Transducer Mounting Options - Screw, Glue or Both?

What are all of you using to mount your transducers on alum boats transoms, especially the larger transducers that are nearly 12" long?
Are you screwing directly to transom or are you using a Plastic/HDPE Block?
How are you mounting the block....glue, screw, or both?

I have fabricated HDPE mounting blocks for mounting my last two transducers, which have been large transducers (Lowrance 3 in 1). One was 3/4" thick and the second one was 1" thick. I feel the 1" thick is preferred so you can use a 1" screw length which provides for deeper screw set and increased holding strength. I use #12 screws to mount transducer to HDPE block.
I prefer not to drill holes directly into transom if I can avoid it, but not 100% confident in epoxy between HDPE and Alum.

I mounted my HDPE blocks using 1. Flex Set by Marine Tex and 2. G-Flex by West Systems. Both of these claim they will bond aluminum and HDPE. I used flame treatment on both applications.

I did not use either boat long enough to determine durability/adhesion.
They appeared to hold up well, but no real data on how they will hold up after time with higher speeds (20+ mph) over time.

On my new Tracker aluminum boat (yet to receive), I reconsidering how to mount the transducer. I do not want to screw directly to transom, so HDPE blocks will be used. To Glue, Screw, or Both are my questions?

Here's what I have been reading about. Most HDPE blocks are available in 3/4" thick and either small or large sizes (LxW):

1. Stern Saver (now out of business but still available at some retailers) that uses a special proprietary blend of epoxy (3/4" thick). It uses epoxy to mount.
Stern Saver

2. Stern Pad made by Seaworthy Innovations. It uses 3M VHB tape to mount. Claims to be waterproof. (3/4" thick).
Stern Pad.
3M VHB

3. There are various HDPE blocks sold that use two stainless #10 screws and some silicone or 3M 4200 to seal the the two screws and help with bonding. (3/4" thick). They use two screws to mount.
Mounting Block
HDPE Block

4. RyTek, Canadian made, 1" thick with milled grove near perimeter for sealant/adhesive. Uses two screws to mount.
Heavy Duty Mounting Block

Update:

Just got off the phone with West System tech dept. Called them a few years ago about HDPE adhesion, but wanted some clarification.

They are confident in using G-Flex 655 with HDPE and bare alum with no screws needed.

They said sanding (80 grit paper) both bare alum and HDPE is critical within 30 mins of epoxy application, in addition to the alcohol wipe down and flame treatment of HDPE. No pressure needed to hold HDPE in place, only strong duct tape (due to vertical mounting) to hold in place for 24 hrs.

They said that bare alum was the best method, and that sanded painted alum would work, but only as strong as paint adhesion. Best to sand down to bare alum using 80 grit.
Flame treatment of HDPE is also critical.

They said that there is a King Starboard (manufacturer) video that provides good guidance on installation. West also has an article on Alum boat repair that is also useful.

King Starboard Video

West System Alum Boat Repair

I used a sample of Trex decking material available for free at my local hardware store. Then I used a marine grade 2 part epoxy to stick it to the boat. Waited 24 hours and it's as solid as it gets. I've had it on there for one season and it is not or will not come off.

I believe Trex Wood (LDPE and wood fibers) to alum may be a stronger bond using epoxy than is HDPE due to the wood fibers. The HDPE is much more difficult to bond with epoxy.

I’ve used your #2 option with additional 3m below waterline around the pad to seal out water. Solid going on four years my tracker Grizzly is powder coated so I was confident in its adhesion they do send a scuffing pad and alcohol wipes also I only used a normal transducer not the longer side scans and I’m thoroughly satisfied

I have only used bolt thru and 5200 to seal them. I used 1/2" King Starboard because that was what I had laying around from re-making a ski locker cover. Over many years, have not had any of the transducer screws pull free of the King Starboard.

While the modern side-scan transducers are very long, their front profile is much smaller than the older ones, like what I have. Do they have a "pop-up" feature in the mount? ie too much water resistance they will pop-up and pivot from a higher point. I have never had my large Si transducers do that, but my top speed with them is only around 30mph. I had a 2D transducer on my bowrider, that would pop-out at 50mph.

I use nylon lock nuts and bolts. I use silicon sealer on the bolts to create a seal.

I have used a small piece of leftover composite exterior trim 3/4" thick that I used on my house. Applied the block with an exterior all-purpose construction adhesive. Stayed stuck to my last boat through the life of 3 transducers under extreme abuse for the entire 7 years I had it.

I'm leaning towards option #2. Called 3M and spoke to a tech about their VHB tape and its adhesion properties. The 3M VHB does stick to HDPE but not as well as to other materials. He said a torch prep on HDPE is in order. Since the Stern Pad already comes with 3M VHB attached, one can only assume it was prepped correctly. He also said that some sort of sealant would be advised around edges (after mounted) to seal out water that could penetrate edges of tape. I'll reach out to Seaworthy Innovations (maker of Stern Pad) and see what I can learn about how they prepped.

