Exhaust/ silencer

[WotEver]

45 minutes ago, Mike the Boilerman said:

I still haven't seen the video. Got a link?

Well, it's post number... oh, a link works better, doesn't it...?

 

[MtB]

Ah, my cutting edge XP laptop doesn't recognise .MOV files....

[WotEver]

20 minutes ago, Mike the Boilerman said:

Ah, my cutting edge XP laptop doesn't recognise .MOV files....

Install either QuickTime Player or (better) VLC player and then it will. Both free. 

[Neil2]

4 hours ago, Mike the Boilerman said:

 

I agree. The main problem with waterbugs is the petrol outboard. A compact inboard diesel running via a Z drive seems a great idea! 

A higher proportion of the work done by a blade is done at the tips, so small reductions in diameter will cut down the thrust especially at low speeds which is exactly what the OP needs. 

I still haven't seen the video. Got a link?

See if this works Mike http://canalworld.net/forums/applications/core/interface/file/attachment.php?id=9424 it's in the thread "my live aboard 20 years ago" 

I guess it's a three blade prop so I agree even a bit off the blade tips should make a difference.

You're right about the petrol o/b, nothing wrong per se but it was a PITA trying to get petrol and you had to be very careful with electricity usage.  Some of them do have a diesel inboard but there really isn't room, Crow's idea seems to be the perfect solution.   

* Sorry I missed a few posts.  I'm using XP at the mo (17 year old tower PC still going strong) it works with quicktime

Edited March 29, 2017 by Neil2

[MtB]

Last time I checked my add-ons, Quicktime had been automatically disabled and declared a security risk, with no upgrade available.

I'll try VLC as suggested by wotever.

[WotEver]

16 minutes ago, Mike the Boilerman said:

Last time I checked my add-ons, Quicktime had been automatically disabled and declared a security risk, with no upgrade available.

I'll try VLC as suggested by wotever.

The disabling of Apple's software is partly a spiteful action on MS's part, partly paranoia, and partly that XP is so old that Apple isn't patching QT Player any longer. 

VLC Media Player is better anyhow. Less bloated and plays anything. 

[Crow]

Did you manage to see it mike

[Dalslandia]

I sugest a half inch smaller diameter to start with, Crow now get 3000 rpm and some black smoke, if we consider a 3600 rpm beeing standard on this Engine size, we would Think 3600/3000=1,2 or 3000/3600= 0,83 would be a good adjustment for the Power the propeller load the Engine. (as aiming Point)

prop diameter change Power with 5th Power (all the other remaining the same)

0,833^1/5= ,964

13"x,964=12,53"

with 12.5" D the Power needed at 3000 RPM will be some 82% of what ever it is now.

going to 12" and 67% is needed, I Think it is to Little.

An extention of the exhaust pipe down into the water with a row of small holes as a piccola on the way down and squize the end oval might do good on the Music, on the video the noise limiter let the mecanical noise be heared, some lead rubber and foam insulation will do good.

Edited March 31, 2017 by Dalslandia

[MtB]

But the OP is not trying to optimally match the blade to the engine power, he is trying to make the boat go slow enough at tickover!!

The engine is VASTLY overpowered for a 24ft waterbug anyway.

Edited March 31, 2017 by Mike the Boilerman

[Dalslandia]

yes I know, he also got the idle rpm down a bit, that will help. a lower pitch would have been the best, thats like changing gear, a boat propeller shop might be able to take the pitch down.

[Kieron G]

Hi Nick, I would be concerned about the water in the exhaust freezing and splitting the pipe in severe conditions.

[Neil2]

Something's puzzling me here, the Enfield outdrive is typically seen on cabin cruisers such as the Nauticus 27 often with a Perkins on a BMC 1.5 ie more powerful than Crow's Mitsubishi.  A Nauticus would weigh less than a Waterbug, so why isn't this set up working?  I don't know anything about these outdrives is the gearbox part of the unit or is it on the engine, and can you specify different reduction ratios?  It looks to me as though the prop is receiving direct drive, is that just the way it has to be with this engine?

[Dalslandia]

It have a 1.65:1 gear ratio,

 

What I can Think is that the strange swim slow down the water into the prop, if if wasn't it might have been different. but it would have been a very big job internal to weld in some fairings.

