Ship's battery

The heart of a small yacht's electrical system is it's battery. It's need for navigation, cabin, anchor and compass lights as well as VHF radio and other electronics if fitted. I wasn't sure how many AMP hours would be needed, probably 30 or more i heard so went on the higher side to make sure it wouldn't get too discharged on a 2-3 day trip.

Charging system

The other factor influencing battery size is the type of the recharging system. Is it a shore-based  12 v battery charger or an independent at sea type such as a solar panel (or use both systems)?

For now i have a 4 amp Arlec 12 Volt battery charger bought at a car accessories shop long ago. It's fed by 240 volt AC power via a long extension lead from the house to the boat in the backyard. It tops it up in a few hours or overnight and regulates the charge level, it starts off with 2-4 amp on the dial and ends up with less than 1 amp when near full charge.

Battery charger 240 volt household AC input plug and DC output alligator clips for negative (black) and positive (red) battery terminals.

The AMP meter shows the amount of power going into battery. 

Many trailer sailers who sail allot use solar panels to keep the battery topped up. I have on hand a very old 35 W panel and recently bought the solar charging regulator and some wires etc and plan to fit this eventually.  (Jan 2016 - Finally rigged up the solar charging system!)

Battery types

It's a confusing subject for the uninitiated. There is a pleothora of batteries out there and many battery shops catering for all types of uses. To simplify the search I chose a boating shop - marine chandlers  to buy one - they have done allot of the homework and probably found the most popular batteries. In my case Bias boating was also the best location, near home.

I bought a 60 Amp hour general purpose sealed lead acid battery for around $150, (The following specs are from Bias's catalog) It's a "Sea master"  ECG expanded calcium grid battery. It's an extra  heavy duty, maintenance free, wet cell with a built in hydrometer eye. Dimensions in mm are 235 long x 172 wide and 220 high. Found out later it has a high cold cranking Amps CCA of 575 so is probably more suited to powerboats.

So in retrospect I should have got an deep cycle battery , such as an 80 amp hour "AMP Tech" for around $180 at Bias, it has similar dimensions at L269, W173 and H200mm).

A 35 amp hour AGM absorbed glass mat may have been enough, certainly allot smaller  but the cost was up per amp hour. 35AH cost around $150  at Bias, it has "significantly longer life" than lead acid batteries and it's fully sealed can be turned on any angle. A 55 AH AGM for comparison cost around $270.

Gel cells are also sealed lightweight, more costly. But you probably get longer life, smaller size etc
The lighter - smaller - longer lasting  AGM or gel cell types could also possibly be fitted in more locations like in the starboard cockpit locker or up forward in the V-berth locker.

Fitting the battery

My lead battery weighed allot and was a hefty size so wanted to keep the weight low and central with the added benefit adding a bit of extra ballast to make the boat more stable.

There is a little used space under the forward end of the cockpit behind the center board lift pipe and companionway step. A previous owner had small blocks of wood here which i removed - these were probably old battery mounts.

The Investigators production companionway step, although a nice piece of workmanship, was permanently riveted onto the bunks each side and made it impossible to access the relatively voluminous space behind the step. Besides wasting valuable space on a very small boat was a sad state of affairs for maintenance too, so drilled out the rivets, cut a bit away at the pipe and removed the production step from the boat.

I cut a battery base from 12 mm plywood. Wood gives a bit of spring and shock absorption. Made up a battery bracket with 30 mm angle steel and 10 mm threaded rods. Two holes were marked then drilled through the ply battery base. The angle iron was fabricated to form the top plate with two holes for the threaded rod drilled.

 The base was positioned in the boat and the holes continued through the fiberglass floor. I took care to make sure i didn't drill through the hull, it gets pretty close but there was about 10 mm spare each side out to the keel sides. It was a bit of a Chinese puzzle and contortionist game to get the bolts in and standing up but it all bolted together nicely and should keep the battery firmly in-place during road trips, rough weather, knock-downs or worse. It should actually help right the boat when it heels over.

The battery has some room each side of it still. One side  is room for the 8 foot long rolled up boom shade awning. It can be slid past the battery. The other side has room for two 8 foot long oars and the boat-hook to be stowed.

Battery under cockpit. Long items stowage is on either side of battery. Awning is to left and oars, and mainsail-boom etc can go to right. Negative power cable is off terminal to isolate battery. Battery hold-down is very robust. 

As long as a battery is about 173 mm wide it could be much larger in the other two dimensions (depth and height). The extra weight in this location would be OK. This may be of use if an electric auxiliary outboard is ever experimented with.

A quickly removable step was needed but I ran out of time to modify the production step for this function. Quickest solution was to make up a temporary wooden step from 25 mm hardwood which sat on the bunk tops. A notch for the centerboard pipe was cut in the wood step and the bunk fiddles wedge the front end in place. It's a  heavy and very strong step.

Removable wooden step

With the step out, it is now possible to access and do maintenance work below the cockpit. Checking the battery, Cleaning the bilge - I think it was the first time  that anyone had ever cleaned the bilge under the cockpit. Quite allot of rubbish from corroded coins,to bits of wire, rusty screws and other accumulated crud were removed.

Battery, bilge sump, lift pipe and stowage access by removing step.

Battery lead removal  to isolate it is easy. 

The location is hopefully a fairly dry one, it is tucked under the cockpits edge and behind the companionway hatch opening.