barryg
New member
advice please my 8hp sailpower 2 stroke it is choking on its own fumes from the exhaust. if I put a small plastic tube into the exhaust bypass hole and run this into the well below the water line will this work ?
exhaust bypass on outboard
- Thread starter barryg
- Start date
chippie
New member
I think the water pressure will be too much for it. I remember sailing on a boat that had a well and similar problems, the skipper used to wave the well lid up and down franticly as a bellows until the engine got up enough revs to pull in fresh air.
I think some means of ducting forced air into the well is probably the best solution , or a direct duct to the carb that can be hung outside the well.
Good luck
I think some means of ducting forced air into the well is probably the best solution , or a direct duct to the carb that can be hung outside the well.
Good luck
steve_cronin
N/A
NO -It needs to be connected...
.. to an outside skin fitting.
it isn't just two strokes that suffer from self choking in an engine well, four t's do also.
I once cured this with a Honda 7.5 in the well of a Newbridge Venturer by making a connector from a piece of rectangular section anodised aluminium tube (a bit cut off a dinghy tiller extension actually) -. I sealed one end with epoxy and fitted a length of car heater hose to the other. The fitting was attached to the engine outlet by drilling the casing above and below the bypass outlet, tapping the holes and screwing two 5mm SS screws through matching plain holes in the fitting. A gasket was provided by a piece of neoprene strip cut to fit. The outboard end was taken to a 1/2inch plastic skin fitting in the transom of the boat well above seea level but it was swan -necked to prevent sea water from coming back.
Heater hose was OK because since the bypass gases have water mixed with them they never get hotter than 83C, the engine running temperature.
This set-up ran with me for seven years including motoring (No wind) all the way from Poole to St Malo, through the Brittany canals, down to the Gulf of Morbihan and back again without missing a beat. Marvellous engines those Hondas!
Steve Cronin
.. to an outside skin fitting.
it isn't just two strokes that suffer from self choking in an engine well, four t's do also.
I once cured this with a Honda 7.5 in the well of a Newbridge Venturer by making a connector from a piece of rectangular section anodised aluminium tube (a bit cut off a dinghy tiller extension actually) -. I sealed one end with epoxy and fitted a length of car heater hose to the other. The fitting was attached to the engine outlet by drilling the casing above and below the bypass outlet, tapping the holes and screwing two 5mm SS screws through matching plain holes in the fitting. A gasket was provided by a piece of neoprene strip cut to fit. The outboard end was taken to a 1/2inch plastic skin fitting in the transom of the boat well above seea level but it was swan -necked to prevent sea water from coming back.
Heater hose was OK because since the bypass gases have water mixed with them they never get hotter than 83C, the engine running temperature.
This set-up ran with me for seven years including motoring (No wind) all the way from Poole to St Malo, through the Brittany canals, down to the Gulf of Morbihan and back again without missing a beat. Marvellous engines those Hondas!
Steve Cronin
G
Guest
Guest
We had exactly the same problem on our Hurley 22. We have done couple of things:
1) the anti syphon exhaust vent we have now piped via a felexible hose to a fitting venting it out of the transom. This reduces the amount of exhaust the lazerette/locker.
2) We have an extractor fan which vents the lazerette/locker. We have noticed tha turnint turning the extractor on gives us anothe 0.5 knots.
Both the above were simple to do, we also have the O/B charging the battery, so far since putting a fully charged battery onboard at the beginning of the season we have been in pretty good shape, the charge generally just keeps it topped up.
1) the anti syphon exhaust vent we have now piped via a felexible hose to a fitting venting it out of the transom. This reduces the amount of exhaust the lazerette/locker.
2) We have an extractor fan which vents the lazerette/locker. We have noticed tha turnint turning the extractor on gives us anothe 0.5 knots.
