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Old 14-08-2012, 08:54   #61
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Re: Hmmmm - Bowthrusters ??

What in the heck is a BW?

The new Vetus RD125 and RD160 are nice but they do have a connection between the motor and the props. The props are mounted on the motor shaft and the stator forms the walls of the motor. Because of this they are water cooled so have unlimited usage time but the boat will probably need to be hauled to do any work on them, other than change props.
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Old 14-08-2012, 09:54   #62
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Re: Hmmmm - Bowthrusters ??

Speaking of thrusters behind doors on big ships, here's one of my favorite vids of my favorite ship, Queen Mary 2, spinning 180*on her thrusters. As I recall one of the big thruster doors fell off during initial sea trials, oops.

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Old 14-08-2012, 11:59   #63
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Re: Hmmmm - Bowthrusters ??

Quote:
Originally Posted by Auspicious View Post
Can you point to thrusters with doors for recreational boats? I haven't seen them on anything but ships.
I believe some maxi have them. There may be no small craft equivalent. (Hence, it is time to design and sell some! ;-)

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Old 15-08-2012, 03:28   #64
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Re: Hmmmm - Bowthrusters ??

Quote:
Originally Posted by Auspicious View Post
Can you point to thrusters with doors for recreational boats? I haven't seen them on anything but ships.
Even bow thruster doors in the commercial are not that common....
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Old 15-08-2012, 03:40   #65
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Re: Hmmmm - Bowthrusters ??

Quote:
Originally Posted by kthoennes View Post
Speaking of thrusters behind doors on big ships, here's one of my favorite vids of my favorite ship, Queen Mary 2, spinning 180*on her thrusters. As I recall one of the big thruster doors fell off during initial sea trials, oops.

I like this one to......



They have had quite a few problems with the BT door systems, going all the way back to her sea trials.....
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Old 15-08-2012, 03:56   #66
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Re: Hmmmm - Bowthrusters ??

BT doors - just something else to fail on a blue water cruiser. Somewhere back there on this thread, someone mentioned that you lose 1/2 or whole knot of speed due to the tunnel. CAn anyone (scientifically) confirm this? 1 whole knot seems alike a lot. If that is true, I can't see racing boats having BTs (and lots of them do)
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Old 15-08-2012, 07:31   #67
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If properly faired at the time if installationthere will be no appreciable difference in boat speed

The difference in manoeuvrability and safety in docking a 59 ft sailing boat without ( and now with) a BT is tremendous

My boat is 26 tonnes

I deliberately didn't get one put in by the factory cos I wanted to sail it properly . After a year I rethought it and installed one in Phuket recently

Lots of moorings in Asia are tricky with wind and tide , even in Marinas.

I wouldn't be without it now

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Old 15-08-2012, 09:50   #68
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Re: Hmmmm - Bowthrusters ??

Any folks with BT's experienced stuff getting caught in them? Seabirds, fenders, seaweed, driftwood, floating garbage, swimmers, dinghy painters, running rigging, docklines, etc?
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Old 15-08-2012, 14:32   #69
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Re: Hmmmm - Bowthrusters ??

Quote:
Originally Posted by carstenb View Post
BT doors - just something else to fail on a blue water cruiser. Somewhere back there on this thread, someone mentioned that you lose 1/2 or whole knot of speed due to the tunnel. CAn anyone (scientifically) confirm this? 1 whole knot seems alike a lot. If that is true, I can't see racing boats having BTs (and lots of them do)
Racing boats use extendable thruster tubes for this reason, I have installed many. They are extremely expensive. People don't install them for no reason. I said I had recorded about a half knot difference, not a knot.
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Old 15-08-2012, 14:37   #70
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Re: Hmmmm - Bowthrusters ??

Quote:
Originally Posted by Carlisle Spirit View Post
If properly faired at the time if installationthere will be no appreciable difference in boat speed

The difference in manoeuvrability and safety in docking a 59 ft sailing boat without ( and now with) a BT is tremendous

My boat is 26 tonnes

I deliberately didn't get one put in by the factory cos I wanted to sail it properly . After a year I rethought it and installed one in Phuket recently

Lots of moorings in Asia are tricky with wind and tide , even in Marinas.

I wouldn't be without it now

Carlisle Spirit
I invented fairing a brow on a thruster tube for sailboat installs in my area as far as I know. While it does help, it certainly does not solve the problem. Anyone who can convince themselves that a 9" or 11" hole in both sides of their cutwater has no effect on the hydrodynamics involved is deluding themselves.
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Old 15-08-2012, 18:26   #71
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Re: Hmmmm - Bowthrusters ??

I would expect quite some loss of boat speed as the flow becomes very turbulent right where you want it to be very laminar.

Right? Wrong?

BTW I am not sure I have seen many bow thrusters on racers, I believe most do not have them. Think the and the weight (and then: the weight in the bow). Racers hate such things.

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Old 15-08-2012, 18:57   #72
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Re: Hmmmm - Bowthrusters ??

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I would expect quite some loss of boat speed as the flow becomes very turbulent right where you want it to be very laminar.

Right? Wrong?

BTW I am not sure I have seen many bow thrusters on racers, I believe most do not have them. Think the and the weight (and then: the weight in the bow). Racers hate such things.

b.
Exactly. Developing turbulent flow at the entry makes it impossible to develop laminar flow anywhere else on the bottom as the turbulence moves down the hull. You are sailing in the thrusters wake. Obviously laminar flow only matters to racers and will never truly be developed by most boats anyway, but it does make SOME difference to everyone.
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Old 15-08-2012, 20:08   #73
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Re: Hmmmm - Bowthrusters ??

FWIW,

I suspect that those who say they experienced no speed loss from their BT installation simply have never had their boats sailing up t o their potential. AS Barny and Minaret and others have said, such a hole in the bow MUST reduce performance.

For some it will make no difference, others would hate it.

Cheers,

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Old 15-08-2012, 20:13   #74
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Quote:
Originally Posted by minaret

I invented fairing a brow on a thruster tube for sailboat installs in my area as far as I know. While it does help, it certainly does not solve the problem. Anyone who can convince themselves that a 9" or 11" hole in both sides of their cutwater has no effect on the hydrodynamics involved is deluding themselves.
If faired properly , there will be no appreciable difference in performance

I am not talking about inventing anything , I am talking about installing it properly - nothing delusional here

( it's not just about creating a "brow" )

Check out the technical pages from manufacturers like Vetus and Lewmar

I am not seeing any practical difference in sailing speed since the BT has been installed on my 1 yr old 59 ft cutter rigged blue water cruiser

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Old 15-08-2012, 21:55   #75
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Struggling with the naysayers here

We really have not noticed any diminution in performance since properly installing our BT

Here we are at 9.1 knots upwind after installing the BT ( just in case you think we don't know how to sail)

Pic was taken a week ago, with 40% mainsail up

Carlisle Spirit

1 yr old 59 ft cutter rigged blue water cruiser
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