Real world anchor winch cable size

[steve yates]

I have a lofrans kobra anchor winch on my longbow for 8mm chain. It’s 1000w and the specs say can draw 150a. It was wired to the house bank with 35mm welding cable and a 100a circuit breaker. The cable run for was 7m one way.
All well & good, in use the breaker only ever tripped once, and that may have been because I decided to sail off the anchor & hadn’t started the engine iirc.
Now I’m rewiring the boat, looking at possible locations for a seperate AGM engine/winch battery from the new lifepo4 house bank. Cable runs vary from 6.7m to 9.5m depending on practicality of final location, and I have 50mm tinned oceanflex to replace the welding cable.
Imagine my surprise when I ran victrons voltage drop calculation app and it said the % loss with 35mm would be between 10.2 and 14.4! And for 50mm still 7.5- 10.6!
I can’t imagine going to 95 or 120mm cable on a 31ft boat, so what am I missing here?
Is it because running the engine lets the alternator ido a lot of the heavy work?
Or is it just a case of theoretical perfection is impractical or unobtainable?

I’m now thinking I might let sleeping dogs lie and see if it still works when she is recommissioned

I’m curious.

Edited to add: Bloody hell, just seen the prices of lofrans 100a breaker, £250, more than all the cable cost!
Are there alternatives at better prices, in case I chucked the old one out when stripping the boat out

 

[RupertW]

Is it such a big deal? Yes the voltage might drop to 11.4 with the engine running and windlass running about that will still power it well enough and the battery will bounce pretty much straight back provided the engine is running the whole time. We have a round cable run of about 18m and have never had any issues. I have often thought of putting a small battery up by the windlass but when a problem has no symptoms it drops right down my “To do” list. The only advantage I can see is if the engine isn’t running and when that did happen once and I couldn’t even drop anchor quickly because the windlass had the anchor in tight, just having the ignition on gave me enough juice to drop it enough to free the chain.

 

[thinwater]

What he said^^. I think you are good.

You should only have that draw for a few seconds. The windlass is NOT designed to pull the boat up to the anchor, or to break the anchor out if deeply set, only to lift the anchor and rode. You motor or sail up to the anchor, and if it does not pop out in a second, you attach a line to the rode and let the bobbing of the boat do the work.

I may or may not start the engines (and a pair of outboards at idle don't really add any charging--a few amps). I've never blown a breaker. But I never work the windlass hard. If the anchor is stuck ... I wait with the rode tight up and down. It will be loose in a minute or a few.

 

[vyv_cox]

I installed my windlass many years ago, long before I had much inkling of voltage drops etc. The cables were 7 mm I think, so around 38 mm2, about 8 metres long. They have always functioned perfectly well with my Maxwell windlass, 1000 watt motor. Never overheated and no evidence that the windlass was short of power

Despite what thinwater says we have always pulled the boat up to the anchor on windlass. When berthed stern-to it is a fundamental rule never to turn the prop until the anchor is aboard - motoring to the anchor is one of the major contributions to total cockups.

I quite often make windlass adjustments without starting the engine.

 

[Otter]

I’ve just installed a new Lewmar Pro windlass - I couldn’t believe how weedy the power cables from the windlass to the relay box are! Made the humungous cables to the relay box look a bit silly.

 

[steve yates]

Is it such a big deal? Yes the voltage might drop to 11.4 with the engine running and windlass running about that will still power it well enough and the battery will bounce pretty much straight back provided the engine is running the whole time. We have a round cable run of about 18m and have never had any issues. I have often thought of putting a small battery up by the windlass but when a problem has no symptoms it drops right down my “To do” list. The only advantage I can see is if the engine isn’t running and when that did happen once and I couldn’t even drop anchor quickly because the windlass had the anchor in tight, just having the ignition on gave me enough juice to drop it enough to free the chain.

I don’t know, hence the question. I don’t think so, but i do wonder why, when according to the theory ( as I understand it) it should be a problem. It bothers me when trying to learn stuff that what I’m told doesn’t relate to whats on the ground.

