Technical Notes: Calculating Prop Performance

Technical Notes: Calculating Prop Performance


Here is a way to calculate prop performance with different props, a formula suggested to us by technician Peter Arneson:

Props slip, so they're about 85 to 90 percent efficient. Multiply mph by 0.85 to determine final boat speed. Here are the calculations for an example motor and two different prop pitches:


Example engine: 115 hp


Engine RPM: 5,000


Lower Unit Gear Ratio:

13:26 or 13/26 = 0.50

Prop Pitch:


19 inches and 21 inches

Formula:

(RPM x Ratio) x Pitch = inches per minute


IPM/12 = feet per minute

FPM/5,280 feet = miles per minute

miles per minute x 60 = mph

19-inch-pitch Prop

(5,000 x 0.5) x 19 inches = 47,500 inches per minute

47,500/12 = 3,985 feet per minute

3,958/5,280 = 0.75 miles per minute

0.75 x 60 = 45 mph

0.85 x 45 = 38.25 mph with 19-inch-pitch prop

21-inch-pitch Prop

(5,000 x 0.5) x 21 inches = 52,500 inches per minute

52,500/12 = 4,375 feet per minute

4,375/5,280 = 0.83 miles per minute

0.83 x 60 = 50 mph

0.85 x 50 = 42.5 mph with a 21-inch-pitch prop

42.5 mph - 38.25 mph = 4.25 mph speed increase with a 2-inch increase in prop pitch

Many variables need consideration in prop selection, such as boat-hull design, boat loading, boat use, motor size, motor mounting, and water temperature. Prop calculations are one part of the total equation.

Get Your Fish On.

Plan your next fishing and boating adventure here.

Recommended for You

Across the Walleye Belt, early spring is prime time to tap some of the year's best bites. Walleye

Spring is Prime Time for River Walleyes

Dan Johnson - February 22, 2018

Across the Walleye Belt, early spring is prime time to tap some of the year's best bites.

These secrets will put more and bigger bass in your boat! Bass

Topwater Lure Secrets for Bass

Jim Edlund - April 26, 2018

These secrets will put more and bigger bass in your boat!

This recipe for Steelhead Trout Niçoise Salad is heart healthy, paleo- and gluten-free diet friendly. Fish Recipes

Steelhead Trout Niçoise Salad Recipe

This recipe for Steelhead Trout Niçoise Salad is heart healthy, paleo- and gluten-free...

See More Recommendations

Popular Videos

As KVD tells OSG's Lynn Burkhead, innovative Humminbird products and cutting-edge technology like that found in the new Mega 360 Imaging sonar are major reasons contributing to his unparalleled success.

Spawntime World Class Crappies

Spawntime World Class Crappies

Doug Stange and Brandon Fulgham illustrate spawntime crappie patterns on one of North America's most famous fisheries.

Simms

Simms' Challenger Raingear

John Frazier of Simms Fishing Products details the warm and dry features found in the new Challenger raingear being brought to market by the Bozeman, Mont. company.

See more Popular Videos

Trending Stories

Catfish are simple creatures that can be caught using the best catfish rigs. Catching them is simply a matter of putting a good bait in the right in front of them. Catfish

The Best Catfish Rigs

In-Fisherman - January 11, 2018

Catfish are simple creatures that can be caught using the best catfish rigs. Catching them is...


Spring is prime time for pike. The Prespawn and Postspawn periods offer excellent odds at catching Pike & Muskie

How To Catch Pike In Spring

Dan Johnson - April 26, 2016

Spring is prime time for pike. The Prespawn and Postspawn periods offer excellent odds at...

To guide your carp quest, we've lined up the best carp baits that are easy-to-fish natural baits and commercial options. Other Fish

Best Carp Baits Today

Dan Johnson - June 29, 2018

To guide your carp quest, we've lined up the best carp baits that are easy-to-fish natural...

See More Stories

More Boats & Motors

Choosing an outboard shouldn't happen until you have a serious discussion. With some experts. Like yourself. Boats & Motors

The Best Motor for My Boat

Matt Straw

Choosing an outboard shouldn't happen until you have a serious discussion. With some experts....

Here are some of the new boats being introduced this year and some with design changes that reflect those angler demands. Boats & Motors

A Wave of New Boats for 2019

Matt Straw - June 04, 2019

Here are some of the new boats being introduced this year and some with design changes that...

Now more than ever, understanding each category's strong suits is critical to choosing a powerplant that best fits your personal needs and preferences. Boats & Motors

2- Vs. 4-Cycle Outboard Motors

Dan Johnson - April 16, 2018

Now more than ever, understanding each category's strong suits is critical to choosing a...

See More Boats & Motors

GET THE MAGAZINE Subscribe & Save

Temporary Price Reduction

SUBSCRIBE NOW

Give a Gift   |   Subscriber Services

PREVIEW THIS MONTH'S ISSUE

GET THE NEWSLETTER Join the List and Never Miss a Thing.