Isolation Loops

By Paul Williams.
Article posted 3rd December 2007.

An isolation loop is simply an extension of the power circuit run outside the boat that allows you to instantly isolate the motor from the drive battery and make the boat safe. It is a safety feature for fast electric boats required by Naviga and Naviga-sanctioned bodies like the UK MPBA. SWAMBC here in the south-west also require the use of an isolation loop if you want to race with them.

Isolation loop wiring diagram.

Isolation loop wiring diagram. The loop is spliced into the red, positive side of the circuit between the cell pack and the speed controller.

Isolation loops, while mandatory for racing in the UK, should be fitted to all fast electric boats. If your boat flips, fills with water and floods the speed controller, the controller may short in the full throttle position leaving the motor (and the propeller) racing away at high rpm. Rescuing a boat is made much easier and safer if you can simply pull out the loop and stop the motor.

Isolation loops also allow you to quickly and safely swap propellers without having to untape the boat each time. Swapping a propeller with the boat "live" is a recipe for losing the tips of your fingers - don't do it!

To the best of my knowledge, there isn't a commercially available off-the-shelf isolation loop, which is a bit odd as every Naviga racing boat has to have one (if you know different, email me). So, it is up to the individual modeller to make their own loop system. This brief article shows how I make mine.

I cut two 30mm lengths of 3/8" oak strip in the mitre block. I then drill a hole lengthways through the centre of each piece to accept the size of connector I want to use. Superglue the two bits together, and finish with a sanding block. You need a block long enough the hold the female connector plus a few mm of cable, to ensure there is no uninsulated cable inside the boat.

Isolation Loop
Cut some square section hardwood.

Isolation Loop
Drill each piece to accept a connector.

Isolation Loop
Glue together.

Isolation Loop
Sand and finish...

Isolation Loop
...and make some cables. Thin cyano these into the block.

Isolation Loop
One half of the loop ready for installation in the boat.

Isolation Loop
The loop - minimum 20mm ∅.

Isolation Loop
The finished loop in the boat.

What The Rules Say

Naviga specifies where you must fit an isolation loop to your models, and some minimum requirements for the loop itself. As I understand the rules, the fixed part of the loop must face backwards, and the loop itself must be of red cable, minimum 20mm in diameter and completely detachable from the boat. The loop may be fitted to either side of the boat or on the deck, but must not be on a removable part of the boat or above the propeller. The commonly accepted type of plug to use is the 4mm "banana" type - using something else like a "Deans" connector may not be acceptable.

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Last modified: 08th July 2010 @ 09:06