Compass Navigation

-- Last Updated: Jan-12-04 1:08 PM EST --

Reference materials:
1. The American Practical Navigator by Nathaniel Bowditch
2. Chapman Piloting Seamanship % Small Boat Handling any revision/author

T True Course
V Variation + west - east
M Magnetic Course
D Deviation + west - east (negligible in kayaks w/o magnetic interference)
C Compass Course
Current correction for set and drift
Leeway correction for wind

Only after computing the above, could one actually steer by a compass "only" and have any expectation of arriving at ones desired destination. We call this Navigating.

T V M D C are readilly available. Current set and drift can be computed (not accurately) from Tide Tables for East Coast of North and South America or Tide Tables for West Coast of North and South America. Interpolation is mandatory but 100% accuracy can never be achieved. Leeway, unless you've done an engineering study of your vessel, is a WAG (Wild A** Guess) at best.

One could proceed w/o compensating for current and leeway by using Dead Reckoning. This would require the use of charts with their related instruments plus a means of determing lines of position. In sight of land this works in calm waters, out of sight, in waves, I just don't see it happening.

Let's assume that an "accurate" course could be attained, how could you maintain that heading? Refer to the diagram under Dead Reckoning from the reference above. Large ships wander across their headings, small boats much more. Think of the thrust needed to move the bow of an aircraft carrier vs a kayaks. Besides the wind, waves, and steering problems of holding a heading, a kayak requires that both the port and starboard strokes would be identical.

I have been brought to task by saying that a handheld or other compass clipped to a vest would be just as accurate. I stand corrected. They would be just as inaccurate for steering a course. Yes on the Hudson I do not really need a compass, even in fog. Assuming that I kept paddling in ever widening and decreasing circiles, eventually I would bump into shore. I would much rather have a compass so I could shorten my paddling time and imagine my depression climbing out on the east shore when I live on the west. Why, I'd just have to get right back in and paddle some more. If you are off the east coast paddle west to reach land, on the south coast paddle north etc. You don't need an expensive compass to effect these directions.

Any comments?

I’ll just keep using my GPS (w/spare batteries)

but I do carry a spare compass! LOL


Good stuff
And I agree with you that the hand held is just as inaccurate, but I think conditions on where one paddles is a major factor as to whether one is as useful as the other. Both are useful as navigation aids, I use a combination of piloting and using my deck mounted compass. Most of the water I paddle is frequently choppy/sloppy/windy water, so having to stop paddling while I futz with a hand compass is inviting a swim, not to mention the wind pushing me backwards or otherwise in a direction I don’t want to go in. I rarley seem to have a tail wind on my return route, even if I paddled a head wind all day, it either changes direction or the wind just stops. I used my compass on Saturday to find an island that is not readily visable from shore, so a heading maintained until I see the island, then I paddle towards it. It really doesn’t matter if I am a few degrees of cause once in view it is back to piloting. So to make a short story long, i agree that both are about as useful, but it is more the conditions which determine which would be a better choice, and besides I am likely to forget to bring a hand held, guess I could tether it to the pfd. This is just my opinion, I could be wrong. Thanks for the info.

Margin of Error
Every measurement for navigation, taken on land or at sea, has a margin of error. So, I think it is more correct to talk about more accurate or less accurate, not accurate or not.

That being said, I guess it is an individuals comfort level with the margin of error, when taking measurements at sea. Is the margin of error so great that the results are useless?

My opinion is that I would rather have an estimate for navigation purposes - even with a high margin of error - than no estimate at all.

Deck compass is just easier.
There is no doubt that a good handheld compass will do everything a deck compass will do and more. However, I’ve crossed bays in absolute pea-soup fog on Lake Superior using my deck compass and picking and “roughly” holding a bearing by simply giving myself some margin of error such that I will hit the far shore, and not paddle out to sea. I’ve found it very nice to be able to simply glance down and make minor course corrections while paddling. I can’t imagine how many times I would have had to stop paddling to pull out my handheld compass. All three of the paddlers in the above situation were checking their deck compasses about every third stroke.

Since no guns are in evidence

– Last Updated: Jan-12-04 7:37 PM EST –

All handheld compasses I have seen are designed to be used steady and level. A nexus 70 P compass is designed to accomodate more pitch than a kayaker needs and 30 degrees of roll. So in sea kayaking conditions I believe I have made a decent argument that the Nexus is going to be more accurate, by it's nature it will be more convenient.

Even great paddlers are lucky to not deviate fron their course by 5 degrees when the seas are up,(I try to keep within 10 in case you are scoring) perhaps the best can accurately cause that deviation to be about their course equally. So do I endorse having a GPS as a secondary navigation tool on the ocean. Yes! (When I told my wonderful wife I was going to start paddling in winter she said, "Honey get the best radio, drysuit and gps that are made. I'll skip birthday and Christmas presents to see that you can" (not necesary)What a great lady!)

Could a paddler with only a compass make the Plymouth to provincetown crossing (30 miles in Masssachusettts bay) as accurately as one with a deck compass and a working gps? of course not! Is a deck compass useless for those with a GPS, or only as accurate as a handheld in the conditions one would encounter on that trip? of course not!

I think folks have read more than enough reason from me on this topic. In the end paddlers will make your own decisions.

It’s (mostly) not about accuracy
Coming from a hiking background, I use my hiking compass while kayaking untill one day I rented a boat that has a deck mount.

With a hiking compass, I have to stop paddling for a stroke or two to see the compass. Not so with a deck mount. I can see a few situations where stop paddling is not a desirable thing:

  1. paddling against stiff upwind: you loss some ground every second you stop paddling.

  2. in total fog: you need to do it so often your speed is affected significantly.

  3. in rough sea: sometimes it’s just not even pratical to take your hand off the paddle.

    So for me, it’s not so much the accuracy, but the praticality of having the compass always visible that I will get a deck mount when I have my own boat.

    A GPS, when mounted on deck in a way to be always visible, can do the same. But then, you’re kind of wasting the (in my view) better functionality of a GPS by using it as a dumb compass. You can’t see the map as to where you’re without changing screens. I think I prefer to have a deck mounted compass, complimented by a GPS that shows either my speed, or the shoreline if I’m in total fog.

    Still, the compass needs no battery when all else failed…