Sound 'er Advice?

[FlyingSpud]

Sound \'er Advice?

I saw in ‘All at sea’ a guy write that it was more seamanlike to have your death sounder set up to read the height of the water. He said in this was because you could use your sounder as a navigation tool.

I do not agree. I have always set mine to read the depth under the keel. After all, sometimes you may have someone on the helm that does not know the boat. He could be making any old assumption about how the sounder is set up, so it is best to give him the most pessimistic. As for using the sounder as a navigation tool, well, I know how much water my boat needs so it does not take a genius to add that to the depth shown.

Or am I just a coward? How does everyone else set their sounder up?


<hr width=100% size=1>

 

[Mirelle]

Re: Sound \'er Advice?

Same as you. If I am using the echosounder as a check on position, I have to correct for tide by subtracting the rise to get to chart datum anyway, so it is no big deal to subtract the draft as well, surely?

<hr width=100% size=1>Que scais-je?

 

[Cornishman]

Re: Sound \'er Advice?

How appropriate that you refer to your machine as a 'death' sounder. Those of us old salts who first began with lead lines had no alternative but to use the actual depth (not 'height' I hasten to add - that is to do with the tide) of water measured - hence, I guess, why it is thought to be more seamanlike.
It does not really matter which you use as long as everybody aboard is aware of what the scale is reading. A piece of Dymo tape suitably labelled is enough.

<hr width=100% size=1>

 

[Sailfree]

Re: Sound \'er Advice?

If you are navigating by depth sounder its the actual height of tide thats a problem not keel depth. The tables are only estimates and surges, pressure etc affect these.
When preparing for the Yachtmaster exam I was told to work out best estimate of height of tide for every hour of the exam - before the exam - purely so you can use your depth sounder for navigation. The usual one of navigating in fog! It had previously been pointed out (during a prep weekend) that in sailing across the Solent by buoy hopping using bearings and distances that I was piloting NOT Navigating as I had not used the depth sounder. Slapped wrist!!
If you do need to navigate by depth the time to do work out and add the height of tide is far longer than that of subtracting the constant depth of the keel. I would therefore agree with you and set the sounder at depth under keel.
While good seamanship demands we should know this method (at the risk of starting a lively debate) most boats probably now have a fixed and a portable GPS . Assuming a choice of the two methods of finding position I know what I would rely on first. Am I wrong in using the GPS as first choice?
More importantly I would always set the depth alarm. I think there is a good debate to be had at what depth to set the alarm. For the Solent I set it at 2m. I am not sure whether the area you usually sail in leads to different preferences. I can imagine that if regularly sailing in known shallow water a 1m alarm would be more tranquil.
What do East Coast sailers set their alarms at? With shifting sands I think I would still stick to 2m but I would welcome experienced East Coast sailer's advice.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by Sailfree on 13/01/2004 11:52 (server time).</FONT></P>

 

[FlyingSpud]

Re: Sound \'er Advice?

I am an east coast sailor, and I have it at 1M, not 2. If you had it set at 2M on the east coats then it would always be going off and so would not take it seriously enough.

I have always been a bit cagey about using the depth (or death) sounder to navigate with when you are in a shallow area as tidal height is, it always seemed to me, a rather imprecise measure, not only affected by tidal surges and pressure but also local factors. Ok, in the fog, I have on occasions (before GPS) aimed wide of the target I was going to, found a contour and then turned and sailed along it, but save for a yachtmasters exam, when else would you do this nowadays


<hr width=100% size=1>

 

[FlyingSpud]

Re: Sound \'er Advice?

How old are you?? I was only a fresh-faced lad at the time and sailing a GP14 wasn’t that bothered about the amount of water (you knew it was too little when you went bump), but weren’t seafarer depth sounders around in the 60’s, or did I dream it?

<hr width=100% size=1>

 

[DeeGee]

Re: Sound \'er Advice?

More to the point, as an East Coaster, there are many places where depth can't be used for navigating: warning - yes; navigating - no. These are places where the sands shift around from year to year (even month to month in some worst cases) so the contour may lead you into a trough or hole not shown.

<hr width=100% size=1>Black Sugar - the sweetest of all

 

[chas]

Re: Sound \'er Advice?

I have mine showing depth of water and it really is an invaluable aid to navigation. When I was taught navigation, the cry was taht the bottom was normally about a thousand times closer than the shore.

The pre GPS technique for finding a port such as Lagos, which is on a long, low lying featureless coast, was to aim off (so you would know which way to turn when you found Africa) and go on until the 10 fathom line. When the sounder read 10 fathom, turn whicever way, follow the contour until you could see Lagos. Piece of the proverbial..............

<hr width=100% size=1>

 

[Stemar]

Re: Sound \'er Advice?

It seems to me that as far as finding Lagos (or Cowes in fog) is concerned, it doesn’t much matter about finding the 10 fathom line on the chart. All that matters is that you know you’re getting close to the shore, but not so close you risk hitting it, or in the case of Cowes, those dirty great yellow buoys.

