How I used what I learned in Math and Science

to help me build 21 foot wooden boat

Ralph Cohen (Portland, Oregon)

Building challenges

• Approximately 350 pieces, mostly different from each other, individually measured and cut

• Unlike a house or furniture, almost no right angles

• Tools to measure angles (demonstrate)• For right angle (90 degrees): “square”

• For other than right angle: “bevel gage”

• Seams (where wood “meets” wood - must be watertight

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Desired features

• Engine

• AC and DC electrical systems

• Inside steering

• Sleeping area

• Galley (kitchen)

• Toilet

• Heater

• Safety equipment

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My preparation

• Woodworking classes

• Made furniture

• Attended 2 week boat building class

• Mechanical engineering degree –experience designing similar “stuff” (mechanical, plumbing, electrical)

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Step 1a: Decide what kind of boat to build

• How big?

• How fast?

• Steer from inside or outside?

• Type of engine?

• My building skill level?

• Availability of suitable wood and materials nearby?

• How many years available to build?

• [next slide for answers…]

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Step 1b: Decision process for boat to build

• How big?

• Sleep 3, galley, under 3000#, 21 foot limit in back yard == 21 foot

• How fast?

• Slow ~ fuel efficient, I like sailing ~ slow == 5 knot (5.5 mph) cruise speed

• Steer from inside or outside?

• Want “year round” use, don’t like to be cold or wet == inside steering

• Type of engine?

• Diesel/inboard ~ efficient but noisy/smelly; outboard ~ easier to maintain == outboard

• My building skill level?

• First boat, flat bottom ~ easier, plywood/framed/epoxy coated ~ easier == big “Skiff” style

• Availability of suitable wood and materials nearby?

• Marine plywood, rot resistant wood boards, bronze fasteners, hardware == all available

• How many years available to build?

• 5 – 7 years == adequate

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Step 2: Buy and study building plans

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Shear

Chine

Half breadth

Height

Table of Offsets

Elevation view, Plan view, and Sections

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Step 3: Building frames (Frames are the boat “skeleton”)

• “Frames” size – 1.5” x 4” (2’6” to 3’6” long)

• “Floors” size – 1.5” x 4” to 1.5” x 11.5” (33-7/8” to 70-1/4” long)

• Available boards were 1.5” x 12” (13’-1” long)

• How many boards did I need to buy?

• Listed all the pieces by size and figured out how to use boards with the least waste

Frames Floors

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Laying out frame material on boards;cutting with least waste

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13’-1”

12-1/4” inch

Frame Length (all 4” wide) Quantity

4 3’-6” 2

12 3’-6” 2

8 3’-1” 2

6 3’-3-1/2” 2

10 3’-0” 2

14 2’-9-1/2” 2

Calculation to cut 1st 4” board – Option 1:2 - #6 & 2 - #14 = 6’-7” + 5’- 7” = 12’-2” or 39.5” +39.5” + 33.5” + 33.5” = 146” = 12.167’ = 12’-2”~ 13” wasteCalculation to cut 1st 4” board – Option 2:2 - #6 & 2 - #8 = 6’-7” + 6’- 2” = 12’-9” or 39.5” +39.5” + 37” + 37” = 153” = 12.75’ = 12’-9”~ 4” waste; Option 2 is better- Also 4 & 14 on “blue” and 10 & 12 on “green” board

33.5” 33.5” 39.5” 39.5” waste1st

board, option 1

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Step 4: Set frames in position on the support

• Set at proper elevation (height above building support) to give the curve of the bottom

• Level (horizontal) and plumb (vertical) [tools]

• Center of frames exactly at the centerline of the building support

• Spaced exactly correct distance from adjacent frames

Elevation

Level

Centerline

Centerline

Plumb

2’ Spacing

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Step 5: Notches have to be cut to install stiffeners (“chines”)

Chines

Notches

11Bevel edge – next slide

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Step 6: Edges beveled so that the plywood “plank” lies flat against the frames and floor

Chine

Inwale

Mylar (clear plastic) pattern Plywood “plank”

Bronze wood screws, 6” and 8” spacing

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Applying some science…• Material Science

• Should all the wood screws and nuts/bolts be stainless steel or silicon bronze?

• Stainless steel in the presence of NaCl (salt), moisture, and limited oxygen will corrode and fail

• Under the same condition, silicon bronze will not corrode.

• What is “corrosion”?

• Wood Preservation• How to protect plywood from absorbing water and eventually rotting?

• Just paint? No!

• Several coats of epoxy + paint? Yes!