Both the above were simple to do, we also have the O/B charging the battery, so far since putting a fully charged battery onboard at the beginning of the season we have been in pretty good shape, the charge generally just keeps it topped up.
rex_seadog
New member
We also have a Mariner 8 Sailmate which we use in a well on our Hunter Delta. When we bought it the Mariner dealer connected a rubber tube to the exhaust by-pass hole (exactly as you propose) and this is led below the water line and secured with a plastic tie to the leg just above the cavitation plate so that it points aft. I was concerned that the exhaust gases would cause the prop to operate in 'dirty' water but it seems to work satisfactorily except occasionally when idling stationary for a long period when the exhaust gases bubble up into the well.
I've considered leading the tube to a transom skin fitting above the water line but in my case this would involve a longer length of tube which in itself would increase the back pressure.
Prior to this we had a Yamaha 10 4-stroke which the previous owner had fitted up with a clean air intake piped from the cockpit directly to the carb. This was possible because the engine was so large that it had to run without its cover to enable the engine locker lid to be closed. The locker still filled with fumes and on the advice of a Yamaha agent we had a tube fitted exactly as described for the Mariner. Again I noticed no problems with this arrangement.
I've considered leading the tube to a transom skin fitting above the water line but in my case this would involve a longer length of tube which in itself would increase the back pressure.
Prior to this we had a Yamaha 10 4-stroke which the previous owner had fitted up with a clean air intake piped from the cockpit directly to the carb. This was possible because the engine was so large that it had to run without its cover to enable the engine locker lid to be closed. The locker still filled with fumes and on the advice of a Yamaha agent we had a tube fitted exactly as described for the Mariner. Again I noticed no problems with this arrangement.
steve_cronin
N/A
Your \"dealer\" is absolutely WRONG....
...and the few extra inches of pipe to go to an above water skin fitting is going to cause unmeasureable extra "back pressure" when compared to that induced by immersing the exit from the pipe. Can you imagine how deep it would be immersed if you just happened (for reason of emergency of course) to be motor sailing on the tack which put the Hunter engine well on the downward side (Stbd tack in my memory?), Hunters not being known for their modest angles of heel! This method also relies upon the gasket/gland or whatever to keep fumes from re-entering the well - don't forget that you will have displaced the rubber anyway to get the pipe down so some will come in especially when stationary. No, get it routed outside completely, apart from it looking as if you have a "real" inboard, you will have a readily visible early indicator of any overheating or blockage problems.
Steve Cronin
...and the few extra inches of pipe to go to an above water skin fitting is going to cause unmeasureable extra "back pressure" when compared to that induced by immersing the exit from the pipe. Can you imagine how deep it would be immersed if you just happened (for reason of emergency of course) to be motor sailing on the tack which put the Hunter engine well on the downward side (Stbd tack in my memory?), Hunters not being known for their modest angles of heel! This method also relies upon the gasket/gland or whatever to keep fumes from re-entering the well - don't forget that you will have displaced the rubber anyway to get the pipe down so some will come in especially when stationary. No, get it routed outside completely, apart from it looking as if you have a "real" inboard, you will have a readily visible early indicator of any overheating or blockage problems.
Steve Cronin
quaelgeist2
New member
Have tried both ways successfully
1) small (rubber!) tube from exhaust bypass -connected using a plastic connector from B&Q, glued with liquid metal- down the leg into the water, approx1-2 inch below surface.
No problem from increased backpressure with 9.9 Mercury; but idling the fumes kept creeping back
2) small tube lead aft through the cockpit drainers through the transom and ending 1-2 inch above the surface.
No noticable difference in engine performance, but no fumes anymore.
You might be able to fit/epoxy in a metal tube through to the transom ?
The real risk of backpressure comes from a combination of an idling engine (needing the exhaust bypass outlet) and a wave pressuising your tube. Under normal operaton most fumes leave through the prop outlet anyway.
chris
1) small (rubber!) tube from exhaust bypass -connected using a plastic connector from B&Q, glued with liquid metal- down the leg into the water, approx1-2 inch below surface.
