Backwards props ??

[wwestman]

Interesting thing this morning. Boat is hauled out for painting. Found it needed cutlass bearing on the port side as well as stuffing box. Starboard side had been done by PO when we found a rock with the prop. At that time both props were pulled and balanced etc.

When the port prop was pulled the mechanic noticed that it is marked "S" and also is marked "25RH23".

The starboard prop is marked 25LH23.

So the question is "huh?" Did the previous yard put the props on wrong and rather than haul the boat again, switched something on the transmissions (Twindiscs) or the shifters to compensate for their ****up.

If so, what is the downside of leaving everything as is? I have not noticed anything when operating the boat, but then again I would not know what to expect.

Or are we just chasing our tails? Anybody have any experience with something like this?

 

[Ski in NC]

I've seen a couple of boats with RH port and LH stbd, one guy said his ran better, the other one owner had no idea. I don't think it matters much.

Another boat had a slipping fwd clutch, so he swapped props and shift cables to run on the other clutch. Bought him some time.

You could swap them and see if you like it better, but it is a fair amount of work to try and then go back.

If you have no complaints, I'd leave it alone.

 

[boatpoker]

Are the engines contra rotating ?

 

[High Wire]

So which way do the shafts rotate with the engines in Forward?
Normal convention, when looking from behind is Port prop turning CCW and Starboard turning CW.
Is there any long term consequence to driving the rated hp with the trans in reverse? Oil flow, Thrust bearings? Clutch size?

 

[wwestman]

Shafts turning opposite, port turning CW starboard CCW.
That is my main question, what is the downside of this being the case.
I seem to remember reading somewhere that Twindisc transmissions were the same in either fwd or rev, but I have no idea where that came from.

 

[Sailor of Fortune]

some gear boxes are made to run either way without harm. The Twin Disc 502 is the one I'm familiar with. You can swap them for either side. there is no "fwd" or "reverse", lever position on gear gives desired rotation.

 

[Ski in NC]

Yea, any TD hydraulic tranny works fine in either direction. Your pick.

 

[LaBomba]

Should make no difference. Our boat is set up the same way. Both engines run in the same direction but one prop is LH and one is RH, so obviously changed direction in the transmission. I would leave it alone.

 

[wwestman]

So far I have not heard any reason to change anything. The yard guru agrees. Cheaper to keep it as is. Thanks for the calming input.

 

[johnma]

Twin Disc transmissions are all the same. the direction is changed at the shift linkage.
John

 

[boomerang]

Regie Fountain ran his props turning inboard because he claimed it achieved lift at the stern but they were hi-turning outboards. I've seen some sportfish boats turn them inboard because they felt it reduced vibration.

 

[koliver]

With your props mounted the opposite way to everyone else's, you will find handling in reverse is also opposite to normal, as your propwalk will be backwards.
Conventionally rotating props will pull towards the keel in reverse, yours will pull away from the keel.
Docking will require putting the engine near the dock in reverse to get a propwalk pull that will assist you.

 

[Rufus]

As an aside, I picked up an inexpensive spare prop a while back to use in the event of damage to one of the installed units. I'm thinking I could use it on either side in a pinch and swap the shifter (Twin Disk) if it's on the "wrong" side. Temporary fix only, but should work in a pinch (remote location, for example). Saves space, weight, and expense of keeping two on board.

 

[psneeld]

It can and usually does make a huge difference in slow speed handling.... But maybe not in this boats case or it was preferred by the PO.

 

[bayview]

The captain of a small tour boat that would walk sideways very well told mi it was partly because the props were reversed.

I don't know why props are installed one way or the other. There must be some advantage to the usual installation.

 

[psneeld]

Depending on your preference on how you drive, yes inboard turning will help some boats walk sideways.....

But once conditions overwhelm that capability, the convenience is reversed...and as posted, doesn't work on all boats.

That's why there is an overwhelming traditional method.

 

[koliver]

As an aside, I picked up an inexpensive spare prop a while back to use in the event of damage to one of the installed units. I'm thinking I could use it on either side in a pinch and swap the shifter (Twin Disk) if it's on the "wrong" side. Temporary fix only, but should work in a pinch (remote location, for example). Saves space, weight, and expense of keeping two on board.

Your theory won't work. If you put it on the wrong side, you will have two props the same, turning together. no balance. No ability to walk to one side or the other, as both will pull to the same side

I have seen some twin outboard installations like this, and they work OK, but counter-rotating works a lot better. In an inboard application you need them to be counter-rotating, as you can't steer the props like you do with outboards.

