Offsets Files

Nathan Titcomb

OFFSETS FILES

OFFSETS FROM DESIGNERS

• Design files need to be verified before use– Builders often modify designs without telling

anyone. – Variations in sheer line heights cause vast changes

in calculated displacement

• Keels and rudders can change depending on model of design

HOW TO VERIFY ANOFFSETS FILE

• Canoe Body Depths at Freeboard Stations– Method 1.• Hang plumb bobs from freeboard station points• Have an assistant hold long level and straight edge so

that it just touches both plumb bob strings and the underside of the hull at centerline• Measure the height from top of (level) straight edge to

freeboard points (just like taking freeboards) • Average both sides• Repeat for the aft/forward freeboard station

VERIFY OFFSETS

• Canoe Body Depths at Freeboard Stations– Method 2:• Locate underbody centerline at freeboard stations• Use transit to measure total depth to freeboard point

– Average both sides

• Scale weight + Overhangs – Provides accurate results. • Use computer to float model relative to Y and BO then

create offsets file. Must Still have Pictures!

VERIFIYING APENDAGES

• Span– Distance from canoe body of hull to tip of foil• Do not include bulb

• Chords– Fore and aft dimensions

• Dimensions– Distances from canoe body where chords are

taken• At bare minimum we need Root Mid and Tip chords

Minimum Dimensions to Verify a Keel for an Offsets File

VERIFIYING APENDAGES

• Thickness– How thick the foil is at each chord with dimension

of max point from the leading edge of foil

• Pictures– Always take pictures!

VERIFYING BULBS

• Bulbs should be treated as a third appendage• Must capture:– Length, Max Height, Max Width, Pictures.

• Height and Width at several locations along the bulb, with dimensions from a reference point.

KEEL DRAWINGS

• Good example but no foil thickness or distance of leading edge to fixed point.

SPLICING APPENDAGES

FRANKEN - BOAT• When someone swaps a

keel/rudder from one design to another

• Very Difficult when working with only offsets files

• Need measurements • Cost to modify the offsets

above the certificate costs – Minimum $150

Questions?