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Old 05-11-2013, 18:15   #76
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Re: How well do cats motor on one engine?

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Originally Posted by colemj View Post
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.

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This is exactly the same for me as long as we are using main and jib.

Another point, at least for us, is that we don't use our main when trying to point into the wind, but rather the jib. We need 30 degrees plus apparent for the main to add any speed. The jib adds between 1 to 1.5 knots at 25 to 30 degrees.
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Old 05-11-2013, 18:26   #77
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Quote:
Originally Posted by Palarran View Post
This is exactly the same for me as long as we are using main and jib. Another point, at least for us, is that we don't use our main when trying to point into the wind, but rather the jib. We need 30 degrees plus apparent for the main to add any speed. The jib adds between 1 to 1.5 knots at 25 to 30 degrees.
Motorsailing, right? Pointing ability is provided by the engine, and the main can handle a closer angle except may be a high aspect jib sheeted centerline.

Without engine, you need the jib plus a wider angle to sustain speed. Try it out using the VMG reading on the instruments, because it can feel counter intuitive because you can do better VMG with a lower STW.
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Old 05-11-2013, 18:43   #78
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Re: How well do cats motor on one engine?

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Originally Posted by Palarran View Post
Another point, at least for us, is that we don't use our main when trying to point into the wind, but rather the jib. We need 30 degrees plus apparent for the main to add any speed. The jib adds between 1 to 1.5 knots at 25 to 30 degrees.
That is the opposite case for us. We have a camberspar jib with internal wishbone that is sprung tight like a windsurfer sail, so it maintains a good shape in all wind directions. However, even this good shape sheeted into trim to the wind angles we would motor sail at, it backwinds the luff of the main. When the slot is opened more so the main has more power, the jib stalls in the wind.

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Old 05-11-2013, 19:30   #79
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Re: How well do cats motor on one engine?

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Originally Posted by colemj View Post
That is the opposite case for us. We have a camberspar jib with internal wishbone that is sprung tight like a windsurfer sail, so it maintains a good shape in all wind directions. However, even this good shape sheeted into trim to the wind angles we would motor sail at, it backwinds the luff of the main. When the slot is opened more so the main has more power, the jib stalls in the wind.

Mark
I guess we all have little idiosyncrasies with our cats. My jib is a relatively small self tacking.
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Old 07-11-2013, 01:29   #80
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Re: How well do cats motor on one engine?

Seems intuitive to me that running the windward engine would correct weather helm when motorsailing allowing less rudder drag through a reduction in rudder angle. This is assuming there is weather helm, and there is no cavitation.

Since running on one engine is so common, has anyone bothered to optimise the gear ratio and props for running on one?

It may reduce top speed with both engines running, but doing this may provide more thrust when motoring into chop and wind on both which appears to be the only time most people use both engines anyway?
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Old 07-11-2013, 06:56   #81
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Re: How well do cats motor on one engine?

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Since running on one engine is so common, has anyone bothered to optimise the gear ratio and props for running on one?
I mentioned in a thread here somewhere that you can set up saildrives as counter-rotating. These are usually set as outward rotating, but if set up as inward rotating instead, the prop walk from either will counteract the rudder necessary when running on one engine.

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Old 11-11-2013, 11:04   #82
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Re: How well do cats motor on one engine?

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Now that there seems to be consensus on the fuel consumption I have another question. When maneuvering in close quarters (ie parking) how much is done via the engines (ie throttles) and how much via the helm? I'm guessing 80% throttles when pulling alongside?
In close quarter maneuvering you use the throttles exclusively (i.e. 100%). This applies to power cats as well as sailing cats and indeed twin engine monohull powerboats (but not single engine monohull sailing boats), with the proviso that the engines have a certain amount of lateral seperation and counter rotating props help a lot. Rudders are only effective in turning a vessel when there is water flowing past them; the faster the water flow (higher boat speed through the water), the quicker the boat turns via rudder action. In close quarters, for example whilst docking or anchoring/weighing anchor, there is little way on, so the rudders will have neglible effect. You will have much greater control by splitting the engines.
This is one of the great advantages of cats with twin engines. You can literally spin the boat to port or to starboard, forward or astern, on the boat's axis by splitting the throttles. You can let go of the helm whilst your two hands are working the throttles, again with the proviso that a hard engine burst astern will kick the wheel (or tiller) violently, so watch out for that or engage your wheel lock. Personally, I hold the wheel steady with my left hand or my knee, whilst operating the throttles.
This really helps when weighing anchor in strong wind also.

