Earthing a generator

[Alan de Enfield]

On 27/02/2020 at 16:47, pedroinlondon said:

I've bought a 2.5K W metal frame petrol generator (Briggs & Stratton Sprint 3200A) and was strongly advised ………………...

Is there any chance you could take it back and get a refund ………… ?

 

I seem to be not the only one having reservations about your purchase.

 

Seriously, I do not think it will stay on your roof very long unless you only moor up 1 mile away from any other boat or house.

[blackrose]

2 hours ago, cuthound said:

When specifying standby generators in cities such as London, I used to require 70dBA 1 metre from any inlet or outlet, including exhaust and 50dBA at 1 metre at the site perimeter.

 

 

At what % of power output?

[blackrose]

1 hour ago, David Mack said:

 

And I assume you can't buy anything that quiet which is portable and at a price the average boater is prepared to pay.

I'm not sure who the average boater is or what price they are prepared to pay, but there are plenty of portable generators like Hondas, etc, owned by boaters around the country which are pretty quiet. Quieter in fact than many boat engines.

[cuthound]

7 minutes ago, blackrose said:

 

At what % of power output?

 

110% (standby generators are expected to deliver 110% of rated electrical output for 1 hour in every 12 of running, and to take 110% load within 30 seconds of starting in a 70% then 40% steps).

[blackrose]

In answer to your original question: You first need to contact the manufacturer and find out whether the generator has a "floating earth". Lots or portable generators do but yours looks more like a bulding site frame generator so I'm not sure. If it does then you need to decide whether to rely on that (which might mean in the event of a fault the breakers in your boat don't trip), or you may want to use an earth spike/earth to the boat's hull in which case you'll need to bond E-N on the generator outputs.

 

On the other hand if the generator doesn't have a floating earth then E-N will be bonded and you must earth to the boat hull or use an earth spike. 

 

Like the others here I think you've gone cheap and it will be noisy so you might regret buying it. Also, running it on the roof seems like a particularly bad idea in terms of carbon monoxide entering the boat and petrol fumes coming into the boat when you refuel it. 

Edited February 28, 2020 by blackrose

[blackrose]

6 minutes ago, cuthound said:

 

110% (standby generators are expected to deliver 110% of rated electrical output for 1 hour in every 12 of running, and to take 110% load within 30 seconds of starting in a 70% then 40% steps).

 

Ok, because without stating the power output that a noise level was measured at (and the distance the measurement was taken) the results are fairly meaningless. For example Honda quote noise levels of their generators at 25% power output @ 7m. It's not my area of expertise but I'd have thought that there were standard procedures for taking sound measurements otherwise it's impossible to compare figures? 

[cuthound]

2 hours ago, blackrose said:

 

Ok, because without stating the power output that a noise level was measured at (and the distance the measurement was taken) the results are fairly meaningless. For example Honda quote noise levels of their generators at 25% power output @ 7m. It's not my area of expertise but I'd have thought that there were standard procedures for taking sound measurements otherwise it's impossible to compare figures? 

 

Unless containerised, standby generators are always bespoke installations, so it is up to the designer to determine noise criteria. 

 

70dBA at 1 metre from air inlets & outlets and exhaust is fairly common, but perimeter breakout noise is very dependent on the location. For example 50dBA at one meter from the generator building isn't unusual for hospitals.

[pedroinlondon]

On 28/02/2020 at 17:44, blackrose said:

In answer to your original question: You first need to contact the manufacturer and find out whether the generator has a "floating earth". Lots or portable generators do but yours looks more like a bulding site frame generator so I'm not sure. If it does then you need to decide whether to rely on that (which might mean in the event of a fault the breakers in your boat don't trip), or you may want to use an earth spike/earth to the boat's hull in which case you'll need to bond E-N on the generator outputs.

 

On the other hand if the generator doesn't have a floating earth then E-N will be bonded and you must earth to the boat hull or use an earth spike. 

 

Like the others here I think you've gone cheap and it will be noisy so you might regret buying it. Also, running it on the roof seems like a particularly bad idea in terms of carbon monoxide entering the boat and petrol fumes coming into the boat when you refuel it. 

Thanks Blackrose.
I did get in touch with the manuf and they suggested exactly that. Either to the boat or to the ground with one or two spikes.

[blackrose]

I think it also needs to be connected to your boats mains system/consumer unit/breakers, unless it has its own internal breakers. If not don't use it direct to power tools, etc, without going though the boat's consumer unit.

Edited July 9, 2020 by blackrose

[Tracy D'arth]

Refueling on the roof frightens me. Petrol is severely dangerous stuff. How are you going to prevent petrol vapour entering the boat through vents, doors and deck?

 

Best to fit a strong chain to it and throw it in off the back deck after you have started it.

It will be very quiet under water.

TD'

[pedroinlondon]

No.

