Re-wiring a 13-foot Skiff

Electrical and electronic topics for small boats
PatSea
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Re-wiring a 13-foot Skiff

Postby PatSea » Tue Mar 17, 2020 11:24 am

I'm in the planning stage for rewiring a Boston Whaler Sport 13. I would appreciate your comments and suggestions. The electrical system consists of a TOHATSU 40-HP engine, a bow mounted trolling motor, navigation lamps, bilge pump, fish finder, and a USB and 12-Volt outlet.

I plan to wire the engine power cables either direct to the battery posts or to a new battery switch.

Is a battery switch necessary?

I would wire the trolling motor either directly to the battery or to the battery switch. In either case it will be protected by a 50-Ampere fuse.

For the accessories I am thinking of using a new product from Blue Sea, a water-resistant Fuse Block item 5056:

https://www.bluesea.com/products/5056/S ... Fuse_Block

Their web site shows it to be available in May. I plan to mount it on the starboard stern just below where the wiring goes to the bow navigation lamp.

I'll also use a new four-circuit terminal block mounted adjacent to the fuse block for the ground wires.

Do I need another fuse block in the positive feed wire from the battery to the accessory fuse block? The distance is about 4 feet.

I know this description lacks a lot of detail but am I on the right track?

Thank you for your comments and suggestions.

jimh
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Re: Re-wiring a 13-foot Skiff

Postby jimh » Tue Mar 17, 2020 12:02 pm

I give general advice on how to configure 12-Volt power distribution on a small boat in a separate article. See

Boat Electrical Circuits and Wiring Practices
http://continuouswave.com/whaler/reference/boatWiring.html

Read that article carefully for content. Do not confuse brevity or my hand-drawn illustrations as being indicative of lack of good advice.


PatSea wrote:Is a battery switch necessary?


I recommend having a battery switch that disconnects the battery positive from all downstream loads. I suspect on a 13-foot open skiff there will only be one battery. If so, you just need a simple battery ON-OFF switch. You do not need a dual-battery switch--unless you are planning for two batteries.

A single-circuit ON-OFF battery switch might be something like this Blue Sea Systems product:

m-Series Mini On-Off Battery Switch with Knob - Red- 6006
https://www.bluesea.com/products/6006/m-Series_Mini_On-Off_Battery_Switch_with__Knob_-_Red

If the switch is to be mounted in an open area at the stern of the skiff, you might want to use a battery disconnect switch that can fit under the cover of a battery box exclosure. Mounting like that will give more weather protection. I don't have a particular switch of that type to recommend.

Or a switch similar to the BEP 701 CONTOUR battery switch might be more suitable, as it looks like it is more protected.

BEP 701 CONTOUR battery switch
https://www.bepmarine.com/en/701

The switch usually has to be very close to the battery positive terminal to comply with ABYC recommendations. Usually not more than about 18-inches of wire of a certain AWG size is allowed. Check the ABYC literature. See Figure 11 on page 19.

ABYC E-09 Direct Current (DC) Electrical Systems on Boats
https://law.resource.org/pub/us/cfr/ibr/001/abyc.E-09.1990.pdf

Now you are not a boat builder trying to comply with federal regulations, so you can use common sense about how long the unfused wire ought to be. Use a plastic flexible conduit to protect the wire from damage to the wire insulation.

jimh
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Re: Re-wiring a 13-foot Skiff

Postby jimh » Tue Mar 17, 2020 12:04 pm

PatSea wrote:For the accessories I am thinking of using a new product from Blue Sea, a water-resistant Fuse Block item 5056


That four-circuit fuse box with weather seal looks like a nice product. It will keep the fuses dry on an open boat.

This product only provides for the positive circuits. You need another bus for the negative circuits. If you can mount the negative secondary power distribution bus under some protection, say under a console, you can use a more open bus product.

Common 100A Mini BusBar - 5 Gang with Cover
https://www.bluesea.com/products/2314/C ... with_Cover


If you have to mount the bus bar in the open then this analogous water-tight negative bus product from Blue Sea Systems may be a choice:

Water-Resistant - 100A BusBar
https://www.bluesea.com/products/2356/Water-Resistant_-_100A_BusBar

jimh
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Re: Re-wiring a 13-foot Skiff

Postby jimh » Tue Mar 17, 2020 12:10 pm

PatSea wrote:Do I need another fuse block in the positive feed wire from the battery to the accessory fuse block? The distance is about 4 feet.


You need a fuse located close to the battery switch. Use an in-line fuse, like this Blue Sea Systems 5068 MAXI fuse holder with 6-AWG wiring pigtails:

Blue Sea Systems 5068 MAXI fuse holder
https://www.bluesea.com/products/5068/MAXI_In-Line_Fuse_Holder

You will have to make a weatherproof butt-splice to the load side of fuse wire pigtail. Make sure you use a conductor with sufficient wire gauge to reduce voltage drop and to be mechanically rugged enough to withstand some possible abuse.

jimh
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Re: Re-wiring a 13-foot Skiff

Postby jimh » Tue Mar 17, 2020 12:19 pm

As a general rule for any sort of electrical wiring, the best practice is to have only ONE ring terminal connector under one terminal post. In reality, that practice is hard to achieve, so a more reasonable standard is to limit the number of ring terminal connectors under one terminal post to a few as possible.

