Yachting and Boating World forums: Tidal streams

I don't know/ use the publication, but tidal rates are fairly approximate anyway. I have just been having a discussion about practical navigation on another forum. What the RYA teach in a classroom is NOT wrong, but may be impractical on a small boat or a fast MoBo.

How long does it take to do an "accurate" RYA style DR plot? How much accuracy is necessary/relevant? How easy is it to use ruler, calculator, dividers, almanac and chart table?

When I got my first sailing cruiser I was given a lesson in practical nav that I found immensely useful. You do not need tidal streams to a tenth of a knot- they won't be that accurate anyway. Estimate to nearest 1/4 knot & assess impact on course, it may be negligible. You have Neap & spring rates on your chart. First use tide table to interpolate between spring & neap, then use 1/12ths rule to estimate rate at given times.

For quick small boat nav without a plotter, have a paper chart folded on your knee, align it to the coast (I'm assuming coastal pilotage) point your flat hand, held thumb upwards, at a known landmark then lay that angle off on the chart by moving your hand (keeping it parallel to the original bearing) so it is over the landmark. Note that line on the chart mentally, then repeat with a second landmark. That will give you a workable position in seconds with no tools or paraphenalia at all. You can do this without leaving the tiller & in any weather or sea conditions.

With an approx position, bearing in mind an egg cup sized area of uncertainty & any potential hazards, you can lay off a course in a similar manner, either using the chart compass or another landmark. These techniques are ideal when shorthanded, needing a sanity check on formal or electronic techniques or if you need an instant solution to a problem.

Don't forget it is difficult to hold a course within 5 degrees anyway, so even 3 degrees accuracy is generally pointless. The point I am trying to make is that you need to understand when close enough is good enough. Thes quick & dirty techniques allow you to check progress quickly, easily & often without spending loads of time below at a chart table making calculations and missing the sailing!

I've written another bloomin' essay again, DOH! Sorry about that!

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