1995 200hp Variable oil ratios.

[zenoahphobic]

Thanks Boscoe and Zano. I pick upped the part in Rodbolts response about throttle angle. I will stick to 50:1 but look into a different oil as Boscoe suggested. I've cut the smoke in half by running on one engine in and out of the canals and whilst *****ing.

2 engine at 1400 rpm gets 7kn
1 engine at 1700 rpm gets 7kn

So another question, do I need to raise the engine I'm not using at these slow speeds?

Thanks for all the responses.

Lifting one engine will reduce drag.

You can test the affect, set one engine at 7kn then raise the other, does speed increase?

I suspect insignificant. Also that one running engine would use more oil than it would in tandem, but I guess not as much oil the non running engine would be used running.

Another thought, stupid I know, if you were able to switch from your tanks to a tank of higher ratio fuel to oil at these long slow distances and not be able to raise RPM past a point then it will switch back to the original tanks.

Just like engine manufactures do, various solutions can be devised, given time, money or bother. I don't really understand why so many people disengage oiling systems - this happens from lawnmowers, motorcycles, to wheelchairs!

[MakoJohn]

Zano I don't have much experience with big outboards but owned a 52' passagemaker (2000mn range at 7.5kn) with two 120hp diesels and Rivieria 43 with twin cats.

The passagemaker was a slow boat and I could run with one engine and let the other prop freewheel but the experts say the freewheeling prop would create less drag if locked. Goes against my logic but apparently it's true.

On the Riv you can only run slowly with one engine because if the freewheeling prop spins too fast it overheats the shaft seal and gearbox. I'm guessing that's not a problem with an outboard because these thing are underwater and cooled when the outboard is trimmed down.

The other interesting thing is as a general rule of thumb when you turn a prop 30% faster absorbs twice as much power. There is alway a gap between the hp an engine makes and the hp a prop can absorb except at WOT.

My 200hp Yamahas run together top out at 5200rpm so at 4000rpm the props are absorbing 100hp and at 3100rpm 50hp and so on 2400rpm 25hp and so on. At 1400rpm for 7kn almost nothing which is propably why these engines smoke and fowl. Running one engine clearly places more load on the engine as WOT falls to circa 4000rpm. Running one engine at 1700rpm to get 7kn probably places more load on that engine and is better for it.

Yes mate I have seen the Castle.

[zenoahphobic]

Thanks Boscoe and Zano. I pick upped the part in Rodbolts response about throttle angle. I will stick to 50:1 but look into a different oil as Boscoe suggested. I've cut the smoke in half by running on one engine in and out of the canals and whilst *****ing.

2 engine at 1400 rpm gets 7kn
1 engine at 1700 rpm gets 7kn

So another question, do I need to raise the engine I'm not using at these slow speeds?

Thanks for all the responses.

Makojohn I would love a Rivera 43 of the motor launch type, but very expensive (the type of boat you cannot afford if you have to ask the dealer what does it cost)
If I understood right you said the experts say a locked shaft creates less drag, I don't agree. Yes a turning shaft turns other things with it and that means wear and cost down the track. Do big boats cool the gear box when the engine is actually running? I'm a bit ignorant about how things are configured on large inboard boats.
An outboard not running actually runs cooler (prop freewheeling) because hot exhaust gases are passed through the gearbox.
Travelling the seas every 2%ters count. I thought sailboats use the freewheeling shaft as a means of turning an alternator for battery charging.

[boscoe99]

Actually, a propeller that is water milling/wind milling (being turned by the medium through which it travels) acts almost like a flat circular plate with the diameter of the propeller. Therefore, it does create more drag.

In a slower moving boat maybe not much. But in a propeller driven air plane a lot. Which is why in a multi engine air plane with propellers a means is provided to feather the propeller on a failed engine to stop it from turning. Otherwise the pilot may lose control and the plane may/will crash.

[zenoahphobic]

Actually, a propeller that is water milling/wind milling (being turned by the medium through which it travels) acts almost like a flat circular plate with the diameter of the propeller. Therefore, it does create more drag.

In a slower moving boat maybe not much. But in a propeller driven air plane a lot. Which is why in a multi engine air plane with propellers a means is provided to feather the propeller on a failed engine to stop it from turning. Otherwise the pilot may lose control and the plane may/will crash.

Aeroplane props are directly connected to the piston engine or gearbox to turbine, it therefore generally undesirable to have it turn because the rotational forces are opposite to what is designed or gearing down forces, all on equipment designed with minimal weight and optimal strength (in forward direct).
There are also giroscopic forces to contend with a rotating dead engine.
Feathering props often is to do with clearance for possible crash landing.
So there are a number of reasons to stop a dead engine from rotating and damn it I am going to have research again whether drag is reduced, as I have believed for many years!My contention is based around the physics that a prop designed to be pushed is different to how it would be designed to do the pushing (same air speed); and why that is.

[MakoJohn]

Aeroplane props are directly connected to the piston engine or gearbox to turbine, it therefore generally undesirable to have it turn because the rotational forces are opposite to what is designed or gearing down forces, all on equipment designed with minimal weight and optimal strength (in forward direct).
There are also giroscopic forces to contend with a rotating dead engine.
Feathering props often is to do with clearance for possible crash landing.
So there are a number of reasons to stop a dead engine from rotating and damn it I am going to have research again whether drag is reduced, as I have believed for many years!My contention is based around the physics that a prop designed to be pushed is different to how it would be designed to do the pushing (same air speed); and why that is.

From PassageMaker Mag...

