Aerotec Cavitation

Patrik · 24 July 2011, 19:11

Hi all

I wonder what's actually happening (sometimes) when I accelerate and the engine digs a hole in the water, so a V-shaped opening occurs around the prop and makes it run in the air instead of in the water. Sounds horrid and must be no good for the engine either. Is this what you guys call cavitation?

The floor is nowhere near stiff enough right now, is that the reason?

Another option I consider is that the engine/prop still isn't far enough below the floor because the 420 really should have a long shaft. My boat has been modified to take a short shaft, but perhaps they havent cut enough out of the wood.

Regards

Courageous · 24 July 2011, 21:00

This is ventilation and is the start of a road to nowhere......... I have this issue and gained considerable ground by fitting a planing plate mounted artificially forward of the norm. It's still not right and so I have bitten the bullet and ordered a leg extension kit. If you have a chopped transom and are happy to chop it further without fear of weakening or increasing the chance of swamping then that's an option I suppose.

C-NUMB · 24 July 2011, 21:09

In a Aerotec i think its mainly due to wrong(low) pressure in the floor. Shape is not correct, floor will bend and this will influence on the water flow to the prop. But guess to short rig will do the same.

Dino89 · 24 July 2011, 21:32

i would check that the boat has been modified properly to take short shaft i attached a few photos of the 380 transform to bottom of V measurement
if this is the same on the 420 you have then its most likely time to invest in a pump that can get it all up to correct pressure i make the measurement from the top of the transform to the bottom of V 15 1/2 inches
let us know what yours measures

Patrik · 24 July 2011, 21:39

Thank you! I will measure it tomorrow! However, there's really an urge for a pump, that's obvious to me now. How long did you say it took for you to inflate with the BST HP? I'm still not certain about that specific one as a hand pump costs just £25... And the battery BST is £220 over here. I think I would go for that one as it would increase the usage even more. You got away with £150 pump and £30 battery if I recall correctly? Perhaps not big enough of a difference, since I think the one without battery goes for £185 here.

However, the floor is really flappy and no fun at all, as soon as I get up to any speed what so ever, it starts wobbling and feels like it's "blowing up" under me. And so I just turn the throttle off immediately! But if it's like you guys say that the floor would cause the cavitation, I will sure get the pump first and go nuts on the transom later

Nos4r2 · 24 July 2011, 21:53

One of these with an inbuilt gauge will get you to the right pressure-just remove the plastic plug from the top and it'll only work on the downstroke, allowing you to get to higher pressure. You'll grow muscles from doing it though.

Dino89 · 24 July 2011, 21:54

my pump in total was 130 with battery and charger but i bought mine about 5 years ago
if the boats not rigid then you basically hae the motor on an airbed wich will fold the moment you put power through it, buy the best pump you can afford you only want to buy it once and not have regrets wishing youd bought the better one
i would guess it takes me about 10 - 15 minutes max to get my boat unwrapped and blown up seat in , bow bag in, launch wheels on and 15hp tiller motor dropped on , you can be do other things while the pump does its job

that looks like hard work Nos

Patrik · 24 July 2011, 22:11

well that was the hand pump I was looking at! Except for the gauge meter though. Looks good..

If I decide my time and effort is worth more than my money and go for the electrical pumps, I've seen there's options. BTP 12 (is supposed to do 1 bar), BST 12 HP (0,8 bar) and then the BST 12 KITE, which I don't know how it differs from the BST 12 HP.

Nos4r2 · 24 July 2011, 22:26

Quote:

Originally Posted by Patrik

well that was the hand pump I was looking at! Except for the gauge meter though. Looks good..

The gauge just screws in the handle.

Don't buy the cheaper versions with a plastic shaft on the handle.
I've got one with a plastic shaft to inflate the rib with-when I tried to inflate someone's air floor with it the flex got too much to get past about 5psi.

Dino-yes, it's hard work. Not £200 extra worth of hard work though!

Dino89 · 24 July 2011, 23:07

Quote:

Originally Posted by Nos4r2

Dino-yes, it's hard work. Not £200 extra worth of hard work though!

your not wrong, and the exercise will do you good, a win win Lol

Patrik · 25 July 2011, 00:12

Hehe, I don't find the pumping with my Bravo 10 THAT painful... However, I havent tried getting the floor to high pressure with one of those, how much more work is that?

Nos4r2 · 25 July 2011, 00:34

Quote:

Originally Posted by Patrik

Hehe, I don't find the pumping with my Bravo 10 THAT painful... However, I havent tried getting the floor to high pressure with one of those, how much more work is that?

It involves leaning on it...

No wonder you were struggling on the floor pressure using a bravo 10-the ones I've used struggled to get to 2.5psi.

Patrik · 25 July 2011, 01:15

So it seems! When I read on the bravo 10 I figured it's able to get about a fourth of the needed pressure

It will be interesting to see what happens to my calzone bubble on the floor if I get it up to correct pressure, might turn my floor into just one big balloon!