• Per supplier: “Apply a minimum of two coats of WEST SYSTEM Epoxy for an effective moisture barrier— three coats if sanding is to be done (recommended for most wooden boats)”

• What is epoxy?

• Related to a property called “permeation” – think of a sweatshirt vs. Gortex jacket in the rain – which one lets more water through?

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Sometimes screws have to go in at an angle (on the bottom) – jig is set to the correct angle with bevel gage [tool]

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Eventually, hull is done – covered with epoxy and glass cloth…

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Hull is rotated (right side up) so that the rest of the boat can be built• How much did it weigh at this time?

Estimated based on weight of each piece of wood

• How could it be turned over? Calculated lifting force required to rotate 90 degrees and how many friends I would need?

168’0”

800 lb.

Moment equationƩMA = 0800# x 4’ - LF x 8’ = 0LF = 400#@ 50# per person = 8 persons

“A”LF

Hull

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Eventually the interior woodwork completed after adding many more pieces of wood, each measured, cut, and fitted…

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Exterior and Interior

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Still many problems to solve after this point…

• Weight distribution so boat stays level under way • Cabinets, stove, toilet, sink, crew (lighter) on the left (25# + 50# + 50# + 10# + 135# = 270#)

• Electrical and engine controls, heater, battery, skipper (heavier) on the right (45# + 15# + 50# + 190# = 300#)

• Water tank, fuel tank, engine on the center line

• Electrical system• Battery size (72 amp-hr), location, engine charger (12 amp), PV charger (5 watt)

• Number of circuits (6 DC + 3 DC and 3 AC)

• Lighting (interior, exterior) and windshield wiper motor

• VHF radio, antenna, instruments

• Wire size to carry current and wire routing• 2 - #10 wire rated 10 amp each (3% drop, 25’ RT) to main switch; 1 ea to Main and 24/7 panel

• Shore power (120VAC) socket connection and ground plate under water for safety

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Control station, electrical panels, battery

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CB1 – Running lights – 3 ampCB2 – Instruments – 0.5 ampCB3 – Interior lights – 2 ampCB4 – Auxiliary socket – 1 ampCB5 – VHF radio – 2 ampCB6 – Fuel gage, wiper – 2 ampFuse 1, 2 – Bilge pump – 3 + 5 ampFuse 3 – Heater – 4 amp (starting) Ralph Cohen

Electrical schematic

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Sink/water system, stove, toilet…• Water system

• How many gallons? (22)

• Tank dimensions? (26”x20”x10”)

• Location? (under V-berth)

• What type pump? (foot)

• Stove• Number burners (2)

• Fuel (alcohol)

• Toilet• Type? (Porta-potti)

• Size? (5 gallon)

• Location? (under crew seat)

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Fuel system, Instruments

• Fuel system• Tank size? (12 gal)• Range? (11 gal/0.5 gph x 4.8

kn ~ 106 miles) • Tank location? (below

cockpit)• How many tanks? (one)• Tank material? (HDPE)• Filter location? (near engine)

• Instruments• Depth gage (sensor at

transom)• Engine RPM / run hour meter• Fuel gage• VHF 2-way radio

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Bilge pumps, safety equipment, heater

• Bilge pumps (1” dia. hole = 20 gpm, 2” dia. Hole = 80 gpm leak)

• Capacity (500 and 1000 gph, 8.5 gpm and 17 gpm)

• Location (cabin, engine compartment)

• Quantity (two electric + one manual + bucket)

• Safety equipment• Fire extinguishers (two 10BC, one 10ABC, 2 cabin, 1 V-berth)

• (A = wood/paper/cloth, B = gasoline/paint, C = electrical)

• Smoke/CO detector (cabin)

• Heater for winter• What size? (1300 watt)

• What fuel? (kerosene – 1 gallon tank, 4 oz./hour)

• Location? (cabin bulkhead)

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On the water…

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References

• How to Build a Wooden Boat by David C. McIntosh

• The Gougeon Brothers on Boat Construction – Wood and West System Materials

• Boatowner’s Mechanical and Electrical Manual by Nigel Calder

• Wooden Boat Magazine - https://www.woodenboat.com/

• Kits –• Chesapeake Light Craft - https://www.clcboats.com/

• Pygmy Boats - http://www.pygmyboats.com/

• Chase Small Craft - https://www.chase-small-craft.com/

• Building club –• Portland, OR – Riverswest Small Craft Center - https://www.riverswest.org/

• Most years there is a summer “family boat building” event

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