Elessar
Well-Known Member
remains the best answer.
Depth Sounder Poll
- Thread starter markleuty
- Start date
remains the best answer.
Seajet
...
I have / had a chum who is the only person I've found impossible to instruct, he just doesn't listen - I've instructed a lot of people.
When we anchored in South Deep, Poole, I noticed he hadn't been watching the depth sounder, reading 1 metre even though I'd got him to lift the keel...
As he dived headfirst I had my camera ready, to see him emerge covered in mud and calling me naughty names.
When we anchored in South Deep, Poole, I noticed he hadn't been watching the depth sounder, reading 1 metre even though I'd got him to lift the keel...
As he dived headfirst I had my camera ready, to see him emerge covered in mud and calling me naughty names.
Sybarite
Well-Known Member
I want to know the depth of the water I am in. I draw 1m70 which I round to 2m for a safety margin; waves etc. A 2m mental adjustment is not difficult to make.
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Otter
Well-Known Member
Depth of water, kind of more intuitive for me, it says I have 3.5m and I know I run aground at 1.4m cos that's my draft. Also depth alarm doesn't work below 1m and Granay reach never has more than 1m under the keel. When I had it set to depth under keel I had to keep working out whether that was actual water depth or under keel depth.
ninky
Well-Known Member
It's the simplest arithmetic either way. If you can't work that out, and are in charge of a vessel, Neptune help us all!
lustyd
Well-Known Member
It wasn't until I read this post that I realised why it's so easy with depth of water! Everyone had been talking about maths and I assumed I did it subconsiously but you're right, I'm in trouble when it says my draft so no maths required!
LONG_KEELER
Well-Known Member
It does seem the most logical when starting out. I remember before GPS, following depth contours for 8 hours due to heavy rain crossing the Thames Estuary on a falling tide. The "actual depth" on the sounder helped enormously although I did get a bit frazzled at times.
If you started sailing and motorboating when sounders did not have offset capabilities it is difficult to make the change. Not that you should do . We all see and feel things differentially'
I know many sailors who still use feet rather than metres with and without offsets. They seem fine with it despite charts being in metres.
The problems seem to start though when relaying information to third parties.
When you consider we have gone from fathoms to feet to metres in quite a short time we are doing pretty well.
BelleSerene
Well-Known Member
An excellent summary as so many of Snowleopard's. But I have to challenge whether showing depth under keel helps you avoid hitting the bottom. I know I haven't hit the bottom because I'm still floating. Knowing whether I'm going to hit the bottom depends on whether the charted depth is increasing or not. If my sounder tells me only depth under keel, I have to keep calculating keel offset. If it tells me the depth of the water, I immediately know whether I'll float in that water or not.
That's the only reason, I agree. When you know that (a) the bank is gradual and (b) tacking will get you straight off, then just counting down to (almost) zero is helpful. The rest of the time - and for anyone who actually navigates - reading the depth of the water minimises calculations.
Norman_E
Well-Known Member
Mine reads depth under keel plus a small safety margin. The boat draws 2 metres, with the transducer about 400mm immersed. I put in an offset of 2 metres. The fun started in the shallow channel which can be used as a shortcut to Bozburun. In places the water is less than 3 metres deep in the centre of the channel. When I put the new instruments in one of them set the offset into the transducer, the other one set an offset in the instrument itself, effectively doubling the offset. It made for a very interesting run through the channel until I realised what was going on.
lustyd
Well-Known Member
Didn't you check it after setting it up? Quite an expensive assumption to get wrong!
Norman_E
Well-Known Member
I was in the process of checking the entire setup, which is a complex one with multiple instruments. It was in fact a totally safe error, as the instrument showing the wrong depth was effectively treating the boat as having a 4 metre draught. I knew that I had put a 2 metre offset into the transducer and had checked the instrument I normally use for depth readings with a lead line whilst tied up to a jetty, so knew it was accurate. I had previously put a 2 metre offset into the other instrument, and forgotten to cancel it. In the channel I had both instruments switched to depth mode for the first time. The one with the double offset counted down to zero. It was the one I was watching because it was showing the least depth, but I know the channel and knew that I had not even reached the shallow bit so I just carried on, and then realised that the other instrument was showing correct depth, which in the shallowest part of the channel recorded less than half a metre below my offset, in other words a water depth of about 2.8 metres.
lustyd
Well-Known Member
haha well done for explaining. Don't feel you have to justify yourself to randoms on the internet by the way, although we appreciate it...you obviously had it all under control
Norman_E
Well-Known Member
I have written an article on the new instrument setup for PBO. What I did not put in it is that a Garmin GMi10 instrument will put a depth offset into the software of the Airmar transducer, and that seems to be their default behaviour, whereas the B&G Triton instruments seem to keep the offset that you put into them internally by default. If you buy either the B&G Triton or the Garmin display as a bundle with transducers they both use the same Airmar depth, log and water temperature tri-ducer, but have their own proprietary masthead wind units.
lw395
Well-Known Member
So long as it does not get too confused ploughing into Lymington with the keel in 20cm of soft mud!
lw395
Well-Known Member
Quote Originally Posted by lw395
It does not matter.
What matters is that everyone on the boat knows what the sounder is telling them.
remains the best answer.
Could that be because I learned this the hardest way?
I admit nothing!
seriously though, these days we have instruments that tell us true and apparent wind at the touch of a button, with words on the dsplay to explain.
I have yet to see a sounder which tells me 'under keel' or 'total depth', maybe I sail boats that are out of date?
YAPP please Angus?
It does not matter.
What matters is that everyone on the boat knows what the sounder is telling them.
remains the best answer.
Could that be because I learned this the hardest way?
I admit nothing!
seriously though, these days we have instruments that tell us true and apparent wind at the touch of a button, with words on the dsplay to explain.
I have yet to see a sounder which tells me 'under keel' or 'total depth', maybe I sail boats that are out of date?
YAPP please Angus?
Elessar
Well-Known Member
Tee hee. We need a super electronic gadget that looks up the astronomical tidal predictions, superimposes a factor for air pressure then looks at wind direction to factor that in.
Then we could display charted depth. Means we dont have to do maths if choosing not to use one of the 6 GPSs we have on board.
Obvious really
Leighb
Well-Known Member
Tee hee. We need a super electronic gadget that looks up the astronomical tidal predictions, superimposes a factor for air pressure then looks at wind direction to factor that in.
Then we could display charted depth. Means we dont have to do maths if choosing not to use one of the 6 GPSs we have on board.
Obvious really
That might work if the electronic charts were likely to keep up with changing depths near sandbanks, hopeless on the East Coast.
