Props in Props Out - NTB

[RiverDave]

This has kind of caught my interest as their seems to be some descrepancy in the marine industry. Today I took a drive down to West Coast Drives for another purpose.. But being that Vern was a world champion offshore racer and setups Skaters and six drives for a living I asked him.

He said turn in for safety, turn out for speed. Pick up 6-8 mph turning out but they are squirley..

I took this pic of primo's boat while I was there.

 

[Tommy Gun Images]

I think they should turn them both the same direction just to make things interesting

 

[Ziggy]

I think they should turn them both the same direction just to make things interesting

Right turn Clyde
Make 'em both Duo-Prop set ups

 

[Stainless]

Dave did he have any comments about docking?

 

[shintoooo]

Have you tried a different prop?

 

[RiverDave]

Dave did he have any comments about docking?

He was in the middle if putting a drive on a boat.. I didn't ask him about docking. What would you want to know?

 

[djunkie]

Have you tried a different prop direction?

Fixed it for you.

 

[Stainless]

He was in the middle if putting a drive on a boat.. I didn't ask him about docking. What would you want to know?

Some say they are easier to dock turning out.

 

[shintoooo]

Stainless, which way are the props in your avatar turning?

 

[Tommy Gun Images]

Stainless, which way are the props in your avatar turning?

They turn in... He's all about safety

 

[djunkie]

They turn in... He's all about safety

I thought out was for safety?

 

[Stainless]

Stainless, which way are the props in your avatar turning?

Out

 

[Tommy Gun Images]

I thought out was for safety?

Out is for runnin loose and pullin chicks...

 

[Hammer]

Out is for runnin loose and pullin chicks...

Always pull out when runnin loose

 

[rivrrts429]

What's up with these props? Are they torched or just dull from hard water?

 

[shintoooo]

I give you props Dave :thumbup:

 

[Outdrive1]

You gotta let it go Dave.

 

[shintoooo]

You gotta let it go Dave.

Dave let go a long time ago.

 

[Ziggy]

Biggest problem I have with this thread is it does not apply to my boat.

From my POS T-mobile thingie

 

[Guest]

Those props should be on the front of those drives!...

 

[RiverDave]

You gotta let it go Dave.

I don't care one way orthe other OD1 but a boating board is about the free exchange of ideas, and education about boats. If I have always been incorrect all these years I'd like to know it. So I checked with some people but everyone keeps coming back the same way?

RD

 

[Stainless]

Stainless, which way are the props in your avatar turning?

Actually its which ever way bilgie wants them to turn.

 

[DeltaSigBoater]

Some say they are easier to dock turning out.

When the props spin outward docking is easier, due to the forces exerted on the prop & vessel.

On a single engine: A RH Prop Pushes the bow & Pulls the stern to Port, as such a LH Prop does just the oppsite.

The same is true on a twin engine vessel where counter rotating props setup to spin outward.

However when counter rotating props are setup to spin inward, even though the forces exerted on the prop are the same, the forces on the vessel are delayed or deflected.

How far part the shafts are also is a factor. Docking a twin engine cat with outward spinning props will be eaiser than a V-bottom of the same size where drives/outboards are closer together.

 

[Buoy]

About 2 yrs ago, I was hauling a boat from HB for a friend back to AZ, and had another person that asked me to stop and pick up a crash box for him at Vern's shop on my way back.
I had no idea what I was walking into.
I thought I'd stop, grab the crash box, and be on my way.
WOW!!!!
I'd never seen so many #6 drives in one place.
Vern took me around the shop for over an hour.
Very cool guy!

 

[Stainless]

When the props spin outward docking is easier, due to the forces exerted on the prop & vessel.

On a single engine: A RH Prop Pushes the bow & Pulls the stern to Port, as such a LH Prop does just the oppsite.

The same is true on a twin engine vessel where counter rotating props setup to spin outward.

However when counter rotating props are setup to spin inward, even though the forces exerted on the prop are the same, the forces on the vessel are delayed or deflected.

How far part the shafts are also is a factor. Docking a twin engine cat with outward spinning props will be eaiser than a V-bottom of the same size where drives/outboards are closer together.