In fact, many professional power boat captains with twin engine vessels and counter rotating props rarely use the wheel at all.
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Old 11-11-2013, 12:24   #83
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Re: How well do cats motor on one engine?

Hello vanWell and welcome to the cruisers forum. That was a good explanation of using twin engines with a cat. I would add that there are times that use of the helm is advantageous in close quarters with no or low headway. The prop wash past the rudders can act like a stern thruster and helps push you off the dock. Also, when doing a full rotation, turning the rudders will assist in the turn, making it quicker and tighter.

I'm personally not fully skilled with the use of rudders while maneuvering in tight spaces but have witnessed two pilots who where. What they could do with the 1450 square foot platform of Palarran in a very small dock space filled with boats and 20 knots of wind blowing amazed me. One thing I noticed and have copied is power bursts verses a gradual ramping of the throttle. When they wanted to turn the boat, it was a full commitment.
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Old 11-11-2013, 13:09   #84
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Re: How well do cats motor on one engine?

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Originally Posted by Palarran View Post
Hello vanWell and welcome to the cruisers forum. That was a good explanation of using twin engines with a cat. I would add that there are times that use of the helm is advantageous in close quarters with no or low headway. The prop wash past the rudders can act like a stern thruster and helps push you off the dock. Also, when doing a full rotation, turning the rudders will assist in the turn, making it quicker and tighter.

I'm personally not fully skilled with the use of rudders while maneuvering in tight spaces but have witnessed two pilots who where. What they could do with the 1450 square foot platform of Palarran in a very small dock space filled with boats and 20 knots of wind blowing amazed me. One thing I noticed and have copied is power bursts verses a gradual ramping of the throttle. When they wanted to turn the boat, it was a full commitment.

Hi Palarran,

Thank you for the welcome. Your comment regarding prop thrust deflected off the rudders to assist in kicking the stern is spot on. However, on some modern cats with sail drive legs (my L440 is an example), the sail drive leg & prop is positioned aft of the rudders so this doesn't work in my case. And of course, in the more conventional & traditional arrangement of prop forward of rudders, it works well, but only in forward gear of course, since astern thrust is projecting forward and therefore rudder position is irrelevent.
This is where monohulls can use prop walk in astern to 'paddle wheel' the stern towards the dock, when approaching port side to (if you have a right handed prop, which is the most common configuration).

Yes, watching competent professional skippers dock & manoeuvre large vessels is always good to watch. And indeed, sustained & consistent power bursts usually works better than cycling the throttle. I also like docking large monohull sailing boats without bow thrusters. In this case, use of way and the lateral resistence of the keel, prop walk, plus turning wind and current into an ally rather than a foe, is a commitment you need to enter with confidence. Ha! Ha!
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Old 11-11-2013, 13:14   #85
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Re: How well do cats motor on one engine?

Quote:
Originally Posted by dennisail View Post
Seems intuitive to me that running the windward engine would correct weather helm when motorsailing allowing less rudder drag through a reduction in rudder angle. This is assuming there is weather helm, and there is no cavitation.

Since running on one engine is so common, has anyone bothered to optimise the gear ratio and props for running on one?

It may reduce top speed with both engines running, but doing this may provide more thrust when motoring into chop and wind on both which appears to be the only time most people use both engines anyway?
There have been a number (a small number) of custom built cats built with one large motor one side and a smaller motor the other the large motor running the water maker, big alternators etc, and the small one used for manoeuvring. There has been one that I know of, with one inboard motor and one outboard.

