Pocket Drive - modifications - photos

I have to ask, is the design just that incompetent, or was it a poor build? Because that tunnel is wretched.

 

Hi, just a bad design. A lengthy & tapered pocket entry was difficult to achieve without raising the engines and transmissions (ie, deck height), as the pocket would touch the oil pans / transmissions. Pulling the boat soon to start making a few mods. I will post / photos of the mods and the results.
Unfortunately, will do several mods at once, so hard to tell which mod added the most benefit.

 

Clear design failure. Only question is how. Given the fact a complete idiot like me sees that and sees a suction potential should beg the question why they at least didn't attempt to close off the shaft a bit more and add radii to the sides.

I still think an angle would help with the suction. If I were ever going to repower, I'd bracket and ob the boat.

 

Is there not enough space for a sigmoid curve transition from the hull bottom to the tunnel bottom.

 

@Mike Goebel , I hope I didn't offend you with my blunt question. I'm not good at filter.

 

us blunting and lacking in 'these' filters types - stick together, but often admonished for being such

 

I'm a generous man. I share my thoughts.

 

Conversationally, not more, I'd get a piece of coosa and glass it well on the back and cleat all around and bond it in and some glass on top and see what happens.

As the idiot in the room, I would really like to know how baeckmo's list of woes lands ito percentage of issues.

Like, for example, current boat is 100%. L/B would offer 18% improvement. Tunnel fairing front x%, tunnel radii on sides, y%, etc.

And if I'm outta line, give me a pass tonight please. Today was a hard day.

 

Yep, agree, plan is to taper and smooth the pocket inlet to be at least be linear to the prop strut.
Looking at grinding off the bottom paint, laying up some closed liquid foam, grind it to a tapered shape, then glass it in.

 

It can hardly make it worse.

 

Unless...
Can you ventilate that pocket? Run air lines down to the unfortunate front ends, and then the merciless suction won't be such an ugly turbulent mess.

 

Nope, that will introduce more air to the already overloaded propeller disc. One of the observed effects of this tunnel shape is air drawn into the prop from behind during hump passing. My first thing to do would be to attach a rubber flap to the tunnel outlet, fencing off 2 to 3 inches of the tunnel roof to prevent ventilation.

 

Easy enough. And just to be clear, this is to avoid the suction pulling air back in from the top of the tunnel and not for compression ahead of the prop as we would see in tunnel for ob?

 

I recently saw several newer large model SF boats with an engine exhaust ring dumping exhaust into the top of the pocket, in front of the props. I saw this also on some offshore racing boats years ago. The thought is that you can put air into the top of the prop, creating quick acceleration of the engine RPMs into the upper Horse Power curve, and allowing the bottom of the prop blades to dig in. This allows running a higher pitched prop producing less drag......ie, kinda like an outboard trimmed up when at speed.

 

Levi drives use the same system. It ventilates the prop enough that the engine can get up into a decent RPM range. And of course, ventilation prevents cavitation.
Naturally this is no solution to an improperly formed tunnel, but at least it might make the flow less brutally turbulent, with a little less performance destroying drag from the flow being reversed in some areas. But of all the potential remedies suggested, this is at least cheap and easy.