This is my latest acquisition, an old Graupner mini prop air boat. I found it on eBay while doing a search for something else and just liked it as soon as I saw it. It is old and has been used, but mostly it was in good condition just needed overhaul and updating motor and electronics wise.
These first few picture show the boat as it was when I got it. The bulk of it was in good working order with only minor wear and tear in places. One of the main areas I thought needed attention was the rather minimal prop guard, which really offered little or no protection against the spinning prop. Apart from that the motor was a tad underpowered and the prop could do with a bit more pitch to get power up. Neither of these posed a problem ad I had the parts knocking around anyway.
My first job as it was the most straightforward one was to change the motor to something a bit more powerful. Luckily I had a few odd motors knocking around from my rc car, and after trying several different power and spec motors i found tuned 27 turn was a huge improvement all round over the standard item.
Next the prop needed to have a bit more power to it, so again after trying several different props I had; I opted to cut down a wooden 11 x 8 to fit, keeping the wide blade profile for maximum power.
To fit this on I had to turn a new prop mounting post on my lathe and also a nose cone as the old prop didnít have one. Once I had it fitted and working, I could then balance the prop to remove any vibrations.
Next I set about making a new prop guard to replace the somewhat sparse item it came with. For this I used thin brass wire and bent and cut it all to shape then soldered it all together. Its perhaps a bit over the top now as I did get carried away while making it, but I like it, and not only does it look better than the original one, it also works much better to.
With the power side of it taken care of I set about sorting the electrics. With newer electronic speed controllers not only do they just plug into the receiver, but they do away with having to carry an extra servo to work the mechanical speed controller.
I opted for an mtroniks marine as they are nice and compact and seem to work well or so I have found so far.
As I had a older radio set from years ago I installed receiver from that and just plugged the servo that came with it in. I did move the steering servo as it was only mounted using Velcro which left it free to wiggle around somewhat, but on changing this I found the rudder was not attached to the steering shaft to well, so had to make a replacement one. I went for slightly bigger brass rudder as I could solder it to the steering post, and then mounted the servo standing up instead of lying down as it had come.
When done all the bits that work it are sealing in the rear compartment leaving the front to just house the battery which is held in place with velcro to stop it moving around.
Here are just a few pictures of it from all angles. With the exception of the new prop and prop guard it looks much the same as it did when I got it. The more minor bits I changed or altered arenít really notable to the casual onlooker. While itís never going to be ultra fast, itís a really nice boat just to sail around on the local boating pond with, and being slightly different to the normal boats there it attracts quite a bit of attention from onlookers.
Last of all a couple of pictures of it in action. Its fair to say itís a nippy little boat, and good fun to play with. Its also one of those boats that will always be tinkered with trying to get more speed out of it.