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Noen som har prøvd EcoDrive??


Birchwood 320

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Jeg synes også at dette drevet så aktuelt ut, for en eventuelt ny fremtidig båt. Men skal du konvertere fra ordinært drev til Eco, så koster nok dette noen kroner. Først pga. at du må ha gear i tillegg, og så kommer en voldsomt kostbar overflatepropell. "Cleaver" type (ca. sånn som på avataren min). Det hele havnet vel på 100K+++ alt etter båttype og størrelse. Så for meg var det ikke særlig aktuelt, selv om konseptet er bra.

 

:sailing:

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Lurer på om dette er noe greier for en Daycruiser på 26 fot?http://www.motormarine.no/

Nå kommer vi vel inn på grenseområdet til overflatepropeller..... hvis vi ikke er der allerede... alt subjektivt selvsagt, og samlet viten her er ikke komplett ... uansett, så bør du diskutere dette med båtleverandør, eller hvis du vurderer å installere i "eldre" båt, så må du få designkriteriene dine på plass først.... som leverandør vil kunne hjelpe deg med....

 

Vanligvis vil en si at overflatepropeller kommer til sin rette rundt 28 knop + for de fleste båter, men det er helt avhengig av konstruksjon, og hva som skaper "drag". Et hekkagregat, spesielt de siste til Volvo er uhyre effektive, og har jo fordelen med at de har forhandlerapparatet rundt hele kysten, hvis noe går galt.

 

Overflatepropell (surface piercing) ) er en propell som er lokalisert slik at underveis, så vil vannlinjen passere midt på propellakslingen og propellen roterende i det relativt rolige vannet som finnes et lite stykke fra hekken .... har gjort en del undersøkelser selv her, da jeg ser dette som en kjempe måte å få mer effektiv bruk av eksisterende maskiner med vanlig strak aksling. Hvis alternativet er drev, er vel gevinsten litt tvilsom.... Den største fordelen som jeg ser er for større / raskere båter, hvor en kan benytte seg av en større, saktere roterende propell, som er mer effektiv enn en liten, hurtig roterende propell ed mye stigning. Det vil også være en del å ta hensyn til underveis, slik som trimming av båten, da en overflatepropell vil generere mer løft i hekken enn en mer tradisjonell installasjon... Se under for hva jeg har funnet / skrevet / summert om emnet tidligere i min søken for kunnskap om emnet ...engelsk desverre, men like relevant .... ellers så finnes det mange alternativer til EcoDrive:

 

Pulse Drive http://www.pulsedrive.net/

Transom Drive http://www.lancingmarine.com/lmtrans.html

Arneson

Trimax

Levi

etc.....

 

The important operating feature is that each propeller blade is out of the water for half of each revolution. And here is another reason for skepticism. Surely a propeller blade is more efficient if it operates continuously in the smoothest possible flow, rather than splashing through the water surface twice with each revolution. Sometimes an unsteady process is actually more efficient than its continuous counterpart (hence the reason for PulseDrive ??).

Why use a surface propeller?

Propeller Efficiency: Traditional propeller design and selection is almost always an exercise in trading off diameter against several other performance-limiting parameters. Basic momentum theory tells us that for a given speed and thrust, the larger the propeller, the higher the efficiency. While there are exceptions, most notably the effects of frictional resistance on large, slow-turning propellers, it is generally borne out in practice that a larger propeller with a sufficiently deep gear ratio will be more efficient than a small one.

A number of design considerations conspire to limit the maximum feasible propeller diameter to something considerably smaller than the optimal size. These include blade tip clearance from the hull, maximum vessel draft, shaft angle, and engine location. While this may at times make life easy for the designer - the propeller diameter specified is simply the maximum that fits - it can also result in a considerable sacrifice of propulsive efficiency. And if these geometric limits on propeller diameter are exceeded, the result can be excessive vibration and damage due to low tip clearances, or a steep shaft angle with severe loss of efficiency and additional parasitic drag, or deep navigational draft that restricts operation or requires a protective keel and its associated drag. In many cases, the best design solution is to live with a mix of all of the above problems to some degree.

The surface-piercing propeller frees the designer from these limitations. There is virtually no limit to the size of propeller that will work. The designer is able to use a much deeper reduction ratio, and a larger, lightly-loaded, and more efficient propeller.

Cavitation: When a submerged propeller blade cavitates, the pressure on part of the blade becomes so low that a near vacuum is formed. This happens more easily than one might think - atmospheric pressure is only 14.7 psi, not a very big number considering the size of a typical propeller and the thrust it is required to produce. If the suction on the low-pressure side of the propeller blade dips below ambient pressure - atmospheric plus hydrostatic head - then a vacuum cavity forms. (To be strictly correct, there is water vapor in the cavity, and the pressure is not a true vacuum, but equal to the vapor pressure of the water.)

