Here's a Thought About Propellors

Lakesailor · 5 Dec 2011

Has anyone designed a boat with a tractor propeller acting acting forward of midships?
Would it work for a small boat like a tender or fishing boat?
By mounting the power head backwards the recoil start and throttle etc would be available to the helm sitting behind it. It would need to protrude through a well in the hull or on a small cat between the hulls.
Would it be self defeating or could it work?

Just idly wondering.

mjcoon · 5 Dec 2011

Lakesailor said:
Has anyone designed a boat with a tractor propeller acting acting forward of midships?

It's not ideal to be sailing through the water that you have just set in motion against you. It would increase the drag a lot.

Mike.

Twister_Ken · 5 Dec 2011

Modern tug boats have a propellor (not exactly) mounted pretty much amidships, which can vector in any direction. Works for them.

http://www.voithturbo.de/vt_en_pua_marine_vspropeller.htm

Deleted member 36384 · 5 Dec 2011

There was an experimental boat on the Clyde years ago that had could move directly up wind under wind power. It consisted of a wind driven propellor which was connected directly to a propellor in the water. I am sure that this was a tractor propellor.

http://www.secretscotland.org.uk/index.php/Secrets/FalconExperimentalTurbineVessel#fn1_1

I can't be sure if it was a tractor to be honest but I have a suspicion that it was.

Grajan · 5 Dec 2011

I remember seeing the boat "Falcon" in the boatyard at Tighnabruaich which was I believe owned at that time by brother /relative of Neil Bose, Arun?
Going forward would have been pretty difficult due to the swing of the air prop when under way!!! From memory the drive was through a standard aft propellor with a long shaft from under the mast, but age and memory do funny things!!
I sailed on a vessel by the name of "Sea King" a 27' yawl designed by Charles Violet ("Nova Espero" fame) and Jack Love of General Developments Ltd. She was built for the Glasgow Herald "build a yacht for under a £1000" competition and had possibly one of the first "S" drives ever fitted, and at that time it was poo pooed because of the TWO right angle gearboxes. So Lakesailor you could be onto something!!

Rigger Mortice · 5 Dec 2011

It works with aircraft.

grumpy_o_g · 6 Dec 2011

mjcoon said:
It's not ideal to be sailing through the water that you have just set in motion against you. It would increase the drag a lot.

Mike.

Aside from that it's a damn sight easier and cheaper to fit an engine and prop at the back where there's more room, buoyancy and a nice transom to stick shafts, etc. through. Plus the engine's weight is raising the bow rather than trying to stuff it and it's protected to an extent by the hull when bashing into head seas. I would imagine you also get a benefit from the "rear wheel steering effect" of having the rudder at the back. Wouldn't the rudder need to be bigger to get the same effect?

Someone's bound to have done it though.

mjcoon · 6 Dec 2011

Rigger Mortice said:
It works with aircraft.

Though there have been pusher-prop aircraft. Don't know why.

Maybe there is an advantage from front-mounted props from increased airflow helping take-off at lower speeds? (Countering drag.)

Mike.

TSB240 · 6 Dec 2011

I am sure Volvo offered a saildrive unit which is front facing.

Seem to remember main advantage was much tighter turning radius.

Expect VP will be here soon.

Found This
http://www.volvopenta.com/SiteCollectionDocuments/VPC/files/PowerboatGuide.pdf

Look at page 12

Seajet · 6 Dec 2011

Pusher prop aircraft started as it leaves a nice observation cockpit right in the front for, err, observers; as in spotting for artillery in WW1.

Plenty of pusher aircraft inc' the Wright Brothers' job; one slight disadvantage with pushers is that in a 'hard' landing the engine & prop will come forward to meet the crew.

As for tractor prop' boats, as said it must have been done, but can't think of one at the moment.

Twister_Ken · 6 Dec 2011

Seajet said:
one slight disadvantage with pushers is that in a 'hard' landing the engine & prop will come forward to meet the crew.

As opposed to the crew moving forward to meet the engine?

Seajet · 6 Dec 2011

Crew = a few hundred lbs weight, engine & prop etc = a lot more 100's of lbs...

Also nice to have a solid engine to take the impact rather than soft crew.

There are still modern pushers though, flying boats for a start where the engine is on a pylon so hopefully clear of the crew.

Billjratt · 6 Dec 2011

There's one up on the hard at Troon.
It has a retractable (I believe) rotateable leg at the bow instead of the usual thruster in a tunnel.
I think the owner brought the boat to Troon using it instead of the main engine.
I assume it must be hydraulic or it would have burned out...

Twister_Ken · 6 Dec 2011

Seajet said:
Crew = a few hundred lbs weight, engine & prop etc = a lot more 100's of lbs...

Also nice to have a solid engine to take the impact rather than soft crew.

There are still modern pushers though, flying boats for a start where the engine is on a pylon so hopefully clear of the crew.

My somewhat indistinct memory of A' level physics suggests there is very little difference in effect between a 1000lb engine hitting a 100lb crew at 100kts, or a 100lb crew hitting a 1000lb engine at 100kts. Both are likely to take the smile off of your face.

Blueboatman · 6 Dec 2011

Needs bigger bolts and safety belts and airbags to restrain a 1000lb engine?

Seajet · 6 Dec 2011

Precisely, it's easier to restrain the crew...also fuel spilling forward onto a crew may well be a factor.

Back to boats...I think one major snag with a tractor prop on a boat is it will pitch in & out of the water.

What with that, the greater buoyancy aft to place the weight of engine & transmission, the snags of having a rudder in the propwash towards the centre of the boat, etc, and it begins to become clear why I for one am struggling to think of a tractor prop boat !

Talbot · 6 Dec 2011

Seajet said:
Pusher prop aircraft started as it leaves a nice observation cockpit right in the front for, err, observers; as in spotting for artillery in WW1.

Plenty of pusher aircraft inc' the Wright Brothers' job; one slight disadvantage with pushers is that in a 'hard' landing the engine & prop will come forward to meet the crew.

As for tractor prop' boats, as said it must have been done, but can't think of one at the moment.

A number of amphibious aircraft use the pusher in order to avoid the spray being sucked into the engine.

pvb · 6 Dec 2011

In the US, lots of fishermen use bow-mounted electric trolling motors.

Romeo · 6 Dec 2011

BMW did an advert in mags a couple of years ago showing a boat with an outboard at the front. The suggestion was that having drive at the front is ridiculous idea, so we should all drive cars with rear wheel drive. Having watched the antics of BMW drivers in the snow last year, perhaps a bow drive is not such a bad idea in boats as well as cars.

geoffatstanpit · 6 Dec 2011

There is a very big Sunseeker mobo in their yard at Poole next to the new RNLI place with two saildrive type arrangements with counter-rotating props in front of the legs. Looks a bit wierd but presumably there's a reason. Looks like the whole leg pivots for steering with the flattened leg acting as a rudder

Here's a Thought About Propellors

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