Strange Raw water pipes..

[icarusbop]

Hello:

I recently bought a 34ft sailing yacht and am servicing the engine.
We have found a strange layout on the raw water system. After the water strainer, the raw water pipe has been extended from the engine (which is under the floor) to the starboard side of the boat.
At the farthest point away from the engine there is a T junction to a 10mm (ish) pipe that goes straight out of a thu-hull fitting (and does pump out sw water when the engine is running)
The main pipe then doubles back and comes along the same route back to the engine.
Partway along the return pipe there is another T where there is a 10mm take off which goes to the prop - I think it's a water cooled bearing?
It then comes back to the heat exchanger and out of the exhaust.

Can anyone think why the water takes such a route under the floor and back again? - There is a leak on this part of the system so am hoping to remove this part of it.

Can anyone clarify what the 'water cooled prop bearing' actually is?

Thanks

Ian

 

[tillergirl]

Instead of have a greaser, some stuffing boxes (mine for example) are water lubricated/cooled. My raw water line is te'ed to feed water to a fitting on the top of the stuffing box (which looks similar to where a greasing point would work. Water is fed into the stuffing box and exits down the stern tube lubricating it and the stern gland at the same time.

 

[Tranona]

Would suggest you can't remove any part of the system. As tillergirl says the bleed to the stern tube is to cool and lubricate it. The other bleed to the through hull is to check that there is flow and to provide a syphon break when you shut the engine down. You could perhaps replace that with an antisyphon valve, but some of those require a bleed overboard anyway. Suggest find the leak and repair it but don't change the layout.

 

[vyv_cox]

The 'water cooled bearing' might in fact be the stern gland. You will find examples of many of them on my website. In most cases a vent pipe is all that is required for sailing vessels, rather than a pressurised supply, but without knowing exactly what you have it is difficult to advise. Can you post photographs?

 

[VicS]

Hello:

I recently bought a 34ft sailing yacht and am servicing the engine.
We have found a strange layout on the raw water system. After the water strainer, the raw water pipe has been extended from the engine (which is under the floor) to the starboard side of the boat.
At the farthest point away from the engine there is a T junction to a 10mm (ish) pipe that goes straight out of a thu-hull fitting (and does pump out sw water when the engine is running)
The main pipe then doubles back and comes along the same route back to the engine.
Partway along the return pipe there is another T where there is a 10mm take off which goes to the prop - I think it's a water cooled bearing?
It then comes back to the heat exchanger and out of the exhaust.

Can anyone think why the water takes such a route under the floor and back again? - There is a leak on this part of the system so am hoping to remove this part of it.

Can anyone clarify what the 'water cooled prop bearing' actually is?

Thanks

Ian

You dont say where in this circuit the raw water pump is located!

You dont mention any antisyphonic loop and valve ( not necessary of course if the final injection point into the exhaust is well above the waterline) or is this the first T junction you mention?

 

[nimbusgb]

The feed to 'the prop' could be to a volvo type stern gland. if the engine is run before engaging gear it pretty much ensures that you don't need to burp the stern gland.

Handy having that tee off to a through hull - could be used to connect a hose pipe to run the engine when ashore but I'd like to have a ball valve or something on it so that under normal running conditions you can prevent all the cooling water coming out of there rather than going to the engine. How big is it? If it's tiny then perhaps just a teltale to let you know it's pumping. Must surely be taken off after the engine pump though.

A few photo's or a diagram might help.

 

[Rossynant]

Yes, water going to stern tube (about the stuffing box) is for lubrication there. Not common on sailboats as they are not motoring so much, but a very good arrangement. May have a reason in the type of stuffing box, but usually it lubricates, cools, and washes out sterntube and cutlass bearing, and this may be necessary in your boat (depends on it's type and placement).

T-piece to small hull outlet is a vent, to allow air into anti-siphon loop when engine is stopped. So this T should be in a high loop, well above waterline - make sure the loop stays high - remark just in case.
Possible to change this for "anti-siphon valve" but vent is much better arrangement, foolproof. I wouldn't change it. Valve may fail.

 

[icarusbop]

Thanks for all the replies:

So the feed going to the stern tube (stuffing box) is to cool and lubricate the prop, the hull vent(which is well above the water line) is ananti syphon setup.

Is the anti syphon there to stop the boat sinking due to water syphoning back through the stuffing box if one of the pipes fail?

Now it makes a bit more sense..

The water is leaking from the pipe from the raw water pump, where it passes through the floor - I think the pipe has chafed on the hole edge (where it comes through the floor). It looks very difficult to get to to replace the pipe.....

Thanks
Ian

 

[icarusbop]

Hello:

Thanks so far.

VicS notes I didn't mention the pump - an omission on my part.
nimbusgb mentioned a diagram might help...

For both of these I have created a diagram attached.
Now I've drawn it, it makes more sense to me as well.

Looks like I need to leave it alone and mend the leak.

Ian

 

[icarusbop]

Hello:


As pointed out, I neglected to include the water pump and a diagram was requested.
I made a diagram of the raw water system(attached) including the pump.
I stuck my head behind the fridge last night to have a closer look at the pipes, the U turn in the pipe looks like it is a metal anti-syphon loop.
Looks like it is an anti-syphon system, another website mentions it is required like this because the engine is mounted below the floor.
I'll be leaving it installed and will have to find a way of mending the failed pipe.
Thanks for all your help.