Here is list of connections and conductors

BATTERY POSITIVE TERMINAL:
--short unfused conductor to SWITCH TERMINAL IN
(Just one ring terminal)

SWITCH TERMINAL OUT:
--propulsion engine primary power positive cable
--fused cable to secondary distribution four-circuit fuse panel positive bus
--fused cable to electric trolling motor positive
(Total of three ring terminals)

BATTERY NEGATIVE TERMINAL:
--propulsion engine primary power negative cable
--unfused cable to secondary negative power distribution bus
--unfused cable to trolling motor
(Total of three ring terminals)

Using the battery terminals themselves as a binding post for three ring terminals will be a reasonable practice. Be sure to use hex-nuts and to NOT use wing nuts. Also include lock washers. I would stack the terminal post as follows, top to bottom:

--hex nut fastener
--split-ring lock washer
--flat washer
--ring terminal for secondary bus
--ring terminal for trolling motor
--ring terminal for propulsion engine

jimh
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Re: Re-wiring a 13-foot Skiff

Postby jimh » Tue Mar 17, 2020 1:02 pm

BATTERY, BATTERY BOX, KEVLOK BATTERY STRAP DETAILS

I recommend a marine battery and a battery box. The battery box should be held down with a nylon strap that passes through two footman's loop fittings that are securely fastened with screws into a part of the deck where there is underlying plywood reinforcement. See the wood locating diagram for details.

The best battery box is the OEM Boston Whaler Desert Tan box. But it has vents. If you use a sealed battery, close the vents with some 3M Scotch-35 Vinyl Electrical Tape in white or tan.

The best hold down straps are Kevlok straps. See

Battery Box Strap
viewtopic.php?t=87

also see

Desert Tan or Off-white Battery Box
viewtopic.php?f=6&t=1101

Footman Loops are widely available. Here is one source:

https://www.strapworks.com/ProductDetails.asp?ProductCode=SSFL


The battery should have a threaded stainless steel terminal post for connections. Avoid any battery that has only automotive type lead posts. Some batteries have dual posts, threaded and automotive. These can actually be somewhat useful because you can use an adaptor to convert the automotive lead posts into a multi-connection bus.

Simpler is better, so a marine battery with terminal posts, three ring terminals on those posts, proper flat washer, lock washer, and hex nut should be very reliable.

A small 13-foot skiff might have a rough ride. For that reason, a good marine battery is necessary. A flooded cell battery can be used, but you will have to keep an eye on the electrolyte level. If you don't mind added cost, an AGM battery made with ultra-pure lead can be useful for boats that go out of service for months and months; the AGM battery with ultra-pure lead will have a slow self-discharge rate and can be left uncharged for six months or more without loss of significant charge.

I use AGM marine batteries made with Ultra-high purity lead in my boat because:

  • it is difficult to get to the batteries to remove them or to add water to them; the sealed construction of the AGM eliminates adding water periodically
  • the batteries have to sit for about seven months with no charging; the use of ultra-high purity lead in the particular AGM model and brand I use gives the lowest self-discharge rate over extended storage without re-charging; this characteristic is from the ultra-high purity lead and is not a characteristic of all AGM batteries
  • my engine charging is well-regulated so the engine alternator is suitable for charging a sealed battery without causing electrolyte boiling, and the charging voltage is suitable for AGM battery chemistry; if you use a sealed battery, your outboard engine charging current must be voltage regulated so it won't boil off electrolyte, and the voltage must be limited to a maximum voltage that is tolerable for the particular battery you use.

jimh
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Re: Alternative Battery Box Strap from TH Marine

Postby jimh » Tue Mar 17, 2020 3:38 pm

As an alternative to the KevLok strap, here is something similar, and much less expensive:

TH Marine Battery Accessories
https://thmarinesupplies.com/products/battery-tray-accessories

From the above page, change the selected item in the "SELECT ONE" selection window to the battery strap with stainless steel buckle. NOTE: they are presently out of stock, but should have them available again in a few weeks. The straps are in the $10 to $12 range depending on length.

PatSea
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Re: Re-wiring a 13-foot Skiff

Postby PatSea » Wed Mar 18, 2020 10:48 am

Jim, thanks for the detailed response! That's a lot of good information.

I would like the battery switch to be more accessible than inside the battery box, like mounted on the stern just aft of the battery, but I haven't been able to find one that is weatherproof. I'm looking for a small weatherproof box with a quick release lid to mount one in.

The Blue Sea fuse block 5056 looks like a real nice product for small skiffs, I just wish it included a negative bus under the cover.

My battery is currently in a well secured battery box as you have described. The box did partially fill with rainwater from the top vents but I am drilling several small holes in the bottom of the box to drain any water.

I'm trying to take into account the very corrosive nature of saltwater. This boat spends two months each winter in the brackish water at the dock, the balance of the year it is trailered to fresh water lakes. I have gained a new appreciation of the corrosion that happens in a matter of days to metals that are near saltwater.

jimh
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Re: Re-wiring a 13-foot Skiff

Postby jimh » Wed Mar 18, 2020 10:55 am

Switching to a sealed battery will eliminate the need for a vented battery box cover. That is another good reason to go to a sealed battery like an AGM.

jimh
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Re: TH-Marine Battery Strap

Postby jimh » Sun May 31, 2020 1:39 pm

The TH-Marine battery strap is back in stock. Here is a URL to the product:


https://thmarinesupplies.com/products/b ... 4593768491