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[rathikrishna]

Good morning Friends..now i am back at home again, and working on my ne war ship...so i discovered a amazing thing last night...is, i was trying to fix a prop to my new water recovery vehicle, by trial and error method...soon i saw that , the prop pulls even more torquely when i tried to fix it facing towards bow, instead of stearn as usual...why this happening..?  i tried with various types of props..all it gave a good pull when i fix it at bow, and in to a puller configuration, instead of a pusher.can some veterans explain this phenomena...?is it positive..?can we adopt this configuration to our crafts..?  please...

[tigertiger]

I am not any kind of expert, but here are my initial thoughts. I do however stand to b e corrected.

The main advantage for a prop facing backwards is that the propwash flows over the rudder, increasing turning ability.

Another thing is that the water being pushed backwards all pushes the boat forwards.
With the prop at the front the wash would hit the bows of the boat. Some of the thrust will push the boat forward, some of the thrust will hit the hull and in effect be trying to push the boat backwards, and some would deflect of the sides creating 2 opposite sideways thrusts (the port side pushing starboard and starboard side pushing port) that would cancel out. You may indeed be pushing more water, but you would make less forward motion.

 Booms/outriggers on each side of the bow to place the motors outside of the lines of the hull would help, but they themselves would cause drag. And now the boat would be looking very odd.

I am sure in the development of boats and steamships engineers tried almost every conceivable configuration of prop, including several props on the same shaft. But all seem to have have settled on the rear prop solution.

I can only think of 2 exceptions.
The first is jet drive, but even here the thrust exits the back of the boat.

The second is Voith propulsion. But this does not use standard props.
It is really radical departure from other forms of propulsion, see it here http://en.wikipedia.org/wiki/Voith_Schneider_Propeller

[Colin Bishop]

Many modern cruise ships have propulsion pods with forward facing propellers but these protrude beneath the hull in the water fllow and are steerable so rudders are not required.

Colin

[dreadnought72]

...all seem to have have settled on the rear prop solution.

Probably because it's much less vulnerable - and yet still at some risk of damage and fouling.

Andy

[carlmt]

4th generation car ferries - 1980's - had forward facing props just behind a bow rudder (in addtion to bow thrusters) to aid reversing and movement in port.

The latest generation just have enormous bow thrusters - due in part to the bulbous bows now fitted to ships.

Carl

[rathikrishna]

Good evening and thank you all respected Friends...i was planning to make a craft , with prop at front..so now i have to rethink...thanks once again...

[nemesis]

Hello, Vic Smeed designed a straight runner with the prop at the front so it pulled the boat rather that it being pushed, it also bites into solid water so it is possibly more efficient.  Nemesis

[Pirate]

The efficiency of a 'fore' prop that pulls the vessel, is only in the ' revolutions per minute/amperage drawn' respect and not in the 'amperage drawn/propulsive distance and speed' relationship. As has been stated before, the prop a 'fore' will bite a quantitatively greater amount of water per revolution than that a 'stern' but its propulsive distance/ speed is reduced by the hull design behind. Inversely the prop a 'stern' bites fractionally less water due to the hull design but is able to 'use' it with more effect. Largely the siting of the a 'stern' prop or props is governed by the shape of the hull. Designers/engineers look at the available volume of water and equate it with the available thrust of the same, with the ideal being the least energy used for the maximum thrust/distance traveled per revolution.
Simply put  ... look at the real vessel and hull design and follow the ££££££££££ worth of research as to size, type and positioning of the propulsive device. Its wasted action to reinvent the wheel. Although scale models do tend to need proportionally larger propulsive devices per scale than the real vessel due to the proportionally denser water/scale factor.

Think, research and adapt.

Kind regards
Pirate

[Martin (Admin)]

An interesting observation & question Rathi....

 It would be interesting to conduct further experiments with say flat plank of wood poited equally at each end and;

1. Measure the speed of the 'hull' going forward then backwards.
2. Measure the current draw forwards / backwards,

You say you tried various propellers, not sure if any of them are "commercial props", which are all designed to be "pusher" props, so for you to find them seemingly more efficiency as puller props is very interesting!
 

[tobyker]

Some Icebreakers have a prop at the bow as well as at the stern - the idea is that the bow is driven up over the ice, the forward prop lowers the pressure of the water underneath the ice and the weight of the ship pressing on the ice cracks it. However in your part of the world you may not have a great need for icebreakers!

[scout]

Hi I once read a book on German first world war war ships that had a prop and rudder at the bow and stern whether it was so they could escape without turning round I do not know Yours Scout

[tigertiger]

An interesting observation & question Rathi....

 It would be interesting to conduct further experiments with say flat plank of wood poited equally at each end and;

1. Measure the speed of the 'hull' going forward then backwards.
2. Measure the current draw forwards / backwards,

You say you tried various propellers, not sure if any of them are "commercial props", which are all designed to be "pusher" props, so for you to find them seemingly more efficiency as puller props is very interesting!
 

Hi Martin

A flat plank would only give you the effects of the prop and the water. But would not show the effects of the hull.

