Seawater intake blockage

[Aeolus]

Twice it has happened to me that something has blocked the seawater intake to the engine. I knew about it when the engine control panel starting sounding its alarm. By which point the fresh water had already boiled itself into the bilge and what could have been a very simple job became a bit more complicated. Plus since my control panel lives inside a locker, and the sound insulation of the engine is poor, it's not that easy to hear the alarm. Ideally something would notify me the moment the seawater flow is blocked.

Any suggestions how this could be achieved?

 

[Fr J Hackett]

Didn't you notice the change in the exhaust noise.

 

[LittleSister]

Exhaust temperature alarm will respond much faster than the engine temperature alarm. Easily fitted - e.g. Home: Silicon Marine (other suppliers available).

You could also, or instead, add an additional 'remote' alarm buzzer (and/or light) somewhere more audible (or visible) to your existing engine control panel alarm.

 

[ChromeDome]

Aqualarm.

Sounds if the sea water flow stops.

 

[Fr J Hackett]

Aqualarm.

Sounds if the sea water flow stops.

Exactly and the exhaust noise changes, it's very noticeable if you leave it long enough it will destroy the exhaust hose.

 

[howardclark]

Twice it has happened to me that something has blocked the seawater intake to the engine. I knew about it when the engine control panel starting sounding its alarm. By which point the fresh water had already boiled itself into the bilge and what could have been a very simple job became a bit more complicated. Plus since my control panel lives inside a locker, and the sound insulation of the engine is poor, it's not that easy to hear the alarm. Ideally something would notify me the moment the seawater flow is blocked.

Any suggestions how this could be achieved?

I had a good long look at this a few years ago- basically I wanted to add an inline flow switch attached to an alarm. I concluded it was possible but clunky and expensive. As a result I did what the others say and put a temperature Alarm on the exhaust. It really does solve the problem as the temperature goes up quickly and you are alerted well before any damage is done.

 

[Neeves]

Install a different, better, means to access the seawater.

What is your water intake, why did it fail?

Jonathan

 

[GrahamD]

Several years ago I made up an alarm based on one of these. STC-1000 12V/110-220V LCD Digital Temperature Controller Thermostat with Sensor | eBay

I connected the thermostat to a loud buzzer and to a strip of red LEDs, all of which are mounted on my engine control panel. The sensor is held against the surface of the exhaust elbow with a large jubilee clip. The display provides a constant digital read out of the temperature of the exhaust elbow, which is reassuring.

I have set the alarm at 32C to give an early indication of any problem. This is fine most of the year but can be triggered by the highest sea water temperatures in summer. When restarting the engine after it has been stopped for some time the alarm will trigger as the heat of the engine has warmed the elbow, but the temperature quickly reduces as the cooling water starts to flow and the alarm turns off - sort of an auto-test feature!

Making and fitting this was pretty simple, and I am no electrician. It was cheap as chips, has been reliable and best of all it did not involve drilling a hole in the exhaust.

 

[Sandy]

Any suggestions how this could be achieved?

Work out why your raw water intake is fouling. Alarms only alert you to the problem, not fix it. Your exhaust sound should alert you within eight nanoseconds unless it is one of those silly ones that are under the water line; whoever thought that was a good idea needs keel hauled.

Hopefully, your raw water intake is easily accessible and you can unblock it quickly.

 

[johnalison]

I have managed to clear my saildrive inlet by using a dinghy foot-pump into the filter, though this failed on one occasion.

 

[cherod]

Exhaust temperature alarm will respond much faster than the engine temperature alarm. Easily fitted - e.g. Home: Silicon Marine (other suppliers available).

You could also, or instead, add an additional 'remote' alarm buzzer (and/or light) somewhere more audible (or visible) to your existing engine control panel alarm.

This is an issue i have ,( being deef as a post ) , is it really just a case of running a few wires from the alarm ( which i suspect is some sort of audio speaker ) up to another speaker / light ?

 

[LittleSister]

This is an issue i have ,( being deef as a post ) , is it really just a case of running a few wires from the alarm ( which i suspect is some sort of audio speaker ) up to another speaker / light ?

It usually is. The buzzer is just a cheap little device that buzzes when 12v is applied across it. Typical engine temp alarms just connect the 12v alarm circuit to earth when a certain temperature reached.

If it were me I'd connect a new buzzer in parallel with the existing one, first checking it out temporarily just touching the wires across the existing buzzer when its buzzing before permanently installing it and running the wires. I doubt an added buzzer and/or LED light would upset things in most boat installations.

Here's a link to a loud splash-proof buzzer for £15 (other suppliers available), but standard ones can be had for around a couple of quid. Plastic Warning Buzzer for 12V Electrical Systems

The Silic exhaust temp alarms I linked to in post above are available with flashing lights and buzzers, with optional remote flashing/buzzing repeaters (I've no connection to Silic, just a customer, other suppliers available).

 

[mikegunn]

Twice it has happened to me that something has blocked the seawater intake to the engine. I knew about it when the engine control panel starting sounding its alarm. By which point the fresh water had already boiled itself into the bilge and what could have been a very simple job became a bit more complicated. Plus since my control panel lives inside a locker, and the sound insulation of the engine is poor, it's not that easy to hear the alarm. Ideally something would notify me the moment the seawater flow is blocked.

