[PnP] Ship Project - Ship Movement
Scott Adams
longshot at darktech.org
Sat Sep 2 06:03:46 CEST 2006
* Naval Navigation
This document covers aspects of naval navigation for the
Powers and Perils RPG system. First a study of Wind is given
followed by Earth based facts. With this rules for navigation
follow at the bottom.
* Wind Information
In order to know the rules and system for sailing on the high
seas and extensive waterways one must have a basic understanding
of the science of wind. After an explanation of wind properties
the document will discuss the rules on ship navigation.
Wind is moving air. Warm air rises, and cool air comes in to
take its place. This movement creates the winds around the globe.
Winds move at different speeds and have different names based on
their speed. Winds are also grouped by their direction. Easterly
winds blow from east to west, while westerly winds blow from west
to east. Winds occur when the surface and atmosphere warms up
by the rays of the sun.
The fastest recorded wind speed is 230 miles per hour and
occurred in New Hampshire in 1934. Although, winds can get faster
in tornadoes. The windiest place in the world is in Antarctica.
Since the Earth spins, the winds try to move to the right in
the northern hemisphere, and to the left in the southern hemisphere.
This is called the Corollas Effect.
Prevailing winds are a series of belts around the globe that
produce steadily blowing winds near the surface. Trade winds are
steady and flow towards the equator. Jet streams are narrow zones
of very strong winds in the upper troposphere.
Winds move at different speeds and have different names based on
the Beaufort Scale. This scale is shown by numbers from 0 to 12 which
goes from calm air to breezes to strong winds or gales .
The jet stream is a fast flowing, river of air found in the
atmosphere at around 12 km above the surface of the Earth just
under the troposphere. They form at the boundaries of adjacent air
masses with significant differences in temperature, such as of the
polar region and the warmer air to the south. Because of the effect
of the Earth's rotation the streams flow west to east, propagating
in a serpentine or wave-like manner at lower speeds than that of
the actual wind within the flow.
The equator receives the Sun's direct rays. Here, air is heated
and rises, leaving low pressure areas behind. Moving to about thirty
degrees north and south of the equator, the warm air from the equator
begins to cool and sink.
The sea breeze is most common along tropical coasts, being felt
on about 3 out of 4 days. The warmer temperatures, increased solar
radiation and generally weaker prevailing winds in the low latitudes
promote the development of the sea breeze. In general, the climatic
significance of the sea breeze decreases with latitude. In temperate
regions, it is generally a phenomenon of late spring and summer when
atmospheric conditions (higher temperatures, weaker large-scale
winds) are most favorable to the formation of the thermally
induced, sea-land circulation system.
Lakes may also develop a similar local wind circulation pattern.
Here the inland moving wind is known as the lake breeze. Lake
breezes are quite common in late spring and summer, for example,
along the shorelines of the Great Lakes, providing local residents
with a place of refuge during hot, humid summer days.
Wind speeds for maritime purposes are expressed in knots (nautical
miles per hour). In a discussion of wind direction, the compass point
from which the wind is blowing is considered to be its direction.
Therefore, a north wind is one that is blowing from the north
towards the south.
The Beaufort Scale:
Wind Speed International Effect of Wind
Scale (Km/hour) Description on the sea
0 <1 Calm Small wavelets
1 1-5 Light Air Small wavelets
2 6-11 Light Breeze Small wavelets
3 12-19 Gentle Breeze Large wavelets to small waves
4 20-28 Moderate Breeze Large wavelets to small waves
5 29-38 Fresh Breeze Moderate waves, many whitecaps
6 39-49 Strong gale Large waves, many whitecaps
7 50-61 Fresh Breeze Large waves, many whitecaps
8 62-74 Fresh gale High waves, foam streaks
9 75-88 Strong gale High waves, foam streaks
10 89-102 Whole gale Very high waves, rolling sea
11 103-117 Storm Very high waves, rolling sea
12-17 >117 Hurricane Sea white with spray and foam
To Convert Km/hour into Knots the conversion is 0.54 km = 1 Knot.
