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Making a Transducer Mounting Plate

9/6/2012

12 Comments

 
One of the long debated topics when it comes to fishing boats is how and where to mount your fish-finder’s
transducer. Often times one has to try several changes (slight) in the mounting position / location in order to get a solid reading when the boat is on plane or at speed. However, making these adjustments, especially when having to do so side-to-side, results in undesired sets of holes in your transom. Even when care is taken to seal these holes, they are opportunities for water to begin to find its way into your transom causing damage down the road.

One way to avoid this issue is to install a transducer mounting plate that you mount to your boat and then you have a surface to mount your transducer to, and if you need to make adjustments you are putting new holes in this mounting plate and not your transom. Starboard or similar HDPE (High Density Polyethylene) materials are popular materials used for marine applications as they will not rot, delaminate or break down in water over time. However, the downside of Starboard or other HDPE materials is that they can be very difficult to bond as very few adhesives will form a bond to the material. Certainly you could screw a block of Starboard to your hull, but you are putting a set of holes in the boat which is what we are trying to avoid, and if those holes are not properly prepared and sealed you can let water in through those. What is needed is a method to secure HDPE-based materials to your hull without the use of screws or other fasteners.

(Click "Read More" to the right for more of this article)
Fortunately there is a method that can be used. With a combination of a specially formulated epoxy, coupled with a little bit of mechanical engineering, you can create an effective bonding system.

Materials needed:
  • Block of 3/4” Starboard or other similar material
  • Dremel or similar tool
  • 1/2” - 3/4” drill bit and drill
  • West System G-flex 655 Epoxy
  • Masking or blue painters tape
  • 80 grit sand paper
  • Acetone or denatured alcohol
  • Clean rag
  • Utility or razor knife
  • Propane torch
1. Before starting, if you have previously mounted a transducer you may wish to seal these holes. If you had used 3M 5200 or similar sealant, it is recommended to over drill these holes to remove any of the old sealant and then fill the hole with thickened epoxy. You can use the G-flex epoxy listed above for this use or some other epoxy material such as MarineTex, as these holes will be “top-coated” when we complete our installation.
Picture
Previous mounting holes ground and drilled clean of previous sealent and filled with epoxy to seal.
2. Cut the block of Starboard to an appropriate size for your application. Make sure it is wide and tall enough
such that you have the ability to make adjustments vertically and horizontally with your transducer.

3. Drill 4 - 8 evenly spaced holes in the back of your Starboard plate making sure not to drill all the way through - leave approximately 1/8” - 1/4” of material (so if you are using a 3/4” thick block of Starboard, drill 1/2” or 5/8” deep into the back of the block) - make sure to take into account any “point” the dril l might have that may penetrate deeper than the rest of the drill bit.
4. Using your Dremel tool and an appropriate bit, create a “dovetail” in the holes you’ve drilled by undercutting the material around the hole. When finished clean up any rough edges with a utility or razor knife.
Picture
Mounting plates after "dovetails" are back-cut into Starboard using Dremel
5. Using the 80 grit sand paper, rough up the back of the starboard as well as the gelcoat on your boat where you will be installing the mounting plate.

6. Using the propane torch, flame-treat the rear surface of the mounting plate. This is done by passing the tip of the flame from the torch just above the surface of the material at a rate of around 2”-3” per second, overlapping the previous pass slightly. If done properly you wil l not see any visible difference (no browning, melting, etc), but the heat creates a chemical property change in the material that aids in the bonding. Make sure you complete the next steps within 30 minutes of the flame treatment.

7. Use the clean rag and the acetone or denatured alcohol to thoroughly clean the back of the mounting plate as well as the area of the transom where you will be mounting the plate.

8. Mix the G-flex epoxy per the manufacturer’s directions and then fill the holes in the back of the mounting
plate and if desired apply a thin coat of epoxy across the entire back surface of the plate.
9. Apply the mounting plate to the transom and use the masking or painters tape to secure it into position until the epoxy sets. Use the rag and acetone to clean any epoxy that seeps from around the mounting block.
Picture
Mounting plate after epoxying with G-flex and the epoxy has set
10. After 24 hours you can mount your transducer to the mounting plate. Keep in mind the depth of your mounting plate and use screws of an appropriate depth. As you will be using shorter screws than what came with the transducer you may wish to step up a size in diameter if possible or use a broad-threaded screw. Remember - use stainless since these screws will be in the water.
Picture
Transduers mounted - Let's go fishing!
You are done!

