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I've seen this mod done before on another forum..
not sure what the outcome was...
but the rudder does need a sharp edge on the back
not sure what the outcome was...
but the rudder does need a sharp edge on the back
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.NAMBA20...Caterpillar UL-1, P-Spec OM29, P-Mono DF33, P-Spec JAE, Aussie 33" Hydro-LSH, Sprintcat CC2028 on 8s, PT SS45 Q Hydro, PS295 UL-1 power, OSE Brothers Outlaw QMono 4-sale, Rio 51z CC2028 on 8s
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It pops up then vanishes every once and a while, I first saw it back in the 80's.
Would add a pile of drag between the pickup and back of rudder!
Unless you have the entire system sized properly you are creating a lot of drag from the excess water not being able to go into the tube due to restrictions farther up the system, like the esc cooler inlets. That massive amount of disturbed water is drag. Be like an underwater bow wave on the bottom of the rudder.
Would be much better with a much smaller diameter inlet tube.
Physics sucks eh?
Thats not even taking into account the trailing edge of the rudder.If my boats upside down then who owns the one I thought I was driving the last two laps?
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Yes I agree, Physics suck and gravity's a bitch.
I will be moding it to be a more streamline inlet with less forward facing drag surface...
That said, I am curious to see how it performs (drag wise) when compared to this forums original post pics of "the best water pick-up ever"
I would contest that that type of pickup creates more direct drag, granted its not mounted on the rudder...
In any case, here is a really redumentary pic of my theorised drag reduction based on the rounded trailing edge of the modified rudder...
The third example may be a better design yet...rudder hydrodynamics 1.jpgLast edited by riksorensen; 11-14-2011, 05:23 PM.Comment
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2008 NAMBA P-Mono & P-Offshore Nat'l 2-Lap Record Holder; '15 P-Cat, P-Ltd Cat 2-Lap
2009/2010 NAMBA P-Sport Hydro Nat'l 2-Lap Record Holder, '13 SCSTA P-Ltd Cat High Points
'11 NAMBA [P-Ltd] : Mono, Offshore, OPC, Sport Hydro; '06 LSO, '12,'13,'14 P Ltd Cat /MonoComment
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A propwash pickup has significant drag, more than a rudder pickup, etc. Try putting your hand in the spray coming off a full-sized boat and then tell me there is no force pushing your hand backwards! The propwash is even worse because the roostertail spray is traveling faster than the boat is moving forward, and when it hits the pickup tube it causes lots of drag. This doesn't mean that a propwash pickup shouldn't be used, but if you think it is better because there is no drag, think again.
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Sorry dude once again fluid dynamics shows that at the speeds we go a sharp square edge to shear the water has less drag, in something like a sailboat a rudder like yours is better as you maintain the laminar flow over the whole length and off the trailing edge.
Once the high speed water gets past the widest part of your rudder it loses its flow and becomes turbulent as it passes back along the width of the rudder, but it never loses it's contact with the rudder, thus more drag.
There is an air pocket behind the rudder with a square edge, the water shears off the sharp edge continues behind the rudder and rejoins back behind someplace where it doesn't matter anymore.
Once again physics.
Do about a half hour of heading on line and you will find all the info you could ever want about rudder shapes at different speeds.
The SAW guys have tried just about every rudder shape you could imagine in search of speed, square sharp edges = fast.If my boats upside down then who owns the one I thought I was driving the last two laps?Comment
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So.. are you saying that if I'm in a full size boat, and stick my hand into the roost that it will slow the boat down?Comment
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Of course. Like fluid said, not only are you creating drag, you're creating it in water that's moving faster away from the boat than the water moving over the rudder or across the hull. That's why some guys sharpen the edges of the brackets and parts that are in the prop spray.
When you stick your hand in the roost, don't you feel the force of the water pulling your hand back away from the boat? Your hand is attached to you, and you are attached to the boat... it's drag on the boat.
Take it easy,
desmobobComment
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2008 NAMBA P-Mono & P-Offshore Nat'l 2-Lap Record Holder; '15 P-Cat, P-Ltd Cat 2-Lap
2009/2010 NAMBA P-Sport Hydro Nat'l 2-Lap Record Holder, '13 SCSTA P-Ltd Cat High Points
'11 NAMBA [P-Ltd] : Mono, Offshore, OPC, Sport Hydro; '06 LSO, '12,'13,'14 P Ltd Cat /MonoComment
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lol. My question was more of a joke.
Do you really believe that. Geez, I'll looka at my speedo next time I'm in my boat and have my bud put his hand in the roost.
If I shoot a fire hose at a wall which way will it try to travel?Comment
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Yeah.. I do believe in the laws of physics. Call me crazy. But I doubt very much your boat's speedometer has enough resolution to measure the tiny loss of speed from the drag of someone's hand in the roostertail. That doesn't mean there isn't any loss.
Take it easy,
desmobobComment
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In that case, the loss is pretty insignificant, huh?Comment
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Of course it is, but that's what we were talking about here: the differences in drag produced by different types of water pick-ups. When I used to roadrace motorcycles, I learned that a few "insignificant" things add up to be significant. If you're after every advantage, you pay attention to those little things. If you're just having fun, you don't always worry about them.
I'm a sport boater and I'm not concerned about how much drag my water pick-up is making. But I am interested in the physics of it, and think the discussion is interesting.
Take it easy,
desmobobComment
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