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Irwin37mkIV 07-06-2007 11:06 PM

1967 Irwin 37 cc with exhaust problem
My boat has a Perkins 4-108 engine with manifold on the port side. The exhaust leaves the manifold and crosses to starboard via an anti-syphon loop over the transmission, raw water is injected on the downstream side of the anti-syphon loop before entering the aqua-lift muffler on the starboard side of the engine compartment. Exhaust then crosses back over the transmission, forward under the hall floor, and out through the port hull at the waterline, via the cavity between the sette and port ice-box (i.e. behind the electrical panel compartment.)

Problem: Exhaust is wrapped with asbestos cloth ahead of the water injection point and is very hot. Exhaust appears to be made of copper pipe with soldered elbows and injection tee, with solder joints ready to fail. The rubber exhaust hose needs to be replaced, and am thinking of rerouting the entire system, as it does not appear to be the original installation...

There is a 2" through-hull fitting below the floor (under an inspection hatch in the Halway. This thru- hull is capped. I suspect that this was the original discharge point for the exhaust. It is about 2' below the water line. Can anyone confirm that the original exhaust discharged at this location?

Would a replacement have been routed to discharge at the waterline to avoid syphoning water into the engine? The present configuration introduces a second loop aft of the muffler where water is constantly trapped, and results in additional backpressure. The 'uncooled' anti-syphon loop is a significant obstruction, particularily when trying to do service work in the engine compartment when hot.

Has anyone done a successful retrofit on an exhaust, injecting cooling water directly after/below the manifold and placing the anti-syphon loop aft of the muffler, then discharging below the waterline at the hall floor hatch cover? I have read several publications suggesting that discharge below the water line is viable with an additional anti-syphon in the cooling water loop. These are generic documents, not specific to this boat and model. I'm concerned that the abandoned thru-hull, while accessible, is too far below the waterline to be put back in service?

Comments welcome. ;)

essman 07-09-2007 05:56 AM

I can tell you what mine has. I have a 1983 37CC.
I do have the Perkins 4-108.
I have a rubber hose that comes off the exhaust manifold on the port side of the engine and goes to the water lift muffler. The water lift is also on the port side, behind the engine. I don't have any hoses that cross the engine, or any anti-siphon loops in the exhaust.
From the water lift muffler it goes to the exhaust outlet on the port side of the boat, directly to port of the engine. Right where you described yours.
The 2 inch thru hull you describe under the hallway is where my engine raw water intake is located.
In thinking about it, I think the exhaust from the water lift goes up the back of the engine compartment, across the top of the engine compartment, down about halfway forward in the engine compartment, then across and to the exhaust port. So, I guess this acts as anti-siphoning.
Doesn't make too much sense on yours why they put the water lift on the opposite side of the engine compartment from the exhaust manifold.
Don't know if having the exhaust under water would work. How could you verify that water was coming out? And, seems like this really would cause back pressure.
And, why would you want to miss the pleasure of having the exhaust sometimes coming back over into the cockpit? :-)

Irwin37mkIV 07-12-2007 08:23 PM

Thanks Essman for your info.

I agree with your comments/concern about exhaust backpressure as a result of discharging 2' below the water line. I just can't imagine why a 2 inch dia. thru-hull would be installed there (and capped) with a hatch in the floor directly above if it wasn't used for the exhaust originally?

The '76 Irwin has 2 steps down to the aft hall from the main salon. To discharge the exhaust below that hall floor (with minimum clearance), the thru-hull has to be located 2' below W/L. Discharge at W/L inherantly introduces an other loop with water in it all the time.

Correct me, but I think the newer Iwrin (i.e. 83s) were beamier ~ 13' (much nicer boat too!), and therefore had a lot more room in the engine compartment to accomodate the muffler on the port side of the engine? The '76 has a 11.5' beam and no room for muffler on port side, hence the double cross over. I was tempted to reroute the discharge to sterm, but seem to be stuck with having to go below the floor which means a wet loop below the floor if I want to discharge at W/L. Only other option (unless I hear differently) is to discharge well below the waterline? I've considered discharging midship on starboard side at W/L, but am unsure how to get through the galley or aft washroom with reasonable estetics. Has anyone tried that?

essman 07-14-2007 09:45 PM

My '83 has the same beam - 11.5 feet. I think what mainly changed over the years with the different models is the interior layout.
The first ones had the split bed in the aft cabin (along each hull). Plus the galley was on the port side in the salon with a dinette on the starboard side. The later ones had a double bed running along the starboard hull. Better arangement, but it took up half the lazerette. Plus they moved the galley to the starboard side, just to the right and behind the companion way ladder. The final models has a double bed running across the back (from port to starboard).

I would bet that the thru hull you have in the hall is the original thru hull for the engine intake. Somebody probably moved it if it is somewhere else.

I've never seen a diesel exhausted below the water line. Must be some reason for it. It would be a good idea if possible. Would make things quieter.

But there are reasons for not doing it -
- You could not verify that exhaust water is leaving the boat.
- Seeing the exhaust is a trouble indicator for the engine, dependent upon the color and amount.

Maybe you should make a post over on the gear maintenance board to get opinions from people that know more about engines. Guaranteed you will get 14 or 15 differing opinions..... :-)

essman 07-16-2007 06:13 AM

I was at my boat today and was looking at the access area we have been discussing. I also have the depth sounders mounted there. One of them is a thru the hull type and has about a 2 inch hole. Maybe that was what was there at one time.....

Irwin37mkIV 08-02-2007 07:03 PM

1967 Irwin 37 cc with exhaust problem
:o Essman,

Regarding your last 2 note (4 & 5), It sounds reasonable that the original depth sounder transducer was mounted in the location of the 2" capped through hull. Their was abandoned wiring in that location and another transducer mounted nearby. I replaced the latter with a new device.

Thanks for pointing me to an other section of the forum. I'm still picking my way through the various sections when I have time.

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