CG and dual battery set up?

[Moody Blu']

how does everyone feel about dual battery setups and the location of them on 18's? I was thinking about mounting two batteries as far aft as possible on the port and starboad side, but then i thought about the center of gravity and how it may upset the boats handling characterisitics. should i be worried about this or is it a non issue? I would think the boat would want to teeter totter with two batteries on the outermost part of the hull and i dont want a quirky boat if i do this.

are thee any other areas to mount them?

and does anyone have pics of there dual setup with the switch etc?

i will not call sea tow again at 150 a pop for a dead cell in my battery:mad:

[hardcrab]

in my opinion, placing the batteries beneath the rear seat would be the area that would take the least pounding. the weight is centered and low.
also, you would run the minimal amount of cables; I'm planning to mount my batt switch on the backside of the rear seat / above the batteries.

[p729lws]

It's a tight fit, but I installed dual batteries under the rear seat of my 18. The switch had to be mounted in the engine bay however.

[Moody Blu']

It's a tight fit, but I installed dual batteries under the rear seat of my 18. The switch had to be mounted in the engine bay however.

what group batteries did you use? i have two 1000 cranking amps batteries i want to use

[Carl C]

Doc Dan's batteries look pretty sweet side by side in front of the motor whereas my bats. came mounted on each side of the motor. However these are 22's. I do believe that center of gravity is a factor in the superb handling characteristics of Classics. Therefore the narrow cockpit and seats placed close to center. Your 18 should be even more sensitive to this. If others have put them under the seat then that is what I would do and mount the switch in the engine compartment. JMNSHO.:)

[Surfer]

Moody, I glassed in platforms directly behind the rear seat, no noticable differance in balance before and after, cables mount easily to the seat rear.

[Tony]

Isn't there absolutely no difference between placing one each outboard of the center line, compared to both together in the middle of the boat? Or am I missing something?

Now, fore and aft placement is another story, and under the back seat IMO seems to be a better location.

[p729lws]

what group batteries did you use? i have two 1000 cranking amps batteries i want to use

I had a pair of the of the dual purpose marine Optima batteries. 750 CCA's I think.
http://bigtimebattery.com/store/optima_d34M_batetry.html

The optimas have a fairly small footprint and I don't think anything larger would fit under the seat. I didn't notice any ride difference with the two bateries in there.

Dan

[hardcrab]

Isn't there absolutely no difference between placing one each outboard of the center line, compared to both together in the middle of the boat? Or am I missing something?
Now, fore and aft placement is another story, and under the back seat IMO seems to be a better location.
I figger that having batteries mounted in extreme outboard corners will produce "hard spots" on the hull resulting in stress points

[Moody Blu']

I figger that having batteries mounted in extreme outboard corners will produce "hard spots" on the hull resulting in stress points


thats what i was thinkin, along with making it want to teeter totter back and forth possibly causing a chine walk

[Moody Blu']

I had a pair of the of the dual purpose marine Optima batteries. 750 CCA's I think.
http://bigtimebattery.com/store/optima_d34M_batetry.html
The optimas have a fairly small footprint and I don't think anything larger would fit under the seat. I didn't notice any ride difference with the two bateries in there.
Dan
please get me a pic of your setup

[RedDog]

In my '98 22, Donzi mounted the single battery on the starboard side very near the transom. I mounted my second battery on the port side to mirror the starboard battery. Mounted at the transom to assist bow lift. I would think having 1 each side vs only 1 on one side would result in better balance. Also, mounting one each on the outside should provide better balance than 2 in the center. I think it is a physics thing. Have you ever noticed that a tight-rope walker carries a balance pole with weights on the ends? Better balance is achieved with the weights moved out rather than held close in. It's like the counteraction of the inertia thing acting on the end of a lever.

Disclaimer - I haven't cracked a text book or worked an equation since - well I can't remember. My theory may be BS but it seems right according to the shadows in my mind :confused:

Ahhh, Jamie! We need a practicing engineer here........

