Moving Battery Out of the Transom Splash Well

[pcloward]

The batteries on my [1991 GUARDIAN 19] boat are in the engine splash well as seen below in Figure 1.

Fig. 1. Engine splash well with two batteries, slightly obscured by added colored circles.

Image 45.jpeg (191.37 KiB) Viewed 625 times

I am planning to move the batteries into the center console, and also to add a third battery for house use.

Is there any reason not to move the two batteries to a more protected location?

[Moderator's note: when seeking advice about a particular boat, please be sure to mention the year, the model, and the length of the boat. This gives readers more information and will permit replies to be better suited to your particular boat.]

[jimh]

Is there any reason not to move the two batteries to a more protected location?

Boston Whaler designed the boat to have the batteries located in the engine splash well, and provided reinforcement material below the laminate of the deck to support the weight of the batteries. Boston Whaler sold many thousands and thousands of boats like yours with the batteries located in the engine splash well.

The idea that you will be making an improvement in the boat by moving the batteries out of the engine splash well and placing them inside the center console is not particularly a sure bet. There are many problems in your plan. I will mention just a few of them.

First, and perhaps foremost, increasing the distance between the engine starting battery and the engine starting motor on the engine that the battery is supposed to crank over is a terrible idea on the electrical perspective. Anyone who understands electrical current flow and the effect of resistance in the wires in the circuit will immediately see the problem. If you need a more thorough explanation of the electrical problem that will be created if you add 10 or 15 feet to the length of the cables, let me know, and I will give you a more detailed explanation. But the simple answer: making the wires longer is a very, very bad idea.

Second, the transom location will generally give the batteries the most comfortable ride, as compared to other locations, there will be less pounding and slamming of the hull in waves at the very stern than anywhere else on the boat. This will give the batteries a longer service life.

Third, the center console was never designed to support the weight of one battery, let alone support the weight of three batteries. Nor was the deck below the center console designed for such a concentration of weight to placed there. Nor will there be room for three large batteries in the center console. Nor will it be easy to service or inspect or remove the batteries from the center console. And the weight off all those batteries when the hull is slamming into waves will be a huge and unanticipated load on the deck at that location.

As long as the batteries are in proper battery boxes, and the battery boxes are secured to the deck with proper straps, and the straps are secured to the deck with proper Footman's Loop fittings, there is really little concern about the location being in the engine splash well.

Even if the boat were to be overtaken at the transom by a huge following sea, the conductivity of freshwater is very small, and the conductivity of saltwater, while much higher than fresh water, should not immediate cause a short circuit at the battery terminals. To prevent any short circuit, you can spray the connection between the cables and the battery terminals with a coating of insulating wax, such as BOESHIELD T9.

More information about use of BOESHIELD T9 in marine applications can be found at

https://boeshield.com/marine/

This will effectively insulate the batteries from any water, and also significantly reduce any corrosion that would otherwise occur in normal use.

WHY THREE BATTERIES

Also, I do not understand your motivation for adding a third battery to carry the house loads. To me this is complete madness. You have only a single engine. Your boat electrical system can be handled by just two batteries. One battery is dedicated to engine starting, and a second battery is dedicated to house loads. In the event of a problem you can parallel the two batteries to get the engine started.

Most outboard engines come with only one battery charging output. Exactly how you will plan to maintain the charge in THREE batteries from one engine charging output is unknown to me--and perhaps unknown to you as you may not have even considered this problem.

If you need more advice on how to configure a modern outboard boat and its batteries, read my article on my own boat's electrical system. See

Auxiliary Battery Charging Kit for E-TEC
https://continuouswave.com/ubb/Forum6/HTML/002758.html

I wrote that article and made those changes 14-years ago, and the system has been working exactly as planned for 14-years.

For advice on what type of battery to use, see my article

Battery Recommendations
https://continuouswave.com/forum/viewto ... f=9&t=4648

Be prepared for the price of these premium batteries to have increased significantly due to the crazy inflation created in our economy by the government printing money in the post-pandemic era.

I am getting about ten years of service life on these batteries. Typically I replace the engine cranking battery with a new battery, and move the previous engine cranking battery over to be the house battery. I use the older house battery as the trade-in on the new battery.


