Perkins to Yanmar, repower on my swan 44 questions Dear Lars,
I am in the midst of repowering my swan 44 hull #9 from the original 40 hp Perkins 4108 to a 56 hp Yanmar turbo. I am sticking with the side exhaust design but am a bit confused with the original exhaust cooling. Does it need to be injected into both the exhaust elbow and again into the upright muffler outboard to port ? Also, should I upsize all exhaust piping 1/2" to accommodate for 28% greater horse power ? That would mean increasing the drain-back tank by the port bulkhead beneath the step. I saw pictures of another Swan 44 with a Yanmar in it, any idea of what was done there, was the piping incased there ? Any ideas would help, thanks, Bob D
Dear Bob
It is sufficent to inject water at the exhaust elbow only, and the upright muffler in the port locker is not needed any more. Removal provides more stowage.
The exhaust hose size is determined by the connection on the engine. If this is a new engine under warranty it is necessary to discuss a possible hose size reduction with the supplier.
It can be commented that reducing the amount of water in the exhaust reduces the back pressure, but this has to be approved by the supplier, and verified by measurement.
Another possibility is a water separator installed after the waterlock, then the hose after the separator may be smaller, and there is no splashing on the outside, only steam comes out.
If the separator can be located on the centerline below the ladder it does not need to be so high up, and the drain-back is reduced.
Will the waterlock/drain-back tank be custom made? Have seen some fitting inside the engine space.
It would be helpful here to measure the actual exhaust back pressure, does the exhaust elbow have a connection for this?
Would say that hose size is according to engine connection for most installations.
Kind regards
Lars
Dear Bob
It is sufficent to inject water at the exhaust elbow only, and the upright muffler in the port locker is not needed any more. Removal provides more stowage.
The exhaust hose size is determined by the connection on the engine. If this is a new engine under warranty it is necessary to discuss a possible hose size reduction with the supplier.
It can be commented that reducing the amount of water in the exhaust reduces the back pressure, but this has to be approved by the supplier, and verified by measurement.
Another possibility is a water separator installed after the waterlock, then the hose after the separator may be smaller, and there is no splashing on the outside, only steam comes out.
If the separator can be located on the centerline below the ladder it does not need to be so high up, and the drain-back is reduced.
Will the waterlock/drain-back tank be custom made? Have seen some fitting inside the engine space.
It would be helpful here to measure the actual exhaust back pressure, does the exhaust elbow have a connection for this?
Would say that hose size is according to engine connection for most installations.
Kind regards
Lars
Thank you Lars,
That's what I thought but I didn't know if the injection had been split to reduce the volume of the cooling water that would go to the water lock, which looks pretty small. At some point my upright exhaust was changed out from the original metal one to a rubber one which gets injected on the down hill side by water from the transmission cooler exchanger. I suppose I could keep the whole thing, eliminate the secondary injection @ the muffler then upgrade all fittings & through-hull to 3 inch (same as the Yanmar). Then modify the waterlock to accommodate the extra pipe volume and increase the size of the pipes within the baffle of the waterlock. I'm not sure though of just what should be included when I re-calculate the drain-back volume. From the downstream end of the waterlock to the vent point on the exhaust, perhaps? Thankyou, Bob D
Dear Bob
Sorry to intervene but it is not a good idea have the drain-back transversely. If she broaches to starboard you will have a problem.
Is there a siphon break on the sea water connection to the exhaust bend?
The drain-back volume to accommodate the water in the hose on its way up to the highest point. Often the hose is assumed to be completely full of water, but in practice this is not the case, there is a water film along the walls, and gas in the middle.
If possible measure the amount of water left in the drain-back on a similar installation with the same engine.
Turbo engines require much lower back pressure, half of that for a non-turbo, therefore the bigger exhaust hose.
Kind regards
Lars
