posted 09-09-2013 11:09 PM ET (US)        

Considering the popularity of the classic (1989) Montauk hull, can someone give me the optimal location for the P66 transom mount transducer from the keel with certainty?

I know Boston Whaler recommends the port side in their documentation, but Airmar told me to use the Starboard side. Airmar also provides a template for drilling that sets the Transducer height. I only need the distance from keel.

Anyone getting good results with a P66 and a classic Montauk hull? If so, can you please share your info?

Thanks to all-Jim.

posted 05-18-2014 03:18 PM ET (US)            

Considering the popularity of this hull and transducer, Can someone pass on a measurement from keel, away from strakes and air, that's performed well at all speeds up to 40mph?

posted 05-19-2014 10:48 AM ET (US)            

I find that the AIRMAR P66 transducer loses signal, probably from losing sufficient immersion into the water, if there is the slightest bit of heel or list on the boat toward Port side, that is, if the Starboard side of the boat raises ever so slightly out of the water. To correct for this, you can mount the transducer slightly lower than recommended, or, perhaps more appropriately, mount it closer to centerline, which will reduce this effect.

posted 05-19-2014 01:07 PM ET (US)            

Maybe Tom Clark has the best advice: either side will work?

My personal experience has been all on the starboard side, a P32 Airmar transducer with Apelco fish finder and a Garmin transducer with Garmin 400C fish finder. The Airmar/Apelco performed better than the Garmin. It was not perfect, though, as it frequently loss lock at speed.

The new set up will be a new Airmar P66 with a Garmin 441S combo sonar-chart plotter. I'm tempted to mount the king-starboard to the port side and try the P66 there as BW recommends. The propeller turbulence argument that the prop trails the transducer while underway keeping turbulence away from the transducer makes sense to me. However, why don't the transducer manufacturers consider this? Hmmmm?

So I will look under the classic, smirked, 17' hull for smooth bottom away from strakes as best I can with the boat on the trailer. I'll mount the king starboard and transducer on the port side as close to centerline but at least 3" away from the prop swing, and based on the make-up of the bottom of the hull for smoothness. The king starboard mounting plate will give me some flexibility for adjustment, if needed. I'll report back with more info after the sea trial. This case study can add to all the data already on the site.

posted 05-19-2014 04:16 PM ET (US)            

If the transducer is 2" wide then the centerline of the transducer is another inch, so call it 11" as a minimum lateral distance from keel to centerline of transducer.

I just installed a transducer (not an Airmar P66) on a classic 1989 Montauk last Friday evening. This transducer had previously been mounted to port in a lousy position at the apex of the transom shape where the main hull meets the sponson. This position is high and tends to have air funneled to it making it unsuitable.

I moved the transducer to starboard and simply placed it about half way between the keel and the apex of the transom shape. I did not measure the lateral distance, but I suspect it is about 12" off-center of the keel.

The placement advice from Whaler dates back to the 1960s when depthsounder transducers were much larger and tended to act as mini-trim tabs. Since small outboard powered boats tend to list to port from propeller torque, adding a stern lifting force to port made sense to counteract this listing tendency.

posted 05-20-2014 03:40 PM ET (US)            

Tom and Jim and their logic have me back to mounting the P66 on the starboard side at about 12" from keel if the bottom of the boat at that distance is free of strakes and everything else. I'll report back after the sea trial.

posted 06-01-2014 01:05 PM ET (US)            

I finished the installation last weekend and launched the Montauk on Friday. The Airmar P66 is mounted on a piece of King Starboard on the starboard side of the transom at 13.5 inches from center-line. There is a bend in the transom at around 11 inches from center-line and a strake in the bottom (at about 1/3 boat length back from the bow) at 12 inches from center-line, both prohibiting placement of the transducer at those points. The P66 is mounted without the included angle-shim and seems fairly parallel to the waterline without it. It is mounted 1/8" below the bottom of the boat on its left side. Everything is done as instructed by Airmar.

Unfortunately, the Garmin GPSMAP 441S loses lock (blinks at last value) consistently at each acceleration to and above 20 MPH and does not restore until speed is lowered. The Garmin unit is a new-refurb, sent as a replacement by Garmin and set to automatic for all sonar functions. I have the ability to move the P66 up and down by about an 1/8th inch without relocating the bracket. I can move the full bracket and P66 about a 1/2 inch to the left and about 2 inches to the right while still mounted to the King-Starboard.(But still difficult to move while the Montauk is in the water).

Any ideas on how to improve the performance? Also...If Jim H. can advise on how to link to a picture of the installation, I can post one if this would be helpful.

