Thru-Hull Transducer Hole Drilling

[SeaHarley]

I am looking for advice in adding and mounting a new Thru-Hull Transducer for my older Garmin 188C, GPS / Fishfinder. I transfered this GPS from my last boat, 270DA to our lastest boat, 310DA because I'm use to it and I like it. It had a transome mounted transducer before. Since I now have "V" drives with the props under the boat I cannot do that. So I need to add a new transducer under the boat.

As it has turned out, I've actually drilled probably over a hundren holes in my boats over the years but for some reason, I'm kinda scared to drill a 2" hole in the bottom of my boat and want to make sure I've done my homework. So, before I buy the transducer, my questions are:

1) Do you drill a 2" hole exactly or do you have to oversize a little (say 1/8" or so?) to account for slop and / or epoxy?
2) What kind of epoxy or other kind of sealer do you put around the inside of the hole?
3) Do you mount the transducer while the epoxy is still wet or let it dry first? I understand that you'd never get it out....... without takin a hammer to it!
4) Besides looking out for strakes, etc. - and not to mount behind them, is there anything else to look out for?
5) Would there be any other option that works well other than drilling a hole that is recommended?

Thanks in advance.

Lee

 

[Sea Gull]

Lee,

Based on the level of questions you are asking you have a pretty good handle on what is involved. Also, based on your comments, you have never installed one of these before. The best advice I can give you is get a professional to do it. You need a fairing block to allow the transducer to point straight down. The process of measuring and cutting the fairing block is not difficult, but could be more than most do-it-yourselfers would want to handle.

 

[comsnark]

I replaced a ducer last year. Drill a 2" hole. .and see if the new one fits. Ream further as necessary.

The old ducer came out with aid of a hammer.

I used that west marine 4200 stuff for the new one. Shmutzed a pile of epoxy on the unit before installing. Put it in wet. Shmutzed a bunch more epoxy around it while it was in the hole. Do not skimp on a $9 tube of epoxy. . .because if you do it wrong the boat will sink. Try explaining that to your insurance agent (I drilled a hole in the boat. . and then it sank. Please give me money. Riiiight. )

 

[Henry Boyd]

Lee,

I'd have to agree with Gull.
But if you decide to DIY you also have to be concerned with the shape of the transducer that sticks down into the water and it's orientation to the rudder/props. These things can cause turbulence that will deteriorate the effectiveness of the rudders.

What about the the original depth sounder? Didn't the boat come with one? Also keep in mind that you should only have one at a time. These are active devices that transmit and receive sound waves.

Henry

 

[jrcinnh]

If you go to the Airmar site http://www.airmar.com/ they make most of the transducers. And they have installation instructions.

Assuming you don't have a cored hull bottom, it looks like the hole should be 2" and the transducer bedded with marine sealant. I don't think epoxy is appropriate. If you wanted to seal the fiberglass with a thin layer of epoxy it couldn't hurt but you probably would still need to seal the transducer to the hull with a flexible sealant.


As to fairing, Airmar makes a transducers with the element tilted. They offer a few different angles. If you can get one within a few degrees of you boat deadrise, then you can skip the fairing.

 

[comsnark]

Ah. . .the question of which way to point the ducer.

Yes, if you have a 21 degree deadrise, and you install "flush", you will be shooting 21 degrees off of verticle. If I remember correctly (too lazy to rerun the trig) this will cause your depth finder to read 9-10% high more water than you have.

So if the depthfinder reports 10', you really have (91% * 10 feet = 9.1 feed under keel, add two feet because the keel is two feet below water line but add a foot back in because you are on plane, and the waterline is elevated ) 10 feet of water. . . .

 

[SeaHarley]

. . .because if you do it wrong the boat will sink. Try explaining that to your insurance agent (I drilled a hole in the boat. . and then it sank. Please give me money. Riiiight. )

I loved this comment........ LOL

I did do google search and I did see and read some of the stuff they had and came across the Airmar site and other forums as well. Some say use epoxy, some say use 5,200, 4,200 etc.
I tought I'd use epoxy around the inside of the hole, let it dry, and then install the transducer coated with 4,200 all around everything. But wanted to make sure this is a good way.??????

No, I haven't done a thru-hull before...... but see no reason I shouldn't or couldn't do it myself........ as long as I do it right. That's why I'm asking, before I try myself.

