Maroathon racing jet boat drag?

[allblowdup]

I race marathon jet boats at speeds of approx 100 mph on courses that are up to 60 miles long. The areodynamic shape of our hull is somewhat unique. It is an air trapping tunnel hull design so we have air exiting the back of the boat below as well as on the sides and above. Ours is an open cockpit design with canard wings on the front for lift as well as wings on our roll bar for lift as well. The shape is not that bad other than the open cockpit design and the square back on the boat. In videos one can see the water mist being held at the back of the boat at speed. My question is what things can I do to help lessen this apparant drag at the back of the boat. I am thinking of insatlling vg's on the sides and top of the back of the boat. As I am sure that you can tell my understanding of areodynamics is very limited and at best just a lemans understanding. Any help would be greatly appreciated.

 

[rb1957]

"vg's" ?

behind your boat you have a low pressure area ... i'd try to duct air from the high pressure areas (at the front) to the low pressure ... not sure how effective that'd be.

with all your lifting surfaces, i wonder about the efficiency of your propeller (which'd work better further away from the surface of the water, no?)

 

[allblowdup]

This boat uses an impeller that pulls or has water loaded to it buy the bottom of the boat. Their is lift created thier also as the suction area of the boat get 40-50 psi at the opening of the intake wich is approx 45 sqin. The impeller is actually above the water.

 

[rb1957]

ok, it's a water jet ...

 

[aafuni]

What do you mean by VG? Vertical guide?

 

[rb1957]

oh ! just realised "vg" = vortex generator ...

don't see how they'd help reduce drag ... airflow should be nicely attached along the sides.

maybe a deflector on the edges of the stern to try and entrain air (like they have sometimes on the top of station wagons ... to deflect air onto the rear window to keep it clean)

 

[MiketheEngineer]

Stream line the back to a point so that the air flows naturally along sides and then smoothly leaves. Look at an Indy racing car - the back looks a lot like the front...

 

[allblowdup]

I had thought of streamlining the back of the boat with a sort of cone but was hopping that the vg's would help at teh back of the boat. I thinnk the sides are pretty good. The back of the boat is a flat pannel 3ftx6ft, abou the same as tailgate in a large pickup truck with a box cover on it. What methods would one use to lower the drag in this application. I was looking at a comercial product called airtab used for big trucks and rv's