Raising my aft cabin bunk to allow for taller batteries

[Stella Maris]

Has anyone tried raising the support for their aft cabin bunk to be able to fit taller batteries.

I was recently talking to one of the experienced marine electrical suppliers here in Trinidad and he pointed out how limiting the battery compartments on the Jeanneau and Beneteau boats are.

In my case I am pretty much locked into a 4D battery as I barely have 10" of height in the compartment under my port aft bunk. He said he had seen many owners over the years put "spacers" on the framing support for the bunk plywood to raise it a bit to be able to install taller batteries. Has anyone attempted this or have any suggestions or comments on how this could be done. I'm thinking of doing it as I would really love to be able to fit some of the 6V batteries but they are a good 1 1/2" taller than my existing 4Ds.

I searched the forum and online a bit, but it seems no one has gone this way in our group.

[vasko]

offtopic - do not forget about ventilation for the batteries when you install under the bunk - you can have a good amount of hydrogen  while charging.

[Stella Maris]

Vasko, I know what you mean. There is just a small hole in this compartment that vents into the area at the back of the engine. Once the engine is on and the blower is on I guess these fumes get expelled this way, but when it's not I am too concerned with any hydrogen that may be building up. 

Is your house bank under a bunk too.

[vasko]

be VERY careful with hydrogen around the engine...  I would never do it this way to be honest...  

I have two battery banks -  one in the starboard side locker and one under the bow bunk -  the engineer installed the one under the bow bunk forgot about ventilation and I had my batteries exploded once- really messy job to clean all the acid under the bed..  now I have two computer case VERY quite fans switching automatic ON when the current is towards the batteries.

and preparing next time I need to change my battery bank I'm switching to Li-ion completely - currently only my starter battery is Li-ion  and I'm extremely happy 

[jdl01]

If the cost of Li-ion batteries seems too high, using AGM [absorbed gas mat] batteries in a low ventilation space will also work safely.

[vasko]

actually if you get in account that you need 1/2 of the wet as you cannot discharge under 50% the price is good and on top li ion last 2000+ cycles

[blueeyes]

Mar 2, 2016 12:04:11 GMT Stella Maris said:

Has anyone tried raising the support for their aft cabin bunk to be able to fit taller batteries.

I was recently talking to one of the experienced marine electrical suppliers here in Trinidad and he pointed out how limiting the battery compartments on the Jeanneau and Beneteau boats are.

In my case I am pretty much locked into a 4D battery as I barely have 10" of height in the compartment under my port aft bunk. He said he had seen many owners over the years put "spacers" on the framing support for the bunk plywood to raise it a bit to be able to install taller batteries. Has anyone attempted this or have any suggestions or comments on how this could be done. I'm thinking of doing it as I would really love to be able to fit some of the 6V batteries but they are a good 1 1/2" taller than my existing 4Ds.

I searched the forum and online a bit, but it seems no one has gone this way in our group.

I had a similar problem when I wanted to install golf cart batteries for the house bank on my 36i. My boat had 3 batteries end to end under the aft bunk, perpendicular to the center line. After a little exploration, I found the curvature of the hull would allow me to lower the floor of the battery compartment under the 2 inboard batteries to fit in the golf carts. I left the floor at the original height at the outboard end and placed the starting battery there. You obviously have more battery capacity than I so I don't know if this could work for you but it might be worth a look. 

[ForGrinsToo]

Hi Blueeyes,

I have two 6V 220 AH AGM batteries in that space, as well, that extend about 3/4" above the framing. It's good to know that you were able to do this, but how? Did you just cut out the floor for the inner two? Did you just lower it, re-secure it with SS screws, and re-seal? Any chance you took photos? I am relieved to know someone has done what I had been contemplating (rather than raising the bunk), but would certainly appreciate additional guidance before I try to do it.

Thanks,
Geoff

[rxc]

The 43DS has four battery trays under the aft bunk, designed to hold 3 house batteries and one engine starting battery. The trays are just about perfect for golf cart batteries, but I did have to do some gelcoat shaving to get one battery to sit flat. Golf Cart batteries also come in different sizes - the terminals can be high or low, and this can give you more room. The first set I installed were high, and I had to excavate a little bit of wood from the cover on the box in one spot to accomodate the terminal. The next set of batteries were the "low terminal" variety (from Trojan), and they have better clearance. I also installed vapor trap caps, to cut down on the acid released when the batteries charge, and did not have a height problem. Golf Cart batteries are also much lighter than 4Ds, and less awkward to handle.

