Project Atlantic ILB
A detailed construction of the final motor design is Here
Brushless motors and a rebuild.
I Have been rebuilding and updating the Atlatic with brushless motors. Here is a link to the rebuild page.
The Idea of building a 1/12 model of an Atlantic inshore lifeboat came while on one of the many visits to Falmouth with Robert and the Severn. It was at a lifeboat Day I think that we talked about having a model of the Atlantic to run along side the Severn.
As there was already a Kit for the Atlantic 21 available from Lesro is seemed pointless to go through the development of the boat although some alteration of the sponsons would be required. Also this kit being in plastic would make for a fairly light boat.
One of the first things that I decided on with this boat was that it had to have working outboard motors the fit comes with dummy outboards and a space for a motor shaft and prop that comes out underneath the boat and uses the dummy outboard as rudders. The other thing I may look at if there is a need and there is weight capacity to take it is to make the self-righting bag work.
Working Outboard Motors
After some investigation it soon became clear that there was not a commercially available product on the market to meet the needs of pushing the Atlantic along at the desired speed. The only thing I found was a toy outboard from http://www.hobby.uk.com although not powerful enough for what I need the cases or part of them may be useful for the finished outboards.
The only solution was to build the outboards. Not too difficult motor, vertical shaft, pair of bevel gears, horizontal shaft all in a case with a prop on the end. The first thing was to find some bevel gears a hunt round the model shop found some for a R/C car 12.5mm in diameter with a 3mm bore. Bearings where found from a local supplier 3mm id X 6mm od X 4mm long. Different ideas for mounting these where tried and the final result of a prototype working outboard can be seen below on the back of the boat.
As this is only a prototype to see if it will work the gearbox has no external shaping its just a square block with 2 holes bored in it at a right angle to each other. The motor is a Graupner speed 400 running at 7.2volts.
Below can be seen the boat with this one outboard on the water. The boat performed well and should achieve the desired performance with two outboards that have a finished case.
Having proved that it is possible to make an outboard that will perform I am now improving the design by looking at ways of reducing the size of the gearbox. The first thing to look at was the diameter of the bevel gears after some searching a supplier of gears just 8.7mm in diameter was found this would allow me to reduce the width of the block from 18mm to 12mm as can be seen in the photos below.
The first and second prototypes next to each other note the difference in the width.
The next stage will be to get the new gearbox mounted on the boat with a motor and tested.
I am also looking at changing the motor to a smaller one though this might not have the power I need.
Latest developments August 2005
Here is the latest built outboard ready to go on the boat. I have started to shape the block to reduce the weight and also help with the flow of water around it.
Before fitting it to the boat I tried it in the sink. It certainly mixed it up a bit.
I got the wife to take some pics while I held the outboard in the water and tried not to get everyone wet.
I don't think she was very impressed but I was!
Here are a couple of pictures from the sink test
After some time spent upgrading some of the machinery used to make the parts for the outboards we now have 2 running prototypes that can be seen here on the back of the boat.
Here the boat can be seen on the water with a reasonable performance.
The results of this testing have shown that the shafts need to be a little longer to put the props lower than the bottom of the boat.
I have now made two new shafts 15 mm longer than the old one's that can be seen here on the boat.
The new shafts do make a differnce and the performance of the boat is much smother.
Here is a short video of the boat on the water
having got the performance to a point that I was happy with I now moved onto finishing the boat and giving it a coat of paint. My plan was to have it finished for the Himley show.
Now there was one thing I was still not quite happy with and that was the shape of the gearbox so after a bit of re-thinking I came up with a new design by moving a gear from the front to the back of the gear box this meant that the vertical shaft would be nearer the front and allow the gear box the be shaped better. It also would allow me to use the blank block from the raw bar in a different way and be able to include the fin on the gearbox.
Another small alteration is the angle of the outboard which have now been set at 15 degrees to the transom of the boat which puts the 5 degrees of vertical when the boat is in the water.
Here are some pictures of the boat on the water. I have not got one of it getting airborne on the wake of the Severn but I’m working on that.
To try and improve the speed I have changed the props to a different design of prop. The ones I have at the moment are 2 blade but have a bigger pitch. This has improved the speed. I am going to try it with a 3 blade version of the same prop I am also going to change the battery to a smaller one that has a higher power to weight ratio that should make the boat about 200g lighter with only a small drop in the power available which should still give me a running time of 15 - 20 Mins.
I have also now added the helm. Here are a few pics of the boat on the water.
Some Pictures of the Atlantic taken at Falmouth.