No offense to the boatyard mechanic, but my experience after I have paid the so-called professional to do other work before, I look at it and know that I could have and would have done a better job. Not that I'm a perfectionist "anymore" but I'm not on a clock and can take my time to do what I feel would be a better installation.

I will have to check and verify, (I'm tired right now!) but I do believe the 310DA is a cored hull bottom and also believe it is 21 degree deadrise. Not sure yet, I forget.

I was also expecting to flush mount it, with the appropriate degree transducer without a fairing. I will verify this as well.

There is an existing thru hull transducer used for the depthfinder. This is also flush mounted, on the starboard side just in front of and forward of the "V" drive transmission. My intentions would be to install the new Garmin thru hull on the port side just forward of that transmission.

So, at this point, it looks like I'll haveta buy the transducer and take measurements of it directly before I drill and see what I need. Everybody seams to say 2" so far.

Thank all of you for you inputs, thoughts and ideas.

HAPPY HOLIDAYS!

Lee

 

[SeaHarley]

Well, answering some of my own questions:
I have a 23 degree deadrise and the tilted design can go up to 24 degrees without a fairing. So, that part will work.

As far as I can tell and determine, I have a solid (FRP) fiberglass hull and it is not cored on the 1999 310DA. So that makes it a little easier.

And the "Airmar" site leads me to a B60-20, 600 watt, which has a 2" diameter outside and would require a 2 3/8" hole.

Now in looking into all that, there seams to be a newer model comming out, (of course!). A B164, 1 KW unit that is suppose to blow away the others as far as detail. Needs a 4" hole..........
Anybody have experience with that?

Lee

 

[fwebster]

Lee,

Sea Ray uses a solid layup in the area they expect to be used for transducers. You can call Sea Ray customer service and ask the dimensions and location for your boat if it isn't readily apparent, but drill the hole in that solid area.

I use West Systems epoxy to seal the fiberglass before installing the transducer. I thin 1/2 the batch with acetone so it will wick into the fiberglass substrate better, paint it on with a disposable brush, let it rest a while, then, before it kicks liberally coat the area with unthickened epoxy.

Don't cut corners....use 3M 5200, not its cousins.

Do you need to replace an existing thru hull with this one? ......I have a method if the hole sizes are different.

Other than that, it looks like you've done your homework........

 

[top*prop]

how about taking your holesaw, cut a hole in a piece of cardboard, then slide your transducer in the ole to see how it fits......... run the holesaw backwards to prevent the tearing of the cardboard......... very simple!!!!!

 

[Sorrento 25]

I use West Systems epoxy to seal the fiberglass before installing the transducer. I thin 1/2 the batch with acetone so it will wick into the fiberglass substrate better, paint it on with a disposable brush, let it rest a while, then, before it kicks liberally coat the area with unthickened epoxy.

Don't cut corners....use 3M 5200, not its cousins.

West is great but an expensive setup to invest in for one small project. A quality SLOW commercial epoxy like PowerPoxy or many others would work well too. Good advice I agree with 100%.

One other tip may be to predrill a pilot hole and then come at it from both sides with the hole saw. Sometimes depending on the thickness of what you are drilling and the quality/depth of your hole saw it can be easier on your drill/arm/saw this way.

Sanding the edges of the hole a little smoother by hand after drilling will allow the epoxy to make a better seal too.

 

[SeaHarley]

.....Sea Ray uses a solid layup in the area they expect to be used for transducers.

I use West Systems epoxy to seal the fiberglass before installing the transducer..........

Don't cut corners....use 3M 5200, not its cousins.

Do you need to replace an existing thru hull with this one? ......I have a method if the hole sizes are different..........

Thanks Frank,
I was hoping you'd chime in on this.........!

On the starboard side, where the existing depth finder transducer is, there is a built-up flat area that looks like a board of some kind was added underneath the bilge area fiberglass top coat. This may be the solid area you are talking about? But it is only about 10" x 10" and only on the starboard side. I wanted to install the new one on the port side, away from the original transducer. And the port side area is not built-up like the starboard side. I will call Sea Ray directly to find out though. Thanks.

I will look into both epoxies. It is interesting that Airmar installation instructions do not mention epoxy use at all.

