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Author Topic: Krick Lisa M  (Read 16382 times)

Graham Smith

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Re: Krick Lisa M
« Reply #50 on: November 05, 2014, 09:14:06 AM »

There. Motor & shaft in line. Steering servo mount made. Nearly ready to fix in place.
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Tug-Kenny

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Re: Krick Lisa M
« Reply #51 on: November 05, 2014, 10:03:57 AM »


That's excellent.  Smooth running, here we come.   :}


ken
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Graham Smith

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Re: Krick Lisa M
« Reply #52 on: November 06, 2014, 12:27:16 PM »

Internal wooden parts given a coat of yacht varnish to protect them from damp.
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Graham Smith

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Re: Krick Lisa M
« Reply #53 on: November 06, 2014, 12:35:38 PM »

Incidentally, I've just got a tube of E6000 glue and I've tested it, glueing a piece of wood to ABS - it seems to stick pretty much anything to anything, but I don't know if I can trust it for sticking the wooden bits (above) into the hull? I was going to use epoxy (with a roughening of the ABS) but what do you think of E6000?
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Graham Smith

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Re: Krick Lisa M
« Reply #54 on: November 06, 2014, 02:35:32 PM »

While waiting for stuff to dry, I turned to the construction of the upperworks.
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Graham Smith

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Re: Krick Lisa M
« Reply #55 on: November 06, 2014, 02:37:18 PM »

Just trying it out on the deck to see how well it fits. It'll probably need a bit of sanding around the bottom edge, but it's pretty close. Of course, the deck isn't glued down yet, so we'll have to see.....  ;)
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Graham Smith

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Re: Krick Lisa M
« Reply #56 on: November 08, 2014, 08:05:58 AM »

All the running gear has gone back in, and everything works OK - BUT - it's very noisy! And I put that down to the UJ coupling. Although it's in line, there's still vibration because the coupling itself isn't "spot on" and allows a tiny bit of lateral movement of the prop shaft. I've damped this down with a couple of foam-lined brackets and that helped, but it's still more noisy than I'm prepared to accept. So - I've sent for a rubber flexible coupling and we'll see if that makes the whole thing quieter.
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derekwarner

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Re: Krick Lisa M
« Reply #57 on: November 08, 2014, 10:21:22 AM »

Graham....the hull itself [smooth shaped without any directional baffle's] is acting as an amplifier for the motor <*<  resonance

You could consider gluing [low weight] self adhesive cork sheeting to all possible surfaces

This will dampen and quieten standing harmonic resonances within the hull.....:-)) .......... Derek
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vnkiwi

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Re: Krick Lisa M
« Reply #58 on: November 08, 2014, 10:30:16 AM »

or very very soft balsa, with a rubber contact adhesive, as long as the solvent don't attack the plastic
Not as good as cork, but lighter
 :-))
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Davenotdone

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Re: Krick Lisa M
« Reply #59 on: November 08, 2014, 11:15:46 AM »

I had a similar problem with a noisy coupling the same as yours. Got a rubber type from Marks Model Bits and what a difference!!!  Still need good alignment of the drive train ( but you should anyway for all types of coupling  ).   Now it is smooth as silk and you can hardly hear it!!!  I will not use the red ( Huco ? ) type of coupling any more, literally too many moving parts and damn noisy!!!    Regards, Dave.
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Graham Smith

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Re: Krick Lisa M
« Reply #60 on: November 08, 2014, 12:21:38 PM »

Yep. I know I could cut down the noise by those methods, but the point is that noise=vibration, which means loss of power, shaken joins (specifically the prop shaft's exit) and so on. Actually it's not all that bad - not enough to cause that much damage, but I want to cut it out as much as possible.
Anyway, I've just found another problem - The steering servo horn is just a few mm too high and will foul the after well deck. No biggie, though. I'll re-site it to the forward part of the hull with a snake running along the side of the hull.
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Graham Smith

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Re: Krick Lisa M
« Reply #61 on: November 08, 2014, 12:27:31 PM »

Graham....the hull itself [smooth shaped without any directional baffle's] is acting as an amplifier for the motor <*<  resonance.


With the motor disconnected from the shaft, there isn't much noise. So it's not the motor itself that's vibrating. Also I intend to use a bit of foam between the motor and its mount to lessen noise from there.
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Tim_M

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Re: Krick Lisa M
« Reply #62 on: November 08, 2014, 02:20:20 PM »

Hi Graham,
If I might chip in (as an engineer, not and experienced boat builder). Why use a flexible coupling at all?

The vibration comes from several sources: the 'kick' of the motor, any out of balance mass in the rotating parts and - if you fit a Hooke's joint - any minute misalignment in the coupling. The first two you can't do much about (although I doubt there is any significant imbalance in the shaft at your rpm).

