Outboard Engines & Prop walk

[Elessar]

Prop walk is more pronounced with big-pitch props. A 30 knot outboard boat might typically have a prop of around say 15inches pitch while a twin diesel big shaft drive P motorboat might have a prop pitch in the order of 45 inches, so you will have much more prop walk with the latter (at the same idle rpm of say 300-350rpm at the prop). All my numbers are ballpark, obviously.

Prop diameter as well J.

The bottom is in higher pressure water so more efficient.

Outboards have tiny props so prop walk minimal.

Add in a big pitch and it’s like a paddle wheel.

 

[Offshore57]

Correct, with the exception of a rather peculiar type of vessel.
Now, is anyone up for a virtual cigar?

I take it you mean a Sub......

 

[MapisM]

We have a winner! :encouragement:

 

[Offshore57]

:triumphant:

 

[stelican]

Difficult to swivel my outboard to steer but it would be useful when berthing to have some prop walk-if it was predictable and was in a useful direction. I am saying that because an outboard slightly tilted has the shaft tilted upwards wheras a fixed shaft is normally tilted down so I am wondering if the prop walk would be to starboard with a rh prop rather than to port as would be normal with a sloping fixed drive shaft?

I bet you do find it difficult to steer your boat if you cannot vector the outboard motor. The steering shaft must be partially siezed

 

[C08]

There is not room at the transon to steer the motor so some prop walk would be nice (catamaran).

 

[stelican]

QUOTE=C08;6862569]There is not room at the transon to steer the motor so some prop walk would be nice (catamaran).[/QUOTE]

So how do you steer the boat a separate rudder?
Ah I see its a Catamaran you better get 2 stern thrusters or a grappling iron.

 

[Boathook]

There is not room at the transon to steer the motor so some prop walk would be nice (catamaran).

Angle grinder and cut a bit more of the stern away!

I was looking at the yamaha 25 high thrust but have put it on hold due to the amount of modifications required to get it to turn enough to help with maneuvering.

 

[C08]

Angle grinder and cut a bit more of the stern away!

I was looking at the yamaha 25 high thrust but have put it on hold due to the amount of modifications required to get it to turn enough to help with maneuvering.

Yes I think that is going to be the answer. Mostly I manage ok with manoervering and better since I fitted a bowthruster but occasionally engine steering would be good. I have not seen or thought of a good way of disconnecting engine steering when sailing, or seen that on any Catalacs!

 

[Boathook]

Yes I think that is going to be the answer. Mostly I manage ok with manoervering and better since I fitted a bowthruster but occasionally engine steering would be good. I have not seen or thought of a good way of disconnecting engine steering when sailing, or seen that on any Catalacs!

I don't have any pictures of my set up but hopefully the quick sketch gives the idea. When sailing I disconnect the clips at the engine (which makes the steering lighter) and drop a couple of lines onto the engine attachment to hold it in the fore / aft position. For me, all quick and easy and the engine is always ready to start. I will get some pictures next week and either post here or email them to you. I should have added that the four 'circles' are pulleys

 

[TheOrs]

We have a winner! :encouragement:

Are you assuming the sub has a nozzle? Or is there something else that I'm missing?

 

[MapisM]

Are you assuming the sub has a nozzle? Or is there something else that I'm missing?

No, I'm not. And to be honest, I don't know where to start explaining what you are missing.
Let me put it this way: which of the factors (if any) behind prop walk effect in a surface vessel do you think are still applicable to a sub (when submerged, obviously)?

TBH, I never bothered investigating this matter in detail, but when someone much more experienced than myself told me that a sub is the only prop-driven vessel unaffected by prop walk, it seemed very logic to my simple mind...

 

[TheOrs]

Let me put it this way: which of the factors (if any) behind prop walk effect in a surface vessel do you think are still applicable to a sub (when submerged, obviously)

Ah, ok.
The assumption is prop on centreline of hull (not all subs have this) & submerged.
I get it.
Sorry; I'm tired. ?

 

[MapisM]

No worries, but I think the principle still stands also on subs with twin screws, where neither are affected by prop walk when submerged.

 

[C08]

View attachment 79464

I don't have any pictures of my set up but hopefully the quick sketch gives the idea. When sailing I disconnect the clips at the engine (which makes the steering lighter) and drop a couple of lines onto the engine attachment to hold it in the fore / aft position. For me, all quick and easy and the engine is always ready to start. I will get some pictures next week and either post here or email them to you. I should have added that the four 'circles' are pulleys

That is very helpful - sent a PM.