A question about prop rotation on twin engine setups?
 

I have been wondering for a long time, with counter rotating props on twin setups, what are the advantages and disadvantages of the props turning in, or out:confused:

if they turn in it will give more stern lift, If they turn out more bow lift, turning in is are to dock sometimes less control

Much MUCH safer spinning OUT! Uh, where's T2x? He should be able to elaborate a little.:) You have the scenario backwards. Spinning in lifts the bow, out lifts the stern.

I think you have that backwards. Turning in will lift the bow, turning out will lift the stern.

On my Velocity I spin them in all the time, sorry T2x. However on the race boat it depended on the water conditions.

Out, stern lift
In, bow lift.
Docking manueverability is
poor when turning in,
( whichever one is in reverse,
doesn't seem to pull )

my .02
jt

OK, now I know why I cant dock worth a sh!t:rolleyes:
:eureka: I need to print this thread and take it to the marina where I hang out and show the dock boys....:crazy:

what would you guys reccomend on a 5k+ pound v hull with 21p 3 blade cleavers? in or out?? they are turning in right now and it seems to carry the bow very well, but docks sh!tty, could I gain anything besides docking ability by switching?? maybe planning easier:confused:

Just to clarify, props turning in, is starboard spinning clockwise and port spinning counterclockwise when in foreward gear.......or is it the opposite?

When looking at the boat from the transom, the starboard prop should spin CLOCKWISE and the port COUNTERCLOCKWISE! You are correct.

Isn't that props turning out?

Yep.
It's what the TOP of the propeller is doing.

That would be.....turning out....The TOP of the blades would turn inward to be turning in !!C,mon guys !!:D
I am about to try mine "IN"...I will be very suprised if this big heavy hull gets to loose !! I have been told i will need to dock like a single engine boat though....Hope to find out Wed. night..I will post what i find

O.K. With this much misinformation, I think we need to "poof" this thread and start over.:D

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

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;) :p

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:crazy:




































LMAO ,all you guys looking over your shoulder to see who's watching:D :D

Both of my Spectre's were set up to turn inbound. I have not seen any problem docking. It must be different on cats.

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!!:eek::p

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:D
It had nothing to do with driving the boat:crazy:

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.

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

for planing....I thought we figured out this at cleveland in the january?

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.

If your props are turning in, you should see a gain in speed if your hull can use it. I have tried both ways and there is a big difference in top end performance. However if your boat docks poorly, it will only get worse if you turn the props in. I have never had a problem docking with mine in, but I have had some big crusiers that I have practiced with and it is no problem anyway, unless you have heavy current and high winds, and then good luck to anyone.

Out/In make sure you can park the thing 2 people apart from you will be looking when you go around 2.69 MPH faster on GPS but 200 will be looking at the guy with the hot boat banging into the dock at the local hot spot. I say OUT and park it like a pro without touching the steering, instead of looking like a doughead pinballing your way into a dock space ! :D:D:D

From the thread, Great Moments in Cat History.
==========================================

My thoughts on "spinning" in..... Simple physics.... Right hand rotation propellers,torque (lean) the boat to the left. Left hand rotation propellers torque the boat to the right. In a twin engine boat spinning outboard or , RH on right side, LH on left, the torque of the propellers tends to return the boat to level when one side or the other leans outward. When props are spun inboard RH on left, LH on right, or counter rotated the torque tends to make the lean worse. This occurs because as a boat(Cat or Vee) leans to one side, the prop on that side buries deeper and exerts more force, while the prop on the other side rises (in some cases out of the water) and exerts less force. So...... If a RH prop is spinning on the right side of a boat leaning to the right, the prop tends to push the hull back over to the left. (spinning Outboard). If, however, the left hand prop is on the right side in a right hand lean , the prop tends to continue to roll the boat over. I submit that this is why there has been such a dramatic increase in barrel rolls (even in straight-aways) in races in recent years. When I flew over races for 16 years, I could always spot the counter rotated boats, because they behaved very differently (and definitely not better)than their properly spun (outboard rotation) competitors.
The reason that many people spin them "backwards" is the fact that on some hulls the boat may gain a mile or two per hour at top speed....or..... the boat has a bottom tune that needs more bow lift. The speed can generally be achieved in other ways without using an unnatural rotation as a "bandaid" (This is particularly problematical on stepped bottom boats that skid first, then catch suddenly, then roll outward......get the picture?)
One can re-tune most bottoms to add rocker to provide bow lift without resorting to ill advised prop rotation changes.

