Saturday, May 13, 2017

Passage Planning Tools: Fastseas

We are still sitting in the Bay of Islands, New Zealand waiting for good weather to head to Fiji. Thought I’d write a little about some of the passage planning tools I use – OK, this blog is not a travelogue, more for other cruisers.
One tool I really like while we still have decent Internet is This is a weather routing program that uses the interface of and the GFS weather model along with the specifics of your boat (polars) to create an optimum route for a passage. Once you’ve selected a Start and Finish location you enter the start date and time and have it calculate a route. In the image above the calculated route is the brown line. Fastseas will route for optimum speed, around land and to avoid high winds.
You can then look at the Stats about the calculated route: how many days, how many hours motoring, percentage of time beating/reaching/running, maximum wind speeds, minimum wind speeds, average boat speed, etc.
You can setup the polars for your boat describing how she points and what speed she does for various wind speeds and directions (or use the generic polar). This tab also lets you enter at what boat speed you will decide to motor and how fast you will motor.

One of the best features is the Departure Planning tab. It creates a route for the next ten days or so, assuming your original start date and time. You can then compare the Stats for each day and make a better decision on what day is the optimum departure date. For us we are trying to number one minimize the beating (sailing close to the wind, which is uncomfortable offshore) and number two to minimize motoring (hate that racket and dinosaur consumption).
There are few things that I’d like to see improved on Fastseas, but Jeremy, the developer of Fastseas is pretty active doing updates and making sure the program scales to the number of users. He’s had to add a small fee for unlimited use (free to use multiple times per month and try out) to help cover the Amazon Web Services Cloud computing costs.
One item I don’t like is that Fastseas uses the current predictions in its optimization. While this sounds good in theory and probably works well say in the Atlantic where the Gulf Stream moves in a fairly consistent river of water. The image above is a display of the current predictions between New Zealand and Fiji. You probably can’t make it from the image but basically the currents are just all over the place. Being 20 miles west of your position might reverse the .5 kt current shown on the display. In practice these predictions are useless on this passage and just add error to the optimization. Fortunately its not much error because the currents are small and somewhat random.
Give a try next time you are planning passage.

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