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Sextant Piloting: The Three-body Fix
This blog post will eventually be a more thorough reference on doing 3-body piloting fixes with sextant, but for now it is mostly background. I will fill it in as time permits.___________Many mariners...
View ArticleAutomatic Motor Routing in qtVlm
Since the very onset of electronic position finding (from LORAN on up to GPS), we have taught that these aids are wonderful tools for telling us where we are, but we must still master traditional...
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How the Fit-Slope Method Works
Since we first proposed the Fit-slope method many years ago, and have used it continually since then, I have just realized that the base reason the procedure works is not as obvious as we might have...
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Lunar Distance Revisited with a 1939 C.Plath Kriegsmarine Sextant
We happen to have on consignment a C Plath sextant made for the Kriegsmarine in 1939 Germany. It is a prized collector's item, but we wanted to demonstrate that it remains a top of the line instrument...
View ArticlePolar Wave Spectra
This is a place holder for soon to follow instructions on the use of polar wave spectra plots for understanding the seaway and for setting up optimum routing corrections for waves, including how to...
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Notes on S-100 and the Eventual S-101 ENC Display Standard
BackgroundAt present all ENC content and structure (internationally) are based on the IHO S-57 standard, and how these ENC should be displayed is determined by the IHO S-52 standard. ECDIS systems are...
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Lunar Distance by Calculator — The Letcher Method
The lunar distance method is a way to find UTC by measuring the angular distance between the moon and an adjacent body (sun, star or planet). The measurements are called "lunars." And finding UTC is...
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Wind on the Water: A Sailor's Perspective
For sailors, wind speed is given in knots, and the direction of the wind is the direction it comes from. A north wind is blowing from the north toward the south. A sea breeze is blowing from the sea...
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New Tidal Current Resource for Swiftsure and R2AK Sailors
The excellent (free for Mac and PC) navigation app qtVlm has just added a new optional feature that is free for testing until May 15, 2026—after which it becomes a subscription option. Namely they...
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Grib Offsets for Routing in qtVlm
When we compute the optimum sailing route in a nav app like qtVlm, we use the polar diagram of the boat to provide its performance expectations in various wind conditions, and we rely on a numerical...
View ArticleAccess Historic OSCAR Currents in GRIB Format
We have long suggested that the satellite based measurements of ocean currents called OSCAR (Ocean Surface Current Analyses Real-time) are often the best guide for optimum sailboat routing. See this...
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Evaluating wind models in 2025 Sydney-Hobart Race
We have been following the TransPac52 fleet in the 2025 Sydney Hobart Race as a way to learn about evaluation of currents and winds and routing for practice in our online marine weather and...
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The Three Sets of Nautical Chart Symbols We Need to Know
In 2025, all traditional paper charts were permanently discontinued, after which the only official NOAA nautical charts are the electronic navigational charts (ENC). The International Hydrographic...
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NOAA's New Nautical Chart Numbering System
Official US charts with chart numbers started with the founding of the US Coast Survey in 1807 that evolved through several forms into the modern NOAA. Historic charts can be tracked down at...
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WA State Nautical Charts in Flux
All paper charts across the country were discontinued at the end of last year, leaving electronic navigational charts (ENC) as the only official charts. The shapes and scales of ENC, however, have been...
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qtVlm Training Mode — Available to all Schools
We designed the Training Mode supplement to qtVlm to be available to all schools that teach marine navigation or weather. The getting_started link explains how to install it for Mac, PC, or mobile...
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Shared Remote Simulation with qtVlm
A unique feature of qtVlm that is a powerful training tool is its ability to share AIS positions amongst simultaneous users. We can have, for example, three users in different parts of the world agree...
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Steering in a following current
There is a video of this article linked at the end. A few years ago we analyzed the grounding of the Ever Given in the Suez Canal just a few days after it happened. The results are presented in a 5-min...
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Symmedian point in a triangle
Some years ago we presented a procedure for finding the most likely position based on a plot of 3 lines of position (LOP). We focused on finding that position when the random uncertainties in each of...
View ArticleRole of qtVlm in the Starpath Coastal Nav Course
Starpath School of Navigation offers several online courses that use qtVlm for electronic chart work. In our Electronic Chart Navigation Course we cover qtVlm from the basics on up to advanced...
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