Why are bow thrusters THAT noisy?

vas

vas

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OK,

I'm tired after 5-6hours work on MiToS, not in the mood for working, uni server is down and I cannot upload and show you my great progress, so got I new Q :D

Was working this morning when I wooden hull, largish keel, single shaft aft cabin f/b 40-45ft craft came to be lifted, the old fashioned way. As he was negotiating and aligning the craft, he hit the b/t a few times.
Noise was awful and v.strong :eek:

OK, I admit I don't spend my time in the marinas listening to b/t, but this sounded godawful, and wrong pitch, and LOUD!

So, WHY? it's just a small motor and an even smaller propeler wrongway within a tunel hopefully pushing some water through.

Is it turbulance and cavitation, or what?

Not trying to start a for/against b/t discussion here, just genuinly asking

V.
 
NO NO NO

No No No they are that noisy so that everyone looks to see who is using it, it stems back from when they were a rarity and only the rich could afford them, so they had to make them noticeable so folks would know how rich they were to afford it. Hence why they are so loud!!!.:D:D:D:D:D:D:D:D:D:D:D:D:D
 
powerskipper said:
No No No they are that noisy so that everyone looks to see who is using it, it stems back from when they were a rarity and only the rich could afford them, so they had to make them noticeable so folks would know how rich they were to afford it. Hence why they are so loud!!!.:D:D:D:D:D:D:D:D:D:D:D:D:D
Click to expand...

Those on the QM2 just hum.....But then she is a royal lady :D:D
 
sorry

virtuvas said:
OK,

I'm tired after 5-6hours work on MiToS, not in the mood for working, uni server is down and I cannot upload and show you my great progress, so got I new Q :D

Was working this morning when I wooden hull, largish keel, single shaft aft cabin f/b 40-45ft craft came to be lifted, the old fashioned way. As he was negotiating and aligning the craft, he hit the b/t a few times.
Noise was awful and v.strong :eek:

OK, I admit I don't spend my time in the marinas listening to b/t, but this sounded godawful, and wrong pitch, and LOUD!

So, WHY? it's just a small motor and an even smaller propeler wrongway within a tunel hopefully pushing some water through.

Is it turbulance and cavitation, or what?

Not trying to start a for/against b/t discussion here, just genuinly asking

V.
Click to expand...

Hi Jacked your thread. it sounds like it on way out.
 
powerskipper said:
Hi Jacked your thread. it sounds like it on way out.
Click to expand...

oh, not to worry, threads are meant to be drifting about... Wasn't really looking for THE elaborate answer that is going to change my life :p (or persuade me to get one myself!)

otoh, where's a photo of QM* thrusters then? I guess I could stand easily on the tunnel (no I'm not a midget, but not v.tall either..)

V.
 
Last edited:
virtuvas said:
oh, not to worry, threads are meant to be drifting about... Wasn't really looking for THE elaborate answer that is going to change my life :p (or persuade me to get one myself!)

otoh, where's a photo of QM* thrusters then? I guess I could stand easily on the tunnel (no I'm not a midget, but not v.tall either..)

V.
Click to expand...

I could find some pic of thrusters but not of her thruster>. .............................................and only the boat variety!!!
 
"Not trying to start a for/against b/t discussion here, just genuinly asking"



Ahh....AKA... The Song-of-The-Thames.......the cacophony when every single boat leaves the marina.... approaches the lock........moves in the lock .......exits the lock.......moors up at the pub.......turns round and heads back down towards the lock......you know the rest :)
 
virtuvas said:
where's a photo of QM* thrusters then? I guess I could stand easily on the tunnel (no I'm not a midget, but not v.tall either..)
Click to expand...
Not specific of QM (not afaik, anyway), but this gives the idea...
1000hpBowThrusterSteelREduced.jpg
 
virtuvas said:
OK,

I'm tired after 5-6hours work on MiToS, not in the mood for working, uni server is down and I cannot upload and show you my great progress, so got I new Q :D

Was working this morning when I wooden hull, largish keel, single shaft aft cabin f/b 40-45ft craft came to be lifted, the old fashioned way. As he was negotiating and aligning the craft, he hit the b/t a few times.
Noise was awful and v.strong :eek:

OK, I admit I don't spend my time in the marinas listening to b/t, but this sounded godawful, and wrong pitch, and LOUD!

So, WHY? it's just a small motor and an even smaller propeler wrongway within a tunel hopefully pushing some water through.

Is it turbulance and cavitation, or what?

Not trying to start a for/against b/t discussion here, just genuinly asking

V.
Click to expand...

Probably because the bowthruster is resonating the tunnel and in turn the structure of the boat. Bit like when you screw an almost silent water pump to a bulkhead and the noise multiplies ten fold as the whole boat vibrates
 
virtuvas said:
OK,

I'm tired after 5-6hours work on MiToS, not in the mood for working, uni server is down and I cannot upload and show you my great progress, so got I new Q :D

Was working this morning when I wooden hull, largish keel, single shaft aft cabin f/b 40-45ft craft came to be lifted, the old fashioned way. As he was negotiating and aligning the craft, he hit the b/t a few times.
Noise was awful and v.strong :eek:

OK, I admit I don't spend my time in the marinas listening to b/t, but this sounded godawful, and wrong pitch, and LOUD!

So, WHY? it's just a small motor and an even smaller propeler wrongway within a tunel hopefully pushing some water through.

Is it turbulance and cavitation, or what?

Not trying to start a for/against b/t discussion here, just genuinly asking

V.
Click to expand...

Its cavitation.
In order to get the turning moment, the thruster needs to be as far foward as possible.
Thus one is juggling
depth - deeper = less cavitation
Tunnel length - the bottom of the tunnel gets short if you move it down, thus increasing cavitation as disturbed water goes out, under the boat and back in.
To increase tunnel length and depth you have to move it aft, reducing turning moment.
 
penfold said:
QM2's thrusters; the dockyard mateys on the dock bottom give the scale.

a07xYnMF.jpg
Click to expand...

nice pic, BUT, on first glance, it looks like the hull is made of lego bricks !!!!! or has someone painted the welds with a white 1" stripe for effect !!........ i like the anchor chain "indicaters"!!!.....i bet they dont stay white for long !!
 
Isn't it something to do with the gears - crown wheel and pinion?

plenty of slack as not made to automotive standards....

Hobbs of Henley have a big (for the Thames) booze boat and it's thrusters are silent, I suspect that they are hydraulic?
 
They are that noisey so that the owner can tell, when the bow rope falls over the side and gets sucked in and the thruster goes bang, that they are working or not, as happened last May on the fuel barge past the chain ferry to some poor sod on the Medina.

he didn't look too pleased.
 
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