Front Propeller

[Mick and Maggie]

I came across an old newspaper article dating from just before the war. It makes some serious claims about suppressing damage from a bow wave even when travelling at higher speeds. Now I know we want water passing over the rudder to aid steering. But has anyone ever seen any such design for a river/canal boat?

Albury Banner

15th April 1938

SHIP'S PROPELLERS ARE IN FRONT.

With two propellers under the bows, an experimental river and canal vessel has just completed successful trials at Mannheim, Germany. This new type of craft is expected to revolutionise traffic on inland waterways. In the past, the wash from propellers of ordinary craft has done colossal damage to river banks. The new vessel goes twice as fast as those with propellers astern, yet leaves no trace of a wave behind it.

[Phil Ambrose]

I don't believe any boat can pass through water without creating wash.

Yes I can see prop wash being minimal with prop at the bows but the hull will still displace water and in doing so wash will be the result, I would go so far as to suggest that prop wash is generally the least destructive wash generated by a boat as it is directed astern while bow wave/wash comes out both sides at an angle, 35 degrees is a figure I seem to recall.

Phil

Edited March 9, 2014 by Phil Ambrose

[Peter X]

I'm no engineer, but was it all a cunning Nazi plan to waste British engineers' time and divert them from re-armament work?

[MHS]

I'm no engineer, but was it all a cunning Nazi plan to waste British engineers' time and divert them from re-armament work?

I thought it was Baldrick who had the cunning plans.

[BGA]

 

 

One of these would reduce wash

[MtB]

Best not to confuse 'wash' with 'draw'.

 

Wash is the waves that spread out from the bow and stern.. Draw is the flow which passes the sides of the boat as the displacement water in front to the boat passes the boat to behind it, as it progresses along the waterway. Two different effects.

 

In narrow shallow canals draw has major effect on moored boats being passed. On bigger waterways e.g. the Thames, wash is the bigger problem affecting moored boats and the bank.

 

MtB

[Theo]

Best not to confuse 'wash' with 'draw'.

 

Wash is the waves that spread out from the bow and stern.. Draw is the flow which passes the sides of the boat as the displacement water in front to the boat passes the boat to behind it, as it progresses along the waterway. Two different effects.

 

In narrow shallow canals draw has major effect on moored boats being passed. On bigger waterways e.g. the Thames, wash is the bigger problem affecting moored boats and the bank.

 

MtB

Spot on MtB!

 

N

[Dalslandia]

The positive thing with propellers at the bow, is for those that sell propellers :-)

a Canal boat push a wave of water ahead of the boat, can bee seen on mirror water Days, specially if there is something that reflect on the water like trees, I can Think that bow mounted propellers can suck back some of that wave.

A front propellers wash increase drag with its higher speed, but a boat prop is small in diameter, not like an airplane there prop disk cover the hole fuselage.

The airplane prop wash is 10-20% extra over the plane airspeed, TAS.

a slow boat prop wash is ~50%

half of this increase in air/water speed is at the propeller disk, the rest half speed increase is behind the propeller.

a stern propeller suck (induce) water into the prop, so ahead of the prop there is also increased water speeds, and low pressure, this low presure on the after body wants to suck the hull back.

The benefit i see is that a front prop work in Clean? water, no turbulant i mean, so the effeciency is higher, so the propeller and Engine don't have to work so hard.

there is some short trip Ferries with both a prop and rudder in each end of the hull, that way they don't have to turn around.

Edited March 9, 2014 by Dalslandia

[Theo]

 

The positive thing with propellers at the bow, is for those that sell propellers :-)

a Canal boat push a wave of water ahead of the boat, can bee seen on mirror water Days, specially if there is something that reflect on the water like trees, I can Think that bow mounted propellers can suck back some of that wave.

A front propellers wash increase drag with its higher speed, but a boat prop is small in diameter, not like an airplane there prop disk cover the hole fuselage.

a stern propeller suck (induce) water into the prop, so ahead of the prop there is also increased water speeds, and low pressure, this low presure on the after body wants to suck the hull back.

The benefit i see is that a front prop work in Clean? water, no turbulant i mean, so the effeciency is higher, so the propeller and Engine don't have to work so hard.

there is some short trip Ferries with both a prop and rudder in each end of the hull, that way they don't have to turn around.

