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A question about prop rotation on twin engine setups?

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Old 07-15-2003, 04:20 PM
  #11
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Quote:
Originally posted by mr_velocity
I think you have that backwards. Turning in will lift the bow, turning out will lift the stern.
Quote:
Originally posted by mr_velocity
Isn't that props turning out?
O.K. With this much misinformation, I think we need to "poof" this thread and start over.
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Old 07-15-2003, 04:22 PM
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Just to clarify, props turning in, is starboard spinning clockwise and port spinning counterclockwise when in foreward gear
Nope, that's out.

I've found some boats like inside rotation,
some don't.
I didn't think .1 mph on my boat was
worth the sh*tty docking manueverabilty,

Sometimes you just got to try switching them,
to see how they work.

If you have bravo's, switch the prop's,
run the shifters backwards,
alphas, TRS, SSM's, swap drives.

jt
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Old 07-15-2003, 04:46 PM
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Mine spin in and Yes docking is tuff but to me it's worth it on my hull it makes a huge difference in bow lift and of course speed.

On My Hull in = Bow lift
Out = Stern lift

O.K. now you can poof this thread

If you are by yourself and no one is looking cup your hands and spin them in see how you are pulling down the stern now try it the other way you are lifting




































LMAO ,all you guys looking over your shoulder to see who's watching
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Old 07-15-2003, 05:03 PM
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Both of my Spectre's were set up to turn inbound. I have not seen any problem docking. It must be different on cats.
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Old 07-15-2003, 05:13 PM
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Scott:LMAO ,all you guys looking over your shoulder to see who's watching

If I had a big boat I wouldnt have to look over my shoulder at all........I mean hell, a blind guy can drive their boat in a straight line, straight up and into to the FRONT ROW!!
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Old 07-15-2003, 05:23 PM
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O.K. Wheeling out the chaulk board (now pay attention)

You are sitting at your desk or what ever and you are spinning your arms around like props. You now look over your shoulder to make sure no one saw you acting like your crotch was on fire
It had nothing to do with driving the boat
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Old 07-15-2003, 05:24 PM
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If you are looking at the transom and the port side prop turns to the left and the starbord side turns to the right this is "OUT". If the port prop turns to the right and the starbord to the left that is "IN".

On my Scarab I had to swap drives to have my props turn in, it carries the boat better with 1-2 mph in top end. It is not the best set up for rough water. If the boat exits the water leaning to one side the torque from the prop tends to make the boat land on it's side. I also have less cavitation getting on plane with the props turning in.

With the props turning out the boat was much more predicable in rough water. The only reason I have mine turning in is the bow would always get pushed down at full throttle. Buy turning them in I was able to carry the bow better giving me more speed.
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Old 07-15-2003, 05:35 PM
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I stole this recent post from elsewhere so I made sure the person's post name is not displayed (out of courtesy). He'll discuss if he chooses. Anyway, his experiment was on a 32 Sunsation. Conventional wisdom says it's best all arounsd to leave'em out but there are a few hulls that can tolerate spinning in....Enjoy
==================================
Spin In vs. Spin Out:

Over the weekend I had a chance to do some serious testing of spinning the props on my 32' Sunsation outwards, verse inwards. Here are my thoughts:

I've always run my boat with the props spinning out (port prop spinning CCW, starboard prop spinning CW). This is the way the factory setup, and recommended, this boat for optimum driving. However, there has been talk that spinning the props in could potentially yield a mph or two in top speed.

I decided to give the old theory a try this past weekend up in Lake **** Michigan. It was a good day for boating; very small wind chop out on the lake, slight 5 mph (or less) breeze out of the West and a dry 75 degree air temperature. I decided to start off my trials by spinning the props in, then switching back to the original outwards rotation for an immediate comparison.

First impressions of spinning in... docking sucks! If one motor is engaged forwards, having the other the other motor in reverse doesn't do a damn thing. Might as well leave it in neutral. I quickly had to relearn docking procedures for a single engine boat... since using both motors would just get me into trouble. Nevermind the fact that the I never reversed the shifter cables (i.e. back = forwards movement, forwards = back movement).

Getting on plane was no problem at all. However, I've never had a problem getting on plane before. The Bravo 32' four blades have an awesome hole shot in my boat, so it was difficult to tell any difference in planing time. One "cool" factor about getting on plane with the props spinning in was the sweet looking "tail" that was getting thrown up while putting the boat up. About 50 feet behind the boat, a nice 5 foot high tail was getting thrown up. Once on plane, the tail was reduced to almost nothing. At about 70 mph though, you could see the tail starting to kick up again, but it was only about 2 or 3 feet.

Once up and running, the boat felt REALLY loose with the props turning in. The bow was much higher and the whole boat was much more effected by trim position. It almost felt like the "moment arm" of the prop thrust vector was a lot lower in respect to the center of gravity of the boat. Three top speed runs resulted in an average speed of 87 mph at 5200 - 5300 rpm (I"ll explain the slow speeds later).

I headed back to the docks and switched the props back to the original "spin out" configuration. I immediately noticed a difference. The boat felt as if it was "lower" to the water when running. Also, the prop wash at speed was noticeably wider with the props turning out (water skiing = props in). The hull felt more "glued" to the water and didn't feel quite as loose as it did with the props turning in. Three more top speed runs with props out yielded an average speed of... get this, 87 mph at 5200 - 5300 rpm.

Nope, no difference in speed what so ever!

However, I was running a few mph off my normal mark. Let me explain. Last week etc. etc..............deleted long non-topic items...............I'm really hoping that this is what caused my decrease in top speed... because I know I didn't just spend big bucks to have my props lab finished so I could drop 4 - 5 mph!!!

Anyway, moral of the story is that I didn't see a big enough difference in speed to justify keeping the props spinning in. If the boat was heavier and needed more trim... maybe. Until then, I'll enjoy the extra stability of spinning the props out.

ANONYMOUS BOATGUY
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Old 07-15-2003, 07:26 PM
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for planing....I thought we figured out this at cleveland in the january?
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Old 07-15-2003, 07:54 PM
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X dimesion is a big factor in considering to turn out or in. In our old sonic with deep ssm#3's turning in got the boat real loose and docking it was terible.
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