How well do cats motor on one engine?

[Canibul]

we brought our catamaran from Jacksonville FL to West Palm via the ICW, then across to West End, GBI and then made our way down to Providenciales. We had just bought this 27 year old boat that had been floating in the river for years on the hook. We had a lot of problems. During the 40 days it took us to get the boat home, We logged less than 48 hours on two running engines. Holding in wind and current in the canal for the drawbridges, and pulling into a strange marina every few nights on one engine got to be routine. There are some techniques to use maneuvering at slow speeds on one engine. The steering works a lot differently, but it can be done. Use the wind, and current, and plan everything out. It's like backing a trailer, it goes well if you get it right the first time. Half of our marina tie ups were dead stick landings. The one engine that was running fairly well would not run above 1800 RPM, and often died at idle. If you haven't handled your catamaran in slow maneuvering on one engine, It might be a good idea to try it. Turning toward your good engine is difficult. I had some success in using the working engine to build up a little extra speed, enough to carry me through a turn, and then putting the engine in neutral and letting the rudders steer the boat.

[Southern Star]

As I said, colemj, if a boat has a hydraulic below-deck autopilot it will also have a rudder position indicator (regardless of the type of steering system); if it does not have hydraulic steering and has a wheel pilot, it will not; if it has a hydraulic steering system then it must also have a rudder position indicator regardless of the type of autopilot.

Brad

[AquaLeopard40]

I agree with these posts, I go from 7.2 knots to 6 knots on one engine and unless beating uphill usually power on one. Less fuel, less wear and tear.

[skipperadam]

Making the move to a Cat in the next year or so after dozens of years on monos, so forgive an easy question.

I've not seen in the thread the decision process for which engine of the two to run.

I don't believe that the dual engines are set with counter rotating props as big twin screw power boats and airplanes are. (Perhaps I'm wrong). I'm not sure the propwalk/wash is a factor on these little tractor motors once there's water flowing past the rudder so I don't know what criteria one uses to choose which engine to use. I think balancing the two by hours is ideal from a maintenance perspective but would one consider the point of sail?

My gut tells me to run the leeward engine if motor sailing as it was mentioned above it might be hard to turn into the running engine, and a little weather helm would fix that.

Suggestions?

Live slow and sail fast.

Adam

[monte]

no and yes, its better to run for longer than 2 hrs per engine. In my view more wear is created from starting/heating/cooling/stopping than actual engine hours. I would split the forecast motoring time in 2, unless its a short trip then just use one.
As far as which engine to use, usually if there is enough wind to motor sail, one engine will give a better angle of attack than the other. ie if the wind is from the starboard bow, motoring with the leeward engine will force the bows to leeward and give a better sailing angle

[Cotemar]

Originally Posted by skipperadam

Making the move to a Cat in the next year or so after dozens of years on monos, so forgive an easy question.

I've not seen in the thread the decision process for which engine of the two to run.

I don't believe that the dual engines are set with counter rotating props as big twin screw power boats and airplanes are. (Perhaps I'm wrong). I'm not sure the propwalk/wash is a factor on these little tractor motors once there's water flowing past the rudder so I don't know what criteria one uses to choose which engine to use. I think balancing the two by hours is ideal from a maintenance perspective but would one consider the point of sail?

My gut tells me to run the leeward engine if motor sailing as it was mentioned above it might be hard to turn into the running engine, and a little weather helm would fix that.

Suggestions?

Live slow and sail fast.

Adam

In most cases you can run a catamaran on one engine If:
1) You have the higher HP upgraded engines the manufacturer recommended
2) You have folding or feathering props, so the engine that is off is not dragging
3) You run any engine you want whenever you want keeping the engine hours close to the same
4) No need to worry about counter rotating props as you’re only using one engine
5) No need to worry about prop walk as it’s not noticeable
6) Set the auto pilot and your rudder will show a slight steer toward the running engine

[s/v Jedi]

If you're motorsailing upwind then furl the jib, put the main tight midships and run the leeward engine. This will make you point (much) higher.

[colemj]

We find running the leeward engine when motorsailing upwind causes weatherhelm (well not really, but the same practical effect) requiring too much rudder compensation. Conversely, running the windward engine removes all weatherhelm and lets us point higher and faster. Which engine is run doesn't really effect the pointing angle because you are using the motor to achieve that either way.

Mark

[s/v Jedi]

Originally Posted by colemj

We find running the leeward engine when motorsailing upwind causes weatherhelm (well not really, but the same practical effect) requiring too much rudder compensation. Conversely, running the windward engine removes all weatherhelm and lets us point higher and faster. Which engine is run doesn't really effect the pointing angle because you are using the motor to achieve that either way. Mark

Time to test that by monitoring VMG on your Tritons I hope you will be buying the drinks haha

[colemj]

Well, as a thought experiment, it doesn't matter which engine you run on Jedi - the pointing angle is the same . Now move that engine 6' off to one side and your rudder will compensate for it by 2-3* and you will still point just as high regardless of which side you move it to. You can't go any higher than straight into the wind.

If you are pointing with the leeward engine such that the weather helm is causing 15* of rudder compensation, then removing that drag by using the windward engine to balance it will allow you to pick up some speed and not fall off your pointing angle.

So what am I missing here?

Mark

[s/v Jedi]

Originally Posted by colemj

Well, as a thought experiment, it doesn't matter which engine you run on Jedi - the pointing angle is the same . Now move that engine 6' off to one side and your rudder will compensate for it by 2-3* and you will still point just as high regardless of which side you move it to. You can't go any higher than straight into the wind. If you are pointing with the leeward engine such that the weather helm is causing 15* of rudder compensation, then removing that drag by using the windward engine to balance it will allow you to pick up some speed and not fall off your pointing angle. So what am I missing here? Mark

15deg rudder to counter weatherhelm and off center engine when motorsailing with jib furled and main sheeted in hard? What angle are you trying? I do this at 30deg true, 15deg apparent angle, in complete balance.

[colemj]

OK, maybe that isn't a good number or example. At 15deg app, we would be balanced also because most of the wind force would be off our sail.

I am just trying to wrap my head around why it would matter which engine is used? Both can point the boat just as high as I want and they only cause 3* of rudder correction.

Mark

[Cotemar]

Maybe it’s because a Sundeer 64 is long and slender with an engine on the centerline and the Manta 40 is a wide 21 foot beam by 40 foot long box.

The Manta 40 with one engine running is 18 feet from the other non-powered hull just dragging in the water.

A slight offset penalty from a Sundeer 64

[44'cruisingcat]

Originally Posted by colemj

Well, as a thought experiment, it doesn't matter which engine you run on Jedi - the pointing angle is the same . Now move that engine 6' off to one side and your rudder will compensate for it by 2-3* and you will still point just as high regardless of which side you move it to. You can't go any higher than straight into the wind.

If you are pointing with the leeward engine such that the weather helm is causing 15* of rudder compensation, then removing that drag by using the windward engine to balance it will allow you to pick up some speed and not fall off your pointing angle.

So what am I missing here?

Mark

You're missing the fact that this guy knows far more about your boat than you do.

[s/v Jedi]

Okay, so we established that there is no weatherhelm. Then running the leeward engine is the best option and a simple test by changing to the other engine at equal rpm while observing VMG will prove it... or not. Problem is when I win, there are now already three to buy me drinks and I might get drunk

Yes, one reason is that the leeward hull is submerged deeper, causing less cavitation for the prop. The other is that it will compensate for drift with as little drag from rudders as needed, increasing VMG again.

This is too easy to win, as using the other engine gives nothing that is better. May as well start deciding what drinks to order