Any suggestions how this could be achieved?

I would suggest the introduction of a flow alarm switch into the seawater plumbing between the filter and pump inlet. It’s basically just a paddle in the flow stream. Very simple. It will give an immediate indication that the water flow has either been significantly reduced or stopped altogether. I‘ve fitted them on my boats since fifteen years ago and found them invaluable. Particularly when I had some plastic sheeting wrapped around a saildrive leg.
Have a look on the Trickett Marine website.
Mike

 

[Neeves]

Sort out why you have blockage - before you invest money in an alarm. As already mentioned the alarm will tell you that you need to switch the engine off - not much use if you are entering a marina in a bit of a breeze.

Though why do I get the impression we are wasting our time.....

Jonathan

 

[Aeolus]

Sort out why you have blockage - before you invest money in an alarm. As already mentioned the alarm will tell you that you need to switch the engine off - not much use if you are entering a marina in a bit of a breeze.

Though why do I get the impression we are wasting our time.....

Jonathan

Apologies for the very late reply, I had missed the barb on the last comment from down under.

The reason I have had blockages is because there is a lot of rubbish floating in the water and some of it is quite capable of blocking a water intake if it gets sucked into or against it. The incident that triggered my original message was probably caused by a plastic bag being sucked against the intake as, once we'd stopped the engine and investigated, there was no blockage there. Because with the suction gone, the bag just floated away.

Unfortunately, it happened again yesterday, altho this time something got sucked into the intake and it took quite a bit of pressure to blow it out. This now makes 3 blockages in 16 years of owning this boat, although two in the space of 3 months makes one suspect that either the rubbish content of the water has worsened, or I was unlucky or a combination of the two.

I could add a cage of some sort to cover the intake - at the moment it's just an unprotected through-hull, and that would reduce the risk of sucking in sizeable debris, however it still wouldn't prevent the external plastic bag problem.

This may come as a surprise to you, dear name-sake, but you're not the only person on the forum who can analyse a problem.

Anyhow, thank you to everyone for all the constructive suggestions.

Jonathan

 

[ChromeDome]

I fitted two intakes, one each side of the keel, connected to a Y-piece for a friend. Would be unlikely for two bags to hit at the same time..

 

[Aeolus]

I fitted two intakes, one each side of the keel, connected to a Y-piece for a friend. Would be unlikely for two bags to hit at the same time..

That's an interesting idea altho if the pre-engine filter got blocked, that solution wouldn't help. As another poster said, being a bit deaf means not hearing the change in exhaust sound and also taking a little while to hear the engine alarm. One of the problems of fitting a cage or additional intake would be that it would require a lift-out which is not currently scheduled before the autumn of 2023. In the meantime I'm looking at the Aqualarm as suggested by your good self and MikeGunn.

 

[ChromeDome]

Well, if you really wanted you could fit two strainers and put the Y-piece in front of the pump.

The twin Aqualarm suits me fine, the friend who got twin intakes wanted that more..

 

[Moodysailor]

An exhaust alert or flow meter is the only way to know what is happening to the sea water flow at any given time - waiting for the overheat alarm to sound is very much closing the door after the horse has bolted - it's far too late at that point.

If you can't hear the alarm, it is easy enough to fit a remote or secondary buzzer in a more promienent position, and fully waterproof ones are available if cockpit mounting. A visual led can also be configured so you get belt & braces.

There are many different reasons why sea water inlets can get blocked, so the advice to change the inlet position or fit secondary intakes is a bit overkill, IMO. Yes it can help, but I prefer the general advice to keep the number of holes below the waterline to a minumum.

As an engineer, I am a fan of having plenty of spare capacity/redundancy in the sea water inatake line so I tend to oversize the through-hull, hoses and strainer. I want to keep as much load off the pump as possible and provide enough redundancy that if a partial blockage were to occur then there is still enough flow to keep the engine running. Having an oversize intake also keep the suction pressure at inlet down a bit which can reduce the chance of something floating nearby getting drawn into the intake. However, it has it's own downsides, not least cost and hassle so this type of change needs to be planned as a haul-out project.

If sailing in an area that suffers from large amounts of weed that is difficult for any sea water system to cope with, the solution is keel/box cooling for the engine - in this setup the engine heat is transferred to the sea by an externally mounted cooler - no sea water is drawn in, so nothing to block. I have only seen this setup used on leisure boats in specific cases (usually expedition yachts) so it is rare and not something that should be retrofitted unless you really know what you are doing.

 

[johnalison]

Sort out why you have blockage - before you invest money in an alarm. As already mentioned the alarm will tell you that you need to switch the engine off - not much use if you are entering a marina in a bit of a breeze.

Though why do I get the impression we are wasting our time.....

Jonathan

I don't have an alarm but would have liked to. In general, it is fairly easy to to spot a blockage from the engine note, or of course by check visually, but there are occasions when motor-sailing, in my case on the port tack, when the exhaust is close to the water or under the surface, and it could be that a change in engine note would not be heard.