Catamaran setup? doesn't go straight after a turn!

[ED66677]

Spray pick-up is somthing I'm not familiar with, I've asked myself what's the value added of something that seems to be way much more difficult to setup than a basic plumbing?
What's the basic of these spray pick-up?

[pompebled]

Hi Ed,

The huge pipes you have under the hull will pick up huge amounts of water (= cool motors and ESC) but also create a huge amount of drag and is most likely the cause of the bad handling out of corners.

The idea of a fast electric is to have as less drag as possible in order to go as fast as you can with the best boathandling possible.

These huge pipes send shivers down my back...brrrr.

A spray pick-up is situated behind the prop in the upper right quadrant (seen from the rear) in the spray, the average waterpressure is 2 bar, so there's plenty of water and virtually no added drag.

If you don't like the spray pick-up, you can make a water inlet in each sponson, as close to the rear as the tube radius allows.
The tube sticking through the hull faces forward and is sanded flush with the hull, no scoop or other drag-inducing stuff, and will provide enough cooling without adding drag.

Combined with the sharpened edges your Admiral should be a lot faster and better handling.

Regards, Jan.

[ED66677]

thanks Jan, I'll try the spray pick-up on my mono this week end following you advice, it will require less modification on it than on the cat, my main concern was the proper position of the pick-up compared to the prop.

[pompebled]

The current pick-up on your mono isn't that bad, as long as it doesn't stick out under the hull like the 'periscopes' on the Admiral.

Judging from the amount of water from the outlet in the video, I guess it does stick out way to far.
Cut it down so it's nearly flush with the bottom, it will pick-up more than enough water and reduce drag.

Regards, Jan.

[ED66677]

I had myself the same reflection about my mono's pick-up this afternoon, I have two (one for the motor and one for the ESC) vertical 6mm OD brass tubes, they are bended at 45° above the bottom, so it represent an elipse of 10mmx6mm facing the water flow, so that's just 10mm below the bottom (on the cat there's around 20-25mm), there must be a huge pressure in there isn't it?!!!
I say to myself that such a flow of water is not needed, and probably not welcome too, the faster the water flows, the less time it's in contact with hot surface, so heat exchange isn't that good! I think I did read something like that in a computer watercooling forum.

[pompebled]

You're right about the water flow, a steady drizzle is quite sufficient for adequate cooling.

I looked at the mono video once more and even in the starting phase the boat looks like a floating twin fountain!
Completely overkill in terms of cooling.

On my competition monohulls, I have one 4mm spray pick-up and the water flows through the ESC, than the brushtab cooling and the cooling coil on the can.
The ESC never gets warm and the motor is only handwarm after a 7 minute run, flat out.
The picture shows my son's 12 cell MHZ Thick Flash.

The outlet on the side has a steady drizzle, no fountain.

Regards, Jan.

[ED66677]

ok then, I'll change that with only one pick-up and will have the ESC cooling plate in serie with the motor cooling jacket.

[ED66677]

I did change the water pick up for a single one on my mono and cooling is sufficient!
So next step will be "the cat that doesn't go straight"!
I had another though about the lengh of prop shafts, on the cat both are 3 inches away from transom, I'm wondering if this is not too much for the following reason...
Imagine the props are immediately behind the transom or consider that half of the prop is hiden, no matter how deep each prop is (as long as it's enough!), they both generate the same thrust
Having the props at 1.5 inch away from transom should help to"hide a bit better at any speed or "left to right angle" of the boat and so keep the same thrust on each prop
Does that sound logic, ridiculous or away from reality?

[ED66677]

I will also try contra rotative props, and the easyer for me is to go for Graupner Carbone but clockwise range is extremely reduced compared to other!!!

[hkusp45]

I have a buddy that built a small 2 motor boat. It made a huge differance in the turning of the boat when he went to counter rotating props....

Let us know what you find out

[ED66677]

hey hey!
it's getting better and better!

we first changed for contra prop, that improved the result, then we made some modification in order to have enough room to put batteries in sponsons, they are now located between motors and transoms almost 1" lower than before so COG is also lower, this is much better now! but they are standing up between prop shaft and outside of sponsons

next step we are going to go for flex drive so that motors will move 2" from transoms and have batteries just in front of motors and not standing up anymore but laying down in the sponson's bottom

flex drive will also permit to orientate thrust in order to compensate turning effect if needed some kind of self straightening effect

the good thing here is that each single modification brought improvement, one after one, step by step...

... to be continued!

[pompebled]

Good work Ed, keep us posted, preferablement avec des photografies...

Regards, Jan.

[ED66677]

IT'S WORKING!!!
we removed the "plumbing" water pick up from under sponsons and put spray water pick up, cooling is not that fantastic but need to be adjusted for sure, now the good thing is that it's going straigh! damned straight! straight as a straigh line can be!
... and the cat is going faster, so these two water pick up were the worst thing to do!

we'll make some vids next time, but it will be a different hull, because my brother in law just crushed it against the metal border of the canal, he was so happy to see it flying and jumping waves that if forgot to pull the throttle back when approaching the border!

[pompebled]

Good to hear the boat has been improved!

The steel walls of a canal always tend to win..., too bad.
Could you save the electronics?

Regards, Jan.

[ED66677]

we saved everything, only the sponson's tip are cracked so still floating allright but just can't run fast, I think we are going to repair with thin ABS sheet and polyurethane foam!