# calculation of number of voyage days

Discussion in 'Boat Design' started by abhishek, Oct 7, 2009.

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### abhishekJunior Member

sir can any one please tell me how to calculate the number of voyage days of a ship and give me some formula,s to calculate them.

2. ### apex1Guest

You are kidding right?

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### John.EJunior Member

Maybe this?

days at sea = int(hours at sea/24)+1

Alright, it rounds up but it works

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4. ### apex1Guest

Wow, now it goes scientific! Thanks John.....

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### Manie BSenior Member

gawds troooof now you know why i want to cruise up the rivers in Europe and North America

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### gonzoSenior Member

Divide the distance of the voyage by the distance you make each day. This is fifth grade math

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### John.EJunior Member

Though this will yield a fair guestimate it makes the assumption that the daily distance over the ground will be constant (an unlikely state of affairs given currents, weather, TSS congestion and tidal access to ports)

OK, so I'm a pedant

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### gonzoSenior Member

That's why you use pilot charts to estimate the currents and winds to calculate the daily distance

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### John.EJunior Member

Aye it is, but it buggers up a simple 5th grade division for a passage estimate don't it?

10. ### apex1Guest

That is the sheer nonsense! When you do´nt have such charts, when you do´nt even know they exist, does that make a difference in "the number of voyage days"?
NO
Ha.........

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### abhishekJunior Member

days at sea = int(hours at sea/24)+1, this is what john has given but here "int" refers what... if i know the amount of fuel i want to know the endurance?

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### John.EJunior Member

int = integer

I have to 'put my hand up' and admit to a 'tongue in cheek' reply to the question. It's my programming background coming through, sorry.

In an ideal universe the daily distance travelled would be constant as pointed out elsewhere in the thread a straight forward...

total distance/daily distance = days for passage (where - daily distance = speed * 24)

will give you an estimate.

However, due to several variables such as weather and currents it is unlikely that this will result in an acurate prediction. To compound this are several other unknows that upset a fixed distance travelled in a day, tidal access to ports, speed restriction in separation schemes, locking for canals and the like.

I suppose that you could err on the conservative side of things...

Assuming a constant 66% of hull speed over the ground for a given passage would give you...

(total distance / ((hull speed * 0.66) * 24) = days for passage

It would not be to much of a problem to substitue the 66% with any other value you felt reflected the actual attainable average speed.

13. ### apex1Guest

So now we go to make it a serious calculation, not these mathematical, crappy estimations.

Use the DRN rule!
Every morning you buy a bag of fresh breakfast rolls in the port you moored overnight, every morning they are fresh, crispy, warm and wonderful (at least around the Baltic), the morning you feel unsatisfied with the quality is Sunday! Now you have it easy to count onwards by using your fingers!
And endurance has nothing to do with fuel! It is the time between two bags of rolls, so max 24hrs!

This method is a proven navigation aid too! On the bag you find printed the name and adress of the bakery, so you know every morning where you are!

*DRN

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### John.EJunior Member

Is that a bit like an 'EP', estimating your position from Empty Plonk bottles (usually the cabin sole)? Or have I got confused with a 'DR' messed up by too much Drunk Revelling (frequently the end of pier)?

15. ### apex1Guest

The drunk revelling navigation is not recommended by the authorized bodies! The piers look too similar , especially on those enjoyable events! The empty plonk nav. is a more reliable way. At least you will almost always end up near your bunk (thats not the case with the DR system).
And moreover as a frequent drinker you know how to answer the original question very exactly! As long as there is some space where you can place one foot on the cabin sole, you sailed less than one day! (24hrs to stay mathematically correct)

Regards
Richard

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