[Moody Blu']

i thought about it, you are right, but there is more stress involved and more force is needed to push the boat(the waves hitting it) in the other direction

I guess it could make the boat more solid in rougher water

thats my concern really..

[hardcrab]

In my '98 22, Donzi mounted the single battery on the starboard side very near the transom. I mounted my second battery on the port side to mirror the starboard battery. Mounted at the transom to assist bow lift. I would think having 1 each side vs only 1 on one side would result in better balance. Also, mounting one each on the outside should provide better balance than 2 in the center. I think it is a physics thing. Have you ever noticed that a tight-rope walker carries a balance pole with weights on the ends? Better balance is achieved with the weights moved out rather than held close in. It's like the counteraction of the inertia thing acting on the end of a lever.

Disclaimer - I haven't cracked a text book or worked an equation since - well I can't remember. My theory may be BS but it seems right according to the shadows in my mind :confused:

Ahhh, Jamie! We need a practicing engineer here........
a tight rope walker is working with the least erratic movement possible; this outboard balance theory will only benefit when running on plane/trimmed out.
low/center gravity will benefit in erratic sea conditions better. ........ (?)

[RedDog]

a tight rope walker is working with the least erratic movement possible; this outboard balance theory will only benefit when running on plane/trimmed out.
low/center gravity will benefit in erratic sea conditions better. ........ (?)

Batteries at the transom vs in the rear seat box results in the lowest center of gravity. If batteries are positioned symmetrically on each side, then the center of gravity IS the center-axis of the boat.

I weigh 220 and sit in the starboard seat. If I don't have a passenger, what does that do to the center of gravity vs having a 25 pound battery sitting anywhere? I'd say we have already wasted more time discussing this than it is worth. Find a spot that fits and can be cleanly cabled.

[hardcrab]

I'm just trying to address the original question ...............

[Moody Blu']

yea its a cool one if ya thnk about it, i run my boat pretty hard and definately want to make sure I can gain some performance out of the hull in rougher seas if possible but i def dont want to hamper it at all, and inertia is playing a roll here and i dont want to hamper my handling.

the tight rope walker does make one think. yes it keeps him stable with little movement but what if you took one of those weights and pushed up on it real hard on the right side? it sounds like the inertia form that upward force would allow the left side to go deeper down then if the weights were in the center.

just like a offset wave could do to the bottom of the hull causing the boat to not recover as quick as if the batteries wer ein the center?

can anyone chime in to set this straight?

[RedDog]

I'm just trying to address the original question ...............
As did I - and the real answer is in the real world it doesn't matter much. Find a spot where they can be efficiently cabled with an attempt to make the weight distribution somewhat symmetrical side-to-side
How much does a battery weigh? How much does a 18 Donzi weigh wet? A battery is pretty insignificant in comparison. My typical boat soda load is more than a battery - for a while

[DonziJon]

I guess I have a slightly different take on the question of where the batterys should go. The IDEAL place to put it/them is AT the center of gravity as near as posable. Make the battery as "invisible" as possable from a physics point of view. I would think under the rear seat is as close to that point as you are going to get. Putting weights "outboard" of the CG would be counter productive to good handling.

Take a Fighter Jet for example: They are usually designed with the greatest weight..the engines.. "Inside" the fusalage, not out on the wings. If the engines..and many fighters have two of them, were mounted outboard, the plane would be unable to do "snap rolls" that are required for maximum maneuverability.

I also like to put the battery in a place where it will see the least amount of movement....Up/Down/Right/Left,.. etc. Battery failure underway is probably caused by Sediment in the bottom of the battery being "shaken up" and shorting out the plates, not because the battery is discharged. Older the battery the more sediment.

