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Old 03 September 2015, 12:42   #1
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Rib battery?

Hi all,

Just bought my first RIB and have been told that it needs a new battery, it has a 75hp mariner 2 stroke engine and also has port starboard lights etc, any ideas on what battery I'd need for it? Fairly new to ribbing you see

Many thanks,
Jack
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Old 03 September 2015, 12:48   #2
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For starters (geddit) I'd find out what the spec battery is for that motor & work from there. Lots of variables, space available, what else you intend to run off it, your attitude to risk, depth of your pockets etc. There are predominantly 2 schools of thought; fit el-cheapo batteries & change them when they fail, or fit expensive marine batteries & err! change them when they fail
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Old 03 September 2015, 12:52   #3
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For starters (geddit) I'd find out what the spec battery is for that motor & work from there. Lots of variables, space available, what else you intend to run off it, your attitude to risk, depth of your pockets etc. There are predominantly 2 schools of thought; fit el-cheapo batteries & change them when they fail, or fit expensive marine batteries & err! change them when they fail
Ahh okay, preferably as cheap as possible for the moment, also is there specific batteries i'd need for a RIB?
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Old 03 September 2015, 13:20   #4
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I used a numax dual cycle with no problems
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Old 03 September 2015, 14:09   #5
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OK there are 3 specifications you might / might not care about:

Ah (Amp Hours) - typically used for Leisure Batteries to indicate how much juice you can draw.

CCA (Cold Cranking Amps) - used for car batteries to indicate how much juice they can give out for a short period at some silly cold temperature

MCA (Marine Cranking Amps) - same as CCA but warmer because most marine batteries don't try and start at -20C!

Are you likely to have lights on without the engine? Do you know what current the alternator can throw out? Presume they are standard bulbs in the lights rather than LEDs. If so they are probably 5-10W bulbs and you might have 3 on at once so 30W, you need 2.5A per hour of use without charge.

What other electronics (now or in near future?) - DSC VHF, GPS, Plotter, Sonar. If you don't have them. With the exception of transmitting on the VHF the rest would draw less than 1A each per hour. Transmit will draw something like 7A from memory. But you only transmit very little. Handheld tests use 5% transmit time so for an hour of being on it only adds an extra 0.5A. Personally I'd work on 5A of power on other electronics, plus 2.5A for lights. If I wanted more electronics I'd switch my lights to LED. I wouldn't ever expect to need my lights, electronics etc for more than 4 hours without the engine, lets take 6 hours to be safe. So 45A. You may need FAR LESS. You cant get all the juice out a leisure battery! 60% is about as good as you'll get. so a 75Ah battery would be about right for your electrics. BUT beware at the end of 6 hrs that might be too drained to crank a tired engine! But that would be 6 hours with all your electrics on.

Can you start your engine manually with a bit of string? If not I'd put my eggs in the Cold Crank/Marine Crank basket. You are probably looking at something like 500CCA? for your size engine. Thats probably only 56Ah and will be less tolerant of being drained down lots. If you'll never be drifting on electrics it'd be fine. If you will be drifting, especially at night with lights on, I'd look at bigger so that you match the Ah to the drain above rather than the cranking amps. But if you only have lights and would only use them with the engine running and the alternator can chuck out enough juice you can just look at CCA...

The trouble with MCA is it has the word Marine. Wherever Marine is involved an extra zero appears on the end of the price label...
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Old 03 September 2015, 14:10   #6
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oh and think about physical dimensions. Is it to fit in a specific space...
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Old 03 September 2015, 15:08   #7
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OK there are 3 specifications you might / might not care about:

Ah (Amp Hours) - typically used for Leisure Batteries to indicate how much juice you can draw.

CCA (Cold Cranking Amps) - used for car batteries to indicate how much juice they can give out for a short period at some silly cold temperature

MCA (Marine Cranking Amps) - same as CCA but warmer because most marine batteries don't try and start at -20C!

Are you likely to have lights on without the engine? Do you know what current the alternator can throw out? Presume they are standard bulbs in the lights rather than LEDs. If so they are probably 5-10W bulbs and you might have 3 on at once so 30W, you need 2.5A per hour of use without charge.

