When is a vented prop right?

[stevens]

Hi guys,<br /><br />See this recent correspondence with www.marinepower.com:<br /><br />

Is a vented prop right for the 1,7L Turbodiesel?<br />Hi, would you know whether or not a vented prop is appropriate or beneficial for the Mercury-Cummins 1,7L Turbodiesel with the Alpha drive? Have tried several vented props, but in the end seem to find the unvented ones to be better, at least at lower speeds. Thanks.<br /><br />------------<br /><br />Dear Customer, <br /><br />It depends a lot of boat type and weight. <br /><br />PVS props are designed to improve acceleration and are used for outboard engines not for diesel ones. <br /><br />Best Regards, <br />Technical Service

OK, so I understand how venting works, but I don't understand why a diesel engine would benefit less than a gasoline engine.<br /><br />My experience is, however, that while the venting does give a slightly better holeshot, it also leads to a lot of "bubbles & noise" from the prop as well as making it a bit more difficult to steer at low speeds.<br /><br />Could the higher compression rate of a diesel engine lead to a higher exhaust pressure or volume, which would then lead to too much exhaust escaping the vent holes? Or is there perhaps some other explanation? Thanks.

 

[WillyBWright]

Re: When is a vented prop right?

The only motors that seem to benefit from ventilating the props are large 2-stroke outboards. I have yet to see a sterndrive of any configuration do well with them. They also don't seem to work well on 4-stroke outboards.

 

[ivar]

Re: When is a vented prop right?

I think its because the typical torque curve on a 2-stroke is quite different from a 4-stroke or diesel.