Think about drilling some shallow holes in the back of the HDPE pad to give the epoxy something extra to bite into.

Option #2 uses 3M VHB tape. if I did go the HDPE and epoxy method, I would definitely use the shallow holes and flame treatment.

The Stern Saver uses that exact method...HDPE with shallow holes and I believe the holes are threaded to aid in epoxy bonding/holding.
Nice product....but they went out of business and are selling off remaining stock to various vendors

LAZY UNCOMMITTED PARANOID ONCE BURNED

When it came to mounting the transducer to my SHARK boat, it was a new opportunity…
This was my first tin boat and on prior fiberglass boats (mostly sail) I used FASTEETH or
POLIGRIP false teeth adhesive to stick the transducer INSIDE the hull in the bilge..
Won’t work on tin boats.. soooo
I had enjoyed my SHARK esp in skinny water, claming, exploring.. Chasing crabs.. Ran
Aground many times..
Thinking about getting a transducer down there and hitting the sandbars .. eeech… I would
Sheer it off for sure..If I have my transducer deployed and hit anything with force worst case,
I break a plastic picket...
And .. AND that damm transducer paint.. That, worked somewhat, lasted
One season b4 the remainder got hard in the little expensive bottle.. Ugg.. wouldn’t it be nice
Not to HAVE to deal with that paint?
Here presented for ya’all’s purview is my solution.. A length of plastic fence picket with the transducer wire snaked thru it.. And a rubber washer/bolt and wing nut to deploy and nest.

"Ya gotta grow olde, but ya hain't gotta grow up !"

I have one boat with a store bought block mounted with 5200 (which wasn't the best choice after reading up on here).

On another boat, I mounted a homemade block using 2 through bolts and Star Brite marine silicone. I made the block out of 3/4" pvc deck board. I'm not sure the deck board was the best option as it doesn't seem as strong as HDPE and I would have preferred a 1" thick piece but it was cheap when broken down to $/ft. I think I prefer using through bolts paired with silicone. My only beef with drilling holes in a boat is what if things change down the road and you need a different fastener pattern. With a mounting block, that isn't an issue as you can move things on the block and replace it if you need to. Bolts and silicone are a lot easier to remove as well if it comes to that as opposed to a permanent epoxy product.

"DRILL HOLES IN THE BOAT"... humm.. I did my time on submarines.... not a big fan of drilling holes in boats.. above the waterline .. ok

HDPE AKA milk bottles. Like most plastic surface adhering epoxy and glue are not reliable. The suggestion of drilling holes is a good suggestion. I would go a step farther and use a die grinder to undercut the holes or counter bore them and add some stainless screws so the epoxy would form around the heads making a mechanical bond. On my boat I used a slab of HDPE and screwed it to the hull, I used silicone around each screw and the perimeter of the slab a double row. Years of service, still tight and zero leaks.

Update on option # 2 the Stern Pad.
This block uses 3M VHB Tape.



Per manufacturer…

The Stern Pad material is a proprietary type of polymer. It is formulated for the marine environment (UV stabilization, saltwater resistance, etc.)

Epoxy paint on an aluminum boat does not need to be completely removed. Any other type of paint (ex. antifouling or paint with "anti-stick" additives) should be completely removed. It is highly recommended to use the supplied scotch-brite to prep the epoxy paint surface to ensure it is clean. This also provides microscopic surfaces for the VHB adhesive to flow into.

By
their mechanical engineer

What are all of you using to mount your transducers on alum boats transoms, especially the larger transducers that are nearly 12" long?
Are you screwing directly to transom or are you using a Plastic/HDPE Block?
How are you mounting the block....glue, screw, or both?

Click to expand...

I used a 3/4" thick block of HDPE (commonly called Starboard) and I took a tap and drilled and tapped several 1/2" holes across the back of the board (careful not to drill all the way through). Tapping gives the bonding material a place to grip on the board. From there you mark and sand the area on the back of your boat where you want to mount the board. Using JB Marine Weld, fill the holes making sure you get the JB Weld into the threads really good then smooth the rest over the board. Mount it on your boat and strap it down with duct tape for a minimum of 24-hours. The one you see pictured has been on my boat for four years now and is rock solid. Costs? If you can find a scrap piece of HDPE, you'll only be out the price of the JB Marine Weld.

Pothole said:

Costs? If you can find a scrap piece of HDPE, you'll only be out the price of the JB Marine Weld.

Click to expand...

And if you can't find a scrap, just shrug you shoulders when wifey asks why the cutting board has a corner missing!