How much power to move a 4,000kg boat?

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a3xloser

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hi
ok 4000kg narrowboat 25 foot and i may fit an outboard engine on it,
Q: will a 10 hp engine move a 4,000k boat on canals, i know it not going to do rivers, many sail boats are as heavy as this so what engine do you need?
thx
 
The obvious answer is 1hp, because they used to do it with one horse, on a bigger heavier boat.
However the horse is rated at 1hp continuous, and has a lot of thrust available to get the boat moving, simply by using its weight.
An outboard only develops its rated power at max rpm, so the prop needs to be right for it to do that. It's probably more economical to run something at half power or so, that gives you a bit of extra to get moving, then you can throttle back. You also want some thrust available for steering if the boat does not have a big rudder.
I would guess a 6hp motor would be OK, with a fine pitch prop?
I would ask around the used engine places, see if you can try one out?
 
A long time ago

A long time ago I got my horse to pull 30 tonne butty from Liverpool to London

there was one place where there was no tow path

so we breasted an avon up to the butty, bunged the 2hp seagull on the back and away we went

we got it up to a good walking pace

I am sure that on the canals a 5hp would have you whizzing along

Dylan
 
Although only 1 hp might get the barge up to some sort of reasonable speed, you ought to remember that stopping quickly will be very challenging. There's a balance between wanting to run the engine at some sort of reasonable efficiency (perhaps 2/3 rated output or similar) and having some power for emergency stops when some clown cuts in front of you or stops their small lightweight boat quickly in front of you.

A few hp should be adequate.... What do other people with similar size/weight barges use?
 
To move that sort of boat you need a large, slow turning prop. Unfortunately outboards have small high speed props so are simply not suitable. Although a 8-10hp will eventually get it moving it will be running pretty much flat out and will be useless in reverse. OK for emergency use just to move the boat, but for continuous cruising use you need a proper inboard installation. BTW 4 tons is a lot for a 25' long narrow boat.
 
this sounds hopeful

was worried i needed a 15hp might be needed. i didnt want to spend money on an outboard to find out it couldnt move the boat, i may well get a nice engine fitted at later date, being able to move around, as let canal boat yard think your stuck and your bill triples,
 
Tranona said:
BTW 4 tons is a lot for a 25' long narrow boat.
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sort of guessing on the 4 tons, but i have put 1000kg balast and fittings in. the braking could be a problem, i think i may just get a cheap outboard to potter about till i can aford a brand new engine fitted, rather than pay out the £3k piece of junk put in that they are quoting me
 
a3xloser said:
sort of guessing on the 4 tons, but i have put 1000kg balast and fittings in. the braking could be a problem, i think i may just get a cheap outboard to potter about till i can aford a brand new engine fitted, rather than pay out the £3k piece of junk put in that they are quoting me
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If you've only got to move small distances and show that you are mobile, then you will easily get away with a few Hp until you get a proper engine installation. I think people were answering as if you were looking for a permanent solution.
 
john_morris_uk said:
If you've only got to move small distances and show that you are mobile, then you will easily get away with a few Hp until you get a proper engine installation. I think people were answering as if you were looking for a permanent solution.
Click to expand...

i was toying with maybe permarnent buying new honda engine, but the advice here is edging me more toward a few hundred for temporary thing
 
If it's only to move a short distance now & again, you can haul it yourself.

But a Seagull will move it OK & at reasonable speeds plus you can rotate it 180deg to stop, or just turn into the bank, which will stop you pretty quickly & quite safely (apart from any unsecured bottles & vases below).

I have used a 2hp o/b to move my 7 ton 31' ketch in a harbour in the past. I just tied the rubber duck to the aft quarter & set the motor straight ahead, using the boat's rudder for steering. I had to leave a guy in the dink to control the throttle for me tho.
 
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Worth bearing in mind that it is about stopping and starting, not speed. If you simply haul on a rope, a boat - of pretty much any weight - will slowly start to move, and the longer the pull is continued, the faster it will go. But once moving, it won't stop moving so easily, as many a person trying to pull a boat into a berth has found out!
 
Searush said:
But a Seagull will move it OK & at reasonable speeds plus you can rotate it 180deg to stop, or just turn into the bank, which will stop you pretty quickly & quite safely (apart from any unsecured bottles & vases below).
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Can't do that with a Seagull - they don't turn through 180 degrees. Having said that a Century Plus would move the boat - if you could stand the noise!
 
dylanwinter said:
nice blokes use four strokes in confined waters such as those you find on a canal

at the very least avoid a seagull

Dylan
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Don't think we are talking about rational (or even sensible) choices in this instance as that would lead to a nice little 20hp diesel inboard which the OP says is not affordable.
 
AntarcticPilot said:
Worth bearing in mind that it is about stopping and starting, not speed. If you simply haul on a rope, a boat - of pretty much any weight - will slowly start to move, and the longer the pull is continued, the faster it will go. But once moving, it won't stop moving so easily, as many a person trying to pull a boat into a berth has found out!
Click to expand...

Stops quickly & easily enough if you just snub it.
 
a3xloser said:
hi
ok 4000kg narrowboat 25 foot and i may fit an outboard engine on it,
Q: will a 10 hp engine move a 4,000k boat on canals, i know it not going to do rivers, many sail boats are as heavy as this so what engine do you need?
thx
Click to expand...

You are asking the wrong question, the question you should be asking yourself is what do you want from the engine / transmission and what is suitable to fulfil your needs. It requires much thought before a decision can be reached.

A 1/3 hp electric motor with a 4 inch prop would move your narrowboat....eventually.

You need acceleration and deceleration measured in seconds however, not minutes. For this heavy boat and operating at low speeds you need an engine turning a large propeller at low RPM, not a small one at high RPM. Cavitation issues will ensue otherwise.

This means a low HP / high torque engine.

Do not forget you also need to steer effectively, therefore you need water flowing over the rudder. At low speeds this is provided by the propeller.

Canals are full of weed and other junk. Narrowboats are flat bottomed and the prop and rudder are protected by the bottom of the hull in a tunnel arrangement.
An outboard, to be efficient requires to dip below the hull into the undisturbed water. This means the prop will readily foul with weeds and smash against old prams ect

Does an outboard really appear to be the best solution?
 
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AntarcticPilot said:
As you say, and of course none of us here would make that mistake, would we :rolleyes:.

I hate to think what the strain on a rope stopping 6 tons going at 1 knot is; I reckon it's the only way most of us are going to test the breaking strain of modern rope.
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That's why one takes a couple of turns & lets it surge - doesn't one? :confused:

But then I used to watch the ferry men stopping a 150' ferry boat in 5kt tides on the Mersey every 15 minutes. 4x figure-8 turns around the bollards & hold the end & lean back.:D

It would stretch & creak a bit, but they stoppped & held 3-400 tons of boat. Not had any trouble holding my own boat when manouvering with warps, or my pal's 70 narrowboat either.
 
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