Hmmmm - Bowthrusters ??

[Lagoon4us]

Originally Posted by Carlisle Spirit

Crisfield Maryland News and Photography: 39th annual Boat Docking Contest in Crisfield - 2010

Fantastic stuff! Enjoyed thanks.

[Lagoon4us]

Originally Posted by carstenb

Minaret,

CAll ahead and specify a landing????????? In Denmark I only know of a couple of harbour where you can even reserve a space - much less one with a starboard landing. Hell, this summer I jockeyed my 40 footer around on the island of bornholm, and the boats were laying 4-5 out on each others sides. The harbours are so small that there basically there isn't enough room to turn a 40 footer. Happy I had a BT.

Worst I've ever seen was 14 boats out fro the pier on the swedish island of Hven 14 boats, you could almost walk dry footer across the harbour on the boats

Same here, in Summer,ACI ZADAR won't answer the radio for bookings and at TROGIR it's months in advance 5 wide rafted at Quay, as i said there is a world outside sometimes it's different to where we live hard for some to understand.
Cheers Frank

[BWB75]

Originally Posted by minaret

I can fully understand why all the charter companies just about everywhere tend to have thrusters on their boats, it's the perfect application for them.

I concur. I recently chartered a Jeanneau 39DS with bow thrusters in the med. Narrow passages between docks coupled with med-mooring made the bow thrusters valuable to me. The plan was never to rely on the thrusters, but they were handy for corrections that otherwise would have required a pull-out-and-try-again. Could I have made it without them? Sure. But, I was glad I didn't have to.

[carstenb]

Minaret,

No I cruise other places than DK. I find that in the Med, when doing Med landings, a BT is quite useful, backing in.

As I noted somewhere else - I sailed for years without a BT and was quite happy. Now I have one, use when convenient, and am still quite happy.

[Dockhead]

Originally Posted by minaret

To each their own. When we call ahead on the radio to a marina to reserve our slip for the night, we always specify a bow-in starboard side tie, because the prop walk will allow us to both enter and exit the slip easily that way. We carefully plan our entrance into the marina on the dock layout in our chart book to accomodate our best turning radius. As one earlier poster said, he got tired of always having to turn left after fifteen years of doing so. I certainly understand that, but for me a little planning ahead doesn't really bother me, I even kind of enjoy it. I also find having all that extra thrust in reverse allows me to manuever a little more definitively in high winds, ie at a higher speed coming in to the slip because I know I have plenty of braking power, and that when I apply that braking power the boat will move sideways to starboard as it comes to a stop. This is very helpful in high winds as the wind doesnt have time to blow the bow off. My teeny wife is my only line handler. The boat weighs 65,000 lbs. tanks empty and has a pilothouse and high sheer, therefore lots of windage.
I find it simple to go in a straight line astern, despite my pronounced propwalk. I was always taught that when going astern, since every boat has SOME propwalk, you apply a burst of throttle in reverse and then drop it back in neutral. Then another burst or two if needed. Almost like a thruster! I thought everyone did it this way. Just putting the boat in reverse and leaving it there and then expecting it to go in a straight line is silly. On some boats I have been on the propwalk is stronger than the helm at any speed under a knot or two, so the boat won't answer the helm at all with the engine in reverse and will only turn one way. That's why you give it a burst to get steerage way in reverse, and then drop it in neutral. As soon as you drop it in neutral the boat answers the helm again. Underbody certainly has a major effect on steerage in reverse, but regardless of underbody you'll never go in a straight line in reverse if you just put the boat in gear and leave it there.

To each his own -- yes, I agree entirely! If everyone sailed exactly the same way, it would be extremely boring and we wouldn't have anything to talk about.

