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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Wednesday, June 27, 2007

My Beautiful Skylight

The beginning..... Nathalie and Olivier have spent the last few years refurbishing a wooden boat that is in France. Nathalie was a huge wealth of information, and taught us how to do this job correctly.

The first step was sanding every surface of the skylight, and then washing it down with soap and water.

The main repair that was needed was reinforcement of the base where it seats on the deck of the boat. Here we are applying the first layer of fiberglass with epoxy. First, you apply a layer of 2 part epoxy, then you lay the pre-cut piece of fiberglass over that area. The next step is brushing on epoxy until you cant really see the fiberglass any more. In the heat, it was quite a tricky operation, because the epoxy would cure in minutes.

Brush on......

After about 3 coats of epoxy it is time to re-sand every surface and prepare for varnishing.

Sanding away! It was kind of tricky to sand off the waxy layer of epoxy, without sanding through any part of the fiberglass.

As I have pointed out before... My dear Nathalie always has a beautiful smile on :-)

Oh ya... The doors for the skylight all had to be done as well! Although they did not require any fiberglass, they still needed to be applied with epoxy and sanded between every layer.
Here is Tamer test fitting the doors, they were marked when they were removed months ago, but the markings had weathered off.

First coat of varnish finished!

First side finished!

Installed, and awaiting one more sanding and coat of varnish. One thing that I learned from this project, was that it is well worth investing in an expensive varnish. It is really easy to apply, and dries super smooth and without brush strokes.

I did not remember to take a picture of the doors installed before we left the boat, I will have to get one when we return!


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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%


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

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. =
  Prop rpm max =
  Prop rpm cruise =
  Pitch =
  Diameter =
  Static Thrust =
  Cruise HP =
  Cruise HP% =
  SL Ratio =
  DL Ratio =
  SL Max =
  HP Required =