Deck (Watchkeepers) Log

[S/V Alchemy]

Originally Posted by jackdale

Nice Alchemy

I like to keep the Speed and True course columns adjacent, as that is what gets recorded on the chart.

As it's a Excel file, it's easily remedied.

I use the right hand side primarily as a "added a jerrycan of fuel" or "replaced impeller" type of notation. This is a Lake Ontario summer farting-around point, so there isn't a lot to record, but the guy I'm sharing it with is a commercial pilot, so you can bet that I keep decent notes!

[S/V Alchemy]

Originally Posted by jackdale

I do not know of any requirements for recreational vessels, but a logbook would be be valuable in a court of law or an insurance claim.

I used a deck log to recreate an incident for an insurance claim. I hit a log at might just after altering course to avoid a tug and tow. We had recorded the regular log entry just prior, recorded the course alteration and the time of the close encounter of a log kind.

I use mine to record known positions so I have a decent DR if the GPS is wonky and everything but the compass goes down in the midnight fog.

I also keep my fixes in a chartbook in light pencil to track my progress. For me, sailing point to point can be a little dull unless I've got some coastal pilotage and math to do. Yes, I whip out the sextant, too. If I'm off taking a sight while passing a fixed nav aid, I know exactly by how much and in what direction.

This leads easily to improvement.

Actually, all this stuff takes about five to six minutes at the top of each hour. It's a good habit to cultivate, like setting your watch to a time signal and noticing the drift over a week, if any.

[David M]

Originally Posted by ZenithOcean

You seem to have most things covered, and I'm sure it will be perfect for your purposes. I've sailed on 80,000 gt cruise ships with little more in our logs then that, and the commercial yachts I sail on now have fairly similar deck logs.
One pendantic point is that the Compass is a heading not a course, so would be HDG and the GPS track would be Course Over Ground, COG.

Happy sailing.

It's not pedantic at all. You have your heading (HDG), your course made good (CMG) and your course over ground (COG). They are three different things and are more often than not three different numbers.

[barnakiel]

We do not have one.

I take down position / course / speed during my tricks, but I let the first mate sail as she pleases. Being only two onboard we always meet face to face every 6 to 8 hours or so ;-) then we swap our stories and that's about it.

b.

[Jim Cate]

Originally Posted by David M

It's not pedantic at all. You have your heading (HDG), your course made good (CMG) and your course over ground (COG). They are three different things and are more often than not three different numbers.

Now I'm confused. What is the difference between CMG and COG?

Cheers,

Jim

[IslandHopper]

Originally Posted by Jim Cate

Now I'm confused. What is the difference between CMG and COG?

Cheers,

Jim

CMG = The bearing from your start point to your present position (as the crow flys) which more than likely, with wind and current, is not the COG you followed...

COG = Your direction of movement relative to a ground position...

Clear as mud....

Or......

[Ex-Calif]

Originally Posted by IslandHopper

CMG = The bearing from your start point to your present position (as the crow flys) which more than likely, with wind and current, is not the COG you followed...

COG = Your direction of movement relative to a ground position...

Clear as mud....

Or......

Not sure if I agree with that picture. They define Track and course line in direction of destination (what?). Whatever definitiions are used should be applied consistently.

Track and COG are equivalent. Track being track over ground.
Course is the rhumb line to the next waypoint
Heading is mag heading
Bearing is angle off heading and waypoint (or whatever feature is being observed)
CMG is start point end point actual course.
CTS (course to steer) is a calculated course to the next waypoint base on xte (cross track error)
Heading to Steer is calculated to factor in set and defines the mag heading to reach the waypoint

A big error many people commit is following cts on the gps or plotter. This guarantees a french curve to the waypoint. You need to steer above the set consistently to describe a fairly straight line to the waypoint.

If I were logging, say hourly, I'd like to know course (the rhumb line), heading (where I am or have been pointing the boat "on average") and XTE (cross track error to know how far off the rhumb line I am). This would tell me over time or with boat speed I can calculate a new heading to reduce xte or maintain xte.

Track is interesting and plotters do it with ease but it is somewhat irrelevant. It is just CMG cut into tiny increments. Some logical average is more useful, say hourly logs.

So the course is 90 mag (course). I steer 90 mag (heading). Boat speed is 5 knots. After one hour xte is .5nm south of the course. The difference between course and cmg is the angle drawn from start point to finish point. Winds permitting I steer to port. How much can be calculated base on the data provided and how quickly I need to get back on the rhumb line. On a long passage xte of .5 is no big deal, especially if set is expected to change (or even reverse) later in the passage. However when making landfall xte of .5 could put you on the rocks or put you in a position that you can't fetch the harbor.

There are simple calculators availble to do the math. I have a manual whizwheel somewhere that does it. It should be noted that distance along the course (rhumb line) is less than 5nm and the boat has to sail additional distance to get back to the line.

