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

[dre414]

Im running a stock BJ 29 with a sharpened and balanced stock prop on 2S and cannot seem to get the bouncing (porpoising) to stop.

I started with the Prop strut flat to the bottom of the boat (placed boat on a flat surface and adjusted the strut so it was also flat on the surface) and the batteries at the front edge of the trays.

The closest setup I have gotten is with the batteries pushed all the way up on the the tray (almost falling off) and the prop strut really high such that the prop is almost touching the bracket. Although the bouncing has reduced some (however still bounces) the rooster tail is very high and it seems the prop is half submerged in the water. This can't be the right setup.

I looked around on the MG forums but I didn't get a clear answer besides having to buy an offset rudder or buying a faster drive system. Any help or tips would be greatly appreciated!

BTW I'm usually running on a very calm lake with the occasional 5mph wind on one direction.

[MAMBA2200]

These hulls are good at bouncing you will find that a cat hull will be smooth then bounce and then smooth out again once you get fast enough. What i have done to calm mine down is set the strut about 1mm above level and angle it down about 1mm. But what you must take into consideration is that no matter how hard they try every hull is different so it will be different for every boat out there on setup. So try to use my setup and see if it works for you it might it might not but it is a starting point. Hope this helps you

[CHIEFY_44]

I agree with mamba2200, every hull can be sorted in different ways, but the most important is making sure you dont have any concavement on the ride pads, these act like suction cups, what I did was blueprint the hull, taking all the concavement out of the pads and making them level with each other, then I made all the edges and things sharp and 90degrees. This helped a lot on my gieco, hope this helps, you can see step by step instructions by Darin Jordan in the miss gieco thread,

[tlandauer]

I agree with mamba2200, every hull can be sorted in different ways, but the most important is making sure you dont have any concavement on the ride pads, these act like suction cups, what I did was blueprint the hull, taking all the concavement out of the pads and making them level with each other, then I made all the edges and things sharp and 90degrees. This helped a lot on my gieco, hope this helps, you can see step by step instructions by Darin Jordan in the miss gieco thread,

My MG had a bounce that just would not go away until I blue printed the riding pads. It really makes that much of a difference, at least with mine.

[mtbenjamin77]

My MG had a bounce that just would not go away until I blue printed the riding pads. It really makes that much of a difference, at least with mine.

Yeah mine has a pretty bad hook in one of the sponson, it's not flat. That can create a bad bounce. I've found if you add lift at the transom the bounce tends to settle. set your strut at nuetral like you had it and score a line on the strut at the top of the bracket. this will give you a mark for reference. if you find a adjust ment that lessens the hop mark it. I'd say try lowering the strut to about 1.5mm below neutral keeping the strut flat. also try different props or add a slight cup to the one you have 1.2" to 1.7 cup. this will also improve your top end.

[dre414]

Thanks guys for the good advice! the Darin Jordan thread was excellent information.. whereas I’ll probably blueprint and true the sponsons, It appears I have some more adjustment and trial and error to get the bouncing out regardless.. Mamba your advice got me really close so far (not too much time to test). I’m embarrassed to say that I didn't even know you can angle the prop as well as raise/lower the strut.. that just added about a thousand more combinations to try out..

What is good news is that having the strut all the way up such that the prop almost touches the bracket is ok.. I may have to grind the bracket a bit but at least it’s been done before.

Thanks guys I didn't think there was much to be done by way of tweaking a boat but after this thread there's tons to try and tons to still learn!

[bob_t]

On my bone stock , other than PB SS prop, MG29 V1, (same hull) I found that the further fwd I moved the batteries, the "bounce frequency" (# of bounces per second, as I will call it for lack of a better term) got shorter and shorter, with more or less same bounce height, or amplitude, but never settled and ran "flat". For my particular hull (I know each is a "little different") it wants to ride "bow high" ... not excessive, but not flat like what you typicallysee/expect for cats. So, I started moving my batteries back, and the "bounce frequency" got longer between bounces, and now, althought it rides slightly more "bow high" than I would like, it doesn't bounce. The boat seemed like it was trying to carry the bow, but it would "drop" due the batteries (really, the COG) being too far fwd, then it would lift the bow again, would try to carry itself, drop again, and keep repeating this cycle. Strut is set with centerline even to slightly ~ 1/32 - 1/16 above rear ride pad. I'm using a PB SS prop that has been balanced, blade matched and slightly sharpened .... which brings up another point ... my friend had a brand new Mystic - it comes stock with the PB SS prop, but they are not balanced! His was so far out of balance that it rather quickly destroyed the aft most bushing in the strut due to vibration. It was significantly out of balance ... the hub was not drilled straight! With a lot of work, it is now static balanced (he has since then also bought a new one, and that one wasn't too bad - it was drilled straight and is now balanced extremely well). Not saying that my setup is ideal, as I would love to see it run fast and "flat" (someday it will probably have an unfortunate "blow-over" event), but it seems to perform well in the wind protected ponds where I run it.