I'll use the 5200.............. don't plan on removing it. And if I do, I know it will be with a hammer anyway. LOL

I'm not replacing one....... adding a new one. But I quess your idea would be to make a predrilled correct sized hole template and placed over the existing hole?

Thanks everyone for your ideas.

Lee

 

[fwebster]

Most boat yards just use 5200 to seal transducers, but it is better to seal the fiberglass with epoxy in case you ever get a leak. Sometimes it happens, and without the epoxy you can get a delamination in the bottom. That is more expensive to repair than the cost and hassle of sealing the hole with epoxy.

To redrill a transducer hole to accomodate a larger size, use a tapered plug and drive it into the old hole, , cut it flush with the hull and then drill a small pilot hole where you want to center the new one. Use a hole saw the correct clearance size for the new transducer.

 

[2000SEARAY280SS]

I saw this hole saw pilot arbor A19 on a program called cool tools on DIY TV. It is made by Starrett . The idea I have used before. You need to make a larger hole than the one that all ready exists. You double up the hole saws with the smaller and longer hole saw being the same size as the existing hole. The longer saw guides the larger saw through the existing hole. Do a search on Starrett A19 OOPs and several sites come up with pictures of the unit.

http://www.tools-plus.com/starrett-...g&utm_source=shopzillabizrate&utm_term=LSSA19

 

[Hampton]

I drilled a hole in the hull of my 250 for the installation of a brass scoop. I used it to provide water for my live well which I mounted on my swim platform.

I didn't know what I was doing, other than to ask around a bit, but I drilled the hole (more like grinding), installed the thru-hull, sealed it up tightly, and it worked great for the next 8 years at which time I sold the boat. My boat had a block in the area opposite the macerator thru-hull which I used for the project. If I could do it 9 years ago, you can do it now with all of the help from these great people at this site.

 

[osd9]

Mike...that A19 looks like a usefull tool to keep in the workshop....do you happen to know the "differential it is good for. In other words, what is the smallest difference between the "oops" hole and the size hole you really want that this tool affords you? If I drilled a 1 7/8" hole but needed a 2" hole....would it work....or do I just get out the radius "bastard" file.....

thanks,

 

[2000SEARAY280SS]

I have not used this before but this is from one of the companies web sites.

“'Oops' Arbor is for use in conjunction with either the A1, A2 or A10 hole saw arbors. Replacing the pilot drill, the 'Oops' Arbor allows diameters to be enlarged by attaching a saw of the same size to that of the existing hole. therby acting as a pilot for the larger diameter saw. Minimum hole enlargement is 4.7mm (3/16") between the pilot saw diameter and the cutting saw diameter. “

So it looks like a delta larger than 3/16 inches should be acceptable. It mates up with one of their traditional arbors.

 

[FourGone]

Lee,

I was really jumpy about boring a hole through my hull in my 260DA too. If you check the Garmin site, they have instructions for a "shoot through the hull" installation. You'll need to check if your transduer will work. I pulled my 172C transom mounted transducer off my old boat, and tested its through ull capabilities per the Garmin instructions. (bascially a large ziplock filled with water - place the active transducer on the bag to see if you get a signal) Need to find an area of the hull that is not lamianted.

If the test works, which it did for me, I made a putty dam in a well cleaned corner of the bilge up against the fuel tank bulkhead, and mixed up a two part epoxy resin, poured it in and set the transducer in the goop - make sure there are no bubbles in the mix or under the transducer. Once its set your set!

It works like a charm, and the benefit is it shoots staight down, whereas the factory installed through-hull shoots at a slight angle off bottom dead centre.

And no new holes in the hull to worry about. Check it out before you start up the hole saw.

 

[SeaHarley]

Thanks Gregg,
I just finished up installing the thru-hull last night.....
Not too bad.

need to try in the water.
Lee

 

[Bodkin Creek George]

Just installed a tilted element Airmar in my 2004 340 DA. The transducer will come with installation instructions. Use 5200 and I used a 20 degree tilted element. Most important decision for you to make is the location of the new transducer. I have three on the boat. Two of them ping and on is just water temp and speed to the smart craft unit. Mind what Henry said about two pinging at the same time. My second unit is a high end HDS Lowrance with adjustable pings. This allows me to run both at the same time. Most of the time a low end unit will not function properly if another unit is pinging.
George