CONTINUOUSWAVE

On my 1987 Montauk 17 I plan to move the batteries to be under the console from the stern. I want the deck as clear as possible. [Moving the weight of the batteries to the console] should also help balance the boat.

Should I mount the batteries on the shelf or on the deck?

[Moved to REPAIRS and MODIFICATIONS for discussion of the structural strength of the shelf in the console on a MONTAUK from SMALL BOAT ELECTRICAL where the electrical considerations of moving the battery were the topic.]

I doubt that the shelf in the console will have sufficient strength to hold the weight of two 12-Volt lead-acid batteries, and particularly not have the strength to withstand the forces to be anticipated when the boat is operating in rough seas. For that reason the batteries are generally mounted on the deck. In some installations the bottom shelf of the console is cut out so the batteries pass through the shelf and rest on the deck. It may also be a good plan to place under the batteries a section of marine plywood (that has been sealed with a resin to make it watertight) so that the load is spread across the deck area. This will reduce the chance of harm to the deck from the weight of the batteries. Making a cut-out in the shelf can also aid in keeping the batteries in place. Otherwise the batteries must be retained by hold-down straps fastened to the deck.

If you use non-lead-acid batteries the weight could be substantially reduced but the costs will be proportionally increased.

Deigh wrote: [Moving the weight of the batteries to the console] should also help balance the boat.

Moving weight out of the stern is often a good idea, particularly if the boat has been re-powered with a modern engine whose weight is significantly greater than the relatively light two-stroke-power-cycle engines for which the MONTAUK was originally designed.

If you use AGM batteries on your boat the weight will be much higher than if you use conventional lead acid batteries. Spreading the weight on the deck as much as possible would be advisable.

Any battery in the console should be installed in a battery box and in such a way that it is resting on the deck. A square of Dri-Dek can be placed under the battery case to allow water to drain.

By recessing the battery(s) onto the floor, the sparse storage area in the console is preserved.

Jefecinco wrote:If you use AGM batteries on your boat the weight will be much higher than if you use conventional lead acid batteries.

I think you have to compare apple-to-apples, which for a battery is the probably the amount of electrical energy it can store in Ampere-hours at a 20-Hour discharge rate. Let's look at some premium batteries from Rolls with a rating of 85-Ampere-hours:

Their 12-Volt lead-acid AGM construction 85-Ampere-hour battery weighs 50.5-lbs:

Their 12-Volt lead-acid flooded-cell 85-Ampere-hour battery weighs 47.5-lbs.

The weight difference is 3-lbs. The AGM does not need a battery box, so we can deduct at least 1-lbs for the no longer needed box. Now we are down to a difference of 2-lbs.

For that 2-lbs you get:

• freedom from acid spills, no need for ventilation, better resistance to vibration and forces;
• a significantly lower self discharge rate, less than 2-percent per month compared to 5-to-10 percent-per-month for flooded;
• significantly higher engine cranking current, 800-MCA compared to 690-MCA for flooded.

If saving the 2-lbs become critical, jettison some beer overboard. :-)

I am sure other comparisons can be made, but generally the ingredient in a battery that makes it more powerful is lead. So when you compare batteries with similar amounts of lead, the AGM construction comes only with a very small weight increase, perhaps a few percent more weight, but the AGM provides better electrical performance.

Because big 12-Volt lead-acid batteries with 800-MCA or higher ratings weigh about 50-lbs (ir more). I don't like to wrestle them out of the boat when the boat is put into unheated winter storage every Fall. The significantly lower self-discharge rate of the AGM is the most attractive feature for me. I can leave the AGM batteries in the boat--where they are rather inaccessible and difficult to move--all winter, and in Spring they will have only a very minor amount of self-discharge. Typically 30-minutes on a 5-Ampere charger tops them off in the Spring.

I think this becomes similarly important if you put the battery into a crowded center console interior. It will be easier to leave the battery in the boat year round rather than take it out for storage.

Further advantage of placing them on the deck is that you gain some additional storage area. When I raised my console by approx 4", the battery lids (I've installed two, with switch) are approx 1.5" above the deck.

One caution; don't just add a splice to your existing cable place it in the tunnel. If you need to add to the cable, and cannot make it a complete new run, do your splicing so that the spices do not end up in the tunnel.

Regards- Don

Thanks for all the feedback. I’m redoing the wiring on the boat. The tunnel was a mess. Gonna build a board with a marine [electrical power distribution bus] and a battery switch. The I will mount the board in the console.

[The boat currently has] a mess of splices and connectors and bundles of wires with cable ties on them.

[I plan on] tearing out [the mess] and redoing the entire [boat electrical wiring].

With the structural problem of the battery installation resolved, you can get back to the electrical part of the project.

Deigh wrote:[I plan on] tearing out [the mess] and redoing the entire [boat electrical wiring].

By the way, your plan sounds good to just take out all the existing wiring. Generally on a small boat there is not that much original wiring, and on older and used boats there is often a lot of haywire added by prior owners.

If you need advice on the electrical portion of this project, just post in SMALL BOAT ELECTRICAL.