See also: Tutorial build ship screw propeller
As we have seen in the brief summary of the evolution of forms of boat's propeller during the last centuries, forms and systems offering improvements in performance of the screw propeller boat have proliferated. The economic and ecological stakes are high. The improved performance of ships screw propeller can save energy. The systems to increase the efficiency of a ship screw propeller can be classified into three categories according to their location:( source Carlton)
- in zone 1 of the boat we find different systems that guide the fluid entering in ship screw propeller
- in zone 2 of the boat we find the systems attached to the propeller.
- As a variable pitch propeller. Since 1960 the number of variable pitch propeller fitted to large naval Units, increased from 5 to 35%. But other systems to improve marine propulsion per propellers have been developed
- The Grim Vane uses Additionnal propeller in its inner part, operates turbine recuperative energy of the first propeller, And its blade tip section uses the torque recovered to produce an aditional thrust to the boat. The second screw propeller is therefore both recuperative and propulsive
- The marine screw propeller can also be equipped with blade tip plates that act as winglets airplane wings. This device helps to minimize losses at the blade tip:
- For the same reasons of economy losses of the blade tip, the fairing will increase the thrust for a heavily loaded propeller,the blade tip losses being due to the pressure difference between the front and rear of the screw propeller, they are important to the propeller whose thrust area ratio is high.The performance gain is real only for boats at low speed because the fairing creates a drag that increases with the square of the speed of the boat .
Whether for vessels of small size, such as sailboats or larger units, manufacturers and designers of propellers, compete of ingeniousness, to evolve the performance of marine propulsion taking account of their operating condition.
Screew propeller of sailboats:
The propeller sailboats has the particularity of being essential for harbor maneuvers (Arrivals or departures under sailis, are evidence of the competence of the captain to salute the art of sailing, but nowadays prohibited in ports, unless you excuse an engine failure... ), or the lack of wind, but this propeller becomes a brake when the boat is under sail. The helices designers we therefore sought solution to this problem. Here are some of these systems of propeller for sailboats and their prices (approximate) for info:
- fixed pitch propeller: If the propeller is properly selected and performance correspond to the operating point of the vessel, Fixed propellers for sailboat, are very effective for boats, often navigating with engine. Effective only if the boat speed and the rotational speed of the motor corresponds to the optimum operating point of the propeller. In fact little sailor know the operating point of their propeller and propulsion engine remains a organne security and troubleshooting, while the performance of their propeller is alow priority detail .If we ignore the drag is the best propeller at, value for money (400 $ new 120 $ on ebay).
CAUTION: If you install a propeller without knowing if its operating point corresponds to your boat you may have a very bad performance, so even if we give it to you, it may cost you a fortune...of energy. Full tank of fuel on a sailboat costs as much as a propeller....
- screw propeller feathering, folding: propeller feathering, folding is derivative from research griffith we've seen in the evolution of forms of boat propellers. When the vessel is under sail and the propeller shaft does not rotate, the blades feathering
above example the screw propeller feathering EWOL (price approximately $ 2,990)
or below the spw variprofil (price approximately $2000 )
- or fold along the axis of a current integrated thanks to the blade axis:
The drag force is considerably reduced, compared to a fixed propeller. Do not confuse variable pitch blade and folding or feathering. The folding blades have a fixed pitch not adjustable during operation, which is always identical irrespective of the rotational speed of the propeller shaft and the vessel's speed. So if the pitch corresponding to the operating point is not correct, the performance is like for a fixed pitch propeller: rather bad.
Here Flexofold ($1700 €)
ou france helice racing ($ 1115)
- automatic variable pitch screw propeller: There are propellers, with automatic variable pitch in operation, whose pitch is automatically regulated, according to the torque on the blade mounted skewed. These systems appear to be the most interesting, rResistance over time is to be evaluated, and automatically varying the pitch requires that the engine torque corresponding to the rotational speed is adapted to the adjustment of the blade..
screw propeller autoprop $ 2200...