Jacking plate set back, running in shallow water.

[poida]

Hi All
I bought a flat bottom to run in a very shallow inlet, well parts of it. To get in and out of the rivers and out to the mouth you sometimes have to chop through (or drag it) water that is about a hand deep.
I have attached some pics of the boat and the motor as it is. I think the motor can come up about 8cm until the cavitation/ventilation plate is level with the back of the boat.
The person who is making the plate is asking me how much i want to go up with to start off with and how much set back. I was going to request 8cm of uplift to start (the plate will have 15cm of adjustment up) to put the cavitation plate level with the back of the boat.
I quite often/always have to tilt the motor and chop in at low speeds whick can take a few minutes.
The inlets levels can vary with the tides and if the bar is open/closed to the inlet.
Any ideas how far i should request the setback? The boat planes well atm.
I need to be able to run this motor and boat in the shallowest possible water, any info of low water intakes would be appreciated. I do often bounce the motor and the hull across the sands and weed.

 

[Teamster]

Re: Jacking plate set back, running in shallow water.

It could come up a bit,...

I doubt you'd see much benefit from setback,..........

 

[mrdancer]

Re: Jacking plate set back, running in shallow water.

You can raise the motor another 25-50cm, possibly more, if you have about a 250cm setback. Of course, this will change the handling and attitude of the boat, but it will get you shallower. Along with that, you might consider a prop with larger blade area to grip the water better - consider a good SS four-blade prop or a prop designed for tunnel hulls. Add an anti-ventilation plate (often called a cav plate) to help hold water around the lower unit and water intakes. You can often plug the top two intake holes to keep from sucking air and still get plenty of water for cooling, unless your cooling system is already compromised. Also, some mfrs. make "racing shrouds" that help force water into the stock intakes when running the engine in higher positions. You could probably do the same thing by laying a bead of silicone caulk directly behind the intake holes to help direct water into the holes.

I'd highly recommend an electric hydraulic jackplate that you can adjust on-the-fly. Bob's Machine Shop Bob's Machine Shop has smaller jackplates that would suit your application without adding too much weight. Mount it so that the lowest position of your motor is even, or slightly lower, with the bottom of the boat, then you can raise it up to 152cm from there, as needed for shallow areas.

 

[poida]

Re: Jacking plate set back, running in shallow water.

I was thinking of the manuel plate to save some $$$ but i imagine by the time i get the height right to skim through the shallows that i will cavitate/ventilate through the chop in the middle of the inlet. I think that the electric/hydralic might be the go for this situation.
Looking at bob's website he has transom mounted water intakes, does anyone know how these work?
I'm not sure the racing cone type ones would be great for me as i often bounce the bottom of the boat and prop/outboard across the bottom.
The boat sits in about a hands depth of water and this is sometimes what i am faced with to get where i need to go.

 

[mrdancer]

Re: Jacking plate set back, running in shallow water.

I was thinking of the manuel plate to save some $$$ but i imagine by the time i get the height right to skim through the shallows that i will cavitate/ventilate through the chop in the middle of the inlet. I think that the electric/hydralic might be the go for this situation.
Looking at bob's website he has transom mounted water intakes, does anyone know how these work?
I'm not sure the racing cone type ones would be great for me as i often bounce the bottom of the boat and prop/outboard across the bottom.
The boat sits in about a hands depth of water and this is sometimes what i am faced with to get where i need to go.

A couple folks on the boating forum at 2coolfishing.com have done the transom-mount water pickup and seem to be quite happy with it. I would avoid the nosecone as you will be more likely to suck up mud/sand into the intakes - those nosecones are more for bassboats running with the engine jacked up to get more speed.

When/if you're going over shallows on plane, your boat will essentially draft 0" of water (since water is incompressible); therefore, whatever is hanging below the bottom of the boat is what will limit your running draft while on plane. I run a tunnel hull, so I can run my 13" prop through 6" of water when on plane. Think about your setup and what you are trying to accomplish. You may be able to drag your skeg through mud/sand while on plane, but it will become an issue (meaning you shouldn't do it!) if you are going over rock, oyster bars or sea grasses. If you're just going through mud/sand, make sure your engine is high enough so that you only have six inches (hand-deep?) of prop below the bottom of the boat. To get the prop that high, you need to set the motor back. If you were running a tunnel, however, you would already have the setback built into the boat and would want no additional setback. Hope that makes sense.