Depth Sounder Setting for Anchoring

[AG3]

Friends:

I am probably going to open up a can of worms here, but here goes.....

1) Do you have your depth sounder set to record actual water depth from the water line to the bottom of the seabed?

or

2) Do you have your depth sounder set to measure the clearance between the lowest point on your boat? (in the case of our R27 ob, it would be the bottom of the motor.)

On my two previous boats, both sailboats, I set the sounder to measure actual water depth. One of those boats had a draft of 4'3", so I knew that I was getting close to the bottom when the sounder registered 5 feet or less.

Currently, our R27 is set up like #2 in my example, which means that I need to add 4 feet to the depth to get the actual water depth, then add another 4 to 5 feet for the distance from the water to the bow roller when trying to determine how much scope I need for anchoring. I'm leaning toward changing my sounder to read actual water depth to make the math a little easier. Of course, I may also add a small margin for error so that the actual depth is actually a foot or so deeper than the sounder tells me it is.

Please share with me your thinking and experience. Am I wrong to consider this change?

Thanks in advance.

 

[American Flyer]

Hi Al,

I don’t think there is any wrong answer to your question. It is more personal preference, whatever you are most comfortable with is the best way to go. Just do not forget which setting you are using, that could be bad!

 

[AG3]

Hi Al,

I don’t think there is any wrong answer to your question. It is more personal preference, whatever you are most comfortable with is the best way to go. Just do not forget which setting you are using, that could be bad!

Thank you!

 

[William Sanborn]

Does your panel have Sonar, That will give a an accurate view of the bottom.

 

[AG3]

Does your panel have Sonar, That will give a an accurate view of the bottom.

Yes, thank you.

 

[scross]

Here’s a bunch of random thoughts on anchoring and scope based on my experience.
We anchor or stern tie 10-20% of our nights out while cruising. Typically we anchor in 10-20 ft of low tide depth which can be 20-35 ft of depth at high tide. Of course, scope is always calculated using high tide depths plus the height from water to bow.
I used a boat pole at a shallow dock to measure my actual depth from water to bottom and then compared it to the depth finder reading. That told me the correction needed for shallow water that use for future reference. Lots of docks in the PNW are in shallow water at low tide. I know the boats draft and just factor that in if I’m worried about being grounded at low tide.
For stern tieing, just put the anchor down as far from the bow as reasonable or as deep as available. Places that have Cove in their name typically aren’t wide or deep enough to anchieve ideal scope when stern tieing. Just try to get a good anchor set.
Many other popular anchorages don’t allow for all the scope you would like just because of the crowding. Just last week we anchored at Garrison Bay and had to limit our scope to 3.5-4:1 to avoid the possibility of swinging into other boats. Not ideal but in crowded anchorages I do the best that I can. That said, I always put down (to the bottom) my full length of 50 ft of chain as a minimum.
If I’m in uncrowded anchorages I will put down up to my full 250 ft of chain and rope just to get the maximum scope possible. But I don’t find to many uncrowded anchorages….

 

[AG3]

Here’s a bunch of random thoughts on anchoring and scope based on my experience.
We anchor or stern tie 10-20% of our nights out while cruising. Typically we anchor in 10-20 ft of low tide depth which can be 20-35 ft of depth at high tide. Of course, scope is always calculated using high tide depths plus the height from water to bow.
I used a boat pole at a shallow dock to measure my actual depth from water to bottom and then compared it to the depth finder reading. That told me the correction needed for shallow water that use for future reference. Lots of docks in the PNW are in shallow water at low tide. I know the boats draft and just factor that in if I’m worried about being grounded at low tide.
For stern tieing, just put the anchor down as far from the bow as reasonable or as deep as available. Places that have Cove in their name typically aren’t wide or deep enough to anchieve ideal scope when stern tieing. Just try to get a good anchor set.
Many other popular anchorages don’t allow for all the scope you would like just because of the crowding. Just last week we anchored at Garrison Bay and had to limit our scope to 3.5-4:1 to avoid the possibility of swinging into other boats. Not ideal but in crowded anchorages I do the best that I can. That said, I always put down (to the bottom) my full length of 50 ft of chain as a minimum.
If I’m in uncrowded anchorages I will put down up to my full 250 ft of chain and rope just to get the maximum scope possible. But I don’t find to many uncrowded anchorages….

Al, very helpful. Just the other day I did exactly as you described and used a fully-extended boat hook at low tide to measure from the water to where the pole touched the bottom. Like you I was then able to adjust the offset until my depth sounder matched my pole length measurement. On the Chesapeake we anchor in 7-10 feet of water. In the northern Bay the tidal range is only about 1.5 feet and more like 3 feet in the southern Bay where we cruise. I’ve cruised the Chesapeake in four different boats since 1994 and have yet to stern tie! Different cruising needs and cruising grounds for different folks. Thanks so much for your very helpful reply.