No raw water flow

[Dave 71]

Yesterday I tried to take the boat out for a sail and was thwarted by no raw water flow.

The engine started as normal and initially there was a good flow of water from the exhaust, I turned my attention to helping slip lines etc.

Heading out of the marina, I noticed that the engine exhaust didn't sound right and I couldn't hear any water from the exhaust, looked over the side, no water, turned round and back in. Once back alongside, I tried the engine again after letting it cool, there was flow but it didn't seem as strong as it should be, so I started to investigate

Attempts to get it working have so far failed, now there is no flow at all.

I checked the strainer first, this was not blocked and as I had to use a strap wrench to remove the lid, must have been making a good seal. I checked the impeller, it was fine, but replaced with new anyway. No joy. So I assume a blockage somewhere, or the water pump.

The boat has an SD20 saildrive, yanmar engine. The seacock is elbow type so I cant push through, water intake on the leg. My next step will be to disconnect the hose from the seacock, open it and see if there is flow (I would disconnect at the filter but it is very difficult to access) I will attached a new length of hose to the inlet and raise it above water level if lots floods in. Assuming it is blocked, is something like this suitable for blowing air back down?
Intex Double Quick High Output Hand Air Pump 29 cm : Amazon.co.uk: Sports & Outdoors

The engine has been perfectly reliable until now. Two things have changed recently - I cleaned the strainer but as said above it seemed to be sealing well. Second, the boat was lifted last week, and pressure washed. There was some growth on the sail drive, but I cant imagine it would have been blown into the intake???
What else to check? Given that I did have some flow after getting back in, water pump?

 

[NickRobinson]

The lack of then return of flow may be that, when hot, the limited water was exiting as steam?
You've tried the things I would have suggested. If the engine has performed recently and regularly OK, suspecting something new, eg the pressure wash, would be a good thing to eliminate by checking inlet cock flow. I found a two inch long fish in my non-working heads inlet. (Norwegian Blue by then...)

 

[davidej]

We have cleared a blockage (which was probably weed at the intake), by taking the intake hose off the filter and inserting the rubber dinghy pump. A few pumps should have bubbles coming up the side of the boat near the fitting.

 

[Aeolus]

If your lungs are in good health, they might suffice to blow a blockage out of the intake. I've got a bit of hose that just fits into the in-pipe in the strainer. I've wrapped it in some tape so that as I push it in, it forms a good enough seal. I can then blow down it and clear a blockage. Much faster (for me) than finding the dinghy pump and setting that up.

 

[footsoldier]

To go quickly from 'good flow' to 'no flow' indicates something drastic like a plastic bag over/into the inlet - especially likely somewhere like a marina.

 

[blush2]

The inner layer of the exhaust hose can collapse and cause a blockage. Happened on Blush when she went back in the water after a winter ashore a few years ago.

 

[LONG_KEELER]

You could also close the intake seacock , and use a buckets of water directly bypassing the filter also. Might help to narrow down the problem.

 

[bobgarrett]

I once had an intermittent flow caused by the plate at the front of the impeller being too worn.

 

[Ammonite]

Yesterday I tried to take the boat out for a sail and was thwarted by no raw water flow.

The engine started as normal and initially there was a good flow of water from the exhaust, I turned my attention to helping slip lines etc.

Heading out of the marina, I noticed that the engine exhaust didn't sound right and I couldn't hear any water from the exhaust, looked over the side, no water, turned round and back in. Once back alongside, I tried the engine again after letting it cool, there was flow but it didn't seem as strong as it should be, so I started to investigate

Attempts to get it working have so far failed, now there is no flow at all.

I checked the strainer first, this was not blocked and as I had to use a strap wrench to remove the lid, must have been making a good seal. I checked the impeller, it was fine, but replaced with new anyway. No joy. So I assume a blockage somewhere, or the water pump.

The boat has an SD20 saildrive, yanmar engine. The seacock is elbow type so I cant push through, water intake on the leg. My next step will be to disconnect the hose from the seacock, open it and see if there is flow (I would disconnect at the filter but it is very difficult to access) I will attached a new length of hose to the inlet and raise it above water level if lots floods in. Assuming it is blocked, is something like this suitable for blowing air back down?
Intex Double Quick High Output Hand Air Pump 29 cm : Amazon.co.uk: Sports & Outdoors

The engine has been perfectly reliable until now. Two things have changed recently - I cleaned the strainer but as said above it seemed to be sealing well. Second, the boat was lifted last week, and pressure washed. There was some growth on the sail drive, but I cant imagine it would have been blown into the intake???
What else to check? Given that I did have some flow after getting back in, water pump?