 

[thinwater]

I installed my windlass many years ago, long before I had much inkling of voltage drops etc. The cables were 7 mm I think, so around 38 mm2, about 8 metres long. They have always functioned perfectly well with my Maxwell windlass, 1000 watt motor. Never overheated and no evidence that the windlass was short of power

Despite what thinwater says we have always pulled the boat up to the anchor on windlass. When berthed stern-to it is a fundamental rule never to turn the prop until the anchor is aboard - motoring to the anchor is one of the major contributions to total cockups.

I quite often make windlass adjustments without starting the engine.

What I said was true. They are not designed to pull the boat up, and the manual will often say as much. Yes, I have done that many times, as well. But NOT if there is much wind or any significant load. If there is, you have someone power up. You can even ease the load, single-handed, by either using low revs or using a cockpit control. Or you can push it and overstrain the windlass. If the breaker is popping, there is the proof.

Pasted directly from the OP's manual:

"Raising The Anchor
Start the engine of the boat. Be sure that the clutch is well engaged. Draw out the handle from the gipsy cap.
Push the button "UP" of the foot switch or remote control. Do not use the windlass to pull the boat to the anchor...."

 

[lustyd]

We do neither. We lift chain with the windlass a metre or two at a time and the weight of the chain pulls the boat forwards.

I imagine some people keep the button pressed and physically pull the boat along a tight chain, but not many.

 

[vyv_cox]

What I said was true. They are not designed to pull the boat up, and the manual will often say as much. Yes, I have done that many times, as well. But NOT if there is much wind or any significant load. If there is, you have someone power up. You can even ease the load, single-handed, by either using low revs or using a cockpit control. Or you can push it and overstrain the windlass. If the breaker is popping, there is the proof.

Pasted directly from the OP's manual:

"Raising The Anchor
Start the engine of the boat. Be sure that the clutch is well engaged. Draw out the handle from the gipsy cap.
Push the button "UP" of the foot switch or remote control. Do not use the windlass to pull the boat to the anchor...."

In the situation I described there is usually very little load on the chain. When berthing stern-to it is normal to have the chain bar tight with the stern tied back to the wall. When these lines are released the boat surges forward, making recovering the chain an easy job for the windlass.

When free anchored we might haul the boat forward on the windlass in light winds, but catenary will usually help here as the windlass is alternately stopped and started. In wind we assist the windlass with the engine but it can be quite difficult to judge just how much engine to use. Crowded anchorages can make this tricky.

 

[PaulRainbow]

I have a lofrans kobra anchor winch on my longbow for 8mm chain. It’s 1000w and the specs say can draw 150a. It was wired to the house bank with 35mm welding cable and a 100a circuit breaker. The cable run for was 7m one way.
All well & good, in use the breaker only ever tripped once, and that may have been because I decided to sail off the anchor & hadn’t started the engine iirc.
Now I’m rewiring the boat, looking at possible locations for a seperate AGM engine/winch battery from the new lifepo4 house bank. Cable runs vary from 6.7m to 9.5m depending on practicality of final location, and I have 50mm tinned oceanflex to replace the welding cable.
Imagine my surprise when I ran victrons voltage drop calculation app and it said the % loss with 35mm would be between 10.2 and 14.4! And for 50mm still 7.5- 10.6!
I can’t imagine going to 95 or 120mm cable on a 31ft boat, so what am I missing here?
Is it because running the engine lets the alternator ido a lot of the heavy work?
Or is it just a case of theoretical perfection is impractical or unobtainable?

I’m now thinking I might let sleeping dogs lie and see if it still works when she is recommissioned

I’m curious.

Edited to add: Bloody hell, just seen the prices of lofrans 100a breaker, £250, more than all the cable cost!
Are there alternatives at better prices, in case I chucked the old one out when stripping the boat out

50mm cable, with a 100A load, over 9m will drop less than a volt under normal use. In reality, 35mm cable would have been OK.

Breaker: BEP Surface Mnt Thermal Circuit Breaker 100a (185100F-01-1) (8-90730) Don't buy cheap crap from Ebay

 

[Neeves]

In the real world

Don't tell me that you have never used the windlass to propel the yacht to the anchor. If you have done it once why not do it again .... or 100 times.

Windlass seem designed to be robust and accept abuse without complaint.

