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Old 07-11-2014, 23:40   #1
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Thoughts about propellors..

I know there is a dedicated prop forum, but cats have slightly different prop needs to mono's so I thought to ask here as I want to replace my props.

Higher sailing speeds tend towards folding/feathering, yet also needing lots of thrust.... especially in reverse for manouvering.

What props do folks have, and on what boats?
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Old 08-11-2014, 09:27   #2
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Re: Thoughts about propellors..

The only cat I have ever owned would definitely have been irritated with me if I had tied a prop to his tail, of any sort or size.
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Old 08-11-2014, 10:02   #3
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Re: Thoughts about propellors..

I would disagree with needing more thrust for maneuvering. With twin engines well separated, they start out far better than an equivalent single engine mono.
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Old 08-11-2014, 10:19   #4
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Re: Thoughts about propellors..

I had Max Props on my 42 ft cat. .. and many other boats. The thrust is superb in both reverse and forward. In reverse better than a stock fixed "sailor" prop is my impression.
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Old 08-11-2014, 10:23   #5
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Re: Thoughts about propellors..

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Originally Posted by GrowleyMonster View Post
The only cat I have ever owned would definitely have been irritated with me if I had tied a prop to his tail, of any sort or size.
Therein my friend lies your mistake...
You think you own the cat...

In fact it is the other way round.
The cat owns you S proven by you feeding it and giving it somewhere warm to stay .
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Old 08-11-2014, 10:27   #6
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Re: Thoughts about propellors..

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I would disagree with needing more thrust for maneuvering. With twin engines well separated, they start out far better than an equivalent single engine mono.
We have very little below the waterline and carry lots of windage wnen the wind is sideways on. Getting off a pontoon, or turning round when the wind is across you is very duifficult.
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Old 08-11-2014, 10:43   #7
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Re: Thoughts about propellors..

Yeah, it's a misconception that any cat will "caterpillar"... in strong winds it wont.
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Old 08-11-2014, 10:47   #8
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Re: Thoughts about propellors..

Just replaced the fixed props on my new to me cat. Went with 2-blade Flexofold folding for following reasons.

1, Cost. 2-blade folding as half the price of 3-blade folding. Even bigger difference to feathering. Kiwiprop is on par though, but not very efficient. Good reverse thrust though, but that's about it.
2, No maintenance. Given that I'm cruising I hope not to haul-out every year where feathering require yearly greasing
3, 2-blade vs 3-blade. Apart from cost, 2-blade is actually more efficient forward. 3-blade has more punch, but a cat has 4-blades (two engines) vs a mono so 2x2-blade should be OK. Only drawback, maneuvering.
4, Folding should be more efficient over feathering as the blades on the feathering has no twist. The folding has proper propeller blades.

In my view, there are two good 2-blade folding. Flexofold and Gori. Went with the first as it has a better locking mechanism.

Compared to the 2-blade standard Volvo fixed, the folding is better in everything, even reverse. I think the shape is better and the blades have bigger surface.

That was my logic and my priorities.
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Old 08-11-2014, 15:01   #9
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Re: Thoughts about propellors..

Sail iC.
Thank you for your thoughts. I have Kiwiprpos at the moment. As you say not very efficient and they also autorotate all the time. Probably because any tiny bit of fouling on one side is enlugh to stop the blades from simkly following the wateer flow. And to boot, they are far too deep pitch for anything powerful in reverse without enough smoke to hide the Nimitz!!!

Hence the question.
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Old 08-11-2014, 16:07   #10
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Thoughts about propellors..

When my ex bought her 45' cat it was equipped with Martec 2 blade folders.
We replaced them with Flexofold two blade folders. Much better performance, especially in reverse.


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Old 09-11-2014, 20:17   #11
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Re: Thoughts about propellors..

Have 3 blade flexofolds on a 44 ft cat.
Have been very happy with them for over 4 years.
Lots of power when we need it in reverse as well. Then good increase in sailing speed when they fold.
they came with my boat so have nothing else to compare them to
Good luck with whatever you choose.
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Old 09-11-2014, 22:20   #12
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Re: Thoughts about propellors..

