That is essentially what he had too.
I'm sure I'd get accustomed to it...not sure how long it would take!
Bruce
Bow Thruster vs Stern Thruster
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That is essentially what he had too.
I'm sure I'd get accustomed to it...not sure how long it would take!
Bruce
dhays
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We have a camera aimed aft as well. We have poor visibility aft from the Pilothouse. There was a NP42 for sale in AK that had a control station in the aft cockpit. Nice feature.
O C Diver
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Just out of curiosity, is the stern thruster the same size as the bow thruster on a boat? It would seem that there generally is more boat below the surface in the stern than in the bow.
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Conrad
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We installed identical 13 HP Wesmar thrusters on Blue Sky, and I can't say that there is a noticeable difference in the forces provided.
One thing that is obvious when using the thrusters is the concept of equal and opposite reactions. I.e., if you use the stern thruster for example, the bow moves in the opposite direction, at least on our NT 42. Meaning that I seldom use just one thruster as Blue Sky otherwise tends to spin on her own axis.
Also, for some reason that escapes me, when just using the stern thruster the boat moves backwards. I'm sure there's a technical reason for that.
bfloyd4445
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Have you considered changing the brand of grog you drink while docking?
...or maybe the issue is the lack of grogI'm sorry I couldn't help that remark. Your information is appreciated as I have never owned a vessel with thrusters besides the main engines. Now I'm curious if what you describe is the same for all vessels?
Conrad
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Have you considered changing the brand of grog you drink while docking?
I'm sorry I couldn't help that remark. Your information is appreciated as I have never owned a vessel with thrusters besides the main engines. Now I'm curious if what you describe is the same for all vessels?
In my less than scientific analysis, I'd have to say that changing from rum & coke to manhattans made no difference!
No idea if other vessels act the same way, as I haven't done a grog survey on them....
bfloyd4445
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Hummm...maybe you should apply for a government grant to research this subject. If you do so I will volunteer to be one of your test subjects
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Conrad, I'll stick my physics neck out here and suggest it is because the thruster is forcing water away from the stern on the one side, while sucking it in from the intake side, with the net effect being a bit like a that of yacht sail, creating in effect a modest negative pressure area behind the stern, which draws the vessel into it. Just a thought....others..?
As to whether to have thrusters or not. I don't, and we manage. But if I was going upscale in size and price, sure, I'm not to proud to use them, and would definitely want them. Both, front and back for the reasons you just mentioned.
I see the issue as similar to how we all managed with vehicles that did not have power mirrors and windows, central remote locking, reversing cameras, etc, etc. Now having had them, we realise they add to the safety and convenience of use, so why would you not..? Hey those powered tailgates seem a good idea. Now I don't have one of those. But when your arms are full...
Conrad
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Conrad, I'll stick my physics neck out here and suggest it is because the thruster is forcing water away from the stern on the one side, while sucking it in from the intake side, with the net effect being a bit like a that of yacht sail, creating in effect a modest negative pressure area behind the stern, which draws the vessel into it. Just a thought....others..?
As to whether to have thrusters or not. I don't, and we manage. But if I was going upscale in size and price, sure, I'm not to proud to use them, and would definitely want them. Both, front and back for the reasons you just mentioned.
I see the issue as similar to how we all managed with vehicles that did not have power mirrors and windows, central remote locking, reversing cameras, etc, etc. Now having had them, we realise they add to the safety and convenience of use, so why would you not..? Hey those powered tailgates seem a good idea. Now I don't have one of those. But when your arms are full...
I like your thoughts on why there is a pull backwards; it fits with my physics and ultralight classes from way back when.
We have a side tie berth facing east west and we are on the south side. An 89 footer sits right in front of us, and a 70 footer right behind. With a north wind of any consequence, you are not going to dock without thrusters. (No dock cleats, only bull rails). So yes, the thrusters are very worthwhile. Even better when your dock neighbours know you have them and you don't use them....
But they also come in handy in unexpected ways such as last winter when we woke up at anchor and were iced in on three sides. The thrusters allowed us to slip out sideways with aplomb.
