Best water pick-up ever!

[Brushless55]

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

[siberianhusky]

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.

[riksorensen]

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.

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.jpg

[properchopper]

Simple propwash pickup. Easy to make, no parasitic drag, flows lots of water.

DSC02752.JPG

[sanyijr]

Simple propwash pickup. Easy to make, no parasitic drag, flows lots of water.

DSC02752.JPG

Tony,

That is the simples, cleanest method yet! Clean install too!

Sean

[Fluid]

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.



.

[siberianhusky]

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.

[Rumdog]

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?

[sanyijr]

[desmobob]

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?

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,
desmobob

[properchopper]

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.



.

I didn't realize this until I tried to lift myself off the ground by my bootstraps while wearing my mobius strip hat. I now stand corrected (and have both a backache and headache from that little experiment)

Jay, thanks for enlightening me

[Rumdog]

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?

[desmobob]

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.

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,
desmobob

[Rumdog]

In that case, the loss is pretty insignificant, huh?

[desmobob]

In that case, the loss is pretty insignificant, huh?

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,
desmobob

[riksorensen]

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.

Thanks...
This is really great info. I just finished wrapping up some research through the tons of info and was kinda shocked at the notion of a square edge in water reacting like this, but it makes sense now especially with how rc boat rudders sit both in and out on the water allowing the air pocket to exist...

I will re-form the trailing edge to be sharp and square...

Lovin the physics on this stuff BTW

Keep the discussion going

I will post shots of a revised design as soon as I'm done

Thanks again for the info...!!!

[riksorensen]

Tapered bottom edge and a square back on it

Should work great!!!

photo 19.jpg
photo 29.jpg
photo 39.jpg
photo 49.jpg
photo 59.jpg

Am very open to any further thought or feedback before I polish it up...

thx

[millzee]

will that create lift?

[riksorensen]

will that create lift?

I am guessing yes,,, but thats why I have a dremel and a sanding block...

I will test it in May and see what it does...

It's all a guessing game...

[Shooter]

I didn't realize this until I tried to lift myself off the ground by my bootstraps while wearing my mobius strip hat. I now stand corrected (and have both a backache and headache from that little experiment)

Now that's some funny stuff!!! Hat's off!! Unless it's this one....


2002423562.jpg

[Jeff Wohlt]

Polishing anything running in the water creates drag or actually does not release the water as fast. Matte finish is better.

[madmorgan]

the faster the flow and less restriction in vehicles lets say forklifts in which i work on all the time cools to much especially if we have to open the thermostat because its sticking and we have to order a new one we gut em and it runs to cool sometimes . its a big factor in the propane world because you need to heat the vaporiser err in lamens terms liquid propane flows into a aluminum housing and converts it into vapor and its then sucked into the engine to make it run. if that hot coolant passing through isnt hot enough then the diaprhams etc inside freeze up and it floods the motor because its putting liquid in instead of vapor i have to agree that the faster the flow with least restriction would be more cooling .

[Cooper]

On cars you have a closed system, in this application you have an unlimited supply of a stable temperature water supply not glycol ( antifreez) thermodynamics- heat transfer, the speed of water passing through these systems is not interfering in this situation, more water passing through system is very simple, the more heat will be transferred , actually it not transferred, heat is always being absorbed by whatever is of a lower temperature, everything is dissipating it's heat into surrounding, (ultimately to absolute zero, when molecular movement stops) so in these boats more water is better, can't compare to autos

[Cooper]

Hey here is the ultimate example for everyone, how fast is your hot 200 degree motor and speed controller going to cool down to the temperature of the water you are running in if you drip that same water over it say for one hour verses if you throw it into the lake? Is that clear enough? I agree with whoever said if you have the right set up this isn't really an issue

[Punisher 67]

Seriously? I thought we put this to bed guys. I'm not sure why this is so difficult to grasp. It's really a rather simple concept. I try to approach this topic without insulting anyone's intelligence, but it becomes difficult after a while. This is one of the oldest redneck theorys out there. I deal with it all of the time and have been listening to people mouth this nonsense for years.
Before anyone gets too uptight, Im not calling anyone a redneck. I call this a redneck theory because in my experience that's where it seems to come from in the automotive world.
LET ME BE CLEAR...There is only one type of person who believes that "cars run cooler with a thermostat/restrictor plate" crap: Someone who doesn't know cars from their rear end.
It's total nonsense. An engine will run coolest at the highest flow rate possible. Before you start to tell me that a car will run hotter with the thermostat removed, do me a favor and go remove your thermostat...let me know how that works out for you.
A thermostat is there to allow an engine to heat the coolant to a specified point. It serves no extra cooling purpose at all. It is an element of the cooling system that is in place to SLOW the cooling of the engine until a desire temperature is reached. I really don't know how this isn't obvious unless you just have no idea how a cooling system in an automotive engine works.
A restrictor can be used (though very uncommon and often unsuccessfully) to create pressure in a system where an insufficient (wrong) pump is used...but is much more commonly a product of stupidity. There are a lot of reasons people in low level racing use these but the primary one is ignorance.

Sorry to rant, but I work in this field and have worked in this field for a long time. It's tough to see the same statement made over and over despite how obviously wrong it is. This is not a subject that can be intelligently debated, because there is no intelligent debate. I thought I provided enough information to put the nail in the coffin on this one, but I guess it will just have to remain a popular urban myth to some people. There is no amount of reality that can can disprove some people's broscience.

Well Put Keith , I am surprised this idiotic theory still stands . a thermostat is to regulate heat and not dissipate it . come on guys get real the more cold water pumped through the more heat pumped out .

