Stabilizer fin positions

[BCRyan]

Our boat has been hauled and I'm starting on a number of tasks, including installing Spurs in front of the props, rebuilding the Hynautic trim tab cylinders, installing a new DFF3D sensor, and installing line cutters in front of the stabilizer fins.

One thing I've noticed with the fins is that they are both sort of "toed out". With them pinned (in what I assume to be "centered"), they are each pointed outward a bit when looking forward. I haven't yet talked to Naiad about this, but first wanted to pick this forum's thoughts on whether this seems correct. Hopefully these pictures show roughly what I'm talking about. Particularly with the starboard fin, I tried to line up the perspective of the camera with the fin, which points it 3-4' inward of the aft corner of the boat. They do, at least, seem to be symmetrical.

Most of my concern stems from the fact that the previous owner had Naiad out numerous times to work on the stabilizer system, and in each case, he mentioned that the techs really didn't seem to have a very good idea as to what they were doing, on the phone with the factory the whole time, lots of iterations, etc. Thus I'm not taking for granted that they have been set up correctly.

Thoughts?

 

[JD5652]

I just had my Naiad Model 252's installed. In my case, they set up the "center" while the boat was in the water. It is primarily dependent upon where the mechanical center of the fin actuator was installed relative to the hull. The "center" is defined by where the pin goes into the actuator to "pin" it in place.

IF the pin is not actually installed and you are determining the "center" by the electronic display, then the fins may not actually be "centered".

You might want to check to see if the pin will easily slide into the actuator if it is not already installed.

If the pin is installed AND the fin is not centered, then other than artificially offsetting the fin alignment by adjusting the fin potentiometer in the setup procedure, I do not know of any other method to realign the fin after the system is installed.

But take my opinion in context as I just had my system installed, but was there when the system was set up and asked LOTS of questions.

Best of luck!

 

[BCRyan]

I just had my Naiad Model 252's installed. In my case, they set up the "center" while the boat was in the water. It is primarily dependent upon where the mechanical center of the fin actuator was installed relative to the hull. The "center" is defined by where the pin goes into the actuator to "pin" it in place.

IF the pin is not actually installed and you are determining the "center" by the electronic display, then the fins may not actually be "centered".

You might want to check to see if the pin will easily slide into the actuator if it is not already installed.

If the pin is installed AND the fin is not centered, then other than artificially offsetting the fin alignment by adjusting the fin potentiometer in the setup procedure, I do not know of any other method to realign the fin after the system is installed.

But take my opinion in context as I just had my system installed, but was there when the system was set up and asked LOTS of questions.

Best of luck!

Thank you! I followed your install with great interest. : )

The fins are currently pinned, and that "pinning" is what's causing the toe-out. However, I don't necessarily trust that "pinning" equals "centered", as the arm that pins them is adjustable in length.

Thus, if we were to decide that the fins should be centered relative to the centerline of the boat, then I would adjust the pinning arms accordingly and then tweak the potentiometer so that the pins would align when the fins are actively being driven to center. Hopefully that makes sense...

 

[Juliet 15]

I have Naiads as well, interested to see how this develops.

 

[AnsleyS]

We also have stabilizers and I have been involved with the removal and rebuilding of some of these. The proper way to do this is to remove the fins with the pins in place and reset them in the proper alignment. One can then align the center position of each fin to the pinned position with the servo ajustment screw under the hex cap on each servo. One then knows that each fin is centered when the centered position is selected on the control.

The centered position is not necessarily straight fore and aft. It is when the fins are straight in the water flow around each fin when under way at cruising speed. An evaluation of your hull shape may indicate that a slight deviation from fore and aft is indicated.

 

[BCRyan]

We also have stabilizers and I have been involved with the removal and rebuilding of some of these. The proper way to do this is to remove the fins with the pins in place and reset them in the proper alignment. One can then align the center position of each fin to the pinned position with the servo ajustment screw under the hex cap on each servo. One then knows that each fin is centered when the centered position is selected on the control.

The centered position is not necessarily straight fore and aft. It is when the fins are straight in the water flow around each fin when under way at cruising speed. An evaluation of your hull shape may indicate that a slight deviation from fore and aft is indicated.

