Making a custom GRP exhaust waterlock.

[Steve_N]

I'm going to be fitting a new Beta in place of my MD21B and one of the problems I need to overcome is the lack of an exhaust waterlock. The existing exhaust is just a run of 2.25" hose back from the exhaust riser to the transom, with a loop of hose up to the underside of the deck and then back down to the outlet. It's never given any problems but I need to bring it up to standard for the new installation. There isn't anywhere to fit an off-the-shelf waterlock apart from alongside the engine made by re-siting the calorifier, but this would involve first running the exhaust forward and could add over 2m to the exhaust length which isn't ideal, plus it would be in the way because the Beta requires good access to that side of the engine.

But.. there is a perfect place in the V of the bilge under the prop shaft right where the hose runs at present and at the very lowest point in the exhaust run. Making a custom waterlock to fit this space would be the ideal solution and I could even fit a 50mm inlet spigot for the Beta and a 2.25" outlet spigot for the existing hose to get over another problem. I have the GRP skills to do this but realise that actually I've not much idea what goes on inside a waterlock or if it could be done in the shape of container that would result so I'd welcome input from anyone who knows about these things. A rough picture of the idea is attached. Thanks.

 

[30boat]

Here you go

 

[Steve_N]

Cheers.
OK, first prototype for shooting down in flames.

 

[pvb]

OK, first prototype for shooting down in flames.

That should work. Can you calculate the safe volume, and compare it with the volume of the exhaust hose?

 

[KevB]

Have you had a look at the VETUS NPL range @ only 110mm

http://www.vetus.com/exhaust-systems/waterlock-muffler/vetus-3-chamber-waterlock-muffler-type-nlp3-50-mm.html

 

[rob2]

Yes, you seem to have the principle right. The exhaust is fed into the bottom of the trap and then exits at the top so it holds some water and the exhaust is blowing through this with quite some silencing effect. In addition the volume should be sufficient for all remaining water in the hoses to drain back into the trap rather than slop back into the engine! Most calculations are done assuming the hoses are completely full of water, although this is obviously not the case but it does leave a substantial safety margin.

Rob.

 

[pvb]

Have you had a look at the VETUS NPL range @ only 110mm

http://www.vetus.com/exhaust-systems/waterlock-muffler/vetus-3-chamber-waterlock-muffler-type-nlp3-50-mm.html

It only has a 4 litre capacity though, which might not be enough. I'd want a 50% margin, so wouldn't want to use this design unless the exhaust hose was only about 2 litres internal volume. And 2 litres is only about a metre length of 2.25" hose.

 

[Steve_N]

Yes, the Vetus NLP50 if the best fit out of all the off-the-shelf solutions and if the volume isn't enough then they do the NLP50S which is a 10 litre version, but it would still need to be sited forward of the engine's exhaust outlet and not at the lowest point of the exhaust which just doesn't seem like the best solution to me. The loops of the hose and the waterlock itself would always be in the way when I needed to get to the LH side of the engine (fuel connections, lift pump, injection pump, air filter, oil extraction pump).

I'll try and do a rough volume calculation.

 

[KevB]

I'll try and do a rough volume calculation.

http://www.handymath.com/cgi-bin/cylinder.cgi?submit=Entry

 

[30boat]

Cheers.
OK, first prototype for shooting down in flames.

I think it needs a baffle somewhere.

 

[pvb]

I think it needs a baffle somewhere.

A waterlock doesn't need a baffle; a muffler would need baffles of some sort.

 

[30boat]

A waterlock doesn't need a baffle; a muffler would need baffles of some sort.

My Vetus waterlok has them.

 

[prv]

My Vetus waterlok has them.

And mine didn't.

An internal baffle might be part of some designs, but it's not an essential part of being a waterlock.

Pete

 

[Steve_N]

In this instance I tend to agree that a baffle would useful. Perhaps a horizontal one below the inlet to stop water splashing back up when the bow pitches down.

Re capacity, 4 litres would be fine according to the Vetus formula.

 

[Tranona]

You don't have to use the common vertical type. Vetus do horizontal types, as do Halyard Marine and Volvo. Provided you have sufficient fall, it does not need to be alongside the gearbox. On my Bavaria (and its predecessor) the waterlock was under the aft cabin bunk. Presumably you have the Vetus catalogue, so you can see the alternate types. The NLP3 would have sufficient capacity.

 

[Steve_N]

I'm afraid that there's nowhere that a waterlock could be fitted aft of the place that I've identified i.e. from the point where the exhaust leaves the bottom of my photo in post #1 there are no possibilities because the exhaust is tight between the aft cabin floor and the hull then equally tight past the steering quadrant and rudder tube and then we're at the transom. If I have to locate it forward of the top of my photo then the only possibility is alongside the engine block. If I did put it there then, yes, a horizontal one may well fit better than the vertical/cylindrical type, but it would have to be one with the inlet and outlet ports at the same (aft) end otherwise the runs of exhaust hose would be crazily long. I haven't been able to find a horizontal waterlock with both ports on the one end - I've seen ones with one swivelling port but they don't really fit the bill.