Improving Trim By Moving The Batteries

[johnr]

[thataway]

Do you really want the "Minimum" starting battery? I want a battery which will be reliable, even if it is cold or one has to crank the engine longer than usual for any one of a number of reasons. There is a reason that engine manufactures give a minimum of MCA (Marine Cranking Amps) The Honda 90 is in the 750 MCA range.

A #1 cable would be minimum. I would use a minimum of 1/0. there will be about a 30' run (up and back). #1 AWG tinned wire weight:.256 per foot= 7#, cost: Defender is $5.22 a foot x 30' = $156. Yes, you might get away with lesser quality and smaller cable in the short haul.

A fuse within 7" of the battery is necessary protect the wire, boat, engine and battery. There should also be a switch close to the battery. How about that bilge pump wire which comes off the battery?....or the terminal post you put aft? How are you going to handle the power to the console?

Playing the devil's advocate to give consideration of best practices.

Remember the more the weight of the battery, the more lead and greater the capacity. 40# is on the light side for a group 24. Most are at least 45# to 55#.

[T.R. Bauer]

My wife likes to sleep in the front and so did my kids on long runs. That's way more weight that a battery or two. The boat really didn't seem much different - might have actually ridden better, but it did slow the boat down 2-3 mph. I don't think you're going to notice the huge difference I have inferred you think you're going to get by moving a battery. In crap seas, I insisted they move back to a seat....I suspect it matters, but it never has that much.

[Marco Flamingo]

My situation in a CD 16 is much different, but might have some value as a weight shifting experient on a smaller scale. I did move batteries and fuel tank to improve balance. To really predict the effect of moving weight aboard would probably require a naval architect and even then you would have more numerical predictions rather than certainty of improvement. Part of the problem with experimenting with shifting weight on an existing boat is that it is difficult to model the exact final effect. You can put weight forward (bags of sand, etc.), but you will still have the batteries and fuel in their present locations. That is not the same as moving the present stern weight to mid ship. That is basically what I did.

I did my unscientific field trials by climbing as far forward as possible while someone else had the helm. That slowed the top end and I had my first real experience with bow steer when we hit a wake. I got bounced around side-to-side in the V berth. But it still seemed that shifting weight had the possibility of improvement. When sitting at the dock, my boat originally had the not uncommon C-Dory squat. I didn't have a permatrim at the time and didn't want trim tabs unless required and, it turns out, they are not.

I moved the batteries (start and house) under the passenger seat and the fuel tank just forward of that, resulting in a very slight bow down position at the dock. By the time I reach hull speed (probably about 4.5 knts), the hull is riding flat. With my "permatrim knockoff" OB fin, the boat trims nicely although I can force the bow down if I want. The stern is now lighter by 100# and the boat now carries a more weight than "stock" (an additional Group 24 and 17 gallons more fuel). That works out to adding an additional 186# to the boat, but the additional weight is very close to the center of the boat, i.e., closer to the center of floatation.

Had I left the batteries and fuel in the stern, I'm not sure if there is any amount of weight I could add to the bow to get the same results. If I had just moved the original weight out of the stern, I would have had a really zippy 16. But I wanted the extended cruising ability of an additional battery and more fuel. As such, I was basically forced to move batteries and fuel forward. And it worked out.

[mikeporterinmd]

We just run with the tabs most to all the way down, and the motor tucked pretty low as well. In really heavy water, I've had to bring the tabs up to avoid having them get caught by stern seas. Bow steer is rare, but it can happen and I certainly would want a quick adjustment to make it go away. Very unpleasant and dangerous. We have a group 27 house and a group 24 starting battery in the area between the tanks. They sit just fine there. That's about the most stabile location on the entire boat.

When we bought the boat it was rigged with an anchor chain specifically for weight. Very annoying to handle and was too short. I replaced it with a long line (for our area - 150' is plenty) and a short chain.

Mike