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Large Scale Tug Boat propulsion

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Large Scale Tug Boat propulsion

Old 03-21-2014, 06:34 AM
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XchosenlegacyX
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Default Large Scale Tug Boat propulsion

First time posting here and am in need of some advice, I am building a large tug boat from scratch, and I cant seem to decide the best propulsion method. I have been toiling over it for a few weeks now. I go back and forth between gas(2 stroke, not nitro)like between a 26-42cc, and electric. I have done both in cars and trucks but never in a boat, I have decided to go gas. But now my question is? how to get reverse? I really want the reverse option, to be scale. This will be a large project, boat being around 4 feet in length and could weigh between 100-200 lbs. I don't want to have $400+ transmissions installed, nor do I want to use jet drives, SO I was thinking, can an rc truck transmission be modified to take the rpm produced from a 26-42 cc engine with max 12,500 rpm? Like a T maxx 3.3 transmission? I could build a full steel gear transmission, do you guys think this would hold up, so I could have forward(2 speed) neutral and reverse? and then we get in to the whole gearing issue.........But will this hold up, or just be a waste of money to do?
Old 03-21-2014, 11:30 AM
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K-H2o
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X-Man- I don't have an answer for ya- but I am looking into a similar type project where I am trying to propel a slow moving boat about 80lbs and I want to go a top speed of around 30mph and do it with electric. I have been looking into low kv motors (leopard 56100), maybe a small-ish prop.
I don't want a gearbox
Are there lower pich props available, less than 1.4
Looking for ideas ?

Last edited by K-H2o; 03-21-2014 at 11:38 AM.
Old 03-21-2014, 11:36 AM
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XchosenlegacyX
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i mean i have seen people use a trolling motor , which is cool because it can be used as a multidirectional pod, however if you are going for the scale look, it doesnt look scale, OR i have seen people put the trolling motor in the hull, either way, im looking to go gas
Old 03-21-2014, 11:40 AM
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K-H2o
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X-man- Have you seen lower pitch props ??
Old 03-21-2014, 11:51 AM
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XchosenlegacyX
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Originally Posted by K-H2o
X-man- Have you seen lower pitch props ??
prop shop has just about any prop you need, its in the uk but its got what u need.
http://www.prop-shop.co.uk/

I am planning on using a Kort nozzle set up with between a 3.5-4inch 3-4 blade prop
Old 03-22-2014, 01:37 AM
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K-H2o
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Hey, Thanks for the tip !! That Kort nozzle is pretty interesting !!! Have you used one before ? It looks like a low speed set up. How fast will they go ?

Thanks !!!!
Old 03-22-2014, 01:53 AM
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I was considering a gas weedeater engine for a large tugboat at one time,but decided against it. A gas engine if not water cooled needs air to cool it and even if it's water cooled it needs fresh air to the carb.Another thing to consider is the heat build up in the hull from the exhaust and cylinder heat.Next to use a reverse, if a transmission works, you would need a clutched engine.Clutches engage and disengage at a certain rpm and it would be like reving up you car then putting it in gear.Not a smooth transition from a dead stop to forward or reverse.You would have to use gears or belts and pulleys to gear it down to achieve scale speed.Most large r/c tugs have dual props.You would have to figure how to drive two off one engine.With electric motors you won't have all these problems and if you have a need for sound or smoke there's smoke and sound systems available.Go to the scale boat section here and they can give you advice.

Last edited by Tidnab; 03-22-2014 at 01:55 AM.
Old 03-24-2014, 12:51 AM
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With a motor that only turns in one direction, options are a variable pitch prop, a gearbox, a "Kitchen Rudder" (look it up via google) or use the motor to drive a generator and move the boat with an electric motor and an associated ESC.
Having reverse is not an optional ornamental extra with a large model boat. Reverse is your brakes.
If the engine drives a 3 phase alternator, that can, in turn, drive a 3 phase motor (or brushess, as modelers know them). Speed control of the motor by the speed of the engine, reverse by operating a relay reversing the polarity of any 2 of the 3 wires.
Old 03-25-2014, 01:14 PM
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XchosenlegacyX
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ok after much thought and all your helpful contributions, I have now decided to go with an electric drive train, your all correct it is much easier and the benefits outweigh the disadvantages(like lugging around a 12v battery)
Old 03-26-2014, 12:16 AM
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Whatever it gets powered by, it will weigh the same. Something about Archimedes' Principle.

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