3 point theory

[anthony_marquart]

I am thinking about why riggers work and how. Then I thought "what is it that makes the JAE seem so effortless". Of course they tested the heck out of and then made a non-adjustible kit that could only be built to the spec.. it works good... but why? What is it about that design that makes it turn so well? I know the over hanging edges help in breaking free from the water,.. I think this is more of a detail than a concept or theory.

This image is of the boat I'm building now, but these numbers are not far from the JAE design.. I'm tying to think about the relationship of these numbers and how they tie together and how can they be optomized..

 

[Grimracer]

I tried a "Foot Print" question on here a few years ago and it met with an astounding THUD!

Not the same as you have here but it was a tough "Share".. maybe its just my current "Situation"

Rocket and ROLL!

Grim

 

[anthony_marquart]

I think it's a good conversation to have. Maybe tough to comment on. It's not rocket science though.

How about this,.. Can some of you guys take some measurements on your boats.

Maybe we can fill in the dimensions for a road runner21, eagle21, FF21 etc.. I will corrolate the data and we can compare the running traits of each boat with the dimensions.

After we have this data we can take measurments in the vertical axis and compare again.. This SHOULD allow us to design a boat with the traits from each boat that we want.,.. (in theory anyway)

Let's try this,.. it should spell out some things for us..

I tried a "Foot Print" question on here a few years ago and it met with an astounding THUD!

Not the same as you have here but it was a tough "Share".. maybe its just my current "Situation"

Rocket and ROLL!

Grim

 

[Speed Jr.]

What makes the JAE so effortless? Here is it oversimplified;

1. Flat running surfaces

2. Motor in center of Triangle

3. This sounds bad but; Very little adjustments, so less for the user to screw up. Thats why I shake my head when someone changes the front booms to be adjustable AOA and use a traditional strut and put angle in it. This boat when built to specs is really hard to screw up....."KISS"

4, Did I mention Flat running surfaces?

Jr.

 

[anthony_marquart]

I do understand why they designed it not to be adjustible. But I would guess that if you took 5 boats, built by 5 average guys, you would find a 2 degree range in the sponson AOA. Yes the boats work very well and the inteneded AOA is probably optimal, but I think the boats could be fine tuned to compensate for build inconsistancies.

When you say "motor in the center of triangle", what are the dimensions on that triangle? Is it a 45deg triangle? Does that imply the center of gravity is at the center of the triangle? this would explain the ease of launch, (equally distributed weight. )

I'm not challenging why this boat works or if it does. I'm just trying to understand why it works so I can apply it to other designs.

quote name='Speed Jr.' timestamp='1290140961' post='386659']

What makes the JAE so effortless? Here is it oversimplified;

1. Flat running surfaces

2. Motor in center of Triangle

3. This sounds bad but; Very little adjustments, so less for the user to screw up. Thats why I shake my head when someone changes the front booms to be adjustable AOA and use a traditional strut and put angle in it. This boat when built to specs is really hard to screw up....."KISS"

4, Did I mention Flat running surfaces?

Jr.

 

[Speed Jr.]

[When you say "motor in the center of triangle", what are the dimensions on that triangle? Is it a 45deg triangle? Does that imply the center of gravity is at the center of the triangle? this would explain the ease of launch, (equally distributed weight. )

Forget the dimensions and angle. Its Irrelavent. Where's the motor on your new boat?

 

[anthony_marquart]

I don't think it's irrelavent,.. There are fundimental design features to all of the good running boats. I think it can be written in a few formulas if we try.,..

But,.. my engine is just a N/R 5port. The hull in the image is coming along great.

[When you say "motor in the center of triangle", what are the dimensions on that triangle? Is it a 45deg triangle? Does that imply the center of gravity is at the center of the triangle? this would explain the ease of launch, (equally distributed weight. )

Forget the dimensions and angle. Its Irrelavent. Where's the motor on your new boat?

 

[Speed Jr.]

If you draw a strait line from your drive dog towards the front of the boat to where the sponsons trailing edge is, put the motor in the center of that line and youll be on your way. Thats it. Go as wide as youd like on your sponsons...no biggie, thats why Angle is irrelavent. The lever is the turn fin, get it back around the front of motor and your gold.

Jr.

 

[TCHedOff]

I hesitate to comment, but.....

From the conversations I've had with Rod, what you asking is like askin "How high is the sky?" (One of Rod's phrases ). There is no magic length-width ratio for an ideal footprint because the ideal footprint varies with the racing conditions. (I'm going w/extra (longer) boom tubes to the .12 races next yr for those 2"+ wave-race-days.) Evidently, after much testing, the JAE team decided that 16" width was best for a @25" long rigger (counting ski) that weighs @ 2 1/2lbs and runs 50-70mph.... so there is your "ideal answer" based on a lot of testing.