[Theo]

On 28/02/2020 at 00:00, Richard10002 said:

I used to put 6 x 20 kilo bags of coal on the roof to keep the boat level. It probably changed the list to port from about 5 degrees, to zero. Not sure at what angle stability would disappear, but I think it would take more than double the 120 kilos, and maybe a lot more, to reach it  

Stability does not disappear ant any particular angle until the deckedge goes under and the waterplane area reduces.  Placing weight up high reduces stability and makes the boat more "tender" in that a smaller heeling moment will cause a greater heel.  I could bore you further but will stop now.

[Theo]

On 28/02/2020 at 12:10, WotEver said:

No, it is twice as loud. Because it is 10dB louder, which is a doubling of loudness (more or less). 

3dB is a doubling of power. 
6dB is a doubling of SPL. 
10dB is a subjective doubling of perceived loudness. 

Quite right too.  It's to do with the logarithmic repsone of the ear.  I have a theory that, because sound intensity in watts per square metre obeys the inverse square law the ear has evolved a logarithmic response so that pecieved loudness is a linear variation with distance from the source.  I must add that I have not had this theory confirmed or deinied by anyone mor qualified than I.

 

N

On 28/02/2020 at 12:18, Alan de Enfield said:

The article I quoted did say that, but the table below showed the loudness' was 2x but the 'sound intensity' was 10x

Which come to the same thing!

[Theo]

On 28/02/2020 at 17:44, blackrose said:

In answer to your original question: You first need to contact the manufacturer and find out whether the generator has a "floating earth". Lots or portable generators do but yours looks more like a bulding site frame generator so I'm not sure. If it does then you need to decide whether to rely on that (which might mean in the event of a fault the breakers in your boat don't trip), or you may want to use an earth spike/earth to the boat's hull in which case you'll need to bond E-N on the generator outputs.

 

On the other hand if the generator doesn't have a floating earth then E-N will be bonded and you must earth to the boat hull or use an earth spike. 

 

Like the others here I think you've gone cheap and it will be noisy so you might regret buying it. Also, running it on the roof seems like a particularly bad idea in terms of carbon monoxide entering the boat and petrol fumes coming into the boat when you refuel it. 

Adding yet another to the list of disadvantages, petrol can be really difficult to coe by on the cut.  You can't buy it at boatyards you need to find a local petrol station.  However you can get kits to convert to gas power which turns out much cheaper than petrol per kilowatt hour and is much easier to get from boatyards.

 

N

[Richard10002]

1 hour ago, Theo said:

Stability does not disappear ant any particular angle until the deckedge goes under and the waterplane area reduces.  Placing weight up high reduces stability and makes the boat more "tender" in that a smaller heeling moment will cause a greater heel.  I could bore you further but will stop now.

I thought it was to do with the Righting Moment, and there is plenty of discussion of "angle of vanishing stability" - here's just one after a simple google:

 

http://sailskills.co.uk/Stability/sailskills_stability_stability_explained_AVS.html

 

It would seem that any particular boat will have a fixed "angle of vanishing stability".

[Alan de Enfield]

32 minutes ago, Richard10002 said:

I thought it was to do with the Righting Moment, and there is plenty of discussion of "angle of vanishing stability" - here's just one after a simple google:

 

http://sailskills.co.uk/Stability/sailskills_stability_stability_explained_AVS.html

 

It would seem that any particular boat will have a fixed "angle of vanishing stability".

Catamarans have very little self righting moment and once heeling will not recover and will turn turtle.

This is why it an RCD requirement for multihulls to have escape hatches that can allow egress from the boat hulls when inverted.

 

2.6 Escape on habitable multihull craft in the event of inversion Linked to the modification of the essential requirement Point 3.3 on buoyancy and flotation, the essential requirement Point 3.8 of Annex I, Part A of the new Directive contains an improved and corrected wording. The essential requirement for viable means of escape now applies to all habitable multihull craft (the limit of 12 meters being deleted) that are susceptible to inversion. Furthermore, it is specified that where the means of escape are provided for use in the inverted position, it must not compromise the structure, stability point or buoyancy of the multihull craft, whether it is upright or inverted.

 

There are emergency hatches in each cabin which, when inverted are above the waterline. In normal conditions it's just a case of telling visitors not to open the window and just be happy watching the fish go by.

 

 

Edited July 23, 2020 by Alan de Enfield

[Theo]

1 hour ago, Richard10002 said:

I thought it was to do with the Righting Moment, and there is plenty of discussion of "angle of vanishing stability" - here's just one after a simple google:

 

http://sailskills.co.uk/Stability/sailskills_stability_stability_explained_AVS.html

 

It would seem that any particular boat will have a fixed "angle of vanishing stability".

That article doesn't contradict what I said but I will leave it at that for the time being as being