It is argued that in this case starting with a mag heading of say 085 while you may stay on the rhumb line it would take longer to go 5nm because you are sailing against the set and that slows SOG (speed oveer ground) - this is true. You can't cheat mother nature... Unless on the 085 course you can tweak an extra point 2 knots of boat speed. Now we are talking vmg. A whole nuther beast.

[barnakiel]

Originally Posted by IslandHopper

CMG = The bearing from your start point to your present position (as the crow flys) which more than likely, with wind and current, is not the COG you followed...

COG = Your direction of movement relative to a ground position...

Clear as mud....

Or......

Now don't try this trick with a Garmin plotter. Neither with your RYA examiner.

b.

[IslandHopper]

It's purely to point out the difference between CMG and COG, let’s try not to get to far off track.....

[terminalcitygrl]

I can't speak to the sailing directly (yet) but my experience in the real world is checklists work! In priority and with fill in the blanks with specific data points (like speed, heading, etc...)

One page that incorporates directions and feedback as a watch unfolds could be very helpful, especially to folks with little experience.

[jackdale]

Originally Posted by Jim Cate

Now I'm confused. What is the difference between CMG and COG?

Cheers,

Jim

CMG = Course Made Good or Course to Make Good

This is the term used in traditional chart navigation. This is can either be the course I actually followed between two fixes without accounting for set and drift and leeway, or it is the course I intend to make good between a fix and a destination. In the latter case I may have to account for set, drift and leeway to determine my course to steer, i.e. my course. I will plot my course on the chart in true, then after accounting for variation and deviation, I will give a course to steer in compass to my helmsman. If he follows that it is a heading.

A bearing is the direction usually in true or magnetic from the boat to an object best determined by a handbearing compass. A line of position is the bearing transferred to a chart.

COG is a GPS term that indicates the course over the bottom at the present time.

[IslandHopper]

Originally Posted by jackdale

CMG = Course Made Good or Course to Make Good

This is the term used in traditional chart navigation. This is can either be the course I actually followed between two fixes without accounting for set and drift and leeway, or it is the course I intend to make good between a fix and a destination. In the latter case I may have to account for set, drift and leeway to determine my course to steer, i.e. my course. I will plot my course on the chart in true, then after accounting for variation and deviation, I will give a course to steer in compass to my helmsman. If he follows that it is a heading.

A bearing is the direction usually in true or magnetic from the boat to an object best determined by a handbearing compass. A line of position is the bearing transferred to a chart.

COG is a GPS term that indicates the course over the bottom at the present time.

1. In the case of CMG a bearing is always to the boat, in other words the bearing in a straight line from your start point to the vessel is the CMG, this is the bearing you would use in calculating you CMG, if it was from the boat it would be a reciprocal bearing...

2. I was plotting COG long before GPS came on the scene, doing fixes on the chart every 5, 10 or 15 minutes (depending on the situation) gives you a great idea of COG, albeit a little delayed. Agreed though, in a GPS the COG indicates the course over the bottom at the present time...

[jackdale]

Originally Posted by IslandHopper

1. In the case of CMG a bearing is always to the boat, in other words the bearing in a straight line from your start point to the vessel is the CMG, this is the bearing you would use in calculating you CMG, if it was from the boat it would be a reciprocal bearing...

CMG is from the point of departure to the intended arrival position. That is, it FROM the current position of the boat to the destination. Your vessel is at the start point.

Or it is from the start point TO your current position, in that case it is to your boat.

CMG can either be what you intended to do, or what you did.

[Ex-Calif]

Originally Posted by jackdale

CMG is from the point of departure to the intended arrival position. That is, it FROM the current position of the boat to the destination. Your vessel is at the start point.

Or it is from the start point TO your current position, in that case it is to your boat.

CMG can either be what you intended to do, or what you did.

I am sorry I disagree. course "made" good is past tense. It is start point to actual arrival point.

Course is the start point to intended destination.

If after 100 miles you are 10 xte to starboard you can plot an intercept any where along the original course - the culmination of which results in "steer heading xyz to intercept" or if you take the new position as start point culminates in, "new course xyz. Steer heading abc." when all the math is done.

Also, willing to be corrected on this one, I have always used bearing as magnetic to the object observed. "Raffles light. Bearing 330." This tells everyone where to look. Raffles light bearing 150 would have me looking the wrong way. The other way is, "Raffles light bearing 040 to port." which would indicate a reference from the centerline of the boat.

Hmmm... Been navigating for 30 years and still get conflicting definitions...

[IslandHopper]

Originally Posted by jackdale

CMG is from the point of departure to the intended arrival position. That is, it FROM the current position of the boat to the destination. Your vessel is at the start point.

Or it is from the start point TO your current position, in that case it is to your boat.

CMG can either be what you intended to do, or what you did.

CMG (course made good) is what you have done, it's past tense only....

CTS (course to steer) is what you intend to do in the future....and usually stated as "course to steer to make good xxx"

I have never heard of CMG used for both.....

EDIT: Ex-Calif beat me to it....