Just my thoughts. I have been accused of "Overthinking" things on occasion. :bonk: John

[mrfixxall]

yea its a cool one if ya thnk about it, i run my boat pretty hard and definately want to make sure I can gain some performance out of the hull in rougher seas if possible but i def dont want to hamper it at all, and inertia is playing a roll here and i dont want to hamper my handling.
the tight rope walker does make one think. yes it keeps him stable with little movement but what if you took one of those weights and pushed up on it real hard on the right side? it sounds like the inertia form that upward force would allow the left side to go deeper down then if the weights were in the center.
just like a offset wave could do to the bottom of the hull causing the boat to not recover as quick as if the batteries wer ein the center?
can anyone chime in to set this straight?

moody,i glassed in a piece of birch plywood in the engine compartment for my batterys..im on my 6th season with the same batterys and no problems..i mounted the batt switch under the back seat and put the battery cover on a shelf for more storage which you all know theirs no storage room in a 18..
i mounted the batterys even with the engine...excuese the dirty engine compartment ive been really busy at the shop and no time to clean it..

[hardcrab]

well Mr. Blu' ...........

Donzijon has further explained the merits of centrally mounted batteries; the least pounding they take, the longer they last.
below the rear seat has the closest to a gimbal effect

for the record:
I never suggested using batteries as counterbalances was useful

[LKSD]

Ahhh, Jamie! We need a practicing engineer here........
__________________
RedDog



Sorry Im late, here is my 2 cents as to my preferences.. :)

Nothing wrong either with putting them under the seat, but you loose that storage space & then instead of having counter balances out to the side you are centered more which doesnt help much with the listing at all..

I like the batts in the engine compartment.. One on each outer side. Good balance & it keeps the space under my seat available for storing other stuff.. Put the battery switch in & mount it on the rear bulkhead.. Badabing go boating.. :) :)

Jamie / Lakeside :)

[boxy]

Ahhh, Jamie! We need a practicing engineer here........

Hey Rootsy, put that engineering degree to use, what's the story....

[p729lws]

please get me a pic of your setup

MB,
I sold the 18 before I picked up the 22 and don't have any photos of the blue top Optimas under the rear seat. It's a tight fit for sure. They sat end to end long ways port to starboard. The sides of the compartment are angled and I had to raise the base of the compartment about an inch with a piece of plywood to get enough space for the base of the batteries. There wasn't much clearance between the top of the batteries and the lid. Hope this helps.
Dan

[Carl C]

I agree with Rootsy's take on this except for one thing. Those .02 mph gains add up!!! The weight should all be at the center line. This is the main reason for staggered engines in the bigger boats. The weight should probably also be as low as possible. IMO the weight of 2 bats is significant.:)

[Cuda]

I agree with Rootsy's take on this except for one thing. Those .02 mph gains add up!!! The weight should all be at the center line. This is the main reason for staggered engines in the bigger boats. The weight should probably also be as low as possible. IMO the weight of 2 bats is significant.:)
I had one boat that between my weight on the drivers side, and the prop torque, I decided to mount both batteries on the other side, (Port side) as far back as I could.

[LKSD]

I agree with Rootsy's take on this except for one thing. Those .02 mph gains add up!!! The weight should all be at the center line. This is the main reason for staggered engines in the bigger boats. The weight should probably also be as low as possible. IMO the weight of 2 bats is significant.:)


Carl,
Thats not the only reason for staggered's.. They also do it because you can narrow the beam & move some weight fwd to help eliminate bow porposing.. Other than that having the stuff mounted outward is fine..

& yes the weight of 2 batts can be significant.. :)

Cuda,
I also have mounted 2 batts on a side in some boats.. It has helped in some situations..

Jamie / Lakeside :)

[Carl C]

Carl,
Thats not the only reason for staggered's.. They also do it because you can narrow the beam & move some weight fwd to help eliminate bow porposing.. :)Yup, and it also gets the drives closer together where they run more efficiently. It is my understanding that the main benefit is in getting the weight closer to the centerline. Any boat designers out there who can clarify this??

[Moody Blu']

thanks for all the replies i suppose my best way to go is in the center, im thinking about putting one in the battery compartment and the other right in back of the batt compartment in the engine bay. then possibly mounting the switch on the side in the storage area


right now im waiting on the tank arrgh