Concerning prop walk: I spent 10 years cruising a boat with a long keel and no thruster, and vicious prop walk (to starboard – v-drive). Certainly I always tried to berth port-to so that I could use the prop walk to get off the pontoon, but like others here, I have never sailed anywhere where you could get the berth you wanted very often. The other very desirable thing with that boat was to have a berth I could get out of in forward. But only a hammerhead berth will allow you to both come in and get out in forward; this was rarely available (although I always begged for one). So in other cases I almost always had to use spring lines or just manhandle the boat off – prop walk is 93% curse, and only 7% blessing, I would say. Not the prop walk itself, maybe, but the failure of my old boat to answer the helm at less than 3 knots or so – which is typical of boats with long keels. No amount of skill or technique in the world would get that boat to back up straight in tight conditions, because you have to have room to get up to the speed where the rudder starts to work.
On my new boat, I use all the techniques you describe, learned during years of torture with my old boat. My new boat kicks to port in astern (right-hand prop, shaft drive), but kicks less, and starts to answer the helm very quickly, at maybe one knot. Such a joy -- this is vastly better than what I had with the old boat. So now I have the practical ability to back up straight in tight conditions, or turn in either direction going astern. If I am docking port-to, I use the prop walk to kick the stern into the dock. I almost never use my thruster when coming into a berth – I use inertia and a turn away from the dock at the last second to bring in the stern – like an airplane flaring for a landing. If I’m port-to, the prop kick is just a bonus -- another force helping me get the stern into the dock, but I don’t really need either prop walk or thruster to get into a berth, unless there is a strong wind blowing me off.
I also use prop kick whenever I have to turn around in a tight space – I don’t need the thruster for this, either. I put the helm hard over to starboard, give a burst forward, then a burst in astern. The burst of power in astern kills the forward momentum without affecting the angular momentum (the spinning motion). The prop walk kicking the stern to port enhances the angular momentum. Like this, I can turn my boat within her own length, without the thruster, something which for some reason impresses spectators. If for some reason I have to spin around counter-clockwise, I will sometimes use the thruster to enhance angular momentum, since in this case prop walk is working against me, instead of for me.
I always use the thruster when coming off a berth, no matter what kind of berth it is. This is simply a matter of good seamanship, since I have the tool available. The thruster with cross-rudder moves my boat sideways, moving me straight off the dock, giving me clearance off the dock, allowing me to maneuver safely and easily around other boats, and preventing any scraping along the dock.
The fact that my new boat will back up straight once I have a knot or so of way on is immensely valuable. It means that I can do all kinds of things which were impossible in my old boat. For one thing, I can reverse into a berth – an extremely valuable maneuver in all kinds of different situations. Particularly in a strong wind blowing off the berth, where the natural weather-cocking will tend to blow the bow off if you are coming in in forward. In such cases, I prefer to back into the berth rather than using the brute force of the thruster to hold the bow in against the wind. In my old boat, it was simply impossible to get into a windward berth without manhandling the boat, if it was a port-to berth, since I could not reverse in under any circumstances.
We have talked a lot about wind. But in a lot of places there are currents to deal with as well. A current running further limits your options concerning what direction you come into or get out of a berth, and creates additional dangers. Here prop kick, which helps you only in one direction, is of limited value, even if you were able to choose a berth which suits the direction of your prop kick. A thruster, which allows you to create sideways motion in either direction, using cross-rudder, to counteract a current, can absolutely save your a$s – if the current is sweeping you onto a hazard in a tight situation, this might be your only option. Having at your disposal this maneuver, using a thruster, is an immense enhancement to safety, in waters with tidal currents.
So in summary, what I am trying to say, is this:
1. Good seamanship demands that you learn to use all the tools you have at your disposal, and learn everything you can do with them. Including prop walk, which occasionally is very valuable.

2. A boat which has strong prop walk and will not answer the helm until two or three knots of speed in astern, like my old boat, is generally a curse. If on top of that, the boat is too heavy to manhandle, then I think it’s positively dangerous. At least, if you are sailing in places like where I have sailed my whole life, where you can’t choose your berth, and have to make do with all kinds of different berths, tight conditions, and unexpected obstacles, and you need to be able to back around in tight conditions. You have much more control and many more options for where you can steer your boat if your boat answers the helm quickly in astern, and does not kick as strongly.

3. A thruster is a very great blessing for a boat which is too heavy to manhandle around. More power to anyone who is able to comfortably maneuver such a boat without a thruster – my hat is off to you. But a thruster greatly increases your options and improves your control, adding to safety, in the hands of a skilled sailor who is able to use its capabilities. To put it another way – if I need to get across a canyon, I will greatly admire a person who is able to do it by walking a tightrope without falling off. But I would never walk the tightrope myself if there is a nice, wide bridge to use to get across that canyon, and good seamanship demands, in fact, that you use that bridge rather than the tightrope, if you have a choice.

4. A bad sailor will not magically become better, just because he has a thruster. In fact, a thruster requires a great deal of skill and technique to use effectively. At best, a clumsy sailor with a thruster might save only those situations where his bow is out of position as a result of his mistakes in maneuvering. It really won't help him at all in "missed approach" situations while docking. A clumsy sailor who can’t handle his boat in close quarters is going to have problems, with or without a thruster.