I think you're on the right lines. If there's no flow from the seacock you've probably had a big clump of weed (or plastic bag) get sucked into the inlet, which if its the same type that floats around chichester and portsmouth this time of year, will block the intake completely. You may find you have to repeat the exercise with the pump 3 or 4 times as the weed gets sucked back in again, although running the engine ahead and astern for a few seconds with the seacock closed may help chop it to bits. Alternatively you may be able to pull it off with a boathook if alongside. Once cleared keep an eye on your strainer as the smaller bits work their way through.

 

[Cariadco]

Disconnect the inlet pipe to the strainer and shove a hose gun on it and give the Pipe/Valve/Intake system a good old Backflush.

 

[Spirit (of Glenans)]

Yesterday I tried to take the boat out for a sail and was thwarted by no raw water flow.

The engine started as normal and initially there was a good flow of water from the exhaust, I turned my attention to helping slip lines etc.

Heading out of the marina, I noticed that the engine exhaust didn't sound right and I couldn't hear any water from the exhaust, looked over the side, no water, turned round and back in. Once back alongside, I tried the engine again after letting it cool, there was flow but it didn't seem as strong as it should be, so I started to investigate

Attempts to get it working have so far failed, now there is no flow at all.

I checked the strainer first, this was not blocked and as I had to use a strap wrench to remove the lid, must have been making a good seal. I checked the impeller, it was fine, but replaced with new anyway. No joy. So I assume a blockage somewhere, or the water pump.

The boat has an SD20 saildrive, yanmar engine. The seacock is elbow type so I cant push through, water intake on the leg. My next step will be to disconnect the hose from the seacock, open it and see if there is flow (I would disconnect at the filter but it is very difficult to access) I will attached a new length of hose to the inlet and raise it above water level if lots floods in. Assuming it is blocked, is something like this suitable for blowing air back down?
Intex Double Quick High Output Hand Air Pump 29 cm : Amazon.co.uk: Sports & Outdoors

The engine has been perfectly reliable until now. Two things have changed recently - I cleaned the strainer but as said above it seemed to be sealing well. Second, the boat was lifted last week, and pressure washed. There was some growth on the sail drive, but I cant imagine it would have been blown into the intake???
What else to check? Given that I did have some flow after getting back in, water pump?

Yes, that pump would be perfect. Tha traditional solution has been the dinghy pump, and the pump in the link can be used for pumping dinghies.
A spare length of pipe to attach onto the seacock to get it above the waterline is a useful addition to your arsenal, as I discovered when I had a similar problem a couple of years ago.
In my case the water inlet is integral to the saildrive, and appears to have a right-angle bend that did not allow me to rod it with adrain snake". My lungs provided enough puff to clear the blockage

 

[Dave 71]

Thanks for the suggestions. I'll try the seacock and then blow air back down the seacock if there's no flow and at least rule it out if nothing else

 

[mikegunn]

Thanks for the suggestions. I'll try the seacock and then blow air back down the seacock if there's no flow and at least rule it out if nothing else

I see that you are in a Marina, so presumably have a mains water supply. In which case, remove lid of seawater filter and identify the inlet port. Connect a hose from mains water supply and insert it into the filter’s inlet port. I’ve found that a tap/hose adapter is a fairly snug fit. If necessary a bit of cloth around it will ensure an adequate seal. Turn on mains water and flush through. The hydraulic power of water is much more effective than a air pump, provided that it is available.
Weed seems to be more of a problem this year, for whatever reason. Particularly the type that has a fine filigree of tendrils.

Mike

 

[Dave 71]

Further (possibly daft) question on the 'bucket' method, can I disconnect the hose at the impellor and simply connect a temporary hose onto the impellor inlet and stand the bucket on the cabin floor? Does that work, or will the pipe going up and over the top of the bucket starve the impellor? Would I better off drilling a hole in the side of the bucket and attaching a hose connector to it?

