This isn't going to work............your boat will probably run 4-5 kts on one engine........she's gonna need one big @$$ drag chute....... If this is an imperative for you, I'd look into installing trolling valves in the transmissions. They are by pass valves that bleed off some pump pressure and significantly reduce speeds.

Technically, if your seals have the crossover water feed, you can kill one engine and run on one at idle without hurting the seals.

 

They are by pass valves that bleed off some pump pressure and significantly reduce speeds.

Frank / Gary - Is there a maximum RPM that should be observed when in bypass mode? I was curious if the transmissions run warmer while using the bypass valves. Unloading pressure or flow generally produces heat. Is there a heat exchanger on the transmissions?

 

Missed this one...

As Frank said... you need trolling valves on the transmissions. For the ZF's on my boat, they are about $1500/side installed. You can save money by putting only one in. You'll probably find, like on my boat, you only have one power steering pump so put the trolling gear on that transmission. With one engine, I can dial it down to about 1 knot. Make sure, like Frank said, you have a crossover on the shaft seals.

 

Gary - Do you have a trolling valve on the starboard tranny?

 

If you are contemplating this, be sure you do both transmissions and that you activate the trolling valves at the same time.

I run a Viking with 1000hp MANs for a friend sometimes and his trolling valves are switched separately. If you forget and leave one in trolling mode and switch the other out, then advance the throttles, hang on.........you really have your hands full trying to control the boat and keep from throwing people and gear everywhere or running over someone for that matter.

 

I have trolling valves on both engines but only use the starboard one. Not that I've ever left one engaged and one not engaged... The engine will scream at you when you do that.

 

There is definitely a max RPM you can run with the valves engaged. My guess is that the valves do produce some heat, but I will let Gary and Frank respond as they will know a lot more about the valves than I do. We had a boat that had trolling valves before and there were very stringent warnings about exceeding certain speeds with them engaged. We don't fish, so we never used them.

 

Now don't laugh...my gassers have a Merc Smartview feature called Trol-Control. I tried it and it syncs both engines to run at a preset RPM. I tried it at 850 and it seemed to work real well in calm water...I don't think it will let you set it for much over 1000 rpm. In my application it would be more aptly named "Cocktail Cruise Control"

Nothing like Frank and Gary mentioned though...

 

Trolling valves release transmission pump pressure and cause the clutches to slip. I don't know about Gary's but those on the Viking I mentioned can only be run a very slow engine speeds. This boat has 1000hp MAN's and will run about 8 kts at idle, so trolling valves are a have to. think of them like a low gear on your transmission.....if you want o go faster in low, you don't firewall the throttle; you just shift into second.

On the other hand, think of the Smart Craft Trol-control as a cruise control to hold a speed once you set it.

 

Without trolling valves, the 480 DB runs about 7 knots with both engines in idle (650 RPM). With a single screw turning, it runs about 4.5 - 5 knots. Trolling for rockfish (striped bass) requires about 2.5 - 3 knots. ZF warns they should not be engaged above 1000 RPMs. Also, I have transmission coolers on both port and starboard that tie into the raw water cooling circuit.

 

My boat has the same setup that Frank describes, since I have nearly the same engines (900 HP MANs). In the normal operating mode I move my single lever shift/throttle controls from neutral to the first detent which puts the transmissions just into gear. All else being equal the boat will move at about 6-7 knots at 600 RPM. To go any slower, I have to take one engine out of gear (gets me down to about 3 knots) or bump in and out of gear as needed to control speed.

Now go back to neutral and pess the troll button on my shifter. Moving the shifter/throttle levers from neutral to the first detent will produce only the slightest forward movement of the boat because there is nearly 100% slippage in the transmissions. Because of the integrated electronic controls the function of the throttle levers has been modified in troll mode. Now, I can move the throttle to the WOT position and the slippage is reduced to near zero, but the RPM of th engine does not change, staying at around 600 RPM. So, in trolling mode, I have entire range of motion of the throttle levers to fine tune my speed, between zero and about 6 knots.