If you want to take advantage of the mounting system above to avoid holes in your transom, but do not want to go to the trouble of making the mount yourself, you can purchase a commercially made unit. The Stern Saver (www.sternsaver.com) makes a mounting block ready for installation and includes the required amount of adhesive and instructions. There is also a product called “Stern Mate” (www.sternmate.com) which is similar in nature that you may want to explore.
12 Comments
John Auerbach link
9/10/2014 10:23:33 am

I really learn a lot and pass it on to my listeners, how do I join your blog

Reply
james
4/19/2017 09:56:37 am

The epoxy west system 655-8 G/flex thicken Epoxy Adhesive really doesn't adhere well to starboard, so the holes are dovetailed acting like anchor points for the epoxy to grip too, is this correct? but the epoxy will adhere to the fiberglass boat correct? then you secure the starboard to your fiberglass boat with stainless screws. Have you any problems with this procedure and has it lasted.
Thanks
James

Reply
Mike
4/19/2017 09:59:28 am

James - when the Starboard is properly flame-treated the G/Flex will adhere - but the dovetails provide a mechanical bond as well. The application shown in the article above is still going strong around 5 years later.

Reply
james
4/19/2017 06:22:34 pm

Thanks Mike
I have ordered my starboard from Boat outfitters on the web. I ordered a piece pre cut 12"x6"by 3/4 " thick, I will make sure I flame treat the starboard.. where is a good source to purchase the west system 655-8 G/flex thickened epoxy adhesive.
Thanks
James

Reply
Mike
4/19/2017 06:30:29 pm

West Marine is a good source - on-line or in their stores if there is one near you.

james
4/19/2017 06:33:35 pm

Thanks Mike

Reply
Lou
5/25/2017 03:43:58 pm

Great article, thank you from Florida for the step-by-step and photos.

Reply
Dan
8/7/2017 01:32:42 pm

I bought a plate from Cabela's. http://www.cabelas.com/product/Cabelas-Transducer-Mounting-Plates/701430.uts

I'd like to follow your instructions. Are the "anchor" holes really required, or will it stay on if i use the torch and epoxy?

Reply
Mike
8/7/2017 02:15:15 pm

I assume by "anchor" you are refering to the dovetail plugs. I was looking at the block on my boat in the water just yesterday - and 5 years and lots of time on the water the plate still seems well adhered to the Fiberglass, so if the starboard is properly flame-treated and the fiberglass scuffed some and cleaned well and you use the G/flex, the dovetail plugs may not absolutely be needed - but they do provide a good mechanical bond - and I can't say if my install would still be as robust if the dovetails had not been used....

Reply
Kendall Everett
9/13/2018 03:21:02 pm

I can not tell but it looks like you attached the starboard with two screws also along with the epoxy. thanks Kendall

Reply
Timothy
3/14/2019 01:52:27 pm

Mike
Your dove tails are required. that's the secret on how the "Stern saver" plate adheres to the boat. The epoxy binds to the threads in the plate as well as to the boat. If you could cut some threads in the starboard you would have the exact same thing. Tap and die set, some Loctite epoxy, some finger nail polish remover and your in business. I went by store to pick up one of the plates for my new transducer. I almost passed out when they told me the price. Even the associate at West marine, who installs fish finders, said he would not buy one at this price.

Reply
Jack
10/23/2019 08:46:55 am

It's unfortunate no one is making these plates from UV-protected ABS plastic. Epoxy and silicone adhesive both bond extremely well to ABS, and it anchors self-tapping screws at least as well as polyethylene. I wouldn't hesitate to attach a transducer to a flat ABS panel that has been glued to the transom with the appropriate adhesive. No screws, no dovetailing, just stick it on and you're done.

Reply



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    The Boathouse by Mike Ward

    In this blog, Mike will share various tips & techniques regarding boat rigging & maintenance to help make your time on the water more enjoyable.

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