canal turbulence - a word of warning - SailNet Community
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post #1 of 9 Old 10-19-2014 Thread Starter
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canal turbulence - a word of warning

In a wee Scottish canal. It had been raining and the canal water volumes were aggressive with lots of turbulence in the locks. We had the motor running on idle.
We motor out of one of them and in to the calm of the canal.
About a mile later, up went the regular command "helmsman, check coolant temperature".
"It's in the red!".
"What????".
Shut-down!
The boat, a USC Polaris 36, coasts to a slow halt in the canal.
One of the crew ties a fender to a line and throws it over a wee bridge rail to hold the boat. There was very little wind.

I let the motor cool somewhat.... a Volvo MD17C raw water cooled unit.
I bleed the system.
Firstly the line to the water pump - clear.
Then the line to the exhaust manifold - hot stuff but still flowing.
Then the exhaust elbow entry. We start the motor briefly and the water gushes out of the coolant line to the exhaust elbow.

We let the motor cool some more, then re-start. The water gushes out of the exhaust as normal.
The temperature reverts to normal - well in to the green.

I can only assume that the lock turbulence made the coolant pump have to work too hard for suction and it cavitated to water vapour. It was pumping nothing.

Be careful out there guys. That one was unexpected. We could have easily cooked the motor. We do watch it carefully. Now we watch it very carefully.

Rockter.
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Last edited by Rockter; 10-19-2014 at 03:58 PM.
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post #2 of 9 Old 10-19-2014
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Re: canal turbulence - a word of warning

Id offer that such a 'heating/cooling incident' would be a prime cause to ... shut down, wait, and while sorting things out ... to enjoy a few wee drams of a noble 'single malt' - to help with the required 'clearer' thinking.

Last edited by RichH; 10-20-2014 at 09:49 AM.
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post #3 of 9 Old 10-20-2014 Thread Starter
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Re: canal turbulence - a word of warning

Rich :

Thanks.
Two problems with that approach....
A: I don't booze.
B : The motor will not fix itself.

But, I guess the scenery makes up for it, somewhat...


The motor (Volvo MD17C) is normally very reliable, and when it is distressed, it really gets our attention.

The single coolant pump normally shifts a fair blast of water, so it caught us off guard. We will watch for it next time.

We made it home anyway, a trip of about 110 nautical miles.

We got well and truly squalled with a NE blaster approaching the Corran Narrows...

Site Record for Corran Point, Lighthouse Ardgour, Corran Narrows; Corran Lighthouse; North CorranDetails Details

....but the motor held good.

It is a very pretty place...

Loch Linnhe - Wikipedia, the free encyclopedia

We are blessed.

Rockter.
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post #4 of 9 Old 10-23-2014
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Re: canal turbulence - a word of warning

There are really only three possibilities for this;
1) something blocked the intake through hull and then fell off when the engine was shut down
2) the body of the raw water pump is worn which happens often. This causes the pump to pump much less water than usual and possibly not be able to create enough vacuum to suck up water if the through hull is temporarily out of the water
3) if the engine is raw water cooled the water passages in the engine barrels (individual blocks or jugs) are partially blocked with silt which causes the engine to run hot.

# 1 will fix itself and # 2 is relatively cheap and easy fix. # 3 is expensive.

Stanley,
Marine Diesel Engine Vendor
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post #5 of 9 Old 10-23-2014 Thread Starter
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Re: canal turbulence - a word of warning

NC :
It pumps like crazy now. It always pumped well anyway.
Looks like it was 1 or 2 then.
I will watch it carefully in future.
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post #6 of 9 Old 10-28-2014
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Re: canal turbulence - a word of warning

I'm guessing #1.

When there's lots of rainwater runoff it often contains lots of debris. I've seen plastic shopping bags float by at the same depth as my raw water intake.

Ken

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post #7 of 9 Old 10-29-2014 Thread Starter
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Re: canal turbulence - a word of warning

Carbon :
I guess I need to fit an overtemp warning.
It may not be as easy as my oil pressure warning. I was planning on putting the existing klaxon in series with a winker relay so the high temp warning would be intermittent. Or I can fit a second, different-sound klaxon.
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Re: canal turbulence - a word of warning

Get the Cole Hersee engine warning kit, part number M-40177-BP. It does both oil pressure and coolant temp. If you can't find it in the UK, order it online from Defender, Jamestown, West Marine, et al. I'd suggest that in addition to or in lieu of wiring it to your horn, connect the winker relay (flasher in the U.S.) to a high output LED, and mount the light where you can't miss seeing it. Also, many horns will exceed the current capacity of the typical flasher, so you would have find one with enough ampacity or employ an additional relay.

s/v My Sweet Girl!
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post #9 of 9 Old 10-31-2014
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Re: canal turbulence - a word of warning

Quote:
Originally Posted by Rockter View Post
In a wee Scottish canal. It had been raining and the canal water volumes were aggressive with lots of turbulence in the locks. We had the motor running on idle.
We motor out of one of them and in to the calm of the canal.
About a mile later, up went the regular command "helmsman, check coolant temperature".
"It's in the red!".
"What????".
Shut-down!
The boat, a USC Polaris 36, coasts to a slow halt in the canal.
One of the crew ties a fender to a line and throws it over a wee bridge rail to hold the boat. There was very little wind.

I let the motor cool somewhat.... a Volvo MD17C raw water cooled unit.
I bleed the system.
Firstly the line to the water pump - clear.
Then the line to the exhaust manifold - hot stuff but still flowing.
Then the exhaust elbow entry. We start the motor briefly and the water gushes out of the coolant line to the exhaust elbow.

We let the motor cool some more, then re-start. The water gushes out of the exhaust as normal.
The temperature reverts to normal - well in to the green.

I can only assume that the lock turbulence made the coolant pump have to work too hard for suction and it cavitated to water vapour. It was pumping nothing.

Be careful out there guys. That one was unexpected. We could have easily cooked the motor. We do watch it carefully. Now we watch it very carefully.

Rockter.
Shouldn't your engine be shutdown when in the lock? Here in Ontario, Canada you are required by law to stop your engines when in the lock.
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