Thanks so much...

posted 06-02-2014 09:11 AM ET (US)            

After installing the transducer on my former Dauntless 16 in accordance with Lowrance and Airmar recommendations I continued to lose bottom readings at higher speeds. The Lowrance employee I spoke with recommended tilting the transducer slightly more downward and it solved the problem.

posted 06-02-2014 06:20 PM ET (US)            

Photo of the transom with P66 attached on the King StarBoard

Thanks for the tips on angle and a lower position in the water. Coincidentally, Airmar is offering identical advice. There is one problem, though. The P66 does not have a continuously variable angle adjustment, it uses a shim (that I did not install) to achieve a greater angle off the transom. Airmar notes in the installation guide that no shim is needed for boats with 12 degree to 18 degree transom angle. Tom Clarke indicates in another post that a Classic 17 Montauk has a 17 degree transom angle. With this info and by seeing the trailing edge of the transducer pitched down just a bit, I chose not to use the shim. It seems this conflicts with the FAQ below.

I will attempt to lower the transducer first and test and then add the shim if needed if I can manage to do this while the Montauk is in low water in its slip.

Here is an excerpt from an Airmar FAQ I found today:

If you are still seeing poor performance at speed, this usually indicates that the transducer needs to be mounted lower so that more of the face of the transducer is in contact with the water at speed.
To make this adjustment, loosen the mounting screws, and slide the transducer 1/2" lower and re-test. You may need to re-drill holes. If you do so, be sure to seal the old holes with manufacturer approved, below the waterline caulking or epoxy.
You also may want to add another plastic wedge (supplied with the installation kit) so that when looking at the side of the transducer the back or stern of the transducer is noticeably lower than the bow or front of the transducer. This angle will not affect depth readings. Doing this adjustment will help keep the transducer in hard contact with the water at higher speeds.

Thanks.

posted 06-07-2014 09:07 AM ET (US)            

With no adjustments left to go without re-drilling, I phoned Garmin Tech Support. Prior tech support from Garmin was superb as they were interested, informative and had made a complete replacement of the 441S last season when I explained the problem at that point. Today's GARMIN tech support (and I'm being kind) was ANYTHING BUT HELPFUL. The agent was APATHETIC. He listened to my story and said the transducer is becoming aerated and losing lock. He said I was fortunate that a P66 held any kind of lock above 12-13 MPH. He offered no other advice, recommendation or tips. Just live with it. I told him I'd be posting a summary of the call with GARMIN on a web forum and would phone Airmar next.

The Airmar agent was eager to hear my story and puzzled as to the performance of the system as the mounting of the unit seemed correct. He said the Garmin unit was not at fault as it was working properly at speeds below 20 MPH . He offered to discuss this with his colleagues and email or phone me back. I sent him the transom picture in this thread for reference.

He got back via email in about 2 hours with the following note that I've reduced to the most pertinent portions:

***Good afternoon Jim,

Thanks for the picture - great/clean install by the way.

That answers the initial questions I had regarding installation. It appears as though you have that transducer as far below the boundary layer as you can get.

You've obviously tried several locations at the current spot but you may want to move farther away from the center-line. There may be less turbulence / vibration.

As far as the system itself goes I doubt it is a performance issue with the sounder, or the package for that matter. You are getting good performance at idle speed up to 20mph. That means that as far as I can tell the system is working fine. The issues mostly arise when the boat reaches a certain speed at which point the transducer loses bottom. Although many transducers advertise they can read bottom at a wide range of speeds the truth is each boat is different.

You may want to look at page 2 of the owner's manual (attached) and consider raising the transducer so that the template is closer to the waterline. Or you could have the transducer tested to make sure it has the proper impedance.

Unfortunately I honestly cannot give you a definitive way to ensure that a P66 will hold depth at speeds 20mph and higher. Other P66 transducers have been able to hold depth and faster speeds so it is possible.

I will continue to check on this and have reached out to Boston Whaler to see if they have any further suggestions.

In the meantime if there is anything else I can do please let me know.

***

I'm pleased that Airmar responded so thoroughly but it seems there is really little advice other than another location more starboard, potentially in less turbulent water. I am also considering asking Airmar for a replacement P32, a smaller transducer that I had more luck with on a previous Apelco Fishfinder on this same boat. Even though mounting the transducer is always recommended as close to center-line as possible, by all manufacturers and members of this forum, the former P32 was mounted farther to starboard and as mentioned, I recollect it was more effective in holding speed lock at that position. The plugged holes from the P32 and former installation to that can be seen in the picture in this thread.