* Earth Based Facts
The following are actual facts from Earth ancient history.
1. Ships can typically sail in a 25 knot wind without suffering
structural damage. But beyond they suffer damage.
2. A ship can typically turn 3 degrees a second or 2 minutes
for a full turn. This was typical of Triremes. Based on Trireme
tests a ship going 6.1 knots at 32 strokes had a turn diameter
of 62 meters (1.9 ship lengths) with only a loss of 50% in speed.
While a ship going at 7 knots speed or 34 strokes had a diameter
of 110 meters and only a 20% speed loss.
3. Typically a fleet could sail 60 sea miles or 110 km per
day in the ancient world.
4. Power rowing was only in light knot winds and only efficient
up to 5-6 knots.
5. Propulsion was done by sails or oars. But with magic that
can also add or supplement another method of travel.
6. The type of sail used depended on purpose and the winds at
the time. Square sails were used in medium winds up to a lot of
wind. Square rigged sails were common in the open sea. The
spritsail was a foremast used to sail with a beam wind. Square
sails gave stability on large ships and heavy seas. Square
sails were typically fore and aft sails. Square sails were
common in the smaller seas like the Mediterranean.
Triangular sails (lanteen sails) gave better maneuverability.
These sails were typically tall and high peaked sails both fore and
aft positioned. Triangular sails were used typically during
weaker winds and in large oceans like the Atlantic.
Warships were oared typically while Merchant ships used
triangular sails typically.
7. Winds tend to blow stronger at midnight and dawn in some
areas of the globe.
8. Best sailing was at speeds of 5 knots generally. A galley
was known to get 7 knots at best speed.
9. Wind speeds: Favorable Winds - 4-6 knots (2-9 range).
Unfavorable winds - 2-2.5 knots against winds. In fleet operations
favorable gave 2-3 knots and Unfavorable 1-1.5 knots.
With wind 14 knots could be done for sailing
10. Typically rowers could get 5 knots at 30 strokes per minute.
With the ship moving 5 meters per stroke. A ship could go 8.5
knots at 46 strokes giving 6 meters per stroke. More trials show
33 strokes giving speed of 5.67 knots with best at 6.65 knots with
a range of 38-49 strokes. The best speed of 6.95 started from
15 stroke burst at 30 seconds in 500 meters. The first 5.67 speed
was over 2,000 meters. Twenty five strokes was the minimum run.
Typically rowers could go 6 knots from standing to rowing in
just 30 seconds. The average was 6.65 knots at 38 strokes in
a 2,000 meter space. It took 32 seconds for 7 knots in trials
and 7.7 knots in short bursts with 1 rudder down. It was possible
for 8 knots with 1 rudder down and one half up. This was done
during trireme trials over days. Thus on average rowing gave
an average of 5.4-5.77 knots or a 6.95 knots at best speed up
to 8.9 knots in a 8 minute burst. The max typical speed under
oar was 9 knots.
It has also been shown with an average 8.6 knots for a 17-18
hour day with 7-8.5 hours of just rowing the ship could make 129
sea miles or 236 kilometers. But this was extreme circumstances.
11. Surface currents makes up only 10% of the water in the ocean
while Deep currents make up the other 90%. Surface currents cover
the upper 400 meters of the water surface. A wind blowing for 10
hours over the water will move the surface water at 2% of the
wind speed. Thus a 10 knot wind improves speed by 0.2 knots.
12. It is common to determine 1 knot of speed equal to 1 nautical
mile per hour of speed. Thus if a ship travels at 20 knots in one
hour, it would have traveled 20 nautical miles.
13. Air at the equator moves with the ground below, so its
east-west motion matches that of the equator.
14. In the age of sailing ships, sea-captains took advantage of
the global air flow system. Sailing from Spain to America, they
would go closer to the equator, a more southern route that took
advantage of the "trade winds." blowing from the east. Sailing
back home they would go further north and use the westerlies.
