Stern thruster

[patrick and linda]

I would like to install a stern thruster to my swim plate form and to do so without robbing the bank! Any ideas?

 

[hardee]

This is not intended to be a smart alek answer, but you already have twins back there. I'm assuming you want the stern thruster primarily for docking, right? Try backing into the dock, and then twist the boat up against the dock with using the engine that is on the opposite side from the dock in forward and the other in reverse. Easy up to the dock, and a lot cheaper than adding another thruster.

Harvey
SleepyC :moon

 

[thataway]

Although a stern thruster can be an aid in many boats--with the C dory outboards, and especially twins, I don't see where there is any advantage, especially considering the costs (thru hulls, the area where the motor will go, the batteries,

I have only owned one boat with any type of thruster, and this was on an aft cabin single engine diesel 32 foot trawler, pilot house, and FB gave huge windage. I didn't use the bow thruster a lot, but it was handy in some circumstances. Where I would have benefitted the most was the 62 foot sailboat we took to Europe and back form Calif. We always worked with what we had, but a thruster would have made it easier.

The logistics and hydrodynamics are an issue. Any stern thruster should go in front of the outboard. If under the swim platform, it will be pushing the water against the lower leg of the outboard. basically it will not move well on way--and may only move in the opposite direction which you think it will--because of the back flow from the outboard leg.

How are you going to protect the motor? (Usually stern thrusters are used in Inboards, with the motor inside the hull.

You may be thinking of one of the "Pod" type of thrusters. SideShifter or Yacht Thruster These start in the $4,000 range installed, and there will be a lot of issues even though the motor is in the "pod"..

What is the typical use that you foresee?

 

[Kushtaka]

You have two stern thrusters already!!!

You can't build this into your hull as it is too flat. If you had a 22* deadrise boat you might be able to put a stern thruster in a tube. This is seriously going to be something that you will spend a lot on and get unsatisfactory results.

Spend that money on a good instructor to teach you how to split your twins and spin your boat on a dime, as-is.

A bow thruster (while also somewhat impractical) is more likely to be useful in helping with close quarters maneuvering. With a bow thruster you can make a flat-bottomed boat like a CD27 move sideways if you do your part splitting the twins.

 

[thataway]

Stern thrusters in small boats are rarely built into the hull like bow thrusters. They are bolted thru the transom, with an integral tube.

 

[starcrafttom]

I always thought that if you cut the head off a electric trolling motor and mounted it under the swim step it would act as a stern thruster using the forward and reverse of the motor to push the boat side to side. you can pick them up cheap at kmart of craigslist.

 

[Kushtaka]

Stern thrusters in small boats are rarely built into the hull like bow thrusters. They are bolted thru the transom, with an integral tube.

Yes, but as you pointed out, the twins, or even a single outboard will block the thrust thereby making it work more poorly. I think it could be done in an outboard config with an amply bracket that would clear the thrust from the outboards.

I just imagine it could be done in the hull like a bow thruster on a deep v with outboards, but not a dory.

I can envision a well-supported metal structure surrounding the outboards (protecting them also) and supporting a stern thruster. But can't see it otherwise. The requirement that this not be expensive may eliminate this option.

 

[Kushtaka]

I always thought that if you cut the head off a electric trolling motor and mounted it under the swim step it would act as a stern thruster using the forward and reverse of the motor to push the boat side to side. you can pick them up cheap at kmart of craigslist.

This is a very cool idea. It could give you the ability to use some of the newer transducers that mount on trolling motors too. The only issue I see is the ability to steer the trolling motor and the regular outboards from the helm, but there has to be remote controls, etc. I don't use these often, so I don't know, but I think AP on my lowrance HDS has a special interphase to run a specific trolling motor. Perhaps they will build a bow/stern thruster patch for their software and you can do it all from the helm!!

 

[ssobol]

Yes, but as you pointed out, the twins, or even a single outboard will block the thrust thereby making it work more poorly. I think it could be done in an outboard config with an amply bracket that would clear the thrust from the outboards.
.

From what I have seen the diameter of thrusters can be pretty small for smaller boats. I expect that there is enough gap between the transom and the engine leg (below the engine mount) to let a stern thruster be effective. You can always tilt the motor(s) up a little if needed.

I would think that with an outboard you wouldn't need a stern thruster. I think a bow thruster would be more useful. However, a bow thruster would be much harder to install than a stern one. The other issue with a C-Dory is that the bow may not sit deep enough to make a bow thruster very effective.

