Effects of extended struts on Hydros .

[Wasted wages]

underneath the tub correct ? ( recurve )

and why did builders start to box in the stuffing tube and make it a ride surface, or ski ?
to remove the rear sponsons ?

 

[dr gary turner]

I like recurve
Keeps the prop in the water
Less blow out
Less nose tipping/stabbing
Overall faster lap times

Fat bottom is a crutch to keep boat up and turn a prop because the rest of the boat is not correct and or motor lacks torque

Prop in the water is fast
Prop coming unhooked is slow

 

[dr gary turner]

The boat in the video has recurve
But runs free but not loose

 

[Steve White]

I have been told, again not ORIGINAL WITH ME, that 17-20 degrees is ideal between the rudder and turn fin

Thanks for sharing that. I guess in the setup for current build, since it's going to basically be an R&D boat - I will make provisions to swap. I had never considered measuring that relationship with regard to the overall boresight or center line of the boat.

This brings a whole lot of thought. To put the rudder on the LH side of the driveshaft is to offset prop walk and natural effect of turn fin pulling boat to the right. It only makes sense that there would be a "happy place" or optimum placement of these critical components with regard to aspect, CG and such. Probably the first hydro geometry concepts that I learned were AOA (Angle of Attack) for both hull and sponsons. Then what I call the aspect ratio or length of after-plane divided by the inside width of front sponsons. If memory serves me correct that was in the range of 1.8 -2.2:1 in the older outriggers. The newer hull designs look to be in the region of 1.5:1 for the aspect ratio. Moving the prop aft increases that ratio if sponson width remains constant.

If they hop, narrow up the front end. If they torque roll, widen the front end. Prop walk, bigger rudder. That's about what I learned about hull setup and tuning. I've only ran four outriggers with flex shaft (ran 6-8 with straight driveshaft) and haven't done much setup tuning with that style at this point - moving adjustable struts. Just set the boats up per kit instructions and left 'em alone. Now the plan is to experiment and do more hull setup testing. First plateau was to learn how to make them run well, reliable and consistently. Hopefully, dusting those cobwebs won't be too difficult. I spent the first phase learning a bit about nitro tuning. Now there is going to be more emphasis on hull tuning.

This topic is very interesting to me.

 

[Wasted wages]

This topic is very interesting to me.

Me too..... love to learn more about the physics and engineering aspects of what makes these hydros fly across the water...

 

[Jerry Muro]

Can someone show what a recurve really is ? I am guessing it is in the tub does it dip down in the back correct? Thanks Jerry

 

[Steve White]

^^^ The aft tub, bottom side tapering upwards from the low tub water line to the transom. In ground effect it essentially turns the center of the hull into an inverted airfoil and provides down force to the prop(s).

 

[dwilfong]

Can someone show what a recurve really is ? I am guessing it is in the tub does it dip down in the back correct? Thanks Jerry

This is recurve.
See how the bottom of the boat curves up at a angle?
It works best if the top of the tub is flat and the bottom is flat till it gets to the rear.
The tub is upside down in this pic.

 

[Terry Keeley]

Can someone show what a recurve really is ? I am guessing it is in the tub does it dip down in the back correct? Thanks Jerry

 

[Jerry Muro]

Understand now thanks all

 

[Wasted wages]

So if I'm understanding this correctly now, is it letting trapped air out to create the ground effect ( as in an airfoil )
or
is it a wetted surface that works via Bernoulli
effect as with the spoon in the water stream
trick to suck the ass end down ?

At speed,,, the center tub should be completely lifted from the water surface right ?

 

[dr gary turner]

We curve the top and bottom
The recurve decreases the air pressure under the transom. If the top is flat it does create a low pressure area under the back of the tub and the rear is pushed down or if you want sucked down.

With curve on top less low pressure
More like a symmetrical wing

 

[Hydro Junkie]

Guys, could I get a clarification on this?
This recurve and aerodynamics you are referring to applies to riggers only, yes? I've never seen it on a scale or sport hydro which, I presume, is due to the higher prop weight on a sport or scale boat. Correct me if I'm wrong but, in the case of sport and scale hulls, to add aerodynamic down force to the rear of the boat would cause lower speeds and a tendency of lifting the front and making the boat more susceptible to blowing over. Would this be correct?

 

[dwilfong]

When the top is curved also it leads to other things.
With the top flat the back of the boat dose not want to lift at speed .
With the curve on the top and bottom you defeat the purpose of both.
Thy cancel each other out.

 

[Mark Anderson]

HJ, yes a couple of very succesful sport boats effectivly have recurve in the air trap.

 

[dr gary turner]

When the top is curved also it leads to other things.
With the top flat the back of the boat dose not want to lift at speed .
With the curve on the top and bottom you defeat the purpose of both.
Thy cancel each other out.

Yep, the boat flies flat with prop in the water

 

[dwilfong]

Race water is a whole different thing than a glass flat pond.

 

[dr gary turner]

Race water is a whole different thing than a glass flat pond.

You don’t think we run in race water?
That is where the recurve works

Flat bottom maybe for SAW to get up on a huge prop quickly to get on the pipe even on a lake as long as Huntsville lake.

 

[Timbo Whalen]

Going to the left crests the wrong angle between the rudder and turn fin unless you run a VERYnarrow spread on the front sponsons/ turn fin

Pivot angle.

 

[dave roach]

I ask Jim Wilson one time If i put a longer strut on my sport 20 will the boat thinking it will trick the boat being longer and Jim's reply was NO.