Broad Ambition - The Model

[Timbo]

4 hours ago, grendel said:

so here is the version that stopped half way.

Poor Griff is taking this keep fit stuff too far, shadow of the man he was! 

[ExSurveyor]

5 hours ago, grendel said:

so here is the version that stopped half way.

Griff legless again and quite armless

[BroadAmbition]

Griff legless again

You have no idea of just how ironic that statement is after yesterday.  Rarely nowadays do I get 'Legless' - sort of just grew out of it an age ago.  Yesterday was different and somewhat amusing (For some bystanders)  I just might put a post on the 'My Day' thread, then again I might not!

Griff

[Guest]

9 minutes ago, BroadAmbition said:

Griff legless again

You have no idea of just how ironic that statement is after yesterday.  Rarely nowadays do I get 'Legless' - sort of just grew out of it an age ago.  Yesterday was different and somewhat amusing (For some bystanders)  I just might put a post on the 'My Day' thread, then again I might not!

Griff

Ah come on be brave 

[Springsong]

Looks more like me than Griff 

[BroadAmbition]

Looks more like me than Griff

 

For those of you that have not met Barry (Springsong) you may not have much idea of just how funny that last post of his is, or ironic, but what it shows time and again with our Barry is how he always seems to be an optimist and a glass half full sort of a guy.

I have a lot of time / respect for Springsong, love the guy to bits and feel somewhat honoured to be able to count him as a friend.  He (Like some others in here) has a very in depth knowledge of Broadland history and I doubt there are many who can match his Helmanship skills.

Of course I would never post the above publicly in case he sees it and starts getting ideas above his station

Word of advice, go easy if you are fortunate to have a social drink with him, no end of times he ends up legless

Griff

[Springsong]

You have succeeded in embarrassing me yet again Griff my dear boy, but at least

this time not in public. The problem now is that I am going to have to do a perfect

stern on mooring in front of all my peers at Beccles so thanks for that. In everything

else you are as ever perfectly correct , how DO you do it.  

[grendel]

well I managed to get some macro rings for my camera, this will enable me to get close up shots of parts.

[Timbo]

2 hours ago, grendel said:

, this will enable me to get close up shots of parts

You can get arrested for that! 

[JanetAnne]

On 15/08/2017 at 09:49, springsong said:

...The problem now is that I am going to have to do a perfect

stern on mooring in front of all my peers at Beccles so thanks for that...

And there's me with a nice new shiny Go Pro to test....

 

[grendel]

one last tiny detail that caught my attention, the pin for the mast, as it was just a pin bent at the end, I was worried about taking it out and losing it, so a new pin has been made up, with the end bent round to form an eye, then attached to the mast support with some of the blue 'rope' that I have, the model will be travelling in bridge traversing mode, ie screens and mast down, the old pin has been stored in the bilges just in case as a spare.

[grendel]

Wow I hear you cry, no updates for nearly 5 days, well yes, I took both models up to the Beccles wooden broads cruisers show, then spent 2 glorious days talking about them, Friday was travelling and a trip to the maddermarket theatre in Norwich to see the production of Swallows and Amazons, then Saturday and Sunday at Beccles, yesterday was unpacking the car and recovering, Today I have to do all the weekends normal jobs and it will be back to work tomorrow, a great 4 days off work.

[deebee29]

Looks great seeing them both together 

[grendel]

one of the things the sea trials showed was a lack of go, while the boat has a fair scale speed, we really need it to be able to parade with Broad Ambition, so 4 knots would be a useful speed. the other thing we noticed was that the boot topping needed to be raised, only by about 1/4", unknown to me was the fact that when Broad Ambition went in the water for the first time after her restoration, exactly the same occurred, and the boot topping line was raised.

To get round the speed issue I am planning to remove the gearbox from the motor, since it is reducing the speed of rotation by 2.5 :1 this should increase the speed 2.5 times. though I did notice on the trial at one point we gos some weed around the prop which slowed her to about half normal speed.

[LondonRascal]

I know not if this could be achieved, but I noticed that her turning circle is pretty wide.  I had a similar issue on a full size boat that was meant to have twin engines but had a single engine mounted transversely then a hydralic drive to the prop - Brinks Royale.

