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

[jwilson]

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

As others have said, almost any small outboard will push it but will be rubbish at reverse.
If it was not for the oil slick it can leave, and no reverse at all, an old Seagull Century or Century Plus would be your ideal cheap temporary propulsion - only about 4/5hp but a big low-geared prop and will very easily shove more than the size you quote.

 

[AntarcticPilot]

That's why one takes a couple of turns & lets it surge - doesn't one?

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.

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.

Sorry - I think we've got cross-threaded!

I meant "None of us would make the mistake of trying to stop a boat by holding a rope or trying to push against it".

Of course, putting a turn round a cleat and snubbing it is the proper way to do it - never meant to imply anything else. I was just curious about the strain on a rope when doing it. I too have seen heavy vessels being stopped that way, though usually with wire ropes.

Using suitably approximate numbers:

However, 1 knot = about 0.5 m/sec

So, stopping a boat from 0.5 m/sec in a distance of (say) 1 metre and in (say) 1 second means something like an acceleration of 0.5 m/sec squared.

So, the force is 6000 * 0.5 = 3000 newtons.

According to Jimmy Green's web-site, the breaking strain of 12mm octoplait is 2,400 kg and the breaking strain of 14 mm Octoplait is 3,800 kg.

So, we do indeed challenge the breaking strain of normal sizes and type of rope by stopping a boat that way. The dodgiest figure in my equations is the time taken to stop the boat; longer means less force being applied; and 1 knot when berthing is probably at the top side of likely speeds; I certainly attempt to be going slower when berthing. But still, we're applying forces in the region of 50% of the breaking strain of the ropes we normally use.

 

[charles_reed]

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

I've moved a boat, weighing 3500kg, in a seaway, using a 3.5hp Tohatsu, on 4 occasions.

 

[NormanS]

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

OK I have to ask. What did you do with the horse? Did it go in the Avon as well?

 

[Momac]

So, the force is 6000 * 0.5 = 3000 newtons.

QUOTE]

3000Newtons is eqivalent to about 300kgforce ?

 

[AntarcticPilot]

So, the force is 6000 * 0.5 = 3000 newtons.

QUOTE]

3000Newtons is eqivalent to about 300kgforce ?

I knew I'd made a mistake somewhere! You're right; 1 kg (weight) = 9.81 Newtons. So, we're not as near the breaking strains of rope as I thought.

 

[onesea]

That's why one takes a couple of turns & lets it surge - doesn't one?

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.

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.

You mean the ferry men did not just rely on 080 they used 0888 on bollard/ cleat....

My thought would be 1 off almost any engine would do... Regular usage at least a 9 to 15 hp or more..

 

[john_morris_uk]

That's why one takes a couple of turns & lets it surge - doesn't one?

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.

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.

I have been reading this thread with interest.

Letting it surge is a technique that you have to be shown or at least practice a bit. Its not difficult, but its not always obvious to a novice and you need to get a 'feel' for what you are doing.

I am also not sure that the Mersey Ferry example is a good one for most situations, or if you are going to try stopping the boat dead with multiple turns etc, then be prepared for some breakages when you start stopping bigger boats! On larger yachts (and even our medium one weighs in at over 11 tonnes!) the forces can be enough to damage marina type cleats, so a bit of surging to slow the boat down is the only way....

 

[Searush]

I have been reading this thread with interest.

Letting it surge is a technique that you have to be shown or at least practice a bit. Its not difficult, but its not always obvious to a novice and you need to get a 'feel' for what you are doing.

I am also not sure that the Mersey Ferry example is a good one for most situations, or if you are going to try stopping the boat dead with multiple turns etc, then be prepared for some breakages when you start stopping bigger boats! On larger yachts (and even our medium one weighs in at over 11 tonnes!) the forces can be enough to damage marina type cleats, so a bit of surging to slow the boat down is the only way....

Go watch the ferries, they've been doing it for about 130 years with 250-400 ton boats & hundreds of passengers. There is about 2-3m of "surge", stretch or slippage, even with 888 on the bollards. If the skipper gets it wrong, they stop the boat & then rewrap the hawser tighter as the boat bounces back.

Who talked about stopping any boat "dead" that's hardly possible even with a dink?

Very impressive to watch, used to be a major part of my day's entertainment in the 70's & 80's when working in an office in Liverpool.

 

[prv]

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.

Narrowboats are made of fairly heavy steel, aren't they?

Pete

 

[john_morris_uk]

Go watch the ferries, they've been doing it for about 130 years with 250-400 ton boats & hundreds of passengers. There is about 2-3m of "surge", stretch or slippage, even with 888 on the bollards. If the skipper gets it wrong, they stop the boat & then rewrap the hawser tighter as the boat bounces back.

Who talked about stopping any boat "dead" that's hardly possible even with a dink?

Very impressive to watch, used to be a major part of my day's entertainment in the 70's & 80's when working in an office in Liverpool.

Narrowboats are made of fairly heavy steel, aren't they?

Pete

I think people are missing the point. I appreciate that the ferries get away with certain lack of finesse in their 'surging' of lines when coming alongside, but I have visions of some alloy cleats being pulled out of pontoons. Barge 'bitts' might be steel and robust, but alloy cleats can be weak in comparison. My suggestion is to be a little circumspect about how quickly you throw your figure of eights onto the cleat...

 

[alant]

That's why one takes a couple of turns & lets it surge - doesn't one?

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.

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.

Are there lots of bollards on canals, so you can snub?
What happens to the narrowboat when you do so, cos unless its a midships tow rope, the stern will swing away if a bowrope is snubbed & the bow if a sternrope. Even with a midships, the boat will end up hitting the near bank or ground in the shallower water.

 

[alant]

Sorry - I think we've got cross-threaded!

I meant "None of us would make the mistake of trying to stop a boat by holding a rope or trying to push against it".

Of course, putting a turn round a cleat and snubbing it is the proper way to do it - never meant to imply anything else. I was just curious about the strain on a rope when doing it. I too have seen heavy vessels being stopped that way, though usually with wire ropes.

Using suitably approximate numbers:

However, 1 knot = about 0.5 m/sec

So, stopping a boat from 0.5 m/sec in a distance of (say) 1 metre and in (say) 1 second means something like an acceleration of 0.5 m/sec squared.

So, the force is 6000 * 0.5 = 3000 newtons.

According to Jimmy Green's web-site, the breaking strain of 12mm octoplait is 2,400 kg and the breaking strain of 14 mm Octoplait is 3,800 kg.

So, we do indeed challenge the breaking strain of normal sizes and type of rope by stopping a boat that way. The dodgiest figure in my equations is the time taken to stop the boat; longer means less force being applied; and 1 knot when berthing is probably at the top side of likely speeds; I certainly attempt to be going slower when berthing. But still, we're applying forces in the region of 50% of the breaking strain of the ropes we normally use.

Stern anchor ready to slip might work.

 

[prv]

Narrowboats are made of fairly heavy steel, aren't they?

I think people are missing the point.

I wasn't making any serious point, just joking about an unstoppable steel narrowboat squishing anything small and lightweight that was foolish enough to get in its way

Coming out of Cowes on Saturday I saw a pontoon with a sign saying:

PRIVATE BERTH
This berth is used by an 80-foot steel workboat
You will be CRUSHED!​

Pete

 

[Bobobolinsky]

Lister ST2, 15Hp, aircooled, 1300 RPM flat out, 600 rpm tickover, no pipework for cooling, just a bit of ducting for air. Fitted with a Lister J box and drop box, 3/4" shaft and 16 x 9 prop, pretty simple stuff.