GX390 Build

[Bansil]

Great info! Thank you.

So its wayyyy in the future BUT what are plans for the finish? Wrap or rattle can/1 stage paint? What will it weigh loaded ready to hit the shallows?

 

[Denny]

I hope he polishes it. I would after all that work.

 

[Mammoth]

A mirror finish would look awesome except the flat surfaces are so large the suns reflection burns eyeballs out. Just the finish on it now is too much in the sun. I've polished enough aluminum to know its a lot of work, and you can't even touch it without leaving a mark. Lake water oxidized aluminum pretty quick. It wouldn't be the same after the first use.

I will probably end up painting it with a spray gun, but I can't get too carried away. If I make it nice I will freak out if I scratch or dent it, and I can't be tip toeing around where this is going.

It will be a bare bones build to keep the weight to a minimum. None of the extra stuff people put on. Anything extra will just make it sit lower in the water, hitting more rocks and causing more drag.

Ive been focusing on keeping it light weight from the start. All the bolts on the engine are either titanium or aluminum except the ones that have to be steel. I'm in decision weather or not I should install a smoke system because it will save a few pounds.

 

[Denny]

Have you given it any thought to having it hard anodized? It can’t be that expensive.

 

[Bansil]

Have you given it any thought to having it hard anodized? It can’t be that expensive.

Finding tanks setup to do hard anodize will be fun, I know Ken built the longest tanks East of the Mississippi maybe 10 years ago, because he got a flagpole contract. they where like 6 ft tall and 2 ft wide and 40 ft long, he sold the business maybe 5 years ago.

 

[Denny]

Check west of the Mississippi then!

 

[Mammoth]

Spending a couple hours each day on the bodywork. It was pretty lumpy after assembly, but with lots of sanding and some hammering its starting to come around.

 

[Mammoth]

Too many builds at once slows me down on this project.

Most people leave the window solid aluminum, then use large seats to where there head is above the windshield. This makes wind drag and exposes them to the elements. This also raises the center of gravity and I've always been taught to keep the weight as low as possible.

To improve upon this I will be running the seats all the way to the floor with a uesable window. I modified the window quite a bit.



Many jet boats have a lexan windshield held in place by a rubber gasket. The rubber gasket makes a big bump which on a windshield is the worst place to have a bump when considering aerodynamics.

To work around this I spent the extra time flush mounting the window making it streamlined.



I cut and sized clear lexan to fit with aluminum tapered head Allen bolts holding it in.



Next obstacle is the prop tunnel. After studying everything i could find on tunnel sterns I figured out how the shape will be and drew the footprint on the hull. Im waiting for a prop thats on backorder to begin this next faze.

 

[madprofessor]

Very impressed with your little squirt boat. Do I understand correctly that you'll power it with a single-cylinder 390, like for a gokart? What kind of pump could you use for that?
Mine was a 23' Spectra hull, bare inside but for some green Astroturf and a stereo, with a Lincoln 460 cu. in. monster under a Holley 751 double-pumper, direct-coupled to a Berkeley pump. Raw exhaust, not a wet exhaust or even dry marine headers, just straight off the manifolds, poked through the transom. Neighbors hated me, so did a lot of the people on Pottsburg Creek and Arlington River. Named it the "Swamp Rocket", 60mph in a foot of water.
Word of experience: Make your tunnel intake ridiculously oversized, with a tight set of steel bars. Mine was 2' long and about 8" wide, and I tried to launch it from a standstill in 6' of water. Sucked up oyster shells from the bottom, jammed in my bars, broke up the vortex too badly to even get it up on plane. Overboard without even a mask, using a 14" screwdriver to pry out the shells.

 

[Mammoth]

It's a mini jet boat hull, but I'm going to use a 12" propeller that will be tucked inside a tunnel to increase efficiency. I'm trying to build a light weight efficient boat that can go long distances and be able to take a beating.
If I can pull this off creeks and rivers turn into roads opening up alot of areas for exploration.

Wasn't expecting the propeller any time soon, but surprisingly it showed up today.

 

[Denny]

This is a cool project!