Canadian Yachting April 2016 - (Page 29)

Perfect Prop for your Purpose This article is the first of 2 parts. Part 1 deals with propellers for displacement boats and Part 2 will cover the rest of the drive train (i.e. coupling, shaft, stuffing box, stern tube and cutlass bearing) and a comparison of fixed, folding and feathering propellers for sailboats. D eciding to change the propeller on your boat is not a binary decision, like "Do I want a red one or a blue one." The science of propeller design dates back to Archimedes (287-212 B.C.). Selecting and fitting a boat propeller is often referred to as a black art, because the terminolgy and mechanics of props seems as much art as it is science. Don't let the term fool you. Prop professionals have the charts, formulae and algorithms to back up their recommendations. Selection of the proper prop for your purpose is based on what you want or need to achieve: greater fuel economy, faster cruising speed, smoother operation or faster on to a plane. In his sixth rule of thumb, Dave Gerr states, "The same propeller can't deliver both high speed and maximum power ... A propeller sized for high speed has a small diameter and maximum pitch. A propeller sized for power or thrust has a large diameter." Propeller Handbook: The Complete Reference for Choosing, Installing, and Understanding Boat Propellers We are here to explore exactly what he means by that. PROPS - WHAT AND WHY To de-mystify the black art you first have to learn the language. I have purposely left out the more basic terms. Hub (or boss) - the centre section of the propeller, necessary to hold the blades in place. Blade face and back - the face is the side of the blade looking forward from the stern, the back is the side of each blade when you are looking aft. Blade root and tip - the root is the part of the blade closest to the propeller hub and the tip is furthest. Leading and trailing edges - The leading edge is the part of the blade that first makes contact with the water as the propeller rotates. The trailing edge is the part of the blade that makes contact with the water last as the propeller rotates. Rotation - props rotate to the right - right hand (RH) or left - left hand (LH). Right hand means the propeller turns clockwise (to the right at the top) when viewed from astern. The majority of single engine boats have right hand props. 29

Table of Contents for the Digital Edition of Canadian Yachting April 2016

Vantage Point: Careers in the marine industry
Waterfront: Ken Read’s Sailing Advice, CY in Miami and Dusseldorf
Club Profile: Cobourg Yacht Club
Destination: Swan Lake - This gentle cruise into Masset Inlet paints a stunning visual depiction of the Masset Sound scenery and a foray into a swimming hole near Swan Lake. By Linda Leitch
Feature: Perfect Prop for Your Purpose - In Part I of this 2 part article, learn about propellers for displacement boats. “Selection of the proper prop for your purpose is based on what you want or need to achieve.” By Rob MacLeod
Power Review: Beneteau GT 40
Destination: Georgian Bay Cruise - Spending five days on the breathtakingly beautiful Georgian Bay will have you starting your packing list and planning your own route for the summer of 2016. By Jennifer Harker
CPS Port Hole
Destination: British Virgin Islands - A weeklong visit to the Pro-Am Regatta at the Bitter End Yacht Club in the BVI’s challenges the author to find the perfect balance between the thrill of competition and the perfectly mixed cocktail in this idyllic setting. By Clarity Nicoll
Feature: Underwater Lighting - More affordable than you might think and more useful than you would imagine – Underwater Lighting is the hot upgrade for Canadian boats of all sizes, power or sail. Light up your cruising nights this summer. By Andy Adams
Crossing the Line: The Shark is Alive and Well

Canadian Yachting April 2016