Speed Jr summed things up.... adding to what he said, the ride surfaces of the JAE are wide enough to keep the boat up on the surface (now there is a formula there somewhere - weight to area displacement required).... I remember Rod once saying "You cant go too wide, but you CAN go too narrow".

 

[Mark Poole ModVP]

I know it is kind of an old book but John Finch's Advanced RC Boating has some good explainations about outrigger hydros. Sponson angle, where the trailing edges should be. Also goes into what makes a good straightaway boat and a good heat racing boat as well as CG and turn fin placement.

 

[Scott Schneider]

Just adding too the general question asked .... after racing a 3 point Gas Rigger for @ 6 years doing countless tweeking always would come back to an @ 15-20% LONGER after plane by simply adding tub length relative too an equal sized 4 point design.

Reason was with the longer after plane hull suffered from less AOA change going slow with prop deeper too wot and tail up. A shorter tub would make the boat flightier at slower speeds which was always a death sentence if you had to throttle down due to wind and waves.

Also found the weight transfer onto prop as boats speed increased, prop lift characteristics were less dramatic on the longer tub as well. So with less AOA change and props running depth more stable on the longer tub length this is how I go about rigging & building my 3 point riggers.

 

[anthony_marquart]

I didn't mean to imply that said formula would work with all variables. (water condition) There is no magic or witch doctor stuff with these boats. I'm having the same result as Mike did with this.

There IS a formula to making a good running hydro. That would be a slightly different formula for rough water conditions. Footprint, weight distribution and a couple other factors would make it up.

I was only trying to look at the boats from an engineering perspective,.. the same way you would optimize a car chassis or anything else.. Compare physical data to performance data and make corrolations.

I give..

 

[anthony_marquart]

I love that book!

I know it is kind of an old book but John Finch's Advanced RC Boating has some good explainations about outrigger hydros. Sponson angle, where the trailing edges should be. Also goes into what makes a good straightaway boat and a good heat racing boat as well as CG and turn fin placement.

 

[Hydro Junkie]

Okay, I'm not a rigger person, but there are several factors that make a boat a runner or a dog. Two have already been mentioned so I'll just put in my two cents and see where it goes:

1) AOA-

This has a couple of points to it.

Too much AOA can and will lead to more drag as the sponson transom will rider lower in the water, thus acting more like a brake than a riding surface. This can be overcome by the amount of push you get from the engine/prop combo, but top end will suffer.

Too little AOA will have considerably more wetted surface while running. The result is a boat that will have a harder time getting on plane and a lower top end.

2) Afterplane Length-Again, this has a couple of ways to look at it.

The longer the afterplane length, the easier it is to have the prop lift the back of the boat if it is balanced properly. This can be compared to putting a board under a log and lifting on the board to move the log. The drawback to a long afterplane is it makes the boat turning radius larger. Granted, you can turn the rudder sharper to compensate, but this adds more drag, slowing the boat in the corners.

By running a shorter afterplane length, the use of a nonlifting prop becomes problematic as there is more weight on the prop. This one would be like having a bucket of water on one end of a board and trying to hold it up at the other end. Conversely, the turning radius will be sharper, reducing rudder throw needed.

3) Thrust Angle-

This can make a world of difference as well. I won't try to go into this one as I'm not a expert on it.

4) Hull Balance-

This one should be self explanitory

5) Hull Weight-

Should be another "no brainer"

6) Aerodynamic Drag-

This is one that is many times overlooked in boating. Rounded surfaces are inherently more slippery than blocky or abrupt ones. This was proven with the Unlimiteds back in the late 80's and early 90's when the Circus and Bud camps both raised the speed of their boats by doing something as simple as rounding off the edge of the sponsons. This one slight change made a world of difference in boat performance.

Okay rigger racers, there are my thoughts, do with them what you will

 

[lohring]

Our design method has mostly been build something, then change everything as you test the boat. Build the next boat like what worked best on the old boat and start again. However, we have learned a little. As I said in the past, water drag is everything.

Get everything out of the water. Minimize and streamline everything left in the water, especially the rudder and turn fin. Trade drag created by air lift for lower water drag. You can deflect a huge rear wing 30 degrees without changing the speed much.

Stability is critical. You need enough prop weight to keep the prop in the water. A skeg or rear sponsons help get the boat up. The main sponsons need to be separated enough for turns. A SAW boat only needs enough width for straight line stability.

Speed always increased for us as we increased the sponson angle. We've run up to 10 degrees. The problem is stability. As the angle increases the sponsons can move in and out of the water a greater distance for the same correcting force. Sponson walk gets worse with higher AOA. Air trap sponsons are one answer, and shingles are another.

Light weight is important. It takes more sponson area, creating more drag, to lift a heavy boat. Our 25cc boat was faster than the 35cc boat with 1 1/2 times the power.

Props are also critical. You have to match engine power and rpm with prop pitch, diameter, blade area, and rake to hull speed and drag. There aren't any stock props available with enough pitch for the current top SAW speeds. Propeller efficiency, the percent of engine power converted to thrust power, becomes apparent in electric hydro racing. When everyone is running the same power plant the propeller makes the difference. Different hulls don't always run the same with the same prop.

Lohring Miller

 

[Terry Keeley]

Our design method has mostly been build something, then change everything as you test the boat. Build the next boat like what worked best on the old boat and start again. However, we have learned a little. As I said in the past, water drag is everything.

Get everything out of the water. Minimize and streamline everything left in the water, especially the rudder and turn fin. Trade drag created by air lift for lower water drag. You can deflect a huge rear wing 30 degrees without changing the speed much.

Stability is critical. You need enough prop weight to keep the prop in the water. A skeg or rear sponsons help get the boat up. The main sponsons need to be separated enough for turns. A SAW boat only needs enough width for straight line stability.

Speed always increased for us as we increased the sponson angle. We've run up to 10 degrees. The problem is stability. As the angle increases the sponsons can move in and out of the water a greater distance for the same correcting force. Sponson walk gets worse with higher AOA. Air trap sponsons are one answer, and shingles are another.

Light weight is important. It takes more sponson area, creating more drag, to lift a heavy boat. Our 25cc boat was faster than the 35cc boat with 1 1/2 times the power.

Props are also critical. You have to match engine power and rpm with prop pitch, diameter, blade area, and rake to hull speed and drag. There aren't any stock props available with enough pitch for the current top SAW speeds. Propeller efficiency, the percent of engine power converted to thrust power, becomes apparent in electric hydro racing. When everyone is running the same power plant the propeller makes the difference. Different hulls don't always run the same with the same prop.

Lohring Miller

Great post, I can add one more thing:

"It ain't as easy as it looks"... :lol:

 

[Alexander King]

6) Aerodynamic Drag-

This is one that is many times overlooked in boating. Rounded surfaces are inherently more slippery than blocky or abrupt ones. This was proven with the Unlimiteds back in the late 80's and early 90's when the Circus and Bud camps both raised the speed of their boats by doing something as simple as rounding off the edge of the sponsons. This one slight change made a world of difference in boat performance.

The above statement is true but most out riggers have very little parasite drag... the real question is why are the JAE sponsons hull combo working? Flat surfaces that are squared off creating less surface tension with more surface area? there is a secret here somewhere to the formula ..... :blink:

YUP lot easier said than done...aint that the truth :lol:

 

[anthony_marquart]

there is a secret here somewhere to the formula ..... :blink:

Yes, there is. We keep getting staements about what doesn't matter,.. what we want to know is what DOES matter. From speaking with a few people the JAE has a few things going for it. First and foremost (I think) are the flat sponsons,then the overhangs, ride suface area to weight ratio is very good, then the balance. I am learing that it's not actually the CG but it's the amount of weight on the prop. Of course this is relative to CG but as boat size varies it's not directly related to CG.

Some ideas are not changing. To go fast it's a package deal,, motor - pipe - prop - boat, all matched.. For me that is the hardest part. This takes lots of testing and $$$,..

 

[MitjaJ]

One thing that I noticed that affect stability/ride of a rigger is the moment of inertia of the boat. I've made two electric outriggers with the same outside dimensions.

With the first hull I didn't put much attention how the gear was placed inside the hull - I laid everything so that it was

easy to work on the boat.

With the the second hull I've made I paid special attention to put all the heavy stuff (motor, ESC, battery) near around the CG.

The calculated moment of inertia of the new layout was about 2.5 times smaller than the original design.

(the design/calculation was done by 3D modelling of the boat with the proper material densities).

The final result after making and testing the new hull is that the boat runs much more stable in race water - instead of sponsons slamming in the water when I hit a big wave - the boat just jumps of parallel with the water. There is also less oscilation of

the boat on the smaller waves - the boat just runs very parallel with the water surface.

 

[Alexander King]

One thing that I noticed that affect stability/ride of a rigger is the moment of inertia of the boat. I've made two electric outriggers with the same outside dimensions.

With the first hull I didn't put much attention how the gear was placed inside the hull - I laid everything so that it was

easy to work on the boat.

With the the second hull I've made I paid special attention to put all the heavy stuff (motor, ESC, battery) near around the CG.

The calculated moment of inertia of the new layout was about 2.5 times smaller than the original design.

(the design/calculation was done by 3D modelling of the boat with the proper material densities).

The final result after making and testing the new hull is that the boat runs much more stable in race water - instead of sponsons slamming in the water when I hit a big wave - the boat just jumps of parallel with the water. There is also less oscilation of

the boat on the smaller waves - the boat just runs very parallel with the water surface.

Interesting ...what finite 3D program did you model the boat in ? ie solidworks, Catia?

would like to see what your design looks like care to share?