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Old 02-07-2010, 01:20 PM   #1
Join Date: Nov 2009
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Default Battery/weight performance question

I just bought a 2008 2900 SE cruiser w/ twin 4.3 MPI engines with Bravo III outdrives. The boat came with two group 27 (65 lbs. each) and one group 24 (53 lbs.) deep cycle batteries and a 5.0 Kw generator. The two original group 27's will be dedicated for each engine and the group 24 will be dedicated to the generator. These three batteries will be mounted on the starboard side of engine compartment. I would like to increase house battery capacity since I throw anchor often. I am installing a 3000 watt inverter (70 lbs.) and four 300 amp hour six volt AGM batteries (90 lbs. each) as a house bank hooked up to the inverter. These four 6 volt batteries and inverter will be mounted on port side of engine compartment (inverter mounted in aft cabin). There is really no other place to put them.
As a result I will be adding approx. 430 lbs. to the engine compartment with these 4 extra batteries and inverter.

Do you think boat performance will suffer with the extra weight (getting up on plane, boat speed, etc.)?

Do you think the boat will lean towards the side of the house bank since combined with inverter since there is a 247 lb. difference of weight on both sides?

Or do you think the boat is big enough to absorb the extra weight both in performance and when it sits still in the water?

Thank you for any advice or experience you could offer.


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Old 02-07-2010, 03:24 PM   #2

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wow..adding that much weight to one side of the boat is gonna be a fun project...however, with the smaller engines that you have, it's going to affect performance in my opinion....lets put it this way about the balance of the boat will definitely show it...take a 250lbs fat guy...put him on your boat...take it out on the water and have him move to the stbd side of the boat...see what happens....the boat will lean to what ever side he's multiply that by a factor of 2 and the lean will increase.....I think your plan might also have a slight flaw in so much as how will you charge them when they are drawn down...I am thinking that your going to use the genny to do that....then you will have plenty of pwr....
it will work..but adding that much weight will affect weight and balance, as well as performance.....just my humble opinion..


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Old 02-07-2010, 07:25 PM   #3
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The inverter is going to be hooked up to the 110 volt board to be able to operate all 110 volt appliances and outlets except AC. While I can see running generator in the morning after a long night. the inverter will also have an auto generator start when battery levels get low. I just wanted the highest capacity possible so generator doesn't turn on every one -three hours while partying on boat. I dont want to turn it on every time I need to work microwave, blender, hair dryer, etc. Plus, inverter charger is 150 amps and will charge all batteries faster than boat charger. Do you have, or know someone, who has a similiar situation?
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Old 02-08-2010, 07:53 PM   #4

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If the 2 starting batteries are going to be dedicated Starting batteries, consider downsizing to Group 24's to shed some weight and if you go with starting batteries instead of Deep Cycle, the plates will be thinner and you should shed some additonal weight. It shouldn't take THAT much to turn over a couple of 6 cyclinder engines. The short peak amperage of a starting 24 will most likely be higher than that of a Deep Cycle Goup 27 anyway. That alone should shed some weight.

You already have a generator. Obviously you need house batteries. However, the 110 will run off of the generator as well. Do you need to also run 110 off of the batteries? How much TV, blenders, etc. are you going to need to run on the hook.................that can't be handled by the genie? There's another 70lbs.

What is the weight difference of a single Group 31 AGM? What is the Amp hours? would it make more sense to look at another option for the house batter?
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