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Bow thruster vs stern thruster

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    #16
    I have often wondered this very question. Obviously I can rotate the boat without any thruster, so would it be feasible to rotate the bow one way while using the stern thruster to stop the stern from moving.

    For instance say you are backing into a slip and either wind or current is pushing you away from the dock toward the neighboring boat. The first goal is to avoid the bow swinging out by using an angled approach, but in some instances by the time you get backed in the bow is pulling out. I typically have the person on the stern lock down a line on the first available cleat and then steer into the dock forward--with the line in place the stern stays against the dock and the bow comes in. Why couldn't we do the same with a stern thruster instead of a line.

    The idea being that you use the engines to push the bow in and use the stern thruster to prevent the stern from moving.

    I think this is the long winded version of what Gordon has been asking and is something I have wondered as well--I can justify the cost of a stern thruster and the installation isn't nearly as difficult--the bow thruster is just not justified imho when we are able to get along without it.

    I am interested to hear how the experiment goes!
    2000 Bayliner 4788 "Perfect Balance"
    370HP Cummins
    Zodiac YL 340 30HP Nissan
    Moored at Roche Harbor

    Comment


      #17
      Gordon, if you do plan to proceed with the stern thruster, I would suggest you get one that has the motorhead protected/enclosed... several aren’t and are exposed for air circulation, Additionally build a dam around it to provide protection from water splashing etc on connections as they sit relatively flat, and even consider a Perspex cover for further protection from water dripping from the cockpit areas/drains. Several friends have had water intrusion into the motor head, that required replacements, which are not inexpensive. Water typically can trickle, slosh around in the back, particularly rain water leaks.

      Depending on the motor projection and angle, you may need to modify the rudder tie arm. A fibreglass block on the water side of the transom may also be necessary to allow for the motor head to sit back. Anyway, careful planning is required to ensure the thruster selected satisfies your needs and fits accordingly... Let us know how you go and the quotes/costing. I think you’ll be surprised that the stern isn’t that much cheaper from the install shops (maybe 70% of the bow cost).

      Cheers
      John H
      Brisbane QLD Aust
      "Harbor-nating"

      2000 - 4788/Cummins 370's

      Comment


        #18
        Thanks again guys. First comes a sync up to do a bit of empirical work, then some observations, then a decision about whether or not to proceed. I’ll get some 4788 specific pricing along the way.
        Patti & Gordon Lewandowski
        Sammamish WA
        1998 4788 (April 2018)
        ”Knot Home”

        Comment


          #19
          We love our thruster and frankly will never have a boat without one. It makes life so much less stressful in docking. I opted for a external thruster and saved about 4k in the process. I had it installed in a boat yard but after all said and done I would DYI the next time. There are pros and cons to any thrusters be it tunnel or external mounts but I really like the one we selected. Here is my you tube coverage

          https://www.youtube.com/channel/UCSz..._as=subscriber

          https://www.youtube.com/watch?v=4-VxtKtAR-Q

          https://www.youtube.com/watch?v=CjsCg5VTJqQ

          Guntar
          1999 3988
          Cummins 270s

          Comment


            #20
            Originally posted by jmoultray View Post
            I have often wondered this very question. Obviously I can rotate the boat without any thruster, so would it be feasible to rotate the bow one way while using the stern thruster to stop the stern from moving.

            For instance say you are backing into a slip and either wind or current is pushing you away from the dock toward the neighboring boat. The first goal is to avoid the bow swinging out by using an angled approach, but in some instances by the time you get backed in the bow is pulling out. I typically have the person on the stern lock down a line on the first available cleat and then steer into the dock forward--with the line in place the stern stays against the dock and the bow comes in. Why couldn't we do the same with a stern thruster instead of a line.

            The idea being that you use the engines to push the bow in and use the stern thruster to prevent the stern from moving.

            I think this is the long winded version of what Gordon has been asking and is something I have wondered as well--I can justify the cost of a stern thruster and the installation isn't nearly as difficult--the bow thruster is just not justified imho when we are able to get along without it.

            I am interested to hear how the experiment goes!
            At the risk of offending some of the posters - simply stating that a stern thruster only is worthless or even dangerous seems to be an opinion and nothing more. Sorry - but I’m looking for experience, not opinions. Once I sync up with Drew and have a chance to do some empirical testing I will report back (as Drew might do as well). I’ve repeatedly asked my question in the context of applied physics and not theoretical physics (to borrow a phrase). How about we put this on hold until I/we have time to do some experimentation or someone with both does some real world testing using only their stern. I’ve made good use of lines, fenders, and dock cleats to handle a lot of tricky situations but I’m not a purist...... So until later, I’m on hold.
            Patti & Gordon Lewandowski
            Sammamish WA
            1998 4788 (April 2018)
            ”Knot Home”

            Comment


            • Shipsngiggles
              Shipsngiggles commented
              Editing a comment
              Gordon, I would say that just physics of bow vs. stern, when applied to the conditions, will show that one is better than the other. The beauty of the world we live in is that it can easily be described through the world of math and physics and any relevant testing to show the difference would need to be in 15-20 knot winds, which would be a dangerous testing ground.

