Propeller tunnels information

[SLC]

I would like to get some information about propeller tunnels, specially the flow and presure behaviors inside them.
I'd appreciate it if someone could give me some explanations or/and recommend me a paper in order to learn about this topics.
Thanks a lot for your help !
SLC.-

[jehardiman]

What type of tunnels? Thruster tunnels, or Main Propulsion tunnels? Fixed shaft or O/B? Shaft rake? Full coverage? And the whys. You havn't given us much to point you in the right direction.

[SLC]

Jehardiman,
Thanks for your reply.
I'm talking about a Main Propulsion tunnels or propeller pockets with fixed propellers shafts.
Anyway, I am not talking about a specific case and for that reason it is not important the shaft rake and that kind of things. I just want to learn how the propeller tunnels work in general (fluid and presion behavior inside them) in order to understand the idea.

Thanks again,
SLC.-

[jehardiman]

All a main propulsion prop tunnel is for is to get a bigger prop (protected from groundings) with a shallower total draft. Losses can be high and cavitation can be a problem that needs to be addressed (i.e. submergence can be low or even negative), but you get a lot more thrust delivered (a function of D^4). In most cases you use a tunnel because you need a tunnel to get the required thrust with a given draft rather than from improved performance considerations.

It functions like any other propeller or axial pump and creates a suction which draws water into it and a pressure which pushes the water out. Realistically you can think of it as an axial pump and use standard prop calculations to ensure proper suction head (i.e. limit cavitation). Open tunnels may cause flow problems, but those considerations are small compared to the increased thrust generated by having a larger wheel.

[ABoatGuy]

Two sources:

I believe it was Don Blount that did a paper published in Professional Boat Builder. Also check the SNAME sight and search for the papers. I don't have it in front of me, but there is a paper dealing with prop/pocket interaction. I'll look it up later and post the author and title.

[SLC]

Thanks both of you for the information.
If anyone have more data please let me know.

SLC.-

[webbwash]

Just an interjection --
Take a look at River Towboats if you really want to get into the dynamics of Propeller tunnels. These combined with Kort nozzles provide the most efficient means of tucking a fully developed propeller into the shallowest hull form. The propellor tips run above the "natural" waterline and redirect the water flow below the water line after a long and gentle entry. Think Hamilton jet but on a 4000 HP work boat.