Outboard vs inboard prop rotation

[krush]

Standard is outboard rotating props (stb prop clockwise, port anti-clockwise). Anybody ever swap on their Hatteras to experiment?

I read on go-fasts it sometimes gives more speed to turn inboard....

 

[Bob Bradley]

Quarantine starting to get to you?

 

[SKYCHENEY]

I thought the purpose of the standard arrangement was to provide a little extra lift.

 

[jim rosenthal]

I was told years ago that the purpose was to avoid pulling objects under the boat- things floating just below the surface.

On my boat, the starboard shaft and wheel rotate clockwise, viewed from the stern, the port rotates anticlockwise, viewed from the stern. (this is with the gears in "forward") My gears can be run in either direction at full throttle. Seems like if you swap the wheels port to starboard, you'd have to run the gears in the opposite direction to get forward thrust, wouldn't you?

 

[Freeebird]

"Anticlockwise"?

Yes, I'm bored too.

 

[rsmith]

"Anticlockwise"?

Yes, I'm bored too.

An old Italian fisherman I knew used to say the motor that runs against nature always wears out first

 

[Avenger]

"Anticlockwise"?

The British spelling.

 

[Boatsb]

Consider a few things

1) thrust direction on an outboard is quite different
2) space between the wheel and hull is quite different from wheel to lower unit as is the surface area for lift.
3) smart guys over many years have experimented and found best practices.

 

[Freeebird]

It seems to be contagious. Dr. Jim caught it from Krush.

 

[racclarkson@gmail.com]

Outboard props, more speed. Inboard props, more maneuverability.

 

[Freeebird]

Outboard props, more speed. Inboard props, more maneuverability.

I'm guessing the speed increase would be negligible at best with a Hatteras. Go fast boats are a whole other animal.

 

[Freeebird]

This is as good as any with a quick Google search. I've seen this discussion many times.

https://www.offshoreonly.com/forums/prop-talk/133194-turning-props-out.html

 

[doc g]

And yes you would have to run transmissions in reverse to go forward . Some can do that . Would make docking .....interesting ...Pat

 

[Top Hatt Craig]

Although not really related to your inquiry, the twin-fuselage Mustang was a big disappointment until they tried it the other way.. from WIKI.. The XP-82 was to be powered by two Packard-built Rolls-Royce V-1650 Merlin engines. Initially, the left engine was a V-1650-23 with an additional gear in the propeller reduction box to allow the left propeller to turn opposite to the right propeller, which was driven by the more conventional V-1650-25. In this arrangement both propellers would turn upward as they approached the center wing, which in theory would have allowed better single-engine control. This proved not to be the case when the aircraft refused to become airborne during its first flight attempt. After a month of work North American engineers finally discovered that rotating the propellers to meet in the center on their upward turn created sufficient drag to cancel out all lift from the center wing section, one quarter of the aircraft's total wing surface area. The engines and propellers were then exchanged, with their rotation meeting on the downward turn, and the problem was fully solved. The first XP-82 prototype (44-83886) was completed on 25 May 1945, and made the type's first successful flight on 26 June 1945. This aircraft was accepted by the Army Air Forces on 30 August 1945, whose officials were so impressed by the aircraft, while still in development, that they ordered the first production P-82Bs in March 1945, fully three months before its first flight.

 

[Entonces]

Outboard props, more speed. Inboard props, more maneuverability.

"Ma Ma MA MA Maneuverability" more important for me!
Hope everyone is fairing well through this!

 

[krush]

His go inboard: https://www.samsmarine.com/forums/s...-Tuna-Tube-Winter-Project&p=369249#post369249

 

[rustybucket]

His go inboard: https://www.samsmarine.com/forums/s...-Tuna-Tube-Winter-Project&p=369249#post369249

I also posted this in the referenced thread, so this is a duplicate.

lol, I was wondering if anyone would pick up on that! It's actually one of the factors that helped us choose the name 'SOUTHPAWS'. The boat is left handed, and my wife and I are left handed also.

Opposite rotation was not done on purpose, it was quite a mistake. When we purchased the boat both engines were fresh off rebuild, sitting on pallets next to the boat, clearly labeled 'port' and 'starboard'. Like an idiot I took those labels as fact.

