Measuring windlass power (sic)

[Davidgabriel]

I would like to measure how many amps my windlass pulls when working. I have a spare Victron smart shunt. I was thinking of using this set to dc meter. Two questions, can this be done? Where do I place the shunt? And what settings on the Victron cerbo?

that’s three questions I realise😀

 

thanks for any input

[Tonka]

Is it a long shaft aluminium windlass?

[Jen-in-Wellies]

2 minutes ago, Davidgabriel said:

can this be done?

No reason why not.

2 minutes ago, Davidgabriel said:

Where do I place the shunt?

In the negative return between the windlass and battery, so only the windlass current flows through it, not anything else. Needs a fused positive power feed as well to power the smartipants features.

4 minutes ago, Davidgabriel said:

what settings on the Victron cerbo?

No idea! Treat it as any other smart shunt.

 

What boat have you got that needs an electric windlass? Most inland boats, when we think of windlass, we think of one of these. https://www.sheridanmarine.com/product/economy-lock-key-windlass

[Davidgabriel]

To be fair I haven’t got a canal boat. I’ve a sailing yacht. I have said this on earlier posts on other topics as I didn’t want to be a secret lurker. Or whatever it’s called. I prefer this forum to sailing ones as the technical advice is excellent and the people on here are a lot nicer 

[MrsM]

2 minutes ago, Davidgabriel said:

To be fair I haven’t got a canal boat. I’ve a sailing yacht. I have said this on earlier posts on other topics as I didn’t want to be a secret lurker. Or whatever it’s called. I prefer this forum to sailing ones as the technical advice is excellent and the people on here are a lot nicer 

There must be some utter horrors on the sailing forums then! 🤣 (Only joking)

[Davidgabriel]

There are. I’m not😀

[Alan de Enfield]

Why not just use a multimeter set to amps ?

 

 

Most boaters these days have one and they only cost ~£20-£30 (but ensure it does DC amps not just AC amps)

 

 

[Davidgabriel]

Yes. That is an idea and I do have one.  Never thought of that. But I would really like to keep an eye while using it. It’s not essential but something I’d like to track more easily than having to go below while someone else uses the windlass. 

[MtB]

8 minutes ago, Alan de Enfield said:

Why not just use a multimeter set to amps ?

 

 

Most boaters these days have one and they only cost ~£20-£30 (but ensure it does DC amps not just AC amps)

 

 

 

Point of Order, that one doesn't do DC. The DC ones by UNI-T have a different jaw shape. 

 

Also, the UNI-T DC ones are nearer to £50. Or were last time I bought one! 

 

 

 

 

[Jen-in-Wellies]

14 minutes ago, Davidgabriel said:

To be fair I haven’t got a canal boat. I’ve a sailing yacht. I have said this on earlier posts on other topics as I didn’t want to be a secret lurker. Or whatever it’s called. I prefer this forum to sailing ones as the technical advice is excellent and the people on here are a lot nicer 

 I reckoned it probably was something salty water and bigger, but I was too lazy to look through your earlier posts! 

[Alan de Enfield]

1 minute ago, Jen-in-Wellies said:

 I reckoned it probably was something salty water and bigger, but I was too lazy to look through your earlier posts! 

 

I don't think that many canal boats have a powered windlass

 

The current will  vary depending on the work it is doing - there can even be a bried peak of 'overload' when 1st trying to un-set an anchor. Our anchor windlass/winch is something around 200 amps.

[Peanut]

 

The Practical Boat Owner Forum, is not known to be hostile, in fact quite helpful, and is predominantly for lumpy water boats, where this kind of thing is discussed. You might have, unwittingly, strayed onto Sailing Anarchy, which is a quite different animal.

[Davidgabriel]

Well at heart I’m a Black Country boy born in Cradley. I sail a yacht but I must have the cut in my heart 

[Tony Brooks]

If what Alan posted is correct, then the OP needs to ensure is Smartshunt has a high enough current rating. If it is a 300 amp one, it may get a tad hot when trying to break an anchor out. Current seems to rise very fast as you slow most electric motors down to below the design speed.

 

(No reason not to believe that what Alan said is untrue, I just don't know or have the experience to judge).

[Davidgabriel]

It’s a bmv500. The windlass is 24v 900w. The battery is a Fogstar drift pro 24v 300 ah

 

[Tony Brooks]

3 minutes ago, Davidgabriel said:

It’s a bmv500. The windlass is 24v 900w. The battery is a Fogstar drift pro 24v 300 ah

 

 

That suggests that the rated current is just shy of 40 amps, but that is unlikely to include the starting surge, or the consumption as the motor slows and possibly stalls. A totally unscientific feeling is that it should be OK, but a bit wary because with LFP batteries their internal resistance will not drop the voltage as much under load as a lead acid battery would, so the stall current may well be higher.

Just seen on another topic that the LFP BMS might limit the maximum current, so perhaps check that to make sure it will deliver the 500 amps your shunt seems to be rated for.

[Alan de Enfield]

2 hours ago, Davidgabriel said:

It’s a bmv500. The windlass is 24v 900w. The battery is a Fogstar drift pro 24v 300 ah

 

 

Mine is a 1kw 12v and pulls ~ 200 when 'working hard'

 

Google AI suggests :

 

Q : what current will a 1kw 12 volt boat anchor winch draw

 

A : This means that the winch will be able to handle 450 Amps of current before it starts heating up. This is the mean value of Amperage for most of the winches. If the winch is heavier or lighter, or depending upon the load being pulled, it will draw anywhere between 100 – 600 Amperes …

 

 

 

[Davidgabriel]

Thanks for all the replies. The winch appears to work fine. And the bms of the Fogstar does not shut off. Was just fiddling really. Seeing where I could put my spare shunt. I think on the windlass will be interesting. I can measure the loads and then scare myself with the data. 

[Tony Brooks]

9 minutes ago, Davidgabriel said:

Thanks for all the replies. The winch appears to work fine. And the bms of the Fogstar does not shut off. Was just fiddling really. Seeing where I could put my spare shunt. I think on the windlass will be interesting. I can measure the loads and then scare myself with the data. 

 

Sounds like an interesting project, especially if you record the results over several uses and post there here, so we have something definite to go by

[Davidgabriel]

I will do that Tony

[Onewheeler]

On 10/01/2026 at 12:00, Davidgabriel said:

Yes. That is an idea and I do have one.  Never thought of that. But I would really like to keep an eye while using it. It’s not essential but something I’d like to track more easily than having to go below while someone else uses the windlass. 

You can get clamp meters with Bluetooth.

[GUMPY]

1 hour ago, Onewheeler said:

You can get clamp meters with Bluetooth.

And they are cheap🫣

 

https://amzn.eu/d/2e0cp3L

 

 

Decided I wanted one a year ago but haven't really found a use for it yet.

[MtB]

5 hours ago, GUMPY said:

And they are cheap🫣

 

https://amzn.eu/d/2e0cp3L

 

 

Decided I wanted one a year ago but haven't really found a use for it yet.

 

Possibly because your boat is a kayak?

[GUMPY]

10 minutes ago, MtB said:

 

Possibly because your boat is a kayak?

There is always the caravan and house to use them in, however like all electricians I have more than one meter, four at the last count. Two clamp, one desk and a cheapo one that I just can't destroy. On top of that there is the insulation tester* and the RCD tester.

 

* Brand new only used once, bought after I retired because I wanted to test the wiring in the house to see what needed replacing.