So, what do you do about the engine starting batteries? Well, when I had my genset installed, the company that did that work cut a hole in the storage bins aft of the port-side battery compartments and dropped in a Group 24 battery in a plastic battery box as a starter for the genset. So, when I installed the Trojans, I cut a hole in the bottom of the bin on the starboard side, and dropped a Group 31 starting battery in there. It is almost as close as it was in the original pan, and I did not have to change any wiring - just re-route it.

You have to install hold-downs for all these batteries. The ones in the original trays are easiest to do, with threaded rod in a plastic sleeve going thru the walls of the battery compartment, and bolted in place. The cutout batteries required fussier hold-downs (angle iron with threaded rods and nuts).

And, for ventilation, I have a tiny fan (about 1" diameter) connected to a voltage sensitive relay that only operates when the battery voltage gets above about 13.2v. Standard device used by campers to prevent their trailers from depleting the car starting battery. Also inexpensive. Fan exhausts to the aft cabin, and any hydrogen rises to the top of the cabin. It is unlikely to detonate, because of the dilution effect. I had noticed that the wood in the battery compartments and the original nylon hold-down ropes had deteriorated from exposure to battery acid fumes, which was another reason to install the vent fan and the vapor trap caps on the batteries.

Oh, and it is possible to set up the wiring so that you have several different possible starting batteries for the engine, in case one battery goes flat. It can get complicated, but it does provide some comfort that you won't be stranded.

Redundancy of electric supply and diversity of propulsion are good things.

I need to take some photos and post them.

[Mistroma]

I have made similar mods. to those mentioned above. I was able to move one side of the battery compartment approx. 25mm and lowered the floor at the same time.

Plenty of room underneath the existing battery box on a 2009 42DS, you might find it's the same on your larger hull.

Notes:
Bulkhead wasn't too difficult to move but base had to be cut into 2 pieces.
I fitted Trojan T105s and found that they weren't quite as large as specs. said, so I might just have squeezed them in. But it would have been too tight for comfort.
I Sikaflex'd hardwood wedges on the hull and mounted the new floor on these using more Sikaflex (not actually Sikaflex but similar from Toolstation).
Fibreglassed the base and part way up the sides.
Fitted inlet & outlet vent pipes with computer fan inside the inlet in aft cabin (fan on 1/2 speed when charging starts and full speed when gassing likely)

Well worthwhile and I keep meaning to write it up and add pictures.

Only real flaw is orientation of the T105s. They should really have been turned 90 degrees so that plates were aligned fore and aft. This minimises the portion of each plate above the electrolyte when heeled. Not major problem but not perfect.

[blueeyes]

Geoff:

I cut out the floor for the inner 2 using an oscillating multi-tool with a flush cutter, leaving the original floor for the outside starting battery. I decided to cut out an extra 1/2" for the new batteries in case I need extra space for future replacements. The outboard starting battery overhangs this small extra cut out a little. I then screwed some wood cleats onto the fore & aft vertical walls to support the new floor. Because space is tight, I made a jig out of scrap wood with a lip to hang on the top of the walls, so the bottom of the jig was where the top of the cleats needed to mounted (making sure to include the width of the floor that sits on top of the cleat). This eliminated having to measure and level down in the bottom of the battery compartment. I just hung the jig on the top of the aft wall, put the cleat against the bottom of the jig and used an angle drill to screw the cleat to the wall (also used epoxy). Repeated for the fore wall. If I recall correctly, the cleats were tapered towards the outside end because of the hull curvature. 

Once the cleats were in place I cut a new floor from marine plywood that was long enough to extend under the old floor. I then cut and attached a filler piece to the end of the new floor to fill the gap between the new and old floor. After coating it with epoxy, I screwed the new floor to the cleats and the old floor to the filler piece. Finally, I sealed the corners.

I didn't take pictures during the construction but stopped by the boat and took a few today.

This picture shows the floor tabs in the front compartment - the left side still has the old floor, the right shows the hole where the tab used to be. Using these tab holes helped me measure the distance available under the floor. like wise in front of the fuel tank.


This picture shows the compartment with the middle battery removed:


This shows the filler piece and the edge of the old floor with the starting battery on top.

[ForGrinsToo]

Perfect! You addressed every question I had. Thank you!

[Tigidal]

Great explanation blueeyes... I had this question while looking into cart batteries as well.