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Generator Soundproofing and Running a Freezer When Away

I suppose this is a supplementary to my previous question... How difficult is it to soundproof a generator - by which I mean soundproofing it from those inside the boat and those in neighbouring boats. Does a generator produce a vibration in the boat itself? If so, how effective are, say, rubber mountings? Is it possible to sound and vibration proof a generator at a reasonable (by which I mean not excessive) cost? How would one do it? The freezer question is 'How much energy would I need to run a fridge freezer while I was away from the boat - i.e. from batteries via an inverter'. I would run the fridge freezer via a separate circuit from any other appliances or electrical load. The fridge freezer would be 230v model with a rated load of 136W and a yearly consumption of 277kWh. If I had a set up of 5 x 110Ah batteries, how long before running flat could these be expected to last with just this load? I would anticipate having a separate battery to start the engine.

Asked by: John Blanning  | 11.23am, Wednesday 11 August

WW says:

Most generators are mounted on rubber mountings to prevent vibration being transmitted through the boat. Many of them can be supplied with a 'cocoon' which is designed to minimise airborne noise. Smaller generators tend to have more streamlined casings while the larger ones, like the Beta range, have rectangular covers.
Alternatively, you could make your own casing from substantial plywood lined with special acoustic foam which incorporates a heavy plastic membrane and has an easily-cleaned surface to prevent oil penetration. You would need to provide air vents but these should be specially designed and lined with acoustic foam so that you avoid a direct air path through which the sound can escape. A good place to start your enquiries is TW Marine on 01663 745757.
These solutions will limit the noise considerably but you will still be aware of the slight hum which may start to get to you - or your neighbours - after an hour or two depending on how tolerant you - or they - are.
On the face of it, the fridge question should be a case of dividing the battery capacity by the energy load to see how long they would last but, like so many things, it is not that simple. If the fridge is run by an inverter, it will take a certain amount of power in addition to the fridge so that has to be taken into account. Your five batteries should behave quite well when they are new but their performance will decline over time and this will happen more quickly if you repeatedly run them down to a low level before recharging them. There is also the question of how good your charging system is at recharging them.
I have always found 12-volt fridges to be more efficient than 230-volt models run through an inverter. A typical 12-volt fridge uses about 22 a/hrs of battery power a day and a freezer would probably be slightly more so let us assume 50a/hrs per day for the pair. Your battery bank would probably have about 185 useable a/hrs (see the Chapter 13 of the new Inland Boat Owners Book for the reason for this reduction). If we divide 185 by 50, we get 3.7 days but don't forget the warning about running the batteries down to empty too often - you may find that this drops to three days or less after a while as the batteries deteriorate.
Perhaps it might be better to look for a mooring with a landline?

Graham Booth  | 4.36PM, Wednesday 11 August

Readers say:

If you wait for my article on electrical auditing to be published in WW you will be able to use try the spreadsheet to give you any number of whatifs regarding battery life and generator running times. We have 240V fridge and and 240V freezer on Theodora but I would not expect to run them if we were not cruising for more than a couple of days.

Nicholas Cooke  | 4.12PM, Sunday 15 August

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