Vids of some fast Mo. boats

[Ranchero50]

Ranchero, Outboards are a whole diffrent beast than your inboard.

This is the second time you've typed this, it's starting to sound like some kind of juvenile put down... [-X
If you don't have anything positive and constructive to add perhaps you shouldn't...

it is a balancing act. There is a point to which you bounce too hard and it does slow you down. Its hard to explain without actually showing you. When some boats bounce, you can feel the boat rise out of the water and lunge forward, this is when it runs at the most optimal. Some boats just feel as if the boats bow sit there and slap the water, this does nothing for performance. You can over trim to where you suck air in the pump and you are hitting the water so hard it slows your momentum. but in theory, water causes friction. the more time the boat is in water, the more friction it fights. in an 800 ft race, if you could measure the time the boat is out of the water, it reduces the amount of friction.

I do understand your thoughts as the boat hits the water more violently causes more friction than a smooth ride. its a constant give and take to what works best.

That makes sense. Any of the boats I've ran (IO, IB jet, OB jet) seemed to run fastest right on the edge of porpusing when the front end feels like it's fluttering in the air as long as the pump was staying loaded. When they porpused they didn't seem faster but I never chased the idea or had a GPS to figure it realisticly. The paddle wheel on my boat shows different speed depending on where it's located (I guess from different pressure levels under the hull at different places). I wondered if the porpuse action is loading the pump and motor harder vs. just changing the hull dynamics.

Like I said, interesting stuff and I love understanding the why and how vs. 'just because'.
Jamie

 

[Lil' Blue Rude]

I'm just telling you the truth, it's not a put down or anything like that. I was just stating a fact. Outboard and inboards are 2 diffrent things. They react diffrently to diffrent things.
Just like the last time I told you that was when you told someone not to trim his motor all the way down to get it on plane quicker. Outboard jets get up on plane quicker when the motor is tucked under.
Kinda think I've got the right to get on and answer a post on a thread I started as long as it's not crossing any lines, don't think I did.

 

[Ranchero50]

Ok, on the first one, if your powerplant is strong enough by having it trimmed out a bit it'll surge the nose up out of the water and over the hump of water you are pushing. If you have to trim down you are trying to push the nose into that wave. The more hull you get out of the water the easier it to accelerate the hull to planing speed. I've found that a simple wing on the outdrive makes the planing hull longer and it'll pop out of the water easier. Trimming the nozzle isn't nearly as effective and could be considered a stop gap by the manufacturers. This is just stuff I've experienced and worked through on boats I've had.

On the second, my IB Jet is a basic jon boat with a different balance point and don't see a huge difference vs. a OB jet hull except the OB has more weight hanging off the back. The thrust angle and point of thrust are pretty close between the hulls. The only real difference I've noticed is once you trim the OB too far out the foot loses it's ram effect and you'll slow down a bit. Found that on my friends 16' Ranger with a 90/65 Merc. It's a very heavy hull and ran faster trimmed out but it lost the ram effect into the pump. I haven't gotten to play with it since rebuiding the pump and adding the wings but he said it runs a lot faster since the repairs. The biggest curse with my IB jet is air ingestion since so much of it's out of the water at speed. I had to build a spoon to keep the pump loaded and it seems to work well. After adding the pods when the hull would porpuse I had to trim it down to keep it from porpusing and the hull slowed down accordingly but even when porpusing it wasn't as fast as it was pre pod or post trim tabs. Interesting stuff.

As I said above, I'm more interested in the dynamics of why porpusing works for you guys vs. a IB/OB peeing contest. I would love to build a spoon fed OB foot or even a hull mounted tunnel in the form of the back side of the spoon to feed the OB pump. The end goal would be to get the foot 3-4" higher so it's further from rocks when coming off plane and maybe if it worked well enough get the OB trimmed out further to increase the speeds.

Jamie

 

[Lil' Blue Rude]

turner032 exlpained it, the more boat you get out of hte water the less resistance you have. I see your point about it slowing you down when the boat comes back down and if you get to slapping too hard it will slow you down.
I know one thing, it works, I always run faster when I'm hopping it and I proved it time and time again with a gps. I'm not tryin to have a pissin contest with you but you can't seem to under stand outboard and inboard act diffrently, what works for yours might not work for mine and works for mine might not works for yours. Here's some food for thought the outboard jet might have some more leverage siince it's on the back and clamped at the top of the transom. Kinda got the pry bar effect.