Thanks, that is what works best for me with outboards. I was not sure if big IO with 6's would be different. I can change mine in about 2 hrs, longest part of that being switching the cables at the shifters, that's a PIA.

 

[530RL]

This has kind of caught my interest as their seems to be some descrepancy in the marine industry. Today I took a drive down to West Coast Drives for another purpose.. But being that Vern was a world champion offshore racer and setups Skaters and six drives for a living I asked him.

He said turn in for safety, turn out for speed. Pick up 6-8 mph turning out but they are squirley..

I took this pic of primo's boat while I was there.

Your statement is consistent with the mercury racing site, in the sense that turning out picks up speed. However, it really depends.

Each hull design is different (V, tunnel, tunnel with pod, blah, blah blah), set ups are different, drive height is different, center of gravity is different, transom weight is different, hull bottom is different, and if we were fluid dynamic physicists, we could probably come up with dozens of factors affecting this general rule.

So, not to argue, but the permutations of factors in boat set-up can result in different outcomes.

For years, helicopter physicists and designers have argued about how in-ground effect really works and the differences between settling with power versus vortex ring state. The truth is that none of this stuff will ever be settled definitively because the variables make the solution more complicated than a simple rule of thumb. However, people will consistently discuss and sometimes argue about it........like religion.

 

[scouter]

This may be a stupid question, but hey, I'm a stupid guy....

I get the whole spinning in and out deal, but my question is how do you swap back and forth? Or is that something that just isn't done? If it is, is it a gear change, or swapping drives back and forth?

OK, bash away.......

 

[Stainless]

In the case of outboards you swap the lowers then go to the shift controls and switch the cables too.

 

[Cajun]

I don't care one way orthe other OD1 but a boating board is about the free exchange of ideas, and education about boats. If I have always been incorrect all these years I'd like to know it. So I checked with some people but everyone keeps coming back the same way?

RD

Right, because this information is right up the hardware lineup for the Internet Dumb Dumbs that frequent this site.

 

[milkmoney]

Right, because this information is right up the hardware lineup for the Internet Dumb Dumbs that frequent this site.

did you jus call yourself a dumb dumb,,,oh hell..

 

[Cajun]

did you jus call yourself a dumb dumb,,,oh hell..

I paint with a broad brush

 

[BDMar]

This may be a stupid question, but hey, I'm a stupid guy....

I get the whole spinning in and out deal, but my question is how do you swap back and forth? Or is that something that just isn't done? If it is, is it a gear change, or swapping drives back and forth?

OK, bash away.......

Stern drive one runs in reverse. The change is made at the controls. Then switch props

 

[LuckyStrike]

Stern drive one runs in reverse. The change is made at the controls. Then switch props

How The Hell Ya Doing...????:champagne::thumbsdown

 

[CampbellCarl]

So, when moving the boat south of the equator it would then be turn in for speed and out for safety.......right?

I mean if the water spins the other way in toilets down under then it would stand to reason that props would need to also.....

 

[milkmoney]

So, when moving the boat south of the equator it would then be turn in for speed and out for safety.......right?

I mean if the water spins the other way in toilets down under then it would stand to reason that props would need to also.....

I would think you would be upside down, another equation in the rotation of props..

 

[KAP]

Ok I will try and explain it...DeltaSigBoater is on the right path.

Note: My experience is based on what I have encountered or learned over the years. Also just because you race offshore does not mean anything. As I know a few offshore guys that don't know anything about set-up. They simply show up and run their stuff.

Now setting up a boat has tons of variables that change things dramatically simply by doing one thing or the other. The primary building block to start with on setup/propeller rotation is hull design. There are also numerous variations of what people consider to be tunnel hulls but really they are variants of the original design.

So for clarity let's stick with one...and one only a true tunnel catamaran.


Basics:

Right hand rotation of propellers....Torques boat to the left[port side].

Left hand rotation of propellers....Torques boat to the right[starboard side].

Twin Engine Boats:

A boat spinning it's propellers OUT tends to keep the boat level when making turns. As you know in cats you do not want the lean out in turns [i.e..rail ride].

A boat spinning it's propellers IN tends to make the boat lean worse to the outside.