 

[mikegunn]

Further (possibly daft) question on the 'bucket' method, can I disconnect the hose at the impellor and simply connect a temporary hose onto the impellor inlet and stand the bucket on the cabin floor? Does that work, or will the pipe going up and over the top of the bucket starve the impellor? Would I better off drilling a hole in the side of the bucket and attaching a hose connector to it?

You could, but I would consider it unnecessary. It is unlikely that the blockage is downstream of the seawater filter. That’s the purpose of the filter. It is my guess that the seawater inlet at the skin fitting is blocked. Therefore you only need to consider the length of inlet pipe from the skin fitting to the filter inlet. If you can adopt the technique that I outlined in post #13. You will easily discover if the inlet is blocked. When you initially turn on the mains water it may meet resistance and spray a bit of water around if the connection to the filter’s inlet port is not sealing well. That resistance is an indication that there is a blockage. Once it clears however, mains water should flow through comparitvely unhindered.
To go back to your question though: Yes, you could feed the seawater pump with water from a hose dipped into a bucket. Just ensure that the hose is primed as much as possible a don’t run out of water in the bucket.

Mike

 

[Habebty]

Have you taken the pump faceplate off and checked the impellor actually rotates by briefly turning over the engine?

 

[Dave 71]

Have you taken the pump faceplate off and checked the impellor actually rotates by briefly turning over the engine?

Having taken the impellor out and back in three times and finally replacing, and trying the engine in between, I'm reasonably sure it is - the pin that it engages on did seem to be at a different angle. I will try this if the intake is clear.

 

[Spirit (of Glenans)]

Having taken the impellor out and back in three times and finally replacing, and trying the engine in between, I'm reasonably sure it is - the pin that it engages on did seem to be at a different angle. I will try this if the intake is clear.

In the past there has been mention on these fora, of the phenomenon of the rubber part of the impeller detaching from the metal hub, allowing the vanes to remain static even though the hub spins.

 

[Dave 71]

Success! Flow has been restored!

Took me all morning for what was in the end a five minute fix.

I started by disconnecting the impeller inlet pipe and hooking up the air pump to the pipe and started pumping. I was sitting in the aft cabin hoping to see air bubbles out of the hull port, I couldn't, but could hear a satisfying gurgle - sounded like someone scuba diving under the boat, so I was reasonably confident all was well with the sail drive leg.

Next I set up a hose into a bucket and started the engine - it did draw water, but very slowly. Very little came out the exhaust and then nothing. The bucket seemed to take an age to empty, so I switched off.

I knew the impeller was sound, I put a new one in the day this happened, so started to think about elbows and heat exchangers. I took the inlet pipe off the elbow and peered inside - looked very clean, no blockage.

I was close to giving up at this point and calling a pro, but then remembered the face plate. I had bought a new one in anticipation of that being the cause, so thank you to those above who suggested it, wouldn't have occurred to me otherwise.

I made sure the impeller was in good nick and rotating by hand cranking the engine, then put the new plate and a new O ring on, and hey presto! I'll be adding another to the spares kit.

I now know what to look for. The old one didn't seem particularly bad to me but compared to the glass-smooth new one, it did have a lot of tiny score marks.

 

[Cariadco]

Success! Flow has been restored!

Took me all morning for what was in the end a five minute fix.

I started by disconnecting the impeller inlet pipe and hooking up the air pump to the pipe and started pumping. I was sitting in the aft cabin hoping to see air bubbles out of the hull port, I couldn't, but could hear a satisfying gurgle - sounded like someone scuba diving under the boat, so I was reasonably confident all was well with the sail drive leg.

Next I set up a hose into a bucket and started the engine - it did draw water, but very slowly. Very little came out the exhaust and then nothing. The bucket seemed to take an age to empty, so I switched off.

I knew the impeller was sound, I put a new one in the day this happened, so started to think about elbows and heat exchangers. I took the inlet pipe off the elbow and peered inside - looked very clean, no blockage.

I was close to giving up at this point and calling a pro, but then remembered the face plate. I had bought a new one in anticipation of that being the cause, so thank you to those above who suggested it, wouldn't have occurred to me otherwise.

I made sure the impeller was in good nick and rotating by hand cranking the engine, then put the new plate and a new O ring on, and hey presto! I'll be adding another to the spares kit.

I now know what to look for. The old one didn't seem particularly bad to me but compared to the glass-smooth new one, it did have a lot of tiny score marks.

Another old trick is to turn the cover plate 'round and use the old outside as the new inside.