Danger with water towing your Tug

Not that this matters but a three hour tow, I hope you had towing insurance. Did your boat insurance cover the boat repairs? Lucky no connecting rods bent trying to start it. Since I'm a bit of a pessimist someone saying the engine was hydro locked and it would be another 1000 dollars to repair that would be a home run if it really wasn't so. I say this not accusing anyone but since other posters seem to lean towards the reason given to the original poster seems like a stretch. I think I would love to hear Rangers take on all this. Maybe it would be a good topic of conversation at the factory rendezvous with Andrew Custis and in my case the Volvo expert as I have a Volvo instead of a Yanmar. Plus I need to track Bruce Moore down in person and thank him for all of his work maintaining this site and all of the other tasks he performs. It's a bit of a ride for us but I'll have face my fear of crowds. :mrgreen:
 
Don Cardinal":2pm9oofe said:
Because we still don't know what the reason for the tow was.
I would guess that the raw water pump impeller and wear plate were worn or had vanes missing. This I would think could be the cause or at least another potential cause of this happening. The speed of the tow over 3 hours may be enough to force water thru an unobstructed (failed water pump) system and into the exhaust.
Don
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Sine Wave stated the reason for the tow. Originally his raw water pump belt broke and he replaced it. When he started the engine the next day and put it into gear he was hearing a thumping noise and thought he had an engine issue because of the loss of raw water cooling earlier. He opted for the tow. It turned out that the thumping noise was a piece of crab pot line wrapped around the prop. So it appears his original problem had nothing to do with the hydrolock. He was told by the Yanmar mechanic that the hydrolock was due to the towing and not clamping the hose from the stuffing box.
 
I'm confused. Why do we have to inject water from the engine into the stuffing box under normal operating conditions if seawater will flow in the opposite direction while the boat is being towed? Does the spinning prop create a low-pressure zone just outside the stuffing box that becomes a high-pressure zone if the stationary prop is being dragged through the water? Is the prop in fact stationary under tow? Would the same thing happen if the boat was towed backwards, assuming that was feasible? Any insights will help.
 
If a boat is being towed, it is common practice to shut the main engine seacock to prevent this from happening. On the bottom of the boats, we use a high speed pickup that is intended for boats that reach higher speeds to make sure the engines have enough water to cool them. It is possible that while towing without the seacock closed that water can fill up the muffler and get back into the motor.
 
Andrew Custis":1rdv20yr said:
If a boat is being towed, it is common practice to shut the main engine seacock to prevent this from happening. On the bottom of the boats, we use a high speed pickup that is intended for boats that reach higher speeds to make sure the engines have enough water to cool them. It is possible that while towing without the seacock closed that water can fill up the muffler and get back into the motor.
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Thank you. That's good to know.
 
Thanks Andrew,

Yes I agree, that is a good piece of info to know. Seems to me then it would be prudent to close the seacock before firing up the outboard kicker for eight or more hours of trolling.
 
Well, I see a few dynamics going on here. You have an exhaust that has no pressure, although there is a flap to prevent back pressure. You have a fitting off the stuffing box, that without pressure, allows water in rather than water being pushed out. That same fitting has a hose that goes to the bottom of the mixing elbow. Then you have a thru-hull that goes to the impeller. Now add to that a boat not under power being towed. I suspect that the least likely place for the water intrusion to occur would be from the thru-hull. The impeller not turning virtually stops water from going up to the heat exchanger. What I suspect happens is that under perfect conditions the towing causes a vacuum from the exhaust. This then draws the water up the stuffing box hose into the muffler. The muffler fills up and the water coming into the mixing elbow from the stuffing box does not have anywhere to go because of a full muffler and backs up into the exhaust manifold. Any open exhaust valve will then allow water into the cylinder. Also any intake valve open will allow water into the cylinder, hence, hydro-lock. This is the only explanation I can think of. And regardless of why or how, it will be good precautionary practice to close the sea-cock and clamp the stuffing box hose off.
 
I too doubt that seawater can pass through a stationary impeller pump. I think that just about the entire drivetrain and its plumbing on my R27 is near or below the static water line. The only exception is the hump where the exhaust hose crosses the transom. If so and assuming a boat under tow squats at least a few inches, I suspect the seawater has a straight shot through the stuffing box into the engine even without an unexpected vacuum. I hope that because the stuffing box on my boat gets its water from the VP D3 transmission cooler, there is no path for for this water into the exhaust system and cylinders. Other boats with different layouts and plumbing might have different results.
 
knotflying":tnctxb7c said:
What I suspect happens is that under perfect conditions the towing causes a vacuum from the exhaust. This then draws the water up the stuffing box hose into the muffler. The muffler fills up and the water coming into the mixing elbow from the stuffing box does not have anywhere to go because of a full muffler and backs up into the exhaust manifold. Any open exhaust valve will then allow water into the cylinder. Also any intake valve open will allow water into the cylinder, hence, hydro-lock. This is the only explanation I can think of. And regardless of why or how, it will be good precautionary practice to close the sea-cock and clamp the stuffing box hose off.
Click to expand...