If you re-power the boat, look for the option of adding a second charging output to the standard engine configuration. Having a second charging output from your outboard engine will made maintaining two batteries at full charge much simpler.

If you re-power with an engine that does not offer the option of a second battery charging output, you will have to get an automatic combiner relay. If that happens, you can start a new thread on the topic of the proper method to install an automatic charging relay and solicit advice.

[jimh]

In Figure 1 I see that the two battery boxes are different colors. The OEM battery box from Boston Whaler was molded in a color called Desert Tan to match the hull gel coat.

For some background on battery boxes, Footman's Loops, and proper hold down straps, see

Desert Tan or Off-white Battery Box
https://continuouswave.com/forum/viewto ... 1101#p6843

For reference, I have calculated the following sizes and fits:

Boston Whaler OEM Classic Desert Tan Battery Box
Batteries that WILL FIT:
GROUP 24
GROUP 34

Batteries that WILL NOT FIT:
GROUP 27
GROUP 31

GROUP 24 = 10.25 L x 6.8125 W x 8.875 H
GROUP 27 = 12.13 L x 6.8125 W x 8.875 H
GROUP 31 = 13.00 L x 6.8125 W x 9.438 H
GROUP 34 = 10.25 L x 6.8125 W x 7.875 H

Footman's Loops
https://continuouswave.com/forum/viewto ... 484#p25523


KEVLOK brand hold down straps

Boston Whaler provided an extremely nice and very well designed woven hold down strap for retaining the battery box. See Figure 2 below.


Fig. 2. An OEM Boston Whaler Desert Tan battery box retained by an OEM KEVLOK strap.

Exactly where you buy a replacement KEVLOK strap is a good questions in 2024. I would contact Sue Lodell at Twin Cities Marine, or what is now known as The Boat House. See contact information at

Twin Cities Marine
https://continuouswave.com/forum/viewto ... 314#p46706

ASIDE
The photograph showing the KevLok strap and battery box seen above in Figure 2 was taken more than 20-years ago, and it does not fully illustrate the proper installation of the strap. In the photograph there is a length of strap to the left that is just laying in place. This portion of the strap has a small clasp or pin device at the end. This strap should be carried back, over the closing mechanism, and the the pin unlatched and threaded through a slot seen in the closing mechanism lever, then re-latched. This will prevent the closing mechanism lever from spontaneously opening under load.

This sophisticated design is a good example of how the KevLok straps are very special straps. Naturally, Boston Whaler would have provided such a strap rather than some random plastic strap with a jaw-like closure that cuts into the weave of the strap and weakens it. At the time I took that photograph, I had not yet figured out the purpose of the clasp at the end of the open strap. But at some point, I either deduced the purpose or saw how the little pin gizmo was to be used on another instance of the strap being installed more properly.

[Phil T]

Moving the batteries to the console is a good idea. The weight distribution change will be beneficial.

You should use 4-AWG marine battery wire. For the run from the console to the engine, use one [continuous] wire, no splices. Remove the four-foot battery wire tail from the engine and run the new negative from the terminal post under the engine cowling to the negative post of the starting battery in the console and the new positive wore to the master battery switch output terminal.

Cut openings in the console floor to allow the battery boxes to sit on the deck. The console floor is not strong enough to support the weight of batteries and consumes valuable space. Recessing the batteries minimizes the lost space in the console.

The need for three batteries appears onerous and unnecessary. Please describe the electrical load planned that requires three batteries.

[jimh]

Moving the batteries to the console is a good idea. The weight distribution change will be beneficial.

As you might expect from me earlier remarks, I am not in agreement.

Regarding moving battery weight out of the transom, in this case the boat is likely to be maintained as a single-engine-powered boat. The GUARDIAN 19 hull could easily accommodate twin engines, so the weight of just one engine and two batteries in the stern is not likely to reduce freeboard at the transom.

Moving the batteries to the center console location will give the batteries a much rougher ride when the boat is encountering larger seas. Keeping weight of of the ends of a boat is a good plane for a displacement hull like a sailboat, but I don't think this rule applies to smaller outboard boats with planing hulls.