 

[riverracer]

Maybe this is something that works on smaller boats, cause when I get into the upper 50's my boat wants to turn into a kite, so therefore I dont want mine porposing like that. I think there is a sweet spot for every boat to run the best. As soon as I get some pics of my new boat I will post them. I havent gps's yet, I cant find anyone brave enough to ride with me and hold the gps !!! lol

 

[turne032]

I'll ride with you!!!

 

[turne032]

inboard vs outboard

"my theory"

the point at which the pump loads has to make a huge difference. As a inboard pump loads about 2 feet in front of the transom and the outboard is 4-6 inches behind the transom. If an inboard is bouncing (porposing) it cant load the pump. No water in pump means no speads out of the pump.

I think power to weight ratio has a big part to play in performance as well. I would really like to measure the speed at which water exits the pump on a 40 hp vs 200 hp vs inboard. (my opionion is that the water speeds are closer than what we think. The difference being the volume. But then again i have no proof for my theory)

there is a point in which the motor is too much for the boat. The result would be the boat taking off like a kite. its similar to car drag racers trying to put the horsepower from the motor to the tires on the track.

 

[Ranchero50]

Stuff I've read and think I've figured out

Mass (vol/sec) x Velocity (ft/sec) = Thrust (lbs/sec), same principle as a jet engine except you can't compress water to ignite it. The thrust of water coming out of the nozzle doesn't have to be aimed at the water or underwater but seems to work best when aimed straight out the nozzle (less angular thrust losses)

On loading, I think the biggest hurdle is getting a bit over the full nozzle volume against the impeller. I think once that volume drops the inlet pressure drops and cavitation will induce behind the impeller blades. Tricks using load gates or spoons on IB or having the OB foot feeding off the pressure of the hull and controlling the inlets angle of attack to ram load the impeller while not inducing excess drag.

One of the things I was reading was to measure the inlet, leading edge of the impeller and outlet pressures at the nozzle on the pump to find areas for improvement. Naturally the higher the inlet pressure the higher the outlet pressure.

Jamie

 

[reedjj]

Would the jet tunnel hull boats that G3 and Lowe offer be better or worse than a traditional flat bottom hull with an outboard Jet.

I would think that the tunnel would serve 2 roles???

1. It would keep the jet foot above the rest of the hull for running shallow, and if you do hit bottom you don't hit the foot.

2. It would act as a ram effect tunnelling water straight into the jet foot, keeping it loaded and because the foot is in the tunnel preventing cavitation even during porpoising?

Im surprised that legend or Blazer don't make a jet tunnel hull? Maybe they do but I have never heard of anyone having one. I have heard that the tunnels lose a little top speed? I know its true for prop tunnells as they are much deeper and would create alot more drag but a jet tunnel is only about 2 inches deep and 6 inches wide. Just enough to feed water to the foot?

Not to hijack but since the conversation turned this way anyway I thought I would ask.

Great videos by the way!

 

[linehand]

Your boat rips Rude. I'm jealous.
And it has reverse...

 

[Lil' Blue Rude]

Thanks guys.
Pretty sure blazers never bothered with a tunnel hull because they don't perform as (speed wise) as well as the other blazer models and for use on stream around here tunnel hulls aren't needed.

 

[turne032]

Ranchero50,


Loading the pump is a little different for each type of jet.

I understand the spoon idea on inboard. But the water flows (for the most part) in one direction. In an outboard the water is sucked into a bowl and forced to change directions. I do agree that the faster more pressurized water going into the jet, the faster more pressurized water is going to come out. However, I have not found any way to load the pump on the outboard jet.

I did think your example of jet engine was a great analogy. I have never thought of that before, and am very interested to research more.

I am not knocking the design of the outboard jet, but I would love to work on trying some different options to increase the performance. It just takes time and $$$ which are in short supply.

Happy Boating