I have both and they are the same model SidePower.
Some movement at opposite end is to be expected - watch what happens if someone fends off at one end - the other end moves opposite...never tried to gauge whether it is the same amount or not.
My sense is that I get more bow movement w/ that thruster and less opposite stern movement - similar w/ stern unit - more movement of stern and less opposite at bow.
If you want to move pure sideways you simply employ both in same direction - It can be simultaneously or pulsed bow then stern - I usually do the latter to avoid overheating especially if wind is strong and I need a lot of thruster.
If I want to turn in place just use them both in opposite directions and you spin
Haven't noticed moving astern but will pay more attention -
Peter - wouldn't you have negative pressure on inlet side and positive on output side w/ net being zero??
I'm wondering if there is a prop walk affect? if so i'd think it would be astern on direction and ahead in the opposite.
Don't have a good answer - I'm usually using thrusters while backing into slip so will have to play w/ them in other situations standing still.
dhays
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I would doubt that there is any prop walk since both the bow and stern thruster propellers are in tunnels.
BruceK
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Older threads are your friend, like this :http://www.trawlerforum.com/forums/s31/bow-thruster-question-26773-2.html. There are several others worth reviewing.
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Stern Thruster
This is an old Thread, but I installed a Lewmar 140TT Thruster on our Albin A27 with a single screw and couldn't be happier. I know there are some traditionalists out there, and yes, I too was proud of backing the boat into a slip with the tide running one way and the wind the other. But, sometimes those were 20 point turns by the time it was said and done. Now it's just like running twins with respect to maneuverability. The A27 lazarette is shallow and the thruster sucked some air and cavitated. On the last haul out I added diverters and the results are far more than satisfying. The admiral loves it
This is an old Thread, but I installed a Lewmar 140TT Thruster on our Albin A27 with a single screw and couldn't be happier. I know there are some traditionalists out there, and yes, I too was proud of backing the boat into a slip with the tide running one way and the wind the other. But, sometimes those were 20 point turns by the time it was said and done. Now it's just like running twins with respect to maneuverability. The A27 lazarette is shallow and the thruster sucked some air and cavitated. On the last haul out I added diverters and the results are far more than satisfying. The admiral loves it
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FatBear
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I know this is old, but it was never resolved. Some have mentioned prop walk, but the thruster prop is in a tunnel. Some have mentioned differential pressures, but water is not compressible.
A thruster is a pump. It sucks in water and shoots out water. Where does it suck the water from? It does not suck the water in a direct line, it comes from all around its intake. Since water does not compress or decompress, something must enter the "hole" that the pump has made. Most of what enters the hole is other water, but one entire side of that hole is where the transom of the boat is, and so the boat is also going to move into that hole albeit very slowly. That would be the reversing effect you are seeing.
You may have noticed that I did not mention the output side. The output does go out in roughly a straight line. It might apply a small amount of pressure against the transom, but relatively small and effectively negated by the boat movement opposite the primary thrust direction.
It is worth noting that your engine/propeller is also a water pump and has a similar effect. The prop pulls water from generally beneath and beside the hull. (Though less from the side in a hard chined hull.) If you pull up alongside a seawall or into a lock, that can suck you slightly towards the edge, no bow thruster needed - until you try to leave and it holds you against the side. In a canal, where there is actually very little water around the hull you might notice this effect when passing another boat. Especially a large one which takes up a lot more of the cross section of the canal and whose propeller is moving a lot of water. In a case like that, polite captains drop their engines into neutral just for a moment as they pass so they do not suck together and bump.
In Europe, if you sit next to a low bridge you will occasionally see a large boat approach the bridge and then firewall the throttle just as the house is about to hit. It looks suicidal, but then it does not hit. Why? Because they use the prop to pump the water out from beneath the hull and it drops low enough to clear the bridge. You obviously need to know this will work before you try it.
You've all seen this effect when a planing hull boat is stationary and then you hit the throttles and the boat falls into "the hole". Then it has to climb out of the hole. I'm sure most people use the phrase figuratively, but it is really very apt. That sudden application of the throttle causes the prop to suck a lot of water out from beneath the boat and so it falls into the hole that has been created.