The electrical considerations are multiple. I just commented on this in another thread. Read more at

Re: Moving Battery
https://continuouswave.com/forum/viewto ... 084#p46660

Regarding what American Wire Gauge (AWG) conductors should be used, the choice of wire gauge will depend completely on the length of the wire. The longer the wire the larger the wire gauge needed. For some very good and very simple to understand advice, see this article, which is based on the OEM recommendation of an outboard engine manufacturer"

Recommended Battery Cable Size
https://continuouswave.com/forum/viewto ... 153#p12497

There you will find that a cable of 4-AWG is only recommended for a maximum length of ten feet between battery and engine. My expectation in the case of this 19-foot boat under discussion here is the battery cable length needed if the battery is moved to the center console will be longer than ten feet, as you have to include the total length from battery terminal, to switch, to engine.

The real concern about the battery cable size is to avoid too much voltage drop in the cable itself during engine cranking. The initial surge current created by an engine's starter motor is several hundred Amperes. With that much current flowing in the battery cables, the potential for significant voltage drop is a real concern.

There is nothing more disheartening for an outboard-engine boater to be somewhere far from home and not be able to get the engine started due to low battery charge.

You are welcome to pursue your plan to move the batteries, but you should expect the expense of the electrical modifications to accomplish this will add up.

For example, a 2-AWG multi-strand tinned-copper high-flex cable will cost about $3.50-per foot. You will probably need 35-feet of this cable for the project, so that is $125 just in the cable.

You will need at least eight ring terminals with closed ends at about $5-each, so that's $40.

The battery fuse holders are $25 each, so add another $50. The fuses themselves are $17, and you will need at least four to start so you will have a set of spares, so another $70.

Let's add up the costs so far:

Cable = $125
Terminals = $40
Fuse holders = $50
Fuses = $70
TOTAL = $285
There will be tax and shipping charges, so the acquisition cost will be well over $300.

If you don't have the proper crimp tools to handle 2-AWG cable, you will have to buy or rent them. And you will need shrink tubing and a heat gun. More expenses.

If you follow the suggested wire size and required terminals and fuses, the movement of the batteries to be farther away from the engine they will be starting will be mitigated, and you can expect that engine starting will not be different than with the prior, short cables provided by the engine manufacturer to connect to batteries just a few feet away from the engine.

[Phil T]

My rational -

Many classic Boston Whaler models and CPD and BCPD have a waterline above the transom thru-hull drains at rest. Helping offset this is worth the work. Gaining an inch or more of transom out of the water is helpful.

Having your battery and cables subjected to saltwater is just helping corrosion. Some owners ship saltwater over their transoms frequently due to water conditions.

Relocating the battery, oil reservoir, and the accompanying cables gives the transom a cleaner look, and it allows passengers to enter or exit via the transom with more ease.

[Phil T]

I used 4-AWG marine battery wire when moving my battery to the console of my 1987 Montauk 17 with a 1987 Yamaha 2-stroke and my current boat, details in my signature.

4-AWG is running closer to $2.15 to $3.35 per foot as of this post.

My prefered vendors -
https://www.customcableusa.com/collections/marine-battery-cable/products/4-awg-gauge-battery-cable-tinned-copper-marine-wire-red-by-the-foot

or

https://shop.hamiltonmarine.com/products/ancor-battery-cable-4-gauge-tinned-42787.html

[jimh]

If the engine splash well drains end up under water, there could be a rationale to get weight out of the transom.

Engine electrical cables in the rigging tunnel will also be likely to be exposed to water.

On my 20-foot classic OUTRAGE hull I kept the engine splash well drains plugged, and I installed a centrifugal pump to lift water out of the splash well and over the transom. The boat had twin engines which were mounted on 10-inch set back brackets, the oil tanks were internal to the engines, there were two batteries in the splash well, an auxiliary fuel tank in the stern, a large cooler in the stern, and a second cooler in the splash well. Water came over the transom only one time, and that occurred when we were in a very narrow passage with a tidal current of six knots or more pushing us ahead, there were very large standing waves, and the boat was making sternway in order to not get swept into a whirlpool. Water came over the transom, the pump came on, and the transom splash well was soon dry.

ASIDE: you might consider using a 10-inch set back bracket when mounting the outboard engine on the GUARDIAN 19. That will make the engine splash well free of all the engine rigging in the center area, and you can put an 86-quart IGLOO cooler in the splashwell. This will effectively increase the cockpit space by two feet. It was a great modification to my 20-foot Boston Whaler boat.