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Old 06-25-2016, 02:16 AM   #1
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run just one of the two motors?

Hi everyone, I posted a long and frustrating post in the mechanical section trying to learn why my stbd engine isn't working right, so I'll try to keep it short and sweet here- what's the harm to running just one of the engines if the other one isn't working right? I have CAT 3208NA twins on a Californian 34. The stbd motor is kaput for now, but I have a friend coming in town next week and the mechanic is taking care of the fishermen and is all booked for a while. I've read that it's fine to do, that it should never be done, that it will ruin the tranny on the engine that's spinning in neutral and keep it in gear even though the engine isn't running, etc... I know backing up will just spin me in circles so anchoring would be tricky, but if I stay close to home and don't do anything too stupid, is there risk of mechanical harm? Should I be concerned about if I go out once in a while until I can get it fixed? If there is reason for concern, have I been causing harm when I've been trolling with one engine these last few weeks? Thank you!

Rob
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Old 06-25-2016, 06:38 AM   #2
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Some transmissions are fine to free wheel while running on the other engine but some require the shaft to be braked or you can do damage to the transmission.
We have ZF boxes on ours and they have no limitations on the amount of time they free wheel. I'd suggest you research your actual transmission for the answer,

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Old 06-25-2016, 06:38 AM   #3
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It depends on your transmission. Some can be damaged by letting it turn over in neutral. Check your owners manual or with a dealer of that brand.


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Old 06-25-2016, 08:33 AM   #4
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The key is to go slow so as to not overload the working engine and make steering easier. 5-6 KTs will probably work. No full or even half throttle stuff.
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Old 06-25-2016, 11:10 AM   #5
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Can or should the offending prop be temporarily removed?
No drag, no free wheel, why not?
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Old 06-25-2016, 01:03 PM   #6
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just go slow. no harm removing the prop but for a short trip I would just go slow.
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Old 06-25-2016, 01:40 PM   #7
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I just got off a boat where the bolts on a transmission/prop shaft coupling sheared off while enroute. The through hull shaft seal was the modern dripless syle. Cooling water to the carbon face of the seal was from the engine heat exchanger. Engine off....no cooling water. So we had to to let the engine idle until we could figure a way to stop the failed, free wheeling shaft from spinning. As an aside, the shaft had slid rearward about two inches, and one of two things was keeping the spinning prop from hitting the rudder....either the clamping mechanism within the seal assembly, or a shaft zink running against the rear support strut. Either way we had to stop the shaft rotation as we were hours from a marina, and the spinning shaft would eventually destroy the seal assembly or eat through the zinc....spinning prop hits rudder...bad stuff happens. A big pipe wrench on the shaft coupling and wedged against a hull stringer did the job.

Anyway, if you have a cooling hose on the stuffing box (conventional style or dripless...you need to deal with that with an interconnect hose so the running engine will cool both. Then you can safely shut down the second engine (assuming the transmission lube issue is addressed).
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Old 06-25-2016, 02:10 PM   #8
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Saw that (too) often on the old crew boat I used to ride on for 20+ years. He had a big pipe wrench in the bilge just for that use.
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Old 06-25-2016, 05:37 PM   #9
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ok, from what I've been able to find, I shouldn't be running it in neutral without a shaft lock (big wrench) in place. Oops. I have no idea how many times that has been done because it's what the PO said he did when he trolled, and who knows before that. Hypothetically speaking, if damage has been done, I assume I would know it, right? Is it possible that this could be related to the knocking my starboard engine now makes? I wouldn't think so, but I've had a lot of surprises with my new boat already
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Old 06-25-2016, 06:58 PM   #10
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1 If you have Velvet Drive trannys, no biggie.

2 If you want to be sure, use the big pipe wrench to prevent rotation.

3 If you need to maneuver, learn to make the left turn your favoured (I really mean ONLY) turning direction. You will find few places you can't get to with only a left turn, or a series of them, once you learn to approach with that turn in mind.
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Old 06-25-2016, 07:14 PM   #11
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All mechanical transmissions, usually more than 30 years old, can freewheel because their bearings and gears circulate in oil. Hydraulic transmissions, cable operated, oil cooler, must not spin for long periods because the oil will heat up and not all bearings are lubricated with the engine off.
I don't see why you can't anchor. No boat backs really well. All your doing is setting the hook, not backing any distance.
Cat 3408 is a good engine. A friend with a log truck gets a million miles between overhauls with his.
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Old 06-25-2016, 08:11 PM   #12
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It would have been simpler to just get a single-engined boat. It's half as expensive to properly maintain one engine than two.
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Old 06-25-2016, 08:30 PM   #13
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The last thing I would want to do is put the teeth of a pipe wrench on my SS shaft. Try to put the pipe wrench on the steel coupling instead.
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Old 06-26-2016, 11:10 AM   #14
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Rob,
Which transmission do you have?

Are your shaft logs cool by a pressure water system?
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Old 06-26-2016, 12:33 PM   #15
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I did some scanning online yesterday and found some info that said they shouldn't freewheel and some that said it'd be fine, so I'm going to call the company tomorrow and see what they can tell me. They are twin disc MG502 transmissions with dripless shafts.


"It would have been simpler to just get a single-engined boat. It's half as expensive to properly maintain one engine than two"

Yes, properly maintaining one engine is cheaper than two. I've done everything I can to properly maintain these, but I've only had the boat a matter of weeks and can't speak to what's happened prior to that. But I'm definitely glad I had two and could shut the one with the problems off and come home with the other instead of pushing it and potentially causing further harm!
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Old 06-26-2016, 12:34 PM   #16
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Another issue is your shaft seal (dripless), unless the dripless has water pressure while the prop is free wheeling it will not take long before horrible sounds begin to emanate. I towed a friend with a Nordic Tug last year and we had to stop the prop from spinning by putting a pipe wrench on the connecting flange to stop the squealing.

The shaft seal became an issue long before the transmission would have...

As previously noted...
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Old 06-27-2016, 01:00 PM   #17
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I have the Cat3208NA and MG502 setup.

Read Section 3.7 of the attached TwinDisk owners manual.

Very difficult to maneuver at low speed in tight spaces on one engine. That said I've trolled for hours on one engine with the other off and the transmission in gear. Hard to hold a straight line even on auto pilot on one engine.

Personally I wouldn't go out of the slip knowing I only had one engine unless it was to move it to a repair facility. Seems like an unnecessary risk.
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Old 06-27-2016, 02:12 PM   #18
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There you go Rob. The operators manual seems to cover your freewheeling question. . . .I think. . . Maybe?

Three of us read and reread section 3.7 several times and came up with three different opinions. Yes you can. No you can't. and I'm not sure.

but I think they're saying you can freewheel if you follow "one" of the options listed.

PS: Like TG, I'm a fisherman and we run on one engine or the other for hours while fishing and I've been doing it since 1977 with no tranny problems. The question of cooling your dripless shafts might need to be addressed though.
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Old 06-27-2016, 05:04 PM   #19
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For drip less carbon faced seals .....2 alternatives to stooling the shaft...at least with the PSS type seals.

Put a T in the feed hoses so one engine can feed both engines.

In a pinch for towing or running under 8 knots or so...you can always just pull the hose off and let it back flood. Just make sure your bilge pump is working. It was standard practice at the Sea Ray dealership till Sea Rays came factory with the crossover T. Did it at least a dozen times and once ran for a couple hours that way.
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Old 06-27-2016, 05:11 PM   #20
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I called twindisc this morning and they don't recommend it. I guess if I leave the harbor I'll go with the pipe wrench method
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