See full version: Troutt and Sons Inc
Aluminum is usually the material of choice. It is light, tough and easy to form in the proper configuration. For outboard jets, the bottom thickness can range from 1/16” (.063) for 20-50 HP to 3/16” (.187) for motors up to 225 HP. The lighter gauge is more easily damaged whereas the heaviest gauge can be a weight problem on midrange power from 50-100 HP.
A properly designed tunnel, combined with a slight V bottom hull can greatly enhance jet boat performance. It should raise the motor 2-3 inches and place the heel of the jet intake flush or slightly above the bottom of the boat. A jet tunnel doesn’t work well with a flat bottom boat due to air ingestion. It’s imperative that the hull is designed correctly with the tunnel for the boat to operate properly. [links]
For over 40 years, Outboard Jets has provided quality conversion units for outboard motors designed to allow a boat to be used in locations where a propeller driven boat is unable to operate – in shallow, ankle deep water.
A slight V of 6-10 degrees dead rise will enhance jet boat handling. Deep vee is not desirable for the Outboard Jet, not just because of increased draft and drag, But because the Outboard Jet needs a flat apron of water about 10” wide leaving the hull on which to set the leading edge of the jet intake, to minimize air intake and frontal drag. The dead rise should be fairly constant and not increase to a deep forefoot at the bow. A deep forefoot can cause spinout on a sharp turn. more
The early type intakes use liners for 6 5/8, 6 7/8 and 7 3/16 impellers. If the liner is removed, and the mounting holes plugged, a 7 3/8 impeller can be used, but there is no replacement liner for wear. The new type intake uses a liner for 7 3/8. The casting is larger on the outside to accommodate the 7 3/8 liner. It is identified by the bolt head relief in the castings for wrench clearance at the six holes. [links]
Stainless steel impellers work well on motors above 100 HP. They give less slippage on start up and therefore can pickup a heavier load. Top speed of, maybe, one to two mph or better. Below 100 HP, the main advantage is longer wear life. more
The height is approximately six inches higher than with a propeller. It varies between different motors and boats. When the jet drive is on the motor, set the height so that the leading edge of the intake is flush with the boat bottom. Then test the boat and adjust the height, if necessary, as high as possible without air entering the pump and causing cavitation (slippage).
You must raise the engine approximately 6 inches higher on the transom than with a propeller until the leading edge of the intake is flush with boat bottom. (See earlier question and answer)
This stands for Spot Facer and Drill kit. It is used to drill a hole and spot face a seat to receive a bolt from above at the rear of the engine midsection. This is not used on all motors. See the Jet Drive Kits list. here
Re: Setting up and outboard jet here
Re: Setting up and outboard jet [links]
I read the info available at the site listed. It doesnt answer any of my questions in my post. I am not building a boat. I am trying to dial it in. I cant change the angle of the transome. All I can do is lower or raise the motor on it. It does not have a tunnel. [links]
I have a 50hp Merc with a jet pump on a 14' Valco flatbottom boat. I think the transome as it is makes the jet nozzle to high. As I cruise almost all of the thrust is above the waterline. I am hoping that If it is not set up properly I will be able to fix it and get another MPH or two out of it. I average 14MPH upstream with 2 people, dog, and decoy bag.
Re: Setting up and outboard jet
Browndog <br />If you don't ventilate in turns and the boat performs well leave it.All you will do is create spray and loose top speed by lowering it.
I don't have a tunnel hull, just a normal transom, with a 6 degree vee to it. After looking at the diagram posted and the other advise, it looks like I am about 3/4"+ too high. The beauty of it is I have a lot of adjustment in the mounting holes on the motor since it is mounted in the highest position and I have plenty of downward adjustment. I think I will try lowering it one hole and that should get me in better shape. Problem is, is, everything is froze up tighter than a wedge and it's gonna be a while before I can try it out. Thanks for the help, JPS here
Re: Mounting height for jet drive?
Re: Mounting height for jet drive? here
I've run a few jets and can tell you that mounting height is extremely critical. And every boat/jet combination will act differently.<br /><br />The best advice would be to mount it on a transom jack, giving you the ability to move it up and down according to load and water conditions. One disadvantage with this is even more added weight than you already have, and that weight being even futher back on the boat. One advantage to the transom jack is that you usually get more power out of the jet because of the water flow there.<br /><br />If only half of your foot is below the boat bottom, I would guess it's too high. I remember the leading edge of the intake grate being level with the bottom. Sometimes even a 1/4" can make a big difference. You'll just have to try it.<br /><br />Remember, the bottom of the boat and how the water flows off of it, is just as important with regard to performance. Expect cavitation from time to time, but in general the outboard should maintain it's "grip" even when turning. here
This isn't the best picture but is the front of the intake level or just below the bottom of the transom ? Does your boat have a tunnel built into it ?