surface piercing props in action

[ash12]

I never understood how they worked up until a while ago, Portofinos explanation describes it well. Great vid aswell, thanks zippy

 

[z1ppy]

really interesting comments and im happy to take the nerd award for this month!!

As an aside, assume they will have separate water pickups to facilitate engine cooling? (which would normally be taken from the front of the outdrive cone on a less high performance boat)

gonna have to have a look at a surface drive boat more closly. not sure i fancy close quarter berthing in one tho!

 

[Portofino]

gonna have to have a look at a surface drive boat more closly. not sure i fancy close quarter berthing in one tho![/QUOTE]


http://www.youtube.com/watch?v=PQnKplso_xg&feature=youtube_gdata_player
Turn your volume up
would fit JFM,s requirements ??


http://www.youtube.com/watch?v=81_6MPWdU-s&feature=youtube_gdata_player
This ones a bit scary

 

[MapisM]

The paddles would have to be going through the water faster than the boat speed....

Thanks (also to portofino) for the explanations on paddles.
They make good sense, I didn't even bother thinking about them before...!

 

[MapisM]

As an aside, assume they will have separate water pickups to facilitate engine cooling? (which would normally be taken from the front of the outdrive cone on a less high performance boat)

That's not so normal, actually.
The LWP (Low Water Pickup), as Mercury calls it, is not even available on Alpha outdrives.
I've had a 70mph boat whose B1XR outdrive had the DWP (Dual Water Pickup), i.e. the normal pickup above the cone, along the leg, and the LWP in front of the cone.
Anyway, yes, pickups are often separate from the outdrive(s), and placed on the transom.
You can see them under the transom notch, at the V bottom, in this pic:

You're 100% correct in fearing the maneuverability of these things, btw. Particularly with a single engine.
In my boat above, the leg-prop was not actually working as a full surface transmission, but the X dimension (outdrive height) was very aggressive, with the cavitation plate well above the keel.
And that was more than enough to make it simply impossible to steer to port in reverse - not a chance!