6 Best Custom Cut Mounting Shims For Boat Bulkhead Displays

Mounting a high-end marine display on a curved or raked bulkhead is the ultimate test of a sailor’s patience and structural ingenuity. Without a proper shim, you are either forcing a rigid chassis against a non-compliant surface or leaving unsightly gaps that invite moisture and vibration. Getting the geometry right at the installation phase prevents long-term hardware failure and ensures your instruments remain readable in any sea state.

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Seaworthy Shims Custom HDPE: Best Overall

Seaworthy Shims excels by offering bespoke CNC-cut solutions tailored to the specific footprint of major marine electronics brands. By utilizing high-density polyethylene (HDPE), these shims provide a non-porous, UV-stable interface that won’t compress or rot over time. This is the top choice for boat owners who demand an OEM-quality fit without the frustration of manual trimming.

The precision of these shims effectively eliminates the structural stress caused by mounting flat electronics frames onto curved cabin walls. Because the manufacturer understands marine tolerancing, the bolt patterns are consistently accurate, reducing the risk of hairline cracks in the display housing. If you want a “set it and forget it” solution that looks like it came from the factory, this is the gold standard.

Boat Outfitters StarBoard: Best for DIY

Boat Outfitters provides high-quality King StarBoard material cut to your specifications, making it the perfect partner for custom DIY projects. This material is the industry benchmark for marine plastic, offering exceptional durability and a textured finish that hides minor imperfections during installation. It is ideal for the owner who prefers to customize the final shape or drill specific cable routing holes on the fly.

While this option requires more labor than a pre-molded shim, the trade-off is total control over the mounting geometry. Because the material cuts easily with standard woodworking tools, you can refine the angle on-site to account for unexpected bulkhead variations. It is the best choice for those who value flexibility and the ability to adjust the mounting plane mid-installation.

Tek-Tuff CNC Marine Shims: Precision Pick

When the margin for error is measured in millimeters, Tek-Tuff delivers the necessary accuracy through advanced CNC milling. These shims are designed for high-vibration environments where a perfect flush fit is the only way to prevent screw loosening or display rattling. They prioritize structural integrity above all else, often featuring reinforced contact points that distribute pressure evenly across the bulkhead.

This product is aimed at the serious cruiser or offshore angler who expects their equipment to handle heavy impacts without shifting. By choosing Tek-Tuff, you are paying for technical precision that prevents the “shim creep” often seen with cheaper, softer materials. For mission-critical navigation stations, this is the most reliable mounting interface available.

Marinco Pro-Fit Service: For Heavy Displays

Marinco’s approach focuses on the massive physical load of oversized multi-function displays (MFDs) that can weigh heavily on delicate fiberglass surfaces. Their shims are engineered with extra thickness and structural webbing to prevent the compression of the underlying bulkhead. This ensures that large displays remain perfectly vertical and secure, even when subjected to the torque of heavy weather.

This is the definitive pick for anyone mounting 12-inch or larger screens where leverage becomes a serious concern. It effectively turns a weak or uneven section of the boat into a solid, reinforced mounting pedestal. If your primary goal is mechanical security for expensive, heavy hardware, skip the light-duty plastics and invest in this robust mounting service.

OC Boat Supplies Cut-to-Size: Budget Pick

OC Boat Supplies offers a practical, budget-friendly route for those who need a functional shim without the premium cost of custom CNC branding. These cut-to-size options provide a solid base for standard electronics without unnecessary frills or inflated pricing. While they may require minor sanding or cleanup after delivery, the material quality remains perfectly suited for marine duty.

This is an excellent option for non-critical displays, such as secondary gauges, digital depth sounders, or auxiliary switches. It keeps costs low while ensuring the electronics are properly sealed against the bulkhead. For the value-conscious sailor who has a clear idea of what they need, this service hits the perfect balance of price and utility.

