grendel

it goes back to the dead

I am having enough problems with this motor at 11,000 rpm, it was fine at about 4500, but at 11,000 a bearing block had to be added at the free end of the prop shaft, greasing the prop shaft helped, but caused too much drag - slowing the motor down yet again.

or behind her.

well they correctly identified it as a broads cruiser, then said they had never seen a model of one before. this evenings bracket was made, motor testing done - after 20 minutes the motor was still hovering around 0.7A and was barely warm - result, next to see how it performs on the water.

with the gearbox on at a 2.5:1 reduction at Beccles we were getting pretty much the same speed as I did at testing on Sunday, this would have equated to about 4500 rpm at the prop, which is why - if the prop under load was only managing 5000 rpm the speed didnt look any different. we will see how she goes next weekend.

getting all technical, I was wondering the difference in rpm between a current draw in the region of 2A plus and 0.6A (remembering the resistance of the water will push the current up a bit) so could I find a chart anywhere - no. the data sheet gives 3 pieces of data - the no load revs and current, the peak load revs and current, and the stall current (0 revs). so from this I drew a graph, now all 3 points are on a straight line - good, that makes it easier. so the new current draw is 0.6A, this equates to over 10,000rpm the current draw with the greased prop shaft was generally between 1.8 and 2.2A (best ever was 1.5A) this equates to between 7000 rpm and about 8000prm. if we say that the current draw in the water is +50% now we are looking at .9A 10000prm we were looking at 2.7 - 3.3A - 5000 - 6000 rpm - and one very hot motor. about 1A is peak efficiency for that motor, so it looks as though it will be just about right now, and we will have nearly doubled the speed through the water, tonight we will be testing the motor at the new out of the water current draw to see if the motor gets hot- or not. oh and making the brackets to reinforce the bearing for the prop shaft and hopefully reduce the vibration there.

yes Tim, But to put 'in case of accidental immersion this way up' with an arrow pointing to his feet was a bit mean I think.

I would have thought he should have shouted " Charlie! "

there are still garages where you can buy leaded petrol - for a price. diesel at least can be home brewed from chip fat, bio diesel being slightly cleaner than the normal variety. I dont see petrol becoming a replacement for diesel on boats though due to the storage and heavy vapour problems associated with it, the marine authorities would just quote health and safety when it came to banning diesel. Price for price wave energy is very expensive - even when compared with offshore wind farms, and every time it is mentioned it stirs up the environmentalists and such as it might alter the sea bed environment. electric hook up at Marinas - well there wont be any fast charging - thats for certain, the electrical infrastructure is not there to provide enough power.

I will wave one in your general direction while you sniff hard if you want. Tim is right though - everyone mucks in and helps, I went up and donated a few days hard graft in the freezing cold, helping with the out of the water maintenance. in return I get the occasional trip on Broad Ambition (well I am also making the models )

surely heels like that would puncture the water bed. If any of you think getting shoes is easy, try getting them in size 14, choice - well they might have a pair. I do have a couple of posh pairs - oxfords and brogues - straight from India, very well made shoes too at a reasonable price, other than that its trainers. I did get some czech army baseball boots. last time I found a whole bundle of shoes in my size, I bought all the ones they had - 6 pairs, when a pair wears out I get a new pair from my stash. my nephew on the other hand takes size 16. when he was in the army he had special permission to wear trainers on parade as it took nearly 3 months to get his boots built - uppers from italy soles from america, built by the army outfitters in London.

hmm further investigations and easing one point, and its still not running as free as I wish - more powerful motor required. The only thing I can think is that the grease in the prop shaft is dragging the speed down, I will try cleaning it out and retest the motor current. OK, so I forgot to post this, but I have been out, blasted the prop shaft through with a light oil, and retested the motor, 0.6A, - so it was the grease causing the problem. I now have a slight problem with the back bearing, where its made up from two pieces, its chattering, if I hold it it quiets down, so I may make some brass bridging pieces and bolt them around that bearing to hold it rigid, if the sound is anything to go by the motor is running a lot faster, so more testing may happen next weekend, before I opt for bigger motors. I did try a bigger motor, but that started at 1.6A and rose to over 3A when on the model.

