Bow or Stern Thruster?

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Greetings,
Thread drift alert!!! Might one install a Thistle/Fishtail/Schilling rudder on a planing hull?


The low speed (600 RPM idle) maneuverability of our "small" boat (1979 Penn Yan 23' Sportfish) is abysmal. Handles quite well at anything above 1200 RPM and corners like it's on rails when on plane (2200 RPM-23 MPH). Admittedly, she does get a bit "squirrely" when approaching 30 MPH.



I suspect she may become "squirrely" at a lower speed and "skivvy soiling"/ dangerous at 30 MPH. Is this a safe assumption?


Thanks.
 
MurryM,

Thanks for the URL link to the Wikipedia article about "Schilling" rudder -- very informative and interesting!
 
A hearty and grateful THANK YOU to everyone who responded to my question, sharing your experience, knowledge, and advice. I greatly appreciate your collective insight and explanations.
 
Comodave said:
Did you do the install yourself or did you pay to have it installed? I have been looking at the Exturn pod thruster if I can figure a way out to access the interior without ripping out all of the forward cabin.
Click to expand...

We also have the Exturn pod thruster, and it is a true DIY install. In fact the physical install can be done in 1 day in the slings- the mounting holes are 1 2" and 2 5/8" holes (double on a Duplex thruster). The larger hole carries the weight of the thruster, and carry the control cabling.

Drill the holes, mount the thruster, and put the boat back in the water.

All the wiring can be done with the vessel afloat.
 
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My problem is getting access to the inside to do the bolting and wiring. President very thoughtfully built the forward berth offset to port so the starboard side of the berth is on the centerline of the deck. Not sure how I can get an access port to the bilge area. Have been thinking on this for a while...
 
i have never seen a boat with a stern thruster and not a bow thruster

a bow thruster is much more valuable if one had to pick

some boats that have it as a factory option may have some stuff in-place making it easier to retrofit. there are companies that can install thrusters quite easily in most boats.

i dont think a boat lacking a thruster would be a reason not to buy unless you really need it and it cannot be retrofitted for some reason.

twin screws are usually easy to maneuver and you only really need to worry about thrusters with single screw
 
Comodave said:
My problem is getting access to the inside to do the bolting and wiring. President very thoughtfully built the forward berth offset to port so the starboard side of the berth is on the centerline of the deck. Not sure how I can get an access port to the bilge area. Have been thinking on this for a while...
Click to expand...

Interesting...how much access do you have? The thruster can go deep on the forefoot...
 
I have not cut a hole to see what room I have, yet. I have to do some more measuring first. I have a water tank that goes way into the bow under the deck. I don’t have anywhere else to put the water tank and can’t get rid of it since I only have 120 gallons now. A bow thruster isn’t on the top of my list so I really haven’t even put much effort into it yet.
 
SOJOURN4 said:
My vote is a bow thruster
We have a 44 Swift Trawler with both bow and stern thrusters.
Bow thruster helps get the bow in control
Click to expand...

I have an undersized bow thruster on my N43, and am considering adding a stern thruster instead of ripping out the bow thruster and replacing it. As the stern thruster is cheaper, I think I am going to start with that, and hope not to have to replace the bow thruster.
Best,
Maldwin
 
I don’t understand why they put undersized thrusters in boats, the incremental cost to get a proper sized or even oversixed thrusters isn’t that much. Then you have a thruster that will work even when the wind is blowing. Understand your pain.
 
Size the thruster for what conditions? If you size it for worst case cross wind and cross current conditions, it will be huge.

Mine could be considered undersized and there have been a few times where it was beat by the conditions. But with some technique I have always been able to do what I wanted to do.
 
I went 1 size larger than what was in the chart. Not overly large but it will move the boat in 25 mph wind easily.
 
My N46 had, IMO, an undersize bow thruster. I almost ended up on the rocks.
Tripled the bow thruster motor, double propeller, 24 vt. Through the magic of the yard, they put in an automatic switch to get 24 vt from my 12 vt 8D house batteries when using the bow thruster. That thruster was so strong, no need to use it beyond 3 or 4 seconds. SMILE A very worthwhile investment. They used the same tunnel.

No need to add a stern thruster..... spring lines or a bow line to the mid ship dock cleat. (bow in) Tinker with the rudder can move your stern in, secure the stern lines, one stern line to the midship cleat on the dock, tinker with the rudder, move your bow in, cleat it off, re-cleat the stern line and presto, secured to the dock. Yup, sound easy.... practice practice practice and you too can impress the folks on the dock. Of course if it is a 90+F, sunny and humid, you will break a big time sweat if you are the line handler.
If you try this, you too will be impressed with the ease you can bring the boat to the dock.
(IF you are a big distance to the dock, use the stern line only, tinker with the rudder and you will move the stern in)

Remember, a left turning prop, position the rudder approx 30 degrees to the port, minimum throttle, you will back straight. Practice practice practice....

Not only will you impress those who are watching but you will also impress yourself. (Remember: look cool, and confident, humble)

Remember to wear the proper ratty old captain's hat and look "cool" while doing this.
If you can impress folks with your docking skills, you are to be deemed "salty".

The key is, practice practice practice (without the hat. LOL)
 
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Comodave said:
I don’t understand why they put undersized thrusters in boats, the incremental cost to get a proper sized or even oversixed thrusters isn’t that much. Then you have a thruster that will work even when the wind is blowing. Understand your pain.
Click to expand...

