Prop to jet foot transition: Duracraft 1860 tunnel/90 Yamaha

[Big Bend Brian]

Objective: Determine if my Yamaha 90 outboard is adequate to push my 1900 - 2000 pound Duracraft 1860 tunnel jon as a ~65 hp jet foot

Goal: Interchange the prop and jet foot assembly per seasonal fishing conditions (i.e. jet for winter time creek fishing, prop for summer flats, hunting, scallops, etc)

I recently bought a used Duracraft 1860 tunnel with a propped Yamaha 90. It runs very nicely but I also wanted a boat capable of shallow water wintertime creek fishing. Since my goal is to be able to switch back and forth seasonally between a prop and jet foot, I had a 6 inch jack plate installed (plus negative feedback steering). Fortuitously, an Internet friend knew of a barely used Yamy 90 jet foot lower unit (< 1 yr old. Thank you yozuriken). After some more extensive consideration about this hull/jet foot application I went ahead and bought the jet foot still not knowing if this was going to work out or not. The sellers boat was similar to mine but with a few differences-the jet did not perform well on his 1860 Duracraft tunnel hull).

For quite awhile I questioned whether this application would work as my Duracraft is extremely heavy for a jon boat. While looking at a jet foot graph of hull weight vs. horsepower I learned that a 90 hp outboard (~65 hp at the prop) can only push a maximum of 2000 lbs before it starts to run sub-optimally. With this in mind I took the boat to a local scale (agricultural station) and the boat and trailer weighed in at 2300 lbs even, which is pushing it for a 90/65 hp outboard/jet foot. I’d also add that a number of people in the marine and jet foot industry (locally and out of state) stated that this application wouldn’t work. I figured this application if anything would be marginal at best but it was still worth a try.

The transformation from idea to reality happened yesterday. One very nice individual I talked to, Captain John Morris out of Inglis, stated he would help me swap out the lower unit. Captain John is a Crystal River guide who has a similar boat (Duracraft 1872 tunnel) and motor application. Since he swaps out his prop for a jet foot during the winter time tides he knew the subject well. With such an outstanding offer from someone I’ve never met before we talked a number of times and got our schedules to jive. Yesterday, I drove to his home with the boat in tow and we proceeded to swap out the lower unit, install the jet foot, and sea trial it.

The dropping of the lower unit and the addition of the jet foot went without a hitch but after the first sea trial, water was spewing up everywhere off the jet foot and the jack plate. Despite this the boat got up on plane well and had a max speed of 28.4 mph @5100 rpms (via GPS, 2 men, almost full fuel (20+ gals), and stiff chop). It would stay on plane at 17 mph @ 4300 rpms but ran best around 4700-4800 rpms. Knowing the motor needed to be raised even more to eliminate the spraying we took it back to his house and under a stout tree we lifted the motor off the jack plate and reset it approx 2 inches higher (using the top hole patterns on the motor mount). This time when we ran it there was less spray, the performance was about the same as before, however John still thought the motor needed to be raised another 2-4 inches to eliminate the remainder of the water spray. He then took me out in his 1874 jet foot rig and if was evident he’s right.

I’ll still have to tweak this a bit (1. rivet/screw a 17â€

[Ybnormal]

BBB
I have been where you are, I just sold my last Jet foot rig on this forum, you can see pics of it in the for sale section of this forum,

There are several things you can do to improve the performance of your rig, My boat weighed about the same as yours However I had a slightly smaller engine. 65EO, 45 Jet. I was getting a little better speed that you currently are,

Step one, LOOK at that impeller, See how dull the leading edge of the impeller is, Fix that with a file,, A sharpened leading edge will improve the bite in the water flow, and pump more water.

Step two,, Look at the Grass grate on the bottom of your jet ,, See how dull the leading edge of the grate grids are,, Fix it with a grinder or file,, sharpening these will improve the smootheness of the waterflow into the pump,, it will pump more water.

Step Three if you can afford it, Buy a stainless steel impeller, They are thinner, sharper, and last longer, and oh by the way pump more water.

ALL this equals speed and perfomance.

There is at LEAST 25-30% of gain to be had doing these modifications.

One more note,,, get that motor as high as possible in the water stream coming from the tunnel, any spray equals drag and wastes performance. My unit was almost 2.5 inches above the bottom the boat and .5 inches above the tunnel at the leading edge and performed great..

Hope you enjoy the jet, I know I always did,,

Dang I think I miss that boat
rs

YBNORMAL

[catchin1]

Intresting read BBB. You never know till you try.

[Second Chance]

BBB,
Great read and interesting one since I bought my first jet boat a little over a year ago. I needed the jet for the fishing we do up here on the Hooch. Lots of big rocks/shoals that require you to be able to run in 6" of water. I setteled on a G3 flat bottom 1652 with a Yamaha jet 40hp. I was curious about your experience with the tunnel hull since without exception all the "experts" and/or experienced jet boaters steered me away from the tunnel. Had something to do with unstable water that is directed at the water pick up vs the smooth water coming from a flat bottom. I'll be interested in how yours performs once you get all dialed in. The only lesson I learned while tweaking mine is the importance of the motor height and buying a good adjustable jack plate. 1/4" up or down can make all the difference in your performance. Anyway keep us posted, you are going to love that you can now run places that you would never have attempted before. Remember the jet boat credo " when in doubt ride it out"