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EZ Tunnel Race Boat Plans
Page Ten
Other Hardware

The area behind bulkhead four, now with equipment in place.

The fuel tank is held down with a ratchet strap.

The battery is held in place with two rubber bungy cords, although a ratchet strap would work as well, maybe better. The (red) cable from the positive pole leads to a battery switch (not in the photo), then continues to the trim pump and the starter motor.

The trim pump is bolted to the motorboard.

On the dashboard I have installed a Tiny Tach tachometer; emergency kill switch (required for racing); water pressure gauge; and choke/primer button.

The water pressure gauge is a good idea as engines on racing boats are mounted very shallow and pumping cooling water can be a problem. My gauge came from Surplus Center.

Trim buttons are mounted on the right side of the steering wheel.

I also like to mount my start button on the wheel.

If you intend to race your boat, you will need four attachement points for your lifting sling, used to hoist your boat at the scales. Keep in mind, when you weigh your boat, you will be hoisting your boat, your motor and yourself. That's 650 lbs. minimum for GT Pro. Strong attachment points are a must.

The two forward lifting points (see plans drawings) consist of two 1/2-inch diameter shackles fastened through the beam at station three. Behind the beam, on both sides of the cockpit, blocks are glued to the coaming to help offset any twisting forces on the beam. Also, two 2-inch-long screws have been driven through the beam either side of each shackle to help prevent splitting of the beam.

The aft lifting points consist of two u-bolt type bow eyes mounted through the motorboard. These are not your typical hardware store variety u-bolts, but significantly heavier ones made for marine use and available from marine hardware suppliers.

These u-bolts come with two metal plates. Use caulk under both of them to keep water out of the holes bored through the motorboard.

A jackplate and hydaulic trim system are excellent additions to your tunnelboat.

You can find more information about jackplates HERE

You can learn more about adding trim to your boat HERE.

A word about motor height.

On a typical fishing boat, the motor's cavitation plate is about even with the bottom of the boat, or up to an inch below the bottom.

Motors on racing boats are mounted much higher. As counterintuitive as it sounds, the idea is to get as much of the prop (or at least the gearcase) out of the water as possible.

On one of my v-bottom boats, mounting a 15-inch motor on a 20-inch motorboard is just about right. Performance-wise, you could go even higher, but will no longer be pumping cooling water, and I'm told that can be a problem.

On a tunnelboat, however, you can generally jack your motor up as high as performance dictates, to the point where the entire "bullet" is actually above the deepest part of the boat. There will still be plenty of spray coming through the tunnel to feed the cooling water intake, and you will have reduced engine drag to the barest minimum.

One caveat: If you wish to take advantage of this sort of engine setup on your tunnelboat, you will surely need hydraulic trim. Without the ability to trim your engine down, pushing your prop deeper into the water, and directing thrust downward somewhat, you will never get your boat on plane.

Another caveat: As soon as you jack your engine much above the fishing boat setup, you will need a prop that has been "cupped" on the trailing edges.

Cup, a slight curl at the edge of the blade, increases the grip a prop gets on the water, and is essential in any situation where the blades are piercing the water surface.

Any prop shop should be able to cup your propeller. Many props come from the factory already cupped.

I bought this Ron Hill cleaver a while ago, and tested it on another GT Pro tunnel boat (since moved up to Sport C). It was slow to get on plane (needs more cup) and slow to accelerate. But that boat was way overweight (by 50 lbs. or so) and yet it still topped out at 49 mph.

I plan to get some work done on this propeller and test it on the EZ Tunnel in 2012. I'm very optimistic.

This prop is 9.75 inches diameter (too small -- 10.25" to 10.5" might be better) and 17 inches pitch.

Ron Hill is in California, USA. See him on ebay: stores.ebay.com/Ron-Hill-Propellers

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