Thursday, May 13, 2010

Pitch Ratio of Ship Propeller

In propeller design, pitch ratio is one of the most important parameters that naval architect must determine. Pitch is the distance (measured in meters) a propeller travels along the direction of a moving ship in one propeller revolution. Pitch ratio is propeller pitch divided by diameter. The determination of pitch is usually carried out through the reading of Bp delta diagrams which were created through extensive open water test over a number of propellers. 

A naval architect or marine engineer cannot choose pitch ratio as high as he or she likes. It is a parameter that affects all of the propulsion parameters of ship propulsion. In other words when a pitch is altered it will change all the propulsion performance of a ship. If the pitch of the blades is too high, it will overload the main engine that drives the propeller. If it is too small, the main engine will work under-load. Both conditions are not good for the performance of ship propulsion. Thus the determination of the right pitch ratio is important to ensure that the ship will move fast at sea surface with efficient consumption of fuel oil and without overloading the main engine.
bp delta diagram
Bp-delta diagram of B-Series propeller
Modern ship propellers (both fixed pitch and controllable pitch propellers) have pitches that are variable. From radius r/R 0.2 to 1, the pitches are not the same. Usually the pitch of a ship or boat propeller that was designed based on B-series standard propeller or also known Troost series propeller will have pitch ratios based on the following table or diagram
Pitch ratio diagram on every radius of the propeller
Pitch Ratio Distribution  of B-Series Standard Propellers
We can see that from radius r/R = 0.6 to 1, the pitch diameter ratios are full, i.e. 1 or 100% where as pitch ratios from radius 0.5 to 0.6 are different. After we get the Pitch/Diameter ratio (only one value) from the Bp delta diagram of B-series standard propeller, we have to develop it into variable pitches according to the above table. When we have entered the values of these pitch diameter ratio, we can continue the calculation of the propeller design by conducting Propeller Mean Pitch Calculation. by Charles Roring


Minahasa is a region in the Province of North Sulawesi that is good for visitors who love nature. Visitors who take this tour can see beautiful scenery of the mountains, farmlands, terraces of rice fields, and traditional villages of Minahasan people as well as enjoy watching various species of tropical birds and butterflies. 

Day 1. The tour will be started from Manado city at 09:00. Participants will be taken to Mount Tumpa to see the scenery of Manado city and its surround areas including several islands at sea. Birds can also watch such birds as Zebra Dove, Spotted Dove, Yellow-vented Bulbul, Finch-billed Myna, and etc. At around 11:00, we will go back to Manado city and visit the Museum of North Sulawesi.
Lunch will be arranged at around 12:30.
We will return to hotel for rest.
Black-naped Oriole, Collared Kingfisher, Mountain White-eye, White-breasted Woodswallow, Pale Blue Monarch, Crimson Sunbird, Sooty-headed Bulbul
Some birds in Minahasa
At 15:00, we will continue the tour again. This time to the a waterfall. We will also do birdwatching and butterfly watching. Finch-billed Myna, Green Imperial Pigeon, Slender-billed Crow, Black-naped Fruit Dove are some of the birds that we can watch.
Terraces of ricefield in Talikuran village of Sonder town
Terraces of Rice Field in Minahasa Highland
For butterflies, there are Manado Yellow Tiger Butterfly, Sulawesi Cruiser Butterfly (Vindula dejone celebensis), Cyrestis strigata and a lot more.
Day 2
Check-out from hotel at n in Manado city and then move to a homestay in Minahasa highland. We will do sightseeing and birdwatching in Mount Mahawu.
Lunch at 12:00. After that, return to homestay for rest. At 15:00, we will do a visit to Woloan village to see the wooden house production.
Hot Spring in Minahasa Highland
Day 3
We will do sightseeing, birdwatching and butterfly watching in Sonder.

Day 4
For more info, please, contact: Charles Roring by whatsapp to: +6281332245180 or by e-mail to:

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