Custom Extended Swim Platform

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

  1. fallguy
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    fallguy Senior Member

    This might seem like a dumb question/point with all you have done, but what is the result of an impact to the platform?

    I would want to make sure it isn't to pierce the hull below DWL, so I would purposely weaken the strut connection at the platform or plate or create a failure point (if needed and where needed).

    I have seen them backed into docks and run into by other boats. The last thing you want is to have the platform indirectly result in the boat sinking.

    I don't know how heavy the transom is or the struts; so I might be off. But I am aware of a few swim platform sinkings. They go fast.

    Kind regards if I missed it and great work and best of luck.

    I am a bit nervous for the release and forming off/of the diamond stuff. It would be good to hear from a few experts on it.

    On the schedule are you trying to get to 0.1875 with only the glass n resin? I think I would expect you to be a bit thinner with 4. I would expect about 0.035-0.037 per layer or less. Much smarter guys here than me, take it with a grain of salt.
     
  2. tpenfield
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    Location: Cape Cod, MA

    tpenfield Senior Member

    All good questions. Keep in mind that this is a power boat with twin engines. The transom is probably the single strongest component of the boat. Similar to most I/O powered boats the transom is 1-1/2" plywood core with 1/4" of fiberglass on both sides, making it 2" thick. The transom is butted up with 3 engine mount stringers.

    I happen to have a 3D model of the structure of the boat (hull only not the cap/cockpit). Here are a few pictures . . .
    F330212.png

    F330211.png



    Shown in the close-up of the transom below, are the areas (Red circles) where I plan to anchor the struts via thru-bolts. They will be just inside the outboard engine mount stringers, which is a boxed in fiberglass structure.
    F330210.png

    Should the platform receive an impact, such as running into a dock, the platform would most likely receive all of the damage, leaving the transom intact. That would be my estimate, based on the relative amounts of structure and material of transom vs. platform. Platform and struts would give way long before the transom.
     
    Last edited: Feb 3, 2019
  3. fallguy
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    fallguy Senior Member

    I have built quite a few things with a 3 layer laminate of 1708 and it is not too stiff. I know you had four in the schedule and to be honest I find that a bit light for walking on...but perhaps I missed other things that will stiffen in your long post.
     
  4. tpenfield
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    tpenfield Senior Member

    Thanks, I have given the layup and core a bit more thought, based on your comments.

    I think if I go with 2 layers of 1708 top and bottom and use 1.5 oz CSM as the core 'weave', it would be better. The CSM will form easier around the foam strips and the 2 layers of 1708 being further apart will stiffen things up a bit. . . hopefully.

    LayupSched2A.png
     
  5. fallguy
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    fallguy Senior Member

    I don't know enough about infusion to know if that will work...sorry

    I would be nervous doing the core that way personally, but I have only done vac bagging, so I am nervous about how things flow doing infusion as a rule.
     
  6. tpenfield
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    tpenfield Senior Member

    Yes, I plan on using what is referred to as ‘Light RTM’ , where the resin is fed from all around the perimeter and vacuum taken from the center of the part. No good way to predict how the resin will flow through the weave, but perhaps I can make a sample piece to test.
     
  7. chowdan
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    chowdan 1980 PAC41 Liveaboard

    Looks like you've designed it well. I wouldn't be too concerned with the transom structurally, I would be more concerned with dispersing the load throughout the entire transom. Maybe glassing in GRP plates to distribute the load across the entire area where the structure bolts through.
     
  8. tpenfield
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    tpenfield Senior Member

    Thanks, I have thought about some reinforcement in the thru-bolt areas. I was planning on waiting until I fit the platform to the boat to determine exactly how much reinforcement, etc. Probably could add a few layers of glass where the bolts go through the underside of the existing platform area.
     
  9. tpenfield
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    tpenfield Senior Member

    I have done some looking and pricing of various foam products for the core material. I decided against PVC foam, in favor of urethane foam. I found some 1/2" thick 4.5 lb density "Last-A-Foam" boards online for about $3.50/sq. foot. Seems like a good deal.