 

[KenMcCulloch]

Hello:


As pointed out, I neglected to include the water pump and a diagram was requested.
I made a diagram of the raw water system(attached) including the pump.
I stuck my head behind the fridge last night to have a closer look at the pipes, the U turn in the pipe looks like it is a metal anti-syphon loop.
Looks like it is an anti-syphon system, another website mentions it is required like this because the engine is mounted below the floor.
I'll be leaving it installed and will have to find a way of mending the failed pipe.
Thanks for all your help.
View attachment 27297

This is quite unusual, antisiphon loop is more usually installed in the discharge end (i.e. just before the exhaust water injection point) of the raw water circuit. There may well be good reasons why yours is the way it is.

 

[Tranona]

Not particularly unusual. That is where it is placed in the Volvo in my boat. It can be anywhere downstream of the seawater pump, but on many installations it is easiest to put it just before the water injection because there is a convenient pipe there.

 

[Rossynant]

Yes, this diagram is showing the proper way.

 

[VicS]

Hello:


As pointed out, I neglected to include the water pump and a diagram was requested.
I made a diagram of the raw water system(attached) including the pump.
I stuck my head behind the fridge last night to have a closer look at the pipes, the U turn in the pipe looks like it is a metal anti-syphon loop.
Looks like it is an anti-syphon system, another website mentions it is required like this because the engine is mounted below the floor.
I'll be leaving it installed and will have to find a way of mending the failed pipe.
Thanks for all your help.
View attachment 27297

That looks fine. As said the A/S loop can be in that position or after the heat exchanger. With direct cooling engine design sometimes dictates which is used

The loop should be well above the heeled water line. If you look at the on -line Vetus catalogue you will see they recommend 40cm minimum.

With a 3/8" outlet you will be pumping out a lot of your cooling water. If you have any problems with cooling you might need to consider restricting this a little

 

[icarusbop]

Hello:

I dug out the old pipes and AS loop over the weekend, the old pipes are not leaking, but very stiff, so I have replaced them with new reinforced pipe with an internal diameter of 25mm (the same as the old pipes).
The leak was on the A/S loop itself, it looks like it's home made from copper plumbing fittings and it has corroded away ansd looks more like a colinder!
So, I need a new one. I tried looking around on the internet and have comea bit stuck.
My old A/S loop was a simple 25mm in then out with a 10mm barb on the top of it - it did not incorporate and air vent or valve. Most of the A/S loops I can find seem to be an in and out with only an air vent at the top, not a barb for the thru hull.
I don't think I want one of these as the unit will not be very accessible (need to remove the fridge) so It will not be obvious if the valve fails (or sticks due to contamination) and lets the water out into my boat. So I think I need a loop with a barb, but cannot really find any.
I have found a vetus (partno V-ASDV ) with looks like it has an air vent, into a pipe outlet (presumably in case the valve jams open) but it seems expensive for a plastic fitting (cira £80)

so here are my questions:
Can I use a loop with just a barb outlet - or should I try to avoid this to get more cooling water through my exhaust (and stuffing box)?
A loop with an air valve will need regular maintenance and it is not in an easy place to get to. If it jams it will be difficult to notice.
Should I get a loop with an airvent then to a barb outlet - so if the valve fails the water is sent through the hull, but still have the maintenance /access issue.
Moving the A/S loop to a more accessible location is not really an option.
Thanks.

 

[vyv_cox]

This photo shows my A/S loop and air bleed, the 'can' right at the top of the photo. It's very simple, just a can made from stainless steel with a smaller air bleed that goes to the exhaust trap. No moving parts. It corroded away after 10 years but cheap to replace.

 

[alahol2]

My old A/S loop was a simple 25mm in then out with a 10mm barb on the top of it - it did not incorporate and air vent or valve. Most of the A/S loops I can find seem to be an in and out with only an air vent at the top, not a barb for the thru hull.
I don't think I want one of these as the unit will not be very accessible (need to remove the fridge) so It will not be obvious if the valve fails (or sticks due to contamination) and lets the water out into my boat. So I think I need a loop with a barb, but cannot really find any.
I have found a vetus (partno V-ASDV ) with looks like it has an air vent, into a pipe outlet (presumably in case the valve jams open) but it seems expensive for a plastic fitting (cira £80)

so here are my questions:
Can I use a loop with just a barb outlet - or should I try to avoid this to get more cooling water through my exhaust (and stuffing box)?

This is the Vetus A/S without a valve... http://www.asap-supplies.com/marine/anti-siphon-devices/vetus-anti-siphon-device-airventh. The pipe is about 5-6mm internal diameter so I don't think you would need a 10mm barb, it would release too much water.
It could be worth trying to modify one of these... http://www.asap-supplies.com/marine/anti-siphon-devices/seaflow-exhaust-line-anti-syphon-device-410081 to remove the valve and fit your own barb?

 

[icarusbop]

So

I've had a look around at my options ans decided to try to avoid a valve which needs maintanance.
I opted for one of these
http://www.asap-supplies.com/search/anti+-syphon/seaflow-polypropylene-antisyphon-loop-507625

It's takes the correct size hoses (25mm), the top valve nut unscrews and the rubber valve comes straigt out, leaving me with an outlet which is 6mm on the inside, and 12mm threaded on the outside and 20mm long.
I hope to adjust this top outlet to attach it to my thru- hull fitting.
I'm hoping to give it a try this weekend and will report back with progress then.

 

[icarusbop]

Hello all:
for final closure on this issue:
As above I bought a plastic anti syphon loop (£15.00 inc delivery) and removed the valve from the top, this has allowed to to install it in place of my corroded copper version.
It needed it to be as maintenance free as possible becaise it is mounted behind te fridge. There is a 25mm pipe in and out as part of the raw water system and a 6mm barb from the loop top going to the thu hull fitting. here is a picture of the final installation.

I replaced the raw water pipes as well, and used new clamps on the system - it looks to be working well.
Thanks to all for help and advice.
Ian