Offset for Raymarine Depth finder

[George Arthur]

Hi All,
New member and first post. I'm sure there will be many more!
I just bought my first sailboat (2007 Hunter 31). I'd like to set up the depth finder offset to show my water depth below the bottom of the keel, vs from the transducer to the bottom. I need to know the vertical distance from the transducer to the keel bottom to do that, and can't seem to find that info in the owners docs. I have the shallower draft (3'11" ?).
Any of you who may have been through this drill and can share your experience, I would be grateful.

Thanks

 

[Ted]

Welcome. There us no way for us to provide that information because we don't know where your transducer is located. For the most accurate information, you should measure it yourself when the boat is out of the water. Another option is to scale a drawing of your boat and measure it on the drawing. You can find drawings on Sailboatdata.com

 

[DayDreamer41]

According to Marlow Hunters web site the shoal draft is 4'-5", personally I would not set the offset to the bottom of the keel, I would set it to the draft depth minimum and then set the alarm to at least 2' below that.

But if you must know here is a link to a great resource,
http://www.marlow-hunter.com/wp-con...tion/31_2005_2011/H31 Shipping_dimensions.pdf

 

[seadaddler]

As said measure yourself and never go by the boat specks and same thing with mast height,I have my depth
set to tell me what the water depth is that my boat is sitting and than to double check I throw a line over board with a weight and I have markings on the line every foot and this way if not sure what the depth is I use the line I always carry to double every so often .
once I check the depth of water and than p[ay with the off set to match my mark on the line and has never failed and no guessing at all what my 5' draft boat needs to not run aground.
After I set my depth gauge this way and if it says 8' than I know I got 3' under my keel.
Nick

 

[Terry Cox]

Hi George, our model has a draft of 4' 11". I've set our offset at five feet and the shallow depth alarm at eight feet. Very close and has worked for us over the years. I know from experience that when my depth reads 0.5 feet, the keel is just starting to touch the bottom. It's just mud, but now I know.

 

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[Parsons]

George, I've sailed on boats where the offset is set at both the keel and the waterline - I'm guessing the majority (3/4) use the waterline method. For your own boat, it's not a problem and most people can do simple math in their heads if they think of it the other way - literally whatever floats your boat! I would suggest adding a simple label on your meter that indicates which it is (and the keel depth if using the waterline method), if you have many guest helmsmen.

I would recommend, however, that you do not get too hung-up on measuring the sensor depth to the inch because it implies a sensitivity that your meter and the environment just do not have. The sonar depth gauges are taking an average depth in a wide cone under your boat. You are not navigating over a smooth gym floor - think about flying a small plane at low altitude over a beach with waves in the sand and dunes. How close to that sand do you want to be? As noted, if you want to be precise, get your boat over a hard, flat surface (say a sandy bottom with few rocks), drop a weighted line over the side, and make your offset based on the designed keel depth. I suggest, however, that you add a foot to that number or you'll be calling TowBoat to get you off the beach!

 

[Ron20324]

After coming to a quick stop at an indicated 6.5 depth(4'9" draft), I ran my B323 to a sandbar(downwind); when I was on bottom, I set my depth meter 4 ' 9", the boat's draft. Then I set the low alarm to 7 feet to (hopefully match the blue/turquoise lines on the charts). That low alarm is usually turned off, as my slip is less than 7.

 

[George Arthur]

Ok, thanks. I assumed the transducer thru hull would be in the same place on all 2007 H31s. I also assumed the vertical distance between the transducer to the keel bottom is a known (to someone) distance. I appreciate all of your replies!

 

[Southpaw]

If you have a fixed keel why would you worry about setting it to the waterline? All that matters is how much water is under your keel.

 

[justsomeguy]

All that matters is how much water is under your keel.

I think in all of Mr. Arthur's 2 postings, that's been his aim all along.

 

[George Arthur]

You are correct Sir!

 

[Benny17441]

The way we have done it is with a soft grounding to determine the actual distance from the transducer to the bottom of the keel, then we added a 6" safety factor and set our offset. We intentionally grounded the boat into a soft sandy bottom at very slow speed. We had calm waters and a favorable wind to ease our escape. Even with the 6" safety factor we have hit rocks and even hard grounded the boat. Here in Florida by necessity we have to deal with skinny water and it is not a question if you are going to run aground or not but the question is when.

 

[Stu Jackson]

The way we have done it is with a soft grounding to determine the actual distance from the transducer to the bottom of the keel, then we added a 6" safety factor and set our offset.

Highly recommended method. I didn't bother with any offsets, just know if my DS reads 4.4 I'm on the ground! Saves a lot of math...

 

[Jerry Clark H356 SV Persi]

Don't panic if it sometimes reads less than the keel depth. In rivers and lakes, plants grow on the bottom and you will get reading to the top of the plants but the mud is deeper. We went into Midway Marina at night on the Tenn-Tom with 4 feet on the sonar and the depth gauge and had no problem with a 5 foot draft. Does make you a bit nervouus though!

 

[George Arthur]

Don't panic if it sometimes reads less than the keel depth. In rivers and lakes, plants grow on the bottom and you will get reading to the top of the plants but the mud is deeper. We went into Midway Marina at night on the Tenn-Tom with 4 feet on the sonar and the depth gauge and had no problem with a 5 foot draft. Does make you a bit nervouus though!

Yikes!

 

[jssailem]

We have that experience. Your sailing along in 130 ft of water minding your own business when the suddenly the depth gauge reads 10 feet. Then you hear a blast of air that smells like 8 day old dead fish. And a large grey creature slides through the water past your boat.
FUN!!!

 

[George Arthur]

Very cool.