              We can talk personal experience and opinions but as someone who has dedicated my life to use of science I have to say that evidence is hard to dispute when you apply basic laws of physics.

            #21
            Hey Gordon - I’m going to risk a partial answer but not offer an opinion. Our 490 had a bow thruster installed by the PO. The bow of the 4788/490 is, obviously, much lighter than the stern and doesn’t draft much water. That allows wind to blow it around much more easily than the stern. I find the bow thruster allows us work against the wind in ways we would not be able to without. I look forward to seeing your results with Drew and appreciate the focus.
            Shawn Hammer and Geri Schaffer
            G-dock, Shilshole, Seattle
            2005 Meridian 490
            2016 Walker Bay
            M/V 2nd Circus

            Comment


              #22
              Well I’ve had over 110 posts on the Trawler Forum which is interesting. Drew and I will do our empirical testing/adult play thing next week. All results are of course filtered thru owners eyes and the fact that we have boats with twin engines, soft chines, moderate windage, relatively small rudders, minimal keel, and moderate (to be generous) forefoot. Let the games begin!
              Patti & Gordon Lewandowski
              Sammamish WA
              1998 4788 (April 2018)
              ”Knot Home”

              Comment


                #23
                Sounds like testing with Drew is the perfect plan. It will be interesting to see what your results are. Sounds like he has the perfect setup to get real data. Just make sure you use it in various conditions that are appropriate for how you use your 47.
                My (biased) guess is the bow thruster would be more effective, but as you say at twice the price is it worth it over the stern thruster only. Having a Sidepower SE100 in the bow of our 38, we find it very effective docking, locking etc. While we can walk the boat sideways, I still think about installing a stern thruster for the ultimate in manouverability.

                James
                1989 Bayliner 3888, 175 Hinos,
                Hurth 630's Onan 8kw MDKD
                Lowrance Electronics!
                Boating on Georgian Bay & the North Channel
                Completed the Great Loop 07/25/19
                AGLCA #8340
                MTOA# 7469

                Comment


                  #24
                  Has anyone installed the new side thrusters I've been hearing about? Seems like a great idea. I got a call from a guy in India asking for my Visa number to send me a couple to introduced them to North America.

                  JV

                  Comment


                  • Jeffw
                    Jeffw commented
                    Editing a comment
                    Too late. I already gave them your Visa number, got a bunch of cool stuff on the way.

                  #25
                  So Drew and I went out on his 4788 today for a brief, yet instructional “cruise”.

                  The wind was light and northerly. Drew’s slip is oriented more or less N/S, stern in, bow facing south. His entryway is narrow, not much wider than is LOA.

                  Drew used transmissions and stern thruster only to exit his slip. The breeze was behind the boat. Using fwd/rev “twist” and the stern thruster he was able to maneuver within the constrained area and not only his slip but also his “lane”.

                  We continued westbound toward a fuel dock under a freshening breeze that was variable in direction by 5-10 degrees and “on the nose”. He maneuvered parallel to the dock with the bow leading and used the stern thruster to tuck in the stern.

                  It was clear that in these conditions the difference in assist between bow thruster only and stern thruster only was negligible. In windier conditions or in the presence of a strong current - YMMV. Our boats have almost no keel, twin engines, and soft chines. It was fairly clear that an assist from either end would result in a pivot at about the same spot fore and aft. Some conditions might favor a thruster at one end or the other; however, that advantage could be offset if a different approach was possible.

                  We could have stayed out for a much longer time testing every possible combination and permutation but it didn’t take long for both of us to reach the same conclusion that any advantage from one or the other is an “it all depends” answer even with the same hull. Proficiency, wind, current, etc. would probably have more impact than thruster location. If a bow thruster was 20%-30% more expensive then for any number of reasons (like resale) I’d spend the added amount. But after our empirical testing, in my opinion a bow thruster does not give a 1.5x or 2x advantage. I can also state that for me - although a thruster is no substitute for skills, prep, intelligent use of fenders and lines, etc. - I do miss having the extra security in close quarters boat handling provided by a thruster.
                  Patti & Gordon Lewandowski
                  Sammamish WA
                  1998 4788 (April 2018)
                  ”Knot Home”

                  Comment


                    #26
                    Post script - I/we should have probably done a bit more “testing”. My one other observation is that if you have a competent crew and a good way to communicate (e.g. headsets) and you’ve got lines and fenders properly set - thrusters are a wonderful nice to have but old fashioned handling skills and a willingness to back off and retry are a rewarding combination. For now I’ll forgo the expense and invest in fuel for an aggressive 60-day major cruising schedule this summer.

                    My thanks to Drew for helping me “prove” that my high school physics grades were not a fluke and to all the folks who responded.
                    Patti & Gordon Lewandowski
                    Sammamish WA
                    1998 4788 (April 2018)
                    ”Knot Home”

                    Comment

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