Adding floatation to the stern under dive platform

Discussion in 'Boat Design' started by the brain, Jul 7, 2018.

  1. the brain
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    the brain Senior Member

    Adding floatation to the stern under dive plateform.


    I’m almost done fabbing on my dive platform here’s the plan slap a few blocks of Styrofoam each side of pod also stuff the POD which I’ve already done.


    Any design tips on secureing the outside blocks is appreciated.


    I’ve got aluminum and am ready to fab.
     

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  2. the brain
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    the brain Senior Member

    will probably wrap w/ aluminum like this,will stuff floatation pod FP w/ 1 an 1/2 blocks to facilitate replacing blocks.

    will secure FP metal w/ revits to engine POD and dive platform DP.

    plan to only have one DP.
    I would like a 2" lip around DP plan to wrape w/ thick plastic so when landing a large slippery fish the lip will prevent from sliding off.

    unless advised differently
     

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    Last edited: Jul 8, 2018
  3. bajansailor
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    bajansailor Marine Surveyor

    Re the polystyrene in the engine pod - are you just going to secure it in place (with the top open to the air), or do you plan to seal it with a water-tight 'lid'?
    If the former, I would be a bit worried about the possibility of crevice corrosion of the S/S plate behind the foam, and water settling in the bottom.
    If the latter, then there would be no need to have the polystyrene for floatation, as it will be watertight and buoyant.

    Re the blocks of foam on the sides, will they be totally enclosed, or will they just have a framework (aluminium?) around them to hold them in place?
     
  4. the brain
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    the brain Senior Member

    don't have different plans for floatation pod concidering options.

    the white styrofoam stuffed inside engine pod is very tight it will be secucred inside pod w/ the dive platform.

    either engine/floation pods cannot be sealed well they can but this enginge pod was designed to take on water, so when I stuff pod water can't takeup any space inside pod.

    the pods need to drain or they would rot from insideout.

    in a pervious related thread,I calculated the amount/area of sytrofoam to provide 600LBs of floatation. making the engine and 200LBs of aft. weightless correct?

    edit: the bottomof floatation is where the strength needs to be. so the back doesn't need to be as strudie.
     

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  5. Ike
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    Ike Senior Member

    Styrofoam would not be my choice for this. Styrofoam is a brand name and is very friable, and breaks easily in to little cells. It doesn't withstand shock and vibration well. There are other polystyrene foams that do better and have much smaller cell structure. Any polystyrene foam is easily attacked by fuel, and oils, cleaners etc so they need to be in a sealed box or chamber or placed where they won't come into contact with these products. Boat manufacturers who use styrofoam or other polystyrenes typically put them in sealed boxes or well up out of any area where bilge water or other liquids would collect. If you have some means of sealing this all up it should be ok. Otherwise you should use a polyurethane or polyethylene foam as they are not affected by these chemicals. Another option is wrapping the foam in vinyl. Bagging it in a sealed vinyl bag, or coating it with fiberglass. But use epoxy resin. Polyester resins will melt it.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I recall doing something similar many moons ago, I used polystyrene block foam with the edges well rounded by sanding, painted with acrylic latex house paint, and wrapped with a coarse synthetic, open-weave cloth wetted out with the same paint. That offered some abrasion resistance, and any fuel spilt did not get into it. When it was removed years later, it was in much the same state.
     
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  7. kapnD
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    kapnD Senior Member

    The third picture shows A black irregular line line running across the transom, well below the added foam.
    Is this the waterline at rest?
     
  8. the brain
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    the brain Senior Member

    excellent suggestion on latex paint.think I will remove the engine pods blocks and paint.
    the house painter way over estimated amount of paint required for house so I have a 5 gallon bucket leftover.
    however this big can of paint has been in the backyard storage for at least 7 years think it can be used to seal up the blocks?

    here's a image of water line port side one objective to lower this a few inches.

    edit:I will be adding blocks inside aft deck also my battery tray/oil reservoir platform is sagging, considering a long block under the platform.

    what do you Guy's think about 3 blocks contributing 600LBs of flotation at the heaviest section of vessel. the remainder of orginal flotation is not poured in foam, will this additional 600LBs of flotation keep a swamped hull afloat no matter how much water is taken on?

    like isn't there a point of swamping that the vessel becomes weightless? seams to me if floatation is greater than hull weight hull can be completey swapped and still float like boston whaler

    I intend on in near distant future to expose forward inside decking remove orginal floation then steam clean each revito then G flex. I suspect hard hull pounding GOM trips are loosening and knocking out revitos that are in high stress midship area's.

    I will be fabbing reinforcing brackets for this midship weak area soon.
     

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    Last edited: Jul 9, 2018
  9. Ike
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    Ike Senior Member

    Hard question to answer. The amount and location of flotation needed to make a boat float, when swamped, especially if you want it to float upright, is based on three factors. The weight of the boat, the weight of the people, and weight of the engines. To float upright the flotation for each of those has to be distributed around the boat. Just stuffing flotation in anywhere, especially under the sole will result in the boat rolling over and floating upside down. Look here Boat Building Regulations | Level Flotation http://newboatbuilders.com/pages/flot2.html If you just want it to float then you can put it most anywhere. I am assuming this is an outboard and the flotation you are putting in is there to float the engines. To float the boat itself there has to be flotation distributed around the hull, as far outboard as you can install it (along the sides and under the gunwales is the usual place). For the People it's basically the same as for the hull. For the engine it has to be aft near the engines and split, half on one side and half on the other to keep the engines high center of gravity from rolling the boat.

    OH Yeah, block foam is far better than pour foam. Pour foam is notorious for soaking up water. Block foam usually does not.
     
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  10. the brain
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    the brain Senior Member

    yes you make alot of sense here "
    For the engine it has to be aft near the engines and split, half on one side and half on the other to keep the engines high center of gravity from rolling the boat."

    so each side pod will have to be exact same size as opposite. I was actually planning the initial FP test run to be w/ just port side.


    The OEM floatation is thick white Styrofoam and in decent condition however it tappers down from very thick forth and very thin aft. remember there used to be a big 6cylinder merc occupying area so this section never got floatation from factory.


    My objective is to stuff as much floatation especially aft. To keep vessel and power head upright even during a swamping.


    I believe extra floatation and its lowered water level, vessel performance/ handling will be improved and will lessen the possibility for swamping.


    I have a Honda9.9 engine I want to install.

    And control throttle from helm.


    Here are some weights American LBs

    Hull 1900

    Engine 390

    45 gallon fuel 315

    Battery/oil reservoir60

    Front rode 50

    Equipment/coolers 200

    People either 1or 2 200/125 estimate 3115 soon to be installed Honda add 120.


    The hull is rated capacity of 2950LBs people/gear.

    I’ll combine fuel w/ people/gear weight 825-925 so vessel is carrying 1/3 of it’s capacity.
     
    Last edited: Jul 10, 2018

  11. the brain
    Joined: Sep 2016
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    the brain Senior Member

    update progress on lip/handle on dive plateform .

    lip will assist in landing extra large fish.

    what do you Guys think?
     

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