Meeting # 3 -- Boats
September 10, 2008
http://historicalcharts.noaa.gov/tiled_jpgs_done/zoomifyURLDrivenWebPage.htm?zoomifyImagePath=00-9-1939
West Coast of US � NOAA # 501 – 1: 3,500,000
http://historicalcharts.noaa.gov/tiled_jpgs_done/zoomifyURLDrivenWebPage.htm?zoomifyImagePath=501-10-1992
Gulf of Mexico and
East River above
Reprieve of 2nd Meeting – Ocean and Local Waters
Tides and tidal currents primarily a coastal phenomenon – Even
there, of differing significance
Rise or fall of 5’ in depth no big deal out in deep ocean [averaged 12000’]
Mediterranean tidal swing --< 1’ --
little resultant tidal current
Bay of Fundy tidal swing in 6 hours of > 50’
6 hours = semidiurnal
(two full swings a day /24 hours 30 minutes)
High tide on Tuesday at 3:00 (1500); on Wednesday at 4:00….
Characteristic of east coast of US – where continental configurations not
crucial
diurnal = every 12 hours à Gulf of Mexico –
Galveston 8:00 à
23:00
varied – varying time spreads
between high and low tides à California coast
Ocean currents
Prevailing water flows over large distances; may have some seasonal
variations
Southern Hemisphere
Humboldt
Current
African heat/winds
moving to S Asian snows in summer
Pacific – Atlantic à both have clockwise
currents in mid northern latitudes (30-60 North Lat)
North Pacific – brings cold air/water from
North Atlantic – brings warm water from Gulf of Mexico to western Europe – The Gulf
Stream
[the left hand/western side of the sub-tropical North Atlantic gyre]
sub-tropical
gyre – down Iberian coast/Canary current
trade winds across 30th parallel
Up east coast and out
across at 50 degrees North
The southern route to the
sub-polar gyre –
counterclockwise
Up Scandinavian coast; across Greenland; down the
The northern
route: Vikings/Cabot/Jacques Cartier/Champlain
Both routes longer but usually faster – northern route with
fewest days off shore à island hopping
English Channel/Bottom of Ireland at 50
Lat – straight across to top of Newfoundland – right into the wind and current
Why do these gyres occur? –
1. Continental configurations (Mid North Atlantic like a bowl)
2. Coriolis Effect/Geostrophic
-- Earth rotating in eastward direction on its axis every 24 hours – pushes
water to the north
of Equator to the right (clockwise)
Other ocean flows that interest oceanographers/submariners – upswells/tsunamis/ temperature/salinity/biomass differences
-- of less interest to our/we surface
skimming sailors
OK?
Boats and ships – boats smaller, carried on ships….boats open to the elements; ships decked??
Ship = 3-masted vessel with > 1 sail per mast
Shipbuilding -- The most impressive technology of the
Ancient and Medieval worlds?
Not as big as temples, cathedrals,
mosques, castles, palaces….
But ships subject to much more
variable/stressful circumstances than fixed buildings
Much more complicated than
cannonry/heavy guns developed in 15th
century
Material requirements – multiple
woods/iron/cordage/cloth/tar…
Ships as labor intensive at a highly
skilled level --
Ships as transportable/self-propelling machines operating at the intersection of two mediums/media – water/air
Water 800 times more dense than air
(.0125)
Air movement upwards of 100 mph –
Force 12 on Beaufort Scale
Ancient accounts of shipbuilding
The Odyssey – Athena helps Odysseus build a ship to get home
The Old Testament – Noah’s Ark
New Testament -- St. Peter’s fishing boats and St. Paul’s shipwreck
Phoenicians/Egyptians/Greeks/Polynesians
Arab vessels crossing
Chinese seagoing vessels of the 1420s…
Motivations for waterborne travel
1. Efficient movement of peoples
(warriors/missionaries/merchants) and goods across substantial distances
exploit the world’s waters as
transportation surfaces
Alternative being movement across the
land – energy expenditures overcoming friction when moving goods across ground
Sleds/wheels not nearly
as efficient --
Human can carry 50 lbs 25
miles in a day’s hike – consume 2500 calories
Horse/oxen/camel/elephant/donkey
go farther
2. Gain access to the resources of the oceans – offshore fishing
3. Adventure/recreation??
Focus on European shipbuilding developments
Not because
they were the most advanced à Arabs/Chinese
How much inter-regional technology
transfer??
Lateen
sail as Arab development? Independently come by in the West?
