Exhaust/waterlock questions

[RobbieH]

Hi:

I'm planning a trip further afield next year and am casting a critical eye over the exhaust system of my boat (Dufour Arpege recently re-engined from MD2B to Beta 722). I reworked the anti-siphon last year - engine installer had mounted it under the cockpit (at virtually the same height as the injection point!) and it had a valve which was completely encrusted and blocked with salt. I now have a Vetus "no-valve" system mounted higher (just below companionway opening) with the telltale discharging into the cockpit. It makes a satisfying gurgle when the engine is stopped

However downstream of the injection bend I have a few worries and would like to pose a few questions to the forum ...

1/ I have the OEM s/s waterlock which has a inlet diameter slightly smaller than the Beta exhaust manifold outlet. Everything downstream of the waterlock is at the same (slightly reduced vs. Beta) diameter. The new flexible hose between them is "shimmed" using the old flexible hose. Will the change in diameter cause any practical backpressure problems for the Beta?

2/ Is there a formula to calculate the required size of the waterlock based on exhaust diameter and length? The s/s OEM looks a bit small but that is just a feeling on my part. I'm also a bit suspicious of old s/s in that corrosive environment so am leaning towards a Vetus (plastic) replacement but want to know what are the recommended volumes (min/max). I understand if I up the hose diameter (see question 1) I may need to consider this question carefully ...

3/ The "gooseneck" is a loop of the flexible hose leant against the same side of the hull as the exhaust outlet (plain s/s outlet - no flapper valve). The top of the "gooseneck" is halfway between the water line and the cockpit coamings. It really looks inadequate so I am planning on fitting a Vetus plastic gooseneck on the centre line of the boat with the top hard up against the deck just forward of the rudder shaft (where the fuel tank used to be for those who know the Arpege layout). Any comments?

4/ Is it possible/advisable to fit a large ball valve inline into the flexible exhaust hose somewhere between the waterlock and the exhaust hull outlet? Or a combined seacock/exhaust fitting if someone makes such a beast? Or is an exhaust outlet with a flapper valve adequate?

Thanks for any light you can shed ...

 

[Tranona]

Welcome to the forum

Have just been through this loop. Installing a Nanni in my boat to replace a Yanmar. Not sure exhaust diameter is too critical as the Nanni has a 40mm outlet and the Beta has a 50mm - same base engine! The Yanmar was 45mm so I am stepping up to keep the existing system from the waterlock onwards.

Anyway if you are going to replace the system completely it make sense to use 50mm throughout. For a waterlock I have used the NLP type Vetus unit, although I previously used the simpler LP type. Both have a capacity around 4.5 litres which is more than adequate. The advantage with the NLP type is more flexibility of positioning of the spigots. My transom outlet is just like yours - a loop under the aft deck and a 90 degree fitting through the hull with a Vetus connector. I have never had any problems with water coming back. Do not see any need for any kind of flap or one way valve. The Vetus Gooseneck only does the same job as the loop of hose, but can make installation easier. If you are replacing the hose, just make it longer so it goes as far above the waterline (minimum 45cm) as possible. It is the waterlock that protects the engine - plus of course the anti syphon valve.

More information on exhaust design on pp 168/9 of the Vetus catalogue www.vetus.co.uk

Hope this helps

 

[RobbieH]

To answer one of my own questions, and to freshen the thread, I have just received an answer from Vetus on the question of waterlock volume.

"The rule of thumb is to take the volume of the hose between waterlock and swanneck. 25% of the total volume , is the minimum of the contents a waterlock must have."

This is more conservative than other advice I have seen of 10%-20% of the volume. Needless to say I shall be going for the 25%+ figure ...

 

[PetiteFleur]

As Tranona says, I replaced all the exhaust components when I fitted a Beta to replace an old BMC 1.5. The original exhaust was 60mm Ø and the Beta was 50mm Ø. I fitted the multiposition plastic Vetus waterlock, Vetus inline muffler and Vetus gooseneck - all with new flexible hose. I initially fitted the vVetus antisyphon but have since replaced it with a bronze type which pumps a small amount of water overboard. I was going to use the original stainless waterlock but on inspection it had several pinholes and the pipework orientation was wrong for the new engine.

 

[RobbieH]

Welcome to the forum

If you are replacing the hose, just make it longer so it goes as far above the waterline (minimum 45cm) as possible. It is the waterlock that protects the engine - plus of course the anti syphon valve.

More information on exhaust design on pp 168/9 of the Vetus catalogue www.vetus.co.uk

Hope this helps

Hi Tranona:

I have a choice of mounting a loop_of_hose/swan-neck either pushed up inside the coamings of the cockpit or on the centre line of the boat (but closer to the water line). Which in your opinion would be better? I'm guessing if the boat is very heavily listed (careened?) it might be possible for the exhaust to flood via the under side coamings mounted system whereas a swan-neck mounted on the centre line is not affected by listing. But then if it is closer to the water line a few good waves punching the quarter might drive water in the exhaust and over the (lower) swanneck

Argggghhh! too many variables

 

[RobbieH]

As Tranona says, I replaced all the exhaust components when I fitted a Beta to replace an old BMC 1.5. The original exhaust was 60mm Ø and the Beta was 50mm Ø. I fitted the multiposition plastic Vetus waterlock, Vetus inline muffler and Vetus gooseneck - all with new flexible hose. I initially fitted the vVetus antisyphon but have since replaced it with a bronze type which pumps a small amount of water overboard. I was going to use the original stainless waterlock but on inspection it had several pinholes and the pipework orientation was wrong for the new engine.

