Where do we Go From Here?

[Charles Perdue]

No U-joints......

 

[Charles Perdue]

No hard shafts.....No u-joints....

 

[dwilfong]

Cavitation in a water jet is a design issue. Read the discussion here:

http://www.boatdesig...prop-11254.html

If you look at the picture of Mike Bontoft's "outboard" hydro you will see that it is basically an articulated surface drive. I don't see why an inboard system wouldn't work well, replacing the rudder with a small skeg. It should have better maneuverability and lower drag.

Lohring Miller

John Otto has a tunnel with a 45RS that the eng mount is like a truck fifth wheel and a skeg strut on two pieces of bar stock hooked to it. He uses a small piece of brass tube to run the shaft in. It is a very innovative design.

David

 

[Tim_Duggan]

A friend of mine experimented with a 21 mono with articulated surface drive back in the early 90's. He utilized a square drive flex cable at the A.S.D end and used a collet at the motor end. No u-joints.

Unfortunately it was plagued with reliability problems and he gave up on it. Didn't show enough promise for him to persist with it and he converted it back to a conventional strut and rudder.

 

[lohring]

The gas monos use a surface drive that allows quite a bit of vertical adjustment with a flex cable. I don't see why you can't build a system that allows horizontal adjustment as well. As Charles said, you need a substantial steering system to take the loads.

Going back to wings:

A ground effects wing gets most of its lift from being close to the surface. That makes it a great height control device. However, the center of lift moves considerably with height making it very unstable. The high rear wings have the same lift characteristics independent of height above the surface. That's why the Russian WIG vehicles as well as unlimited hydroplanes have big horizontal tails. The reason unlimiteds blow over is that the center of lift moves forward rapidly as the boat lifts. The rear wing eventually gets blanketed by the main wing, loosing its stabilizing effect. Another solution is two ground effect wings in tandem. This has been tried and can work well. The three wing unlimiteds needed lots of power and engine restrictions made one big wing necessary.

Lohring Miller

 

[Charles Perdue]

Lorhing, you are right about a wing running in ground effects as to the lifting area moving forward. But the wing and a rigger hull have different lifting characteristics, partially because of the large differences in the chord of the lifting area.

Moving the lift farther forward on a rigger is not all bad if that is taken into consideration when the hull is designed.

My "Walmart Wind Tunnel" really helped in this area.

Many ways to skin a cat......

Charles

 

[Paul Traufler]

In general the "ground affect" occures when the wing is about half the wing span above the surface, since the air under the wing is trapped under the wing and surface more lift (and yes a small increase in drag also) is produced. With the higher lift the forces acting on the wing also "move" a bit so the center of pressure (CP) changes. SO a higher lift airfoil, small wing span, and higher above the surface will all help with this issue. BTW full sized hydro's have some active control surfaces to help control the blow over air forces.

 

[Charles Perdue]

Paul, yes, yes and yes. On my toy boats, I am using the hull as a long slice of "Wing".

This is beyond the theory stage as I have 4 boats that will run in ground effects.

I think that I saw you at the lake in Huntsville in January. I spent so much time trying to stay warm that I did not have a chance to meet and talk to you.

Charles

 

[lohring]

Air traps are a great way to make a low aspect ratio wing, like a rigger tub or sponsons, lift in ground effect. Look carefully at Mike Bontoft's designs. We've tried air traps on everything. You do need to keep enough weight on the prop, though.

Lohring Miller

 

[Paul Traufler]

Yes I was at the Jan Huntsville one, WAY too cold for boats! That was my "introduction" back into this sport... now I may need to attend a 12 step program!

 

[Charles Perdue]

Air traps are a great way to make a low aspect ratio wing, like a rigger tub or sponsons, lift in ground effect. Look carefully at Mike Bontoft's designs. We've tried air traps on everything. You do need to keep enough weight on the prop, though.

Lohring Miller

I love air traps. I am not smart enough to calculate in advance the proper arc of the entrance curve, hull area, skirt shape and height and the shifting of the lifting points on the hull. I just have to cut and try, but hey, even a broken clock is right twice a day. If you can learn from cut and trying, sooner or later you just might get something that works.

The shifting of the lifting point forward helps to keep weight on the prop on narrow hull riggers. I cannot answer about any other styles of hulls.

