bow or stern thruster

Have any members had success in making their own bow/stern thruster able to fit into a few cm of hull cross section? I am making a model icebreaker and need thrusters to achieve realistic manouvering, but only have two or three cms in the sections with access to the water? (Much larger hull section remote from the thruster level).

For me I’ve not made one that small, that said I will be in a similar situation in the near future as a model tug I have requires a bow thruster that needs to fit in the 15mm hollow space of the bow bumper...

My plan was to make a T shaped gear system, the props fitted on the end of the T via shaft with a gear system for corners ( I know there’s a name for that but I can think of it for the life of me right  now) the props with the shaft are fitted in a sealed tube with only the drive motor shaft and gear drilled through, ( I was to make up sealed bearings for that input on the lathe. Which can be run from a motor further Back in the boat for clearance.) 

I was going to use standard small props for mine bother LH and RH on a small 2mm shaft, and just some micro P skeg housings to keep shaft inline with the tube housing...

On a side note.... would you believe that at if you used a DC motor you can actually wire those up and submerge in water fully, without shorting it out!!!!

So if all else failed think kiddie toy in the bath, those little dc motors can be fitted and flooded with no real ill effects... ( apparently that’s how some motors are used, or run in submerged!) so all you would need in a worse case for size is a small motor with the spindle both ends and attach “props” to each end and just some mounting bracket in a tubular housing, the wires poked through wi tv a drop of silicon and done, ....

Experimentation is the key, but I can promise a dc motor submerged fully will still work...


Or the other option... use a robbe bow thruster kit and mod it!

just found these on ebay……..

are they any good to you. 

https://www.ebay.co.uk/itm/For-RC-Model-Boat-Bait-12V-KV800-Underwater-Thruster-Waterproof-Brushless-Motor/153768851315?hash=item23cd567773mGri1qLggyeR2y1uV3kr8GQ

Those look like some knarly  3D prints..

no idea matey just looked quirky...…….what does knarly mean.

Bad print quality as in they look shit

Thanks for the replies. I have waited a while to see if anybody had a better solution.
Suggestion 1 is very good, but I have tried it with plastic bevel gears and failed. The gears need to be fairly small otherwise they obstruct the water flow too much. The bevel gears I used appear to be nylon, 0.45 inch (11.6 mm)diameter which is OK with a 20mm three bladed prop (cut down from a 25 mm to produce larger blade faces) each side. Ok in the pure water of the bath but jambs with the slightest contaminate of a real lake.
Suggestion 2, of items on ebay - Diameter: 63mm Length: 80mm - much too big.
Suggestion 3 Using a motor actually in the water. Back in the 1950's in Model Maker magazine, they published a picture of a boat with an outboard motor consisting of the motor with a propellor directly fixed to it mounted on a plate extending below the hull. As the editor said "it was OK for this boat, it was owned by Colonel Taplin, he owned the factory that made the motors". My own experience with such a system didn't do too well, the brush springs and comutator disolved away, admitedly I was operating on a salt water lake then (Canoe Lake Southsea) but don't think a motor would do too well in a normal lake.

Nylon gears wasn’t my chain of thought for the system, I fact I avoid plastic gears for most projects that end up mechanical just as they end up as the largest point of failure, that said I deffo alt wouldn’t use nylon gears where torque is needed... 

There are options to locate steel, stainless, alu bevelled gears, usually an older kids toy can harbour a few, older Hornsby trains also have brass gears, music boxes and other items tend to yeild good results for small gears, just have a look about for some metal gears and try again...

I had thought about suggesting use of a windscreen washer pump ( or other pumping device) to use as a “blower” effect over a prop, however that sadly will only give you one direction since they can’t reverse.... that said maybe you could mod/find one to go forwards and back! This would only require Then tubing to fit in the gap,allowing the motor to be places where Needed.

https://www.amazon.co.uk/gp/aw/d/B01MTIKACZ/ref=psdcmw_1939518031_t3_B0001P197M

Further to my experiments, I too considered using a pump connected to two elbows. I purchased a caravan water pump, the type that drops into a tank of water. Unfortunately the pump uses an impellor, moving water by centrifugal force, so swapping the connections to the motor reverses the rotation but still pumps the water in the same direction.

Look into the mini brushed drones.  There are some ducted fan style ones with brushed motors that can't be much bigger than 4-5mm diameter and maybe 8mm long.  I don't know exactly the mechanics of a bow thruster, but I suspect one of these motors would be easy to get working.  And I can grab a whole drone off Banggood for under $15 usd.  These guys move a lot of air and I suspect would move some water too.  There are upgraded motors too for pretty cheap.