BJ29 Pilots, what is your setup to avoid the bouncing?

[olwarbirds]

I always do what tlandauer shows ....nicely done man... DJ

[AlanD]

Its the little details that make the difference. Great idea tlandauer. I'll try that.

Olwarbirds, what was your motivation to upgrade your flexcable to the OSE cable?

[olwarbirds]

Alan, the OSE cable is just better quality than the stock stuff.... DJ

[hydro_pyro]

In the 1:1 world, performance outboard catamarans such as the Skater have this same porpoise tendency. We call it "clearing the bubble." Trim gives the driver some control over it. As the boat builds speed, the tunnel begins to pack air. The air lifts the bow somewhat, increasing the angle of attack and thus packing more air. As the tunnel compression lifts the rear, the bow drops and the air "burps" out the back, starting the cycle over again. Typically, the driver trims UP to keep the bow from dropping as he accelerates through the porpoise zone. Once the boat achieves a higher speed, there's enough air entering the tunnel to lift the entire hull including the stern, and the driver lowers the trim back to a near-neutral setting as the angle of attack flattens out on a bubble of flowing air.

In the case of our scaled-down catamarans:

This is why a rearward COG holds the bow high to reduce porpoise, but increases blowover risk at high speeds;

This is why hanging the batteries far forward reduces porpoise, it forces a flat ride and stops the tunnel from packing air altogether;

This is why a high strut setting reduces porpoise-- it reduces bow lift and increases stern lift.

With our electric boats, we can't overcome midrange porpoise with trim adjustment, so handling and speed are always somewhat of a compromise. The best solutions seem to involve circumventing the benefits of aerodynamic catamaran design, and trying to make the boat run more like a hydroplane.

[ray schrauwen]

Interesting...

In the 1:1 world, performance outboard catamarans such as the Skater have this same porpoise tendency. We call it "clearing the bubble." Trim gives the driver some control over it. As the boat builds speed, the tunnel begins to pack air. The air lifts the bow somewhat, increasing the angle of attack and thus packing more air. As the tunnel compression lifts the rear, the bow drops and the air "burps" out the back, starting the cycle over again. Typically, the driver trims UP to keep the bow from dropping as he accelerates through the porpoise zone. Once the boat achieves a higher speed, there's enough air entering the tunnel to lift the entire hull including the stern, and the driver lowers the trim back to a near-neutral setting as the angle of attack flattens out on a bubble of flowing air.

In the case of our scaled-down catamarans:

This is why a rearward COG holds the bow high to reduce porpoise, but increases blowover risk at high speeds;

This is why hanging the batteries far forward reduces porpoise, it forces a flat ride and stops the tunnel from packing air altogether;

This is why a high strut setting reduces porpoise-- it reduces bow lift and increases stern lift.

With our electric boats, we can't overcome midrange porpoise with trim adjustment, so handling and speed are always somewhat of a compromise. The best solutions seem to involve circumventing the benefits of aerodynamic catamaran design, and trying to make the boat run more like a hydroplane.

[olwarbirds]

Interesting stuff....yes we are giving up some handling for speed...running the BJ29 on our setup using 6S is more of a SAW running type setup as Lenny previously mentioned...2/3 throttle is max turning speed for sure and the water had better be smooth!...I cant tell you how many times the BJ has cartwheeled/flipped/barrelrolled/sumersaulted and any other none boat type manuevers you can imagine, but it has shown to be a very resilient hull...one thing I did want to point out was that we were not looking to race our BJ29, I have other cats for racing, our goal was to see what kind of topend speeds we could achieve before loosing all control...we are just insane like that

If your going to use a mtr upgrade like the Leopard 4082 using the stock motor mount, you will need to add rear motor support or get the OSE mtr mount...the way I insure not having cooling line leaks is to use Dubro fuel line clips, their a very secure seal around nippled and smooth fittings, plus I use quality cooling/fuel line.

[Barrel Roll Joe]

Any vids yet DJ?

[hydro_pyro]

I got rid of nearly all the porpoising.