[drwayne]

I thought this thread was dead ?

[Stephavee]

Is it possible to have water cooling lines that are too big? I have some 1/4" od pvc tubing that is thin walled. Will it at some point be harder to push the extra volume of water through the cooling system and stat decreasing efficacy? More cooling water=more weight to push.?

[TristanJones]

Stephavee, I think you will be surprised at the amount of water the rudder pick ups can provide at 40+mph. I run 4mm ID piping with stock genesis rudder pick up split into 2 circuits with a Y piece for motor/mount and ESC, the water still shoots about 1mtr (3ft) from the side of the boat when I run it above 30mph. I suggest adding an extra pick up if running 2 circuits instead of the Y piece to keep the speed of the water flow up, each time you increase the ID of the pipe U potentially slow down the flow of water, or decrease the pressure in the line.

Some very interesting info in here, can't believe there is any argument as to weather more flow of water over the cooling plate will work better or not.... Simple test, get a system that runs hot, hook up a 12v windscreen washer motor to it (3rd channel) and pump water through it with that. Log temps during an otherwise normal run but with the pump on, and then run again with pump removed and a restriction placed in cooling system of boat and check temps (if you even need further convincing after running with the pump on).... Guess what!!! It's cooler with the pump on. (do the test and show video to prove before you argue)
To me its common sense, but I've also been working with high performance turbocharged race engines for years. A good debate gets people thinking outside the box which is always a good thing. Hope I haven't come across arrogant here, definitely not my intention.

[drwayne]

You have compromised the cooling effect of the pick up by splitting the flow pathway.
Fluid ( water, and likely Ray ) will always take the path of least resistance to the exit...
Here, limiting cooling effect on flow bypassed areas. ( I read an earlier thread where your motor was wickedly overheating )
Run one line from in to out...

burn and learn

DocW

Stephavee, I think you will be surprised at the amount of water the rudder pick ups can provide at 40+mph. I run 4mm ID piping with stock genesis rudder pick up split into 2 circuits with a Y piece for motor/mount and ESC, the water still shoots about 1mtr (3ft) from the side of the boat when I run it above 30mph. I suggest adding an extra pick up if running 2 circuits instead of the Y piece to keep the speed of the water flow up, each time you increase the ID of the pipe U potentially slow down the flow of water, or decrease the pressure in the line.

Some very interesting info in here, can't believe there is any argument as to weather more flow of water over the cooling plate will work better or not.... Simple test, get a system that runs hot, hook up a 12v windscreen washer motor to it (3rd channel) and pump water through it with that. Log temps during an otherwise normal run but with the pump on, and then run again with pump removed and a restriction placed in cooling system of boat and check temps (if you even need further convincing after running with the pump on).... Guess what!!! It's cooler with the pump on. (do the test and show video to prove before you argue)
To me its common sense, but I've also been working with high performance turbocharged race engines for years. A good debate gets people thinking outside the box which is always a good thing. Hope I haven't come across arrogant here, definitely not my intention.

[dogg]

Actually that's not correct. It is both the amount of water AND the speed in which the water travels. All the water in the world may not properly cool if it does not spend enough time around the object you are trying to cool. This can be done by either restricting the outlet (typically done by the size of the hole on the outlet fitting) to slow the water down or restricting the inlet side to slow the water (the water slows once it passes the restriction) as well as reducing the amount. Controlling the rate of exit is very effective but you need to be careful with too much restriction at speeds over 90 as alot of pressure can build in the lines as a result. On my record trials boats I'll typically restrict both the inlet and outlet using both to achieve the desired temperatures. Using your car analogy going back to when I raced real cars, if you take out the thermostat completely the engine can and usually will actually overheat due to insufficient thermal transfer between the motor and the water. Companies like Moroso make restrictor plates with various size holes that fit in place of the thermostat to help regulate flow rates on race cars. The same goes for the water pumps, we used different sized pulleys to control the speed of water to improve thermal transfer. It is no different with our boats as it is possible to over cool as well as under cool. It doesn't matter if it's nitro, gas of FE powered, all have optimum operating temperature ranges and playing with the rates and speeds of the water will help you get there.

I'll probably cop some flak for this as I'm a newbie on this forum; but when it comes to heat transfer in cars, I would like to clarify something...
It is a totally different scenario to the one you are relating it to.
Firstly the overheating of the motors in cars (be them race or road) without use of the thermostat is NOT due to too much flow through the motor but due to the speed of flow through the radiator being TOO HIGH/FAST to effectively cool it before it re-enters the motor to begin the cooling cycle again.

It is however true with an internal combustion motor that too much cooling can cause increased wear and less efficiency with fuel consumption and overall performance.

With boats, be them model or full scale (bearing in mind the less efficient and higher wear of internal combustion engines that may result) the fact is that no matter how fast the flow of the water/coolant passing through the motor (water jacket in the case of an inrunner), the higher flow of water will always cool the motor faster and more efficiently.

Try cooling your motor with 80 degree water when its running at 130 degrees and it will only ever cool to minimum of 80.
Try cooling it with almost freezing point and the minimum possible it can get down to is the same as the almost freezing water.

The higher the flow rate, the faster the cooler water reaches the motor replacing the preheated water from the motors water jacket, resulting in better cooling period.

I hope I don't offend people with this frank description but I believe this to be true and am interested to know if anyone else finds fault with the logic. I've been in the automotive industry for almost 22 years and have had both road and race cars and this has been my experience and is the only logical explanation in my opinion.