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Which is generally the most efficient location to pick up cooling water rudder, transom or through the hull in a mono hull?
Starting to pick up parts for my salt water boat so there are likely to be lots of dumb questions like this so be forewarned. :confused2::biggrin:
The rudder is your best option
trim tabs, one for motor, one for esc.
you don,t want to add extra unwanted water drag which will slow down your boats speed so the best water intake is a [ water blast design ] this is a water pick up tube which comes out through the transom above and over the prop and curls around to line up behind the prop, very effective and is used on SAW boats. next in line would be the Single water pick up type which is on the rudder. you don,t want a piece of tube sticking down in the water as a water pickup as this causes alot of drag plus it will pick up weeds etc. so the simplest pickup to use is the rudder type single or rudder type double for twin motors.
Actually, the “water blast” pickup is one of the draggiest around, and one of the least efficient. The speed of the water coming off the prop is higher than that of the pond passing under the boat and it hits most of the tube, not just the end. This causes a lot of extra drag.
Too, the water which hits it is full of air, and foamy water in the motor jacket is a poor conductor of heat. It “works” but few (if any) top SAW boats use it anymore. Many have no water pickup at all, I haven’t used one for four years.
IME the two “best” pickups are 1) the rudder and 2) flush-mounted fittings on the hull bottom. The rudder is easiest and very good.
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Fluid do just use a fan instead or any other tricks?Quote:
Originally Posted by Fluid
I find the flush Thru-Hull the most efficient on Monos and Cats. Unfortunately, hydros don’t have a good spot. The rudder pickup rules there.. So I agree with Fluid. I’ve thought about putting a side port on the turn fin... Fluid, anybody try that on a hydro?
I had a pickup on the heel of the sponson on an old vintage woody, just like the full size boats used to have. It was pretty effective.
But I agree, the rudder pickup is probably the best. Certainly the easiest. On any type of boat.
Attachment 156152
The downside to a through hull pick-up is lack of contact with the water in rough/race conditions.
Yes, you can lose water flow. It’s a down side... I haven’t seen a heat problem, but I’m sure there are setups that will not tolerate that. So that leaves the rudder pickups.
I really can not see how the water blast behind prop intake could possibly be the draggiest water pick up around and less efficient. i have used this method for many years with gas powered boats with great success where water cooling is crutial for top 2 stroke performance. i have never had any weed in the pick up where i have had issues with weed around the rudder blade a few times . the water blast pickup is set up to catch prop water from its tip and is naturally forced induced, zero drag and plenty of water supply is given. the only down side is for race craft where if another boat should make contact with this tube during a race theres good chances of the tube being bent thus zero water flow to motor.
water blast is most common with SAW boats and still is unless as Fluid mentioned , no water cooled motors and esc,s are used. so the answer to original post would be the inbuilt Rudder water pick up for the ease of set up as most commonly used .
What you cannot “see” doesn’t trump physics. Ever stick your hand in the wake of a full-sized boat? Bet it pushed your hand back pretty hard. Imagine that force multiplied by the higher rearward velocity of prop wash. The wash hits the entire length of the pickup while with a trim tab mounted pickup only the tip of the pickup is in the water. Too, propwash isn’t solid water, it is mixed with plenty of air. And who said anything about weeds???
The fastest FE boats in the world don’t use prop wash pickups for a reason - they are draggy. I participated in NAMBA and IMPBA SAW events for many years and haven’t seen propwash pickups on record holders for a long time.
Hey, I said propwash pickups work, just that they aren’t the best. Back on topic, I agree that the rudder pickup is probably the best overall.
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Fluid, the water exiting the prop tip is directed into a hollow tube not a solid face so by rights there should not be much drag atall providing the water can get into and out of the motor jacket as quick as possible just like the art of fine tuning a race engine you must get fuel into and out of the engine as quick as possible. example; blow water through a straw with your mouth and feel any drag.
http://3.bp.blogspot.com/_1EKtN-2yN0...126MPH-saw.jpg
Never seen a water blast pick-up on a saw boat in Germany
i've seen them using very thin rudder blades without a pick-up and used a through the hull pick up with a pump to cool things down between the 2 runs
I was of the understanding that a prop wash pick up interfered with the water leaving the prop blades & not allowing the prop to work as it should & causing drag. I also like the rudder pick ups best, through hull pick ups work well but you cant be sure if you are getting constant water flow. Especially if you have a boat coming up out of the water at times.
Has anyone tried adding a water pickup to their turning fin? I would prefer a dual outlet rudder but so far I haven't found one for the UL-19.
I am thinking of making a brass turning fin and solder the pickup tube to the trailing edge. It will add some drag but not as much as it would
if I just mounted it on the transom. Not sure how well it will hold up but I need additional cooling dedicated to my ESC that gets much hotter
than the motor. Any ideas would be welcome.
i wouldn,t mount the water pickup on the trailing edge of turn fin as you might have steering / control issues due to the excess drag caused . why not just have the single rudder pick up like we all use ? single motor and esc i take it ?
I'm not sure about the fin, but here's what the full size hydros run on their rudders.Quote:
Originally Posted by John P
If just the ESC is getting hot, get a bigger ESC & just use the single line like most people use.
Attachment 156399
thats the way we used to make up our own water cooled rudder pick ups, stainless steel blade and silver solder a brass tube on the trailing edge with a 45 degree cut just below the rudder bottom.
RC Boat Bitz makes a dual cooling rudder for the UL-19 and Veles
I know it’s been tried in Unlimiteds, but created too much turn fin lift. I think that would happen in model boats too.Quote:
Originally Posted by John P
I JB welded a tube to the backside of a rudder in the mid-80’s. It worked great and never broke off! I was going to do that on my new FE boat, but they have many rudders with side ports adequate to do the job. I can put my efforts in another direction.Quote:
Originally Posted by rol243
I was of the understanding that a wedge rudder should be flat @ its rear vertical edge, putting a water pick up tube down the rear edge changes the shape to a curved edge creating more drag than a flat edge.
That's true Martin. If I were going to do it, I would use a square section tube, to keep the trailing edge of the blade flat.