Thank you - very helpful. From this, I'm deducing that the proper way to do this might be something like:

1) Determine "centered" by running the boat at speed with the stabilizer system unpowered -- the fins should freely be able to align themselves with the water flow.
2) Note the position and then adjust the servo to match this when the system is on and centered.
3) Finally, align the pinning arm to also match this position.

 

[twistedtree]

Thank you - very helpful. From this, I'm deducing that the proper way to do this might be something like:

1) Determine "centered" by running the boat at speed with the stabilizer system unpowered -- the fins should freely be able to align themselves with the water flow.
2) Note the position and then adjust the servo to match this when the system is on and centered.
3) Finally, align the pinning arm to also match this position.

You have identified the two key positions; 1) being hydro-dynamically centered, i.e. zero lift from the fins, and also minimum drag. And 2) the locking position.


The key is that these may not be the same, and may not be required to be the same. I can't speak for Naiad, but with ABT they don't have to be the same position.


And your approach is sound to let the fins tail freely underway and they will find the hydro-dynamically centered position on their own. But allowing them to tail freely may be easy or hard depending on what the control system provides. You just need to be sure teh system isn't holding them hydraulically in some position that it thinks is "centered".

 

[BCRyan]

You have identified the two key positions; 1) being hydro-dynamically centered, i.e. zero lift from the fins, and also minimum drag. And 2) the locking position.


The key is that these may not be the same, and may not be required to be the same. I can't speak for Naiad, but with ABT they don't have to be the same position.


And your approach is sound to let the fins tail freely underway and they will find the hydro-dynamically centered position on their own. But allowing them to tail freely may be easy or hard depending on what the control system provides. You just need to be sure teh system isn't holding them hydraulically in some position that it thinks is "centered".

Thank you -- great points!

You bring up that the locked position doesn't need to be "centered", which I would generally agree with... but it seems like it would be easier to pin them if the locked position equals the centered position when powered.

My system has three modes, OFF, CENTERED, ACTIVE. I'm assuming that when OFF, the fins are allowed to move freely.

Once the boat is back in the water, I'll give this all a try.

 

[twistedtree]

Thank you -- great points!

You bring up that the locked position doesn't need to be "centered", which I would generally agree with... but it seems like it would be easier to pin them if the locked position equals the centered position when powered.

My system has three modes, OFF, CENTERED, ACTIVE. I'm assuming that when OFF, the fins are allowed to move freely.

Once the boat is back in the water, I'll give this all a try.

Again, my knowledge is with ABT, so Naiad may be different.....


I think in a perfect world all these positions would be the same. I think the issue arises because at installation time the guidelines are to set the fins parallel to the keel because you have no way of knowing where the hydro dynamic center is. Then the locking mechanism gets installed as close to that position as possible. But parallel to the keel isn't necessarily hydro dynamically centered since you can have all sorts of flow patterns over different hull surfaces. Parallel is as good a starting point as any, and for some boats may be hydro dynamically centered too. It's just not guaranteed to be right, hence the need to allow for different positions.


With ABT, Off would pin the fins, Centered would hydraulically hold the fin at what is believed to be the hydro dynamic centered position, and Active has them moving to stabilize the boat. There is a separate maintenance setting called "Free" that lets the fins self-tail.


A friend and I spent a summer experimenting with this, and tuning our fins to their hydro dynamic centers. The revised center positions on both our boats ended up different from the factory-built parallel to the keel position, his boat more than mine. He got a detectable improvement in efficiency and speed, but I don't recall the numbers. But it wasn't very significant. I was never able to conclusively measure an improvement on my boat, but it definitely handled better after correcting the centered position.

 

[catalinajack]

Last August I had to have my Naiad fins replaced. As many here might know, they are mounted on a tapered shaft that slides into a close tolerance mate that is molded into the fin. In my case they were torqued to 300 ft-lbs. Whatever the centered position is, with locking pins in place it is simple matter of sliding the fin onto the shaft properly oriented. I doubt precision is required but very good accuracy probably is. My technician measured from a point on the existing fin to the boat's keel and installed the new fins to the same distance, accurate but not precise.

The day of the swap, I helped as the tecnician's helper was on vacation. It was an eye-opener. A hard stand must be placed close to the bottom of the fin before removing the large gland nut that threads onto the the shaft because, when that 300 ft-lbs of torque is released, the force shoots those fins downward with a loud bang. The hard stand is for safety.

I used a local technician that was recommended by the Naiad factory folks in Connecticut.