Archive for October, 2008

Octura Coupling still not quite good enough

Thursday, October 23rd, 2008

So we took the boat back down the pond for another shot.  It went superb!  I would have to say that it was the fastest it has run yet.  With no real problems causing us to take it home it gave us the opportunity to give it a bit of a tune and get some more speed out of it.  The latest video shows it going significantly faster and now on 98 octane fuel and a different plug there is no missfire.  It was truly singing!

The water level was getting a bit low in the pond now uncovering 2 ‘islands’ in the middle.  It proved to be a little hard to negotiate between them so i stayed in the bigger area.  It looks like i’m just doing circles but infact the back run is quite straight.

The boat flipped a couple of times, the last one got caught on video but the first one was much more spectacular.  The boat held up well tho and once the water was out of the engine it started fine.

So, on to the coupler.  Well, i would say that it’s still the best solution so far but it’s still not quite up to the task.  After a full tank of juice (first time!) it was a bit melted. The problem is that most gas powered boats have water cooling the exhaust header so any product that i get is likely to only take 200 deg or so.  Mine does not have any cooling at the moment.  So, what i have decided to do is wrap some 1/4″ copper pipe around the header about 4 times.  I am going to run cooling water through it from the rudder and see what that does.  Hopefully this will help reduce the temp of the pipe and therefore preserve the coupling.

I have also got some stainless sheet to put on the back of the boat as trim tabs to help get it out the water a bit better.

I’m working on trying to get an onboard cam going too :)

Quick update

Thursday, October 16th, 2008

With the leg now complete, i moved back to the exhaust.  This has been a problematic area from day 1.  The problem is associated with the poor balance and vibration in the motor.  Basically, the exhaust is shaking itself to death…


Originally it was solid all the way through but the thinner stainless of the pipe fatigued and cracked from vibration.  So, in the last run i tried a silicone coupling i got from rcboatbitz but it only lasted the previous run before splitting and that’s what caused the boat to stall at the end.  It was not really good for the job as it is designed for much smaller pipe and it was stretched to go over the 1″ pipe of my setup.

I’ve now just fitted a product that is made by octura.  This one is still silicone but it’s reinforced with 4 layers of fibre as well.  This one was 7/8″ so it’s still a slight strech over the pipe but not as bad as the other one.  I have since found that octura do the same part in 1″ as well so if this one splits i’ll order one of them.

The bigest problem is the heat – it’s classed as a ‘high temp’ coupler but i have no idea on the actual rating of it.  I tried to find some specs via the oracle that we know as google but it turned up nothing so far. With any luck it will actually hold up…


Skeg/Leg redesign

Wednesday, October 15th, 2008

So after the last run I saw the need to redesign the bush/bearing setup in the leg.  the original design simply used 2 collars of teflon around the shaft.  After visiting a few sites and seeing how some other ‘DIY’ designs were done i settled on one developed by the guys over at Oxford County based on some K&S brass tubing.

The outside is 5/16″ and the inner is 9/32″.  The 1/4″  shaft perfectly slides inside the 9/32 and that slides perfectly inside the 5/16 tube.  The smaller of the 2 tubes is cross drilled to allow for lubrication between the shaft and larger tube.

The bearing holder is a little bigger as well as now going for a stainless ferrule.  No real advantage here but the only reason i went for brass on the original one is because the tradition is to solder the flex shaft in.  Instead, i ended up using Loctite shaft lock.  This is super strong stuff and never even hinted at breaking loose uner the torque of the ryobi.  So, to keep it looking nice this time, i used stainless.  Also, this time i have used a roll pin to atttach it to the shaft rather than grub screws (which were a little problematic last time).

Almost ready to rock…

Another run with the boat

Saturday, October 11th, 2008

I’ve been getting all my RC toys back in working order over the last couple of weeks.  One being my Traxxas T-Maxx monster truck and the other is the boat.  I sorta stripped the radio from the Maxx to put in the boat so i got another RX and a couple of servo’s to get the maxx running again.

The boat also needed a new radio box and some other minor repairs.  With a little work and some help from Tim, i got it back up and running.  I also found a new/better site to run the boat.  It’s the old (now abandoned) Lakeside Leisure park site.  There’s a nice little pond in the middle to run the boat on.  It has a couple of downsides like limited access to the bank and a shallow spot in the middle but the huge plus of it being FRESH water and not salty onkaparinga river water far outweighs them.  It’s not all festy and stagnant either like one might suspect.

I’m not 100% sure on the legalities of using the pond since it is infact private land but there are no signs up telling me to stay away and i did not even have to jump a fence or anything- just walk straight in.  Not only that, other locals seem to be using it extensively for riding motorbikes on. I don’t think i’m going to have too much to worry about.  That is, until the land gets sold off and subdivided as the land is for sale…

So, we got the boat in the water and even remebered the camera this time!  There’s a couple of problems with it after the run.  Mainly the fact that the rubber/silicone header -> pipe joiner split which caused it to stall (no back pressure).  I’m going to have to find something else to do the job. The engine also seems to either detonate or misfire every now and then – you can hear it in the video.  I think with 98 octane fuel and a bit more oil it should go away tho.  I’ve also made up a stand for it now.  Makes transport and use so much easier.

I’ve also now decided to make up a new skeg.  The current one is not ideal, it uses teflon as the bearing and wears too quickly.  I’m changing it to use brass and to have more bulk. More on that later.

In the mean time, enjoy the vid…