Ask SAIL: Replacing Propellers and Diesel Engines - Sail Magazine

Ask SAIL: Replacing Propellers and Diesel Engines

I have a 1977 Pearson 28 and have replaced the old Atomic 4 gas engine with a three-cylinder Universal 20hp diesel engine. Do I need to change the original propeller that was driven by the Atomic 4?
Author:
Publish date:

Algirdas Vilkas, Mt. Kisco, New York asks:

I have a 1977 Pearson 28 and have replaced the old Atomic 4 gas engine with a three-cylinder Universal 20hp diesel engine. Do I need to change the original propeller that was driven by the Atomic 4? If so, how do I determine what propeller is correct for the new diesel engine?

atomic4engine

Nigel Calder Replies

The Atomic 4 is rated for 20hp at 2,500 rpm, with a peak power rating of 30hp at 3,500 rpm, whereas the Universal is rated for 20hp at 3,600 rpm. The critical missing piece of information concerns the reduction gears used with the two engines. Basically, if the propeller shaft speed at 20hp is about the same for both engines, then the existing propeller should work. If there is a significant difference, the propeller will probably need to be replaced. The best reference for working through the sizing process in detail is Dave Gerr’s Propeller Handbook. The steps are clearly laid out and are easy to follow.

NigelCalder

Nigel Calder is an author and expert on boat systems and diesel engines

Do you have a question for one of our experts? Send it to sailmail@sailmagazine.com

Related

SouthernOcean

The 50th Anniversary of the Golden Globe

Here we go! The 50th anniversary of the Golden Globe, the first singlehanded nonstop round-the-world race, is upon us. On July 1 one tribute event, the Golden Globe Race 2018, will start out of Les Sables d’Olonne, France, with a fleet of 19 amateur skippers setting out in ...read more

180621-X01-Landing-Page

Volvo Ocean Race Cliffhanger

After racing over 44,000 miles round the world and battling their way past the world’s great capes, including the Cape of Good Hope and Cape Horn, it’s all come down to the final 700-mile leg from Gothenburg, Sweden, to the Hague. Brunel, Mapfre, Dongfeng: going into the ...read more

Stearns Photo

Racing the Solo Mac for a Cause

There are plenty of reasons to do a Chicago-Mac race, and Rich Stearns, who has done literally dozens of ‘em should know. This year, though, he’s doing the Solo-Mac for an especially important reason: to help those with prostate cancer.“Two years ago, I was diagnosed with ...read more

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell.Got a tip? Send it to sailmail@sailmagazine.comRafting dangerOne unseen danger when sailing yachts lie alongside one another for a convivial night is that if they happen roll to a wash or begin to move in an unexpected sea, the spreaders can clash ...read more

180615-01 Lead

A Dramatic Comeback in the Volvo

After winning three of the last four legs in the Volvo Ocean Race (and coming in second in the fourth), Dutch-flagged Brunel is now tied for first overall with Spanish-flagged Mapfre and Chinese-flagged Dongfeng following the completion of Leg 10 from Cardiff, Wales, to ...read more

MFS-5-2018-Propan-SP02

Tohatsu LPG-powered 5hp Propane Motor

Gassing it UpTired of ethanol-induced fuel issues? Say goodbye to gasoline. Japanese outboard maker Tohatsu has introduced an LPG-powered 5hp kicker that hooks up to a propane tank for hours of stress-free running. Available in short-, long- or ultra-long-shaft versions, the ...read more