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Old 12-08-2019, 10:35   #1
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Noob questions

Hi All,


I recently upgraded to a Hunter 33 from a Macgregor 26m (man, what an upgrade!). I love the boat, but I have a question about depth readings - I have raymarine and garmin units that have been showing me pretty shallow depths (2-3 ft). However I have a draft of 4.6ft. Shouldn't I be running aground in these conditions? Is it inaccurate soundings or am I just plowing through mud/weeds in these situations and I am too ignorant to notice a difference? It is really only one spot in the bay where I sail, but I often see other boats go through there and I sailed the mac through the same spot with no trouble with a 6ft daggerboard. I consulted charts and they too show the shallow 2-3ft spots. What am I missing here? I am planning a short trip, but I noticed the potential destinations have the same kind of depths on there charts. Charts say "soundings in ft."


Thanks in advance for any advice!
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Old 12-08-2019, 10:55   #2
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Re: Noob questions

The depth displayed is the depth from the location of the tranducer in your hull +/- any configured offset. Look in the documentation for each unit and it will explain how to set the offset.

If offset is set to zero then the depth displayed is from the transducer to the bottom.

Common offset configurations are to set so value displayed is adjusted to show depth relative to waterline or bottom of keel. Its just a personal preference. My guess is that the PO set the offset to bottom of keel so that what you are seeing is depth under keel.
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Old 12-08-2019, 11:00   #3
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Re: Noob questions

Thanks - that would make sense and I will check that. The charts should be accurate though right? if it says "2" on a nautical chart, I should expect the depth to be 2 ft deep? I'd hate to get to a distant marina and be out of luck when I try to dock.
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Old 12-08-2019, 11:16   #4
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Noob questions

Depth shown on the chart is mean low water as of the datum of the printing of the chart. Mean low water is the average depth at low tide. It can vary with the tide. During a spring tide it can be shallower by a few inches or a few feet depending on your location. You need to check tide tables for the area.
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Old 12-08-2019, 11:24   #5
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Re: Noob questions

As T42 said, the chart doesn't account for height of tide. To determine what if any offset has been programmed into your depthsounder, it would be a good idea to manually read the depth. While alongside, use a weighted line; drop it into the water until the weight touches bottom, note where the line exits the water and measure that. Best to take a measure from port and starboard sides even with the transducer, and average those two - compare that to what the depthsounder says and adjust the offset as necessary.
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Old 12-08-2019, 13:31   #6
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Re: Noob questions

Thanks! Excellent advice and information. Much appreciated!
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Old 13-08-2019, 09:13   #7
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Re: Noob questions

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Originally Posted by Tayana42 View Post
Depth shown on the chart is mean low water as of the datum of the printing of the chart. Mean low water is the average depth at low tide. It can vary with the tide. During a spring tide it can be shallower by a few inches or a few feet depending on your location. You need to check tide tables for the area.
Just on the off chance you aren't American, American charts show Mean Lower Low Water i.e. the mean level of the lower of two lows each day. Canadian charts show Lower Low Water i.e. lowest normal tide. Therefore negative tides can be common in US tide tables and not in Canadian ones. I have no idea what European charts are like (yet ).
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Old 13-08-2019, 13:03   #8
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Re: Noob questions

I am American - thanks for the knowledge!


I have another question regarding batteries; I have a battery selector that is currently set to "both". Should this be the case for all situations or should I keep it on 1 to start, 2 while cruising? Saving the number 1 for running the motor. I have 2 batteries, Number 1 is more cranking amps, so I assume it is for turning the diesel. Should I be switching to off while on shore power? If so, will my batteries still charge in the off position? I can probably deduce what to do here by looking at the wiring, but I figured deferring to the experts is wise :P
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Old 13-08-2019, 13:41   #9
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Re: Noob questions

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Originally Posted by disciplefk View Post
I am American - thanks for the knowledge!


I have another question regarding batteries; I have a battery selector that is currently set to "both". Should this be the case for all situations or should I keep it on 1 to start, 2 while cruising? Saving the number 1 for running the motor. I have 2 batteries, Number 1 is more cranking amps, so I assume it is for turning the diesel. Should I be switching to off while on shore power? If so, will my batteries still charge in the off position? I can probably deduce what to do here by looking at the wiring, but I figured deferring to the experts is wise :P


Normally, with these awful switches, you would use one setting for normal operations (sailing, anchoring, anything not running the engine), the. Switch to both or the other position to start the engine.