What did you do for the thru-hull? I'm guessing you had to replace that too?

 

[tel1]

to avoid any potential back pressure, the whole exhaust system should be of the same diameter of what comes from the engine. even if its only 5mm. it is expensive to do this as ive just done it, but for peace of mind, its worth doing.

 

[PetiteFleur]

What did you do for the thru-hull? I'm guessing you had to replace that too?

The original exhaust for the BMC 1.5 was under the transom underwater, which I didn't like as it was difficult to see the exhaust water so I moved it to the transom. I filled up the original hole with GRP with several layers inside the boat. I fitted a new Vetus ehaust outlet which fitted directly onto the Vetus Gooseneck

 

[jeanne]

No waterlock !

I don't suggest that anyone follows my example, clearly one should do the installation as well as is possible, but it may put all the advice flying round into perspective to learn that my engine has no waterlock, and that this has given no trouble in 25 years use. The hull aft of the engine is too narrow to fit one, and I was reluctant to move the engine further into the cabin just to do it.
I fitted a small diameter drain tube to the lowest point of the exhaust, led to the bilge sump where there is a tap. I try to remember to open the tap (A) when running under sail in heavy seas, (B) when turning the engine over without it firing, i.e. bleeding the engine, (C) when laying the engine up for the winter, and (D) when running aground on a falling tide! At all other times the tap is closed, with no ill effects.

 

[RobbieH]

...but it may put all the advice flying round into perspective to learn that my engine has no waterlock, and that this has given no trouble in 25 years use.

Ah yes - but a steam engine is designed to run with water inside it

That's a helpful piece of input about leaving the drain open under certain conditions.

Actually that was another reason i was thinking of fitting a Vetus waterlock - it looks relatively easy to drain the waterlock (two drians as it is a dual canister) and I was thinking it would be easy to drain it if rough weather was expected on a long sailing passage and to leave the drains open and pump the bilge as required. The OEM Waterlock that I have has the drain very inaccessibly mounted so it's not really an easy option - indeed I've never drained the waterlock so for all I know the threads are seized!

I suppose the only time this theory falls down is on a rough passage under engine (but then the exhaust gas should be pushing hard enough to avoid problems) or if I forget to do up the drains before starting the engine!

 

[doug748]

4/ Is it possible/advisable to fit a large ball valve inline into the flexible exhaust hose somewhere between the waterlock and the exhaust hull outlet? Or a combined seacock/exhaust fitting if someone makes such a beast? Or is an exhaust outlet with a flapper valve adequate?

Thanks for any light you can shed ...

I have a gate valve which is screwed to the bronze outlet in the usual way, because of its position it is a pain to operate and I have never used it in anger. Neither would I fancy trying to use it in poor conditions - having to empty the contents of the stern locker, sticking my head in etc. The previous owner used it, then forgot, started the engine and blew the head gasket. I would repalce it with some form of internal clapper valve if one were available but I have not been able to find one that is suitable.
My freeboard is less than yours and I have not had problems with my simple exhaust loop, offset exit (set almost vertical in the stern overhang) and water trap set as low as possible. The old engine didn't even have a syphon loop.
If I were crossing an ocean I might look a bit harder for a sutable valve .

 

[Tranona]

Hi Tranona:

I have a choice of mounting a loop_of_hose/swan-neck either pushed up inside the coamings of the cockpit or on the centre line of the boat (but closer to the water line). Which in your opinion would be better? I'm guessing if the boat is very heavily listed (careened?) it might be possible for the exhaust to flood via the under side coamings mounted system whereas a swan-neck mounted on the centre line is not affected by listing. But then if it is closer to the water line a few good waves punching the quarter might drive water in the exhaust and over the (lower) swanneck

Argggghhh! too many variables

My outlet is on the portside of the transom - mainly because the original hole for the Stuart Turner dry exhaust system was there. Incidentally that just had a loop and no water trap and survived 30 years with no water ever getting in. So my new exhaust hose actually runs almost down the centre line of the boat, then loops up as far as it will go under the aft deck and down to the outlet. This is a pretty common arrangement - much the same on my Bavaria except the exhaust outlet is through the hull rather than the transom. Vetus recommend a minimum of 45cm above the waterline so if you can achieve this on the centreline that seems to be the way to go.

Re your calculation for watertrap volumes. 3M of 50mm hose has a volume of 6 litres, so 25% of that is 1.5 litres - the smallest Vetus waterlock is 2.3 litres and the most commonly used is 4.5 litres.