One thing that did occur to me might be to use a bi directional water pump and some hose or piping. You could install the hose outlets lower on the bow (and they could be smaller than a thruster). The pump could be mounted where necessary (don't need a straight through pipe). A pump of sufficient capacity (gpm) could produce sufficient thrust for a boat like a C-Dory (I think).

 

[Aurelia]

They do have trolling motors with remotes and even steering but the steering motor adds a lot of bulk so hiding it under the swim step would get really tough. Mounting one of the simple motors to the back of the boat somewhere oriented sideways and wired to a simple three way left/off/right switch at the helm seems feasible to me, but the standard underslung swim ladder would complicate mounting it to the underside of the swimstep.

A folding top mount ladder could solve that.

I would rather mount it to a simple pivot like a outboard so it could be tilted easily into and out of the water when needed.

We have a bow mount motor with remote but I have never used it for docking. I have used it twice for un-docking. We have used it to quietly leave a marina very early without starting the main and waking up the neighbors. It works very well for that.

Greg

 

[thataway]

There are certainly ways that a trolling motor could be utilized as a stern thruster on a C Dory, but in reality, especially with twins, it is just not necessary. Prop walk will work well. (Now just get the counter rotating lower hp outboards--maybe adapt the lower units of larger motors?

One of the major problems with any tunnel in the hull is turbulence. In the bow, you will notice all sorts of dips and bumps to minimize this effect. If you put a tunnel in the stern, even with 26 degree dead rise, the turbulence would kill any outboard efficiency.--and most likely make the boat unmanageable at planing speeds. The reason they are put on the flat of the transom on inboards, is to get away form any running turbulence at semi displacement speeds on up.

There are several "pod" type of bow thrusters, which might work for the C Dory--in fact, I believe that some one did put one in. Again, this is really overkill, but if you have a lot of money, and don't want to trailer, it will work.

Note that the last graphic does show a stern thruster mounted on the swim step of an I /O. It will be in a turbulent area, but will still give some increased drag. It is aft of the I/O unit--and would work as a thruster in this case.

There are also bow deck mounted thrusters...but that has its whole set of issues, with mounting and deck space. I have an 83# thrust trolling motor on the Caracal--works well on the cat because of almost square profile, and lays on the gunnel forward[/url]

I am sure that the jet type of Thruster, has improved, but I delivered a Morgan 62 a number of years ago, with the 2" jet type of thrusters, and they were almost worthless.

One of the smallest stern thrusters, is the modified Lewmar 2 hp bow thruster (about $1800, with stern thruster kit, $1300 without). It has a tunnel diameter of 140mm. about 5.5". This is pretty good size stuck under a swim platform. Lewmar makes a 110 mm (4.3"), but no conversion kit--possible, that could be used, but so many issues keeping the motor dry! A trolling motor or pod would be much better.

 

[Kushtaka]

I'm learning! This is fun!

 

[thataway]

Kushtaka's comment about putting a thruster aft of the motors, brings out that there is a thruster made for pontoon boats. It sits between the hulls, and a touch of a button at the helm lowers the thruster (sort of like a trolling motor) down into the water. That could be adapted to a bracket, or even the bracket could be made to pivot down into the water...! Lets see, maybe we could dual purpose that "motor" into a wind generator, while it is flopping around in the breeze! :roll:

 

[Aurelia]

That is a clever product I had not seen before Bob. It's about 16 inches wide by 36 long by 10 inches deep in the retracted position. That would take a pretty large swim step!

I am sticking with the throttle and wheel. We love our trolling motor but don't always carry it, and would not have considered adding it for docking use alone.

Greg

 

[starcrafttom]

Now that I think of it they make a trolling motor that mounts to the back of your out board. If you mount it side ways it would act as a thruster. At cruising speed it would be out of the water.

trolling motor

 

[Sea Wolf]

Now that I think of it they make a trolling motor that mounts to the back of your out board. If you mount it side ways it would act as a thruster. At cruising speed it would be out of the water.

trolling motor

Like this?



That's my Engine Mounted Tolling Motor by Minn-Kota. It would be OK at full speed where it would be out of the water (being above the anti-ventilation plate), but would drag some at displacement speeds. Would work find as a thruster, though. Would be nice to have a servo to turn it from forward to sideways use as needed.

Joe. :teeth :thup