2.6 feet? Depth from where exactly?

[KevinReston]

I have a Garmin 188C gps/sounder and the smartcraft ECMs. I keep Starboard tach on depth. I was getting a reading yesterday of 2.6 and 2.3 but wasn't sure where the measure is from. The bottom of the drive/prop (lowered/raised?) or the bottom of keel? or somewhere else?

I'm trying to figure out if I should add/subtract anything to account for the drives when in the trimmed fully up position. We like to go into a shallow (3ft at low tide per charts) bay called Belmont Bay. I noticed bigger boats further in but didn't like the low read.

Just trying to make sure the depth finder and I are speaking the same language.

 

[Dave S]

Usually it's the depth from the location of the transducer (which is generally around the keel) to the sea bottom. I have those kind of depths around parts of our dock area so I always have to keep an eye on our lake water levels because that doesn't leave a lot of room. :wow:

 

[fwebster]

However, if you want ot change to a more revelant measurement, almost all depth finders have the ability for the user to insert an offset for depth adjustments. If your lower unit is 1.5 ft below the transducer, you can load a -1.5' offset to measure the depth below your drive.

 

[Dave S]

Just to follow up on Frank's comment, Smartcraft does allow you to enter an offset for your depth.

 

[gerryb]

Re the offset feature, if you disconnect you batteries as part of winterization, smartcraft will reset itself to no offset. This gets a bit confusing - one more thing to remember to do each spring. I decided to just leave it as is and make a mental note of the physical offset when looking at the guage. I do admit I've often wanted to jump in where the water is shallow and use a ruler to see how accurate that darn transducer/depth guage really is :huh:

 

[Aquia185]

Hey All... Is it true that underwater growth (grass) affects the depth finder? Thanks...

 

[chuck1]

Re the offset feature, if you disconnect you batteries as part of winterization, smartcraft will reset itself to no offset. This gets a bit confusing - one more thing to remember to do each spring. I decided to just leave it as is and make a mental note of the physical offset when looking at the guage. I do admit I've often wanted to jump in where the water is shallow and use a ruler to see how accurate that darn transducer/depth guage really is :huh:

Ditto :thumbsup:

 

[KevinReston]

Thanks everyone! :smt001

So if I have my drives are all the way up, I should subtract 1.5 ft from the reading? So at 2.3 ft I had 1.8 ft of clearance left? Or is 1.5 ft assuming the drives are down? I'll get this eventually :smt021

I had a known sand/mud bottom so no potential for misread from that source, interesting question though.

I assume the Garmin is reading from the same transducer and "feeds" the ECM?

 

[chuck1]

Thanks everyone! :smt001

So if I have my drives are all the way up, I should subtract 1.5 ft from the reading? So at 2.3 ft I had 1.8 ft of clearance left? Or is 1.5 ft assuming the drives are down? I'll get this eventually :smt021


I assume the Garmin is reading from the same transducer and "feeds" the ECM?

I don't think you can have them both reading/feeding from the same transducer. Also they are giving different depths.

IMHO would not want to run for long with drives up. When the drives are down they would be below your hull, so if the hull is reading 3 feet you only have 1.5 feet below your drives.

 

[Dave S]

FYI..............on the accuracy of the depth reading you get from Smartcraft........... I had some concerns about the first slip they put me in because it was shallow. So I actually measured the water depth and then subtracted the measurement to the keel and it was close enough to tell me that the reading is pretty darn accurate.

 

[Stray Cat]

Hey All... Is it true that underwater growth (grass) affects the depth finder? Thanks...

Greg - My experience in a shallow grassy area is the display will flash because it cannot get a fix on what the signal is bouncing back from.

Okay, back to the topic at hand :wink:

 

[comsnark]

My view on powerboat depth finders:

If the water is shallow enough that you have to worry about the offset. . . .you need more water under the keel.

Keep in mind that
1) Your drives will churn mud even if they have a few inches under the keel.

2) Weeds grow above the bottom. So you may have grass in your coolant before you have your props in the mue.

3) Your depth transducers are at the stern. What's the depth at the bow?

4) If you are on plane, and you are reading 2'. . . .pray. Remember that your stern will sink DOWN in the water when you come off plane.

 

[chuck1]

My view on powerboat depth finders:

If the water is shallow enough that you have to worry about the offset. . . .you need more water under the keel.

Keep in mind that
1) Your drives will churn mud even if they have a few inches under the keel.

2) Weeds grow above the bottom. So you may have grass in your coolant before you have your props in the mue.

3) Your depth transducers are at the stern. What's the depth at the bow?

4) If you are on plane, and you are reading 2'. . . .pray. Remember that your stern will sink DOWN in the water when you come off plane.

Big Ditto :thumbsup: :thumbsup: :thumbsup: :thumbsup:
I love the last one "reading 2'.....pray' Had that happen to me on a section of the TN river once. Running in the channel 15+ feet next thing in about 3 feet of water in the middle of a wide section just outside the marked Chanel. Sure will make up sit up :smt101