If I have twins and one dies.....

[Fl_Richard]

I know lugging an engine is bad news. My boat running on one engine runs about 30 mph at 4300 rpm, on two it runs 47 mph and 5800 rpm

Since I have twins, if one dies and I run 50-60 miles will it damage the good engine?

 

[jay_merrill]

Re: If I have twins and one dies.....

What kind of engines do you have and what is the recommended WOT (wide open throttle) rpm range? If your motors are outboards, 4,300 is probably below the recommended range, but depending on the year/brand, might be either be a little bit below or a lot below it.

All of this said, unless you are trying to outrun impending bad weather or something, you don't have to push the boat up onto plane in a single engine situation. You can always run the boat at 6-7 knots just to get home. While this makes for a long trip, its better to get home eventually than to overwork/overheat your remaining engine and end up offshore with two dead motors.

You also have some options in regard to props. One is to carry a spare with less pitch, for use during single engine operations. If you do this, buy a couple of extra nuts, thrust washers and cotter keys, and keep them in the boat. I recommend this simply because Murphey's law is likely to come into play, with the possibility of dropping/losing one or more of the parts during a prop change.

When offshore in a single configuration offshore, my choice would be to run in slowly if I had to, rather than to try to go in the water to change a prop. This is true unless the seas are dead calm or nearly so. Even then, a PFD is an absolute neccessity and you should be teathered to the boat, with someone tending to you and the line. Extra lines should be used to teather the prop coming off (around the hub and one or more of the blades) and the prop going on. Tools should also be teathered to you.

Finally, you can also use props of less pitch all of the time. By selecting a pitch that keeps rpm within the acceptable limits on one engine, you can eliminate the problem altogether. The drawback to doing this is, of course, reduced fuel economy and top speed, when both engines are operating. You will also have to operate at less than WOT to keep the engines within the upper end of the recommended range.

As with most things concerning boats, there are a number of tradeoffs to be considered, but you will be able to make things work well if you do a little homework. Let us know what motors you have and we can offer more advice.

 

[QC]

Re: If I have twins and one dies.....

If she'll run 30 on one she'll definitely run 20 or 25 on one . . . Many think this is a lug condition, and although it has more load on it at say 3500 RPM than recommended, it is still less load than at 4300 and 30 MPH . . . Propeller load curves are almost linear, there is no hump, so when you back off at all, you are out of a lug condition, so probably much better than keeping her wide open at below the recommended WOT RPM.

I have to add that I am not a 2 Cycle expert by any means, but . . . I guarantee that there is less load than at WOT if you back off some once you are on plane.

jay's assesment is a good conservative one, especially if you are a long way out . . .

 

[Fl_Richard]

Re: If I have twins and one dies.....

150 Johnsons- 1995 - They do run 5800 WOT with both running on a plane. With only one it maxes out at 30-32 MPH and 4300 RPM -

So to get back today... if I run one at 3600 and 26 MPH I'm OK?

 

[QC]

Re: If I have twins and one dies.....

So to get back today... if I run one at 3600 and 26 MPH I'm OK?

Weeelllll, uh, I thought this was a theoretical situation . . . If you are asking if I would try it? Definitely, but it's not my wallet and life we're talking about . . . I guess I'd slow even a little more, as long as she's on an efficient plane, then slower is less load.

 

[Fl_Richard]

Re: If I have twins and one dies.....

Thanks QC

I know many posts here usually involve boats that are improperly propped and wont reach maximum rpm. These peopels engines dont seem to die in a trip or ten moreso long term damage from lugging. Is lugging something you never want to do or something you never want to do for a long peroid of time?

I always assumed it was a dont do it for or a long period of time kind of thing.

 

[jay_merrill]

Re: If I have twins and one dies.....

In most cases, I think its more of a long term problem than a short term problem. To me, this is true because the motor involved, is usually not so overpropped that it is being worked to a point of overheating, in the short term.

You should check your manual, or talk to your OMC/BRP technician to be sure, but I think your recommended WOT range is 5,000 to 5,500 rpm. Since your are running at 5,800 WOT with both engines, you are already slightly under-propped. If the boat were mine, I wouldn't run it over 5,500 for a couple of reasons, First, because the extra 300 rpm aren't going to push the boat much faster, and second, because you will get much better fuel economy by backing off the motor a bit.

In smooth water, you could probably get away with running on plane with one engine, and could probably back off in the way that QC mentioned. If you do this, just pay attention to engine temperature. I also wouldn't do it frequently, or for very long distances.

Where I think you will run into difficulty, is in single engine operation in good sized seas. At 4,300 rpm, you are quite a bit below minimum recommended WOT rpm. This will give you essentially no reserve in terms of torque, and every time you have to push throuh a sea, you will most likely come off plane. The constant cycle of doing this, could stress the engine to some degree. As to how much of an unacceptable stress that might be, I would defer to the experts on the matter.

 

[HighTrim]

Re: If I have twins and one dies.....

You should check your manual, or talk to your OMC/BRP technician to be sure, but I think your recommended WOT range is 5,000 to 5,500 rpm. Since your are running at 5,800 WOT with both engines, you are already slightly under-propped. If the boat were mine, I wouldn't run it over 5,500 for a couple of reasons, First, because the extra 300 rpm aren't going to push the boat much faster, and second, because you will get much better fuel economy by backing off the motor a bit.

