Log of SV Free Spirit and ships company

The chronicles of the schooner Free Spirit and her crew, embarking on an open ended journey upon the great rolling heap. Free Spirit is currently pursuing humanitarian and commercial goals in the Dominican Republic, on the island of Hispaniola. Working under the Ocean Reach USA and Paradigm Research banners, she is serving as logistics headquarters, workshop, and development laboratory for many ongoing projects. This is the log of her journey.....

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Saturday, September 30, 2006

Hole in the ground.


Desert Sunset, on the way to Wagontire.






Valin, Dad, Tamer, Drake & Blayde

Between Junction City and Wagontire, there is a place called "Hole in the ground", not to be confused with nearby "Big Hole", or with similarly named "Crack in the Ground".

Suprisingly enough, it is a gigantic hole in the ground. More precisely,
Hole-in-the-Ground is a volcanic explosion crater or maar located in Central Oregon on the edge of Fort Rock basin. At the time the crater was formed between 13,500 and 18,000 years ago a lake occupied most of the basin and the site of the eruption was close to the water level near the shore. The create is now 112 to 156 meters below the original ground level and is surrounded by a rim that rises another 35 to 65 meters higher. ...

The crater was formed in a few days or weeks by a series of explosions that were triggered when basaltic magma rose along a north-west-trending fissure and came into contact with abudnant ground water at a depth of 300 to 500 meters below the surface. After the initial explosion, repeated slumping and subsidence along a ring-fault let to intermittent closures of the vent, changes in the supply of ground water, and repeated accumulations of pressure in the pipe. - (Lorenz 1971)




Looking down, thinking about it...




Eventually (some would say inevitably), I succumbed to the temptation to ride down the rugged trail to the crater floor some 600 feet below - which turned out to be quite technical at times for a bycycle - motorized or not. Nonetheless, my trusty steed delivered me safely to the crater floor and whisked me back up to the trailer rim with only a modicum of exertion. Quite an impressive view, especially from the crater floor. Sadly, I did not find any artifacts or debris from alien spacecraft, though I must admit to expectations given the erie nature of the scene.



That tiny speck in the smooth area (3rd from right) is me. My bike is the other tiny speck well to the left. The pictures do not effecively convey the scale, but you can imagine it if you think for a while.

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Introducing Propcalc 4.0

Use Propcalc to easily match your hull with your engine, transmission, and propeller
Put the known data in the top fields, then hit the Update button to get the answers.
Results, of course, should be verified by a Naval Architect or qualified surveyor.
Data is provided for three bladed propellers of average type
For two or four bladed props, use the modifiers shown below.

Fill out the fields as follows:

Vessel LWL (ft) = Waterline length
Vessel Disp (lbs) = Vessel displacement
(max) HP = Rated Engine Max HP
Engine RPM max = Engine RPM at Max HP
Engine RPM cruise = Desired or estimated cruise rpm
(Cruise or Max) Kts = Speed to work the calculations for
Slip = Propeller efficience. 45% is average for a displacement cruiser.
Gear ratio = 1: Gear ratio of transmission
SL Ratio Adj. = This value will be added (or subtracted, if a negative value) to the calculated S/L ratio.

Key information:

If the "hp required" is greater than the "cruse HP", you have your cruise RPM set too low for your engine parameters.
If the "hp required" is significantly less than the "cruse HP", you have your cruise RPM set too high for your engine parameters.
If the "hp required" is greater than the "Max HP", then your target speed is too high for your engine/hull parameters.
The S/L ratio is calculated automaticaly based on your input. It can be adjusted if necessary, but normally it should be left alone.
If the calculated S/L ratio exceeds S/L MAX, then the results are likely to be non-predictive. Try a lower speed requirement.
SL Ratios of 1.1 - 1.4 are typical of displacement hulls. Semiplaning or planing hulls can go higher.

Typical propeller slip values:

Sailing auxiliary, barges, etc less than 9 Kts............45%
Heavy powerboats, workboats 9 - 15 Kts....................26%
Powerboats, Lightweight Cruisers 15 - 30 Kts..............24%
High speed planing boats 30 - 45 Kts......................20%
V bottom race boats 45 - 90 Kts...........................10%


Note:

it is possible to get irrational answers by irrational input , I.E specifying excessive speed for hull type and length
Any attempt to exceed hull speed (1.34 times the square root of the waterline length in feet) with a displacement hull are likely
to fail unless the hull is extremely fine (multihull) or otherwise exceptional. In such cases, an S/L adjustment would be in order.

2 and 4 bladed props:


For two bladed propellers, multiply the diameter by 1.05, and the pitch by 1.01
For four bladed propellers, multiply the diameter by .94, and the pitch by .98


PROPCALC
  Inputs:
Vessel LWL (ft) =
Vessel Disp (lbs) =
  (max) HP =
  Engine RPM max =
  Engine RPM cruise =
  (Cruise or Max) Kts =
  Slip =
  Gear ratio = 1:
  SL Ratio Adj. =
   
    Solutions:
  Prop rpm max =
  Prop rpm cruise =
  Pitch =
  Diameter =
  Static Thrust =
  Cruise HP =
  Cruise HP% =
  SL Ratio =
  DL Ratio =
  SL Max =
  HP Required =