15. Merchants sailed with an average speed of 5 knots. They
tended to sail zigzag to go with winds. This resulted in twice
as long trip usually.
16. The Trireme was used before penteconters. They had 25 Rowers
on each side with 3 tiers of oars (1 oar per man). Some were known
to travel 14 knots per hour but only in good weather. They were
so light they could be easily blown off course in high winds. They
used broad bladed steering oars (2 of them) each handled by 1 man.
27. Quinqueremes came after Triremes. They were 3-4 tier oared
boats with 1 oar having 2 men. They were more heavy and less prone
to being blown off course.
28. Cargo ships typically had an average speed of 5 knots. They
had to sail zigzag courses to go with the best winds. This
typically made trips twice as long though.
* Sailing in the Perilous Lands
The following information is on rules for navigation and sailing
in the Perilous Lands. Obviously there are two methods to navigation
in the game - sailing and rowing. Rowing may not require a full day
of rowing but when the winds are short or when a constant speed is
needed, rowing is used. One can alternate between the sailing and
rowing rules as needed. Magic may improve both methods of travel.
A Referee who wishes to create realistic weather systems for
weather and navigation should decide where the equator is. According
to Richard Snider the equator runs through the Ro'babza hidden
city. This places the equator far to the south on the Perilous Lands
map. This would clearly make the northern continent far cooler than
those lands in the south for sea heat patterns. Based on earth
global air flow patterns we can then associate certain patterns to
certain areas of the Perilous Lands. The northern edge of the Sea
of Tears would tend to have strong winds going west to east while
the southern edge would have moderate winds going east to west but
may tend to stay non-constant. The top northern edge of the Lands
would have west to east winds. The great islands like A'korchu,
Fomoria and Lemasa may have their own patterns. But tend to have
west to east in the northern side and east to west in the southern
portions.
But the Referee can assign his own wind and current systems for
each area he is gaming in. If you sail near Clima on the north
side the winds would tend to be from west to east. But if the
Referee wishes them they could move north to side like many areas
of the nortern areas may tend to do.
For ships navigating the Perilous Lands waters the following
rules can be applied:
1. Design Global and Local Weather, Wind and Water currents.
This would include direction, speed and general climatic conditions.
This will setup the typical sailing patterns. Referee should apply
seasonal data to these local systems. In summer winds may be stronger
with more storms compared to winter when direction of wind may
change randomly. At the very least the Referee should determine
local weather and water systems for his area of play.
2. The Referee should also determine specific water navigationl
sites and areas. This would include reefs, sandbars, unusually
fast water currents, seamounts, marsh and swamp areas and even
underwater hazards like sunken ships.
3. To add realism the Referee can also determine navigational
aides that might be present. This would include buoys, beacons,
flags, lights and lighthouses.
4. The Referee will then have to determine the type of ship
that is being used for travel. Some may only sail while others
only row. Others may do a combination of rowing and sailing.
Once this is determined the following charts can be used.
* Movement Charts
The following information is on rules for navigation and sailing
A. Rowing
A average NPC class rower will have a starting EL of 1 with a max
EL of 4 typically. A PC class character will average EL10 with
a range of EL 10-20. It is estimated 4.5 strokes is equal to 1
knot of efficient speed roughly. Use the first chart if you wish
to have a simplified movement scheme. Use the second if you wish
to determine more exact methods of travel under good winds. Use
the Burst chart for quick start speeds like in combat. Fast
Triremes are known to have been 20-50% more agile.
