Custom Extended Swim Platform

Discussion in 'Boatbuilding' started by tpenfield, Jan 8, 2019.

  1. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Junior Member

    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.

    01image_298260.jpg

    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).

    02image_304716.png
    03image_304737.png

    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.

    04image_304738.png
    05image_304785.png

    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.

    06image_304791.png

    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)

    07image_304845.png

    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.
     
    Last edited: Jan 8, 2019
  2. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Junior Member

    Continued from first post . . .

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

    08image_301240.jpg

    Then I fitted the swim ladders . . .

    09image_303395.jpg

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

    10image_304562.jpg

    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 . . .
    11image_304563.jpg

    And these are the hatches which were made from the cut-outs in the extension.
    12image_304561.jpg

    Continued on subsequent post . . .
     
  3. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Junior Member

    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 . . .

    13image_304658.jpg

    Then I sanded it down and put on fairing compound . . . Love the color :)
    14image_305420.jpg

    Lots of sanding and some additions to the plug . . .
    15image_306212.jpg

    Then another coating of epoxy w/ glass filler.
    16image_306276.jpg

    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 . . .
     
    Last edited: Jan 8, 2019
  4. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Junior Member

    Continuation of plug fabrication . . .

    I found some floor runner material that was pretty similar in size/shape to the Formula boat pattern . . .
    17image_305009.jpg

    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 . . .
    18image_306535.jpg

    and the hatches . . .
    19image_306585.jpg

    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. :)
     
    Last edited: Jan 10, 2019 at 5:26 PM
  5. JamesG123
    Joined: Mar 2015
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    Location: Columbus, GA

    JamesG123 Senior Member

    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.
     
  6. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Junior Member

    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.
     
    Last edited: Jan 8, 2019
  7. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    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.
     
  8. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Junior Member

    Thanks Ondarvr.

    The resin infusion will certainly be a challenge. We will have to see how it goes.
     
  9. Barry
    Joined: Mar 2002
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    Barry Senior Member

    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?
     
  10. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Junior Member

    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.
    .
    ESP-Attachment-1C.png
    .
    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.
    .
    ESP-Attachment-1A.png
    .
    Here is a cross section view (Section 'A') showing the details of the hardware mounting.
    .
    ESP-Attachment-1B.png
    .
    So, that is my current plan.
     
  11. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Junior Member

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

    ESP-Attachmnet-3C.png

    ESP-Attachment-3A.png

    ESP-Attachmnet-3B.png

    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.
     

  12. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Junior Member

    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" .
     
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