But those that permitted/enabled the
seaborne settlement of the
“The Invention of the Seagoing Ship” -- in place by time
of
Basic considerations:
1. Use of materials that float/have buoyancy/less dense than
water (or can be shaped to be so)
Wood – but also air-filled skins,
clay pots, à iron/steel/gold….
Advantages of wood:
Widely available, if exhaustible
resource (Mediterranean by time of X;
density/permeability
properties
Carpentry possibilities
2. Wood shaped to accommodate passengers/gear/cargo
John White’s burnt out log boats
of 1580s --
“The
Manner of Making Their Boates”
“Indians
Fishing”
Tree trunks/logged à sawed/milled into
lumber/planks – required iron technology
Eastern Mediterranean/Northern
Europe
Cheops funeral boat of 2500 BC
Greek Bireme (350 BC)
Gokstad boat (890 AD)
Exterior planking overlapped/or
joined? à
abutted
Build outside in or inside out
(skeletal)? à
frame out
Propulsion developments:
Earliest known boats propelled by river water movement –
floats/rafts
Pulled along from riverside paths
Self-propelled boats – by oars and oarsmen -- kayak
Galleys – Algerians in 19th century
Propelled by the power of prayer – St. Brendan
Secondary propulsion -- Auxiliary sail set from a removable/stowable mast (“stepped”)
Odysseus’s sleek black ships
Single mast stepped and braces/stays;
Single rectangular sail sheeted
Used when wind (not much in Med)
blowing from astern
Oar-propelled boats – not dependent upon wind or wind’s direction à kedging out of harbor
Oarsmen needed to be close to the
water à
limited freeboard à limited decking
Greek
Trireme
Limited
seaworthiness
Limited cargo space; high labor costs
(slaves/captured enemies)
Northern
Earlier
greater reliance on wind as primary propulsion
Clunky
high-in-the-water wind-driven boats – clogs/hulks…
Vikings across the top of the
Gokstad boat (890 AD)
Bayeux tapestry boats of 1066
1200 in Mediterranean, North Sea and Baltic Sea
emergence of an amalgam – the ship of the late 15th century
Wooden boxes with rudder astern; stout mast carrying substantial sail
Reasonably watertight;
storm-worthy; increased cargo
capacity
Reluctant to set forth in winter; reluctant to sail at night – “hugging the
shore”
Not ready to venture out into the
What’s still needed;
1. Ships with more elaborate/versatile sail systems
Permanent masts/ multiple sails
per mast
2. Some additional navigation aids (next meeting)
3. Some routes that permit ships/crew getting back from long
forays into/across Atlantic
Portuguese proceed down the
West African coast
Azores
Madeira
Canaries
Cape Verde
Route back – Not reverse course -- wide clockwise swing out
into Atlantic and up until catching the North Atlantic limb
and sailing down to
Use of fore and aft sails to cope with winds off and forward of beam – Lateen sails of Arab design
Portuguese caravel redonda – early 1400s
Caravel à Carrack àgalleon à full-rigged ship
Increasing the sailing arc – purposeful movement/sail
propulsion when wind not directly astern
Stay sails
Flying jib
Lateen or spanker mizzenmast
Bernoulli principles operative in a fore and aft sail – sail
an air foil much like a plane’s wing
Plane is lifted by the creation of a partial vacuum (because air passes more
quickly over its surface tha it does over the surface
of the bottom side of the wing)
on the upper side of
wing à
plane lifted
Ship is pulled forward by creation of partial vacuum on the front side of sail
(because air passes more quickly over its surface than it does over the surface
of the back side of the sail)
Sailing arc of a square sail set perpendicular to the ship’s
center line -- 160°
Sailing arc of a
triangular/trapezoidal sail set parallel to the ship’s center line -- 240°
Beating to windward
Wind from the north -- 0°
Ship’s sailable courses trying to sail north
-- square rig à starboard tack (to the east) >110°
-- or
port tack (to the west) < 250°
-- fore and aft rig à > 60° starboard tack (to the east)
<
300° on port tack
Can make headway along rhumb line while tacking 60° either side of the wind
So why were the explorers’ ships all three-masted square-rigged ships?
Sail surface of square/rectangular sails larger
Prevailing winds proved to be regularly astern
Ample crews to work the sails from aloft
Fore and aft rig comes into favor for smaller, faster, less
labor-intensive undertakings
Sloops
Schooners
Variations:
Gaff-rigged to enlarge sail surface without needed more crew
Recreational boats of 19th/20th
centuries….
Most Tall Ships (The USCG
Eagle as an exception)