-Custom tuned factory prop... Thinned, tried, sharpened, balanced.
-Three 2s hard packs in series
-COG at 7.75" from the rear edge of the running surface.
-Strut top 1/4" above the mount. Prop tips have 2mm of clearance.



Stock boat and electronics. Tiny bit of hop with GPS in the boat. :D

[hydro_pyro]

On smoother water this evening, I was not able to repeat those numbers, or the bounce-free ride. Only got 51 mph, with lots of hop. Almost blew over a few times. This boat LOVES a bit of windblown ripple-chop on the surface.

[olwarbirds]

Any vids yet DJ?

No...its been snowing here in the NC mountains again...hopefully we will have something new to show soon... DJ

[olwarbirds]

Thats the speeds we came up with for the stock setup on 6S was right around 60MPH...with the leopard setup we are in the 70MPH range.. sure looks good all sharpened and shined up ....yes on glass smooth water it does seem to like to hop more...

[AlanD]

The good news: tlandaur, your silicon tube seal on the flexcable worked perfectly. I also removed and silicon-sealed the strut. Found some water leaks there. Not a drop of water in the motor or radio area now. Great pointer. Thanks.

The bad news: I fried the wiring going into the stock Dynamite3830 motor. Ran for 8 minutes on 6S/65C see saw runs. Minimal hopping and great speeds. Proboat says the motor is rated for 6S but that wiring is totally underrated for 6S.

I guess I'll be moving ahead with my leopard 4082 upgrade sooner than expected. Olwardbirds, what motor mount did you order from OSE for your Leopard upgrade?

DSC06444-1.jpgDSC06445-1.jpgWaterSeal-1.jpgDSC06441-1.jpg

[hydro_pyro]

The electronics can handle 6s. However... Inconsistencies in the quality of the physical connections can be the weak link. I did numerous top end runs on 6s, and the only things I experienced we're a little bit of burnt smell from the motor (Horizon tells me this is normal, just breaking-in the winding enamel), and flinging all the grease out of the flex-shaft.

The failed motor connections aren't happening to everyone running 6s.

[tlandauer]

The good news: tlandaur, your silicon tube seal on the flexcable worked perfectly. I also removed and silicon-sealed the strut. Found some water leaks there. Not a drop of water in the motor or radio area now. Great pointer. Thanks.

The bad news: I fried the wiring going into the stock Dynamite3830 motor. Ran for 8 minutes on 6S/65C see saw runs. Minimal hopping and great speeds. Proboat says the motor is rated for 6S but that wiring is totally underrated for 6S.

I guess I'll be moving ahead with my leopard 4082 upgrade sooner than expected. Olwardbirds, what motor mount did you order from OSE for your Leopard upgrade?

[ATTACH=CONFIG]96502[/ATTACH][ATTACH=CONFIG]96503[/ATTACH][ATTACH=CONFIG]96504[/ATTACH][ATTACH=CONFIG]96505[/ATTACH]

Good to hear the water issue is gone, 8 min. run is extremely long and on 6s it is not surprising for something to fail. Assuming that your run was continuous. The wiring and especially the plugs are always a joke to me, anyway.
For my curiosity: does the motor still turn or it is completely dead? I can see the insulation has suffered hight temp.

[AlanD]

The motor turns as normal but won't run. It didnt get over 120F degrees on the previous runs. I'm returning it to Horizon Hobby today.

I'm keen on the leopard 4082/2000kv with a T180 upgrade only because other posters have had success from this setup. I will only ever be running 6S since that's what I've invested in battery wise, but I'm unclear on prop choice and expected run times. I know I need to prop down so can someone recommend a sharpened/balanced prop that I can use with my proposed setup that won't fry things, still give me crazy speeds, and allow me to run until LVC?

Most of my runs are 80% + on the throttle which I understand to be less of an amp strain. Am i expecting too much?

(These questions may seem noob like, but I'm coming from a nitro background and although I have a degree in light current electronics I'm perplexed by some of the rational I'm reading on this forum :) )