****Why does this happen because in a turn.... one propeller is getting buried and bites harder exerts greater force.... namely the outside one and thus when you turn props in it makes the lean that much worse. Because the propeller torque wants to continue rolling the boat over.

Now conversely, if the propellers are turning OUT the torque of the propeller wants to push the boat back over the left[port] which is the natural torque of the boat and propellers. Thereby, keeping the boat level.

This does not mean that you cannot turn them in....you can but it requires more experience and finesse to turn even more so at high speed.

In a single engine set-up RH props like left turns and LH props like right hand turns.

Now having said the above you need to understand that CG and tunnel depth and height also play a huge role in what the boat is doing.

Turning in will make the boat carry the bow easily and depending on the hull design is several MPH faster....however the handling characteristics are more akin to muscling the boat to get it to turn properly.

Offshore only and the Hull Truth have a lot of experienced, and knowledgeable people viewing those forums and can provide far greater insight than I can. Each set-up is affected by many variables so the above is a general statement...that works perfectly for me.

If you see it on video you will say Ahhh ha! Take your single engine boat set up for a turn and most are RH rotation and make a left turn it will be smooth as glass then try it at the same speed turning right....it will be rougher.

Hope this sheds some light on the subject and thanks for reading.

KAP

P.S. Dave if you took the Performance boating school. I am sure they talked about hull design ad nauseum the reason they do that is so people understand what the boat does in relation to water. No I have not taken the course

 

[Outdrive1]

I don't care one way orthe other OD1 but a boating board is about the free exchange of ideas, and education about boats. If I have always been incorrect all these years I'd like to know it. So I checked with some people but everyone keeps coming back the same way?

RD

Just bustin your balls Dave.

My thought on the subject is, there is no standard. What works on one type of boat or hull may not work on another type. I don't think you can say a always works better than b. Or a always has this effect and b doesn't. Or this boat with a top speed of 90 works different than this boat with a top speed of 180. Spindler sets of v hulls, seems to me they always spin in.

It's not cut and dry IMO.

 

[shintoooo]

Just bustin your balls Dave.

My thought on the subject is, there is no standard. What works on one type of boat or hull may not work on another type. I don't think you can say a always works better than b. Or a always has this effect and b doesn't. Or this boat with a top speed of 90 works different than this boat with a top speed of 180. Spindler sets of v hulls, seems to me they always spin in.

It's not cut and dry IMO.

Let it go Paul

 

[Outdrive1]

Let it go Paul

Lmao.

 

[Ragged Edge]

The props on my 38 Fountain spin out. When I first bought it I thought I would need to change them to spin in as the boat is used mainly for the Catalina Ski Race but it works fine the way it is. However I was told by a number of guys that spinning out is faster, spinning in is more stable but slower. I was not asking for info about how to set up a Cat.

 

[spectras only]

However I was told by a number of guys that spinning out is faster, spinning in is more stable but slower. I was not asking for info about how to set up a Cat.

We spin the props in to get to 100 mph in my friend's 35 Fountain. Ask Reggie why he sets most of his boats with props turn in? Because he wants to go faster I think he sets his cruisers with props turning out so the heavier barges get on plane quicker . The props turning out makes the stern ride higher and a bit squirly compared turning in [ depends on hull design ] but the boat won't lean as much thus better control for turning.

Turning in carries the bow higher without positive trim here > http://www.youtube.com/watch?v=e1tv8mTeIDM

 

[RiverDave]

Just got back from OCM.. Was talking to Tim from CRC. Said spinning out 6-8mph faster. Spinning in turns better / tighter.

 

[94Nautique]

So then what happens if you are the big baller that decides to have three outboards? Which way does the middle spin? And for the Uber-Baller with four (like the dude with the 4x300 fishing boat at DS) do you have the inside pair spin inward and the outermost spin outward for both speed and safety? lol

 

[RiverDave]

So then what happens if you are the big baller that decides to have three outboards? Which way does the middle spin? And for the Uber-Baller with four (like the dude with the 4x300 fishing boat at DS) do you have the inside pair spin inward and the outermost spin outward for both speed and safety? lol

Triples middle spins right. Quads two on left and two on right will match.

