Anchor chain marking

We came across the following post on Facebook:

We got tired of constantly thinking about depth, length etc. so we have marked the WATER DEPTH with yellow colour: 3 yellow lines = 3m of water. And we found a more realistic formula than just 7xdepth or 4xdepth:

12*square root(depth)

It takes more into account that the chain hangs. And remember freeboard! We have about 1.5m of freeboard, so at 2.5m of water the depth is actually 4m. So with this formula we have marked the following (in parenthesis chain at the 7xdepth formula):

  • 3 yellows (3m water, 4.5m total height) : 25m chain (7xh= 31.5) (In brackets: are we the only ones who lay 25m at 3m water?)
  • 5 yellow: 31m chain (45.5m with 7xh)
  • 10 yellow: 41m chain (80m with 7xh)
  • 15 yellow (15m water) : 49m chain (our nuv Max) (115m with 7xh)
  • And in strong winds, we lay out to 1-2m more than the depth.

No calculations while fiddling with anchorage, we just need the water depth.

We have a 44-foot steel boat of 19 tons and must have at least 100 m of chain for long-distance sailing. But has been in England with 16ms constant wind at 8-10m depth with these markings (however laid out for a little deeper and on a good bottom)

It sounded like a really good idea, which we have translated into the following:

The anchor chain is marked according to the current water depth calculated from the following formula, which takes into account that the chain hangs in a parabola:

12*square root (depth+headroom)

Clearance is the height of the anchor roller above the surface. In our case, it is 1.5 m.

Marking is done with blue, split PP cord. Each tag consists of 2 cords (so the marking is still visible if a cord is lost)

Depth (meters)Meters of chainNumber of marks
12452 x 2

The table is written with marker on the back side of the anchor well cover, so you just need to know the reading of the depth on the sonar.

If it’s windy, we put a few more meters out. We have a Kobra anchor and a total of 75 m of 10 mm stainless chain for our boat of 13 tons in total. We have set out using this formula in 7m of water in Vliho bay in Greece and at 22m/s we have held both ourselves and another 40ft sailboat lying across our bow.

And then we use two “anchor snubbers” or chain relievers, especially if there is little wind or there is sea.

There is a lot of literature on the subject, an app has also been made for the calculations, which of course depend on hull length, weight and much more, see e.g. here: Ancher chain calculator


The boat is continuously maintained, of major things can be mentioned

2006 New teak deck
2006 Vacuum osmosis treatment incl. 2 layer rowing
2012-15 New Simrad navigation equipment incl. 2 plotters and 3G radar
2014 New windlass
2018 New Force 10 stove
2018 New fixed sprayhood
2019 New cover for roof hatch in wheelhouse
2020 New water-cooled compressor and evaporator Isoterm 2507
2020 New 40 l hot water tank
2020 New washing machine Whirlpool TDLR70230
2020 New batteries for windlass and bow thruster
2021 New consumer batteries
2022 Renovation of bow thruster


The Seafinn boats have to some extent been self-adapted and perhaps also built in relation to the customer’s wishes. At some point, a standard version of the Seafinn 411 came out, for which there is also an old sales brochure. This is the version we have. There is only one side door in the wheelhouse, instead there is a staircase with a sliding hatch up to the aft platform. We really appreciate that, both during sailing and when we sit outside in good weather.

Compared to the original layout, rebuildings and additions have been made that make the boat even more suitable for living onboard.

Before 2010

  • Rebuilt pantry with extra upper cupboards, large fridge/freezer to port and stove to starboard
  • Rebuilt wheelhouse with folding table and large shelf for all the boat’s papers and pilot books
  • Washing machine and storage room in side cabin (before 2009)
  • Extra upper cabinets in aft cabin (before 2009)
  • The aft toilet has a separate shower cubicle (before 2009)
  • Cover for the roof hatches (before 2009)
  • Both white cover and shade cover for the windows in the wheelhouse (before 2009)

After 2010

  • Insulation with 38mm armaflex where possible (2010-2011)
  • Water-borne heat with several heat sources:
    • Reflex Oil stove with heat recovery that provides a very dry bathroom (2010-2011)
    • electric cartridge or heat exchanger for engine heating (2014). This can be supplemented with heat from an electric radiator in the wheelhouse and in the bathroom (2019)
  • Front triangle – here the front toilet has been removed in favor of a 1½-man berth and desk with office chair and bookcase (2010-2011)
  • Cockpit table on pedestal (2011). New table top from 2019
  • Foldable bar stool (2012) that matches the height of the table in the wheelhouse, so that 5-6 people can sit and eat
  • 200 l holding tank (2014)
  • Salon with 32” TV and cinema sound (respectively 2015 and 2010), new foam in cushions (2019), new carpet and cushion covers (2022)
  • Floor heating in half of the salon, in the pantry and parts of the toilet room (2016)
  • 75 m stainless anchor chain (2018)
  • Condensation-free double glazing in all windows (2018-2022)
  • New Mastervolt charging system (2018-2021) with Chargemaster Plus 12/75-3, SCM60 MPPT-MB solar charge controller controlling 1000W solar cells, Mastershunt 500, EasyView 5, 700W inverter (AC Master 12/700). The system automatically supplies 3 battery banks and we can see the charging current/consumption together with power status on the consumption battery bank. In addition, the system can be programmed for individual needs.
  • LED lights everywhere, including several with the option of red (night) light (2019)
  • Tent for the aft deck (2022)

Factual information

  • Seafinn 411, year of construction 1987, construction number 73
  • Fiberglass with teak deck and keel embedded in fiberglass
  • Shipyard build by SeaFinn Yachts Oy. Finland
  • Length 12.4 m (without bowsprit and bathing platform/davit)
  • Width 3.6 m
  • Draft 1.55 m
  • Weight 12.5 tons
  • Engine Perkins 4236, 78 hp
  • 2 furling masts
  • Sailing area with standard masts 93 square meters, with furling masts slightly smaller
  • Almost new sails (2017-2018, but not used much)
  • Bottom painted with coppercoat in 2013, 4 new layers in April 2022. Unfortunately, there has been too high humidity in the air, so blisters have appeared between the layers. However, according to the Danish importer, this should not mean anything for durability
  • Ruggerini diesel generator 3kW

Original purchase receipt with documentation of paid VAT included