Edited March 31, 2017 by Dalslandia

[Neil2]

48 minutes ago, Dalslandia said:

It have a 1.65:1 gear ratio,

 

What I can Think is that the strange swim slow down the water into the prop, if if wasn't it might have been different. but it would have been a very big job internal to weld in some fairings.

There's an extension on the stern of that boat so the prop on the Z drive is well away from the swim, possibly even below it as well, like on a planing boat.  But 1 to 1.65 means you need very low revs on the canal with the standard prop maybe that is the problem.  Take the old BMC it will tick over around 500rpm maybe that little Mitsubishi just won't tick over at low enough revs.  

[Dalslandia]

I Think he said he had 1000 rpm minimum when he tested her, but have screwed it down to 900, might still be a bit on the high side.

Edited March 31, 2017 by Dalslandia

[Crow]

Thanks lads I'm pleased your still on the case,I've got 900 rpm at tickover now   It's as low as I can get   Same as the book says

It same engine as vetus mariniise and call a m3 09.   ,reason tickover  was 1000  was the rack in the pump was to loose and  was hunting real bad  at 900 so that's all sorted now, all I can do is try it again then keep grinding prop  blades  till it comes ok,

at least I can wind leg up to do it,    

[Neil2]

The old single cylinder Sabb would have been perfect for this boat - really low tickover, I guess it's difficult to find a small light engine these days that will rev down to 3-500rpm.  

Keep us posted Crow - this is really interesting. 

[Crow]

I will but   There's limit on what I can send on video  it's not happy to let me send one 

[Dalslandia]

2 hours ago, Crow said:

Thanks lads I'm pleased your still on the case,I've got 900 rpm at tickover now   It's as low as I can get   Same as the book says

It same engine as vetus mariniise and call a m3 09.   ,reason tickover  was 1000  was the rack in the pump was to loose and  was hunting real bad  at 900 so that's all sorted now, all I can do is try it again then keep grinding prop  blades  till it comes ok,

at least I can wind leg up to do it,    

If you wind the leg up it will not go so fast :-)

[Crow]

Yes Jan ,I might just lower it enough to get 5 knots at  3000 revs  ,it'll be as bad on diesel as the outboard petrol I took off

if you get anymore good ideas keep them to yourself,   (  Joke).   All the best  for your new seasons cruising ,nick.

[Dalslandia]

If you can get the prop in a lathe and take of a 1/4" on each blade, with 3 blade that will reduce diameter with 3/4" (well yesterday it would)

[Sea Dog]

All well and good  buggering about with the prop to slow the boat down at lowest engine revs, but Crow's original issue was trying to silence his noisy engine, wasn't it? That's only gonna get worse if he needs more revs for the same cruising speed, so easing one problem will exacerbate the other.

I'm not sure the prop is the biggest issue here. Silk purses and sows' ears spring to mind. 

[MtB]

On 02/04/2017 at 18:51, Sea Dog said:

All well and good  buggering about with the prop to slow the boat down at lowest engine revs, but Crow's original issue was trying to silence his noisy engine, wasn't it? That's only gonna get worse if he needs more revs for the same cruising speed, so easing one problem will exacerbate the other.

I'm not sure the prop is the biggest issue here. Silk purses and sows' ears spring to mind. 

 

But Crow's problem is the boat is exceeding the speed limit on tickover so getting up to cruising speed is hardly gonna be a problem.

And 1/4" off each blade = 1/2" off the dia....

[Sea Dog]

9 hours ago, Mike the Boilerman said:

 

But Crow's problem is the boat is exceeding the speed limit on tickover so getting up to cruising speed is hardly gonna be a problem.

And 1/4" off each blade = 1/2" off the dia....

I don't disagree with that being an issue (or a fix to one) but it's not the original issue of this topic which, I was offering, will get worse as a result of the prop being smaller. He wanted to route his exhaust outlet underwater to get better silencing of his noisy engine. Listening to his video I can understand why too!

[WotEver]

9 hours ago, Mike the Boilerman said:

And 1/4" off each blade = 1/2" off the dia....

Surely only if it's a 4 blade prop? If a three blade then it's only 3/8" off, no?