I'd be interested in any comments for improvement from others on the forum. This has become quite a puzzling project and case-study.

posted 06-08-2014 09:04 AM ET (US)            

1-second/4,911-feet x 200-feet = 0.04-seconds

Now we consider the boat is moving at a speed of 30-MPH. In 0.04-second the boat will advance

(30-miles/1-hour x 5280-feet/1-mile x 1-hour/3600-seconds) x 0.04-seconds = 1.76-feet

We know that the sound from the transducer is spreading in a cone. Even with a very narrow cone angle, say 10-degrees, after the sound has travelled 200-feet the cone will be covering a distance of

beam spread = 2 x tan(ConeAngle/2) x 200-feet
beam spread = 2 x tan(5) x 200-feet
beam spread = 35-feet

As long as the transducer is pointing straight down, it will be very unlikely the boat can outrun the return echoes, unless the boat is amazingly fast or the cone angle is as narrow as a laser beam. The instructions from AIRMAR clearly say:

quote:

---

For the best performance, the transducer beam must be aimed straight at the bottom.

---

When the P66 is installed on a transom without the added wedge, and the transom is on a typical Boston Whaler, the orientation of the P66 toward the bottom is going to be to aim a little bit forward of the boat, if anything, and not aim astern of the boat. With the typical trim on the boat when on plane, the bow is going to be higher than the static trim, so this will aim the sound even farther ahead of the boat.

I think the real source of the problem is loss of signal through turbulent and aerated water close to the transducer face. The bottom face of the transducer should be operating in clear, non-aerated, non-turbulent water.

I have given more information about the installation of the AIRMAR P66 on my boat in another article, and it may be of interest to readers, too:

http://continuouswave.com/ubb/Forum6/HTML/003429.html

The other article mentions this procedure, suggested by AIRMAR:

quote:

---

AIRMAR gives a valuable method to determine if the transducer is too high or too low. They suggest watching the echoes while making a turn to the left and right. If the transducer is mounted on Starboard, and you turn to the right, the Starboard side of the transom will lower into the water. If the SONAR echoes improve in a right turn, the transducer is mounted too high and should be lowered. If echoes improve in a left turn, the transducer is too low and should be raised. Using this method, I saw the echoes improve in right turns.

---

AIRMAR also notes in their FAQ that transom mount transducers can be the hardest to get working properly:

quote:

---

Transom mount transducers—while they are the easiest to install, can be the hardest to get working properly at speed. Fine adjustments are needed for good high speed performance.

---

Cf.: http://faq.airmar.com/index.php?action=artikel&cat=1&id=196&artlang=en

Another article in the AIRMAR FAQ suggests the diagnostic technique of making a turn to the left or right and observing the echo signals:

quote:

---

...gradually increase speed while making moderate turns in both directions. Note, if the performance improves while the boat is turning toward the transducer side, the transducer is probably in aerated water or coming out of the water. You probably need to adjust the transducer's position.

---

Cf.: http://faq.airmar.com/index.php?action=artikel&cat=1&id=77&artlang=en

Finally, that same article suggests:

quote:

---

If all else fails, move the transducer closer to the centerline of the boat. Repair unused screw holes.

---

posted 06-08-2014 09:51 AM ET (US)            

Thank you both for your comments.

Basshole--it's a 2003 Yamaha 90HP 2S that weighs 263-lbs. A light motor for the 1989 Montauk.

I cannot send a picture of the side view. The boat is in the water for the season. I was fortunate to be able to work out the adjustments on Friday by jumping in the water at low tide for the minor adjustment down and beaching the transom with help for the addition of the angle shim. Incidentally, the shim is now making certain the trailing edge (back) of the P66 is definitely deeper in the water than the leading edge (front).

Considering the original installation position per the Airmar template placed the lowest portion of the transducer (port side)at 1/8" below the hull, moving it down Friday brings it to about 5/8" below the hull with the shim pointing the rear trailing edge down. Exactly as recommended in the Airmar FAQ.

Unless Basshole's or his suggested expert can offer advice, I'm left to try:

-- the C-clamp and 2x4 temporary testing technique of trial and error by moving the transducer around various points on the transom until something works better. I'm skeptical, however, as there is a lot of stuff in the way on a Montauk's transom that will interfere with clamping a board securely.

-- just moving the p66 more starboard where the P32 used to be (see plugged holes to starboard side of P66 in picture in this thread. This may not happen soon, though as the boat's in the water for the season

-- asking Airamr for a replacement, smaller P32 (limited to 200 kHz, though) that won't act as a trim tab like the large P66 does and will fit back in the original holes as long as I can back out the sealed stainless screws. This position seemed to perform better when I was using an Apelco with a P32.

-- nothing. Live with it per the apathetic advice from Friday's Garmin rep!

Thanks for your interest and comments guys...I'm all ears.