It is interesting to note that Beneteau has come up with a system which goes far beyond the capabilities of the humble bow thruster -- their computerized joystick system which automatically controls a bow thruster plus swivelling sail drive so that you can move your boat in any direction you like merely by pushing the joystick in that direction. Now that's push button sailing for you! I don't really see anything wrong with it other than complexity, cost, reliability questions. Unlike the humble bow thruster, this system promises to allow unskilled sailors to dock and maneuver with some safety -- perfect for charter boats. I won't be having such a thing myself -- too complicated, and I don't like sail drives. But I think it will be a boon for many sailors.

[minaret]

Originally Posted by Dockhead

To each his own -- yes, I agree entirely! If everyone sailed exactly the same way, it would be extremely boring and we wouldn't have anything to talk about.

So in summary, what I am trying to say, is this:
1. Good seamanship demands that you learn to use all the tools you have at your disposal, and learn everything you can do with them. Including prop walk, which occasionally is very valuable.

Couldn't agree more. I just feel that a thruster, like most things on a boat, is a compromise which has drawbacks as well as advantages. No one here seems willing to discuss the drawbacks, only the advantages. They do exist.

2. A boat which has strong prop walk and will not answer the helm until two or three knots of speed in astern, like my old boat, is generally a curse. If on top of that, the boat is too heavy to manhandle, then I think it’s positively dangerous. At least, if you are sailing in places like where I have sailed my whole life, where you can’t choose your berth, and have to make do with all kinds of different berths, tight conditions, and unexpected obstacles, and you need to be able to back around in tight conditions. You have much more control and many more options for where you can steer your boat if your boat answers the helm quickly in astern, and does not kick as strongly.

That does indeed sound like a curse. I have never driven a boat that won't answer the helm at all in reverse until you hit two knots. That would suck. I find it interesting that everyone here who is saying "get out more, most places you can't choose what berth you want" all live in Europe, a pretty small area. Admittedly I have only cruised the west coast of the Americas and a bit of East Coast and Carribean, but I have never had a problem with that. In fact most places I go it's the second question they ask on the radio, right after how long are you. From talking to my many friends and neighbors on my dock who have cruised extensively worldwide in large boats, they have had no difficulty with that either. Perhaps it's just Europe which is very crowded and has few slips available in the first place? After all, many people use moorings in that part of the world.


3. A thruster is a very great blessing for a boat which is too heavy to manhandle around. More power to anyone who is able to comfortably maneuver such a boat without a thruster – my hat is off to you. But a thruster greatly increases your options and improves your control, adding to safety, in the hands of a skilled sailor who is able to use its capabilities. To put it another way – if I need to get across a canyon, I will greatly admire a person who is able to do it by walking a tightrope without falling off. But I would never walk the tightrope myself if there is a nice, wide bridge to use to get across that canyon, and good seamanship demands, in fact, that you use that bridge rather than the tightrope, if you have a choice.

Definitely agree about using available tools. Was just trying to make others aware that a thruster is not the only available tool to increase maneuverability. We have both a fixed prop and a Max Prop. The difference in maneuverability with the feathering prop is huge. I doubt I could do what I do without it. People should be aware that there is an available option which both costs less and has fewer drawbacks, even if it is slightly less effective. I don't know why that concept seems to anger anyone who owns a thruster so much.



4. A bad sailor will not magically become better, just because he has a thruster. In fact, a thruster requires a great deal of skill and technique to use effectively. At best, a clumsy sailor with a thruster might save only those situations where his bow is out of position as a result of his mistakes in maneuvering. It really won't help him at all in "missed approach" situations while docking. A clumsy sailor who can’t handle his boat in close quarters is going to have problems, with or without a thruster.

Yup!



It is interesting to note that Beneteau has come up with a system which goes far beyond the capabilities of the humble bow thruster -- their computerized joystick system which automatically controls a bow thruster plus swivelling sail drive so that you can move your boat in any direction you like merely by pushing the joystick in that direction. Now that's push button sailing for you! I don't really see anything wrong with it other than complexity, cost, reliability questions. Unlike the humble bow thruster, this system promises to allow unskilled sailors to dock and maneuver with some safety -- perfect for charter boats. I won't be having such a thing myself -- too complicated, and I don't like sail drives. But I think it will be a boon for many sailors.