I have not had the luxury of using a bow thruster inside of a lock, but I suspect that the apparent thrust would be greatly magnified by proximity to the walls. Imagine if you were thrusting the boat towards the wall. The actual thrust is away from the wall and the intake is on the side of the boat that is approaching the wall. Hit your bow thruster and you will pull a lot of water out from between the boat and the wall. The boat will "fall" into that hole and could approach the wall more quickly than you had expected. A similar, but opposite "magnifying" effect would happen if you thrust away from the wall. You are going to pump a lot of water into that small space between the boat and the wall, so in addition to the direct thrust from the water jet, there is also that additional water pushing the boat away from the wall. I'm just guessing about this last paragraph, but it seems likely.
bfloyd4445
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I know this is old, but it was never resolved. Some have mentioned prop walk, but the thruster prop is in a tunnel. Some have mentioned differential pressures, but water is not compressible.
A thruster is a pump. It sucks in water and shoots out water. Where does it suck the water from? It does not suck the water in a direct line, it comes from all around its intake. Since water does not compress or decompress, something must enter the "hole" that the pump has made. Most of what enters the hole is other water, but one entire side of that hole is where the transom of the boat is, and so the boat is also going to move into that hole albeit very slowly. That would be the reversing effect you are seeing.
You may have noticed that I did not mention the output side. The output does go out in roughly a straight line. It might apply a small amount of pressure against the transom, but relatively small and effectively negated by the boat movement opposite the primary thrust direction.
It is worth noting that your engine/propeller is also a water pump and has a similar effect. The prop pulls water from generally beneath and beside the hull. (Though less from the side in a hard chined hull.) If you pull up alongside a seawall or into a lock, that can suck you slightly towards the edge, no bow thruster needed - until you try to leave and it holds you against the side. In a canal, where there is actually very little water around the hull you might notice this effect when passing another boat. Especially a large one which takes up a lot more of the cross section of the canal and whose propeller is moving a lot of water. In a case like that, polite captains drop their engines into neutral just for a moment as they pass so they do not suck together and bump.
In Europe, if you sit next to a low bridge you will occasionally see a large boat approach the bridge and then firewall the throttle just as the house is about to hit. It looks suicidal, but then it does not hit. Why? Because they use the prop to pump the water out from beneath the hull and it drops low enough to clear the bridge. You obviously need to know this will work before you try it.
You've all seen this effect when a planing hull boat is stationary and then you hit the throttles and the boat falls into "the hole". Then it has to climb out of the hole. I'm sure most people use the phrase figuratively, but it is really very apt. That sudden application of the throttle causes the prop to suck a lot of water out from beneath the boat and so it falls into the hole that has been created.
I have not had the luxury of using a bow thruster inside of a lock, but I suspect that the apparent thrust would be greatly magnified by proximity to the walls. Imagine if you were thrusting the boat towards the wall. The actual thrust is away from the wall and the intake is on the side of the boat that is approaching the wall. Hit your bow thruster and you will pull a lot of water out from between the boat and the wall. The boat will "fall" into that hole and could approach the wall more quickly than you had expected. A similar, but opposite "magnifying" effect would happen if you thrust away from the wall. You are going to pump a lot of water into that small space between the boat and the wall, so in addition to the direct thrust from the water jet, there is also that additional water pushing the boat away from the wall. I'm just guessing about this last paragraph, but it seems likely.
Wll said. I learned something. Thanks
rsn48
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I quit reading all the responses. But I'll comment on one issue - noise. It really doesn't matter if you have a hydraulic, electric or nuclear powered bow thruster. What makes the noise is cavitation. Most bow thrusters on smaller boats are too close to the water surface with the results air gets sucked in, thus making that dishwasher sound. Larger boats with deeper hulls don't make that sound as the thruster is deeper in the water and no air sucked in, thus no dishwasher sound effects.
By the way some of you guys who think hydraulic is the way to go, you might want to contact BC Ferries and let them know electric thrusters are not the way to go.
