Our boat is a 34' Mainship Pilot with a single Yanmar 370, and has both a bow and stern thruster. I have 2 Interstate 8d batteries that serve as the starting battery and house batteries. One of the batteries crapped out and needs replacing. I am assuming that the batteries are the automotive type since my information is that Interstate does not carry a marine type 8d battery. In talking with Interstate, they mentioned the SRM-4d marine Battery which has 1314 cca, 390 rc, 1645 ca, 117 lbs, amp hrs 195. Their 8d-MHD has 1400 cca, 450 ca, 1750 ca, and weighs 132 lbs. Do you think I am better off switching to two SRM-4ds, or going with the automotive type 8d? Should I switch to 6v golf cart batteries? Are two 6v golf cart batteries in series equivalent to one 8d battery? Your recommendations are greatly appreciated! Thanks for your time!
Any Experience with Interstate SRM-4d Battery?
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Pete Meisinger
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Get rid of the 8D s. Everyone will agree with me on this.
Now to start a controversy. I recommend a single group 27 starting battery for the engine. I also recommend 3 group 27 deep cycle batteries for your house bank. Two might be enough.
Now the first person to recccomend golf cart batteries wins the boobie prize. I better get this posted quick or someone will beat me to it.
G.C. batteries are good also, I just prefer group 27
pete
Now to start a controversy. I recommend a single group 27 starting battery for the engine. I also recommend 3 group 27 deep cycle batteries for your house bank. Two might be enough.
Now the first person to recccomend golf cart batteries wins the boobie prize. I better get this posted quick or someone will beat me to it.
G.C. batteries are good also, I just prefer group 27
pete
I bought a Pilot 34 in 2013 which was equipped with the same pair of 8Ds as yours. One was getting weak.
I replaced both, the "starting" 8D with a good quality Group 31 with a 900 CCA rating. The "house" 8D was replaced with a pair of golf cart batteries- GC2s wired in series to give 220 Ahs, the same spec as the 8D but it is a real deep cycle battery.
Worked fine and the G31 started the single Yanmar easily. Lots lighter than the 8D beast.
And Pete: Where did you find a real deep cycle G27 battery. I have never seen one.
David
I replaced both, the "starting" 8D with a good quality Group 31 with a 900 CCA rating. The "house" 8D was replaced with a pair of golf cart batteries- GC2s wired in series to give 220 Ahs, the same spec as the 8D but it is a real deep cycle battery.
Worked fine and the G31 started the single Yanmar easily. Lots lighter than the 8D beast.
And Pete: Where did you find a real deep cycle G27 battery. I have never seen one.
David
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ranger58sb
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Two 6V GC2s in series to 12V would give you about 220 Ah, compared to about 245 Ah for a typical 8D. Four GC2s in series/parallel would give you abouot 440 Ah compared to the 390 Ah from a pair of 4Ds. The GC2s would be deep cycle; 8Ds and 4Ds more likely dual-purpose or starting, depending.
Each GC2 would weigh about 70-lbs-ish. If one of four GC2s goes bad, you can still cobble together a 12V system until replacement. Six GC2s (~660 Ah) will fit in the same space as two 8Ds.
If space is available, and depending on your engine, a single good 12V G31 can make a decent starting battery, should start a Yanmar 370. And six GC2s for the house would be reasonably robust (4x would be pretty good, too).
-Chris
Pete Meisinger
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David, you might be right. My house bank batteries are the same size and about the same weight as the group 27 starting battery. A little heavier I guess. They may be group 24, I'm not certain. I know they are 12 volt lead acid.
My boat came with 8D s, They were nearly dead when I got the boat, I made it through the year with them and replaced them with more 8D s. That was a mistake. I didn't get two years out of the new ones. That is when I switched.
Been happy since.
pete
My boat came with 8D s, They were nearly dead when I got the boat, I made it through the year with them and replaced them with more 8D s. That was a mistake. I didn't get two years out of the new ones. That is when I switched.
Been happy since.
pete
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Your thruster is more like an engine starting than a deep cycle load. I use a separate battery for my stern thruster that is a AGM battery with it’s own 15 amp charger. That way the battery cables(4/0) are really short. When I put a bow thruster it will also have a dedicated battery and charger. 2 6 volt GC batteries will be roughly equivalent to 1 8D. However they would not be my first choice for thrusters, but for house deep cycle they are the way to go.
I wired the bow thruster to operate with the Group 31 starting battery, the theory being that the heavy current, short term duration thruster load was more like starting than house use. But I always used the 1,2,all switch in the all position after I started the engine, to charge the house battery with the engine alternator, but also to provide some boost to the starting battery during operation of the thruster.
Worked fine that way.
David
Sammy999
I am sort of " in the same boat" as you. My MS 34HT with the single Yanmar 6LYA, has the same B&S thruster served by 1- 8D and 28Ds for the combined start/ house. Only difference mine are AGM.
Currently working up a plan to be prepared when the time comes to replace the 8Ds.
I plan to stay w/ AGMs but will NOT replace the 8Ds.
I am seriously looking at moving the main eng start to the thruster bank. It looks fairly simple as it's only one 2/0 pos start lead to move and the run to my thruster bank is shorter as irs on the port side near the starter. I'm thinking a pair of GP31 AGM would serve thruster and start very well.
For a purely house I tossing around 4 GCs or 4 - Gp 31s. I'm kind of leaning towards everything being the same GP 31 batty format so if 1-2 house battys get weak the remaining 2 might still serve as start/ thruster bank vs just tossing them to have all house bank battys the same age.
I dont think FLA GCs are comparable the FLA Gp 31s re CCA OR MCA for starting due to different plate designs for FLA start vs deep cycle. I have checked with both Trojan and East Penn re plate design of AGM and both said there is no difference in plate designs or deep cycle capability or hi A start draw for GC vs Gp31.
Hope that helps... I can provide more details if interested.
I am sort of " in the same boat" as you. My MS 34HT with the single Yanmar 6LYA, has the same B&S thruster served by 1- 8D and 28Ds for the combined start/ house. Only difference mine are AGM.
Currently working up a plan to be prepared when the time comes to replace the 8Ds.
I plan to stay w/ AGMs but will NOT replace the 8Ds.
I am seriously looking at moving the main eng start to the thruster bank. It looks fairly simple as it's only one 2/0 pos start lead to move and the run to my thruster bank is shorter as irs on the port side near the starter. I'm thinking a pair of GP31 AGM would serve thruster and start very well.
For a purely house I tossing around 4 GCs or 4 - Gp 31s. I'm kind of leaning towards everything being the same GP 31 batty format so if 1-2 house battys get weak the remaining 2 might still serve as start/ thruster bank vs just tossing them to have all house bank battys the same age.
I dont think FLA GCs are comparable the FLA Gp 31s re CCA OR MCA for starting due to different plate designs for FLA start vs deep cycle. I have checked with both Trojan and East Penn re plate design of AGM and both said there is no difference in plate designs or deep cycle capability or hi A start draw for GC vs Gp31.
Hope that helps... I can provide more details if interested.
Thanks all for the replies. I bought a re-conditioned 8d for $80 from Interstate do get me by for the season. Then going to take your recommendations and get a single start battery, 2 group 31s with their own charger, then the 6v GCs for the house bank. Not sure why MS configured it the way he did. Thanks!
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