Tunnel Hull, please help

[viper1]

A question for the tunnel hull guru's out there;

Setting up my new tunnel hull and this is where I'm at:
Running on 4s to start with, later planning for 6s. O.S. Lower leg behind a Hornet hull with severe 'make-over'
(see http://www.rcgroups.com/forums/showthread.php?t=1840066 for details)
Bottom is blue-printed as well.

Started out with leg everything at 0, angle and thrustline at sponson bottom. CoG is at 30%
At WOT she looked perfectly balanced, good speed and attitude, very stable.

My issue is at anything below let's say 60% throttle, starts porpoising heavy and all the way down to crawling speed.
cornering is bad as well.
I understand that tunnel hulls have a "hump zone" where the location of the center of Lift quickly changes as the boat accelerates, they all do it at a certain speed. But here it is happening at a wider speed range.

What I tried so far: theoretically ,at least what I found in various threads, I should have lowered the leg, more negative angle and bring the COG more Fwd ?

Did that (I gave it 1 degree down without adjusting the height, so that automatically lowers the prop as well ) and brought the batteries fwd.
porpoising was now worse, even at WOT where she was rock-solid before.

I was thinking of raising the leg this time, any thoughts?
I have a feeling the COG was good where it was before, at 30%

Any input appreciated, Thanks in advance.

[HTVboats]

We refitted my grandsons Hornet with a real wooden radiobox, 3S and a 70a esc with a 2860 3000kv motor a REK lower. That is about the limit on that hull and is upside down easily over 30mph. If all you need to do is stop porpousing go down further and or different props but don't shift CG if it runs well at speed.
As for your 6S plans I would recommend a TS-3 for that OS lower and will run 50+mph comfortably. http://www3.towerhobbies.com/cgi-bin...?&I=LXZJB9&P=0 Not sure what price is in AU but US for $120 is inexpensive for a proven hull. NAMBA record holder at 72mph on 4S.
Mic

[NorCalZ71]

I have read your build thread and I am inspired to attempt to mod my hornet. Yours looks amazing! I probably won't go as in depth with my build as I have a 35" tunnel on the bench as well and that takes priority. Keep experimenting with adjustments and props and you will find stability. I remember reading you added a lot of weight? These hulls run better on top of the water and I could guess at the added weight causes the porpoising at low speeds because it is hopping on and off plane. If that is the case the only remedy is speed... Or weight reduction? Again just a guess as I have little experience with tunnels yet.

Kevin.
Nsr customs.

[viper1]

Thanks Mic

Maybe my expectations are too high when it comes to handling, on the other hand, I've seen many video clips posted where it simply corners way better than mine, no or little porpoising and with no work done on the bottom.
I can try going down further, but a little was making it worse, that's why I thought to try the other way...

As for the 30mph hull limit I think that is a bit conservative;
Initial runs didn't look fast but the GPS gave 44mph on a 42mm CNC, when I switched to a X445 it is 46.6mph. This is rock steady even on choppy water. On 6s it should easily go over 50.

If I could only make it round a (virtual) buoy

[viper1]

I have read your build thread and I am inspired to attempt to mod my hornet. Yours looks amazing! I probably won't go as in depth with my build as I have a 35" tunnel on the bench as well and that takes priority. Keep experimenting with adjustments and props and you will find stability. I remember reading you added a lot of weight? These hulls run better on top of the water and I could guess at the added weight causes the porpoising at low speeds because it is hopping on and off plane. If that is the case the only remedy is speed... Or weight reduction? Again just a guess as I have little experience with tunnels yet.

Kevin.
Nsr customs.

Thanks Kevin,

Weight sounds more plausible, I thought about that. Although I think she doesn't weight that much extra, most of the extra weight is relatively high above the waterline. Extra carbon in the cover, the ply sides in the radio box which forces the 2 battery packs to stand on the side. Things like that. Would a higher center of gravity contribute to the hop?

I didn't put her on the scale yet, I will and post it later for comparison.

Can't loose much weight, except for smaller batteries but I can bring it lower by cutting the sides out of the radio box and laying the packs flat.
Not really something I want to do though unless really necessary.....

EDIT:
Weight is 1880 Gram (66.3 oz) + batteries 720 Gram (25.4 oz) total 2600 Gram 91.7 oz

[HTVboats]

Sorry to shoot low on speed but my opinion of a hull is predicated on being able to run in traffic and turn at speed. Yes it will go faster but not reliably IMO.
Mic

[NorCalZ71]

Came across your other thread thought I would share this.
http://forums.offshoreelectrics.com/...ad.php?t=30359
If I remember I saw a thread discussing how to set trim on OBs I'm trying to find it still but for the most part the center of the prop shaft should be at the same height as the bottom of the sponsons and kicked up a couple degrees.

Edit: found it.
http://forums.offshoreelectrics.com/...d.php?p=497441

Kevin.
Nsr customs.

[kendt]

I need another tunnel like a hole in the head but you made that one look dam nice. I'm tempted!!

[NorCalZ71]

Be prepared to be disappointed by the stock form but with some work it can be a pretty nice sport runner.. I wouldn't race it but it sure looks good!

Kevin.
Nsr customs.

[BHChieftain]

I run a woodstuff OPC hull with an OS lower. I have the strut up pretty high, but with a tad of negative angle on the prop shaft and that works well on my boat.

Here's a thread which helped me:

http://forums.offshoreelectrics.com/...el-strut-angle

Chief

[viper1]

Thanks Chief and others for the links,

I did another run the other day with the shaft 1 deg pos, 3.5 mm / about 1/8" high (from sponson bottom)
And the overall feel was better, at slow acceleration the humpin' stopped earlier. For the first time an actual improvement over the "all at zero" set-up.
I don't think I can lift it up higher though, as I was getting the 'slurpies' sometimes.
I will experiment with the angle only, for now keeping the prop at the height it is.

First I need to beef up the steering cables, might go to rods, as I keep having troubles with the steering.

To be continued....

[viper1]

Video

Here is a video of the thing running: