There are several primary variables that must be identified when choosing a prop. Some are stamped into the hub of your existing prop. They tell part of the story. For example: 12 X 10 RH is diameter, pitch, and rotation in that order.
- Diameter, the overall diameter of the prop, is the first number of the designation. In this case 12".
- Pitch is the theoretical distance the prop will move through the water in one revolution assuming there is no slippage. In this example the pitch is 10"
- RH specifies the rotation is right hand (or clockwise when viewed from aft of the boat). All factory engine installations at Catalina Yachts are right hand.
Not specified are:
- Shaft Diameter: All Catalinas smaller than the C-42 use a 1" shaft. However, since there is a taper at the aft end of the shaft, the hole through the prop is smaller than 1". The Catalina 42 uses a 1-1/4" shaft. Shaft diameter is not stamped into the hub of the prop because the prop is manufactured with a small ID hole. When you order the prop, it is machined to your specifications to match the diameter and taper of your prop shaft.
- And the one parameter many sailors are not aware of, blade area: The ratio of blade surface area to the total area of the circle described by the diameter.
Most Catalinas have two blade props as standard. Some larger, heavier Catalinas have standard three blade props. On boats whose standard props were two blade, three blade props were usually offered as an option. In either case, Catalina Yachts (with a few exceptions) typically supplied props known as "Sailer" props. These propellers are made by Michigan Wheel. Note that a boat that sails particularly well is said to be a fine sailer, and the crew aboard that boat are referred to as sailors, hence Michigan Wheel's choice of name.
A typical Sailer prop
A Sailer prop has a blade area to total area ratio of about .44. In other words, the blade area is about 44% of the total area described by the diameter of the prop. The Sailer prop provides additional thrust compared to a two blade prop and helps stop the boat more quickly when entering your slip. It is a compromise between a two blade with minimal area, limited thrust under power and minimal drag under sail and an MP style with greater blade area.
The MP version has a blade ratio of about .50 to .53 depending upon the manufacturer. With more blade area, the MP prop provides more thrust under power but also a bit more drag under sail.
As you can see from the selection on our web site, the MP prop is our most popular. There are two reasons for its popularity. First, when a customer's two blade prop is not doing the job, he is typically sailing in an area where conditions dictate the most thrust you can have from your engine. If your marina has a narrow entrance with a nasty breakwater on the leeward side, a two blade prop may not provide a secure feeling when motoring out into a 25 knot breeze. If you find yourself trying to punch into a steep sea and just not getting anywhere, you'd probably happy to sacrifice a bit more drag under sail for the ability to claw off a leeward shore.
Cost is the second factor. The Sailer prop was developed by Michigan Wheel. Although similar props are theoretically available from other companies, due to the small sales volumes, very few are actually imported. Since Michigan Wheel has a corner on the market, there is no need for them to shave profit to compete. For example, as of this writing the price of a Michigan Wheel Sailer prop in a 13 X 12 is $611.60*.
A typical MP style prop
Due to the small volume of Sailer props sold, we do not display each of the sizes available on our web site. We are happy to quote you a current price if you would like to compare the Sailer and MP prop prices.
* These prices were current as of 11/23/2009 and are supplied for comparison purposes only. Prices change frequently and are automatically updated on the pages where each prop is featured. Prices embedded within articles such as this are not automatically updated and will soon be inaccurate.