Simviation Forums

Can somone explain to me how the concept of the Ships Bells work?  I know it measures time, but not exactly how.

The other thing is the origin of Knot as a measure of speed.  As I understand it, a stick would be placed on the end of a line with knots at certain increments, then thrown overboard and however many knots played out in a certain time indicated the speed?

Wierd stuff.  Very arcane.  ::)

I'm not sure how they measured knots, but it is one nautical mile per hour.  So maybe it was a rope with a weight on the end with knots every foot or so and they divided the number of knots that went through by the time.

Confused yet?

I need to stop studying for that big physics exam tomorrow.  ;D

http://www.physlink.com/Education/AskExperts/ae400.cfm

That link contains some info

That's a very good link Eno. I can understand how it works but what I've never seen anywhere is how far apart the knots are on the rope. There must have been a standard measurement & an easy way of doing it. Surely this is the most important thing to get right for accuracy.

This link explains the Ships Bells & Watch system. http://www.boatsafe.com/nauticalknowhow/shipbee.htm

I think the spacing was about 6ft or the length apart of the sailors arms at full stretch.
Don't take this as verbatum more research required.

cheers
eno

I think the spacing was about 6ft or the length apart of the sailors arms at full stretch.
Don't take this as verbatum more research required.

cheers
eno

That makes sense. I'll go with that unless anyone can come up with something different.

http://www.navyandmarine.org/planspatterns/speedlog.htm

Yup ........... tis 6 ft approximately.

Don't ya just love Google.

http://www.navyandmarine.org/planspatterns/speedlog.htmYup ........... tis 6 ft approximately.

Sorted. Thanks.

Don't ya just love Google.

Couldn't do without it.

Next question.

So if it is a approximate 6', then how is it possible to be accurate enough for messuring speed of a aircraft?

How did they come up with the standard using the "rope practice" for wind speed?
I mean a ship, no two would weigh the same do to passengers, cargo and the likes, so surely if you had two ships side by side each weighing a different amount the "knot" speed would differ???

I'm confused better go check out the links provided before asking any more questions.

So if it is a approximate 6', then how is it possible to be accurate enough for messuring speed of a aircraft?

More accurate methods were used by the time aircraft came on the scene. The system gives the name to the "knot" which is 1 nautical mile per hour.*

How did they come up with the standard using the "rope practice" for wind speed?
I mean a ship, no two would weigh the same do to passengers, cargo and the likes, so surely if you had two ships side by side each weighing a different amount the "knot" speed would differ???

The size & weight of the ship is immaterial. If it's moving in relation to the water anything dropped over the stern will appear to move away from it at an equal speed. This in effect measures "airspeed" as opposed to "ground speed" or in this case "water speed", the speed through the water.

*PS. This is very useful for navigation purposes as 1 nautical mile = roughly 1 minute of latitude.

PPS. I just remembered the simple mechanical airspeed indicator originally fitted to the Tiger Moth & other similar types as recently as the 1930s. This was a lever attached to one of the wing struts with a blade at the free end. By blowing back against a spring the airspeed could be measured by the movement of the lever against a graduated scale fitted behind it. This is a very similar principle to the "Chip Log". I believe it worked very well. The more basic something is the less chance of it going wrong.

I posted this shot in the Photos forum some time ago. You can see the mechanical ASI on the front wing strut. Sorry it's not clearer.

Some of this has already been said, but to clarify:

In the "good ol' days" (before steam power) they measured the speed of boats by throwing a rope tied to, essentially a parachute overboard.  The rope would hit the water and stop, and spool out over the side of the ship.  They would use an hour glass like device to measure the time and the number of knots which passed over the rail would be the ship's speed.  The hour glass was sized such that this translated to nautical miles per hour, a nautical mile being related to roughly the size of a minute of lattitude.

When airplanes finally came around the "knot" was a commonly used unit of measure.  The nuatical tradition kinda stuck with planes and the "knot" was adopted by the aviation industry.  Now, I don't think anyone ever measured the speed of their planes with a knotted rope, parachute, and hour glass, but old terms die hard, especially nautical terms.

Consider this:

The terms "port" and "starbord" were invented by the Norse.  The vikings would head out of port and go left (because of geography.  They didn't have any particular fondness for left as such).  Therefore "port" was always off to the left side of the boat.  The right side of the boat was where the rudder or "steerer board" was.  This translated to "starbord".  So the right side of the boat was "starbord" and the left side was "port".

Here we are a couple thousand years later and we're still calling left "port" and right "starboard" despite the fact that we're leaving port and going right just as often as we go left and the rudder is no longer on the right side of the craft.

The terms "port" and "starbord" were invented by the Norse.  The vikings would head out of port and go left (because of geography.  They didn't have any particular fondness for left as such).  Therefore "port" was always off to the left side of the boat.  The right side of the boat was where the rudder or "steerer board" was.  This translated to "starbord".  So the right side of the boat was "starbord" and the left side was "port".

Your almost correct here. Starboard is called starboard for the very reason you said. On a longship the steering paddle was on the right hand side of the vessel hence steerboard and so starboard. Now, because the rudder was on the starboard side, and bear in mind the rudder is quite important in a boat, they would want to avoid damaging it at all costs. So when they went into port they moored up to the quay with the left side inboard hence "port".

Ships bells kept time using a half hour glass. A traditional watch system contains five four hour shifts with two two hour "dog watches" between four and eight pm. This was to ensure that everyone knew that they wouldn't have the same watch two days in a row. Anyway, every half hour a bell would be struck. So one bell after the first half hour, two after an hour, three after an hour and a half etc. Bells were struck in groups of two. E.g. Ding-ding -pause- Ding for an hour and a half.

The principles of the "knot" system has been done to death here. But I must throw in that this too was done with an hour glass. Usually a 30 second glass, or if they were going really quick, a 15 second glass.

Now, how did this get transfered onto the airways? My guess is through airSHIPS. The whole thing works on exactly the same principles, only slightly faster.

I must also say that all i've just written is probably in one or all of the links supplied in this thread so far.

Thanks guys some good knowledge there!!
I have now learned something I never knew and never really thought about.
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