Size of battery

[Tahitibelle]

How does one determine the optimum size battery for a small (22') minimalistic sailing vessel being prep'd for the Jester 08.

Parameters:
No aux engine apart from O/B, therefore no mechanical charging available; Charging by 30 Amp solar pannel only; Optimising power availability against weight saving v.important; Potential 20 days between mains battery charging facilities; Use of P/S & Stern Nav lights only in areas of heavy shipping otherwise one all round white LED at the masthead; Minimum use of LED cabin lights (battery driven torch light preferred); Hand held battery operated VHF radio and GPS only; Main DSC VHF radio to be used only for distress and in one off situations where the extra range is needed (spare small 12 v motor cycle type battery carried for emergency use only). Simrad TP10 autohelm used if/when Hasler wind vane cannot cope.

Present batteries are 2 x 110 AH leisure type - seems way over the top. How small can I go and is it best to carry one larger or two smaller batteries. any advice gratefully received.

 

[sarabande]

At SIBS I was impressed by these Lifeline AGM batteries. Small size, high capacity, deep discharge, and multiple cycles. A bit expensive, but the Merlin people are ready to talk about their products.

For redundancy sake, I'd go for 2 batteries, rather than one, unless you can 'prove' the one battery you have, well before you go.

 

[Ceirwan]

How does one determine the optimum size battery for a small (22') minimalistic sailing vessel being prep'd for the Jester 08.

Parameters:
No aux engine apart from O/B, therefore no mechanical charging available; Charging by 30 Amp solar pannel only; Optimising power availability against weight saving v.important; Potential 20 days between mains battery charging facilities; Use of P/S & Stern Nav lights only in areas of heavy shipping otherwise one all round white LED at the masthead; Minimum use of LED cabin lights (battery driven torch light preferred); Hand held battery operated VHF radio and GPS only; Main DSC VHF radio to be used only for distress and in one off situations where the extra range is needed (spare small 12 v motor cycle type battery carried for emergency use only). Simrad TP10 autohelm used if/when Hasler wind vane cannot cope.

Present batteries are 2 x 110 AH leisure type - seems way over the top. How small can I go and is it best to carry one larger or two smaller batteries. any advice gratefully received.

I'm assuming you meant a 30 WATT solar panel?

Assuming great sunlight conditions (haha) then you should be:
I = P / V
I = Current P = Power in watts and V = Voltage
30/12 = 2.5A

So I'd say you can rely on that to put out 1 amp (averaged) for 02 hours every day.
So say 10ah of juice back into the battery daily, less near the uk, more as you get further south.

You need to look at the power draw of all the items you have listed in Amps and multiply that by the time in hours you will be using it for.... Add the numbers up to get your daily power draw.

Personally I think you would be fine with a single 100AH battery, the weight isn't to bad, it's far less than when you go sailing with a friend

 

[G12]

Just wondering why you don't have an LED tricolour instead of all round white? Will be a lot more helpful for someone trying to identify their aspect on you at night with the same power consumption.