"Support that a locked propeller produces less drag comes from the aviation world, where the turning rotor of a gyro-copter or helicopter with lost power can produce lift to support flight or ease the ship to the ground. When the rotor is stopped from spinning, the reduced frontal blade area is not enough to support flight-and the aircraft falls from the sky!"

[MakoJohn]

Zano my Riv 43 was a 2002 model, not the latest million buck model.

With the engine off and the prop freewheeling heat is generated in the transmission from the turning shaft and gears. The transmissions cooling circuit is linked to the engine and with the engine off the transmission is not cooled. Transmission manufacturers normally state if their transmissions can be free wheeled. Some manufacturers offer shaft locks. Normal procedure on a boat like a Riv is go slowly if operating on one engine.

I haven't seen sailboats freewheel to charge batteries. Most sailboats have folding props to reduce drag and use solar panels or wind generators now.

Makojohn I would love a Rivera 43 of the motor launch type, but very expensive (the type of boat you cannot afford if you have to ask the dealer what does it cost)
If I understood right you said the experts say a locked shaft creates less drag, I don't agree. Yes a turning shaft turns other things with it and that means wear and cost down the track. Do big boats cool the gear box when the engine is actually running? I'm a bit ignorant about how things are configured on large inboard boats.
An outboard not running actually runs cooler (prop freewheeling) because hot exhaust gases are passed through the gearbox.
Travelling the seas every 2%ters count. I thought sailboats use the freewheeling shaft as a means of turning an alternator for battery charging.

[boscoe99]

Aeroplane props are directly connected to the piston engine or gearbox to turbine, it therefore generally undesirable to have it turn because the rotational forces are opposite to what is designed or gearing down forces, all on equipment designed with minimal weight and optimal strength (in forward direct).
There are also giroscopic forces to contend with a rotating dead engine.
Feathering props often is to do with clearance for possible crash landing.
So there are a number of reasons to stop a dead engine from rotating and damn it I am going to have research again whether drag is reduced, as I have believed for many years!My contention is based around the physics that a prop designed to be pushed is different to how it would be designed to do the pushing (same air speed); and why that is.

The number one reason to stop a wind milling propeller is to reduce drag. All other reasons are moot if the air plane will crash.

[zenoahphobic]

The number one reason to stop a wind milling propeller is to reduce drag. All other reasons are moot if the air plane will crash.

Yes of course (smack to side of face), a gyrocopter has a windmilling propeller that is not driven by an engine. It produces lift when rotating; one cannot have lift without drag on an aerofoil. Does that also mean drag produces lift?

You see I have difficulty associating a water screw (propeller) as a having blades with aerofoil sections. If blade strength was minimal a water propeller would only consist of thin blades proportionally curved to push the water (solid medium) the same distance from the centre out to its fullest diameter.

A water propeller is designed to screw through a solid medium. It's push or thrust is very much purely derived by pushing a certain amount of water mass out at a certain velocity. An aircraft propeller I would think derives a significant pull (vacuum created on front of aerofoil section) as well as the push of air (significantly lower mass than water and compressible that water isn't).

Thus on the point of drag, I would think where a water screw is milling the water speed over the blades would be far less than when it is not turning - almost zero if there is no slip. this very small amount of water flow over the blade therefore produces less drag. Drag being friction between two surfaces exponentially increasing with speed.

Conversely, a stationary prop has a large water flow over the blade surfaces and therefore must create a lot of drag. There must also be a lot of turbulence behind these blades as well adding to the drag!

However, do I hear someone say, turbulence on an aerofoil reduces drag (vortex darts, rough paint etc on leading edges. are commonly engineered into wings).

I say water does not act like air because it is incompressible, so no comparison can be made.

[ausnoelm]

Is this still about oil mixture?

[zenoahphobic]

Is this still about oil mixture?

Whiskey and Coke mixture

[MakoJohn]

Hope you go richer than 50:1🤓

Whiskey and Coke mixture

[zenoahphobic]

Hope you go richer than 50:1🤓

No 50:1 is fine. That is 50 whiskey to 1 coca cola!

[TownsendsFJR1300]

On an outboard, where the prop /gear case can be set to neutral, freewheel, the drag has to be less than leaving it locked in gear and trued OFF.

Raising the "off" engine, obviously, no drag at all. Maybe some less steering (less rudder, especially at slow speeds).

Aviation with a DIRECT DRIVE PROP TO ENGINE, it won't free wheel with a dead engine obviously and cause major drag. Try sticking you hand out the car window at 60 MPH and turn vertical, (like signalling stopping a car). Major drag with that small area. Point your hand into the wind flow, it works like a wing with CONSIDERABLY less drag.

I drift the shallows fishing, leave it in neutral, the prop will just spin away. And that's drifting up to 1 MPH per the GPS. Anchored up, the same.

If someones in the water, (say at the beach) turn off the engine IN GEAR, to stop the prop from free wheeling and potentially hurting someone in the water..

[boscoe99]

On an outboard, where the prop /gear case can be set to neutral, freewheel, the drag has to be less than leaving it locked in gear and trued OFF.

Why does it have to be less?

Ever played with a pinwheel as a kid? The propeller is not connected to or turning anything. When held out of a car window at 30 mph the spinning blades will create muccho drag. Moreso when spinning than if not spinning.

A propeller in a free turbine gas turbine engine is not directly connected to the main engine. Walk up to one on a ramp and you can turn the propeller with a single finger. If the engine fails the propeller will wind mill just like the pin wheel. In an air plane if the propeller can not be feathered to stop it from turning the outcome will not be good.