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

SWTR005_SWJK022

MPX Pro Offshore Jacket

Heavy Duty JacketMusto’s new MPX Pro Offshore Jacket features the same waterproof, breathable three-layer Gore-Tex fabric as its predecessors, but weighs 15 percent less. Changes to the hood make it easier to adjust and the fleece-lined collar and hood pod provide both warmth and ...read more

2018-BestBoatNominees

Best Boats Nominees 2019

As we approach the upcoming fall boat shows, perhaps the best word to describe the boatbuilding industry’s latest crop of new designs is “consolidation.” Specifically, in recent months we’ve seen a number of innovations introduced in years past continue to work their way up and ...read more

9781472947666

Book Review: The Atlantic Crossing Guide

Jane Russell & the RCC Pilotage FoundationIf you have a yen for sailing across the Pond to explore the delights of Northern Europe or the Mediterranean, you’d best do some homework first. There’s no better primer than this weighty tome, now in its 7th edition. It’s crammed with ...read more

shutterstock_63705382

Raytech Gelbox Line

Well GelledEvery so often you run across a product you never knew you needed, and then you wonder why it took so long for someone to come up with it. Thus it is with the Gelbox line from Raytech. These reuseable plastic boxes for low-voltage connectors are filled with gel, so ...read more

shutterstock_295810247

Cruising: Nova Scotia’s Bras d’Or Lake

I have rarely had a cruise that wasn’t different from my expectations, and my Nova Scotia travels have borne that out. For my friend and shipmate, Steve White, and me, our 2017 trip to Cape Breton Island and the Bras d’Or Lake on One Timer, my Sabre 362, was a much anticipated ...read more

ElanGT5-a

Boat Review: Elan GT5

Aboard many modern yachts, it can be hard to remember exactly what boat you’re on until your eye happens to light upon a logo. However, this is most definitely not the case with the Elan GT5, a performance cruiser with a look all its own and style to burn.Design & ...read more

01-Lead-P1060210

Handheld VHF Radios

For many sailors, cell phones have become their primary means of both ship-to-shore and ship-to-ship communication. Even the Coast Guard will often ask for a cell number after it receives a distress call. None of this, however, makes a VHF radio any less important—and this goes ...read more

Seascape24

Boat Review: Seascape 24

Since its inception in 2008, Slovenian builder Seascape, founded by a pair of Mini Transat sailors, has focused solely on creating boats that are both simple and loads of fun to sail. With their 18-footer and then a 27-footer they succeeded in putting out a pair of trailerable ...read more