1. Simple Rowing Speed [Per Strategic Turn if no replacement crew]
Ship/Boat Type Range
Barge 10 miles
Merchant 20 miles
Warship 80 miles
2. Typical Rowing Movement for an average rowing ship
Number of Knots
Strokes Speed Meters Per stroke (average)
* * *
25 4.88 3.5
30 5.00 3.55
33 5.67 4.025
35 5.89 4.18
38 6.65 4.72
39 7.92 5.62
40 8.50 6.00
44 9.00 6.39
* - Under 25 strokes was rare
Average - 5.4-5.77 knots cruising, 6.95 knots in a burst
Meters per Knot was determined at 0.71 per knot.
Above table is based on historical data.
3. Speed Bursts
Given a area of 2,000 meters the following is based on
trials for speed bursts:
Number of Number of Burst
Strokes Seconds Speed (knots)
15 30 5.65
20 32 7.00
21 33 7.70
22 35 8.00
4. Speed Modifiers [Optional]
The first speed modifier number is for cruising speed and
the second is for speed bursts of quick speed. All modifiers
are additive. Number of Rowers may influence a ship's speed
as well as Tonnage but there is no hard data to reflect in
this chart at this time.
A. Ship/Boat Type
Ship/Boat Type Speed Modifier
Barge x0.125 / x0.20
Merchant x0.25 / x0.10
Warship - / -
Fast Trireme x1.25 / x1.20 to x1.50
Wind Speed
[With Ship] [Against Ship]
No Winds - / - - / -
Poor Winds x0.25 / x0.125 x0.125 / x0.05
Average Winds x1.00 / x1.00 x0.25 / x0.10
Good Winds x1.25 / x0.25 x0.375 / x0.125
Superior Winds x1.50 / x0.75 x0.50 / x0.25
Crew Skill
EL Modifier EL Modifier
0 x0 / x0 11 x0.165 / x0.330
1 x0.015 / x0.030 12 x0.180 / x0.360
2 x0.030 / x0.060 13 x0.195 / x0.390
3 x0.045 / x0.090 14 x0.210 / x0.420
4 x0.060 / x0.120 15 x0.225 / x0.450
5 x0.075 / x0.150 16 x0.240 / x0.480
6 x0.090 / x0.180 17 x0.255 / x0.510
7 x0.105 / x0.210 18 x0.270 / x0.540
8 x0.120 / x0.240 19 x0.285 / x0.570
9 x0.135 / x0.270 20 x0.300 / x0.600
10 x0.150 / x0.300 21+ x0.015 / x0.030 per EL
Should use a Crew or Group Average EL.
Magic - As stated by the Magic Item or Spells.
Example: A Barge is being chased by a Warship. The Barge
has a typical cheap crew. Barge captain orders ship to oar.
The Rowing Officer beats 30 strokes giving a 5 knot speed.
The Barge crew EL is only 1. The Warship orders a 35 stroke
beat giving it a 5.89 average knot speed. Both ships only
need to cruise to close in before doing any burst speeds.
There are good winds with both ships. The Warship crew is
skilled with a EL3 on average. With modifiers the final
speeds are as follows:
Barge - Speed - 5.00 Warship - Speed - 5.89
EL - x0.015 [1] EL - x0.045 [3]
Winds - x1.25 Winds - x1.25
Type - x0.125 Type - -
Final Speeds - 6.95 - 7.63
The Warship should be able to catch up in a short time.
B. Sailing Navigation
Use information in the first chart (1) for a quick and dirty
system of sailing speeds. But you'll still need to determine the
type of winds that are in the area (see #2). Once the Wind Type
is determined use #3 to determine the random wind speed.
1. Simple Sailing Speed
The Following figures are for one strategic turn of sailing.
These figures are for ships that hug the coastline (90% of the
ships tend to do so). At night these ships lay anchor.
