80’s Sundancer / Weekender Swim Platform Extension

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 The size of the swim platforms on the 80’s boats were really far too small as were a lot of boats of the 90’s . The information in this file will show you not only how to repair your swim platform but extend it from its depth of 22” to 40”, big enough to put a couple of lawn chairs out and a cooler full of beer.

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There a few reasons that I can think of for doing this project; the swim platform is rotting or water logged or you are just tired of such a small platform. Once the integrity of the platform is compromised it is just a matter of time before it will need to be replaced or repaired. Figure 3 and 4 show the seam of the top shell and the bottom shell. Once water gets and if you live in a cold climate like I do it’s just a matter of time before the water freezes and the damage gets worse.

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I decided to cut the platform open using a cut off wheel and a dust extractor to keep the dust under control. A 4” grinder with a 1/8” blade on it will work just as well, I also wore a dust respirator suitable for this type of work. Notice in figure 5 and 6 how wet the wood is underneath the bottom fibreglass layer.

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Notice in figure 7 you can read the label from the original wood that Sea Ray used when they built the platform.

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The wood used is exterior sheathing, not marine plywood that many people believe is used in boat construction. None of the holes on this platform were sealed with any type of sealant. This probably led to the failure of the wood.

Once all of the bottom skin is cut off you can now remove the wood. I used an air chisel with a 1 1/2 “ flat blade bit.

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Figure 10 shows how the original platforms wood was cut and fitted with three pieces of wood. The wood was not cut and fitted equally in the top shell before the fibreglass bottom was poured. The swim platform is not perfectly flat there is a slight curve starting in the center and going out to the edges. The platform is over 9 feet wide and requires the use of at least 2 pieces of plywood. I decided to use 3 pieces, one small piece in the center and the two outside pieces exactly the same size and shape.

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This picture shows the seam in the center with one large piece of wood and 2 small pieces. Notice there is no sealant around the holes for the swim ladder.   

Here are some pictures of the wood that was removed from the platform, even if I was not stretching the platform I would remove all the wood and re-glass the bottom. This process is very easy, quick and insures that you have removed all the contaminated wood.

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You would not know by looking at the above pictures in the left corner that the wood needed to be removed and replaced. The other 3 pictures show not only rot but also mold, the picture in the lower left shows a redish tint to the wood, the cause, the inner layer is wet.

Now that all the wood has been removed the top part of the platform can be trimmed and cleaned ready for the next process. Now would also be a good time to grind the inside of the shell.

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In figure 12 you will notice that I left the edge that bolts to the boat but cleaned the flange on the opposite edge. The reason I did this so the edge will keep the plywood in the contour that I want. This also gives me a depth that needs to be built back up again to ensure proper strength. If you just want to rebuild the platform then your next step would be to fit the wood to this shell. I did this by turning the shell upside down on the plywood and tracing the outline of the shell.

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Figure 13 shows the plywood has been cut and is ready to be inserted in the platform shell. You can see in this picture that I have cut the upper shell of the platform to extend the platform. You would not be making this cut if you are just rebuilding the platform. The holes for the teak inserts need to be cut once all the trimming and fitting of the edges. I also drilled about 15 -1/8” holes in the plywood.

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Figure 14 shows all 3 pieces of the wood are dry fitted and ready for fibreglass. Before you start pouring resin into the shell you need to remove the wood and cut 2 pieces of fibreglass cloth that will cover the shell. This picture is of an extended platform but the process is the same.

Figure 15 shows the fibreglass cloth has been cut and fitted, the cloth needs to be removed and some resin mixed. Once you have about a quart of resin mixed pour it into one side of the shell. Take a piece of the cloth and lay it back down in the shell. You need to use either a fibreglass cloth roller or a 1 ½” scraper like I did and force the cloth through the resin. You might need to mix more resin as the cloth needs to be wet enough to bond to the wood as well as the shell.

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Figure 16 shows the wood has been laid on the wet resin and fibreglass cloth and is clamped and weighted down. The resin should ouse out of the 1/8” holes, if it does not you need to remove the clamps and pour some resin around the edges and re-clamp.

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Figure 17 and 18 shows the resin is almost level with the new plywood, you can also see the resin has oused through the 1/8” holes that were drilled. The platform needs to remain clamped for the next 24 hours this gives everything time to dry. Once it is dry it is time to grind the excess resin that came out the 1/8” holes and any that might have come over the edges. I now cut enough fibreglass cloth for six layers of mate and resin. As each layer is applied it is important to get all the air bubbles out and to make it as smooth as possible, I used my 1 ½” scraper to force the cloth through the resin to form one solid unit. When I got to the 3rd layer I started to build the sides edges up and the edges of the cut out for the teak inserts. As you can see the edges are still transparent, even though the sides are a ½” thick. 

Figure 19 the picture is of an expanded swim platform but the process for gelcote and drilling the holes is the same for a normal depth platform.

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The last process is to gelcote the underside of the platform. This is when you can practice getting the gelcote the same color as the boat. To get the cream color of the gelcoat on my 1988 hull I used white gelcote and used a little strong yellow tint and a touch of red strong tint. You do not add brown or beige gelcote tint to make a cream color. You also want to practice with a small amount about 4 ounces, you only need to add a few drops of the yellow and one of the red to change the color. If you are mounting the platform in the same location then you need to drill the old holes 2 sizes larger and then coat the holes with gelcote. Once that has dried you can drill the holes the correct size and mount the platform back on the boat. All fasteners should be coated with 5200 or 4200 to insure a water tight installation.

Material List

1-   4X8 sheet of exterior glad plywood (same material used in 1988).

1-   Quart white gelcote.

1-       1 oz strong gelcote yellow tint.

1-      1 oz strong gelcote red tint.

1-      50 ft X 36 inch fibreglass mate.

5-    Gallons of non-waxed resin and hardener don’t get the waxed.

1-      Quart of acetone used for cleaning up any spills or cleaning tools.

3-    3” rollers and a handle used for gelcote, don’t clean them throw them away 3 coats.

8-    ½” paint brushes, I bought the non name cheap ones, used to mix resin and help with spreading resin

8-       1” paint brushes, I bought the non name cheap ones.   



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