A small electric stern thruster
Discussion
Struggling to get off a lee shore single-handed I thought 'Wouldn't a bow thruster be a great idea'. OK so the old-school types think this is cheating, but then they have wives and kids to do the pushing off. I can't push the front of my boat off and get back to the wheel before the f
ker blows back in again.
Now a bow thruster is more DIY work than I'd want to try, but I had an idea for a simple stern thruster. Imagine a piece of 4" soil pipe, maybe a foot long, fixed to the transom underwater so the ends point left and right. Now put a propeller in it, perhaps direct-drive from a submersible motor, and run a suitable cable to the batteries. Current drain isn't a problem as the engine will be running. Three-position switch on dashboard does left-off-right. Probably need a relay as well.
What did I miss? Home for <£200?
ker blows back in again.Now a bow thruster is more DIY work than I'd want to try, but I had an idea for a simple stern thruster. Imagine a piece of 4" soil pipe, maybe a foot long, fixed to the transom underwater so the ends point left and right. Now put a propeller in it, perhaps direct-drive from a submersible motor, and run a suitable cable to the batteries. Current drain isn't a problem as the engine will be running. Three-position switch on dashboard does left-off-right. Probably need a relay as well.
What did I miss? Home for <£200?
Edited by Simpo Two on Monday 6th June 22:03
P924 said:
put a fender on the bow, keep the bow line attached and motor forward and the stern should come out.
then work out how to get the bow line off.
A bit like winding on the nose, yes. It would work on a soft bank like a field, but not a low hard edge as you'd need fenders every 6". I don't see (b) working though. then work out how to get the bow line off.
I'd also have to get off to recover the mooring stake, which would be impossible unfortunately.
Edited by Simpo Two on Monday 6th June 22:18
Paddy_N_Murphy said:
Sounds fugly, potentially dangerous, and not very sea worthy.
Well, it would be between waterline and bottom of transom, so invisible and sea(river)worthiness unaffected as it's not in the 'slipstream'.Paddy_N_Murphy said:
They munch Battery power - you probably would need to bank a few more up.
If you think of the thrust you are going to want this to make to picot you round, and every force has an equal and opposite...... It is not going to last two blips of the button without whizzing itself off its mounts across the estuary trailing its battery lead like a torpedo !
Proportional control would be nice so there'd need to be some electronics, some square wave jobbie perhaps. That might cost a bit as it'll have to handle some current.If you think of the thrust you are going to want this to make to picot you round, and every force has an equal and opposite...... It is not going to last two blips of the button without whizzing itself off its mounts across the estuary trailing its battery lead like a torpedo !
Paddy_N_Murphy said:
What's the boat ?
Freeman 23 - about 2 tons. This photo may help:
So it goes on the blue bit between exhaust and rudder... it has to be possible...
Motherboards?
The submersible motor is probably the killer - all stern thrusters I've seen appear to have the motor sticking out of the top and presumably a gearbox in the middle.
Paddy_N_Murphy said:
Have you looked to a Bow Thruster though ? Got to be more of them out there and guides to follow than trying to reinvent the wheel? Surely you want the Bow to thrust not the stern ? Unlike a Rag'n'Stick with a keel it's not going to pivot round is it?
There are two reasons for favouring the stern. One, I don't have to drill a socking great hole through my boat for a project that may or may not work. Secondly, one on the stern could counter the paddlewheel effect (stern pulls to one side when reversing) which is either handy or a PITA depending on what you want to do.The submersible motor is probably the killer - all stern thrusters I've seen appear to have the motor sticking out of the top and presumably a gearbox in the middle.
I'm likng the thinking Jon. Have you considered a paddlewheel? Much easier as you won't have to source waterproof motors. 
But more seriously why not look at an electric outboard motor that you can just plug in and you get to have something you could use as emergency / dinghy use too?
But more seriously why not look at an electric outboard motor that you can just plug in and you get to have something you could use as emergency / dinghy use too?
Matt Harper said:
What about a transom-mount trolling motor.....
Funny enough I was thinking that myself too but only if Simpo posts video the way Bill Dance does.http://www.youtube.com/watch?v=SrA_kGB007U
http://www.youtube.com/watch?v=hCXrIcEDrS4&fea...
Just drop an anchor on your way in and use it to pull yourselve back off the bank.
Or if it is a soft bank push the stern off and stick the nose in motor ahead with the rudder hard over that pushes the stern out and then motor away backwards.
Or if it is a soft bank push the stern off and stick the nose in motor ahead with the rudder hard over that pushes the stern out and then motor away backwards.
Edited by thinfourth2 on Tuesday 7th June 07:11
MOTORVATOR said:
I'm likng the thinking Jon. Have you considered a paddlewheel? Much easier as you won't have to source waterproof motors.
You're a dangerous man... I could operate it by hand-crank through the transom... (these are the ideas that made Britain great you know...)MOTORVATOR said:
But more seriously why not look at an electric outboard motor that you can just plug in and you get to have something you could use as emergency / dinghy use too?
Problem is not just cost but storage. Permanently hanging off the transom would be naff (and people would say 'Look his boat must be unreliable!'. It couldn't be used with the main engine for docking either.Paddy_N_Murphy said:
Not much mention of stern thrusters though....
Thanks for looking though. I didn't pick it up earlier because it was like someone saying 'look on Pistonheads' 
If no-one can find a submersible 12V motor of sufficient power then the other answer is probably an oar! Start the engine, untie, lean over the stern, paddle like a b
d then leg it back to the driving position before the fker blows back in.These things are so much healthier than staring at a PC screen
Simpo Two said:
MOTORVATOR said:
I'm likng the thinking Jon. Have you considered a paddlewheel? Much easier as you won't have to source waterproof motors.
You're a dangerous man... I could operate it by hand-crank through the transom... (these are the ideas that made Britain great you know...)I have however spent most of the morning in research for this project and have come up with a system that will be cheap and effective......
Home made pulse jets!
Short burst use only so can be made out of old copper pipe and solder so very cheap. The copper can be handily polished to look like brass and sort of nautically.
You will of course need to make 2, one above the other, so that you can operate in two directions, I would however suggest some form of interlock so that both can't be operated at the same time turning your Freeman into a large catherine wheel.
Geez, some people, you try to help and all you get is negativity.
Right so working on your original theory which included a lump of drainage pipe (which you have obviously already aquired from a building site hence the negativity to my previous inspired ideas) I have another plan involving said drainage pipe, 2 very large coil springs, a ratcheting mechanism and a pair of boxing gloves.
Interested?
Right so working on your original theory which included a lump of drainage pipe (which you have obviously already aquired from a building site hence the negativity to my previous inspired ideas) I have another plan involving said drainage pipe, 2 very large coil springs, a ratcheting mechanism and a pair of boxing gloves.
Interested?
I think you're probably right but if it could be achieved I would have expected Lewmar or similar to have taken up the idea.
I'd been racking my brain for the name of a jet thruster system that was on the market but it seems they've gone bust.
A water jet system that ran off hydraulic pumps and motors from your existing engine via PTO. Very clever but obviously not successful.
Might be possible to think along the same lines with electric power.
Some old docs outlining the system here.
http://www.google.co.uk/url?sa=t&source=web&am...
I'd been racking my brain for the name of a jet thruster system that was on the market but it seems they've gone bust.
A water jet system that ran off hydraulic pumps and motors from your existing engine via PTO. Very clever but obviously not successful.
Might be possible to think along the same lines with electric power.
Some old docs outlining the system here.
http://www.google.co.uk/url?sa=t&source=web&am...
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