Im going to have to disagree, 5800 RPM WOT is perfect, not underpropped at all. Those loopers hate being lugged, and have heard Dhadley reccomend 5800 RPM minimum. You will do much more damage running her at 5-5500 RPM WOT.

Better fuel mileage comes from backing off the throttle once on plane, I would not look to changing the WOT RPMS for that.

 

[jay_merrill]

Re: If I have twins and one dies.....

I know that maximum WOT rpm is a matter of opinion. Some say run them higher, some say not too. That said, if the info that I found on his motor is correct (5,500 max WOT), he is under-propped by the manufacturers specifications.

Since his motors are long out of warranty, and some with expertise say that running the motors higher is OK, he may choose to do so. I would not recommend that a person with in-warranty motors, run them over max specified rpm, however, since they will most likely have memory chips in them. You can bet that anyone who does, and ends up with major engine problems, is going to have warranty problems too.

One other point is that, in this case, I wouldn't recommend going to less pitch on the props. Why? Because he is already a bit under-propped by OMC specs, and mounting props with less pitch will push up into the 6,000 - 6,200 rpm range, depending whether he went down an inch or two inches. In single engine operation, he would get much better performance, but the old question of trade-off rears its ugly head in this scenario.

 

[Randybeall]

Re: If I have twins and one dies.....

If you are speaking of a need to get to home port then make the best of the situation. If it is possible, raise the dead engine to eliminate drag. Will the boat get up on plane with one engine? If so run it up on plane and back off the throttle to keep it there, don't run wide open just keep the boat on plane for efficency. If necessary move weight in the boat to keep the best plane/cruise speed possible. You want to minimize drag on the single engine. I would think about adding a small amount of oil to the fuel mix on a two stroke to offset the additional heat and load of slight lugging. Watch engine temp, it will be your warning of any excess loading. Trim the engine carefully to avoid getting the water pick up too high. Hope the dead engine is not too hurt. Happy boating!

 

[tashasdaddy]

Re: If I have twins and one dies.....

ideal situation is it borrow a prop, that will turn up near recommended WOT.

 

[jay_merrill]

Re: If I have twins and one dies.....

One thing that I neglected to mention ... if you don't have trim tabs on the boat, this might be a good reason to get them. Lots of folks here like Smart Tabs, which are both relatively inexpensive and efficient. With the right setup, you might find that you can hold your boat on plane with less power, thus reducing load on the remaining engine.

 

[cdnfthree2]

Re: If I have twins and one dies.....

My OEM 150 manual says 4500-5500 WOT range. Of course everyone says you should be at the top of that range. I can get 5600 out of it. Some here say 5800-6000. Why, I don't know.

 

[jay_merrill]

Re: If I have twins and one dies.....

My OEM 150 manual says 4500-5500 WOT range.

Very interesting info because it means that the OP is running pretty close to minimum WOT when on single engine. I think that changes the view of this quite a bit. He should be able to come to plane, back off the throttle a bit, and run in to port without hurting his engine. This may be especially so if trim tabs are used.

 

[tashasdaddy]

Re: If I have twins and one dies.....

the reason for the increase rpms, is with the crappy fuel we now have the engines run better and cooler at the higher rpms.

 

[F_R]

Re: If I have twins and one dies.....

Lugging, combined with crappy fuel or lean fuel/air mixtures, invites pre-ignition and detonation. The fuel/air charge is supposed to burn at a controlled rate. During detonation, it goes off more like a bomb by comparison and before the piston is at the correct ignition position. That leads to high combustion temperatures and blown pistons and rings. If it happens, it can happen in just minutes. High combustion temperatures are not necessarily detectable by higher overall engine temperatures. More oil won't help that situation either.

I agree, in the question at hand, unless it is a life or death situation, just back off on the throttle a bit on the running one engine and come back home. If the boat can't be operated with the dead engine tilted up, it should be. Get that problem resolved before you need it.

 

[HighTrim]

Re: If I have twins and one dies.....

My OEM 150 manual says 4500-5500 WOT range. Of course everyone says you should be at the top of that range. I can get 5600 out of it. Some here say 5800-6000. Why, I don't know.

As Tash stated, that may have been true, in '95, although the lower end of that range is pretty low, but with todays fuels 14 years later, and all the other reasons mentioned, the upper end of that range has been increased. This increases the longevity of your outboard. This number is also while under a normal load. It is not really feasible for Johnson/Evinrude to recall all of the Service Manuals to change that information

 

[jay_merrill]

Re: If I have twins and one dies.....

I agree about the service manuals, but I am wondering if there have been any service bulletins recommending higher rpm limits.

 

[slasmith1]

Re: If I have twins and one dies.....

every twin engine operation manual I have read specifically tells you not to attempt to plane the boat on 1 engine as it is off center, dragging a dead prop. (from the other eng) and can cause unsafe handling issues but its your wallet and life.

 

[QC]

Re: If I have twins and one dies.....

Inboards, yes, but OBs???? Tilted out of the water?