[rathikrishna]

Good morning my Friends...i was burning my brain and body with my new project..that is "THE PROP AT FRONT" . and by night i have compleated a hull, slim, but not much, with a wide keel, that holds the propeller at bow..and made a prop for this...its not nothing but same as an usual craft , just like a Stearn of PUFFER..the both ends are identical...so i have tested a lots with this configuration..all my test shows that , in the foreward mode means in pulling mode, my motor drops around 1.5 amps, and gave me a big pull and violent foreward speed, while the same setup, with inverted same propeller , it drops 1.8 amps but gave me some sluggish fore speed and pulling force...in my first set up..( puller co fig), it pulls three bricks (each weighs 3 kgs),on a playform of expanded polystyrene with ease...but in reverse the pulling force as lesser at same voltage and current...so i increased the voltage..still the result as disappointing...after a high voltage the prop starts to cavitate...so now i know some thing is happening on this puller configuration..its sure...i will post a detailed article and step by step videos within time for great discussion...if it will works well all of my latest crafts will be an unorthodox in configuration...i always wonder while experimenting with wind tunnels, as many of our studied theories melts out in real life...so i experienced a new phenomena at least for me...so i am working on this new craft...i have a little doubt that, what kind of body that i can fix on that hull is...so i will post a whole idea here...but no i need a little time..to finish my life boat and water crane with working booms...yuuuuummmmyyyy days.....

[rathikrishna]

and much thank full for the inspiration from our respected Administrator...Sir, i am already in expiriments with it...soon i will post a detialed discussion here, so i hope, that many of our friends can go for this once...its fun to do more unorthodoxical configuration...thanks once again...

[barefootgoth]

Some years ago I went on holiday to Norway.  There were small car ferrys running across the fjords carrying about 20 cars at a time or so.  The design of the hull appeared to be completely symmetrical side to side and front to back with the bridge being on a bridge across the middle of the boat.  I can only imagine that they had propellers and rudders at both ends having watched their maneuverability and the fact that they never turned around.  I don't know if they used all the propellers all the time or just the ones at the current rear end, but their bow wash did show something of the sideways wash mentioned earlier.

[slug]

an aircraft has the propeller biting into solid air if the propeller on a ship bit into fresh water would this be the same after water has run the length af a hull it picks up air bubbles water no longer solid mass propeller is biting into diluted water less bite just a thought most likely wrong   slug

[pugwash]

slug I am sure this has been studied over the years- but props are still on the stern - this must tell you something - also it is surprising how many
ships have minor bumps with other ships/jettys and debris in the sea and it would be dead in the water if it damaged the prop
There is a thread somewhere on mayhem about a French torpedo boat destroyer that was so poor at manoevring in harbour that it had a bow prop
fitted but I believe it was lowered into position as required ( could be wrong there)
A non-starter I think.
Geoff

[nick_75au]

Sydney to Manly ferries have a bow and stern prop, due to double ended design, unsure if only one prop was engaged at a time however, smaller vessels are using Volvo IPS systems regularly now with a fwd facing prop, QM2 uses fwd facing props, all but the ferry have them aft.

Nick

[pugwash]

Must admit I was very surprised when I saw the QM2 had forward fcing pods. I assumed they would face aft.  Mind you I see she carries 8 spare blades in case
of incidents.

Geoff

[slug]

pugwash i thought i maybe wrong just wandered if it was possible no fortune to be made by me will just  have to keep working ha ha!  slug tony

[Colin Bishop]

Cunard have recently successfully sued Rolls Royce over the propulsion pods which have proved to be rather less robust than expected thus necessitating more frequent dry docking for maintenance than anticipated with the ship out of service.

Two of the pods are fixed, the other two provide steering.

Colin

[slug]

just been on the webb a commercial ship is being made with 2 pods at the front only re www.physicsforums.com introductory physics still no
real answer  slug

[pugwash]

Slug, Technically you may be right and they may be more efficient facing forward (its my wife has A level physics not me) BUT in a
practical sense why put the props in harms way - there was a quote a few years ago from one of the maritime safety organisations
stating approx 80,000 containers are lost overboard per annum and a lot are awash and don't sink - they would really spoil your day
if a bow prop met one of those at 16 knots.  then there is the rest of the debris in the sea lanes.  Seems an unnecessary risk

Geoff

[slug]

pugwash thank you for the comments point taken now the silly question how many containers are in use tried to find out cant  have a lovely easter tony

[pugwash]

Hi Slug There are many safety reports online about cargoes lost overboard but no figures of total number in use.  The best I could find was in 2006 there were estimated
to be 5m to 6m containers on the move at any one time and that worldwide the major ports handled about 500m containers in that year.
Most sobering figures estimate up to 10% contained household or industrial chemicals harmful to the marine enviroment
How much has the container traffic built up since 2006. 90% of the worlds non-bulk cargo is now shipped by container.
Having an interest in yachting I know there have been several cases of yachts hitting semi submerged containers and sinking.

Geoff