Originally Posted by Adelie
If you want to follow a schedule why are you on a cruising boat
The formula is not good for figuring out how far you can sail tomorrow, too many random variables.
It might be OK estimating how far you can go next week.
What it’s good for is figuring out how far you can go over a long period when the random variables average out.
Other than doing your own calculations there are products available which can do the passage
planning you are discussing. Here are three I use plus one which I wrote. I am sure there are many others, and tools such as Navionics
or the big MFD chart plotters probably do a lot of it as well.
1. A product I have used for many years, on the PC, is Visual Passage
Planner II. from Digital Wave.
It has a basic VPP for many boat types and sizes built in plus pilot charts
and all that that entails, wind
speed and directions for percentages of the time, current
information, percentage of gales, percentage of calms, for the whole world, all months of the year and a lot of other features, plus a world map/chart. Lots of reports such as predicted average speed, sea states, etc. It does great circle routing and weather
optimizing (based on historical data only).
It has proven useful for long passage planning, less so for short trips. It is available here for $119 Digital Wave - Visual Passage Planner 2
2. I have my own software
which I developed for short trips which takes into account current local conditions and can plan for routes of up to four legs, and is quite effective. I enter the true wind
speed and sea state plus the heading of each leg, the boat type, length, and some additional factors about the boat and conditions, (most of that is constant data). It produces predicted apparent wind speeds and directions and predicted boat speeds plus gives me the best heading to sail for optimal VMG. We we use it for deciding which direction to go, for sail choices, or whether sailing is even worth it, maybe motoring is a better choice sometimes. It does not tell us when to tack or gybe or calculate durations.
3. The best tactical information we use is "Sail Racer" an Android app connected to our B&G
via Blue tooth and a proprietary Bluetooth data server. I have it running on a daylight viewable (barely) rugged tablet. I can enter destinations, marks, courses, etc and it feeds back lots of tactical information for a racing
sailboat such as time, distance, and bearing to a mark, When to tack or jibe, what the apparent wind conditions will be at the next mark, what the heading to the next mark after that will be, what the wind has actually been doing (shift trends etc,) as well as start line timing, favored ends, etc. This device requires a full time navigator to get the most out of it, and is useful mostly for racing
4. We also use GRIB files, for several days in advance, and show them on our OpenCPN
. With tool #2 above, we can then predict the distance we will go on a day. Then we advance our position along the path that amount and place a waypoint there and look at the GRIB for the next day, at that point. This has been very accurate on some passages, less so on others since the weather is often not as predicted on the GRIBs. OpenCPN
has a lot of this functionality built in to it's plug
Everyone has their own approach to cruising, navigating, and route
planning. Some do none of the above and are happy that way. We use a lot of computing on our boat, but for us it does not detract from the fun of sailing, anyhow, passages can get boring, what else is there to do? We have not had major sea condition surprises during our travels except when the passage is more than about four days, even then we have some warning of changing conditions, and we rarely miss our ETA's by more than a few hours. We have not had a major grounding or wreck and that we account to robust passage planning and route
planning. The computer helps.
Before the computerized tools we used, and still refer to them, British Admiralty Ocean Passages for the World, brilliant book, and Jimmy Cornel's World Cruising Guide and Ocean Routes of the World. There are online versions I believe.
For racing, these tools help us win.