Battery location?

[bigskymudflaps]

I'm in the process of installing a ballast system in my RZ2. The question that has popped up is where is the best place to put two batteries? We surf both sides, so keeping the fixed weight equal on both sides is a must.

There are to obvious places to mount the batteries. First, behind the motor, centered at the transom. Second, the standard place, behind the ski lockers against the transom. From the factory, mine came with two batteries in the storage area at the transom behind the ski locker on the port side. The starboard side storage area had a lead counterweight and the taps pump inside. No factory ballast in mine, which would have put the batteries in rear of the ski locker.

I have asked a few people about the best location for the batteries, one being a high school math and science teacher. The question is actually really complicated when water displacement is involved. The answer the math teacher gave is that it could be as much 250lb benefit having the two batteries centered behind the motor. Force, distance, torque, and leverage equations...... The boat floating in water makes it crazy, she really didn't know how to figure in that variable. Her answer was based on the opposite battery having to be lifted less when the batteries are close to the centerline.


Anyone done the math?

Any anecdotal evidence?

[mls6722]

The question has been discussed. Here is one solution in this thread.

http://www.tigeowners.com/forum/showthread.php?t=15959

I am in the process of moving my batteries forward to the port mid-ship locker and many have commented on the adverse effect of 80 lbs moving forward. I think we all need to balance our boats. They don't put the helm right in the middle.

[bigskymudflaps]

I saw that thread, really thorough install and a fantastic writeup. The questions and answers in the 24ve thread did come to the same conclusion as my science teacher. However, the answer of why it's better and how much better it is to keep the batteries centered at the stern, still looms.

Here're a few quotes which are part of the explanation from the WABoating's 24ve thread:

"Putting the batteries under one of the side seats also interferes with additional ballast options such as "arms" (think Enzo fat sac) and decenters their weight, which plays havoc with keeping things as symmetrical as possible to obtain good waves on both normal and goofy sides. The proper solution is to keep the batteries aft and centered."

"I wanted to keep the weight concentrated at the transom. If it's important that the ballast be as far rearward as possible, then all that battery weight matters too. Plus relocating all components to that area kept the underseat storage area open for fat sac arms, storage, whatever."

"True, but the batteries being back there means you must have a protected volume for them to live in. Then there's the cables that must route to them. And so forth. The batteries themselves don't represent that much volume, well under a cubic foot. The key here is to get EVERYTHING out of the ballast area, so you can have nothing but ballast back there. Meanwhile, my approach keeps the batteries back against the transom. Moving them forward under the seats, as many people do, offsets the weight of the ballast in the stern. The batteries have to live somewhere - best to have them in the stern where their weight is an asset instead of a liability and the battery cables can be kept short. The primary design goal here is to concentrate weight in the stern. The batteries are back there, with their weight centered so they don't bias to either normal or goofy side. The bias comes from the fat sacs, and with the batteries relocated to the center I have maximum flexibility for normal or goofy."

WABoating does come to the same conclusion as the science teacher I mentioned. However, it's always the why it is better and how much is it better that has begged my question. It's not going to be a simple task to bring the batteries to the center. As I understand it, when weight is on the opposite side, the distance from center can have a huge impact. The phenomenon reminds me of how surprising it is that you can more than double the fill capacity of a through hull intake by only increasing the diameter by 50%. The math isn't linear and drives a simpleton like me nuts....

[skippabcool]

You didn't mention what year of RZ2, did you measure the space to even put them in the transom? The different engines and transoms don't all allow for that mod. IMO if I was even slightly considering putting them one on each side I would move them to mid ship. Then make the mode to get the sacs in the very back corners.

[bigskymudflaps]

2007 rz2 without factory ballast. Marine power 340 motor. I have measured the distance between the water pump and transom -- about 12". Batteries are a little less than 7". Seems like I could get them between the motor and transom without touching either. It's either the batteries or the ballast pumps behind the motor. I ended up with 8 Jabscos.

[NICKYPOO]

I think the answer you're going to find on the exact effect is, why ask it at all. Is going to have an effect? Obviously. How much effect? Too many variables to calculate it accurately in any sort of reasonable time frame. In other words, you can run numbers all day long. In the end, you still want to move them and have the project turn out nice. It's easy to get lost on the details of one aspect of a project and when you finally figure out the why, you can easily find out that the how just ain't possible. You need to keep that big picture at the front of your mind and stay within your capabilities. At the end of the day, you're talking about a wake that is going to change everytime someone moves their butt anyways. Find a reasonable solution that is doable and do it. Take it from someone who has though and thought and thought about a project. Eventually, you need to turn that saw on and start cutting. Chances are, once you start, you're gonna have to make some sort of change anyways.

Happy modding.

[chpthril]

Without getting technical or scientific, here are a couple things: 1) you will always have the weight of a driver on the starboard side. 2) no matter where you move the batteries, they will weigh 80 lbs and will have some sort of effect on the wake. It may be big or may be small and it may be positive or it could be negative. Too some degree, the weight of the batteries are countering the weight of the driver.

IMO, moving the batteries are not as high as a priority, unless one is looking to fill that space with ballast water.

[houstonshark]

We just completed my stereo install where we installed 2 stereo batteries on the port side and the cranking battery on the starboard side. The net effect in weight was roughly 130-140lbs on the port side. Like Mike said, since the driver is on the opposite side I thought the extra port side weight would actually help even out the wake if we only have a couple people in the boat. Boy was I wrong!

With the 400lb bow sac full, the rear ballast at 50% (surf ballast pkg), TAPS at 1 and about 22mph the port side wake was huge and the starboard side was washed out. In order to even it out I had to bump the starboard side ballast to 75% and drain the port side to roughly 25%. Both wakes cleaned up but I never got both wakes to match the size and shape of the original port side.

I need to find some weight for the starboard side to go near the cranking battery. If I can get the weight just right I think the wake will be pretty impressive without a ton of additional PNP ballast.

Mike, I'm still interested in whether or not the dual 400lb sacs will work in the bow.

[bigskymudflaps]

We just completed my stereo install where we installed 2 stereo batteries on the port side and the cranking battery on the starboard side. The net effect in weight was roughly 130-140lbs on the port side. Like Mike said, since the driver is on the opposite side I thought the extra port side weight would actually help even out the wake if we only have a couple people in the boat. Boy was I wrong!

With the 400lb bow sac full, the rear ballast at 50% (surf ballast pkg), TAPS at 1 and about 22mph the port side wake was huge and the starboard side was washed out. In order to even it out I had to bump the starboard side ballast to 75% and drain the port side to roughly 25%. Both wakes cleaned up but I never got both wakes to match the size and shape of the original port side.

I need to find some weight for the starboard side to go near the cranking battery. If I can get the weight just right I think the wake will be pretty impressive without a ton of additional PNP ballast.

Mike, I'm still interested in whether or not the dual 400lb sacs will work in the bow.

Good information, I am still on the fence regarding what I am going to do. Try and bring the batteries to the center? One on each side? Don't know. Mine came with two batteries against the transom on the port side. On the starboard side by the transom, there was a hunk of lead wrapped in carpet and the taps pump -- about 25lbs. All the variables -- suppose we deserve it for modifying what the factory did.

[skippabcool]

BigSky, where do you boat? Utah Lake, Willard, or up in the mountains?