You'll get MUCH better performance from a Max-Prop than you will even from fixed ones. And when it comes to getting off of end ties in a cross breeze (and other sticky situations), have you tried springing the boat with an overlength line? Such is one of the first manuvers I/we were taught in Naval ship handling. And it definitely works/is worth practicing.

I've done it with a 600' single screw steam ship, with LOTS of windage (in a 15kt cross breeze), & an engine & prop who's response time can be measured on a sundial, so... And this is when you've got another ship 40' both ahead & astern of you, who are just as wide as you are. Plus you CANNOT put any headway or sternway onto the vessel, as you've not the luxury of distance for stopping it before you ram your neighbors.

Springing lets you put enough of an angle between the longitudinal of your vessel & that of the dock, without moving fore & aft, until you can go full reverse or full ahead. Regardless of it being a one or twin screwed vessel. Just make sure to drop a couple of fenders between the hull & the dock, at the pivot point. And use an XL dockline, with both ends on your boat, not affixed to the dock at all.

As to turning around in strong winds, is kedging not an option? Particularly given a cat's width, I'd think that dropping a hook off of the bow or stern of one of the hulls would actually give you an edge over a mono in such situations.
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Old 10-11-2014, 01:22   #13
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Re: Thoughts about propellors..

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Originally Posted by UNCIVILIZED View Post
You'll get MUCH better performance from a Max-Prop than you will even from fixed ones. And when it comes to getting off of end ties in a cross breeze (and other sticky situations), have you tried springing the boat with an overlength line? Such is one of the first manuvers I/we were taught in Naval ship handling. And it definitely works/is worth practicing.

I've done it with a 600' single screw steam ship, with LOTS of windage (in a 15kt cross breeze), & an engine & prop who's response time can be measured on a sundial, so... And this is when you've got another ship 40' both ahead & astern of you, who are just as wide as you are. Plus you CANNOT put any headway or sternway onto the vessel, as you've not the luxury of distance for stopping it before you ram your neighbors.

Springing lets you put enough of an angle between the longitudinal of your vessel & that of the dock, without moving fore & aft, until you can go full reverse or full ahead. Regardless of it being a one or twin screwed vessel. Just make sure to drop a couple of fenders between the hull & the dock, at the pivot point. And use an XL dockline, with both ends on your boat, not affixed to the dock at all.

As to turning around in strong winds, is kedging not an option? Particularly given a cat's width, I'd think that dropping a hook off of the bow or stern of one of the hulls would actually give you an edge over a mono in such situations.
Thank you for your thoughts.
Indeed we do spring away when necessary. As you say it is a very useful tool in the box. With regards using the kedge.. I am not sure I am brave enough to try it in our local marinas when the wind is across the allyway which is only twice as wide as we are long..

So far we have two votes for maxprop and three for flexofold...
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Old 10-11-2014, 18:22   #14
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Re: Thoughts about propellors..

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Sail iC.
Thank you for your thoughts. I have Kiwiprpos at the moment. As you say not very efficient and they also autorotate all the time. Probably because any tiny bit of fouling on one side is enlugh to stop the blades from simkly following the wateer flow. And to boot, they are far too deep pitch for anything powerful in reverse without enough smoke to hide the Nimitz!!!

Hence the question.
Mine used to autorotate as well, until I replaced the blades with the new style which has a lip on the base to prevent this. No problems since. As for efficiency, they do not do badly in comparison testing. In the following test the Flexofolds did better, but were over-propped. You can over-prop your Kiwi's as well and might be worth a try if you feel they are not giving you enough thrust. The over-pitching in reverse just sucks and there's nothing you can do about it. What I'm getting at is that you may consider replacing your blades ($600) rather than new props ($3600)

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Old 10-11-2014, 22:49   #15
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Re: Thoughts about propellors..

Two blade max props. Seem to work very well on my boat. Excellent thrust in reverse and having them 20 feet apart makes docking or maneuvering in a confined space a breeze. If I ever have to dock a mono again I'm hooped!
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