Why shorten rudder length on hydros?

[battlefury]

What are the effects that will influence behaviour on a hydro?

When should shortening of a rudder apply? is there a symptom or tell tale sign to be expected prior?

And why should be done?

[Coug90]

There are a couple of things that might be a factor when considering shortening a rudder blade. One is drag. If the boat handle fine with a shorter blade, then the longer one is just creating unnecessary drag. The other is the rudder's influence on the boat ride. If the boat is rather flighty, then one thing you can try is a slightly longer rudder blade to hold the front end down and give you better control. Conversely, if the boat is running too wet on the sponsons or needs to get freed up a bit, you can try reducing the depth of the rudder to free it up more. It's just one thing to try. At any rate, I would use the least amount of rudder you think you can get a way with before you start losing handling or turning ability that you want. Hope that helps.

[monojeff]

I know my hydro would spin out and dive with to short a rudder.
Had trouble in the turns and a longer rudder has pretty much fixed it alone.

Doesn't take much 1/8-1/4 inch can make a huge difference.

[Fluid]

The rudder is the only think keeping the transom from spinning around due to prop walk. The larger its side area, the better job it does of this. Cut it off too short and you have to dial in left trim to counteract prop walk - adding back all the drag you thought you removed by shortening the rudder. The correct way to cut a rudder is to chop it off in 1/4" steps and test it each way. Once you have gone too far, buy another blade and cut it off to the shortest length that worked with the test rudder.



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[battlefury]

Great stuff thanks for the input guys i am learning a little more everyday.

[egneg]

The length also depends on what the boat is used for. In SAW it only needs to be long enough to make small corrections during the run. In oval racing obviously it needs to be longer to make it through the turns.

[Fluid]

In SAW it only needs to be long enough to make small corrections during the run. In oval racing obviously it needs to be longer to make it through the turns.

In SAW racing the rudder's primary function is to maintain a straight line through the traps. Experienced SAW racers don't touch the rudder while in the traps. If you have to "make small corrections" in the middle of your run, then you are slowing the boat down and will likely not set a record. The rudder needs to be large enough to maintain a straight line by counteracting propwalk. Too short and you need to dial in left rudder - adding more drag.



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[BHChieftain]

The rudder is the only think keeping the transom from spinning around due to prop walk. The larger its side area, the better job it does of this. Cut it off too short and you have to dial in left trim to counteract prop walk - adding back all the drag you thought you removed by shortening the rudder. The correct way to cut a rudder is to chop it off in 1/4" steps and test it each way. Once you have gone too far, buy another blade and cut it off to the shortest length that worked with the test rudder.

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Hey, thanks for that info. I have a 1/10 shovelnose hydro, and it was "warbling" around especially coming out of a turn. I dialed in quite a bit of left trim at the problem "went away"... I'll play around with a longer rudder.

Chief

[Darin Jordan]

Rudders that are too long are a total DRAG...

[detox]

Shouldn't rudders have more width (more distanced measured from front sharp edge to back trailing edge). For instance the Speedmaster Sport 40rudder is a bad design (too long and narrow). Shorter and wider is better. Just ask my wife