Hi, I have a Graupner Rhod Island tunnel running on a 3 cell rest is all stock, it’s fast in a straight line but just hooks on the corners and spins out no matter how gentle I am on the steering, anybody help me out here ?
Thanks

Is the steering servo strong enough to turn the motor / leg at force ? have you set the c.o.g. balance abit to the rear ? have you tried raising the back of leg a few degrees so the front of hull rides dry of water spray ? most of the time this issue does come from a bad servo or servo to motor pushrods that bend which are not supported or not thick enough in diameter. nice looking tunnel hull .

Originally Posted by crapshooter

Is the steering servo strong enough to turn the motor / leg at force ? have you set the c.o.g. balance abit to the rear ? have you tried raising the back of leg a few degrees so the front of hull rides dry of water spray ? most of the time this issue does come from a bad servo or servo to motor pushrods that bend which are not supported or not thick enough in diameter. nice looking tunnel hull .

I found out one of the push rods come lose could that be the problem ?

Yes i would say thats the problem for sure. sometimes with these rtr kits you do need to replace some parts with heavier duty gear for reliability. this goes for a stronger metal geared / digital rudder / leg servo as well. radio compartment must be totally waterproof if the hull flips over you don,t want and water in with the radio gear.

The servo that comes with it is very small but metal geared, the rods are very thin and do bend easy, they also go down to the smallest servo horn I have ever seen, they start off wide on the outboard say 50mm then down to I would say 20mm to the servo horn, see pic. Thanks for the replies guys could really do with this help

that servo horn connection to the rudder control arm is like a gearing where you will get more torque from the servo by having the control rods set in close to the servo center and set wider on the motor / rudder control arm. what you could do is replace those 2 rods which are no doubt 256 size to a more solid 440 size pushrod. i would be doing this.

Ok, can you buy stainless wire that size? Thanks for your help, I found out the servo is 3.5kg on 6 volt

yes you can get the 440 size rods in stainless steel . your servo is abit underpowered at 3.5 kg,s at 6v. you can buy good cheap servos of around the 7 kg size for approx $10 [ tower-pro ] brand metal gear and digital. if you upgrade both the rods and servo your hull will go well without any spin outs.

I took the Graupner F1 tunnel hull out again yesterday with the new rods and both connected, it was no different I spent most of the morning in the rescue boat retrieving it, it’s such a shame as it runs so nice in straight line and fast. This is what I have found, when the boat is flat out I can give it full steering both ways and it just gives a little wriggle and carries on in a straight line, as soon as I let off the throttle a little to turn it just hooks in and spins out, it’s like as soon as the front of the boat lowers a bit it digs in and hooks out and spins. I got a bad feeling it’s just the design of the hull, but if anyone knows what else I can try drop me a line, I can’t find anyone else who has had this boat to chat about it.
Thanks

sorry to hear it runs like crap, I can say the same thing about the Hobby King Hornet........ the same issues...JUST A CRAP DESIGN.

look at the first photo where the arrows are, that line the entire length of the sponson ....it is rounded off which causes this hull to slide sideways and not turn well.
still a crap design overall but this makes it worse so I ran a bead of epoxy the length of the sponson's then filed them flat 90 degrees and sharp edged....this mod will cut a better corner IF your sponson's are NOT sharp edged

I also made wedges that I epoxied into the hull bottom at the front of the sponson's so that when the sponson's dip to turn then spin out the wedges keep the tips upwards they dont touch the water when running untill they dip to turn and this mod reduces the spin outs considerably
try a test by hot gluing wedges temporarily in place to see if it helps

your results may vary!

good luck

I would still consider using a stronger servo for steering as you say all is fine at full speed straight ahead as there is no load on the servo but as soon as you back off slightly and turn , it then spins out. also is the hull getting air under the front ? or does the hull look like its running wet [ nose in ] ?? trimming this hull such as a good c.o.g. with battery placement plus setting the motor height and motor angle will surely get this tunnel hull performing . a model that runs abit nose down will spin out in turns, so make sure you get plenty of air under the nose without the hull porposing up / down .

No hull is well out of the water when flat out, but soon as you slow down only a little it drops and digs in, I have ordered a 5g servo today, I will get this sorted it’s such nice boat I will not give up on it, it’s not a hobby king boat so don’t want to start gluing bits on it. I have strengthened up the transom today and fitted it with captured-nuts so can adjust it a little easier. Thanks for the replies

yes the brand of your hull was and maybe still is made in Germany which is good quality for sure and it really does look like a very neat looking and well presented scaled race hull. a pic of the rear of hull would be nice to we could check out the position of prop / leg to hull bottom etc etc.

Turning the steering input down on Tx may help with the spinning out , I dont have that exact hull but all tunnels have this problem

I have the rates turned down so much on the steering that it hardly moves the outboard, but it still hooks and spins out, I will get it back together today and take tome pics of setup.
Thanks.