well that was enlightening, I took the model to Herne bay, to the pond used by one of the local boat clubs, and took some advice. The motor - even running flat out wasnt really pushing the model any faster (well maybe a little) but no spare power, when I bought her out of the water the motor was well hot, the binding somewhere in the drive train, and the resistance of the water on the prop was making the motor work hard. The motor guru at the club showed me one of his models with the same motor, andthough a much smaller model it was a lot faster. he recommended a bigger motor for the size of boat - a 555 motor - low revving - high torque. I tried different props - no real difference. bigger motor will be looked at next.

having been out to sea on the old girl, when filming Broad Ambition, an in company with two of HM finest, even with the engines she has - she has got a fair turn of speed, and if you ever get the opportunity to go to sea on her you should, its a magical experience.

without a change in technology I think diesel will be around for a while, all plant will still run on it, mostly due to safety issues (you dont want to be storing petrol on site) and electric wont keep site machinery running day in day out.

well I have eased the baseplate, removed 1 layer of the ply at the back end, and its still 1.5A, I think there is some drag of the grease in the prop shaft, but that is better than running it dry. it sounds 100% better than it was previously, I now know what to expect on model #2 so I can start progressing that. maybe if I get the chance tomorrow I will take a run to the local boating pool and test the new power levels, see if it is what is required.

a busy day so far, shopping done and out to the workshop, the new stiffer baseplate has been constructed, everything lines up, out of the boat its drawing 0.6A, but its still at 1.5A in the boat running at full speed the motor gets warm after about 20 minutes running, the prop shaft gets warm, I am thinking of removing the wood support and re packing it into position to see if I can get it running smoother. I am wondering if the wood support is too high at the back, lifting the end of the prop shaft and trying to bend it. the good news is that its running quietly.

They were supposed to be hexagonal.

The point that is trying to be made is that supposing you have a main systems electrical failure, your batteries are fine but all your wiring has melted, you still have engines, but you are in the middle of the ocean. How do you cope, if you are fine with a small hand held, self powered system as a backup then you dont need to know how to use the charts, but suppose you enter a strange harbour, or take a pilot on board who wants to see your charts (though the pilot should of course know the waters like the back of their hand). I think a set of paper charts and the training to use them (even if just printouts) would be a handy thing for an emergency backup. as even the battery on a handheld device will go flat eventually.

but for a bit of variety they could find a nest of pygmy shrews surely.

try the M25 sometime - sorry you said drive, not park

the plastic spacer will be replaced by some 1/4" thick Brass bar I have 6.4mm is about the perfect height for the new spacer (the old one was printed at 7.8mm, and came out at 7.7mm, once installed I can eyeball the two shafts and file the spacer to give me a perfect fit, from my pictures the shafts are currently off by not quite half the diameter of the prop shaft (4mm) so between 1.2-1.6mm the spacer reduction is 1.3mm so it will be in the ball park, ready for fine tuning. I also now have my workshop up and running so can drill the holes using the proper pillar drills etc which will increase the accuracy of those (rather than using a hand held drill). you work with what you have at hand, and the first attempt was really just a proof of concept anyway.

Looking at this now I am more awake and at work, I neglected to say, that the difference is about 1mm on the height of the bearing, this means I can raise the baseplate by that 1mm (or make it 1mm thicker) and still have the clearance i need. at the moment I am looking at two options, one is a thicker brass plate or secondly an even thicker aluminium plate, trust me I shall be measuring the clearances very carefully before I start building the new baseplate, - if the thicker aluminium plate will fit, it will be used. once I have model #1 sorted I will do the one for model #2, this will be easier as I have been holding off the construction work to keep the clearance to get in to the hull on model #2 for measuring etc (in case you were wondering why I had not cracked on with model #2) I wanted to get this little problem solved before progressing to a stage where I had to do any deconstruction to be able to fit the proper solution. I want to get the current draw down to about 1A when running, with no load its 0.5A, so I dont expect to get it that low when the prop is doing some work, but 2A plus seems a bit much to me

no it has to remain the same- after all you can take the rascal from London, but you cant take the London from the rascal.

that is a neat way to use the space, love the fold up bed.