The down side to this is that the changes are not instantaneous so you really have to be in open water to use this function. It is not helpful in tight channels, or anywhere that you would need to quickly change speed or direction.

 

I don't have the trollimg option, but instead have a slow vessel mode. This drops the engines down to about 500rpm. It's good for moving around the marinas. Gets the boat down to around 5kts. Without it idle speed is about 9kts.

 

Be careful about running boat with a slow idle option in slow idle for extended periods, like for trolling in open water. Running an engine below minimum idle setting established by the manufacturer usually causes excessive valve train wear.

 

When I hit that slow idle button, the RPM's go down to about 500 RPM and it shakes the boat so much it feels like the thing is going to fall apart. Even if you wanted to use that for trolling, it would scare all the fish away for miles.

 

I think having both the slow idle button (which I don't have) and trolling valves you get the most benefit. The trolling valves are for open water, extremely slow, travel (as in trolling for some fish) and the slow idle button is OK for maneuvering around the dock.

 

If your boat shakes that much, just think what the valves, valve guides, push rods and rocker arms must be going thru.

 

Along with the 4000 bolt on brackets.

 

Funny, my wife is quite fond of the slow idle feature..... :grin:

 

Funny, my wife is quite fond of the slow idle feature..... :grin:

Somebody had to say it....:smt043

Merry Christmas!

 

Frank, thanks for the tip. I only use it to get to my slip or the fuel dock. Fortunetly it's only a short distance from the entrance to my slip. I don't get any vibration when in slow vessel, but the engines definetly don't run as smooth. I've learned that if we don't come off plane about 2 miles out my neighbors are quite unhappy. Maybe I'll try it with one scew.

 

....... Maybe I'll try it with one scew.

With both engines in gear, I idle at about 6-7 knots, and make too big a wake to leave my neighborhood . I do not have trolling valves, so I have to leave the "harbor", about 3/4 miles, on one engine. There is an "S" turn to navigate and traffic both ways in the narrow canals. It deffinitely takes some getting used to to control your boat in close quarters, at low speed, on one engine.

One "trick" that I've learned that works pretty good for me is I put the port engine in forward, and fully lower the port trim tab (the Stbd switch at the helm bow down). That configuration kind of counters each other a bit. I also throttle up the port engine to about 700-750 RPMs. I still have to go in and out on the stbd engine a bit around the "S" turn, but going straight is a lot easier this way.

 

Is there any detriment to the diesels themselves when running them at idle for extended periods (with trolling valves installed). Do you have to "clear them out" after so much time etc? Do they cool themselves properly etc?

 

Nope....diesels are quite happy at any speed as long as it is at or between the manufacturer's recommended idle and cruise speeds and as long as the engine load is proper. In fact, after they are broken in, diesels are more efficient when run at a constant engine speed, but that seldom happens in a pleasure boat.

Diesels don't "load up"...........like some gas engines seem to, but when you run a diesel at rated rpms in an unloaded condition some of the fuel charge isn't needed and leaves the engine as carbon which is a solid and can plug up exhaust passages. This almost never occurs on main engines but frequently does happen on generators since we often run them with less than a full load. If we only need one a/c or don't need the water heater, we leave them off and the generator, which is designed to run under a full load, ends up running with a 50-70% load and the exhaust passages can get cloggged with carbon. Westerbekes are particularly bad to clog up their exhaust risers when run in an unloaded condition....the good news is that a Westerbeke replacement riser only costs about $70 and a 6 year old can change it.

 

Thanks Frank, looks like with Trolling Valves I'm good to go.

Thanks Dom, I will have to try that method as I noticed the boat made more "wake" than I liked when in a no wake area.

 

Dom, I'll give it try when we are at the boat over New Years.

 

Don't expect miracles, but it does make a difference with my 410DA. Play with your throttle on the engine that's in gear. If your single tab down pulls more/less adjust the throttle.

Let me know how/if it works for you....I'm curious

 

Will do. I'm a novice so I'll try it in open water. The conditions should perfect on the lake as this time of year the water is usaully flat. These cats have soooo much torque that even with one scew the boat moves along smartly.

Andre'