You knew that the commercial joystick steering would come into the recreational world sooner or later. I agree that it's much too complicated for a cruising boat, but it is cool to watch tugs and big ships use it to do their magic.

[nigel1]

Originally Posted by minaret

You knew that the commercial joystick steering would come into the recreational world sooner or later. I agree that it's much too complicated for a cruising boat, but it is cool to watch tugs and big ships use it to do their magic.

Got a joystick system on my tug, but its crap for fast manoeuvering, much prefer to keep all the controls separate, and you have a much better feel for what the boat is up against, plus its a lot more fun to drive.

[Dockhead]

Originally Posted by minaret

Quote:
Originally Posted by Dockhead
To each his own -- yes, I agree entirely! If everyone sailed exactly the same way, it would be extremely boring and we wouldn't have anything to talk about.

So in summary, what I am trying to say, is this:
1. Good seamanship demands that you learn to use all the tools you have at your disposal, and learn everything you can do with them. Including prop walk, which occasionally is very valuable.

Couldn't agree more. I just feel that a thruster, like most things on a boat, is a compromise which has drawbacks as well as advantages. No one here seems willing to discuss the drawbacks, only the advantages. They do exist.

2. A boat which has strong prop walk and will not answer the helm until two or three knots of speed in astern, like my old boat, is generally a curse. If on top of that, the boat is too heavy to manhandle, then I think it’s positively dangerous. At least, if you are sailing in places like where I have sailed my whole life, where you can’t choose your berth, and have to make do with all kinds of different berths, tight conditions, and unexpected obstacles, and you need to be able to back around in tight conditions. You have much more control and many more options for where you can steer your boat if your boat answers the helm quickly in astern, and does not kick as strongly.

That does indeed sound like a curse. I have never driven a boat that won't answer the helm at all in reverse until you hit two knots. That would suck. I find it interesting that everyone here who is saying "get out more, most places you can't choose what berth you want" all live in Europe, a pretty small area. Admittedly I have only cruised the west coast of the Americas and a bit of East Coast and Carribean, but I have never had a problem with that. In fact most places I go it's the second question they ask on the radio, right after how long are you. From talking to my many friends and neighbors on my dock who have cruised extensively worldwide in large boats, they have had no difficulty with that either. Perhaps it's just Europe which is very crowded and has few slips available in the first place? After all, many people use moorings in that part of the world.


3. A thruster is a very great blessing for a boat which is too heavy to manhandle around. More power to anyone who is able to comfortably maneuver such a boat without a thruster – my hat is off to you. But a thruster greatly increases your options and improves your control, adding to safety, in the hands of a skilled sailor who is able to use its capabilities. To put it another way – if I need to get across a canyon, I will greatly admire a person who is able to do it by walking a tightrope without falling off. But I would never walk the tightrope myself if there is a nice, wide bridge to use to get across that canyon, and good seamanship demands, in fact, that you use that bridge rather than the tightrope, if you have a choice.

Definitely agree about using available tools. Was just trying to make others aware that a thruster is not the only available tool to increase maneuverability. We have both a fixed prop and a Max Prop. The difference in maneuverability with the feathering prop is huge. I doubt I could do what I do without it. People should be aware that there is an available option which both costs less and has fewer drawbacks, even if it is slightly less effective. I don't know why that concept seems to anger anyone who owns a thruster so much.



4. A bad sailor will not magically become better, just because he has a thruster. In fact, a thruster requires a great deal of skill and technique to use effectively. At best, a clumsy sailor with a thruster might save only those situations where his bow is out of position as a result of his mistakes in maneuvering. It really won't help him at all in "missed approach" situations while docking. A clumsy sailor who can’t handle his boat in close quarters is going to have problems, with or without a thruster.

Yup!



It is interesting to note that Beneteau has come up with a system which goes far beyond the capabilities of the humble bow thruster -- their computerized joystick system which automatically controls a bow thruster plus swivelling sail drive so that you can move your boat in any direction you like merely by pushing the joystick in that direction. Now that's push button sailing for you! I don't really see anything wrong with it other than complexity, cost, reliability questions. Unlike the humble bow thruster, this system promises to allow unskilled sailors to dock and maneuver with some safety -- perfect for charter boats. I won't be having such a thing myself -- too complicated, and I don't like sail drives. But I think it will be a boon for many sailors

Originally Posted by Dockhead
To each his own -- yes, I agree entirely! If everyone sailed exactly the same way, it would be extremely boring and we wouldn't have anything to talk about.

