same engine rotation on handed propellers

[igbani agwu]

Two engines of rotating in same direction are installed on a boat. The propellers are left and right handed. Hw can I achieve counter rotation of the props if the engines are rotating in same direction. Are there any adverse implications for doing so?

 

[RichardS]

Two engines of rotating in same direction are installed on a boat. The propellers are left and right handed. Hw can I achieve counter rotation of the props if the engines are rotating in same direction. Are there any adverse implications for doing so?

Welcome to the forum.

The propellors must be "handed" to suit the rotation direction of the engines. If the engines and gearboxes rotate in the same direction you cannot achieve counter rotation by fitting different props, assuming that I have understood the question.

Richard

 

[sarabande]

usually achieved in the gearbox. One outputs L, the other R.

 

[scottie]

usually achieved in the gearbox. One outputs L, the other R.

One reduction gear has 2 gears the other 3

 

[tcm]

Two engines of rotating in same direction are installed on a boat. The propellers are left and right handed. Hw can I achieve counter rotation of the props if the engines are rotating in same direction. Are there any adverse implications for doing so?

Offhand i suppose the quickest way would be to put one of the engine in reverse position, the other in forwards, at which point you'll either be going forwards (or backwards). Move both controls in the opposite direction would make the boat go backwards (or forwards).

However, I do recall a pal with a catamaran where both controls were inverted by the yard after they fitted new control cables, and he launched... only to smash the boat quite soon afterwards - he didn't work out what was going on in time. And this situation would be potentially worse. Altho i have to say that my pal was probably drunk, and in any case a bit of a klutz at figuring things out quickly if at all. It's ok - he would never be on a boat forum, ever.

So, anyways, although i don't think that there are any paricular engineering issues with this....the adverse implications of this option (dealing with the thing as is, instead of getting the correct gearbox fitted...) are that even if you don't smash the boat up, the very next person to drive it (perhaps helping out, perhaps a yard/marina guy moving it in emergency) almost certainly will drive the thing into something else, cos it will not be like driving anything else. Out at sea is no problem with boat engines - it's in marinas etc that one tends to do the spectacular damage.

I suppose one has to wonder - what else might be weird about the boat in question? You speak of it as though it's a potential purchase, not your boat? It must be ashore, surely? Offer very low, cos they ain't gonna move it anytime soon, and they'll be hoping that you won't ask for a sea trial ...

****** EDIT: Um, since you're new... perhaps you don't know that this is how most if not all twin-engined boats are set up? The engines are the same and do indeed rotate in the same direction... but the gearboxes are "handed" (but invisibly so), as are the (visibly handed, as you saw) propellors. I suppose this also shows that it's ashore, hm? And you daren't quite ask the boat salesbod for fear of looking a bit of nitwit. Very wise course of action, i think! Gosh it's tough answering these questions yerknow.... Anyways, again, you being a logical person who looks at things and then goes and asks questions... the answer is (very likely) that the engines both spin the same way all the time, but the port/starboard gearboxes are "handed", just like the propellors. So, the engines don't counter-roate - but the output shafts of the gearboxes on to which those props are attached DO counter-rotate - so nothing to worry about, I think! Actually, no engineer would ever fit the wrong gearboxes like this, unless they were perhaps forced slaves. Is it a North Korean boat, perhaps? If not, i think you will find that it's fine Not to worry - perhaps a long time ago you wondered how the car went around corners when surely one or another tyre would have to spin at a different speed and would this shred the tyres or jam the wheels somehow? In that case the answer is a differential drive units, and kind-of likewise in this case it's the "handed" gearboxes. Oh how you will laugh at yourself (one day) for asking this question! Don't worry- i won't tell anyone. If tthis IS the case... then perhaps start a new thread along the lines of "newbie questions for a boat broker" where you ask everyone what testing and awkward questions you should ask a boat broker/dealer, so instead of them pah! laughing and smirking, you get them quaking and searching the paperwork. I am not sure if that specific question has ever been asked...

Hope this helps. Let us know?

 

[Niander]

 

[Niander]

don't have time to do long posts....wish I had btw...

 

[jfm]

Hiya tcm. Actually the gearboxes aren't intrinsically handed. I mean, ZF's and TwinDisc's production lines just spit out gearboxes that are all the same. When installed in a boat, the cables or electronics are set up so that when the user whams both throttle sticks forward one gearbox is set to run in forward and one in reverse, and so the two propshafts turn in different directions even though both engines turn in the same direction. (Except on Stingo's boat of course haha!)

On major 10,000 hour or whatever overhauls on some boats when they rebuild the engines, some mechanics swap the gear boxes port-to starboard, so that from then onwards the one that was running backwards is now forwards, and vv, so as to spread the wear on the faces of the gear teeth

 

[tcm]

Hiya tcm. Actually the gearboxes aren't intrinsically handed. I mean, ZF's and TwinDisc's production lines just spit out gearboxes that are all the same. When installed in a boat, the cables or electronics are set up so that when the user whams both throttle sticks forward one gearbox is set to run in forward and one in reverse, and so the two propshafts turn in different directions even though both engines turn in the same direction. (Except on Stingo's boat of course haha!)

On major 10,000 hour or whatever overhauls on some boats when they rebuild the engines, some mechanics swap the gear boxes port-to starboard, so that from then onwards the one that was running backwards is now forwards, and vv, so as to spread the wear on the faces of the gear teeth

Ah right, so it's just the props that are "handed" - the controls are set back to front on one side and one gbox works in "reverse", gottit. That makes (even) more sense.

I think if I was one of the 10,000hr engineers i would just (tellem to) swap over the controls to be the opposite direction, and swap the props over ....cos swapping the physical gearboxes is a bit of a (massive) pain, esp after 10k hours with loads of cack everywhere. Cept that the prop walk thing in reverse would be opposite, meh, whatever. But at least no need to do the shaft alignment blah, and still doing the opposite gear teeth faces....

 

[jfm]

Yeah but I'm talking major rebuilds where the engines are out in the bench in buts so prop shaft alignment is neither here nor there. You cannot just swap the props willy nilly especially on a mobo. I think you're underestimating the effect of going from outward to inward turning props - it is pretty massive in a marina and the owner would definitely notice, cept praps stingo

Mole Sud update and blast from past. Your mates Les and Linda ( they say hi) from Alderney have elegantly sold mio amore to your mate Bart, and bought a 2010 squadron 78 off my mate, thru Bart as broker. Chocolate cakes all round - it's all 'appenin down ere.

 

[tcm]

OK, I will leave the heavyweight grease monkey stuff to the pro's....

Ah yes, the lovely Linda of the Gigantic On-Deck Laundry, and nice Les (who is a dead ringer for the one-time Australian Cultural Attaché Les Patterson) ... sounds all fine down on Mol Sud )