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, April 22, 2006

Sophia



In 1943 under the black gloom of war, the Knarr was born in Norway.

Designed by Erling L. Kristofersen, approximately 150 Knarrs were launched in Norway over the next 25 years, and she became the most popular boat of her size in the region.

Today, the Knarr fleet numbers approx. 120 boats in Norway, approximately 50 in the USA,
and well over 120 in Denmark. In 1954 she was approved as a national one-design class
in Denmark. Borresen's yard in Vejle, Denmark, is the only licensed builder of the Knarr,
with a production so far of more than 160 yachts, since 1974 built in fiberglass.

The Beautiful wooden Knarr Sophia is berthed next to my slip in San Francisco, and this morning I had the opportunity to talk with her crew about her history. Her keel was laid 1963, and she has undergone a couple of refits since, including a complete rebuild from the rail up. She is now in beautiful condition and is lovingly cared for by her crew, daysailing and racing in the bay.

Credit must be given to those who, like the crew of Sophia, keep little pieces of our history alive through their passion and dedication to the task. It is a minor credit to humanity to see works of art such as this little Knarr out sailing as living history, rather than collecting dust in some cryptlike museum - keep up the good fight, lads!

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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 =