Rudder length sport hydro

[ezhitz]

I was wondering if there is a rule of thumb for the length of rudder below the strut. Or is it just a matter of keep trimming until you find what the boat needs to turn and run straight.

Thanks Jack

[TRUCKPULL]

No rule of thumb, it depends on the size and hull design.
You could buy two rudders, for when you find that you have cut too much off.

Larry

[rayzerdesigns]

Good rule of thumb is 1"below bottom of prop

[rol243]

not sure if 1 inch of rudder below strut would be sufficient for oval , maybe saw . rule of thumb is normally start with the longest length and gradually cut 1/4 inch per time until you still have good turning control .

[rayzerdesigns]

I don't do anything but race.. even offshore.. 1 inch below bottom of prop is plenty.. I'm sure my results will back that up.. gas or electric

[rayzerdesigns]

not sure if 1 inch of rudder below strut would be sufficient for oval , maybe saw . rule of thumb is normally start with the longest length and gradually cut 1/4 inch per time until you still have good turning control .

And is u noticed I said bottom of prop not strut

[fweasel]

I don't do anything but race.. even offshore.. 1 inch below bottom of prop is plenty.. I'm sure my results will back that up.. gas or electric

Just for clarification, 1" below bottom of the prop blade at its lowest position?

[rayzerdesigns]

Correct

[rol243]

just remember if your running a Lifting Prop there will be less rudder in the water at speed.

[MarkF]

I will say 1 to 1.5" below prop. I like 1.5 on some monos and 1" on others. This is boat dependent. I start at 1.5" on hydros too and start cutting down but stop at 1" below the prop. Having a longer rudder helps in choppy water in the turns and could help keep you right side up. The difference is only a few mph so don't get to caught up in rudder lengths unless you're longer than 1.5"

Mark

[rol243]

maybe electric sport hydros don,t need much rudder in the water but i just measured my Gas sport hydros prop depth and it is 2 1/2 inches below the lowest prop blade [ prop being 2917 ] i had a shorter rudder on this hydro but i didn,t want to turn sharp around the bouys , the longer rudder blade helped alot.

[Fluid]

There is no one-size-fits-all measurement, that is why there are rules of thumb* which are not intended to be gospel. Larger, heavier boats may need a deeper rudder than an N2 mono does. I know that if I try to run a rudder 1" below the prop arc I will unhook in turns when racing my hydros on the rough water we have here in Texas. The width of the rudder matters too, a .20-sized rudder on a Q hydro may need more depth to have adequate rudder area in the water. How tight the turns are matters too, non-NAMBA/IMPBA members may want to turn tighter, and a 1" rudder may not work for them. If interested in the 'optimum' rudder length for your boat and style of running, I like post #2 above.


* Wikipedia: A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation.
.*

[ezhitz]

Thanks for all the great answers. My rudder is about one inch below so I will leave it alone. I do mostly fun run but it is on a impba course so my turns are not that tight.