[dre414]

Thanks Bob agree with the frequency based on the battery location.. I found the same thing when I moved them al the way up.. faster bounce but not as high. Although not static balanced I did balance and shapen the stock prop. I howevr never looked at the shaft bore being straight. I have a few extra batteries coming in today and I pulled out my calipers so this weekend (wife's honeydo list permitting) Ill be doing some methodical testing.

I took a quick look at the hull and although my right sponson is nice and flat the left sponson is somewhat cupped and tapered towards the center of the tunnel. I plan to bluprint and flatten but not till I get it smoothed out as much as I can.

[ray schrauwen]

I find the combination of blueprinting sponsons, homemade offset and extra weight settled mine down very nicely. Too much weight and the motor will burn up though!

[dre414]

Update, I tried every variant I could get and still come back to the setup I described in my OP. Prop almost touching the rudder bracket and the batteries all the way forward falling off the tray.

Bob, I got it to settle w/ the batts back far however the bow rides way too high and almost blows over at speed (esp. upwind), IMO I'd rather have the higher frequency bouncing instead... thanks for confirming the behavior!

Ray when you say extra weight.. what did you use? where and how much? I was thinking about using fishing weights to see if that would balance things out further but ran out of batteries and daylight yesterday.. if it worked, I would switch out to those self sticking airplane weights..

I'm sure blueprinting is required but I'm hoping to get as close as possible to balanced before I go there.

Thanks!

[dre414]

Guys so I finally dialed it in without bluebrinting.. I set the prop to the best I could get it on 4S and then popped in 5s for the first time.. boy did it run fast! and it settled down allot!! Seems that the added weight and power balanced out the bouncing effect.

I ran it for a few laps around the lake on 5s and no temp propblems.. I took it back out and unfortunatly I made the mistake of trying to reverse out of a tight spot of grass and POP there goes the motor!! Why I didn't program the ESC to remove the reverse and why I tried to reverse out is beyond me!!

So now that I have an opportunity to buy another motor (ESC seems to be working still) I was hoping for some suggestions. I really liked the 5s speed.. can you either confirm or recommend a solid 5s motor? I was thinking about either the old version of the PB 1500Kv or a OSE leopard 3650 1600Kv.. I'm using the stock ESC (80 amp Dynamite) and stock prop and am willing to get another prop if you can advise the best motor/prop combo. Thanks in advance.. can't wait to get this baby back on the water. Looks like now Ill have time to finally blueprint it..

[ray schrauwen]

I find the combination of blueprinting sponsons, homemade offset [B]and extra weight settled mine down very nicely[/B]. Too much weight and the motor will burn up though!

Imagine that adding weight settled it down, hmmm....

[bob_t]

dre414, where did you have the batteries positioned, fwd or centered or back, in their trays? I have a spare (new) 60A PB esc (part number PB4018, parts list part number for the Mystic) and the package says "with reverse" ???? Programming card for those controllers doesn't have a setting for turning reverse "off". Does the dynamite 80A programming card have that option? Would love to know how to disable reverse on the one I have, if anyone knows, as a side note.

[dre414]

Imagine that adding weight settled it down, hmmm....

Thanks Ray, I tried some additional weight using wheight strips on 4s and still had bouncing.. I feel the additonal power helped as well. Any suggestions on the replacement motor??

[Doby]

I find the combination of blueprinting sponsons, homemade offset and extra weight settled mine down very nicely. Too much weight and the motor will burn up though!

Just buy an AQ Motley Crew!