TackleDirect Shim Blocks: Angled Dash Mounts

TackleDirect offers specialized shim blocks designed specifically for console or dash mounting where the angle of the mounting surface deviates from the desired line of sight. These blocks are manufactured with pre-set angles, allowing for quick adjustments that improve the viewing ergonomics of fishfinders or chartplotters. They provide a clean, professional aesthetic that integrates seamlessly into a helm station.

These blocks are particularly useful for center console boats where dash space is limited and viewing angles are frequently poor. By installing a pre-angled block, you gain better visibility without the need for complex fabrication or custom carpentry. This is a must-have for any helmsman looking to optimize the ergonomic layout of their cockpit.

Choosing Your Shim Material: HDPE vs. ABS

Selecting the right material is a choice between long-term durability and ease of fabrication. HDPE (High-Density Polyethylene) is the industry darling because it is nearly indestructible, impervious to moisture, and completely UV-resistant. Its only downside is that it cannot be glued with standard adhesives, requiring mechanical fastening for all connections.

ABS, on the other hand, is significantly easier to paint, bond, and shape, making it a favorite for complex custom enclosures. However, ABS is susceptible to UV degradation over time if it is not properly finished or kept out of direct sunlight. Generally, if the shim is exposed to the elements, HDPE is the superior choice, whereas ABS is best reserved for protected indoor cabin installations.

How to Measure Your Bulkhead Angle Correctly

Accurate measurement is the difference between a secure mount and a display that binds or pulls away from the wall. Begin by using a digital angle finder or a contour gauge to capture the precise slope of the bulkhead. Do not rely on visual estimation, as even a two-degree variance can cause significant stress on the mounting points of a rigid electronics housing.

Always measure at the exact four points where your mounting screws will penetrate the bulkhead. If the surface has a compound curve, you must account for the high and low spots to ensure the shim sits flush. Mark these points clearly and double-check your readings; a shim that is cut slightly too thin is a common reason for fractured bezels and mounting failures.

Mounting Your Shim: A Step-by-Step Guide

1. Dry Fit: Place the shim against the bulkhead and confirm the orientation, marking the exact screw locations on both the shim and the boat surface.
2. Sealant Prep: Apply a high-quality marine-grade silicone or polyurethane sealant to the back of the shim, ensuring a continuous bead around each screw hole to prevent water ingress.
3. Mount the Shim: Fasten the shim to the bulkhead using stainless steel hardware, tightening firmly but being careful not to crack the shim material or compress the fiberglass too aggressively.
4. Attach the Device: Once the shim is cured, mount the electronics display to the shim itself, ensuring the machine screws have adequate thread engagement without bottoming out.

Avoid over-tightening at every stage of this process, as marine bulkheads are often thinner than they appear and can easily deform under excessive pressure. If the shim doesn’t sit perfectly flat, do not use the mounting screws to force it into place, as this introduces internal stress. Always use a backing plate or oversized washers on the reverse side of the bulkhead if the material is thin, as this prevents the screws from pulling through during heavy vibration.

Common Mounting Mistakes to Avoid at All Costs

The most frequent error is neglecting to seal the cable pass-through hole, which allows saltwater to migrate behind the bulkhead and rot the core. Another common pitfall is the failure to use backing plates or fender washers on the interior side of the mounting surface. Without these, the vibration of the boat will slowly enlarge the screw holes until the entire display unit becomes loose or tears away from the mount.

Additionally, avoid using carbon steel or non-marine grade fasteners, which will rust and stain the bulkhead within weeks of exposure to salt air. Never mount an electronic display directly over an existing seam in the hull or bulkhead, as these areas are prone to flexing and will eventually lead to display housing fatigue. Prioritize structural solid ground over aesthetic convenience every time.

Properly shimming your electronics is not just about keeping the screen steady; it is about protecting the life of your equipment and the integrity of your cabin walls. By selecting the right material and ensuring a flush, waterproof fit, you create a mounting system that can withstand years of active service. Invest the time in measurement and mounting now to avoid costly hardware repairs later.