 

[Mako]

On a related but unrelated note...

I’ve come across several shipbuilders who install singles with a LH counterclockwise prop. I’ve always understood the opposite was “accepted norm” and had singles that were RH.

 

[psneeld]

My Albin is left handed.....steering station to starboard.

Seaboards discussion on industry standard....

https://www.sbmar.com/articles/which-way-does-my-engine-turn/

 

[Ski in NC]

On singles, it depends!!

On my planing hull, shaft torque does affect trim when up on step. I run a RH wheel and that tends to lift stbd side, so the helm (and thus helmsman's weight) is on stbd. A truly minor consideration as my weight on that moment arm is way less than the torque put down in the water with the prop. But every little bit helps, and with an otherwise balanced load, it runs at speed at level trim.

Downside is my reverse propwalk is pretty strong, and takes transom to port. So docking is naturally easier port-to. But my visibility is better stbd. My home port is port-to, but most times when I visit a dock, it is stbd-to. I've run the boat enough to where it is easy either way.

On a hull speed boat, torque/trim concerns are nil.

Regarding gears: Modern three-shaft gears such as the ZF 280PL that I use, the preferred output shaft rotation is opposite the engine. So my std rotation Cummins the preferred prop is RH. You can run LH, but that puts another gearset and bearings under load so a LITTLE more drag. Just a tiny bit.

If running a Borg Velvet Drive, there is only one fwd rotation, and whether it reverses the rotation of the engine depends on which reduction gearset is bolted to the back. Some reverse, some don't. But fwd still is whatever when selector lever is pushed fwd.

That is probably why some BW VD boats are RH and some are LH. I'd guess I'd prefer LH on a boat with helm to stbd.

Lower helms on boats are opposite those of cars so you can balance the suntan on your left and right arms!! That's my logic!!

 

[Rufus]

Your theory won't work. If you put it on the wrong side, you will have two props the same, turning together. no balance. No ability to walk to one side or the other, as both will pull to the same side

I have seen some twin outboard installations like this, and they work OK, but counter-rotating works a lot better. In an inboard application you need them to be counter-rotating, as you can't steer the props like you do with outboards.

I thought I explained that it is a short term emergency contingency. We often cruise the remote rock infested North Channel of Lake Huron. People who ding a prop wait weeks (and pay a fortune) to send out a dinged prop for repairs. This spare would allow me to get to a place with reasonable access to a prop shop, where I can get it fixed properly. Don't much care how it handles just so it gets me home. In fact the pitch on the spare is two inches greater than those installed (same diameter). Again, I can deal with it in the short term.

 

[Bkay]

To the OP - so your props are inboard rotating, in my opinion that's neither wrong nor backwards. I understand with recreational vessels, the overwhelming majority are outboard rotating. In my experience a significant number of commercial twins and cats have inboard rotating propellers.

I discussed this with an NA recently who said he sees inboard rotating a lot on fast sport fishing boats because it provides some speed advantage in certain boats. I'm not sure I understood his explanation of why that's the case, but I'm not very bright so that's no surprise. He said it also increases possible damage to the prop from debris.

Someone mentioned single screw boats with left hand props - I see that frequently with working fishing boats (mine included). Typically you haul traps from the starboard side and a left hand drive allows you to back down on your traps from the working side of the boat. Again, I don't believe it's wrong, just how the builder or designer envisioned that boat's set up.

I would not recommend changing your set up. It doesn't sound like there was any mistake made.

 

[JDM]

Interesting thing this morning. Boat is hauled out for painting. Found it needed cutlass bearing on the port side as well as stuffing box. Starboard side had been done by PO when we found a rock with the prop. At that time both props were pulled and balanced etc.

When the port prop was pulled the mechanic noticed that it is marked "S" and also is marked "25RH23".

The starboard prop is marked 25LH23.

So the question is "huh?" Did the previous yard put the props on wrong and rather than haul the boat again, switched something on the transmissions (Twindiscs) or the shifters to compensate for their ****up.

If so, what is the downside of leaving everything as is? I have not noticed anything when operating the boat, but then again I would not know what to expect.

Or are we just chasing our tails? Anybody have any experience with something like this?

It’s much more important on airplanes, but as you go to high power and the deck angle increases, the downward moving blades dig in more. If the props are CW on port and CCW on starboard, the center of thrust will move inboard as you add power. Opposite effect if the props are reversed, so small differences in power setting will create more directional control variation.

 

[sailbellaluna]

Backwards....Bill, you should be used to that after working 30 years for you know who.....

 

[wwestman]

That is SO true.