Step Up to a Swim Platform

If you have a boat with a stubby swim step, there’s an easy fix you can do yourself (with a little help from your friends).


I own a 1999 Chaparral 1930 SS that I like a lot, but the swim platform was really small, so I went online to search for a new one. My main concern was finding one that looked like it was designed especially for my boat, not a generic one-swim-platform-fits-all model. I discovered, which has hundreds of models, including 30 for Chaparral alone. I found one listed for my model that could be color-matched to my boat. I wasn’t sure if I could handle the project myself, but Art at Swim Platforms said that if I was comfortable drilling holes in my boat, I could do it, as about 70 percent of their buyers install it themselves.

Tools Used

DIY-Boat-Swim-Platform-tool-01Drill and bits, 5/32, 13/64, 1/4, 3/8 inch // Sockets // Wrenches // Allen wrench, 5/32 inch // Countersink, 3/4 inch // Philips screwdriver // Safety glasses // Rags and towels // Solvent for cleaning adhesive // Caulking gun and caulk // Two-by-four boards or some suitable support system

Here is the cost breakdown:

Platform with black trim:   $1,145
Two-tone gelcoat:   $250
Crate:   $92
Freight:   $215
Beer and pizza for my helpers:   $30
Total:   $1,732

The instructions said I might have to make a few cuts to ensure a proper fit, and when my friends held the platform up to the transom so I could eyeball it, I noticed we would have to cut out a small section of the platform (1) where my MerCruiser outdrive housing protruded from the transom. The cutouts for my lifting eyes were already made. After marking it, I used a jigsaw to cut out a rough 6-inch section (it’s on the underside and won’t be seen).


My existing boarding ladder needed to be repositioned. To uninstall the ladder, just remove the bolts and refill the holes with the same bolts, after applying 3M 5200 Marine Adhesive Sealant to the underside of the bolt heads.

Next, support the platform into position before drilling the holes (2). The rubrail is cut long to allow you to trim it to match the angle of the transom, but to temporarily get it out of the way, unscrew it from the inside and let it hang down. We used two-by-four-inch boards to support the front of the platform, and I had adjustable support racks that were perfect to prop up the back of the platform.


To make sure the platform is centered properly, orient the center of the platform directly over the outdrive, which is always positioned dead center. To make sure the swim platform was level, I used a wood slat as a spacer (3) to make sure it was the same distance below the boat’s rubrail all the way across. Don’t use a smartphone app leveler, in case the boat is slightly askew on the trailer.


With the platform securely propped up, it’s time to drill. Start with the two holes on either side of the lower unit (4). First, check out the inside of the engine box where you will be drilling to make sure you don’t hit anything with the drill bit. As you are drilling, have someone watch inside the engine compartment, to be doubly sure the drill bit is coming out in an unobstructed area.


When the two holes are drilled, put the longest bolts through the holes and attach the locknuts, making sure to use washers on both sides (5). The shortest bolts go toward the outside of the boat where the hull is thinner. All the lag bolts should protrude at least three-quarters of an inch. Don’t worry about caulking them yet; the bolts are going in temporarily, to make sure the platform doesn’t move while you drill the other holes.


Using the 13/64-inch drill bit, drill three or four more holes on each side (6), evenly spaced, and staggered a bit (up and down) to create different stress points. The outermost bolts should be near the corner of the platform. Once all the holes are drilled, remove the two (or three) center bolts and remove the platform. Use the 3/8-inch drill bit to enlarge the holes in the hull and swim platform. Clean up all the holes and countersink them to prevent gelcoat cracking from the bolts. Around the outside of the hull, apply a ring of 3M 5200 around each hole (7) and to the underside of the bolt heads, so they form a water-tight seal when they’re tightened.

DIY-Boat-Swim-Platform-Step-06 DIY-Boat-Swim-Platform-Step-07

Re-support the platform into position and install the bolts, starting with the middle two and partially tightening all the others. Then, fully tighten one on each side, alternating sides until they are all tight, making sure they extend at least three-quarters of an inch inside the hull (8).


Next, install the two stainless steel support bars. Each rod should be positioned about an inch or so above the bottom of the boat (9) where the hull is very thick. You might have to bend the flat tabs at the end of the bars for them to lie flat to your hull and swim platform. Before drilling, hold them in place and turn the outdrive to make sure you have clearance. Each of the top tabs’ holes closest to the bend will be secured with a 2-inch Allen bolt. Drill from the bottom and countersink the top so the head lays flat. The other two top holes will be secured with ¾-inch lag screws, but when drilling your slightly smaller pilot hole underneath the platform, take care not to drill all the way through. Each of the bottom tabs will be secured with a 1¼-inch lag screw and, again, use a smaller bit to drill and make the holes shorter than the screws’ length. Use the 3M 5200 on each screw to ensure a tight seal.


The final steps are to reinstall the boarding ladder in the new location and reinstall the rub rail and trim it to fit. It helps if you heat the PVC rail first with a hairdryer.

Now we have plenty of room out back, and the new platform looks like it was installed at the factory.

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