Your prop shaft is (presumably) supported at the prop end by a bearing. The other end is not supported so it's free to wobble about. If you couple it rigidly to the motor shaft (in a straight line) then the whole shaft is supported at both ends and it won't vibrate. I use a simple rigid collet style coupling and I don't get vibration even though I'm running close to 20 000 rpm (until I crash {-))

What I did was to support the prop shaft at the prop end, fix it to the motor and then fasten the motor down. That way the shaft and motor are in a straight line automatically. Finally I glued the prop tube in place nicely centred on the shaft. It's too late for you to do that but you could fix the shaft to the motor and then bed the mount down on epoxy to centre the shaft in the tube. The alignment of the tube is not critical - it's just the shaft and motor need to be in a dead straight line - hence the rigid coupling.

You know that the style of coupling you have currently isn't going to work for geometric reasons. You don't need a flex coupling at all and if you fit one (any type) you are actually inviting the shaft to flail around and vibrate. A lot of people don't realise that the way to kill vibration is to make everything as stiff and rigid as possible. (If it can't move, it can't vibrate  %%)

I'm not sure how much success you will have with putting foam under the motor mount. Soft mounting will actually amplify the vibration below a certain speed. Just what that speed is depends on how stiff the mounting is. I'd bolt it down solid (but see my PM). I do agree that a lot of the noise you are hearing is the hull responding to the vibration. It'll probably be a lot better when the deck is glued on.

So that's my five eggs. Make the motor and the shaft one nice rigid unit and fit everything else around it. The prop tube can sit wherever it likes!   :}

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Tim_M

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Re: Krick Lisa M
« Reply #63 on: November 08, 2014, 02:34:21 PM »

Just looked closer at the photos. Looks like there is a bearing at the motor end of the tube as well. In that case, rigid coupling and bed the motor in wherever it ends up. Simples!
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Graham Smith

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Re: Krick Lisa M
« Reply #64 on: November 08, 2014, 04:32:32 PM »

OK - now, then.... I've just been testing it all again, and I've found that the noise is definitely coming from the coupling. At max revs the shaft isn't vibrating at all, so the seal at the stern end isn't going to suffer. I could live with the noise, since once the deck etc is on and it's in the water it won't be as noticeable. Anyway, the rubber coupling I've sent for is virtually a rigid one. It wasn't expensive anyway so worth a try. If it makes it quieter, all well and good, but if not, I'll put up with the noise. I've checked that nothing is vibrating badly enough to really worry about. Motor and everything remain solid and putting a finger on the solid parts while running doesn't detect noticeable vibration, so I can live with that. I'll let you all know what the rubber coupling does.
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Graham Smith

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Re: Krick Lisa M
« Reply #65 on: November 08, 2014, 07:14:19 PM »

Just been checking out Marks Model Bits. I see he has a nice Zodiac type dinghy that would be excellent for my Lisa M - and at a fiver it's a lot cheaper than the Krick one!
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Graham Smith

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Re: Krick Lisa M
« Reply #66 on: November 08, 2014, 07:16:31 PM »

This is the Krick one - 13
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Tim_M

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Re: Krick Lisa M
« Reply #67 on: November 09, 2014, 08:01:22 AM »

I trust you are going to motorise it....   {-)
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Graham Smith

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Re: Krick Lisa M
« Reply #68 on: November 09, 2014, 04:40:34 PM »

Strewth! Just struggling with the front cabin window frames! To say that they are a lousy fit is to be overly generous! I won't show you what they look like yet - suffice it to say that once the glue is really set hard, I've a fair bit of filling and sanding to do. I ended up scrapping the original front window piece and making a new frame out of four separate pieces of wood.  >>:-(
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Graham Smith

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Re: Krick Lisa M
« Reply #69 on: November 10, 2014, 07:15:29 PM »

That's the front windows of the cabin done now.  I've also re-sited the steering servo and I'll get the snake installed tomorrow.
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Graham Smith

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Re: Krick Lisa M
« Reply #70 on: November 10, 2014, 07:24:37 PM »

I'm wondering if it might be a good idea to paint the cabin as it is now, before the roof is put on, since the overhang at the front might make it difficult to do the rub-down after the primer coat....
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Tug-Kenny

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Re: Krick Lisa M
« Reply #71 on: November 10, 2014, 08:47:40 PM »


It can't do any harm.  Don't get paint on the top edge, else the glue will not stick.

Cheers

ken

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Graham Smith

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Re: Krick Lisa M
« Reply #72 on: November 11, 2014, 06:49:49 PM »

THat's the steering servo re-sited and the snake connecting it to the rudder.
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Graham Smith

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Re: Krick Lisa M
« Reply #73 on: November 12, 2014, 03:19:18 PM »

The deck has been glued down, and the superstructure (so far) has been given a coat of primer. It turns out it's a pretty good fit on the deck without being sanded round the bottom edge. Yay! %%
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Graham Smith

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Re: Krick Lisa M
« Reply #74 on: November 12, 2014, 03:22:13 PM »

That's a good price with free shipping, sadly they are now sold out 😞

They're back in stock now! :}
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