Some propaganda from the BC Ferries site on one class of ships the corporation owns.
The Island Class are battery-equipped ships designed for full electric operation. The ships are fitted with hybrid technology that bridges the gap until shore charging infrastructure becomes available. From the exterior details to the engines, the design of the new vessels reduces underwater radiated noise, lowers emissions and improves the customer experience on board.
On my boat during refit I wanted tunnel bow thruster technology but due to the fact the boat had a wooden keel in the interior, I had to go external, I used Exturn. This is an electric drive system. The real advantage of an external thruster such as I have is it is mount below the hull and down about 14 inches or so. Hence no dishwasher sound as air isn't sucked in, this air sucked in phenomena also effectively reduces horsepower as the props can't dig in as well. With my Exturn, there is no cavitation thus effectively increasing horsepower.
The reason I prefer a bow thruster is that in narrow channels such as in my marina, I like to stick to the starboard side of the channel as a blind spot exists where I have to make a port turn. As we all know, when turning a boat, the stern swings like pushing a shopping cart backwards and the bow in essence follows the stern, unlike a car where the front of the car leads the back. When I go to make my port turn, I only use the thruster as this eliminates stern swing and the stern follows the bow as in a car scenario.
I am of the school of thought that states you already have power in the stern so logically having power in the bow will be helpful.
There is a thruster system made in the state of Washington. The units slide up and down on a rail. I don't like this system for the bow thruster but I don't mind it for the stern thruster. It runs from a lithium battery, the builder claims ten minutes of run time, but even if you only get five minutes, that's all you'll probably need. You run the thruster from a wireless remote.
I decided when I installed my bow thruster and I found I still wanted a stern thruster, I'd use the unit out of Washington. Installation is dirt easy, I could even do it. But I decided to wait until I discovered how my boat performed with the bow thruster. So far, I have no reason to install the stern thruster.
By the way some of you guys who think hydraulic is the way to go, you might want to contact BC Ferries and let them know electric thrusters are not the way to go.
Some propaganda from the BC Ferries site on one class of ships the corporation owns.
The Island Class are battery-equipped ships designed for full electric operation. The ships are fitted with hybrid technology that bridges the gap until shore charging infrastructure becomes available. From the exterior details to the engines, the design of the new vessels reduces underwater radiated noise, lowers emissions and improves the customer experience on board.
On my boat during refit I wanted tunnel bow thruster technology but due to the fact the boat had a wooden keel in the interior, I had to go external, I used Exturn. This is an electric drive system. The real advantage of an external thruster such as I have is it is mount below the hull and down about 14 inches or so. Hence no dishwasher sound as air isn't sucked in, this air sucked in phenomena also effectively reduces horsepower as the props can't dig in as well. With my Exturn, there is no cavitation thus effectively increasing horsepower.
The reason I prefer a bow thruster is that in narrow channels such as in my marina, I like to stick to the starboard side of the channel as a blind spot exists where I have to make a port turn. As we all know, when turning a boat, the stern swings like pushing a shopping cart backwards and the bow in essence follows the stern, unlike a car where the front of the car leads the back. When I go to make my port turn, I only use the thruster as this eliminates stern swing and the stern follows the bow as in a car scenario.
I am of the school of thought that states you already have power in the stern so logically having power in the bow will be helpful.
There is a thruster system made in the state of Washington. The units slide up and down on a rail. I don't like this system for the bow thruster but I don't mind it for the stern thruster. It runs from a lithium battery, the builder claims ten minutes of run time, but even if you only get five minutes, that's all you'll probably need. You run the thruster from a wireless remote.
I decided when I installed my bow thruster and I found I still wanted a stern thruster, I'd use the unit out of Washington. Installation is dirt easy, I could even do it. But I decided to wait until I discovered how my boat performed with the bow thruster. So far, I have no reason to install the stern thruster.
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That wouldn't be an inverter.
Why not get a 12 volt bow thruster? Keep things simple.
bfloyd4445
Guru
What he meant was a converter. Means you need wiring sized at least three times larger than the exsisting 12v wiring to the converter or there will be smoke.
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