A thought. These days, if the GPS isn’t telling you where you are to a far greater degree of accuracy than the chart is telling you where the bumpy bits are, there must be a fair chance that it’s because your batteries are flat and the depth sounder has packed up as well... Ah well, back to the lead line – or in my case, a hammer on a bit of string!


<hr width=100% size=1>

 

[VicMallows]

Re: Sound \'er Advice?

Interesting. I've just replaced my old Seafarer (which had no offsets at all) with a Clipper Duet and had similar thoughts regarding the offset. Then I discovered it was ONLY possible to offset to depth BELOW keel. (I tried entering a negative offset but it wouldn't accept it). I'm quite happy with 'below keel', but do think that for a couple of lines of code they could have kept everyone happy!

Vic



<hr width=100% size=1>

 

[Robin]

Re: Sound \'er Advice?

Firstly ours is set to read in old money. I know how much more 6'10" is than 6'6", the metric version (2.08m v 1.98m) makes little impact on my tired brain, though I have worked in Metric for business since time began, but in small bits like up to 100mm.

Secondly I want to know how deep it is. Any idiot can work out that for 6'10" draught I need at least 7.5ft of water say. If going along with just 0.6ft showing as depth under the keel I would be a nervous wreck.

Don't tell me charted depths are in metres. We are bang up to date with electronic charts from C-Map and can switch to display either in metres or feet, ah the advantages of technology!

Our alarm (S Coast) is set at 8ft, even that drives me nuts as we enter marinas and it constantly goes off just as you get busy!

<hr width=100% size=1>

 

[FlyingSpud]

Re: Sound \'er Advice?

Whatever way one looks at it, I think the old salt in ‘all at sea’ was wrong about it only being seamanlike to set the depth at the depth of water. I suspect that this was just a throwback to someone being ‘in the chains’ chucking a lead line (or string with a hammer) into the water. Seems like Nasa took the same position

<hr width=100% size=1>

 

[snowleopard]

Re: Sound \'er Advice?

it doesn't matter how you zero the reading as long as (a) everyone knows how it's set and (b) can do the arithmetic. i have the good fortune to draw 1.0m which makes it nice and easy.

the setting for the alarm depends on where you sail. over a soft muddy bottom, no more than 0.5m clearance under the keel, over rock 2m would make more sense.

<hr width=100% size=1>

 

[FlyingSpud]

Re: Sound \'er Advice?

Feet!! Feet? Surely fathoms would be more appropriate

<hr width=100% size=1>

 

[Cornishman]

Re: Sound \'er Advice?

I am not declaring here how old I am, but a peek at my profile will give you some idea. Indeed the Seafarer Mk 1 was around in the 60s, but I was sailing a 'windfall' 100 sq m yacht in the mid 50s when most had lead lines.

<hr width=100% size=1>

 

[VicMallows]

Re: Sound \'er Advice?

Does that boat in the 'pic really draw 6'8" ?? (I'm happy to work in either currency). (OK, have looked, it's a Legende 41). And to think I'm worried whether I can get down the Brittany canals at 1.15 m!

Sorry, you can't borrow my mooring while I'm away ..... you couldn't get close at high springs!

Vic

<hr width=100% size=1>

 

[Cornishman]

Re: Sound \'er Advice?

You're not alone with that problem. Try entering Teignmouth some time where the sands change position from tide to tide and back again on some occasions.

<hr width=100% size=1>

 

[Robin]

Re: Sound \'er Advice?

Well yes, but now you are back into picturing small bits of a big measure again if in shallow water, then you get to looking at 2 places of decimals which is difficult to visualise. Actually on the electronic plotters depths above a minimum can be hidden to help remove clutter on the screen, so depths above 5 fathoms say need not be shown unless required for some obscure reason.

<hr width=100% size=1>

 

[FlyingSpud]

Re: Sound \'er Advice?

I guess 104 /forums/images/icons/smile.gif

Given's Robins point, as a matter of interest, how did you deal with depths of fractions of a 1 fathom, were they expressed as feet and inches, decimals of a fathom or was it considered unnecessary?


<hr width=100% size=1>

 

[Robin]

Re: Sound \'er Advice?

Actually the draught is 6'10" or 2.08m and to be really picky it's a SUN Legende 41 from Jeanneau. There have been too many harsh posts on the forums about USA Hunter 'Legends' on here to be wrongly associated with them! the boat in the Pic isn't ours though it is a Jeanneau movie pinched from their website. You get used to the draught and anything less on this size of boat compromises upwind performance, for example we can go upwind at 7kts at 28 degs apparent which is still part of the wall to wall grin factor for me after previous boats. So far there is nowhere on our visits list we cannot visit with this boat versus our old W33 at 5'6", still too deep for the canals I guess. Mind you at your 1.15m draught SWMBO could get off and push if we went aground...

<hr width=100% size=1>