Heck, I am just a Tennessee Country Boy, have a little mercy on me.........

Charles

 

[dwilfong]

I found this at my local hobby shop and will give it a try. I am going to put it on the front sponson boom. It is a very snug fit on the 1/4 CF rod so it will stay at the angle I set it at and can turn by hand to adjust. I think with it being on the front tube it should change the CG by using the ride pad as a fulcrum. The air trap sponsons should keep the surface wetting in check. Well it sounds good on paper. Should make for some interesting play time.

David

 

[Archie Stanton]

d

 

[dwilfong]

i have kicked this around for a couple of yrs.. i have yet to have time to sit down with my dad and we work something out. but, i hope to in the future.

SHOCKS. i will leave it at that

chris

thinner boom tubes could do the same as shox.

Just throwing this out there as an analogy:

I ride mountain bike ALOT (too much). The ability for a mass to continue along a constant trajectory without axis translation has MUCH to do with maintaining momentum (first law of Thermodynamics stuff). My Bike and I tip the scales at around 200lbs total. in the small bumps I can OWN a more rigid setup since my total mass can suck up the out-of- axis through suspension rather than translate it to out-of-axis movement. I can change my setup through pneumatic lockout at the track, Knowing this isnt practical for a boat.......but my thoughts are that a PLUSH/ quick action setup would benefit a rigger.

smaller diameter carbon tubes?

plush ride and less drag??

Archie

One of the guys at the lake noticed that the booms on my rigger would flap like a wing on a plane and the boat would hook up then unload. This was with hollow tubes so I put solid CF rod inside the tubes and it stopped. But then the front would hop in the rough water. So I messed with only putting the solid in half of the tube and found a balance. I now use a composite of glass and carbon with the glass running liner in the tube. Kite tubing comes in many different forms and degree of stiffness. This is the simplest way of tuning the set up. The only problem with bow in the tube is the ride surface changes on the wrong axis. Well you can't have it all I guess.

Now if you could come up with a magnetic suspension like thy have on the seat of the Navy attach craft that would be something.

David

 

[lohring]

Mike Bontoft had to buy me a lunch over boom streamlining. He built a great test setup with a leaf blower that showed a huge reduction in boom drag with streamlining. I bet him it wouldn't increase top speed by a measurable amount. It works to adjust the down force on the sponson, though. Once again, water is 800 times as dense as air. Air drag is not the problem. Any way you can use air lift to reduce water drag won't have a significant drag penalty.

By the way, the way we design anything like air traps, sponsons, or wings is make it big and then cut it down. It's just as fast as fancy math and the lessons stick better.

Lohring Miller

 

[Tom Foley]

Great stuff here and lots of creative thinking going on , a lot of it above me !LOL . I cant help but thinking that a lot of it really wont be practical for heat racing as the changes in water conditions , crashes , and the ability to repair quicly and get back to the original baseline setup pretty much control the ability to win . I'm not sure what I would do if relacing sponsons and boom tubes etc couldn't get me on the water quick and back up to speed . Great reading though !

 

[dwilfong]

Great stuff here and lots of creative thinking going on , a lot of it above me !LOL . I cant help but thinking that a lot of it really wont be practical for heat racing as the changes in water conditions , crashes , and the ability to repair quicly and get back to the original baseline setup pretty much control the ability to win . I'm not sure what I would do if relacing sponsons and boom tubes etc couldn't get me on the water quick and back up to speed . Great reading though !

I hear ya Tom last race with the 21 took of the left sponson on the mill lap first heat.

Done for the weekend.

David

 

[dr gary turner]

An idea I have had for a few years (but am too lazy to build!):

https://www.intlwaters.com/gallery/displayimage.php?album=241&pos=13

Ian.

Don Pinkert built a similar boat and ran it at an SGRA race. Gary

 

[Tim_Duggan]

All of this talk of aero and Wings In Ground Effect has me re-thinking my current project a little. What tub height's are people running with what width tubs and sponson pads (+AOA's if you are in a sharing mood?)

 

[lohring]

The great thing about air traps is that it's the fence height above the water that counts. When you cut away some of the fence, the lift stops. If the fence hits the water, it has a fraction of the drag of a tub bottom. It's hard to lower the fence into the water, though. The increased air pressure pushes a trough in the water. We took some onboard video of an air trap at work to show some of this.

Lohring Miller