Warning -- Plastic Bag in Cooling!

[Dockhead]

It happened to me today -- plastic bag in the main engine cooling intake.

The first sign was slightly elevated engine temperature -- 85 instead of 80 degrees, and steam from the exhaust. What to do? No wind and sailing out of the question, I contemplated throwing the anchor down. This happened right in Southampton Water at the entrance to the Thorne Channel -- some of the busiest water anywhere, with ships all over, and shoals on either side. I finally decided to drift and do it super fast. I looked into the secondary strainer -- no water flowing! I popped open the fisherman-style intake strainer, and there it was -- a f******* plastic bag. I had it all back together again in seconds, started the engine up, and got back underway, all before the Red Jet ferry could run me down


What did I learn from this? Engine temperature is a poor guide to cooling water flow, at least on this engine, which must have a lot of thermal mass. I could have easily melted the exhaust.

I have an exhaust alarm, but haven't connected it yet. I use raw water pump temperature as a proxy for cooling water flow on my genset. But I think on the main engine, I will connect a temperature sensor (I have one spare one for my Maretron N2K temperature module) to the exhaust elbow, and set an alarm.

[accomplice]

You were fortunate that the bag got pulled into the strainer where you could easily remove it. A few days ago I had a soft-ball sized clump of sea-grass and plastic pieces wedge itself into the outside of the through-hull that feeds the aft sea-chest -- which, in turn, feeds many things including the genset and the engine. The flow through the mess of grass was sufficient to keep the refrigeration circulation pump and salt-water washdown pumps happy, but when the genset was on it pulled so hard it filled the sea-chest with air, causing the refrigeration pump to run dry and fail.

The only solution was to dive on the boat and remove the clump of debris.

I was wondering about how to solve this problem without getting wet. Has anyone ever placed a fitting on their sea-chest for pressurizing with compressed air, to blow out anything clogging the intake?

What would you have done if the blockage were exterior to the hull?

[weavis]

Originally Posted by Dockhead

It happened to me today -- plastic bag in the main engine cooling intake.

The first sign was slightly elevated engine temperature -- 85 instead of 80 degrees, and steam from the exhaust. What to do? No wind and sailing out of the question, I contemplated throwing the anchor down. This happened right in Southampton Water at the entrance to the Thorne Channel -- some of the busiest water anywhere, with ships all over, and shoals on either side. I finally decided to drift and do it super fast. I looked into the secondary strainer -- no water flowing! I popped open the fisherman-style intake strainer, and there it was -- a f******* plastic bag. I had it all back together again in seconds, started the engine up, and got back underway, all before the Red Jet ferry could run me down


What did I learn from this? Engine temperature is a poor guide to cooling water flow, at least on this engine, which must have a lot of thermal mass. I could have easily melted the exhaust.

I have an exhaust alarm, but haven't connected it yet. I use raw water pump temperature as a proxy for cooling water flow on my genset. But I think on the main engine, I will connect a temperature sensor (I have one spare one for my Maretron N2K temperature module) to the exhaust elbow, and set an alarm.

Time to connect the alarm.

[Dockhead]

Originally Posted by accomplice

You were fortunate that the bag got pulled into the strainer where you could easily remove it. A few days ago I had a soft-ball sized clump of sea-grass and plastic pieces wedge itself into the outside of the through-hull that feeds the aft sea-chest -- which, in turn, feeds many things including the genset and the engine. The flow through the mess of grass was sufficient to keep the refrigeration circulation pump and salt-water washdown pumps happy, but when the genset was on it pulled so hard it filled the sea-chest with air, causing the refrigeration pump to run dry and fail.

The only solution was to dive on the boat and remove the clump of debris.

I was wondering about how to solve this problem without getting wet. Has anyone ever placed a fitting on their sea-chest for pressurizing with compressed air, to blow out anything clogging the intake?

What would you have done if the blockage were exterior to the hull?

I would not want a strainer or sea-chest arrangement which did not allow me to poke a screwdriver through the through-hull to clear any blockage. I would not think that pressurized air would deal with every eventuality.

[weavis]

Last week in the Bristol Channel, I had to clear my prop twice and clear the strainer once. Coke plastic ties for a 4 pack.

Its a problem. I know the sound of my engine and the water expulsion and I noticed it spluttered........

Lucky me.

Lucky you Dockhead.

[accomplice]

Originally Posted by Dockhead

I would not want a strainer or sea-chest arrangement which did not allow me to poke a screwdriver through the through-hull to clear any blockage. I would not think that pressurized air would deal with every eventuality.

Do your hoses come off the seacocks/thru-hulls easily? I've had some that have needed to be softened with heat or worse, cut-off.

[SVNeko]

Apparently a lot of pollution in the waters over there .

Sent from my SM-T210R using Cruisers Sailing Forum mobile app

[TeddyDiver]

Originally Posted by accomplice

I was wondering about how to solve this problem without getting wet. Has anyone ever placed a fitting on their sea-chest for pressurizing with compressed air, to blow out anything clogging the intake

IMO a sea-chest extending well above the waterline, with a bolted lid and a grate/strainer combo inside and removable throw the lid. Preferably mounted over the propeller for obvious reasons..

[accomplice]

Originally Posted by TeddyDiver

IMO a sea-chest extending well above the waterline, with a bolted lid and a grate/strainer combo inside and removable throw the lid. Preferably mounted over the propeller for obviously reasons..

TeddyDiver -- that works fine when the blockage occurs in the sea-chest -- as dockhead had. But in my situation this week the blockage was a large mass of debris on the outside of the hull.

Are you suggesting that if the through hull were closer to the prop that the prop would disturb this mess such that it could either be sucked in (to the strainer and removed) or cast free?

[a64pilot]

I've had a similar event, no alarm went off, but the exhaust note chaged, engine got louder and water out the exhaust was way less than it should be, I was able to cut way back on throttle as I had a partial blockage and limp back, if you don't have a complete blockage, you may be able to get by at reduced throttle.

[Dockhead]

Originally Posted by accomplice

Do your hoses come off the seacocks/thru-hulls easily? I've had some that have needed to be softened with heat or worse, cut-off.

The fisherman sea strainer is attached directly to the through-hull. Pop the top off, open the valve, and you have direct access to the sea.

WATER STRAINER (FISHERMAN MODEL) 1.1/2"

My last boat had something like this, too. I can't imagine doing it another way.

[Dockhead]

Originally Posted by weavis

Time to connect the alarm.

Indeed!

[DumnMad]

Ours got blocked - temperature rose and found no raw water flow. Put motor in idle and made the 1 mile back to berth without the temp gauge rising above 90c (200F).
All good but don't know how far we could have gone just relying on boiling water to control the hot spots. !980's Ford.

[Dockhead]

Originally Posted by DumnMad

Ours got blocked - temperature rose and found no raw water flow. Put motor in idle and made the 1 mile back to berth without the temp gauge rising above 90c (200F).
All good but don't know how far we could have gone just relying on boiling water to control the hot spots. !980's Ford.

The problem is not -- as I discovered -- the fresh water coolant temperature, but the exhaust system. You might melt the exhaust hose before the engine overheats, and you might not even be aware of what is going on, which is what bothered me.

[DumnMad]

True. Last summer a very nice boat burnt to the waterline a day out from Nelson due to fire started by the exhaust pipe.
Ours did not seem too hot running on idle.