So is this stuffing box hose large enough to hold the required amount of water to fill all those spaces or are you saying additional water is pulled in from the exhaust due to a vacuum?

Jake
 
The ID of the hose is maybe !/4 inch, But a sufficient amount of water flows out. Just remove the hose from the barbed fitting when the engine is off and you are stationary. So not too much force would be necessary to get the water up a little higher so that it enters the mixing elbow and starts to fill the muffler. Remember, water seeks its level. If the mixing elbow is lower than the loop on the exhaust hose from the muffler to the exit vent, once the muffler is full the only place to go would be back to the engine. I can't think of any other explanation. And also keep in mind this was a 3 hour high speed tow. A small amount of water over that period of time can add up.
 
The ram pressure effect on the high speed intake used on our engines can force water past the impeller and into the exhaust. Gensets and sailboat engine installations use flush raw water intakes for this reason. The installation manual for the Mase genset specifically mentions this.

From another genset/sailboat diesel engine installation manual:
CAUTION: Do not use a high speed scoop-type through-hull fitting for the raw water supply for generators and auxiliary sailboat engines as it will tend to encourage siphoning. Water pressure against this type of fitting while the vessel is underway with the generator off or when sailing can push water past the raw water pump impeller and into the exhaust system, filling it and the engine as well.

When the impeller and raw water pump are new it may be difficult for water to be forced through but a slightly worn pump and older impeller may allow leakage past the vanes.

I really doubt the issue was the water feed line to the shaft. Was the raw water seacock open or closed during the tow?

Howard
 
Ok, I can see that there is a difference of opinion about where the water is coming from or how/why it gets there.
I had a long tow back home on Friday night. My boat is at the boatyard right now waiting for diagnosis on Monday. The first thing I want the mechanic to do is to check for waterlock ... turn the engine over by hand.

Now that I've read this thread of horrors....
We can do a lot of things to be sure we're safe. I'm even going to be putting a towing checklist into my logbook.
I even have an additional task for towing that I did during my tow. With the propshaft turning at a pretty good clip, the transmission got warmer and warmer over the first ten minutes. We stopped and I secured the propshaft with a dockline and a pair of visegrips. Worked nicely.

BUT here's a possibly crazy proposal.
Would it be possible to drill and tap into the side of the muffler and install a small gascock valve. While under tow it would be opened to the bilge. In any of the above theories about the origin of the water it would protect the engine. If a vacuum was sucking water in, the open gascock would break the vacuum. OR if the water was being forced in under pressure, it would be free to drain out into the bilge and get pumped overboard. It would also, very likely, answer the question of which theory was the best.

Comments?
 
The factory installed muffler on my R 27 has a drain plug. This plug is below the exhaust inlet, near the bottom. One could easily replace the plug with a valve. On my previous boat I routinely drained the muffler in this way.
 
I don't want to wish ill on anyone, Osprey, but if you ever get towed, open the plug.
Let us all know if it "sucks" or "blows".

I'll have to take a closer look at my muffler.
Thanks
 
After reading all the discussion on the topic, I tend to agree with H Rowland's and Andrew's assessment on the possible culprit being the high-speed thru-hull raw water pick up. A possible worn impeller would certainly add to the potential of water intrusion through the high speed fitting over a long tow. I am not sure why the water pump belt initially broke . But...a worn and broken water pump belt might also indicate the presence of a possible worn impeller that could exacerbate the problem. Closing the sea cock seems like a very simple possible solution when under tow.
 
Awww come on, it was a 3 Hour Voyage - we all know how those turn out :lol:
 
That thought had occurred to me too.
 
I had the seprentine belt fragment and disintegrate on my R31 about 2 months ago (Due to the belt tensioner failing) and I had to get a tow back to home port. The tow was about 2 hours long and we were towed at between 7 - 8 knots.
The engine was shut down but I did nothing else about closing the through-hull or clamping off any hose.
There was no back flushing of water and all was well when a new tensioner was fitted and new belt installed.
It is a Volvo D4, so perhaps it is quite different from the situation described by Sine Wave.
 
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