Custom Extended Swim Platform

Hello,

New to the forum. I've been a member for a while, but have not posted. Anyway, I am currently waist deep in a DIY project to build an extended swim platform for my Formula 330 SS. Some of the Google searching has taken me over here to the boatdesign.net forum.

I see quite a few questions being asked on this forum about building an extended swim platform . . . homemade, one-off kind of thing, but few if any of the threads have come to fruition.

I've had my Formula 330 for about 6 years now and one thing I have wanted was an extended swim platform to get the boarding ladder out beyond the outdrives. Currently the standard platform and ladder puts you right between the outdrives, which extend about another 18" beyond the platform edge. I also wanted to have 2 swim/boarding ladders, as we have dogs on the boat occasionally and use a dog ramp that needs to be connected to a ladder. Having only one ladder now, makes it tedious to alternate boarding people and dogs, as you have to detach the dog ladder each time. Here is the stern area of my boat and the standard swim platform and ladder.



Anyway, I took some measurements of the boat's platform area and worked up a design for an extended swim platform that would go over the existing platform and extend out about 2 feet, putting the ladders beyond the outdrives. Here are a few pictures of the design that I made on my computer (using 3D CAD software).




The outdrives are Mercruiser Bravo 3, and having dual propellers on each, they are a bit tricky to design a supporting strut system that clears the propellers at all possible angles of tilt & turn.




I also wanted to bring the extension portion of the platform a bit lower to the water. The current platform sits about 15-16" above the waterline, so I designed in a 6" step-down.



Here is a view of the design with the ladders folded out and all the trim & hardware (grab handles, cup holders, rubrail, pop-out cleats)



I wanted to make a full fiberglass platform (no wood) and given the design complexities, I figured a plug/mold approach would be the way to go, although fairly labor intensive and costly versus other approaches.

As I mentioned, I am 'waist deep' in the project having nearly completed the 'plug' from which to make the mold. I'll post some additional pictures leading up to where I am at. I thought it would be good to post on this forum to get any input and comments on the steps ahead, and also for the benefit of anyone considering building an extended swim platform.

 

Continued from first post . . .

So, not knowing any better, I started off with building a rough frame of the platform using EPS foam boards.



Then I fitted the swim ladders . . .



These are going to be hidden under hatches made in the extension portion of the platform . . .



I used some joint compound to fill in the voids in the foam structure and continued to shape things. . .

Here are the ladders set in place for sizing . . .


And these are the hatches which were made from the cut-outs in the extension.


Continued on subsequent post . . .

 

I was at a point where I needed to start glassing the plug, So I got a couple gallons of epoxy and some fiberglass cloth . . .



Then I sanded it down and put on fairing compound . . . Love the color


Lots of sanding and some additions to the plug . . .


Then another coating of epoxy w/ glass filler.


I wanted to add a non-skid surface to the main walking areas. I came across Gibco as a maker of both positive and negative non-skid patterns. Their pattern #315 is what Formula boats use. However, the material is wicked expensive, it would be about $750 for this project. So I looked for some alternatives.

Continued on subsequent post . . .

 

Continuation of plug fabrication . . .

I found some floor runner material that was pretty similar in size/shape to the Formula boat pattern . . .


The pattern is actually a 'pyramid' pattern and I sanded the points down a bit to make them more similar to the boat's pattern.

I have fit the non-skid pattern to the plug . . .


and the hatches . . .


I still have a bit more sanding and polishing to do on the plug, and that is where I am at as of today (January 8, 2019)

Once I have the plugs all ready to go, it looks like I will need to wax them and put PVA on them. I will probably need to test the non-skid material to see if the styrene from the tooling gelcoat will do it any harm.

My next major step will be to make the molds from the three plugs (platform, plus 2 hatches.) I plan on using a VARTM process and have seen the 'LightRTM' video series that has been discussed a while back on the forum.

I figure that I can 'practice' on the hatches, since the penalty of failure will be low as compared to starting on the main plug.

Anyway, that is where I am at . . . waist deep about to go deeper.

In terms of fiberglass experience, I have done some fiberglass work involved with structural repairs on this boat and also my previous boat (can you say rotten bulkheads ??? ) along with some other small/medium projects, but have not done VARTM yet.

Thoughts, advice, encouragement, discouragement all welcome at this stage.

