HELP Please....Porpoising Hull

[syncronized77]

Hey guys,

I'm a super noob when it comes to boats...I still have to look at pics to figure out where the transom is LOL

Can you guys help me out with my hull which keeps porpoising?? I know there's not alot of things I can do as its a RTR boat...but I can't even get past half throttle before the hull lifts out of the water. She's running an 1800kv motor on 4s with a Graupner 42mm prop.



Should I go to a larger prop? smaller prop? longer rudder? Angle of the rudder?

Here's a link, if the video doesn't work:

Brushless CEN Waveshark

Thanks in advance!

[Jesse J]

none of the above. I would say either too much weight back or thrust angled too much up. Try to add little weights to the bow to see if that helps. otherwise drop angle of prop, otherwise add trim tabs.

[syncronized77]

none of the above. I would say either too much weight back or thrust angled too much up. Try to add little weights to the bow to see if that helps. otherwise drop angle of prop, otherwise add trim tabs.

Ok...I'll add weights to the front of the boat to see if that helps. I'm not trying to break any speed records here...but I guess my best bet is to try and keep the nose as low in the water as possible?

[mschaffer66]

Maybe it has too much dolphin in it...

Seriously though what Jesse said. The weight distribution and driveline angle were probably fine for the old brushed motor. I know it took a lot of dicking around with my Widowmaker to make it run flat on 4S when it was designed to run on 2S.

[adamb]

nice vid! can u move the battery forward at all?

[syncronized77]

Maybe it has too much dolphin in it...

Seriously though what Jesse said. The weight distribution and driveline angle were probably fine for the old brushed motor. I know it took a lot of dicking around with my Widowmaker to make it run flat on 4S when it was designed to run on 2S.

Yeah...I don't remember it ever jumping out of the water when it ran the 700BB motor LOL

One thing I did notice though is that when it starts to jump out of the water and porpoise/dolphin...if I steer it slightly right or left it stays in the water...but only for a brief second before its jumping out of the water again

[syncronized77]

nice vid! can u move the battery forward at all?

No, not really. The batteries already fill the battery slot of the hull...



I guess I can change the orientation of the battery and have the leads facing the front??

Also, I found an article that stated that you can change the attitude of the boat by also changing the rudder angle, so I'm thinking this negative angle should help??

[adamb]

Darn. I was thinking you could have them alongside the motor but I didnt know how that hull was situated

[Jesse J]

Still think you need to add weights to bow. At least this will tell you if moving the batts will help or if it is a hull design issue,

try getting damfurst wes into this, I know he is a pro at these guys

[treystoys]

Before I'd add any weight to the hull, I'd relocate the speed control to the front of the motor, then by standing your batteries on their sides (or that may not even be neccessary) maybe just put some form of padding between the batteries and the aluminum motor mount to prevent damage to the batteries. This way not only will the center of gravity be pushed forward by the esc being forward, but you'll have plenty more room for cg adjustment with the batteries.

The above being said, the angles drive shaft combined with the prop your using is more than likely the root of your issues. Moving to a full surface system will eliminate the issue and increase speed, but you may be able to locate a more appropriate prop, something with less rake, more designed for semi submerged use...it'll be a more rounded looking prop.

And of course there's yet another solution by simply just adding some small trip tabs to the transom you could altogether eliminate the problem and with moderate angle they wouldn't hurt speed much.

Lastly I'd add weight...lol...I say last choice for weight because I was racing fast electrics way before lipo's, brushless, neodymium magnets, nihm cells and the last thing we did was add more weight to the hull...lol

Good luck man hope that gives you a few things to try!

Trey

[BHChieftain]

Ok...I'll add weights to the front of the boat to see if that helps. I'm not trying to break any speed records here...but I guess my best bet is to try and keep the nose as low in the water as possible?

I believe the principle isn't actually to keep the nose as low as possible-- all other things being equal that would result in a hull running "wet" -- with too much drag which reduces speed and overloads the drive train. Also, with the nose too low you can "submarine" the boat (my last run on my syncron I had the batteries too far forward and sub'd it several times-- luckly, it came back up running and dry... a few months ago the boat stayed under for what seemed like 5 seconds and then shot out of the water 3+ feet like a missle--quite a show!)

I think you'll want to play around with the weights, striving for as little as possible which solves your porposing problem, but keeps the nose as *high* as possible.

Chief
disclaimer: I'm also a noob... and I compensate for my crapping driving with a boat with a flood chamber...

[syncronized77]

The above being said, the angles drive shaft combined with the prop your using is more than likely the root of your issues. Moving to a full surface system will eliminate the issue and increase speed, but you may be able to locate a more appropriate prop, something with less rake, more designed for semi submerged use...it'll be a more rounded looking prop.

OK...I've got the original prop that came with the WaveShark, and a Graupner 2317.40 prop which are both slightly smaller than the 2317.42mm I've got running on it. I'll give those a try.

And of course there's yet another solution by simply just adding some small trip tabs to the transom you could altogether eliminate the problem and with moderate angle they wouldn't hurt speed much.

I take it you mean "trim" tabs? Which would mean I would have to do a little drilling into the hull..hmmm...is there a tutorial somewhere on this site that shows how to do this properly? The last thing I want to do is ruin the hull LOL

[syncronized77]

And in regards to Jesse and Chiefs comments about weight, I found these...

Modified CEN Waveshark 1

Modified CEN Waveshark 2

These videos seem a little dated but it shows his Wave Shark not porpoising as much.

Soooo I guess I'm supposed to find balance between staying wet and vice versa?? Man...boating is harder than I thought!!

[syncronized77]

Hey guys...

Well I took all of your advice and put a little weight in the bow of the boat. Used a couple of screwdriver bit sets encased in foam to dial in the weight...and actually gained over 10+ km/h!!!



Takes a little longer to get on plane but she definitely rips harder now, but still porpoises at around 3/4 throttle. I'm just looking for those last few MPH to break 30mph :) I think I may try and go up one more prop size to a 45mm...Or maybe just try on a day where the water is calmer??

[Shooter]

Nice job. Looks fun!

Your problem reminded me of my 12ft row boat. I put a 15hp outboard on it and it was doing the same thing. Up and down she went. The bow was straight up in the air! I had the wife get in front and it ran like a champ! Ha!