Lifting prop recommendation

[G Doggett]

In my mission to tame my twin Jolly I am looking for some r/h and l/h lifting type props to replace the Graupner K40s.
I have been told that the Prop Shop cleaver props have quite high lift so have shot an email off to them but no answer yet.
Do any of you guys have a recommendation.
The boat has twin counter rotating 8XLs on 12 cells each.
Graham.

[shockerman80]

whats the boat doing? Why does it need to be tamed??

[G Doggett]

The boat porpoises violently until it reaches full speed.
I have moved the batteries forward to achieve 40% c/g and trimmed the drives down 2 degrees which reduces the porpoising but it is still almost out of control.
The other club members love it but it is too hard on my nerves !
I think I need to find some props that will lift the stern and help hold the bow down.
It has also been suggested that the weight of 24 cells is too much for this hull and may be contributing to the porpoising.
I intend going to lipos but not till next year.
Graham.

[Fluid]

Many cats will porpose as they transition from hydrodynamic lift to aerodynamic lift. My SAW cats have all been bad about this, due to being set up for maximum speed the differences between the two lifts are dramatic due to the narrow tunnel. If the boat has sufficient power you can drive through it....with nerves.

The high weight of the boat can make this worse. I'm not certain that lifting props will help, I've used both X and V series Octura props on SAW cats and the porposing is similar. It is probably worth a try, but finding L and R props may be tough. Why not try two L props just to see if they work? That may be a lot less expensive than custom props.


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[shockerman80]

Try reversing the counter rotation of the props. aka switch the left and right drive cables and props.

[G Doggett]

Thanks Shockerman but been there done that !
I'm starting to think that because the motors are going waa waa waa as the boat bounces up and down that maybe the props are loading and unloading from water exiting the tunnel.
I had a similar thing occur with my gas powered Victory cat which I cured by installing an air bleed tube ahead of the top arc of the prop to stop it loading up.
The Toysport Jolly cat has been around for a number of years now but most ( sensible ) people just have a single central prop, not me I had to go with twins.
Graham.

[G Doggett]

Hi Fluid
I'm used to a certain amount of porpoising with my other cats but nothing like this.
It is possible to drive through this stage but only on dead calm water and poised to get off the gas if it starts going crazy.
At about half speed it will even start bouncing in the turns.
With 2 8XLs I don't expect to be able to give it full throttle from a standstill without a fairly spectacular 'wheeley' but even gently increasing speed it wants to start bouncing the bow.
I have a selection of Octura X series l/h props I can try as you suggested.
I am starting to think that it is a hull or tunnel issue as mentioned above, as even with the c/g at 50% it will still try to porpoise and once it starts it wont stop until I back off.
I have run lots of cats ( not as many as you ) and am pretty familiar with setting them up but this my first attempt at twins.
Toysport are selling their own version now so I am waiting and watching this forum with interest to see how theirs handles.
My home made drives are very similar to those pictured on the forum but I have them mounted as close as possible to the inside edge of the sponsons while the Toysport ones are mounted in the centre of the sponson.
Don't really know what difference this would make other than maybe keeping the props further away from the wash from the tunnel.
Graham.

[ED66677]

I think your props are too small, this is an issue when using a 8XL, this motor is really powerfull but only at high rpm, so you can only spin K40 or K42 prop, may be 43,5 because you have 2 of them but very few are available L & R, I think you are in the situation where, when the bow lift, props are going down and then generate more thrust so the bow goes down and bounces (because prop are pointing downward) and props are then coming out of water generating then less thrust and so on (that's the wa wa wa), moving the COG forward help until a certain point but increasing drive angle should help a bit too.
Also important is the distance between the transom and prop, it might not be sufficient as it is, increasing this distance will considerably improve longitudinal stability, because props get deeper in water while the bow does not lift as much!!!
I recently saw a H&M Intruder with extremely long drive lines coming out of the transom so that the distance between props and transom was 12% of the hull lengh!

[G Doggett]

Hi Ed.
Thanks for your input.
The front of the props are 90mm behind the transoms, and the hull length from transoms to the bows is 750mm, so this works out to exactly 12%.
I must admit this wasn't calculated, the drives just looked about right at that length!
The more I think about it I am sure it is a loading and unloading of the props causing the 'porpoising' effect.
Maybe some different props will help but as you say there is limited choice in counter- rotation.
I am still hoping someone can suggest a pair of props that have worked for them on a similar set up.
Graham.

[SJFE]

I agree with moving those props/drives back. If you look at the pictures of the single Jolly in the store...& then at a picture of mine there is a diffrence. My version of the cat has a 4 inch or better stand off. I watched a video of the (gen 1 jolly) as I call it. I noticed it bounced around more so than mine used to. For me extra weight up front was a problem. When I reduced the weight of my motor, ajusted my cg & learned how to drive a cat it all just fell into place.

[ED66677]

Also moving the COG to the front, at a certain point, may increase porpoising, if the thrust is still able to lift the bow at startup, the hull goes deeper ( because it is heavier) and bounces back, I.E take too pieces of wood, one balsa, one oak same size, both can float, throw them in the water, balsa will stop right when hit the surface, oak will go very deep and come out, and fall again...
Increase the prop angle downward and move the COG backward!!!

[G Doggett]

I now have a pair of X442 ( r/h and l/h ) props to try in place of the K40s before I resort to drastic measures like repositioning the drives.
If it is a loading and unloading issue I'm hoping the better blade shape of the Octura X series will stay hooked up.
Fingers crossed.
Graham.

[G Doggett]

Nope - no better !!!
I can get a pair of r/h and l/h ABC H1516/3 props locally, do you guys know if these will have more lift than the Octura X series?
I'm not familiar with this brand so don't want to buy them if they wont be any better.
I can't angle the drives down any more without redesigning the mounting brackets.
I'm still waiting with interest to see if other twin Jolly owners have similar issues.
Graham.

[jfabcustom]

Check this out. I can't solve my porpoising issue either. Brushless proboat mini c with ammo 2700Kv motor, SV27 ESC, 11.1v 1500mah Lipo, Octura X427 prop, and a custom inline strut rudder bracket that I designed. My dad helped me cut it out on his mill. In these videos the strut is bolted in one position meaning only the angle is adjustable. I have since then slotted the hole on the mill so that I can adjust both hieght and angle. Despite all this it still porpoises. I haven't tried changing C/G yet. That will be next. Here's the link to my videos.

Click play all videoshttp://www.youtube.com/view_play_lis...598D4690290161

[kevinlew211]

Nope - no better !!!
I can get a pair of r/h and l/h ABC H1516/3 props locally, do you guys know if these will have more lift than the Octura X series?
I'm not familiar with this brand so don't want to buy them if they wont be any better.
I can't angle the drives down any more without redesigning the mounting brackets.
I'm still waiting with interest to see if other twin Jolly owners have similar issues.
Graham.

Yes, ABC's prop has much lift than Octura x series, im using a pair L/R Abc 2016/3 on my cat, its has alot of lift (helped me alot to keep to noise down at 73mph) also its not bite the water right away like Octura prop did, but when its hook you will love them, look like you and me are in the same boat, i bet you will happy with abc prop