What other electronics (now or in near future?) - DSC VHF, GPS, Plotter, Sonar. If you don't have them. With the exception of transmitting on the VHF the rest would draw less than 1A each per hour. Transmit will draw something like 7A from memory. But you only transmit very little. Handheld tests use 5% transmit time so for an hour of being on it only adds an extra 0.5A. Personally I'd work on 5A of power on other electronics, plus 2.5A for lights. If I wanted more electronics I'd switch my lights to LED. I wouldn't ever expect to need my lights, electronics etc for more than 4 hours without the engine, lets take 6 hours to be safe. So 45A. You may need FAR LESS. You cant get all the juice out a leisure battery! 60% is about as good as you'll get. so a 75Ah battery would be about right for your electrics. BUT beware at the end of 6 hrs that might be too drained to crank a tired engine! But that would be 6 hours with all your electrics on.

Can you start your engine manually with a bit of string? If not I'd put my eggs in the Cold Crank/Marine Crank basket. You are probably looking at something like 500CCA? for your size engine. Thats probably only 56Ah and will be less tolerant of being drained down lots. If you'll never be drifting on electrics it'd be fine. If you will be drifting, especially at night with lights on, I'd look at bigger so that you match the Ah to the drain above rather than the cranking amps. But if you only have lights and would only use them with the engine running and the alternator can chuck out enough juice you can just look at CCA...

The trouble with MCA is it has the word Marine. Wherever Marine is involved an extra zero appears on the end of the price label...
Thank you for the excellent advice! Forgot to mention that the boat has GPS and a fish finder (doubt I'll ever use this). I get the boat on Monday and I believe it only has electric start for the engine, I'll have a look at the marine batteries you mentioned in your last paragraph, do you think the battery mentioned above would be adequate? Won't be used for more than 3-4 hours on each trip and probably just using the GPS and engine controls etc?
Once again thank you for the great advice!
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Old 03 September 2015, 15:40   #8
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Originally Posted by jack.watts View Post
.... and a fish finder (doubt I'll ever use this). !
The fish finder is arguably more important than the GPS, the fishfinder/sounder will tell you how much water is under the boat, pretty important imho Personally, I'd avoid leisure batteries as starter batteries, leisure batteries are for discharging relatively small currents over long periods, whereas starter batteries are designed to deliver high (starting) currents over short periods. That said, plenty of folk swear by leisure batteries for starting, probably as they tend to be cheaper due to their lighter weight construction i.e. not as much lead per amp.
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Old 03 September 2015, 15:58   #9
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If this is your engine:
Mariner | All Models (I am assuming you are not on the Direct Injection Optimax) [Yours is presumably older as you can't buy the non DI model for recreational use these days]

It has a 227watt alternator which should chuck out something around 15 - 20 amps. So as long as your engine is running you are miles off killing the battery. So that just leaves starting the lump.

That engine uses 450CCA/525MCA

Something like this would do the job:
075 Powerline Calcium Heavy Duty Car Battery 12V - Peugeot Porsche Renault etc | eBay
There would be NUMEROUS similar available. I have no experience of this seller / this specific battery...

If you want a leisure battery instead I suspect you'd struggle to beat this price for a cheap one. You'll notice it doesn't have a CCA / MCA labelled:
75 ah amp Leisure Battery DEEP CYCLE Low Height maintenance free sealed 80 85 | eBay
But I'd be a little surprised if it couldn't handle your engine. But it prefers to do gentle discharge rather than starting. You may want to consider how you'll use the RIB. Lots of start, stop - a CCA rated battery may be better. Start - long run - stop - use electrics at anchor / drift - restart -long run - home: leisure.

Don't get sucked into a Marine battery - they are usually meant for Yachties who live on board and guzzle electrons...
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Old 03 September 2015, 17:29   #10
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Thanks for the advice guys, how and where should I store it as well, it's a 5.3m tornado Rib, I assume it needs to be waterproof?
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