§ 16
Which pitch should propeller have when engine only reaches 5,200 rpm at full throttle?
Answer: At wide open throttle (WOT), the engine must be within the rev range stated in the engine's manual. If it is below, the propeller is too heavy (too much pitch), and the engine becomes overloaded. If it is above, the pitch is too small. Propeller manufacturers reckon that one inch of pitch shift changes the WOT revs by roughly 150–200 rpm. The calculator uses your measured WOT and the target you are aiming for, and gives you the pitch you should try. Always do a trial run with normal load.
Ændring i stigning = (målt WOT − ønsket WOT) ÷ omdrejninger pr. tomme
For low revolutions a negative change: the propeller should have less pitch
Mercurys tommelfingerregel: én tomme stigning ≈ 150-200 o/min ved fuld gas. Brug 200 for små, hurtige både og lavere tal for tunge både, hvis du har erfaring med bådtypen
Aim for the middle or upper half of engine's WOT range
| Symbol | Meaning | Unit |
|---|---|---|
| stigning_nu | Current propeller pitch | tommer |
| wot_maalt | Measured revolutions at full throttle (WOT) | o/min |
| wot_maal | Desired WOT revolutions (from the motor's manual) | o/min |
| rpm_pr_tomme | Revolutions per inch pitch (rule of thumb) | o/min |
| = | Rise you should try | tommer |
| = | Rounded to whole inch | tommer |
| = | Ændring i stigning (minus = mindre stigning) | tommer |
| = | Deviation from target | o/min |
Does not apply when
The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.
Substituted
Giver
Members only
Create a free user account to unlock all articles, calculators, templates and range — and get access to quizzes and classes. It takes less than a minute: name, email and a password. No payment card.
Want to try something first? See what you can use without an account — the junior zone, the encyclopedia, the videos and more.
Når en båd ikke når op i motorens omdrejningsområde ved fuld gas, er propellen for tung. Når den drejer for højt, er stigningen for lille. Med propelproducenternes tommelfingerregel om 150-200 o/min pr. tomme kan du vælge den stigning, der skal prøves.
En påhængsmotor skal ligge på 5.000-6.000 o/min ved fuld gas. Med 19"-propellen når den kun 5.200. Du sigter efter 5.600.
It means: Propellen skal have 17 tommer. Ændringen er -2 tommer (minus = mindre stigning), fordi motoren lå -400 rpm fra målet.
Efter at kunden har fjernet meget udstyr, drejer motoren 6.100 o/min med en 21"-propel. Målet er 5.600.
It means: Prøv en propel med 23.5 tommer, rundet til 24 tommer. Mere stigning tager omdrejningerne ned.
1 tomme stigning ≈ 150-200 o/min ved fuld gas.
Ligger WOT under målet, skal stigningen ned. Ligger den over, skal den op.