 

Looks good but you need to take care of "beaver tail slap" of the platform in waves and when under power settling the rear into the water and during turns. Its going to put tremendous stress not only the platform but also the transom structure.

You should enclose the bottom of the platform and tab it DEEP into the boat's aft structure. Simply bolting it to the existing platform and face of the transom face is a recipe for serious structural problems or failure.

 

OK, thanks for the advice.

No good way to see how it performs in real life conditions. I wonder if I can find any good comparisons. I know Formula sells an extended swim platform on some of their boats that has a similar drop-down design.

While on plane the platform will be another 8-10" away from the water at the outer edges, which are about 1' inboard of the beam of the boat. At the keel, it is 25" of additional depth, beyond the 5-6" where the platform sits above the static waterline. So, I'm thinking the platform will be out of the way, but could catch a 'bite' or two during rough conditions.

Coming on and off plane are probably going to be the most problematic. Perhaps I can enclose (or skin) the bottom of the platform, as you suggested, so it does not want to 'drag' if it catches any water. I'll have to spend some time on the design of the underside.

 

That's an ambitious project.

To see how the platform is affected by water flowing under, over and around it, you may want to make a very simple plywood shape and fasten it in place.

That will be a challenging shape for a one-off first infusion, the resin flow can surprise you when the shape becomes more complex.

 

Thanks Ondarvr.

The resin infusion will certainly be a challenge. We will have to see how it goes.

 

What is your plan to mount the grid to transom supports?
Because it is extended perhaps solid glass from top to bottom for through bolting?

 

Here are a few diagrams depicting how I plan on attaching the swim platform to the boat.

There will be 6 Stainless Steel 'L' Brackets - 4 attaching to the underside and 2 on the sides attaching as shown.

Three support struts bolted into the bottom of the platform.

The 'slab' portion that goes over the existing platform will be attached with adhesive (3M 4200 type or maybe 5200)

Red areas are where the 'L' brackets will be.
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Here is the stern area of the boat, shown in black lines, and the extended platform shown in purple dotted lines. The adhesive is shown in green, hardware is shown in red.
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Here is a cross section view (Section 'A') showing the details of the hardware mounting.
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So, that is my current plan.

 

Here are a few more pictures with enhancements to the hardware illustration and a bit of re-engineering on the underside.







I'm thinking that I will have to fabricate the 'L' brackets out of bar stock (0.2" thick x 2" wide), since I cannot find anything suitable that is pre-made.

 

I plan on using 316 Stainless Steel tubing for the 3 struts that will support the platform from underneath. The outer struts are going to be about 48" ( 4 ft) in length, which seems a bit long. I anticipate that the platform could see load of up to 1,000 lbs. if a bunch of peeps were sitting along the outer edge.

Just wondering what tube diameter might be a sufficient for the struts? I figure the tube wall thickness would be about 3/32"-1/8" .

 

I highly suggest you contact Formula Boats and get their suggestions on your plan. Of course they are going to say its a bad idea, but they may take the time to explain why or perhaps even point out ways it can be done without ruining the back end of your boat.

 

I do have an inquiry into Formula Boats about some aspects of the platform, but I could expand upon that. I'm not sure that they would say it is a bad idea, other than the fact that they basically make/sell a similar thing on their boats and would prefer to sell rather than advise. Regardless, I'm sure their input would be beneficial.

One thing is that Formula Tech Support has curtailed their responses on older boats, favoring inquiries about newer boats (< 10 years old). I have not heard back on my initial inquiry after a week's time , whereas in the past, it has only been a couple of days and I would hear back. Sometimes, their tech folks are on the Formula Boat Owner's forum, so I could always try that route.

Anyway, I press on . . .

 

Quick update . . .

I sent my contact at Formula an email asking how they secure their swim platforms and directed him to a forum thread that I have on the Formula Owner's site. So, I shall see what he has to say.

In the meantime, I did find a few pictures of the underside of the Formula extended swim platforms, which is an option on many of their boats.

Here is the platform, similar to my design . . .


And here is the underside . . .


It is interesting that the platform extension is fully cantilevered and has no struts supporting it. Basically secured top and bottom to the build-in platform with fasteners of some sort. Doesn't seem like much, but it must work. Maybe I won't even need the struts that I was planning !

Anyway, I'll wait to see if I hear back from the Formula guy.