Now, what no-one can tell you with any certainty is how your particular boat is wired. Some will charge all batteries when the engine is running, no matter the position of the switch. But most with this type of switch won’t charge a battery by the engine that isn’t selected by the switch.

So if you’ve depleted “2” at anchor, then switch to “1” to start the engine, there is a good chance you’re not charging “2”. Most of these switches will allow you to switch from 1-both-2 with the engine running, with the caveat that you DO NOT PASS THROUGH OFF.

The battery charger may or may not charge the batteries in Off while on shore power. But you’ll need the switch on to one bank or another if you want to use power while the boat is plugged in anyway.
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Old 13-08-2019, 14:41   #10
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Re: Noob questions

First question I would ask is “Do you have some form of battery monitoring system?” If not, it’s probably a good idea to get one.

My philosophy (tempered by what Sailmonkey said re wiring) is to treat my “house bank” as the normal functional electricity source and what most people call the “start bank” as an emergency source. Hence the three-way switch is routinely set to bank 1 even for engine start.

I only switch to bank 2 if there is insufficient charge to do what is required including engine start. But the switch is rarely left on bank 2. To give the emergency bank some activity (stop sulphation, etc.) it runs my anchor winch as well.

As far as charging goes, that’s a complete moving target and many boats have methods idiosyncratic of the owner’s thinking. I have 3 alternators on my boat. I have two connected to the house bank (with switched fields) and one dedicated to the emergency bank. My passives (solar and wind gen) feed directly to the house bank and if the emergency bank needs a little help, I combine the banks with an “all” setting on the 3-way switch.

@ Sailmonkey - why “these awful switches”? I have used them without any adverse issues for decades. Do you have one of those “awful” multiple-isolators setups where you need to switch this off, switch that on, switch them all on/off?
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Old 13-08-2019, 14:49   #11
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Re: Noob questions

Quote:
Originally Posted by disciplefk View Post
- I have raymarine and garmin units that have been showing me pretty shallow depths (2-3 ft). However I have a draft of 4.6ft.
It's as other have said, unless you adjust the settings the depth gauge just reads the distance from it to the bottom. My boat drafts 6'4" and goes aground when the gauge says 4.5' (everyone should go find a soft place to ground on during a rising tide and find out what their gauge reads)
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Old 13-08-2019, 14:51   #12
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Re: Noob questions

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Originally Posted by CassidyNZ View Post



@ Sailmonkey - why “these awful switches”? I have used them without any adverse issues for decades. Do you have one of those “awful” multiple-isolators setups where you need to switch this off, switch that on, switch them all on/off?


Not at all!! I’ve got a very elegant, completely hands off system of start battery connected to nothing but starter and a house bank connected to nothing but house loads. Charging of the start battery is handled by an ACR from any charging source that is attached to the house bank. All of my charging sources are connected to the house bank.

I’ve had quite a few friends leave their switches in all and have dead batteries in the morning (granted none had significant battery capacity).

But if it works for you, it works fine. Just not my cup of tea!
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Old 14-08-2019, 18:29   #13
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Re: Noob questions

Thanks for the help all! I went to the boat tonight and sure enough there was a -3.5 programmed into the unit. I also found a chart with the dates that the soundings on the nautical charts were recorded, the last one in the shallow area was taken in 1974. I am sure that the depth has changed since then, lake levels are noticeably higher even since a few years ago. The deeper, more traveled sections have been recorded more recently (2007).


Thanks on the battery advice also - moving to primary/emergency battery method rather than start/house.
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Old 18-08-2019, 06:18   #14
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Re: Noob questions

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Originally Posted by disciplefk View Post
Hi All,


I recently upgraded to a Hunter 33 ...
What year? I have a Hunter 33 from 1982 that I recently got this season. If you have similar we should stay in touch. I'm guessing you have a newer model, but you never know.
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Old 19-08-2019, 00:38   #15
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Re: Noob questions

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Originally Posted by Sailmonkey View Post
Not at all!! I’ve got a very elegant, completely hands off system of start battery connected to nothing but starter and a house bank connected to nothing but house loads.
So there’s always the expectation that the start battery won’t fail when you need it most? Or a convenient set of jumper cables?

But if that works for you, that’s fine.

Flick of the switch is easier.
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