Though caring for your windlass is desirable and you will be rewarded by a reliable windlass, see final sentence.

In strong wind you will have the engine running and will direct the yacht to be moved toward the anchor, simultaneous with retrieving the rode.

Once the vessel is moving you will not strain the windlass by 'using the windlass to pull the yacht forward). The catenary will add to the momentum of the yacht.

The real work for the windlass starts when it has to lift 15m of chain (say 25kg) + a 20kg anchor full of mud (and a correctly sized windlass will do this with ease - and still leave a hefty safety margin).

How many threads does anyone recall of a windlass failing because it pulled the yacht to the anchor or it was ripped out of the fabric of the yacht because the windlass was overloaded. Windlass fail for other reasons - not because they are used to pull a yacht to the anchor. Most windlass fail because they are not serviced, gear boxes need lubrication, the shaft needs to be cleaned and lubricated. The others fail because they are made from mixed metals, stainless mixed with aluminium, and corrode. l.


Reading appropriate threads, I deduce, most windlass are serviced with chain that is unnecessarily big for the yacht and one would think the motor is also more powerful (to match the chain). This implies that in addition to any safety factor to which the windlass is designed the owner or yacht builder also added to the safety factor by specifying that big chain and windlass to match.

A conclusion might be that cabling is also oversized, to match the, over specified, motor.

Jonathan

 

[Sea Change]

I don't see where 150A comes from, it should be more like 80A. Possibly a brief startup load only, in which case it would be unnecessary to size the cables for that number.

I just use a thermal breaker, I think mine is a Blue Sea, around £50, there is some cheap rubbish around.

 

[steve yates]

80a for 24v,150a for 12v is what the specs say here , just going from this.

 

[Sea Change]

80a for 24v,150a for 12v is what the specs say here , just going from this.

Ohms law disagrees. Not sure what to make of that!

 

[steve yates]

Ohms law disagrees. Not sure what to make of that!

Me neither

 

[oldmanofthehills]

The reistance of 10m of 7mm cable comes out as 0.0246 per core so say about 0.05 for the loop. If one knows the resistance of the motor it is easy to calculate the volt drop along the cable. It is a reactive load when moving but when motor stalled at start the current draw is enormous, and then when it moves the reactive element comes into play and current reduces

We had this trouble with point machines on the railways fed from 110V and needing 1KW power. The 10A circuit breakers never popped but to our astonishment we found by using very fast oscilloscope that it was momentarily registering 10k Amps draw at start (theoretically impossible according to common sense) and this current spike was radiating into the system and causing our electronic interlockings to fail or misbehave. A few capacitors and coils were added on interlocking motherboard to buffer things and all sorted.

Not a problem with actual winch operation, but it might glitch any delicate electronics in use at the time. However as chart plotter not critical at point of anchor lift, one probably will never notice

 

[PaulRainbow]

The reistance of 10m of 7mm cable comes out as 0.0246 per core so say about 0.05 for the loop. If one knows the resistance of the motor it is easy to calculate the volt drop along the cable. It is a reactive load when moving but when motor stalled at start the current draw is enormous, and then when it moves the reactive element comes into play and current reduces

We had this trouble with point machines on the railways fed from 110V and needing 1KW power. The 10A circuit breakers never popped but to our astonishment we found by using very fast oscilloscope that it was momentarily registering 10k Amps draw at start (theoretically impossible according to common sense) and this current spike was radiating into the system and causing our electronic interlockings to fail or misbehave. A few capacitors and coils were added on interlocking motherboard to buffer things and all sorted.

Not a problem with actual winch operation, but it might glitch any delicate electronics in use at the time. However as chart plotter not critical at point of anchor lift, one probably will never notice

Don't run the windlass from the domestic bank, run it from the engine battery. You never know how depleted the domestics might be after a spell at anchor, you don't want to upset electronics and the engine will usually be running when lifting the anchor.

 

[oldmanofthehills]

Don't run the windlass from the domestic bank, run it from the engine battery. You never know how depleted the domestics might be after a spell at anchor, you don't want to upset electronics and the engine will usually be running when lifting the anchor.

Good point. Ours is run from engine battery, and indeed we have only rarely up-anchored when engine off, as not often practical to sail off