Our Tahatsu 6HP stopped shortly after our annual launch during the trip to our mooring. We had throttled back because the cooling water telltale had stopped running. The engine failed to re-start immediately so we assumed we had some overheating problem. Subsequently, the firm that had serviced our engine advised that we try to clear the telltale and restart the engine. We successfully restarted and got the water flowing using a piece of thin wire jiggled in the telltale hole.(probably some small piece(s) of debris loosened when we moved the engine before installation on the boat and blocked the telltale). However, we found that the engine wouldn't run for long at slow speed.(We have had a few occasions before where the engine stopped at low revs when we were manoeuvring and not very helpful!) The agent thought that this was because, at low revs, the exhaust doesn't get expelled via the prop into the water but exits into the well via bleeder holes in the upper part of the leg, eventually starving the engine of air. It was said that about 75% of 4 stroke engines in wells have this problem as they are sensitively balanced to achieve low pollution levels. Two-stroke engines are less of a problem.

Has anyone else had this problem? The agent suggested that (a) we don't run the engine slowly or (b) pipe the exhaust from the engine bleeder holes out of the well at the same level as the holes (to avoid back-pressure) probably through the transom (if practical). The latter requires the bleeder holes to be modified by blocking one and drilling out the other to take an alloy hosepipe spigot. Before doing this it would be useful to know if there are any other "solutions" in use or perhaps this isn't the cause of our problem!?

Chris Cobb

235/48 "Tarakihi"

I had just that problem in the '80s with the Mercury 75 (7.5hp 2 stroke)in a well in my Seal Sinbad. Not only did the engine falter due to being choked by its own exhaust gases but much the same fate befel the crew in the cockpit if there was a following wind! I cured it by making an adapter that clamped over the leg vent and led out through the transom.

I have very much the same arrangement on my Parker 21 with a Merc 5 4-stroke but no problems. I had assumed that it was because of it being a 4-stroke but it may be due to it having a much lower revving tickover than the 2-stroke so it just doesn't make as much gas.

Geoff Harwood p21/30 Cygnus

And me too with a 7.5hp Johnson 2-stroke in a well on a Seal 22.
I agree with Geoff and your Tohatsu agent - only way to go is to rig a flexible connection between your telltale outlet[s] and the transom.
And make sure that the connection falls to the transom without any rise in the hose that might result in a water trap, otherwise you'll get a waterlock and be even worse off!
Even this arrangement is not perfect since the primary exhaust outlet is in the bottom of the leg, or through the propellor hub in some cases, and when you are stationary, some exhaust will still bubble up into the well, whereas the faster that you are moving [whether forward or astern] the more of the exhaust will get sucked away by the negative pressure created by the propwash, reducing the exhaust that exits through the telltale.
Geoff Sheddick

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Hi Chris,
6 hp Tohatsu
I too have had similar problems when motoring slowly to pick up swinging mooring. Engine falters and dies just as I run forward to pick up ropes. I have tried motoring a bit faster but this sometimes means that I miss ropes and have to go round again.
I may investigate rerouting exhaust through transome although this sounds a bit complicated.

Regarding blocked cooling water system, could this be down to impeller breaking up? I had my impeller renewed at start of 2009 but have not had it done this year. I believe that O&M manual states changing impeller every 12 months. Any thoughts?

Brian Banham 235/59

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Hi Guys,

Thanks for your responses and suggestions. It would seem that I am not the only one who has suffered this problem perhaps there are many more but they "live with it"?

In terms of doing the mods, on the 235, there is a gap between the transom and the well moulding directly aft of the well. This makes it nigh on impossible to route the exhaust pipe directly out the back of the boat and provide gas-tight fittings in both bulkheads. A possible solution is first to go out of the well into either the main locker space (to port) or into the storage area near the double berth to starboard, and then through the transom. Going to starboard seems easier in terms of access unless one is small enough to go into the main locker (which I have done to do some wiring but not to be recommended if you are at all claustrophobic!)

It would be nice to try a temporary solution before making holes in the engine and boat in order to test if this will cure the problem but can't see how we might do this practically. Looks like we will have to do the mods!

On the point made about the impeller, ours wasn't changed because it was "in good condition" when serviced and the engine was test run by the agent for 20 minutes without problems.... I would take the engine back to the agent but it's rather too much effort to get it off the boat on the swinging mooring! Hopefully our impeller is ok and the telltale blockage wasn't fragments breaking off. If the engine fails completely, we will have to take the engine ashore but it's definitely a last resort which might kill our backs finally!

Chris Cobb

235/48 "Tarakihi"

Brian,

I've posted a reply to your question about impeller break up in a new topic in the general Technical forum.

Geoff Sheddick

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We have a Yamaha 6hp 2-stroke on Northern Sky, which we bought last year. We also had the smoke issue at low revs, and had a small pipe fitted which channels the low-rev exhaust gases out to a fitting on the cavitation plate. This eased the problem, and we didn't have any problems stalling at low revs.

We also had a high-thrust prop fitted, but still have the issues of too much noise and too little power, so we're looking for ideas for a replacement.

Most P235s seem to have 5 or 6hp engines - has anyone found anything bigger that still fits in the well?

Doug O'Malley
P235/55 Northern Sky

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