So we hired a crane to drop the engines in. The evening after the crane left I was admiring our fine work, very proud of our accomplishments and tidy work and wanted to check the oil in the engines.... that's when I realized the dipsticks were on the outboard sides of the engines.... major oh-shit moment ensued....

That night I could hardly sleep, the thought of having to hire another day of crane operator @ $3k/day made my stomach hurt, but then I thought, well, the dipsticks are easy just swap them inboard, but what else could be affected by it....? That night I stayed up til 3 or 4 am reading articles and studies on prop rotation theory and my conclusion was that having the engines reversed was not a big deal really, lots of race boats actually do it on purpose. It's supposed to be more efficient and faster, but slow speed handling would be affected. How much it would be affected was the million dollar question.

So the decision was made to proceed as-is and have the engines in on the wrong sides. We had to re-route some raw water lines and move dipsticks on engines and trans but other than that it really wasn't a big deal.

The biggest difference I can tell is low speed handling. It's not that it handles bad, it's just different. I can still make the boat do anything I want it to do, you just have to slightly adjust your mind to get there. I can actually make her crab walk sideways in low wind/current situations.

Many marine gears can spin backwards, sadly my allison mh20's cannot do that. But if we ever upgrade to twin disc's with trolling valves we would then be able to set prop rotation back to normal if we wanted.

So, that's the story of how we put the engines in on the wrong sides lol.

 

[krush]

I also posted this in the referenced thread, so this is a duplicate.

lol, I was wondering if anyone would pick up on that! It's actually one of the factors that helped us choose the name 'SOUTHPAWS'. The boat is left handed, and my wife and I are left handed also.
................
So, that's the story of how we put the engines in on the wrong sides lol.

Did you notice any change in cruise or WOT performance?

Dock handling changes are well documented on the internetz. Many go fast guys say inboard makes handling around the dock atrocious. They also say inboard rotation = bow lift...outboard rotation = stern lift.

I have twin discs, and maybe one day I'll experiment lol.....

 

[rustybucket]

Did you notice any change in cruise or WOT performance?

Dock handling changes are well documented on the internetz. Many go fast guys say inboard makes handling around the dock atrocious. They also say inboard rotation = bow lift...outboard rotation = stern lift.

I have twin discs, and maybe one day I'll experiment lol.....

Well, I cannot really say anything about change in performance b/c we bought the boat with the engines out, I never experienced it with proper rotation. I will say that I have been very happy with our performance, the boat rides like a dream.

For your twin discs you would just need to swap your props then work the gear shifters in reverse (to go forward). Would be a really cool experiment.

I would not call the low speed handling atrocious. Well, I guess it is atrocious if you try to drive it like a normal rotation. It's just different. Many people would say low speed handling of a single screw inboard is atrocious yet some capts drive them every day and can put the boat wherever they want. A few benefits are, I can easily move the stern port or starboard just by bumping one side fwd and one side reverse, it just squats the stern and shifts the whole ass one direction without moving the boat fwd or rev, almost like having a stern thruster. It took a little getting used to, but hey, every boat handles differently, after a few times playing with low speed handling in the open bay my brain made all the connections it needed to handle the boat appropriately. I can still spin the boat on a dime, you just have to do it a little differently. Rather than one in gear fwd and the other in gear reverse and run the throttles up, I put one in fwd, one in rev and then alternate the throttles up/down. So rev throttle port, rev throttle stbd, rev throttle port, rev throttle stbd, boat spins like a top.

One really cool benefit is that we can troll on a single engine and the boat runs very straight. On my old boat if we trolled on one engine the boat always wanted to turn away from that engine. With opposite rotation the prop is pulling that side in, resulting in a straighter run, allowing us to utilize autopilot on a single engine.

The VAST majority of our use is underway, we regularly fish 100's of miles offshore, not low speed handling. So if it's more efficient and faster to turn them in honestly that's what I would want. We run thousands of gallons of diesel through her every year, so if I can do anything to pickup some range or efficiency I'm game.

As far as bow/stern lift, the boat's attitude on plane is great, she doesn't like much tab unless I need to pave some 4-6' waves while on plane.