Propulsione

[prop]

(10-10-2015 08:38)Giada0959 Ha scritto:  Raccontaci la fesseria più grossa !

Perle ce ne sono tante. Una? quella che l'elica con diametro maggiore cavita di più.

Già che ci sono riporto dall'ultimo Nigel Calder*:
The ways in which most engines develop power, and fixedpitch propellers absorb power, mean that if a propeller is “matched” to an engine to absorb the engine’s full rated power at its full rated speed (the standard method of matching a propeller to an engine; full load/full speed becomes the “design point” for the propeller), at almost no point along the propeller curve is the engine operating at its peak efficiency for that particular engine/propeller speed. Almost always, adding more load improves engine efficiency. If this load is added by oversizing the propeller, in displacement and semi-displacement hulls there is usually also a gain in propeller efficiency. The combined gain in engine and propeller efficiency is often about 10%–20% across the full speed range of the vessel.

The obvious downside to a propeller oversizing strategy is that if the vessel is operated at wide-open throttle (WOT), the engine will be overloaded and potentially damaged.

However, in many applications, the vessel is never operated at WOT, in which case the standard design point for propeller sizing does not correlate with the propeller’s operating point.

In such a situation, oversizing the propeller, or adding load at various points along the propeller curve (which is essentially what is done in a parallel hybrid application) can have significant efficiency benefits without negative consequences.

* Nigel Calder is the author of Boat owner’s Mechanical and Electrical Manual and other marine titles (includ ing, earlier in his career, Marine Diesel Engines), and is a member of the American Boat & Yacht Council’s Electrical Project Technical Committee.

P.S. Rispondo a tutti, gratuitamente, ma datemi tempo.
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