    Not sure how many folks have used Last-A-Foam vs. the more commonly used foam like Divinycell or others. :) I had not come across Last-A-Foam until just recently.

    This would put the laminate at about 3/4" thick rather than 5/8" per my planned layup schedule.
     
  10. fallguy
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    fallguy Senior Member

    Never heard of it.

    Thicker is good.
     
  11. tpenfield
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    tpenfield Senior Member

    Quick update . . .

    I have done some research on the core design that I am planning to use. It is often called a 'navtruss' or 'corrugated core' in some scientific papers that I have found. Key benefits seem to be added strength/rigidity vs. a solid core.

    Here is the updated laminate schedule, based on using last-a-foam as the core.

    layup-sched3.jpg
    One reason that I wanted to do the core in this fashion is because I plan on using resin infusion and wanted to be sure that resin would flow through both the top and bottom layers of fiberglass in an equal fashion while in the mold. My hopes are that the 'weave'/'corrugation' will aid in that process.

    Time will tell . . . :rolleyes:
     
  12. tpenfield
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    tpenfield Senior Member

    Mold making update . . .

    I tried my hand at making the swim ladder hatch molds using resin infusion, figuring it would be good practice for the platform mold.

    The first mold did not go so well, but the mold is usable with a little bit of touch-up. I made a few adjustments on the second hatch and that went much better. Here are a few pictures . . .

    Infusion (second mold)
    IMG_2070.JPG

    The first mold . . .
    IMG_2060.jpg

    The second one . . .

    IMG_2074.jpg

    One thing that has got me puzzled a bit is that the tooling gelcoat does not seem to be curing properly. Traces of the gelcoat are being left on the plug, as you can see below.
    IMG_2073.jpg

    The gelcoat in the mold remains a bit tacky. So, I'm not sure what is wrong. I'm using 2% MEKP on the gel and 1.5% on the resin.

    I am applying the gelcoat, letting it set up/harden for about 90-120 minutes, then doing the infusion. Not sure if I should be waiting longer, or if there is something about the mold that is affecting the gelcoat. :confused: :(

    There are 6 coats of mold release wax on the plugs, plus PVA on the non-skid and flange sections. I am keeping the mold under vacuum for about 2 hours on the initial cure, then letting it cure another 2 hours before wedging it off of the plug. The resin is well cured, but the gelcoat is not.

    The resin is described as . . . "AOC, ASHLAND and REICHHOLD GENERAL PURPOSE POLYESTER RESIN. A rigid, low reactivity, pre-promoted, medium viscosity, thixotropic, orthophthalic laminating resin. Designed for production and repair of marine moldings and general glass-reinforced fiberglass parts. Available with or without wax. The most commonly used type of polyester for fiberglass work. "

    The tooling gelcoat is described as . . . "Tooling gelcoat is primarily used as a surface coating for the interior of fiberglass molds. To complete the mold this gelcoat is typically backed with our 404 Tooling Resin along with a combination of fiberglass mat and cloth."

    The only thing that I can see is that the "404" tooling resin referred to in the gelocoat description is "isophthalic" vs. the resin I have is "orthophthalic". I got the gelocat and resin from 2 different sources.

    Should I be waiting longer for the gelcoat to fully cure? Is the resin (poly) attacking the gelcoat? Other thoughts? :confused:
     
    Last edited: Feb 11, 2019
  13. Blueknarr
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    Blueknarr Senior Member

    I think the gelcoat was not fully cured.

    You didn't mention temperature. Both ambient and max rise in the part's temp affect cure time.
     
  14. tpenfield
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    tpenfield Senior Member

    Working temperature was about 68 F. I did move the mold to an area that was about 80 F after the infusion was complete. I can certainly wait a longer time . . may even do an additional coat of gel coat and let fully cure before laminating.

    I am also wondering if the presence of resin on the gelcoat before it has more fully cured prevents it from curing :confused:
     

  15. Blueknarr
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    Blueknarr Senior Member

    The resins are 100% compatible. Iso, ortho and gelcoat can even be intermixed with out curing complications.

    Four hours of cure before demolding is extremely quick. I try for 100° max exotherm and maintain 80° over night on my repairs.
     
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