Wind speed
Ship Type Poor Average Strong
Merchant 10 miles 20 miles 40 miles
Warship 20 miles 60 miles 100 miles
2. Wind Type
Roll D100 for the Season of the year:
Season
Wind Type Spring Summer Fall Winter
No Winds/Trace 01-05 01-03 01-02 01-02
Low Winds 06-21 04-19 03-17 03-13
Poor Winds 22-35 20-35 18-32 14-29
Average Winds 36-55 36-76 33-68 30-50
Good Winds 56-95 77-93 69-94 51-97
Superior Winds 96-100 94-100 95-100 98-100
3. Wind Speed
The Wind Speed could be for one hour of time or serve as
an average speed for the entire Strategic turn. Roll D100
on the following chart:
Wind Type Roll Knots Beaufort Scale
No Winds/Trace 01-50 0 0
51-100 1 0
Low Winds 01-33 1 1
34-66 2 1
67-100 3 1
Poor Winds 01-25 3 2
26-50 4 2
51-75 5 3
76-100 6 2
Average Winds 01-20 6 3
21-40 7 3
41-60 8 3
61-80 9 3
81-100 10 3
Good Winds 01-17 10 4
18-34 11 4
35-51 12 4
52-69 13 4
70-87 14 4
88-100 15 4
Roll Knots Scale Roll Knots Scale
Superior Winds 01-02 15 5 51-52 40* 8
03-04 16 5 53-54 41* 9
05-06 17 5 55-56 42* 9
07-08 18 5 57-58 43* 9
09-10 19 5 59-60 44* 9
11-12 20 5 61-62 45* 9
13-14 21 5 63-64 46* 9
15-16 22 6 65-66 47* 9
17-18 23 6 67-68 48* 9
19-20 24 6 69-70 49* 10
21-22 25 6 71-72 50* 10
23-24 26* 6 73-74 51* 10
25-26 27* 7 75-76 52* 10
27-28 28* 7 77-78 53* 10
29-30 29* 7 79-80 54* 10
31-32 30* 7 81-82 55* 10
33-34 31* 7 83-84 56* 11
35-36 32* 7 85-86 57* 11
37-38 33* 7 87-88 58* 11
39-40 34* 8 89-90 59* 11
41-42 35* 8 91-92 60* 11
43-44 36* 8 93-94 61* 11
45-46 37* 8 95-96 62* 11
47-48 38* 8 97-98 63* 11
49-50 39* 8 99-100 64+* 12-17
* Over 25 Knots ships begin to take damage.
To determine distance traveled 1 knot = 1 nautical mile
thus a ship sailing in a 5 knot wind for one hour sails 5
nautical miles in that hour.
4. Drifting
A ship can be carried away by currents causing the ship to
drift off course. To determine the Navigator should roll
each day 2D10 + his Navigator Skill EL. Then consult the
following table:
Final Result Drift Situation
01-11 High Drift
12-17 Low Drift
18+ No Drift
Low Drift [Roll 1D6]
1-3 Move North-West or South-West 1 Hex
4-6 Move North-East or South-East 1 Hex
High Drift [Roll 1D6]
1 Move North 1 Hex
2 Move North-East 1 Hex
3 Move South-East 1 Hex
4 Move South 1 Hex
5 Move South-West one Hex
6 Move North-West one Hex
[For Low Drift the direction depends on the previous direction
they were moving. Example: If ship is sailing south and low
drift occurs a 2 is rolled. The ship moves south-west since the
ship was going south.]
* Final Notes
The above information is not meant to be all inclusive for every
boat and ship type. Given two boats a rowboat and a merchant
ships the rules above may have to be slightly modified. The Referee
will have to play with the above rules to fit their needs.
There are many other aspects of navigation not covered here like
techniques and technology. Some ancient techniques include
latitude sailing and "dead reckoning". In latitude sailing a
boat would sail on the lines of latitude. Sailors would use the
sun's position using sun dials, hands or other sun devices at noon.
This would yield a angle used in calculations. They would then
sail parallel to known points of existing lands. This method
was more accurate than dead reckning which used guesses of where
a ship was at any one time when the sun was not handy. Technology
for sailing would include advanced instruments like the astrolabe,
sextant, sun dials among many other items. These items are
beyond the scope of this article as I meant to cover only movement
in navigational terms.
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