Most Depth Finders have major drawback?

[frank2644]

I am looking for a new depth finder but the units I see have a minimum depth reading of 2.5 feet. Since the transducer will be mounted in my keel which has a draft of about 2.5 feet. That means the minimum actual water depth I can read will be about 5 feet.

Given that the water in my area is frequently less than 5 feet these depth finders seem pretty useless to me. Frequently I need to know when the water depth falls to maybe 4 feet and I would like to read even lower as I approach the beach, etc. It doesn't sound like these depth finders will do that.

Am I misunderstanding something?

I need a 2 1/4" round display to replace my broken Lowrance DF. Is there a DF that size that that will read shallow water as explained above? If not, is there any type of DF that does read shallow water (fish finder, etc)?

BTW, I prefer a shoot thru the hull transducer since the boat in in the water.

Thanks,
Frank

 

[Lazy Daze]

Look for units that advertise a "keel offset" feature.

I wouldn't trust a depthfinder to be as exact as you're looking for. However, have you physically measured your draft with the boat in the water? Along with the drive in various positions and different loads in the boat?

As far as sizing goes, measure the hole you'll be using. But, for the most part, it's a standard size. Or, look at the install directions for the old unit as it'll tell you what size hole to drill.

 

[frank2644]

Look for units that advertise a "keel offset" feature.

I wouldn't trust a depthfinder to be as exact as you're looking for. However, have you physically measured your draft with the boat in the water? Along with the drive in various positions and different loads in the boat?

As far as sizing goes, measure the hole you'll be using. But, for the most part, it's a standard size. Or, look at the install directions for the old unit as it'll tell you what size hole to drill.

I don't think the keel offset feature changes the absolute measurement capabilities of the DF, it just adds or subtracts a bias to the actual reading.

As far as "trusting" the depth finder, I agree but I obviously will be going very slow in shallow conditions (hopefully).

Yes, I probably need to to more draft measurements as you suggest.

Sometimes I get caught in shallow water and quickly raise my outdrive. In that situation it would be nice to know if I am progressing into deeper water or not.

Thanks for the reply.
Frank

 

[Dave S]

I don't know if you will get the answer that you are looking for. I boat in a lot of shallow areas as well and I know when I am in water that gives me a reading of less than 5 feet (without an offset) I just need to slow down and be careful. I draw about 40 inches with my drive down and of course it can be more than that if the boat is loaded or I am trying to come up on plane and the rear end is dug in. Caution is the only thing that works in my opinion. My Chart plotter gives me approximate water depths for the areas I travel and I constantly watch that as well as the depth gauge when I am in skinny water.........and I go slow and raise the drive too as the situation dictates.

Dave

 

[Henry Boyd]

I have a Raymarine st40 depth gauge with Airmar transducer. It will read as close as 1' between the hull and bottom. I set it to read the "keel" (tip of outdrive skeg) as the zero point, and it works great.

The ST40 will fit into the 2.125" diameter gauge hole and although rectangular, should fit between existing gauges.

Henry

 

[Henry Boyd]

Same here, mine reads as shallow as 1'2" below the keel, which is all I need, because that point, I am aground. (for the record, this has only occurred when anchored on the beach, so far not anywhere else....knock on wood)

1' for us is low tide with the drive up on our mooring! :smt043:smt043:smt043:smt043

 

[frank2644]

Thanks guys for the Raymarine st40 suggestion. I looked up the specs and it has a zero to 400' range. Zero minimum is exactly what I'm looking for.

One problem, I don't see a shoot through the hull transducer. Although I'm still looking, hopefully they have one.

If anyone has other suggestions, I'm all ears.

Frank

 

[Loneranger]

I am sure you realize this but in that shallow depth your depth sounder could read down to 1 foot and your bow will already be grounded assuming your transducer is toward the stern.

Sometimes if you find yourself in that shallow depth an old fashioned sounding line is advantageous. If you are trying to find the side of the boat with the deepest water to navigate out, then a small weighted line with depth marks is very helpful. Otherwise you are out of the boat in the water to determine depth or are try to reach over the side with a boat hook, etc to determine the depth.

As for a transducer, check out:

http://airmartechnology.com/2009/marine/product-search.asp?Type=SS

Aimar makes most of the transducers out there.

John

 

[Lazy Daze]

I don't think the keel offset feature changes the absolute measurement capabilities of the DF, it just adds or subtracts a bias to the actual reading.

Yes. That is correct.

 

[frank2644]

I am sure you realize this but in that shallow depth your depth sounder could read down to 1 foot and your bow will already be grounded assuming your transducer is toward the stern.

Sometimes if you find yourself in that shallow depth an old fashioned sounding line is advantageous. If you are trying to find the side of the boat with the deepest water to navigate out, then a small weighted line with depth marks is very helpful. Otherwise you are out of the boat in the water to determine depth or are try to reach over the side with a boat hook, etc to determine the depth.

As for a transducer, check out:

http://airmartechnology.com/2009/marine/product-search.asp?Type=SS

Aimar makes most of the transducers out there.

John

Thanks for the low water advice. I think you are saying that my bow is lower than my stern when the outdrive is lifted. I never thought of that since most times the outdrive is the problem.

I took a quick look at Aimar and it seems to have the transducer I need.

Looks like posting my question here solved my problem....

Thanks to all who posted.

Frank

P.S. Any additional information is welcome.

 

[Loneranger]

Thanks for the low water advice. I think you are saying that my bow is lower than my stern when the outdrive is lifted. I never thought of that since most times the outdrive is the problem.

I meant that if you are traveling forward into progressively shallower water then by the time the depth sounder registers 1 foot then it is even shallower at the bow; not because the bow is lower, but because the transducer on boats of our size are typically towards the stern.

John

 

[Loneranger]

I now carry a small sounding line on board. I once grounded my boat, got out and walked around the boat, and discovered the best course to get back to deep water was not to go back out the way I came. I was just off the channel and by pushing the bow to port the whole boat was in deeper water a lot quicker and easier than moving the boat to the stern.

John

 

[frank2644]

While the st40 initially looked like the answer to my prayers, after taking some measurements on my dashboard it doesn't fit without having to move my GPS mounting bracket. It also seems overly big for just displaying depth readings.

While I could move the GPS bracket I'm wondering if any other depth finders exist that fit my needs (ability to measure very low water).

Frank