depth raider vs lowerance question

[grumpys toy]

my new depth raider and my lowerance lms334 are showing different speeds, is this normal or should i use a 3rd unit, a cell phone gps to see which 2 are more accurate?

[1mainiac]

I don't think any of them are the same but your Depth Raider is reading down speed all that matters is being able to repeat your speed and presentation.

[SeaCatMich]

Except for GPS systems, no two units using paddle wheels or venturi tubes will ever give the same speeds.

As for the Depth Raider, and 1 Maniac says it is measuring the speed at the ball (down speed) and it is the one to pay attention to. The DR is showing the speed of your lure relative to many things that can affect the actual speed of your lure -- sub surface currents, surface waves, cross currents... Let's say you are getting hits while trolling at due north 1200 rpms with a 1.5 mph current at the surface and the DR says the boat is going 2.5 mph. You run out of fish on the graph and want to go back through them so you turn around to go south. Now your boat is going into the 1.5 mph surface current an will need to increase your RPMs to get the lure speed (Depth Raider) back up to 2.5 mph so the lures have the same action as when you were going north and getting hits.

There may be different currents at different directions depending on how deep your downrigger is at or your location on the lake. Where you have steep drop offs (such as the shelf from Ludington to Frankfort) this can happen depending on where you are relative to the shelf. Around river mouths the river plume will also create currents. This can cause your lures at one depth to be running a different speed than another.

Overall with a downspeed unit on a boat, it is the speed that you want to pay attention to when trolling. The other speed measuring devices (GPS, fish finder paddle wheels, engine speedometer...) are not giving you a good representation of the speed your lures are running at.

Even between different makes/models of downspeed units -- Depth Raider, SubTroll, Cannon Intelitrol, FishHawk...) the speed shown is rarely an actual measurement of the MPH the probe/cannon ball is running at. Consequently when another boat that is running a different downspeed than you are gives you a speed, it really does not mean much. What you want to do is watch what the speed is on your downspeed when you get a hit or catch a fish and then duplicate it. Like 1Maniac said... its all about repeatability.

[grumpys toy]

thanks for the help, my 15 year old and i are going to ludington later this month and hope to box more fish with the help of our new depth raider