Counter rotation is adviseable on SINGLE engine race boats when the courses change from counter-clockwise to clockwise. LH props like right turns and handle better, RH props like left turns. Since the Bravo drive allows for a simple flick of a lever to reverse rotation, one would expect that Factory 1 racers would have a supply of left and right props depending on the course ....... up until this year most F1 racers don't...... I guess nobody has "invented" this yet.

It's T2x....NOT "Tx2" please

I agree with Shawn. On my cat it docks find with the props turning either way. In does provide more bow lift but I can't yet say if in is faster or not:frog:
Damm, I hate when I agree with Shawn:mad:

My stepped 32' Fever had the props spinning in. I couldn't dock worth a chit. Thought it was because I was a twin newby this yr.
I switch to spinning out and docking is now a breeze. World of difference. Never really ran the boat when spinning in, so no idea on top end, but I hit 78 mph easily with them spinning out. Been told 78 is about norm for this boat, so figure I didn't loose any top end. Handleing feels the same, or at least not enough noticable difference that I can tell.
I dock more than run WOT, so docking ability takes precedent. I'm leaving them spinning out.

Logic taking over!!! Some people are in trouble!:D

My props have been turning in since I bought my boat in '96. It's my first boat with twins so I learned to dock with it this way, so I guess I wouldn't know what I'm missing. The previous owner did the experimmenting to find that my boat is faster turning in (and it still needs more bow lift). My boat has a notched transom and a decent sized pad.
I'm certianly not going to swap my drives (TRS) to see if my boat goes slower and my docking improves.
But that's just me.
DS

Michael, I feel your pain. I hear your boat looks great with the new colors. Are you going to be out this w/e? Can't wait to see how it turned out

Shawn

To experiment with this can't you just change the props and shift the drives the opposite way? This whould really make docking a trick but a easy way to try it out.

With bravos - Yes
With TRS - Nope, must swap drives.

I finaly tried it on my Bullet............It sucks ! ....Boat just did'nt feel good at any speed.....Nothing major just not near the great handling im used to...Docking ? Forget about it !!! With the blowers surging you can't crank the wheel fast enough !!
Top Speed ? maybe a couple.....But i know i can't run the big stuff with any confidence........Maybe a calm lake boat...NOT a boat that sees Erie all the time. Here me Thrillseeker ??!!:D

Shawn
 

Shawn I am going to try to get out. If I can drum up a crew. Still have some graphis to install on the deck. Hope to see your new rig.
Michael

Thankyou for your post I just bought a 26; ARONOW CAT and 2 people told me my motors were wrong rotation I'll swap drives and inform you of my changes...

Good thread, all the way back to 2003. I had'nt seen it before.

Before you change anything you might want to post a picture of the back of your boat showing the props, drives, and everything else. A change in drives might also mean a change in the way the shifter cables are hooked up.

Blast from the past:party-smiley-004:

LMAO :picard1:

.
This thread is back again in 2015! Occasionally I read something online from 2007-2012 and think "this is outdated". Glad google pointed me to an OSO thread from 2003.

I just winterized today and heard about swapping props to make docking easier. Can't wait to try it out!

Lol all. I just posted the below in the Prop Section...

LH/RH vs RH/LH prop install on twin screw

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#1
imartin , Today 08:02 PM
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Ok, at the expense of laughter, I have to ask. Been racking my brain on if my props on on correctly. Baja 35 Outlaw, twin 525s, Bravo 1s, Maximus 5 blades. LH rotation was on port and RH on starboard when I bought boat from original owner. That means water being thrown to outsides of boat and believe that's the correct way from factory. Today, some how RH is on port and LH is on starboard, believe that means water thrown to inside. I'm only getting 4800 WOT. If the props are truly flip flopped, would that compromise performance, create strain, etc? I have to get things right before I drill into cavitation plates to install drive showers. Welcome thoughts and comments, TIA.