So in summary, what I am trying to say, is this:
1. Good seamanship demands that you learn to use all the tools you have at your disposal, and learn everything you can do with them. Including prop walk, which occasionally is very valuable.

Couldn't agree more. I just feel that a thruster, like most things on a boat, is a compromise which has drawbacks as well as advantages. No one here seems willing to discuss the drawbacks, only the advantages. They do exist.

2. A boat which has strong prop walk and will not answer the helm until two or three knots of speed in astern, like my old boat, is generally a curse. If on top of that, the boat is too heavy to manhandle, then I think it’s positively dangerous. At least, if you are sailing in places like where I have sailed my whole life, where you can’t choose your berth, and have to make do with all kinds of different berths, tight conditions, and unexpected obstacles, and you need to be able to back around in tight conditions. You have much more control and many more options for where you can steer your boat if your boat answers the helm quickly in astern, and does not kick as strongly.

That does indeed sound like a curse. I have never driven a boat that won't answer the helm at all in reverse until you hit two knots. That would suck. I find it interesting that everyone here who is saying "get out more, most places you can't choose what berth you want" all live in Europe, a pretty small area. Admittedly I have only cruised the west coast of the Americas and a bit of East Coast and Carribean, but I have never had a problem with that. In fact most places I go it's the second question they ask on the radio, right after how long are you. From talking to my many friends and neighbors on my dock who have cruised extensively worldwide in large boats, they have had no difficulty with that either. Perhaps it's just Europe which is very crowded and has few slips available in the first place? After all, many people use moorings in that part of the world.


3. A thruster is a very great blessing for a boat which is too heavy to manhandle around. More power to anyone who is able to comfortably maneuver such a boat without a thruster – my hat is off to you. But a thruster greatly increases your options and improves your control, adding to safety, in the hands of a skilled sailor who is able to use its capabilities. To put it another way – if I need to get across a canyon, I will greatly admire a person who is able to do it by walking a tightrope without falling off. But I would never walk the tightrope myself if there is a nice, wide bridge to use to get across that canyon, and good seamanship demands, in fact, that you use that bridge rather than the tightrope, if you have a choice.

Definitely agree about using available tools. Was just trying to make others aware that a thruster is not the only available tool to increase maneuverability. We have both a fixed prop and a Max Prop. The difference in maneuverability with the feathering prop is huge. I doubt I could do what I do without it. People should be aware that there is an available option which both costs less and has fewer drawbacks, even if it is slightly less effective. I don't know why that concept seems to anger anyone who owns a thruster so much.



4. A bad sailor will not magically become better, just because he has a thruster. In fact, a thruster requires a great deal of skill and technique to use effectively. At best, a clumsy sailor with a thruster might save only those situations where his bow is out of position as a result of his mistakes in maneuvering. It really won't help him at all in "missed approach" situations while docking. A clumsy sailor who can’t handle his boat in close quarters is going to have problems, with or without a thruster.

Yup!



It is interesting to note that Beneteau has come up with a system which goes far beyond the capabilities of the humble bow thruster -- their computerized joystick system which automatically controls a bow thruster plus swivelling sail drive so that you can move your boat in any direction you like merely by pushing the joystick in that direction. Now that's push button sailing for you! I don't really see anything wrong with it other than complexity, cost, reliability questions. Unlike the humble bow thruster, this system promises to allow unskilled sailors to dock and maneuver with some safety -- perfect for charter boats. I won't be having such a thing myself -- too complicated, and I don't like sail drives. But I think it will be a boon for many sailors.


You knew that the commercial joystick steering would come into the recreational world sooner or later. I agree that it's much too complicated for a cruising boat, but it is cool to watch tugs and big ships use it to do their magic.

So we are in violent agreement

Naturally, as you say, bow thrusters have many disadvantages, I think everyone would agree -- weight, cost, drag, another hole in the boat, power requirements, hull volume occupied. Most of these disadvantages become relatively harsher the smaller the boat is, and above a certain size, on the contrary, start to become almost unnoticeable. So cost/benefit ratio changes radically with changing boat size, and on my 54 footer (60+ LOA and 25+ tons) the disadvantages are hardly noticeable. I reckon I probably wouldn't want a thruster on a boat less than about 45 feet, and I would certainly never want one on a catamaran, where weight is so important to performance, and where you can do magic with dual engines anyway.