I rarely use the bow and stern thruster. One time I was pinned against the dock though in strong current and 20-25+ wind gusting 35+. Had to use thrusters and a lot of engine power to get off during a break in the gust.
 
Bow Thruster

As an installer of thrusters I always recommend a Bowthruster first. The reasoning is that with both a single or twin engine vessel the control (movement of the vessel) is always at the stern when docking. The bow thruster will move the bow in the desired direction and the engines will move the stern. Now as some have mentioned here the biggest problem I see is that people undersize their thrusters so they do not get the desired results. I usually size the thrusters based on the boat being in an average wind of 15mph and some current.

Remember the major cost of installing a bow thruster is installing the tunnel, price wise there is not much difference say installing a 6"tunnel vs a 10"tunnel. Equipment cost is a little more but you can achieve a lot more thrust with a 10"in lieu of a 6"thruster. Now there are other factors involved as well, draft at the bow, height of the vessel, tunnel location 12VDC motor (say 5 HP) Vs 24VDC motor (13HP) on the same drive leg will also give you more.
 
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Bow thruster before stern.
Hydraulic before battery.

One thing I've learned recently with my Wesmar Hyd. Thrusters is cleaning the back (inaccessible), side of the counter rotating thruster props is essential. Any barnacle, even when just on one side of the blade, makes them useless - lots of wash but no thrust!.
Luckily I'm in the tropics so I need to make a tool to be able to scrape the back side clean and still have knuckles.
Just one more job!
:facepalm:
 
I would chose a bow thruster wither a single or twin screw boat,
you can always work the stern with the engine(s) and/or rudder.

Also, when going astern a bow thruster becomes a very effective "rudder" as the vessels pivot point is now near the stern of the vessel which creates a long lever arm and thus a lot of leverage.

I have handled many ships with bow thruster and single screw, I can't ever remember one that had a only a stern thruster.

Always remember that bow thrusters lose 50% or more
of their effectiveness once the speed is greater than 2 - 3 knots,
when going ahead.
 
No one has mentioned the difference between hydraulic and DC electric thrusters. If the boat has stabilizers and at least one PTO, then hydraulic is nicer because you can toggle a hydraulic thruster for much longer periods of time. Our boat came from factory with a Keypower hydraulic bow thruster so the addition of a hydraulic stern thruster at our yard was a matter of some fabrication and running of hydraulic lines. Obviously this is all a mute point if the boat does not have a hydraulic setup with a PTO.
 
On my single screw Apollo 32 I had a terrible time within the marina fairway getting the bow to come up against the wind. A 3.5 hp. Lewmar bowthruster made an incredible change in handling. The local boatyards quoted $12-15,000 for an install, albeit with a slightly pricier thruster unit.


In the end I completed the parts, controller and installation, including the assistance of a marine electrician to install breakers and heavy cables for just under $4,000. Best possible upgrade.
 
Even a single engine boat can prop-walk the stern to the dock once the bow line is set and your line-handler has a fender in her hand. Keep hold of the fender line, drop the fender down to the waterline near the bow, don't tie it to the boat, keep it loose so the handler can slide it along to where it might be needed. If you are starboard to (the dock, that is), put the wheel hard a'starboard, put the engine in idle reverse and with a little practice the stern should walk to the dock. You can even leave it running in this configuration while you leave the cockpit to affix your stern line. Don't forget to go back to the cockpit to put the transmission in neutral and shut down the engine when temps and pressure have stabilized.
 
Confetti

We have a Krogen 39 that came without either thruster. We installed a bow thruster 3 years ago and have been thrilled with the performance
 
All you need on a single engine boat is a bow thruster and to be able to swing the rudder 40 degrees. The side push from the engine in forward with the rudder hard over will be more powerful than a stern thruster.

Ted
 
Power accordingly

steelydon said:
I have a 40 Eagle w/single engine. It came with a bow thruster and 4 years ago I installed a Lewmar stern thruster. If I could choose only one it would be the bow for all the reasons rsn48 cited. I have installed both and the stern is much easier but with a reasonable amount of fiberglassing and wiring skill you can do either.
Click to expand...

Agree with steelydon, but also want to reiterate the need for Power. I have Vetus 75 kgf on bow and stern but like many here, stern is a nice to have while bow will keep you nice and close
 
Boilermaker75 said:
To all owners of 40-foot+/- single-screw trawlers, who have experience using either bow or stern thrusers:

If you had your choice between two nearly identical boats, one with a bow thruster (only) and the other with a stern thruster (only), which would you choose?

What are the advantages of having a bow thruster over having a stern thruster?

What are the advantages of having a stern thruster over having a bow thruster?

Thank you in advance for your consideration and feedback responses, experience, opinions, and advice.
Click to expand...

We have a Mainship 34 with single screw, though it’s closer to 40 feet then 34. Our marina is very tight and even center consoles have difficulty docking at times. The boat came with the bow thruster which is terrific but not sufficient for tight docking. It was relatively easy (write a check) to add a stern thruster once we knew we needed it to safely get into our narrow slip. I do not believe it would be as easy or cost-efficient to add a bow thruster.
 
How about a Jet thruster? Put the nozzles at both ends of the boat.
I saw one of these in operation on a 120' boat that managed to squeeze into a mooring that was a challenge for me on my 44 ft. Much of the movement was done with the jet nozzles. That was maybe 20 yrs ago and I haven't seen another.
Google "Jet Thrusters" and lots of availability shows up, especially for smaller boats.
Yet nobody here is talking about them.
 
My bow thruster (24-volt) spins me like a top. :)
 
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