Jim S.

posted 06-09-2014 04:05 AM ET (US)            

Also, looking at your bottom paint I noticed it's very rough and clefted. It has the appearance of slate tile almost. If the bottom of your boat looks like your transom then I would also suspect some turbulent water coming off the back of the boat which would likely get worse as your speed increases. Even small bumps can cause cavitation interference in the same way a thru-hull pick up or a strake can. The StarBoard block being too close to the bottom of the transom could also be the problem as already suggested. It it at least 1/4-inch above the bottom? A 1/2-inch above would be even better, hence why we chamfer the top edge of the Stern Saver to reduce the likelihood of water hitting the bottom corner of the block.

Also, West Marine sells the Garmin 441S without a transducer so you can choose from a variety of options. Did you "tell" your unit its got an Aimar p66 connected to it when you installed it? My Lowrance HDS units require me to select what transducers I am using so that the unit can properly calibrate itself to the transducer I selected off the menu.

Also, what frequency are you running at? It's a dual frequency transducer. Are you at 50-kHz (55 degree cone angle) or at 200-kHz (11 degree cone angle)? What depths are you at when losing signal? What are the water's surface conditions: big swells, tight chop, flat and glassy? What is the bottom contour: flat, sloped, variable? I think we just need some more info. This is not going to be solved by using JimH's "perfect world" assumptions. It's going to go beyond that, although his turbulent water theory is a possibility.

The more I think about it, I feel like it might have more to do with your settings on the Garmin unit rather than the transducer placement itself.

If all else fails give Gil Travis from Semper Fi Fishing a call at 1 (800) 925-0341 or email him at travis.g@sbcglobal.net. He knows more about this topic than anyone I know, even JimH, believe it or not! Tell him Scott from Stern Saver sent you. Actually, JimH should probably give him a call, too, so he can finally get his sounder working properly as well.

posted 06-09-2014 06:49 AM ET (US)            

http://i123.photobucket.com/albums/o316/sterios/DSCN2167_zps21c4f290.jpg

http://i123.photobucket.com/albums/o316/sterios/DSCN2166_zpsd7b2d4cd.jpg

http://i123.photobucket.com/albums/o316/sterios/DSCN2169_zps63a3db75.jpg

http://i123.photobucket.com/albums/o316/sterios/DSCN2170_zpsb925fc73.jpg

posted 06-10-2014 12:40 PM ET (US)            

The next pic [was taken at a] speed of 40.6 mph and I still have bottom lock.

At all speeds, and even when getting up on plane, I never lost bottom lock. I configured the HDS Unit to recognize the Airmar and enabled the paddle wheel speed but it only worked sporadically. I will tinker with it some more and hope to get it working.

The only thing that concerns me is that junction box. That red lid is only press on. While under way,or sitting still, the bottom half of the box is in water. Airmar sais it's water proof but i don't trust it so i'm going to recheck all my connections and silicone that lid shut.

posted 06-30-2014 09:37 AM ET (US)            

I spent a few days on the boat and had the cables for both the Lowrance Skimmer and the Airmar P66 available at the back of my HDS-8, so I could quickly switch them. We found some deep water, about 590-feet, in Lake Michigan. I compared the two transducers. They both seemed to give good echoes from 590-feet.

To switch the transducers, I was setting the HDS SONAR to STOP. I figured this stopped the high-power pulse to the transducer from the head unit. I was then disconnecting one cable and connecting the other, but not shutting off the power to the HDS. I did this a few times. Then I happened to read the warning label on the Airmar cable. It warns specifically to not connect the transducer to a sounder when the power is on due to a risk of damage to the speed sensor circuit. Oops. I was fortunate. I did not damage the speed sensor circuit in the P66, and I stopped hot-switching the cables.

The P66 worked worse at any boat speed than I had recalled. Perhaps the boat was always heeling the wrong direction--we were running with some cross winds all the time, and that tends to make the boat heel. The performance at speed was just not very good. I decided the P66 in its current mounting location was not usable.

posted 07-18-2014 10:00 PM ET (US)            

I had the Montauk out last Friday. The Airmar P66 and Garmin 441S are now working the poorest they have since the original installation this Spring. The P66 is mounted with the angle shim and is well submersed into the water. Depth readings are not acquired at the dock in 3 to 4 feet of water. I have to reboot the unit in at least 6 feet of water to get a reading at all. Once sending a valid reading and then I exceed 20 mph, lock is lost and the reading blinks. If I slow the boat down under 20 MPH all the way to idling with no movement in clear, non-aerated water, the unit does not re-establish lock, it continues to blink and will not get a reading until I reboot the Garmin. Once rebooted, the system repeats the same problematic cycle.

I'm extremely disappointed with this equipment. I can understand loss of lock in aerated water and am willing to try relocating the P66 again, but not re-establishing lock after returning to no forward movement in non aerated water is very frustrating and puzzling and seems to indicate a defect with either the NEW P66 or NEW 441S.

posted 07-26-2014 05:15 AM ET (US)            

Jack H. writes: