Where do we Go From Here?

[Andy Greene]

Chris Harris carbon rigger circa 2007. Helld the IMPBA electric SAW record at 111 mph for 3 years. Many interesting Aero design features.

All the best,

Ray

Im glad I had the chance to see Chris "Mr. Hammerhead H20 " run his designs at Blue Lake-

Have not heard much from Chris or Jeorge as of late :unsure:

Makes ya wonder. these guys could pull out another bullet and up the bar -real fast like B)

Looks like a ton of ways to skin a cat "rigger" if you ask me.

 

[Hydro Junkie]

I like the fact that many of you are looking at aerodynamics for increased speeds. What many of you may not know is that the study of aerodynamics is what made the Bud boats so dominant over the years. In fact, what is not common knowledge is the Bud team was working with engineers at US Marine in Arlington WA, where they took their designs and had them tested in computer simulations using the same programs that US Marine used in updating old and designing new hulls for their Bayliners and later Meridian Yatchs. This is where the rounded sponsons came from, along with the now standard engine cowling design. If Budweiser was looking at air penetration back in the early 90's, sounds like we need to be looking at it now

 

[Paul Traufler]

Ok guys (and gals) the simple math here for drag is:

D = 1/2*p*v*v*Cd*A

p = density (AIR 1.275 Kg/M^3, WATER 1000 g/M^3))

V = Velocity

Cd = drag coef. (let us assume .7)

A = Area, based on the Cd is used lets assume 1

So given the same object stuch out in water or air at the same speed is see ~750 times MORE drag in water than air. (We will assume the speeds are slow enough that air is incompressible as is water)

Botom line WATER drag is WAY more important, aero drag is just not as important with our application. (OK a barn door in the wind is a very high drag item!)

Class over, there will be a test next week... ;-)

 

[Hydro Junkie]

Not wanting to cause an arguement, but you are forgetting something. When a hydro, be it an unlimited, limited, scale, sport or rigger is on plane, the only parts that are truly in the water are skid fin and rudder. There is less than three square inches of surface contact with the running surfaces and the water while running an R/C. Conversely, over 95% of the hull is exposed to the drag caused by the air. Looking at the differences in contact area between the air and water, to say hydrodynamics is more important is to say the rest of the boat is running in a vaccuum. Wind drag is a very real part of the equasion that CANNOT be discounted. You have to remember, it's not contact with the water that causes blowovers, it's contact with air.

 

[Paul Traufler]

I agree, however the "rest" of the boat is pretty "slick" also. We are not pushing a barn door into the wind here! So unless we can cut aero drag by a great amount we are only looking at a small gain. Drop 10% areo drag and the force is still WAY below the of the water drag. All good points, but in the end drag reduction will get us part way there, control will be the next step to make extra gains in speed.

 

[Charles Perdue]

Control is a balancing act.....what does it mostly balance on.......AIR.

All in fun....

 

[Paul Traufler]

Well really it is the air to water interface that we balance on, this is a very tricky area to model or calculate anything in. Sort of jet flow, air trapped and water tension surface all come together! Perhaps some "water affects" will come in play on the next step in boats?

 

[Martin Hamilton]

The wing that we use on tethered boats is their to prevent the boat from taking off in a blow over. This is something that use to happen a long time ago as speeds increased especially on a slightly windy day.With this wing we are able to trim how the boat rides, How much the front comes up off the water (ideally around 1"). If the front comes up more through wrong set up on the boat or wind the wing is working all the time to stabalize the boat. If a boat should lift to much the wing brings the front of the boat down or the back up depending how you wont to look at it.If the front comes up to much through incorrect design/set up/wind the hole boat lifts of but with the wing working like its designed to do the boat flys straight and true. This happens from time to time where a boat may be running at 100+ and lifts of for say 25 yards and simply flys level with the water and comes down slightly prop down and continues the run. We were forever breaking boats or props with blow overs in the past but this prevents this most of the time now. The boats are also much faster as well because of the way were able to set up and trim the boat with the wing. As far as aero design goes we are probabally as far as we can go with current designs with the knoledge that us modellers have but theirs always room for further expert info in these areas. I should stress these things are particular to a boat on the end of a wire running in a circle.Regards Martin.

 

[Charles Perdue]

Well really it is the air to water interface that we balance on, this is a very tricky area to model or calculate anything in. Sort of jet flow, air trapped and water tension surface all come together! Perhaps some "water affects" will come in play on the next step in boats?

You are right Paul on calculating the air/water interface. Beyond my abilities to do that. I will take a design as far as I can then build a boat to those specs. The boat in the pic is the 7th that I have built chasing the magic setup. I learn from each boat.

The ground effects direction has been the most successful so far....using the forward motion of the boat thru the air to compress the air slightly AND contain it between the hull and the water to lift the boat and all the while maintaining the balance of the boat.

Sometimes when making very small adjustments, it changes the boat a lot.

It has been fun.

 

[lohring]

We've done a lot of SAW rigger testing. As was mentioned, air DRAG is not significant. Air LIFT is very important. Too much is as bad as too little. Our SAW sport hydro used spoilers to destroy the lift and increase the speed from 75 to over 100 mph.

Stability is also critical. I've seen a lot of SAW boat crashes in boats where stability was marginal. We have succeeded in getting everything out of the water except the lower blade of the prop and the rudder at speed while still maintaining stability. Joerg's 140 mph boat manages to get nearly all the water rudder out of the water as well. He has air rudders for directional stability at speed.

Currently, props are a limiting factor. In all but 3.5 size boats, the standard props don't have enough base pitch to push the boats much faster. This is due to the maximum rpm the engines can run. This limit is really noticeable in gas hydros. A gear up drive is being tried as a way around this. However, the speed break through to over 100 mph in NAMBA G class boats has come from new propellers.

Lohring Miller

 

[shoboat]

Lohring,

I have to disagree on the propeller limits. RPM is the limiting factor.

I have customers going over 100 MPH on a X-450/3 propeller. Most engines

can only rev so much, I think the tuned pipe is also one area of more RPM.

Fuel is also a place for another big gain, it is a combination of things to

extract more from our engines and set ups. We are currently working on some

propellers that will help also, don't forget the blade profiles either, it

makes a difference.

Thanks For Reading,

Mark Sholund

 

[Charles Perdue]

We've done a lot of SAW rigger testing. As was mentioned, air DRAG is not significant. Air LIFT is very important. Too much is as bad as too little. Our SAW sport hydro used spoilers to destroy the lift and increase the speed from 75 to over 100 mph.

Stability is also critical. I've seen a lot of SAW boat crashes in boats where stability was marginal. We have succeeded in getting everything out of the water except the lower blade of the prop and the rudder at speed while still maintaining stability. Joerg's 140 mph boat manages to get nearly all the water rudder out of the water as well. He has air rudders for directional stability at speed.

Currently, props are a limiting factor. In all but 3.5 size boats, the standard props don't have enough base pitch to push the boats much faster. This is due to the maximum rpm the engines can run. This limit is really noticeable in gas hydros. A gear up drive is being tried as a way around this. However, the speed break through to over 100 mph in NAMBA G class boats has come from new propellers.

Lohring Miller

And as Jorgen mentioned, when you add running in a circle with other boats in a heat race, everything changes. Some setups that will work on a SAW boat, will not work at all in a heat race.

 

[Jorgen Andersson]

Hello

Yes, Heatracing and SAW are very different in most ways.

Pitch and RPM are limiting factors, more RPM is more speed, but normally you loose out on torque when you get the RPM up.

As we all have discussed, Aero and Hydrodynamic drag and balance are vital factors in order to get the balance of the boat correct, but what I would like to hear is more detailed suggestions and ideas on how to achive this, like the stabilizer that Martin did mention that they use on tether boats.

No idea is too crazy, you never know what will come out of it.

Lohring - Do you have any pictures of the spoilers you did use?

Jorgen

 

[Charles Perdue]

One thing that I found is as you get a more rounded design, to control the air over and around the boat, you loose some directional stability. A small vertical fin at the rear of the boat corrects this problem. Like feathers on an arrow.

 

[Hydro Junkie]

It's almost funny that you say that Charles. When Anchor Jensen and Ted Jones were building the Slo-Mo-Shun IV, driver load and directional stability were a serious problem to be overcome. By installing the 1" thick vertical fin and offsetting the rear of the fin to the right, driver workload in keeping the boat going in straight line dropped to almost nothing as compared to earlier boats. Between that and turning the boat into a prop rider, the boat topped out around 50 MPH faster than any previous boat

 

[Martin Hamilton]

We used single vertical fins on our tether boats 40 years ago, They worked ok but they wouldnt stop boats taking off or control the trim of the boat like the horizontal wing. Like i said we started with the vertical fin then added the horizontal wing let into the fin so we had both of these together at that time. Now we just use the wing, The secret to what this wing does is in its shape top and bottom reverse aero foil section. You wont find a single modern competitive tether hydro any where in the world that does not use these wings. Regards Martin.

 

[TUNLBOTR]

Let me ask this.

Does water depth create issues relative to lift in a boat? A lake with a "cold spot", a hole to say, in the middle of the straightaway cause the boat to unsettle. Is it the pressure difference in that spot? Water pressure or air pressure? We have lakes where we race that have a magic "manhole", where the boat will lose its lift characteristic and dunk out.

 

[Charles Perdue]

Let me ask this.

Does water depth create issues relative to lift in a boat? A lake with a "cold spot", a hole to say, in the middle of the straightaway cause the boat to unsettle. Is it the pressure difference in that spot? Water pressure or air pressure? We have lakes where we race that have a magic "manhole", where the boat will lose its lift characteristic and dunk out.

I always thought that was where the Troll lived and when we drove above him he would reach up and grab our boats, pull them under and drink the nitro out of them..............

Just kidding Randy, I do not have the slightest idea what the answer is to your question.

 

[Kevin Krogness]

Let me ask this.

Does water depth create issues relative to lift in a boat? A lake with a "cold spot", a hole to say, in the middle of the straightaway cause the boat to unsettle. Is it the pressure difference in that spot? Water pressure or air pressure? We have lakes where we race that have a magic "manhole", where the boat will lose its lift characteristic and dunk out.

I always thought that was where the Troll live and when we drove above him he would reach up and grab our boats, pull them under and drink the nitro out of them..............

I do not have the slightest idea what the answer is to your question.

Sounds like your a step in the right direction!!! LOL

 

[Tim_Duggan]

The secret to what this wing does is in its shape top and bottom reverse aero foil section. You wont find a single modern competitive tether hydro any where in the world that does not use these wings. Regards Martin.

Hi Martin,

Do you run a particular wing profile and width, or is it more of a "trial and error" approach?

Tim.