I was curious if it's possible To add length to a power cable for a fish finder. I'm installing it into a  kayak, and the cord is Too short. Can I extend the length without creating interference into the unit? I'm considering adding a plug next to the mount, to plug into a dedicated power plug for power.

Yes you can.  The only way you can mess it up is to use wire that is to small.  Small wire run over a longer distance will result in lower voltage at the plug.  A small fish finder does not  pull a lot of current.  A kayak will not require long wires.   Hard to mess it up.

Garmin has a chart for replacing their power cables, and the wire size for extending them. 

"If the installation requires a power cable extension, extend the power cable using the appropriate wire gauge for the length of the extension."

 

https://support.garmin.com/en-US/?faq=aLjDGPpDM47pHY7gcp8dk6

 

For instance, line one of the chart:

 

Device Series	Part Number	Gauge Size	Under 15 ft	Under 23 ft	Under 36 ft
STRIKER series	010-12199-04	22 AWG	16 AWG	16 AWG	16 AWG

My Lawrance unit shows a power cable extension in the accessories availiable book.  Try contacting your mfgr.  Mine shows plugs on each end for a plug and play...

Awesome. Thanks for the replies. I figured it was 16 gauge, so I went n extended the length to what I need. Wrapped it in plastic sleeve from an auto parts store, n went overboard with wrapping it electrical tape. Works like a charm.

i wish fish finders had shorter transducer cables.  i have 25 feet or so wadded up and tucked into my kayak.  i could get by with 5 feet.  the clump will occasionally fall loose and jam up my storage area.  

 

power?  i run my battery nearby.  2 feet away.

3 hours ago, Darth-Baiter said:

i wish fish finders had shorter transducer cables.  i have 25 feet or so wadded up and tucked into my kayak.  i could get by with 5 feet.  the clump will occasionally fall loose and jam up my storage area.  

 

power?  i run my battery nearby.  2 feet away.

I coil my transducer cable up and secure the loop with a couple of zip ties.  Then I use carabiner to quickly secure the loop to a plastic pad eye behind my FF screen on my kayak, so it doesn't flop around.  I'd shorten it, because I'm pretty good at soldering so I bet I could pull it off, but I'm afraid that going from 25 feet to maybe 2-3 feet would mess with the impedance too much.  

 

Also, instead of using shrink wrap and electrical tape on a boat, I prefer to use liquid electrical tape.  A couple of thick layers of that stuff keeps connections water tight and seems to last longer than the other two options. 

Cords are like haircuts.  You can always take more off.  You can't add more back on.  Better safe than sorry.

I terminate cables for offshore use quite frequently. I solder the two together, use heat shrink on each set, and then use a scotch cast kit to seal them all together snug as a bug. Adding a few feet shouldn't hurt it as long as it's the same type of cable.

Power cables are usually not a problem to extend.  Since most units will draw about one amp or less, you have to get pretty long with 18 or 16ga cable to cause resistance as long as you are careful what you run the cable next to.  All that extra tape and plastic conduit does is protect it from wear, it does nothing to keep induced RMF out.  A metal shielded/braid is required to prevent that.  Transducer cables, you pretty much have to buy a manufactured extension cable to go longer.  

One note: if your transducer cable is way too long, roll it up into a round coil no less than eight inches in diameter.  Since it has a pulsating signal, it can do similar to AC current and create a magnetic field which can cause interference if coiled too small.