SaltyCajun.com - Jack plate on a tunnel?

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Jack plate on a tunnel?

I know I'm opening pandora's box, but what are some thoughts and theories on using a jack plate with a tunnel hull. I am speaking of the 18'-20' variety with a 40 HP. I had a 17' tunnel with a 25 HP with no jack plate that I ran for years. Like to hear pros and cons with and without.

In JB, we run a 18ft vented tunnel with jackplate that I bought from you, and a 25 tahustu.

I've seen/ran that boat in some shallow grassy stuff. if you get your weight distributed out, it hops up in shallow stuff.

Quote:

Originally Posted by huntin fool (Post 369633)

Have you ever run the same rig without he jack plate?

Here's a good explanation from someone that's pretty good with this stuff:

Quote:

Originally Posted by 1995 US1 (Post 7922743)

First, flatbottoms and marsh tunnels are two totally unrelated animals. I have an 1844 AlWeld Tunnel. The transom is 20" tall from the flat bottom to the top of the transom. My motor is mounted 1 1/2" above the top of the transom, for a total motor height of 21 !/2'. My motoor is a short shaft, 15" shaft.
Now the reason why a jackplate is nearly useless on a tunnel. The tunnel is shaped in a way to funnel water to the prop right at the back of the transom. The minute the water in the tunnel under the hull clears the transom, it goes to the sides, down, up, all directions. Because the area behind the transom is a low pressure area, compared to the boat bottom or the tunnel, there is nothing to direct a water flow to the prop. The further behind the transom you move, the more the water is spread out. Think of the tunnel as a water hose, the further from the nozzle, the more spread out the stream becomes. If you keep the prop right behind the tunnel exit, that is the area of least dispersment, the prop bites better. With my motor sitting 21 1/2" above the bottom of the boat, the hull can hit something and the motor never touches it. Why go any higher or further back? Hope this makes sense.
D

Quote:

Originally Posted by scott craft (Post 369639)

Here's a good explanation from someone that's pretty good with this stuff:

I agree. I just wanted to hear it from someone else.

If you run in a lot of grass or lillies, get a skag in the tunnel also.
I ran a 20' X 36" with a tunnel and jack plate with a 40 Merc.
I caught less weeds on the foot with the jack plate, but got a
skag due to where I hunted gators and never had issues with grass
again.

Tunnel hulls work best without a jack plate. The closer the prop is to the tunnel the better. It will run with a jack plate too but you will have to add more cup than normal to the prop and will loose bite more in turns. If you do use a jack plate get one with no more than 4" of setback.

Quote:

Originally Posted by scott craft (Post 369639)

Here's a good explanation from someone that's pretty good with this stuff:

Quote:

Originally Posted by 1995 US1 http://www.saltycajun.com/forum/imag...e/viewpost.gif
First, flatbottoms and marsh tunnels are two totally unrelated animals. I have an 1844 AlWeld Tunnel. The transom is 20" tall from the flat bottom to the top of the transom. My motor is mounted 1 1/2" above the top of the transom, for a total motor height of 21 !/2'. My motoor is a short shaft, 15" shaft.
Now the reason why a jackplate is nearly useless on a tunnel. The tunnel is shaped in a way to funnel water to the prop right at the back of the transom. The minute the water in the tunnel under the hull clears the transom, it goes to the sides, down, up, all directions. Because the area behind the transom is a low pressure area, compared to the boat bottom or the tunnel, there is nothing to direct a water flow to the prop. The further behind the transom you move, the more the water is spread out. Think of the tunnel as a water hose, the further from the nozzle, the more spread out the stream becomes. If you keep the prop right behind the tunnel exit, that is the area of least dispersment, the prop bites better. With my motor sitting 21 1/2" above the bottom of the boat, the hull can hit something and the motor never touches it. Why go any higher or further back? Hope this makes sense.
D

a good after market cavitation plate and the right prop can solve this problem.

http://www.boatrightmarine.com/cuerp...ies&modelid=55

problem solved tunnel extension and I can run my cmc trim with set back

i ran a 15foot tunnel with a 40hp, picked up 2-3mph with a cmc jackplate and another 2-3mph once i got the prop cupped properly,