When these vacuum cavities collapse, water impacts on the blade surface with a local pressure singularity - that is, a point with theoretically infinite velocity and pressure. The effect can approximate that of hitting the blade with a hammer on each revolution. Cavitation is a major source of propeller damage, vibration, noise, and loss of performance. And although high- speed propellers are often designed to operate in a fully- cavitating (supercavitating) mode, problems associated with cavitation are frequently a limiting factor in propeller design and selection.

The surface propeller effectively eliminates cavitation by replacing it with ventilation. With each stroke, the propeller blade brings a bubble of air into what would otherwise be the vacuum cavity region. The water ram effect that occurs when a vacuum cavity collapses is suppressed, because the air entrained in the cavity compresses as the cavity shrinks in size. Although the flow over a superventilating propeller blade bears a superficial resemblance to that over a supercavitating blade, most of the vibration, surface erosion, and underwater noise are absent.

Appendage Drag: Exposed shafts, struts, and propeller hubs all contribute to parasitic drag. Inclined the exposed shafts not only produces form and frictional drag, but there is also induced drag associated with the magnus-effect lift caused by their rotation. There is a surprising amount of power loss resulting from the friction of the shaft rotating in the water flow. In fact, for conventional installations a net performance increase can often be realized by enclosing submerged shafts in non- rotating shrouds, despite the increase in diameter.

Surface propellers virtually eliminate drag from all of these sources, as the only surfaces to contact the water are the propeller blades and a skeg or rudder.

Variable Geometry: When a surface propeller is used in conjunction with an articulated drive system, the vessel operator then has the ability to adjust propeller submergence underway. This has roughly the same effect as varying the diameter of a fully submerged propeller, and allows for considerable tolerance in selecting propellers - or it allows one propeller to match a range of vessel operating conditions. This capability is somewhat analogous to adjusting pitch on a controllable pitch propeller.

When the articulated drive is used for steering, the result can be exceptionally good high-speed maneuvering characteristics. On single-shaft applications, drive steering can also be used to compensate for propeller-induced side force, without resorting to an excessively large rudder or skeg.

Shallow Draft: This is the characteristic that motivates many designers to investigate surface propeller propulsion in the first place. The vessel's navigational draft can be as low as half a propeller diameter. Compared with other options for shallow water propulsion - most notably waterjets - surface propellers enjoy a very significant efficiency avantage. This advantage is most dramatic for low-speed applications, but is still present throughout the performance spectrum.

In the case of articulated drives, the propellers can be trimmed up until just the tips are submerged for intermittent operation in very shallow water, including beaching. Sometimes the design allows the propellers to trim sufficiently above the baseline so that the vessel can "dry out" with the props well clear of the bottom.

These are the intrinsic performance advantages of surface propellers. Other desirable characteristics include flexibility in machinery arrangement, ease of maintenance and repair, and simplified installation. In some applications involving hybrid propulsion systems, such as the combination of diesel cruise engines with a gas turbine sprint engine, the ability to retract one set of propellers completely clear of the water when not in use is an overriding consideration.

Vibration: One of the amazing features of surface propulsion is its smoothness at high speed, due mainly to the suppression of cavitation. This is contrary to intuition, and must be experienced to be fully believed. However, some installations have experienced serious vibration problems. In most cases this is due to improper design or alignment of the shafting between the gearbox and drive input shaft. When double universal joint drivelines are required, as is the case with articulated systems, it is especially important to plan the driveline geometry so that operating angles of the two joints are approximately equal and within accepted tolerances. This is because a universal joint does not transmit rotational velocity evenly, causing angular acceleration and deceleration twice with each shaft revolution.

As a general guideline, joint angles should not exceed six degrees per joint, and the difference between the two joint angles should be less than one-half degree. This allows the angular accelerations produced by one joint to be almost exactly compensated by the other joint. (Depending on the orientation of the universal joint yokes, the joint angles can be opposite with driveline flanges parallel, or they can both angle in the same direction for a net total shaft angle change of up to twelve degrees.

The less common vibration problems that are not driveline-related can almost always be solved by using propellers with a larger number of blades, although there is some cost penalty involved.

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Jeg synes også at dette drevet så aktuelt ut, for en eventuelt ny fremtidig båt. Men skal du konvertere fra ordinært drev til Eco, så koster nok dette noen kroner. Først pga. at du må ha gear i tillegg, og så kommer en voldsomt kostbar overflatepropell. "Cleaver" type (ca. sånn som på avataren min). Det hele havnet vel på 100K+++ alt etter båttype og størrelse. Så for meg var det ikke særlig aktuelt, selv om konseptet er bra.

 

:sailing:

Altså 100K for dette er det verdt.. Sjekket pris på nytt Bravo3 X drev og da snakker vi om 110K for dette.. Og da er det aktuelt med service kvart år..

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