[minaret]

Originally Posted by Dockhead

So we are in violent agreement

Naturally, as you say, bow thrusters have many disadvantages, I think everyone would agree -- weight, cost, drag, another hole in the boat, power requirements, hull volume occupied. Most of these disadvantages become relatively harsher the smaller the boat is, and above a certain size, on the contrary, start to become almost unnoticeable. So cost/benefit ratio changes radically with changing boat size, and on my 54 footer (60+ LOA and 25+ tons) the disadvantages are hardly noticeable. I reckon I probably wouldn't want a thruster on a boat less than about 45 feet, and I would certainly never want one on a catamaran, where weight is so important to performance, and where you can do magic with dual engines anyway.

I think we mostly are in agreement. But as I said earlier, our yard has done a full set of polars on a 54' boat before and after installation of a faired thruster tube. The differences weren't great, but they were there. So I wouldn't say the disadvantages on a boat that size are "hardly noticeable". Though I suppose it depends on how you cruise whether you would notice or not. It really comes down to performance in very light airs and fuel efficiency. I can however totally understand not being too worried about losing a bit of fuel efficiency and light air performance if those are not problems for you, I just think people who read this that may be considering a thruster should do so with their eyes open. As an earlier poster said, the Amels all come with retractable thrusters because they did a lot of testing on tube thusters on boats in this size range and didn't like what they saw. They are not the only ones. I certainly agree that many of the drawbacks are mitigated on a larger boat, such as the amount of space taken up. But I don't think the performance hit is much less. Bigger boats have bigger tubes.

[Nibiruwayne]

Yes, and the center cockpit helm of an amel suits a particular type of sailor.
I wonder if a thruster tube on a cat would negatively affect the windward point of sail and tacking ability? Any thoughts?

[Auspicious]

Originally Posted by Nibiruwayne

I wonder if a thruster tube on a cat would negatively affect the windward point of sail and tacking ability? Any thoughts?

Probably. Want to know for sure? Drop a bucket on a line off the bow and go sailing. It's just resistance.

[Tim Godber]

So much depends on the boat, and the docking methods in your area!
I had a Sabre 38, I loved it but HATED going astern, sometimes hated going forward, because those boats had the shaft offset 15 degrees which caused it to sit alongside the boat, some maneouvres were well night impossible til I fitted a BT, and at the same time a saildrive on the centre line. There will be those that say I dont know how to drive a boat, but this was the only boat to cause me problems in 45 years of cruising!
Until I bought my Little Harbor! No offset problems here, but the same long keel, luckily though she has a BT because I cruise in the Med where it is all about going stern to, on occaisions the BT has failed, and whilst I can cope, I really do want the BT!

[Dockhead]

Originally Posted by minaret

I think we mostly are in agreement. But as I said earlier, our yard has done a full set of polars on a 54' boat before and after installation of a faired thruster tube. The differences weren't great, but they were there. So I wouldn't say the disadvantages on a boat that size are "hardly noticeable". Though I suppose it depends on how you cruise whether you would notice or not. It really comes down to performance in very light airs and fuel efficiency. I can however totally understand not being too worried about losing a bit of fuel efficiency and light air performance if those are not problems for you, I just think people who read this that may be considering a thruster should do so with their eyes open. As an earlier poster said, the Amels all come with retractable thrusters because they did a lot of testing on tube thusters on boats in this size range and didn't like what they saw. They are not the only ones. I certainly agree that many of the drawbacks are mitigated on a larger boat, such as the amount of space taken up. But I don't think the performance hit is much less. Bigger boats have bigger tubes.

I care a whole lot about sailing performance, so I would be concerned if you are right about the performance hit. It seems to me that tube size -- area of the tube openings and thus drag - falls off sharply as a % of total wetted surface as boats get bigger, but I admit that I have not done the math.

I have no way to compare my boat's performance with and without a thruster, as all M54's were built with thrusters (all 55 or however many were built; it was not a production boat). But I don't feel any hit - I average well over 8 knots on long passages - on a pace for 200 mile days. That's an average over 12 Channel crossings. Despite now 12 year old sails, and in-mast furling main - another thing certain old salts will tell you will turn your boat into a slug and utterly ruin its performance

[Irish rambler]

Just following the thread and someone mention the Benetau cruisers with joystick controls, it's not rocket science, simply a sail drive/bow thruster controlled by joystick. They are used as hireboats here on the canal du Midi in France. The hirers don't need any permit and get 10 mins training maximum, to see them maneouvering after they leave the hireboat bases is mind boggling and the boats have the battle scars on the hulls to show for it.