No problem from increased backpressure with 9.9 Mercury; but idling the fumes kept creeping back
2) small tube lead aft through the cockpit drainers through the transom and ending 1-2 inch above the surface.
No noticable difference in engine performance, but no fumes anymore.
You might be able to fit/epoxy in a metal tube through to the transom ?
The real risk of backpressure comes from a combination of an idling engine (needing the exhaust bypass outlet) and a wave pressuising your tube. Under normal operaton most fumes leave through the prop outlet anyway.
chris
fjweaver
Member
if you're based on the South Coast try Fairweather Marine in Fareham (01329 823927). They did a neat job (& cheap) on my Mariner 8hp Sailmate by screwing in a brass fitting to the exhaust hole & connected a hose from this down to the cavitation plate. No problems with the engine since & runs a lot quieter with the well locker closed
rex_seadog
New member
Have followed this discussion with interest especially in view of Steve's strong and, I'm sure, well informed opposition to exiting the exhaust bypass tube underwater. This despite us and other respondents apparently using this technique successfully. I therefore contacted EP Barrus' technical department and it is their recommendation (no stronger than that) that the exhaust relief tube is not led underwater. There should be no problem with the engine in gear and driving normally but they say that when idling there is an increased risk of plug fouling. In 4 years we have never experienced any fouling problems although we do not allow the engine to idle more than necessary.
If I remember my physics correctly, the increase in back pressure is about 0.5 psi for every 12" in depth of water which is about the depth of the tube with the boat level. Even when heeled to port with the tube submerged about 2 feet the increased back pressure would be only 1 psi. Is this significant?
Our engine is too large to take advantage of Hunter's tilt and lift feature but to reduce prop and leg fouling we sometimes unclamp it, lift it and store it horizontally in its locker. We can just about perform this operation without disconnecting the control cables, fuel line and charging cable. I'm concerned that a longer 'transom' tube would complicate this procedure as well as pose the risk of kinking. Nevertheless, over the winter I shall look at ways of exiting the tube through the transom so that we can compare the difference with our existing operation.
BTW Steve, is the gasket you refer to surrounding the outboard leg? Is this normal practice with engines in wells? We have nothing - just a hole open to the sea through which the leg protrudes and I am always concerned at the extra drag this may cause.
If I remember my physics correctly, the increase in back pressure is about 0.5 psi for every 12" in depth of water which is about the depth of the tube with the boat level. Even when heeled to port with the tube submerged about 2 feet the increased back pressure would be only 1 psi. Is this significant?
Our engine is too large to take advantage of Hunter's tilt and lift feature but to reduce prop and leg fouling we sometimes unclamp it, lift it and store it horizontally in its locker. We can just about perform this operation without disconnecting the control cables, fuel line and charging cable. I'm concerned that a longer 'transom' tube would complicate this procedure as well as pose the risk of kinking. Nevertheless, over the winter I shall look at ways of exiting the tube through the transom so that we can compare the difference with our existing operation.
BTW Steve, is the gasket you refer to surrounding the outboard leg? Is this normal practice with engines in wells? We have nothing - just a hole open to the sea through which the leg protrudes and I am always concerned at the extra drag this may cause.
steve_cronin
N/A
A lot of the earlier outboard wells had a rubber or neoprene "gasket2 or gland to streamline the hull shape as well as stop too much exhaust coming in. You can make one with a piece of colliery conveyor belting cut to shape. I found this the best material beinmg much more durable than sheet neoprene available from industrial sheeting suppliers but the very devil to cut without a jigsaw. Most collieries throw large amounts of it away.Trick - locate a miner!
Steve Cronin
ps the rubber pipe to the fitting I described just pulled off for engine removal. Since this outlet isn't the primary exhaust exit back pressure is almost irrelevant once the motor is running.
Steve Cronin
ps the rubber pipe to the fitting I described just pulled off for engine removal. Since this outlet isn't the primary exhaust exit back pressure is almost irrelevant once the motor is running.