 

 

I would have thought that the major problem for a vessel in very limited depths of water is that the exit flow would have to impinge on the front of the boat. This would slow the boat down. (Like towing a butty on cross straps.)

 

N

Just a thought.

 

Hope you don't mind. I am going to move this to "Equipment" for the sole purpose of not clogging up "General Boating".

 

N

Edited March 9, 2014 by Theo
Wrong sign off intial! Typo

[Dalslandia]

WHAT happend with that i wrote???? I didn't write that above. "NO such topic"

 

Other front propellers

 

https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-ash3/t1/1780754_589564401120703_639857649_n.jpg

 

The Bugatti 100P

Confusing, now it is back on my screen, it said "NO such topic", for som moment.. in #8

Edited March 9, 2014 by Dalslandia

[harve90]

Slow down whats the rush the M25 is for rushing.

[Arthur Brown]

There are modern ships with multiple steerable power pods under the hull. The transmission is a huge cable as they are electric, but they steer as well. Their problem for canal use is that they hang below the ship so you would be testing for debris with the prop tip.

[nb Innisfree]

Their problem for canal use is that they hang below the ship so you would be testing for debris with the prop tip.

 

Not if the prop was located in the normal position behind the swim, that construction could be repeated at the front. If both props were in a tube, as in some outboards, then the front one could be rotated 90° to protect the prop and also act as a bowthruster. Effectively the boat would have a stern swim at both ends.

[Paul's Nulife4-2]

Wouldn't it be great if there could be a massive advancement in propulsion along the same lines as the new Blade-less Dyson type cooling fans,,it wouldn't matter where you mount them then !.

Edited March 9, 2014 by Paul's Nulife4-2

[Dalslandia]

Wouldn't it be great if there could be a massive advancement in propulsion along the same lines as the new Blade-less Dyson type cooling fans,,it wouldn't matter where you mount them then !.

 

This have been discussed for airplanes. but a hint, there is non flying.

 

It is hard to replace the propeller, and the piston Engine with something better, a ducted prop do well, but not without COSTs.

this self spell correction is funny too.

 

the azimuth pods often dont have a duct

[b0atman]

If no dredging then why not fit wheels and then decide front or rear drive. Trads would be sold as mid-engined

[davidc]

Not if the prop was located in the normal position behind the swim, that construction could be repeated at the front. If both props were in a tube, as in some outboards, then the front one could be rotated 90° to protect the prop and also act as a bowthruster. Effectively the boat would have a stern swim at both ends.

That is the method that is used on the royal engineers heavy ferry four engines one at each corner the prop is waterjet system but for easy steerage the back two are aimed into the centre of the ferry.

 

quote

 

The Heavy Ferry comprised 3 pontoon sections, main, buoyancy and propulsion. The inner main pontoon could carry a Class 80 vehicle, the outer buoyancy pontoons provided extra lift and the propulsion pontoon powered the ferry at speeds up to 7.5 knots using a Rolls Royce B80 powered Gill waterjet system, the same engine as used on the Saladin and Saracen armoured vehicles.

 

unquote

Edited March 9, 2014 by davidc

[onionbargee]

 

 

One of these would reduce wash

Not on a narrow boat it wouldn't, I don't think a super tanker is concerned about wash, they are for fuel efficiency, and only work on moosive ships.

[Paul's Nulife4-2]

Obviously that particular excitable ship is in it's prime !.

Edited March 10, 2014 by Paul's Nulife4-2

[BGA]

Not if the prop was located in the normal position behind the swim, that construction could be repeated at the front. If both props were in a tube, as in some outboards, then the front one could be rotated 90° to protect the prop and also act as a bowthruster. Effectively the boat would have a stern swim at both ends.

You could adapt the weed hatch for this and if it had a hydraulic drive motor it wouldn't be a major issue to withdraw it for maintenance or debris clearing.

[nb Innisfree]

You could adapt the weed hatch for this and if it had a hydraulic drive motor it wouldn't be a major issue to withdraw it for maintenance or debris clearing.

Yes I've often pondered that but if I recall a standard (ish) weedhatch is a bit on the small side, would need a smal diam prop and a shallow 90° final drive.