Rudder length below prop hub

[anthony_marquart]

How much rudder do I need below the prop hub on a sport boat? specifically a .21 this time,. but in general also.

 

[Dasboatman]

No specific measurement. Start long and cut off a little at a time. When you cut off too much - the hull will let you know with little ceremony. Chop the throttle and go back to what previously worked. Ride height of hull, and whether you're running in smooth or choppy water will make a difference. CHEERS !!! Bob

 

[Jeff Barnhart]

The speedmaster mini blade does well on sport 20s.

 

[anthony_marquart]

that's what I have, but it's running about 2in below the hub,.. a good bit more than on my rigger..

 

[RobertWurster]

I would run it then start to short it as needed,I might start at 1/2 to 5/8 under under the water pickup,And have a new blade if needed.

 

[anthony_marquart]

noy into cutting a part till it's no good and then buying another.. need to make an adjustable depth rudder design

 

[Jeff Barnhart]

If you're using the speedmaster mini, I'd build a tall bracket that bolts to the boat and cut a vertical groove in it so that the rudder can slide up and down. Use one big bolt to hold it in place and start experimenting to find the depth you want. You might have to use a temporary linkage while testing to get it over the transom instead of through it, but I'd say pushrods are much cheaper than new rudders. Just an idea.

 

[RobertWurster]

Ya I know what you mean on the cutting of new parts. I have runed some.but like i said just run it and see how it works.Pitch that thing in the water see how it runs.

 

[anthony_marquart]

im going to try this weekend.. I'm going to check the fuel flow through the tank and start the motor tonight.. I have never run this motor yet..

 

[RobertWurster]

Cool,Hope it gose good.

 

[Hydro Junkie]

I see a problem with moving the whole rudder up and down:

the blade has a taper so it isn't the same width top to bottom, thus raising the rudder will give you a narrower blade than one that's cut off

This can give you a false "reading" and put you into the position of cutting the blade the wrong length anyway

 

[Jeff Barnhart]

I see a problem with moving the whole rudder up and down:

the blade has a taper so it isn't the same width top to bottom, thus raising the rudder will give you a narrower blade than one that's cut off

This can give you a false "reading" and put you into the position of cutting the blade the wrong length anyway

Last time I checked, the Speedmaster mini that i'm referring to is not tapered. Maybe you've found a different speedmaster mini?

 

[anthony_marquart]

no,.. it's not tapered.. that's the standard .21 rudder

 

[Hydro Junkie]

I was thinking the sport 20 rudder which is tapered forward on the rear surface as I have two or three of them

 

[Dasboatman]

 

[anthony_marquart]

exactly

 

[Jeff Barnhart]

I was thinking the sport 20 rudder which is tapered forward on the rear surface as I have two or three of them

Got it. Did not realize there was another 20 size blade.

 

[Hydro Junkie]

I had forgotten there was two as well