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Old 25-10-2013, 09:42   #46
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Re: How well do cats motor on one engine?

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Originally Posted by markpierce View Post
Found having a rudder indicator a worthwhile investment.
Yes, of course, that is how I know our offsets. Rudder indicators are standard with autopilots.

Mark
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Old 25-10-2013, 14:04   #47
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Re: How well do cats motor on one engine?

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Yes, of course, that is how I know our offsets. Rudder indicators are standard with autopilots.

Mark

The previous owner set the rudders dead amidship and then wrapped some tape around the wheel at the 12:00 position. It works for me.
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Old 25-10-2013, 14:20   #48
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Re: How well do cats motor on one engine?

I put some loop side of velcro at the TDC on the wheels, its soft to touch and it its easily felt in the dark (I have a rudder indicator - but looking at - or indeed feeling - the velcro is quicker
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Old 25-10-2013, 14:39   #49
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Re: How well do cats motor on one engine?

I made a Turk's Head from light black cord for our TDC.

Mark
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Old 25-10-2013, 16:36   #50
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I have nothing to say. All you other cat people have already said it all. And we all agree. Actually, It is fantastic to see such a beautiful consensus without any bitching - ok, ok, apart from from one lone mono bloke who interceded briefly.
I've sailed cats, no worries
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Old 25-10-2013, 16:38   #51
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Next round is on Nick! And just coming out of Colorado, he should be serving some good beer! Mark
We're into cocktails lately, don't you follow it on your secret facebook account ?
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Old 25-10-2013, 16:57   #52
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Re: How well do cats motor on one engine?

Well you were the one who bet a beer...

Mark
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Old 25-10-2013, 18:29   #53
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Re: How well do cats motor on one engine?

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This was standard on Manta's - I don't know about others, but for Volvo saildrives it is only a matter of switching the shift cable attachment to the other side of the shift lever and using a different-handed prop.

If you have fixed props now, that is contributing a lot to your helm offset because that prop is responsible for 0.5kts of drag on that side that must be compensated.

Mark
Thanks for the info. I can't believe I haven't read about this before. Definitely something to think about. I'd put new feathering props on now but the $10k is prohibitive given the amount of motoring we are doing.
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Old 25-10-2013, 19:58   #54
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Re: How well do cats motor on one engine?

10K is a lot - folding props should be half of that or less (the last Volvo folders we bought were 1K each).

Only saildrives with identical reverse and forward gear ratios, as well as thrust bearings, etc can be reversed. Volvos are, but I don't know about Yanmar.

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Old 25-10-2013, 20:19   #55
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Re: How well do cats motor on one engine?

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Originally Posted by colemj View Post
10K is a lot - folding props should be half of that or less (the last Volvo folders we bought were 1K each).

Only saildrives with identical reverse and forward gear ratios, as well as thrust bearings, etc can be reversed. Volvos are, but I don't know about Yanmar.

Mark
Yanmars can be reversed as well. The shift lever on the drive has two holes, one marked CW and the other marked CCW you can choose which ever one you want to use. The Autostream props I have can also be set for left or right hand rotation.
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Old 25-10-2013, 20:53   #56
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Re: How well do cats motor on one engine?

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Originally Posted by colemj View Post
10K is a lot - folding props should be half of that or less (the last Volvo folders we bought were 1K each).

Only saildrives with identical reverse and forward gear ratios, as well as thrust bearings, etc can be reversed. Volvos are, but I don't know about Yanmar.

Mark
I don't have enough clearance between my rudder and shaft for folding props. I found that out the very hard way when I bought two flexofolds, had the boat hauled to put them on, then had to pay to have them shipped back to Denmark and pay a restock fee. Like holy crap should the diver have taken better measurements!!!

Maxprops are $5k each.

Sorry but I'm not an expert on this. Can you explain what I'd want. Like counterclockwise on port and clockwise on starboard?
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Old 25-10-2013, 21:31   #57
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Re: How well do cats motor on one engine?

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Sorry but I'm not an expert on this. Can you explain what I'd want. Like counterclockwise on port and clockwise on starboard?
No. The opposite.
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Old 26-10-2013, 08:47   #58
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Re: How well do cats motor on one engine?

Outboard rotation makes the stern walk in the expected direction when in reverse. Also, when steering with two engines, their prop walk works with each other in turning. For this, it would be CW on starboard and CCW on port. Most counter-rotating setups on catamarans are this way.

Inboard rotation takes out most of the rudder correction required when running on one engine. This would be CCW on starboard and CW on port.

So it depends on what you want to take advantage of. Ours is set up like the first example because we like to use the prop walk to our advantage in slow, tight maneuvering situations. Our helm correction with this setup when operating on a single engine is minimal, so the second example is not really needed.

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Old 31-10-2013, 12:05   #59
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Re: How well do cats motor on one engine?

A couple of observations:

1. If your cat has hydraulic steering and an autopilot (or a below deck hydraulic autopilot) you must have a rudder position indicator in order for the autopilot to function. A very useful tool, as has been pointed out, for calculating the amount of steering offset required in various conditions under power, or sail (including changes in weather helm). It is also useful in harbour as, with steering that requires more than one turn lock to lock, it will unfailingly tell you the position of your rudder on start-up; centerd tape on the wheel, however, will be centered on each turn of the wheel and not only when the rudder itself is centered.

2. When motoring, I too typically run only one engine. In all but strong headwinds/seas, I am able to maintain hull speed on one engine while keeping the engine in the 'sweet spot'. We must also bear in mind that diesels are less efficient at very low RPM's and moreover, that there is a greater tendancy towards carbon with an unloaded engine. Most modern diesels, including my Yanmar 3 GM30's, are most efficient in a range of approximately 2200 to 2700 RPM's, keeping in mind a maximum of 3500 RPM's.

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Old 31-10-2013, 12:12   #60
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Re: How well do cats motor on one engine?

Non-hydraulic steered boats with autopilots also have rudder position indicators. Those AP's need it to function too. Many of the indicators are now completely separate and simply feed data onto the network bus for all instruments and displays to use.

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