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northerncat · 08-09-2006, 17:47

given that im going to be installing 2 9.9 yamahas explain to me why i would bother having a seperate starting battery and not just put extra battery capacity into the house banks, i realise that if there is not enough power left in the houes bank i cannot start the motor however i have hand started one of these before and they are not that hard to pull over so what reason would i have to have a whole other battery just for starting ?? if i just had one bank then i could use my outboards for charging the house bank as well as the solar panels as well as elimate a bit of wiring, as for hand starting the things i planned to cut a hole in the side of my seat and put a screw out access hatch there so i could pull the motor over from the side, so are there any reasons why i really need a seperate starting battery
sean

btrayfors · 08-09-2006, 19:00

Two possible reasons: redundancy and convenience. Redundancy in the event your house batteries go flat, and convenience so you don't have to cut a hole or bother with hand-starting.

Re: extra wiring, yeah, there'd be a bit. You could still rig your Yamaha's to charge the house batteries, though, and use a little device like an EchoCharger to keep the starting battery topped off. Easy, relatively cheap, effective.

But, you've gotta decide whether or not it's worth it.

Bill

**Alan Wheeler** · 08-09-2006, 22:09

The main reason for a "house" bank and a "start" bank is that the two types of battery are very different from each other. A house bank is or should be a Deep cycle battery. Deep cycle is very poor at supplying the laod requirements of a starter motor or anchor winch. A "start" battery is very poor at suppling the demands of long term low energy drains.
However, in your situation, the demand of starting a 9.9 outboard is so low that a deep cycle "house" battery would do it with ease.

delmarrey · 08-09-2006, 22:44

Is there any reason why you're not running (1) 25 hp OB instead of two 9.9's?

northerncat · 08-09-2006, 23:01

my house bank will be 400ahrs which i would think would be plenty for starting 2 9.9s which dont require a lot of current to start any way, delmarryey the 9.9s push my boat along at 10+ knots so i cant see the reason to go for the 25's which will just use more petrol for a small increase in top speed
sean

**Alan Wheeler** · 09-09-2006, 00:20

Sean, what delmarrey was meaning was why two 9.9's as against ONE 25hp.
I would love to know more about your boat. What is it, weight, length, hull shape etc. Reason why is that I ahve just been talking to a friend about putting outboards on the back of his boat. He has a VERY old VERY heavey Ford diesel that is probably about 90Hp. The boat has a planing hull, but they don't plane it, they may push it to 11knts tops. The time is soon aproaching that the engien and old leg may have to go, so I have suggest why not look at twom small outboards on the back. They are going to loose 500Kg odd in old engine and leg and I reckon this boat will require very little to push it along. She is 36ft and 6500Kg. I reckon two 25's or 40's would be more than adiquate. So how does your boat perform?

delmarrey · 09-09-2006, 01:02

is since you have two motors, why not two batteries. One smaller for each motor. With a 1-2 switch to your main pannel. I'm assuming this is a power boat. The charging system on those smaller motors are not the greatest for depenability (around 6 amp). And if your using a bunch of electronics, two batteries would help reduce the load on the charging systems. a 400 ah battery can put a real strain on a small O/B if it happens to run down e.i. At anchor.

Where as, a 25 hp motor has a more dependable charging system. and can EZ'ly keep up with a higher load like; radar, VHF, lights, and starts plus what ever other toys a man/woman may have on the boat.

If your running an inverter your 400 ah will be fine but you wouldn't want to drain it down very far......................._/)

northerncat · 09-09-2006, 01:25

it is a sailing cat with the 9.9s as auxilarys, im looking at cutting weight and have started to ponder the necessity of a starting battery as it would seem to be extra hassle i.e extra weight,wiring and if i just go with one bank i can have my outboards charging it and save a few dollars as well
as for the boat it is under construction but you can check a few photos of it here check out sean and tania cairns http://easycat.50webs.com/easy_cruising_general_005.htm

Sunspot Baby · 09-09-2006, 05:05

Another reasons catamarans have dedicated starting batteries is to avoid the long cable runs and associated voltage drop. With the battery close to the engine, a wire run from the switch to the solenoid is much lighter. I have a 30A relay so assure the solenoid gets full voltage.

Since your running 9.9 outboards that are, as you say, easy to pull, maybe you want to save the weight. Another consideration would be a motor cycle battery as a dedicated start battery at each engine. Much lighter and you still have the redundancy and convenience.

Seems you are really making good progress on construction. Good on you mate!

George

hellosailor · 09-09-2006, 07:51

Sean-
A couple of reasons that you can weigh. As others have said, reliability. You preserve the starting battery isolated, and that ensures you'll have one if there is *any* type of battery, cable, or systems failure in the main bank. Let's say the wind is slack and the USS Ronald Reagan is coming down at you doing 40 knots and you'd like to motor out of the way NOW. Nice to know the starting battery is going to be reliable.

Bear in mind that a dedicated starting battery can be a WEE THING and that also makes it a cheap thing, which won't hurt to replace as needed. And by locating it near the engine, you can use smaller cabling for it, another convenience and cost cutter. Or one starter battery cabled out to both of your engines, located between them or directly AT one.

I can't see that a 9.9 would take a heavy starting current, and most deep cycles can provide a strong enough surge to start larger engines with no damage to them, but I would also check the starter motor draw, against the current rating for whatever battery you plan to start them with. It shouldn't be a problem, but it is easier to check.

What's the worst thing that can happen with only one battery bank? You become a sailboat, you need patience, and the USS Ronald Reagan chalks up another silhouette on her island.<G>

northerncat · 09-09-2006, 15:59

my main house bank is only going to be about 2m from one motor and 4m from the other
sean

Jon D · 09-09-2006, 16:43

Sean

FWIW and IMHO with 9.9 outboards I would not add the complexity.

Dedicated starting batteries become real important when you can't pull/crank start you main engine. Then you don't want to be caught without a way to start it if you can avoid it.