Flunking my sailing navigation math. Exam soon

Posted by Financial_Candidate6@reddit | sailing | View on Reddit | 27 comments

Book says the correct answers are

8.4 c

8.5 c

8.6 b

8.7 b

8.8 b

9.1 c

I seem to completely flunk all my answers but some answers i really doubt if they are correct

9.1 for example im pretty sure is D

And 8.6 has A. 7 B13 c3 d9 none of wich i think are correct. I actually calculated 11??

Im at a loss and stuck. My exams are coming soon.

Any math enthousiasts willing to help?

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MissingGravitas@reddit

Have you worked out how to get the correct answers on each of these yet?

I've been traveling so didn't see this when you first posted it, but I quickly did each and agree with the book answers.

Many have at least one bit of unnecessary detail as a distractor, like the headwind in 8.6. For 8.8 and 8.9 you should write out the "TVMDC" in a vertical line and use that to get the arithmetic correct, e.g.:

T 120  
V 3W  
M 123  
D 13E  
C 110  
(+W when going ↓)

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DiscussionSpider@reddit

So each ' is one knot per hour.

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Hour_Papaya_5583@reddit

You could try one of the Ai platforms. They can be terrific tutors and you can always ask why something is the way it is to really understand.
Source: grad student who has learned s lot with Claude, Gemini and Chat as a tutor

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drillbit16@reddit

8.7:

2knot = 2 nm/h
90 deg = east
so 1/2 h later, cob is 1nm east of recorded position

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kor0na@reddit

The annoying thing about 8.7 is that you just have to internalize that current directions are given as the direction that the current flows towards, which can be counterintuitive as we talk about wind direction as telling you where the wind is blowing FROM.

If something else is the problem you are having with this question, I think you are not ready for this exam.

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Imaginary-Clock6626@reddit

14 o’clock? 🤪

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DontDeleteusBrutus@reddit

WOW. I never thought I got motion sickness. Is that what the goal of that text is?

I have never had an issue reading books on rough water, speed boats or upside down in the backseat of a speeding car...but holy hell that did a number on me.

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senorpoop@reddit

It's what Google Translate looks like when you use the camera. The text book doesn't actually look like this.

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DontDeleteusBrutus@reddit

I thought there was this secret technique for teaching critical thinking on dry land or something.

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castironglider@reddit

I've been sailing since 2021 and I don't know any of these. Guess I should just open my drain plug and jump overboard, may god have mercy on my soul..

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millijuna@reddit

I just pull out my tide prediction app and look at that. Much easier.

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HotMountain9383@reddit

Which exam is this please?

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Financial_Candidate6@reddit (OP)

Navigator i guess? Algemeen stuurbrevet in dutch

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augtism@reddit

What is 14 o’clock? It’s either 2 o’clock or 1400. Therefore it’s a trick question

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Financial_Candidate6@reddit (OP)

Its google translate lens mistake

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Gaddpeis@reddit

For ALL of these - make a quick sketch on scrap paper of what is going on. With a tiny sketch - the math becomes easy (Without sketch = failure). btw - does not sound as if you are ready for the exam. This is basic and simple stuff. This is not about math, it's about understanding principles of navigation.

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Solfidric@reddit

Sorry for the stupid question, I'm not from a english country and I'm not surely a RYA certificated skipper, I'm just an amateur but how come 8.7 question has b as the right answer?

The question says that the current is at 90° so it comes from east from the ship perspective. How is it possible that the MOB will be east of the current? Since the current is coming from east, I tought that the MOB after half an hour should be located one mile west of the initial point.

I'm not posting to criticise the answer, since you all agree with b being the right answer, I just want to understand what I'm missing

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x_driven_x@reddit

Current is described in the direction it is going. Wind is described in the direction it is coming from.

So the current doesn’t “come from” the east, the current is flowing east.

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mmomtchev@reddit

AFAIK, this is the same in all languages (I can testify for English, French and all Slavic languages).

Wind is historic, everything else follows the mathematical definition of a vector.

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Solfidric@reddit

This changes everything, I missed the point from the start. Thank you for clarifying this!

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flyingron@reddit

It's actually (in English) the rule of 12'ths

The rule says that given the nominal six hours between low an high tide, for the first two hours between the low and high tide (which your question is referring to), the tide rises 3/12's.

The difference between the tides is 3.6m. 3/12 of 3.6m is .9 m, you add this to the low tide value of .9 and you get 1.8.

C is the correct answer.

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Gaddpeis@reddit

13 You do 10 through water, and the water is 3 over ground in same direction. So you do 13 over ground. And yes, wind is red herring!

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mmomtchev@reddit

When you say that the wind is North - which is 0°, this means that the wind is coming from the north and going to the south.

When you say that the current is North - which is 0°, this means that the current is coming from the south and going to the north.

The correct way to refer to the current is in fact northward current.

Mostly everything else works the same way as the current - however when it comes to wind, historically, it has always been inverted.

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olddoglearnsnewtrick@reddit

Doing 8.6 for you

•   Current 235° + course 235° = following current → add it  
•   Wind effect is already in the log reading → ignore it  
•   SOG = 10 + 3 = 13 kn

So yes the reply is B

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At 10, 2 hours have passed, so 1/12 + 2/12 = 3/12. This corresponds to 3*0.3, which means 0.9 meters increase.

0.9 (begin) + 0.9 (increase) = 1.8 meters