Exhaust systems

[Vitalba]

I posted a question on this subject on the Classic Boat Forum but without too much response. I`m still not convinced as to which way to proceed and it now occurs to me that this, the Motor Boat Forum would have been a better place to start. If you know about these things please go to the foot of the current CB Forum page and select - last 75 days - on the "from the" dropdown. Select -Page 3- and see the entry for 07-09-09. ( and if you can find the question, I will certainly value your answer !) VITALBA

[carlton]

Originally Posted by Vitalba

I posted a question on this subject on the Classic Boat Forum but without too much response. I`m still not convinced as to which way to proceed and it now occurs to me that this, the Motor Boat Forum would have been a better place to start. If you know about these things please go to the foot of the current CB Forum page and select - last 75 days - on the "from the" dropdown. Select -Page 3- and see the entry for 07-09-09. ( and if you can find the question, I will certainly value your answer !) VITALBA

You'd have been better advised to simply cut and paste the question here yourself rather than expecting everyone else to play 'Hunt the problem and then come up with its solution', dontcha think?

Anyways, is this it?

The exhaust gases and cooling water are mixed immediately prior to the outlet of the water cooled exhaust manifold of Vitalba`s 3 cylinder Nanni.
"A". Due to physical constraints (the prop shaft) it is impossible to get the inlet of the Waterlock (Vetus LP40) much below the the exhaust manifold outlet and even so entails a sharp bend in the rubber pipe immediately after the manifold (not good as the hot gas may not be adequately cooled at that stage).
"B". The alternative and current arrangement (though not original) has the Waterlock inlet 2 or 3 inches higher than the exhaust manifold outlet but with 32 inches of rubber exhaust pipe between the two forming a `U`bend 12 inches deep. This presummably becomes the sump to take the residual water in that length of pipe when the engine is not running. From the outlet of the Waterlock to the to the top of the swan neck there is a good fall over 65 inches of pipe any residual water going into the Waterlock as normal.

Having spent a couple of days making brackets for system "A" I`m still not sure that "B" is not the better solution particularly when one takes into account a boats pitch and roll.

It may be of interest that waterlock manufacturers seem to use 10 to 20% of pipe volume as the residual water volume.

I would much appreciate the thoughts/comments of the Forum. All replies will get an A but only the top 90% A*. VITALBA

[volvopaul]

I am always fitting generators and come across your problem a lot.

I also attend jobs where the genny has seized as its been stood idle withe sea water in the bores, the last one had no waterlock just the hose pointing up towards the sky then back down to the silencer, hence net result.

Looking at your problem the 32 inch run up hill is out of the question, the longer the run of hose the more water in the pipe to run back when the engine is switched off, so keep the run of hose from manifold to waterlock as short as possible.

Can you not fit the waterlock at the side of the engine with a very short run to it.

I also see many builders especially aft cabin boats that have problems and cannot use the manufacturers exhaust elbow, therefore one has to be made to inject the water further down the line where it points downhill, thus the new part has to be a dry exhaust that has to be lagged with a jacket, Broom boats have to do this a lot.

I would look at doing a short dry run if you can and make up the mixer head further down the run if that helps.

[Vitalba]

CARLTON - I had no idea that one could "cut and paste" from one Forum to another and only expected that "people who knew about these things" would bother to hunt the question but thank you for doing so.

VOLVOPAUL - Thanks for your reply but :
1) The exhaust manifold and outlet elbow are as one
with a water cooled jacket. The mixing takes place prior to the outlet so I can`t do a dry run as you suggest.
2)The up hill run is not 32". With the Waterlock inlet only 2" higher, the exhaust pipe drops 12" vertically and rises 14" with the remaining 6" taken up inthe U bend at the bottom. If the water in the pipe while the engine is running is 20% of the total pipe volume there will be about 6" of pipe length full on switch off i.e. only the sump (bottom of the U )will be full. I do have an anti-siphon device so in theory no more water should come in.
As I under stand it a Waterlock is no more than a sump to hold the water contained in the "up-hill" pipes prior to the engine being switched off, abeit that the Waterlock has a greater capacity than the equivalent length of pipe. So what is wrong with using the sump/`U`bend as a substitute for a Waterlock in that part of the exhast system ?
I ask the question only because I have found traces of corrosion on the top of the pistons. But did this occur before the "U" bend or antisiphon was fitted by a previous owner ?
3) There is no room to fit the Waterlock either at the side of or aft of the engine where it would be significantly below the outlet of the mixed exhaust.
Any thoughts or comments from anyone would be much appreciated. VITALBA.