I thought I needed a leadline about as much as I needed an eyepatch, a parrot and a wooden leg, but it didn’t take long for Dick to convince me that it’s still a useful part of any cruiser’s kit. Its portability, simplicity, utility and reliability are its strength – and it’s a mighty strength. Let’s not forget that many of the Admiralty charts we use today, charts on which a trading empire was built, were sounded, and the bottom type identified, using a leadline. Here are some of the reasons you should have one on board and how you need to use it.

The lead is cast, weighs 3-8lb, and is spliced onto a three-strand line

How to use a leadline
The lead is heaved forward from the ship’s point of maximum beam and the line allowed to run (the leadliner will have the bitter end’s lanyard round a wrist, or secured to the ship, to prevent losing it over the side). A reading is taken when the line is taut and vertical, and the weight is just taken up, indicating the lead has touched bottom. Smear tallow or beeswax (marine grease will do) into the recess on the base of the lead so that a sample of the bottom can be brought up, providing important pilotage information in rivers and estuaries.

It sounds simple enough, but the necessity of having the line vertical and the lead touching bottom means that it’s not possible to take an accurate sounding while the boat is moving faster than three or four knots. The need to take soundings suggests that
waters are shoaling, so it’s sensible to slow down anyway. For very accurate soundings, a ship would heave to. If she were anchored, tidal set and rate would be another consideration. Leadlining is quite a skill and you’ll need practice to master it.

Sticky tallow is smeared into the recess so the bottom can be sampled

With no tallow, we used grease

And found Kentish mud

Calibrate your sounder
It’s the instrument that, for many, rendered the leadline redundant, but do you know how accurate yours is? Does it tell you depth to the nearest 0.1m (3in), 0.5m (18in), or don’t you know? Does it display depth below the keel or below the hull?
Next time you are in a marina berth or on a fore-and-aft mooring, check your sounder’s reading, then take leadline readings from port and starboard, approximately over the point where your transducer is fitted, and you’ll soon know whether it’s accurate or not. Then you can either calibrate your sounder properly – the best option – or at least you’ll know how much to offset when reading its screen.

Pete Willetts’ Seal 28 Aztec stands off while Dick sounds the bar

Piloting an 
unmarked channel
Part of the joy of cruising is exploring creeks and backwaters, nosing up narrow unmarked channels where solitude and shelter await. There are a couple of rules of thumb: choose a rising tide in case you do go aground and, where possible, choose the windward side of a channel so the wind will help you off if you hit the mud. Generally, the outside of the bend is deepest – but not always. And how deep is it? Chart datum is all well and good, but these slow-moving channels often silt up.

You can add certainty to your decisions by sending crew ahead in the tender to sound the channel as you crawl along, so you know exactly how much water you have, and where. Often there are small deeps where you can stay afloat anchored at low tide. Leadlining from the tender will tell you where they are, how deep they are, and whether there is good holding.

Sounding a bar
Many navigable rivers have a shallow, shifting bar at the entrance. You can use a leadline to find the deepest route across the bar before entering port in fair weather. Heave to off the bar and send your crew ahead with a leadline, first to find the bar, because they can move after storms, secondly to find the deepest part of it, and thirdly to find out how deep that part is. Once those data have been established and the position marked with a GPS, or transits noted, you can return to the boat and set off towards the bar in absolute confidence.

The traditional leadline
Leadlines are marked in fathoms (6ft intervals), so-called after the Old Norse word ‘fathmr’ for embrace, the distance between the fingertips of outspread arms. The lead weighs 3 to 8 lb, or up to 14 lb for deep-sea vessels. It has to be heavy, and streamlined in shape, so that it sinks rapidly and presents a small surface area to the tide. The line is spliced to the lead at one end and 25 fathoms long, with a lanyard spliced into the bitter end.

The traditional leadline is marked at fixed intervals in the following way, and the variety of marks enabled the sounder to determine depth in the dark:

Leadline depth markings
2 fathoms    Two strands of leather
3 fathoms    Three strands of leather
5 fathoms    White calico strip
7 fathoms    Red woollen bunting
10 fathoms    Leather loop
13 fathoms    Blue calico strip
15 fathoms    White calico strip
17 fathoms    Red woollen bunting
20 fathoms    Line with knots at either end

Twenty fathoms (120ft, or 36m) may seem a touch long, but it helped a ship’s captain to know when he had returned to soundings, which is useful for navigation. The lead would be swung and the mark called. If the sounding was two fathoms, the leadliner would call ‘By the mark two’ (or ‘twain’, whence the eponymous author allegedly took his name). Quarters and halves were also called, so ‘A quarter less five’ is 4¾ fathoms, and ‘A half seven’ is 7½ fathoms. Unmarked soundings were estimated as ‘deep’, so nine fathoms would be ‘By the deep nine.’

Finding deeper water
If you’re unlucky enough to find yourself aground, the best option is to go out the way you came in, as you know the water there is deep enough. However, if you can’t get off straight away, or it’s a falling tide, you’ll need to make a plan.

Central to that plan will be getting afloat again, and there are a variety of methods, many of which we explored in our Crash Test Boat series (June 2011). However, once afloat, the last thing you want to do is end up on the putty again while trying to find a route to deeper water. Once again, get your crew to grab the leadline and get into the tender to survey the area around you. Look for deep water and channels to reach it, and note any shoal patches that may block your path.

Coiling down
Traditional leadlines were made of natural fibres. Today, virtually all leadlines are synthetic, so we don’t have to worry about the leadliner’s traditional foes, rot and stretch. Dyneema, which has a slippery coat and zero stretch, would be ideal if you can afford it. Whatever you use, a leadline needs to be carefully coiled and secured with a gasket hitch so it’s ready for use in an instant.

Jury rig a leadline with taped cord and a heavy shackle, or use a telescopic boat hook as a sounding pole

Soft lead, sounding poles and jury lines
We leadlined with Pete Willetts aboard his Seal 28, Aztec. Pete sewed his lead into a toy rugby ball to prevent it damaging the topsides on retrieval. The sounding pole has been in use since Egyptian times. Poke the pole over the side and you’ll have an exact sounding for the spot you’re in. There are leadlines for sale today, marked in metres and costing around £25, but you can jury rig one with a heavy shackle and some knotted line. Be aware, though, that a shackle won’t sink as fast as a purpose-made lead, so won’t be as accurate on a moving boat and will be prone to drift with the tide.