How Much Water Pressure Should A Typical Rudder Pickup Generate?

[JoeOvercoat]

How tall should the plume of water be, from a rudder with a water pickup?

That is, how much water should be spouting up how high from a typical rudder that has been properly tuned running at speed, say 30 mph, with the tubing removed?

[carlcisneros]

all depends on the entry hole in the rudder and the actual bore for the water to flow thru.
you should get maybe a good 6 plus inches or so. hard to say and pin point an actual flow height.

If you are not getting a good spray of water thru the entire cooling system, then you really need to
start looking for blockages thru out the entire water cooling line system.

[Rumdog]

Hook up the tubing and quit worrying

[Fluid]

No one needs a firehose spraying out of their boat to achieve good cooling. You can achieve good cooling (as I and my fellow club members have) without the firehose effect. Sometimes we can barely see the water exiting, but the motor and ESC are coming back at reasonable temperatures. My 10S cat blows large volumes of water out of two exits, but at 65 mph the spray is only about 3" above the deck before it turns back towards the stern.

What is important is the temperature of the motor and ESC - if they are not too hot then you are fine regardless of the size of the spray out the cooling exit. Note that water cooling efficiency is a lot better in the Fall and Winter than in the peak of Summer; what works well in November may burn you down in July.


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[JoeOvercoat]

Thank you for the info ~ that is very helpful. I was getting about six inches running a used UL-1 from eBay with a stock rudder that is somewhat dull, so I thought perhaps it was coming up short.

I get flow through the ESC & motor, and it if I put the rudder tube under a running faucet, pressed against the aerator, I get a steady dribble out the exit, or a bit more if I turn the faucet up, and when I turn the water off the ESC drains quickly & cleanly. If I blow water through I can get a steady stream out the exit.

After the last run when I had an 'ESC out' (did not seem like the battery stutter-bump) my IR thermometer put the ESC at only 85 degrees, and it seems unlikely that it dropped almost 20 degrees in two minutes while I walked the boat to shore. So between your information and that experience, I suspect that I have a dodgy ESC. Or, I have the boat trimmed poorly, and drive it badly enough, to trip some kind of amperage cutoff in the Aquacraft ESC inside of five minutes of running.

Thanks for helping. You got me another step down the troubleshooting tree.

[Rumdog]

What cells are you using?

[JoeOvercoat]

I am running new 4S batteries: 4200 mAh 30C from GrimRacer with a deans connector running through a deans-to-5.5 bullet adapter to 5.5 bullets on the ESC. The batteries seem healthy. The 4S battery still has plenty of juice, and has been above the low-voltage limit of 11.6V, when the boat cuts out. Swapping in a fresh battery does not help. Waiting overnight and re-binding the Tx-Rx restores it to operation but only for a handful of lap.

The seller had told me to run it on 3S, but the boat would only run a few moments before the voltage cut-off would kick in...or at least I presumed that was the case when I looked up the Aquacraft 60A ESC (I have the version with the larger cap) spec and learned it was supposed to run on 4S.

[TheShaughnessy]

5 min is a long time in a ul1 with only 4200 mah on board. Don't forget batteries sag under load and if you are getting a reading of 11.7 after your run it was likely well below that during the run. Also i wouldn't use less then 12 v as the cut off for 4s.

[JoeOvercoat]

Thanks for the advice. 11.7V is a long way from 14.8V, isn't it? But, my understanding is that the Aquacraft ESC is not programmable. If I can change that would be great. And I had hoped to run on two 4S 4200 mAh batteries in parallel, but the GrimRacer 4200 mAh battery is a tad too tall for front the hold to fit lengthwise (cowl will not fit properly, under the forward canopy).

The run times seem reasonable, but the boat seems to be skipping over the stutter-bump at 12V and going straight to the ESC cut-off at 11.6V: I wonder if battery sag is the cause. And, my lousy driving the culprit, as it puts long-lived high-torque loads on the motor.

However, I have not been measuring voltage levels, though I have a mini-reader. So I'm off to collect more data, to include 'V'.

[siberianhusky]

When you charge your batteries your charger should tell you how much went back in, you shouldn't put more than 80% of the packs total capacity back in, if you're putting more in then you are discharging your batteries to far.
Using this and timing how long you ran you can figure out how long you should be running. Some radios have a built in timer, some of the guys I run with velcro a little digital timer to the radio.
This can also tell you your average amp draw, which can help a bit in setup. Not super accurate but it gives you an idea.

