SWIM PLATFORM EXTENSION
A "how to" story with tips and tricks for a 1975 28' Express.
The original platform wasn't big enough for scuba diving so we decided to extend it My neighbor Mike owns a metal fab shop and had the materials and tools we would need. I wanted it to match the old one so we came up with a plan to make it look similiar to the original. We didn't need it to be as wide (X) as the existing because of the kicker mount (see pics below). This is a crude representation of what we are building:
Y |____|
.......X
Materials:
X' x Y' sheet of 1/4" 6061 aluminum - We used 6' x 2' smooth but you could use diamond
3 - 8' lengths of 1/4" x 2" 6061 flat bar stock
aluminum welder with skills (Mike)
cost = $400
time ~ 10hrs
Before taking the boat to Mike's shop, I sanded the paint off the existing platform in the areas where he would be doing the welding. This is how we did it but I know, "There's more than one way to.....".
First you bend a 85 degree angle (or so) approx 18" inches from one end of a piece of flat bar. This will be the shorter port end. Then bend a slight curve into the long length to mimic the arc of the existing aft edge. Measure where the other end should be bent and bend another angle to match the first one. Position your |___| shaped piece up against the platform and cut off excess from SB end. Level and tack in place to make it
flush and level with the existing. You can fill the mating ends with weld to make it smooth. Author's note: The above procedure sounds easy and it was for Mike. But I would have screwed it up for sure.
Lay your plate atop the |___| positioning it to cover but keep one side as close as to the edge so you will only have to make minimal cuts. Clamp into position. Scribe/mark along the INSIDE contours of the |___| onto the plate from underneath to complete the pattern. Cut along your pattern lines with a band saw or jig saw. Be sure to make your cuts with tight tolerances to prevent excess gaps.
Now for the hard part. It is necessary to cut holes into the plate to allow water to pass thru and minimize the hydraulic effect when awash. After laying out the location of each slot, Mike used a
plasma cutter to make short work of it. I used a high speed air die grinder and a carbine burr bit to clean up all the rough edges. This process took longer than anticipated. Note: Docsnow (big M forum member) used a jig saw (see additional tips below). Either way there is a lot of labor to clean up the edges of the cuts. If a person had access to a water jet cutter.....
After the holes are cut, place the plate in the |___| and clamp to close any gaps. Check to make sure it is level. Weld in place, cut the 1/4" x 2" support stock to the measured lengths. Each one will be different. There should be one support to match the existing platform supports. We used a total of 10. The two at the ladder bracket are 5/16" X 2". Cut the corner off the bottom aft end of each and grind to smooth and shape. Your expert welder will know how to zap it all together to minimize the distorting effects of expansion and contraction.
Apply a
couple of coats of nonskid paint and you are ready for a dive trip.
From Docsnow and others:
Use a cheap 1/8" luwaune (sp?) backing or some scrap thin wood backing made the cutting easier & only used 1 blade as opposed to 3 to cut the first 1/3rd of the inner arc.
To bend AL without fracturing. Heat at or near place of bend till U can make a hickory hammer handle leave a mark by rubbing on it. Then it is ready to be formed. This annealing will last up to 6hr & will return to it’s original temper.
Use kerosene when ever possible to eliminate galling of blades, drills, etc.
Click
here for more useful tips on working with aluminum.
Surface Interval
1975 28' Express, Single M360
Specs:
http://www.boatm8.com/my...amp;page=boats&arr=0