When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. I recently bought the moulds from a procrastinator who left this sitting in his yard for a few years.
The only thing that strikes me is the potential for turbulent water flow at the leading edge of the tunnel. Location: Canada firth_andrew007 - if this is a planing tunnel hull, then you may find some help on my website. I'm not sure that the reduced buoyancy from the tunnel is worth the reduced wetted surface.
It will be a question of whether your AoA is reduced sufficiently at speed to negate the loss of buoyancy at the stern.
Location: Coastal Georgia You might have to vent the tunnel to break the suction.
The transom is lifted 6 inch high, and my doubt is the shape of the pocket tunnel, because I see several diferent shapes (semicircular ,rectangular,trapezoidal)Which one provides more water flow to aviod cavitation or prop ventilation? Location: Milwaukee, WI I don't think anyone can give you good advice unless they know what the design is. As noted by Gonzo, you must understand what happens to your hull when you change the buoyancy. Location: Milwaukee, WI With the cost and time of all that, it may be better to install a jetdrive. Location: Milwaukee, WI Both boats you are showing, have sponsons that provide extra floatation aft.
Depending upon how much you raise the engine you inital acceleration will wb slower, however, with the right porp your top speed will be higher.
Location: argentina Gonzo, my idea is, if is necesary add sponsons to mantain original flotation level.
The intended purpose would be shallow river operations AND, retaining the outboard, not changing the lower unit over to jet drive.
Location: goldcoast hahah yeah i might just build the extension for the outboards for the moment.
Location: goldcoast but a mono hull at the bow and a tunnel hull come stern??
Location: Australia The boat I built looked eerily similar, looking from behind the stern, as yours, it had one outboard centrally mounted behind a nacelle in the tunnel, the cav plate about half way between the roof of the tunnel and the bottom of it.

Location: Australia I can't speak to the motives of the designer of your curiosity-piece, but my intent was to create a vessel with the kind of ride quality and resting stability of a cat, without the need for twin engines.
Location: florida Pocket tunnel design HELP We are working on a new boat model but are having problems with the pocket design. Location: florida We use tunnels to pull water up in the hull so you can jack the motor up higher to run in shallow water. Location: Upper Midwest Have you considered shaping about the aft third of the hull into a great big NACA duct?
Location: florida The problem is that this is a wide flat bottom design with a outboard that only runs in 2-3 inches of water so I am trying to pull the water up into the boat so I can raise the motor up below the bottom of the boat or close to it. Location: florida I want the boat to draft less than 6inches and run in 3-4 inches. This would require a boat that lifts while running at speed, and it also leaves out the Seabright skiff hull design -- along with its well-known seaworthiness in offshore conditions -- so I think the flatscat suggestion is more along the lines of what you need.
Note that the top of the tunnel will be vented to allow compressed air to escape rather than be forced into the water in the tunnel.
You will probably also note that the boat is designed to use an inboard engine installed in the center console (not shown, nor is the rudder and other non-hull features).
I like the inboard diesel for fuel economy as well as the fact that the stern is completely free from equipment, so you can walk around the aft end of the boat and fish from there with no obstructions to get in your way. Note that the transverse section is not critical, since there is very little rotation in front of the propeller; a smooth longitudinal curvature is what matters in addition to the correct transverse areas! The tunnel shape given above, is the shortest possible (=least loss of volume) for good inflow to the propeller. That worked OK, don't worry that the forward part of the hull will interfere with water flow, the level just rises to meet the prop. I'd say it met those criteria, but I was never happy with the tracking in an arc between beam and stern quartering.
This is a flat bottom boat design and because it doesn't ride deep enough in the water we cannot get water in the pocket. CANADA Pocket Tunnel The pocket tunnel design on the Henderson skiff is interesting. I came up with the design and notified Jacques Mertens owner and designer of the company.We put our heads together and came up with the XF20.
If you look at the modern inboard tunnel jets ( Phantom sport jon, Seaark predator, Harbercraft extreme shallow ) you will notice some major differences.

Many of them are very knowledgeable, have decades of experience, and are generous enough to lend sound advice. Also observe that the section aft of the prop cannot have a horizontal roof since that causes a reversing flow that will aerate the propeller from behind!!
Seems like a tunnel to me, the inlet part of the tunnel I referred to is still relevant with an outboard. A word of caution, MAKE SURE THE CENTERLINE OF THE PROPELLER IS BELOW THE BOTTOM OF THE BOAT! ASSEMBLY INSTRUCTIONS 12455 Click to write a caption for this image.Copyright 2010 Ceasar Infatable Boats,A US. It did have some handling peculiarities inasmuch as it tended to jink around a bit in beam seas, but ride and stability were good. My boat was considerably deeper forward than yours, but a differently proportioned thing altogether, not long and skinny.
I can put a full tunnel in and get all the water we need but then loose the draft I have to keep. You may want to have a look at the Glen-l builders forum as there is an archived discussion regarding pwc powered boats. See also a boat called Rescue Minor built more or less to Atkin design by the late Robb White. Chris Ostlind also designed a pocket tunnel I saw on Duckworks (Blackwater 16) which is a scaled down version of Capt. I did not use low water pickups or expensive double cupped props and achieved some pretty skinny water results with no cooling or cavitation issues. This week we will look more closely at the third part of the picture - the Dynamic Force Balances. I have also read that these tunnels are also sometimes vented at the top of the entrance with an elbow and tubing thru a ball valve and then discharged over the transom to alleviate priming problems.
1 Lift and WeightThe hull weight (including engine, driver, fuel, accessories, payloads, etc.) must be EXACTLY equaled by the lift forces generated.

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