 

[Go Big]

Your statement is consistent with the mercury racing site, in the sense that turning out picks up speed. However, it really depends.

Each hull design is different (V, tunnel, tunnel with pod, blah, blah blah), set ups are different, drive height is different, center of gravity is different, transom weight is different, hull bottom is different, and if we were fluid dynamic physicists, we could probably come up with dozens of factors affecting this general rule.

So, not to argue, but the permutations of factors in boat set-up can result in different outcomes.

For years, helicopter physicists and designers have argued about how in-ground effect really works and the differences between settling with power versus vortex ring state. The truth is that none of this stuff will ever be settled definitively because the variables make the solution more complicated than a simple rule of thumb. However, people will consistently discuss and sometimes argue about it........like religion.

Bingo, We have a winner!!! All depends on the many various chartactoristics of the Hull and setup. My boat spins out and I can put 2G's+ of lateral force on you in a corner no problem.

 

[Racey]

Stern drive one runs in reverse. The change is made at the controls. Then switch props

For clarification for everyone reading with bravos it's just a control change, you run one drive in reverse and switch the props, one drive is driving off the top gear in the upper gear case, the other off the lower gear.

TRS, III and i believe IV & V drives the reverse rotation is in the lower gear case, they require the lower gear case to be swapped, one drives off the front of the prop shaft, the other off the rear.

I think VI (number 6 drives) are also reversed in the upper gear case driving with the gear at the top or at the bottom, but i'm not 100% positive on that, never had a VI apart. which would mean a complete drive swap to reverse rotation.

 

[timewarp]

Physics disagrees with you Dave, this is not about how it makes the boat feel, but actually which is less likely to go over once on the ragged edge. I'm not much at explaining stuff without talking with my hands so I am stealing content from a 2001 thread on Offshore only, this first is from Rich Luhrs

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.

Yes boats do barrel roll or spin out with standard rotation, but require much more drastic driver error to do so....
Bottom line..... Boats that spin in assist in the barrel roll....boats that spin out do not.


This from George Linder,

On the subject of prop rotation. There should be no discussion. Those who think inboard rotation is better also think the world is flat! Wake up, the laws of physics cannot be disputed. T2x has covered the basics very well.

During my 6 years (1995 to 2000) as APBA Tech. Chairman I tried in vain to mandate outboard rotation without success. Too many manufacturers and racers have rewritten the laws of physics and are convinced the world is flat.

T2x is right, inboard rotation is a dangerous fix for poor hull design, boat balance and prop selection. Single engine boats also benefit as T2x points out. I found it interesting that the vast majority if not all single engine racers did not have a clue to the advantages of switching rotation depending on the direction of the course and turns. If you are turning left use right rotation and if turning right use left rotation, make the torque and physics work for you and not against you. When you reinvent science to suit your self you are inviting trouble.

These quotes came from this thread

http://www.offshoreonly.com/forums/general-boating-discussion/14410-great-moments-cat-history.html

KAP is explaining it correctly.

 

[Hasselhoff]

Turning out raises the stern and allows the boat to fly with less wetted surface. This makes it faster but a little looser.
Turning in carries the bow better but leaves more of the stern in the water. This makes it slower but with more of the stern and drives in the water you can turn harder. There is Simply more tunnel and drive surface in the water so you can load them harder in the turn.
At cruising or higher speed your cat should lean in, not out. When you are turning watch your tachs. As you go through your turn you will notice the outside prop starts to aerate and the RPMs start to climb on the outside motor as it has less and less water to bite. The inside motor will stay the same or even drop RPM's as the load increases the deeper it goes in the water from the inward lean. If the theory about the loaded prop rolling the boat held true then an outward rotating prop would actually roll the boat to the outside because the prop that's deeper in the water and more loaded is the inside prop. This would also mean an inward rotating prop would further lean the boat inward.
Ultimately the inward rotation creates a safer and more predictable boat because it keeps more of the important part of the boat in the water. But looser is faster...

 

[RiverDave]

Hasselfhoff your backwards on which rpm climbs according to Tres Martin class.

 

[DaveC]

White people problems