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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Sunday, May 06, 2007

The Bow Sprit ~ Part 3 ~ A Work Of Art

Putting on the new bowsprit would require hours of prep and some fabrication.


The naked cutwater, ready to be refinished.



Grinding the top smooth. The flame cut edge was rough in spots, so a bit of grinding was required to get a smooth finish.



The new bowsprit would bolt on, rather than be welded to the cutwater. This is closer to the original design - which calls for a wooden spar bolted to the deck and cutwater, and allows the bowsprit to be removed for service.



Welding a stainless insert into the cutwater. This is where the bobstay will attach.



Welding the deck pad, where the aft end of the bowsprit will be bolted to, onto the deck.



The mounting bracket gets welded to the deck plate....



.... And the bowsprit gets ready for paint.



Lifting the finished bowsprit onto the deck. Even though the spar is entirely of steel, it only weighs about 200 lbs.



Getting ready to mount the aft end into the bracket on deck....



...Like this....



...and there it sits. You can see the old bowsprit down below.




Then the 'sprit is bolted to the cutwater. Note the space for fingers in between, giving room to paint and inspect.



Setting up the whisker stays. These keep the bowsprit centered side to side.




The whisker stays attach with 5/8" galvanized shackles.




The axles and anchor rollers must be put on and adjusted....



...and the dolphin striker (petter) attached.



The bobstay chain being installed and adjusted.



And with a bit of tuning, the bowsprit installation is complete.

posted by CT | 10:51 AM

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 =