A small electric stern thruster

[Simpo Two]

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 fker 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

[Simpo Two]

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.

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

[Simpo Two]

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.

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...

[Simpo Two]

Motherboards?

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.

[Simpo Two]

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 bd 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]

There are some ideas that made Britain great... and some that didn't.

I fear that the Motorvator Twin Pulse Copper Thruster falls into the same category as Brunel's Vacuum Railway...

[Simpo Two]

Now you're talking.

Bring me a working prototype

[Simpo Two]

Niet, I mean nein, er, no.

[Simpo Two]

That is one advantage of river cruising - the 'opposite bank' is at least in the same country!



Still think it's a good idea though. There are loads of 20'+ boats out there and I reckon they'd pay £400 for a bolt-on 12V stern thruster.

[Simpo Two]

The infuriating thing is that there's a pefectly good propulsion source two feet away, but pointing in the wrong direction!

We need vectored thrust... but a bit smarter than a rudder...

[Simpo Two]

MOTORVATOR said:

Look up Volvo IPS. 360 degree propulsion and if you have 2 then supposedly the software can send any part of the boat where you want it by joystick.

If powered craft had just been invented that's what they'd have - the thinking man's outdrive. Contra props too, perfect.

It makes the standard prop shaft and rudder look very primitive. However that is what I have as my starting point!

[Simpo Two]

'HTR'...!

It's a nice idea Les but in the end I solved the problem another way - by buying a new boat with a thruster at both ends! Only 25kgf so not much use in a strong wind, but usually very helpful.

(Unless the freshwater tanks in the front are low and I have passengers in the cockpit, in which case the bow one doesn't bite... but then I have helpers...)

[Simpo Two]

mrpurple said:

I feel for the OP....I bought this earlier in the year and after a few nice trips up and down the river I still ahve not managed to make a dignified return arrival and there always seems to be a few more experienced boaters about with big grins on their faces

Stern mooring is the ultimate challenge - if the wind and prop-walk are against you forget it!

[Simpo Two]

You could always moor nose first and move the little step thing to the end. On the Fens most boats moor nose first; stern in seems to be more of a Broads thing - and more boats have rear access. (I have to moor stern on because the jetty is several feet shorter than the boat!)