Quote:
Originally Posted by Palarran View Post
Hello vanWell and welcome to the cruisers forum. That was a good explanation of using twin engines with a cat. I would add that there are times that use of the helm is advantageous in close quarters with no or low headway. The prop wash past the rudders can act like a stern thruster and helps push you off the dock. Also, when doing a full rotation, turning the rudders will assist in the turn, making it quicker and tighter.
Very true, this is useful even when still tied, up, when you are laving a dock tied side to and stern in, you can take all the lines off except the aft dockside one and have the engines idling forward to keep the boat from moving around, turn the wheel to port and the bow will go to port, and starboard for starboard, useful when you want to get the stern closer for people to get on/off or to "aim"the boat for the departure.

Of course this only works if the rudders are behind the props, there are a few boats where the props are behind the rudders.
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Old 11-11-2013, 14:18   #86
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Re: How well do cats motor on one engine?

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And indeed, sustained & consistent power bursts usually works better than cycling the throttle.
Actually, my observations where the opposite. Instead of 30% throttle for 10 seconds, they give it 90% for 4 seconds (example). This is for maneuvering, not making much headway. The first time I experienced this it was "WTF are you doing?" which quickly turned to "Oh, that's how it's done"
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Old 27-12-2013, 12:03   #87
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Re: How well do cats motor on one engine?

my catalac 10m cruises also at 7 knots on the one volvo d1_30 engine, at 2700rpm under normal conditons, with which i mean not against current wind or wave direction. It is of course good to note for novices that the autopilot when working correct will compensate nicely for the proppeling from starboard or port on a cat. I must say i am surprised Capt Bill's cat, is it not a 40 foot diesnt cruise faster than my short old cat on one engine.
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Old 27-12-2013, 23:10   #88
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Re: How well do cats motor on one engine?

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Originally Posted by Goosebumps View Post
my catalac 10m cruises also at 7 knots on the one volvo d1_30 engine, at 2700rpm under normal conditons, with which i mean not against current wind or wave direction. It is of course good to note for novices that the autopilot when working correct will compensate nicely for the proppeling from starboard or port on a cat. I must say i am surprised Capt Bill's cat, is it not a 40 foot diesnt cruise faster than my short old cat on one engine.

My cat has very inefficient feathering props. Reportedly the original props (folding) were about a knot faster. The original owner put on the feathering props so I can't testify to this my self. Then again I have a good positive reverse on both engines which he reported to be problematic with the stock props.
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Old 28-12-2013, 02:56   #89
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Re: How well do cats motor on one engine?

thanks cap Bill, it is very important to mention the props, and have the right props for the right purpose, engine and sail drive. I have fixed two blade props and find that they do well for my sail cat. If it would be power cat ofcourse three fixed blade would be much more power efficient but would cause drag on sail yacht.
Your privilege cat is my personal dream cat, but i settled for what incan afford, my catalac 10 m, as gunkholer very commendable, capable of passage making, and comfortable living space. It is important to note that for a couple, or individual a 10m cat with reasonable interior space and proper rigging is more than sufficient in size and much cheaper to maintain, compare 15 liter bottom paint for my cat, and 60 liters plus needed for 40 foot cat.
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Old 28-12-2013, 03:23   #90
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Re: How well do cats motor on one engine?

I read some posts which compare fuel consumption for number of engines used ...

I have done extensive research on our vessel now having covered 2 years at sea over large distances (Cape Town to Raiatea) and must say I have found the following link to be exceptionally accurate. I like statistics ... especially the ones I have tested for our specific environment ... you may find the web below helpful ...

www.twixter.us/docs/Performance%20Worksheet.xls‎

www.twixter.us/docs/Performance%20Worksheet.xls‎


When we powersail .. only ever one engine and at slower speeds. On the Yanmar cone clutch saildrives I have a hunch that a prop ticking over when wind propulsion is higher than that of power causes resistance on the prop and wears the cone clutch pack. As I say ... a hunch ... and I certainly am getting more hours out of my cones applying this theory.
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