlock treatment !

.... hopefully, there's been a change of shift ...

[dennisail]

I find that often attempts use calculations can lead people astray as there are too many unknown variables.

The fact is the sail drive of mine with the water had positive pressure and was so full of fluid that it significantly overflowed once I took the cap off. No calculations needed to see that this fluid volume and pressure did not get there by someone filling it via the filler cap.

Probably the heat expansion cycles allowed some kind of one way valve effect to occur somewhere on a dodgy seal allowing water in, but nothing out.

Also a vent without a header tank could actually lead to more water getting in than without the vent in some situations since oil floats. If there was a bad leak in the seals, water could continue to flow in through the leak displacing the oil upwards until theoretically the whole sail drive was filled with water, and all the oil was in your bilge (having come out of the breather). So I would not do the vent idea without a header tank.

[Andrew Troup]

dennisail:

My calculation was not intended to model the real world, nor have any bearing on water ingestion.

It was a narrow rebuttal of a narrow point by a specific poster

I did the calculation to test ggray's hypothesis that the differential thermal contraction of an aluminium housing, in comparison with the lesser thermal contraction of the oil (and steel) contents, might explain or contribute significantly to the sort of oil displacement he had noted.

I think you make a good point about venting without a pressure head from a higher tank being unlikely to help in the case where a leakage path was sufficiently borderline as to require relatively low pressure difference to drive it.

[DotDun]

Originally Posted by dennisail

I find that often attempts use calculations can lead people astray as there are too many unknown variables.

The fact is the sail drive of mine with the water had positive pressure and was so full of fluid that it significantly overflowed once I took the cap off. No calculations needed to see that this fluid volume and pressure did not get there by someone filling it via the filler cap.

Probably the heat expansion cycles allowed some kind of one way valve effect to occur somewhere on a dodgy seal allowing water in, but nothing out.

Also a vent without a header tank could actually lead to more water getting in than without the vent in some situations since oil floats. If there was a bad leak in the seals, water could continue to flow in through the leak displacing the oil upwards until theoretically the whole sail drive was filled with water, and all the oil was in your bilge (having come out of the breather). So I would not do the vent idea without a header tank.

I would suggest that if the seals have completely failed, neither venting nor header tank would be the correct solution. At that point replacing seals and/or shaft is the only solution.

The system works as designed from the factory, double lip seals on the prop shaft. Lip seals are maintenance items that require periodic replacing. Lip seals wear the shafts. When the wear on the shaft is such that the lip seal can no longer keep the oil in/water out, the correct solution is to replace the shaft and seals. Venting and header tanks are stop-gap solutions, easing the urgency to get hauled out, enabling deferred maintenance, if you will.

My experience is the shaft is good for >2000 hours with periodic seal replacement. Unlike a traditional prop shaft design, one cannot simply move the seal to an unused part of the shaft.

[dennisail]

I would suggest that if the seals have completely failed, neither venting nor header tank would be the correct solution. At that point replacing seals and/or shaft is the only solution.

Any solution that keeps water out is good, one that invites even more water in is bad.

Obviously the best thing is to get new shafts or sleeve them. Haul outs are very expensive and if you are not due for one for a year or so something like a header tank will give you time. Also it will be an insurance policy for if your working seals do fail for whatever reason even if you think they are good.

[DotDun]

Originally Posted by dennisail

Any solution that keeps water out is good, one that invites even more water in is bad.

Obviously the best thing is to get new shafts or sleeve them. Haul outs are very expensive and if you are not due for one for a year or so something like a header tank will give you time. Also it will be an insurance policy for if your working seals do fail for whatever reason even if you think they are good.

No doubt, just as rescue tape will fix a leaking hose. IMO, neither are a long-term solution.