This present a problem - where do you put a skeg and rudder? They chose to get round this by not having a usual skeg and rudder affair but to mount the rudder some distance back from the prop on a top mounted tiller (there is a name for rudders like this which have no bottom mount but I forget it now)

Anyway the result was pretty vague steering as by the time the thrust from he prop passed over the rudder it will already have lost some power and some more complex matters will be at play.  This seems the case with 'Baby B.A' where the rudder is of reasonable length but some distance from the prop. Could it perhaps be extended toward the prop or the prop shaft bring the prop close to the rudder for more 'bite'.

 

[grendel]

I will try it without the gearbox first, the extra thrust from the prop should make the turning better, I have literally just taken the motor out to do the changes, I have to work out a mounting plate to raise the motor and move it backwards towards the prop shaft , the gearbox output is above the centreline of the motor, which is why it will need raising.

[grendel]

although the prop shaft is in model #2, I still have some leeway with positioning the rudder, and I may be able to adjust the skeg to allow the prop to be moved further back. failing that I do have a couple of high speed 5 blade props I could try, these came with a destroyer model I picked up at a boot fair.

[grendel]

I have just checked, I have some similar sized motors, these rotate a lot faster, the no load current of the existing motor is 0.2A, the other motors are pulling nearly 3x that, and are probably rated at 20000+ rpm - the current motors are 11000rpm- which currently drives the prop at about 4600rpm. first to try the current motor without gearbox though.

[Jonathan]

Grendel,

I realise that you want more speed too, but with regard to turning circle:  I don't recall a picture of your model prop' and rudder, but would it not be possible to extend the rudder a small amount ahead of the pivot?  That way you gain rudder area and get nearer to the propeller too.  I know nothing about model boats so apologise if it's a stupid suggestion!  I recall that the handling of the full sized version was improved by adding a bigger rudder, but presumably that addition was all behind the pivot.

[grendel]

So this is the rudder and prop, we do have a small amount of extension in front of the pivot, the prop is a bit far away, but if I bring it much closer it will clip the skeg. it has more movement available, but the travel is already quite large, I think we just need a few more revs at the prop.

[grendel]

well that isnt as easy as I thought, the drive gear on the motor for the gearbox is heat shrunk onto the shaft, so I dont think i can get them off short of cutting the gear off, then I cant go back, so plan B is to use the lowest revving other motor I have, this should easily over power the model, but will cut back the sailing time, I dont have a problem with that, as it has a duration over 7 hours at the moment, it will only be once I can test it in the model that I will get an idea of the actual consumption, and thus the duration of run, the speed controller I have is rated to 10A, and I do have a 25A one in case I blow that up. just waiting for a motor mount to print out.

[Jonathan]

Thank you for the picture.  That makes the problems you describe much clearer!  I can now see the difficulty you would have extending the prop' shaft, it would mean either using a smaller propeller or moving the bearing up a bit, and changing the angle of the drive shaft and motor, which would be a major modification at this stage!  I hope your faster motor solves the problems for you.

[lakesailor]

Been quietly following this project on here for last year. Superb skill and patience Grendel . Well done

[grendel]

ok plan B has failed and I have located a problem, I now know the source of some of the noise, the vibration when using the much faster motor is tremendous, one of the couplings on the universal joint was off line, at the revs of the faster motors it was trying to shake the boat to bits. I have now replaced that coupling, but at these revs the motors are getting hot, the universal joint is getting hot, I have no idea what the revs are, but if the standard motor is at 11,000 these are easily 20-25000 revs- way too much. so I have sacrificed a gear and ground it off, testing with this motor is a lot better, quieter. I think those motors must have been plane ones at those revs.

 

[grendel]

well the application of a bit of research and google has come up trumps, the universal coupling I thought I had - isnt, its half of a universal coupling, these are commonly known to run off true and create a racket, and also are not rated for more than a few thousand rpm (no wonder that at 20,000+ rpm they were trying to shake themselves apart) there is a solution, add a second part to make it a true universal joint, or, just replace it with a length of silicon tubing.

I do have an old radio control car (picked up at a boot fair for parts)- this might have a coupling closer to a CV joint that I can use, I will have a look tonight, either way I am closer to a solution (and stopping that noise and vibration)