ZX1

Hi can some one explaine cavitation / wat is it and how can i find out wats causing it
and how to rectify it the boat a mono deep V sits in the water and screams before taking off

ob nut

My Feedback: (1)

Not an expert, but do believe that cavitation is caused when the prop can't bite the water to get going. Cause may just be that the prop is too high in the water. If the boat is fast once under power, give the boat a slight forward toss when putting into water. Other options would be to drop the prop down a bit or use a slightly larger prop.

ozbryan

i work for a company that sells pumps to pump water and cavitation in a pump is when there is air in the pump and it looses its prime which then means a loss of flow or pressure. not sure if this is similar.

ZX1

thanks BUT IM STILL lost about cavitation
i have a shockwave with a 230 prather prop and a 225 prop
both polished and ballenced [ come on ron lets have yr input ]

treedog

cavitation is caused basically by water boiling off the blades causing air bubbles and thereafter not biting in the water. simple explanation also causes noise and loss of thrust for submarines making detection easier usually as a result of overspeeding the blade designed rpm range

pinky_d_brain

Don’t no if you have read (Prop sharpening & other tips for new boaters) at top of form but it is vary helpful on prop questions here is one of the links that explains cavitation other then that I cant help still new at this my self
http://www.rcprops.com/TechNotes/rcprop_tech_info.htm

ZX1

thanks but how do i get rid of it i have tryed both props and no difference i am about to venture in the rudder and strut adjustments but have no idea of what the changes are SUPPOSED to do

Ron Olson

My Feedback: (1)

Seeing how you asked, my theory that may or may not be true. From what I've seen, the SW 36 is set up for the prop that came with it, including the strut depth and how high or low it's mounted on the transom. It could be that with them using a larger prop than what should ordinarily be used for the .32 that they have the strut higher to help free up the prop. When going to a prop size that makes more sense, you are actually taking more prop out of the water allowing it to rev higher but at the same time losing "grip" because of the smaller size.
Somehow the strut needs to be lowered to get the prop down where it needs to be. Usually if a prop is too high, you will run into chinewalking problems.

How does this sound for an uneducated guess?

ZX1

hi ron well thanks for your info so i will try and drop the strut.
i dont think you can though not on a budget RTR boat .
wat if i fit a larger prop than the 230 and try some mods on it [the prop ]
do you think it could work ?????

Ron Olson

My Feedback: (1)

You're not the first one to complain about that boat cavitating. If it's only doing it on the launch, give the boat a toss instead of just setting it in the water.

ZX1

Thanks ron but you never answered my post re the PROPS it also cavitates some times when im turning also

Ron Olson

My Feedback: (1)

What's happening when you turn is that when the hull tilts it is raising the prop out of the water. When surface drives and higher torque engines started appearing on the scene, boaters found that offsetting the prop to the right helped to compensate for torque on the hull. An added plus was that in right turns it helped to put more prop in the water helping to prevent cavitation in the turns.
Seeing how you really can't go much lower with the strut, try experimenting with the trim tabs. First, they should be 1/16" above the bottom of the hull. If they aren't, it should be an easy fix. Adjust the angle of the tabs in TINY increments to see if you notice and changes in how it handles. A little adjustment goes a long way.

pinky_d_brain

Do you have any pics of your boat it helps if they can see what you are working with and I would like to see it sorry I cant help I learning with you

ZX1

Thanks ron what i did is cut the trim tabs down the centre so i have more
precise adjustments also i fitted a 225 prop as you sugested in one of your earleyer posts
well it is going perfect now hardley no cavitation . the hull is riding a bit wet but i will keep it
that way untill i learn how to drive it . the prop i cut back 4 mm from the drive dog to the tip of the blade and the motor is still very cool i can lean it out a bit more but will leave it for now . and the trim tabs work perfect no chine walking at all THANKS ONCE AGAINE

ZX1

YES I CAN POST PICKS IF YOU EXPLAINE ON HOW TO DO IT I TRIED BEFORE AND NO LUCK

ZX1

hi pinky d brain OK this is wat i done so far. [1] trim tabs; cut down the centre to give more precise adjustments [2] curve the rudder and round the bottom edge also grind away that bevel going all the way down it and polish [3] turning fins; swop around and cut/sharpen/polish also angle them at 90 deg from the hull [4] split the water intake to feed the ehx header also. fit a seperate water outlet [5] fit a fuel header tank next to carb and take the batterys and fit them on the oposite side of the hull to ballance the waight
seal the fuel tank [main] and feed fuel to it with a pump also take that crappy exh header nipple and toss it fit a slightly bigger one
all this means is NO pressure loss and works well also fit tampons in radio tray [ just in case ] hope this helps you

pinky_d_brain

cool i just geting info for when i get my boat on the water thanks

Macleod

Do you think that the 'water absorbtion devices' you are using in your radio box will cause some problems if they increase in size?[X(]

And what you using the 'rubber' for?

Bit close to the exhaust....It's only good for one thing......[:-]

Ron Olson

My Feedback: (1)

Condoms are use to wrap the recievers to help waterproof them. Expensive to me plus having to explain why they are in my toolbox to my wife don't make them worth it. I've been using disposable baby bottle liners to wrap my RX's in. Cut them off at the 6 oz. mark and most will fit in there.
The tampons I'd have to explain too.
If you guys can find a use for pink thong panties for R/C let me know.

Macleod

I had a hard enough time explaining why I had vasalene (petroleum jelly)in my tool box, I wouldn't even try using condoms & tampons.

I find the large party balloons better for sealing the RX. Condoms are too fragile. As guys with kids will find that they are easy to get a hole into.

As for the tampons, are good for absorbing any water that gets into the radio box, but do swell too a larger size. Can stop servo movement.[]

ZX1

but if the boat is under water then you dont need to use the servos ? and hopfully the tampons will help all depends on how well the tray is sealed . as for the condom its all i had at the time

pinky_d_brain

LOL
"pink thong panties" rags maybe lol or a flag on the receiver or remote