[TheShaughnessy]

I am running new 4S batteries: 4200 mAh 30C from GrimRacer with a deans connector running through a deans-to-5.5 bullet adapter to 5.5 bullets on the ESC. The batteries seem healthy. The 4S battery still has plenty of juice, and has been above the low-voltage limit of 11.6V, when the boat cuts out. Swapping in a fresh battery does not help. Waiting overnight and re-binding the Tx-Rx restores it to operation but only for a handful of lap.
.

Any way you can get 5.5 bullets directly to the batteries? Don't think that would cause cut out issues but it would be good to do. Kinda pointless to use 5.5mm bullets if you still have a deans in the loop.

I'm a little confused as to what exactly your problem seems to be. The boat just cuts out when it isn't suppose to?

[JoeOvercoat]

Any way you can get 5.5 bullets directly to the batteries? Don't think that would cause cut out issues but it would be good to do. Kinda pointless to use 5.5mm bullets if you still have a deans in the loop.

I'm a little confused as to what exactly your problem seems to be. The boat just cuts out when it isn't suppose to?

The ESC was modified by the previous owner to one set of bullets instead of the stock Deans in parallel, but the 4S batteries that I have in hand came with Deans. I'm uncertain if it would be progress to swap in bullets because my soldering skills aren't so hot. I understand, and hope to follow, your recommendation to go straight bullets where I can (I also share batteries across vehicles so I'll always have some Deans in the mix), though the Deans have not gotten hot, or seized up, or discolored yet.

As for the problem, it was failure in several cells of one of the batteries, and my failure to recognize that. I carried two batteries into the field, both new, and both fresh off the charger. Then I think I drove straight through the stutter-bump low-voltage warning to the low-voltage cutoff: I'm guessing, but my driving might have been bad/inattentive enough to mask that effect. My confounding error was taking the bad battery to be good because it would spark at connection and drive the servo, but it turned out it was only providing six volts. I thought I had a hard time-out on the ESC that would reset overnight, and that the boat was cutting out when wasn't supposed to, but actually it was a bad battery in the mix (and the other one deeply discharged). It all became clear when I connected a tester to the batteries after the second mission failure, and found one dead at the balance connector with 6V at the deans.

Washing & blowing out the tubing after the first outing may have cleared some obstruction that drove run time down on the first day...but the basic problem was the bad battery, and that I would mix up the matching batteries once they were off the charger.

I got all the run time I could expect on my third day out. I pulled the boat from the water because the boat was growling when under load/accelerating so I decided to bring it in and take it home to inspect & grease the drive shaft, and check the motor. Battery was still well over 14V after more laps than any other day.

The assistance on this board was very helpful in ruling out other issues, and it has been most appreciated.

[JoeOvercoat]

When you charge your batteries your charger should tell you how much went back in, you shouldn't put more than 80% of the packs total capacity back in, if you're putting more in then you are discharging your batteries to far.
Using this and timing how long you ran you can figure out how long you should be running. Some radios have a built in timer, some of the guys I run with velcro a little digital timer to the radio.
This can also tell you your average amp draw, which can help a bit in setup. Not super accurate but it gives you an idea.

80% sounds like a good rule of thumb. I'll run with that. My charger provides a mAh reading, and I need to be more disciplined about reading it.

I think I need to attach a timer to the Tx. I going to look for an audible warning device. I've been spoiled by my ground vehicle RCs, where it is easy to spot battery drop-off. Along those lines, I need to spend a day doing nothing but learning to recognize stutter-bump in the UL-1.

[JoeOvercoat]

About Half A Foot Or So At The Rudder Outlet

all depends on the entry hole in the rudder and the actual bore for the water to flow thru....should get maybe a good 6 plus inches or so. hard to say and pin point an actual flow height.

Thanks carlcisneros.

It's great to know what to look for, especially when it is so hard to see that spout, much less the typical outlet, while the boat speeds by. The flow rate of 6 inches (15 cm) or so at the rudder outlet is lower than I expected, but is about what I am getting, so I now have a better picture of what is going on in the water loop. I plan to sharpen the rudder to see if that bumps the height up. I might have to get the HD camera out on the water to see if I can capture the spout on video as part of a before & after test.

And thanks to everyone for all the suggestions - my boating will be better off for it.