any benefit to having new swim platform extend hull?

Discussion in 'Metal Boat Building' started by Northeaster, Apr 17, 2019.

  1. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    Hi Folks,
    Many of you have helped me when i first built my aluminum 25" Glen-L design Double Eagle powerboat a few years ago. I have used the boat for the last 3 summers despite not being finished, and continue to work on it when time permits.
    I would like to build a swim platform that goes across most of the stern, except the far corner where my kicker lowers.
    I am considering just building a pipe or solid platform at desired level (just above resting waterline) with bracing underneath for strength.

    But, I have a lip or approx 4" hull extension now so I could extend this at hull depth for the required size of the platform, and then add bracing / stringers above and top off with pipework or flat panels.

    So, my question - is there any real improvement in speed/ efficiency, etc from having the hull extended approx 1.5 - 2 ft on a 25 ft hull (powered by a 150hp inboard cummins diesel, 1:1 gear. top speed around 20-23 kts and cruising speed about 16- 18 kts.)
    Hull moves well (I think) from displacement speeds to semi-displacement to planing.
    attached is old pic of stern.
     

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  2. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    With the tucked under IB propeller, none really. Maybe a little, but a wash with the skin friction. Too many variables to say with one picture.
     
  3. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Doubtfully, as jehardiman said.

    Is there any other benefit to you to have it?

    You could make a buoyancy pod out of it.

    Drawings?
     
  4. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    IMG_20160417_101202.jpg IMG_20160626_154059.jpg IMG_20161009_101142.jpg IMG_20160417_101023.jpg IMG_20160417_101202.jpg IMG_20160626_154059.jpg IMG_20161009_101142.jpg IMG_20160417_101023.jpg IMG_20160417_101023.jpg View attachment 146667 IMG_20160417_101202.jpg IMG_20160626_154059.jpg IMG_20161009_101142.jpg Thanks for the replies!
    I guess i could use it for bouyancy (had not thought of that). Other than that, no - i don't see any other benefit myself, if there wouldn't be some performance gain. Re: bouyancy though, I struggled alot in the last couple of years with the decision to add foam (or a combination of foam and plastic bottles, etc) and finally decided not to add either.
    I think the chance of hull breach / holing is very low, and we are not typically too far from shore, and normally tow a zodiak. The way the hull frames and stringers are planned out and built also does not allow me to easily weld airtight cavities, due to weep holes, frames not weld directly to the hull, etc.
    Here are a few more pics from construction and in the water.
     

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    Last edited: Apr 19, 2019
  5. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Re buoyancy, do you have any existing transverse watertight bulkheads in the boat, or is she effectively 'open' from bow to stern?
    Perhaps just the bulkhead of the rope locker in the bow, or not even this one?

    She has got a very nice hull form, and she should have good seakeeping.

    If you don't actually 'need' extra buoyancy at the aft end, and you have enough existing buoyancy to support the extra weight of a platform above the waterline, then doing this might be the easiest solution?
     
  6. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Is the designer available to discuss such a modification with?
    This could be of considerable value.
     
  7. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Put your money towards finishing out the boat as designed before launching into modifications.
    You really won’t know how it will eventually perform until then.
    Looks like there is plenty of flattish planing surface already, so not likely that additional surface will have much effect.
     
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  8. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    It is an older design and no the Designer is no longer available.
    re: bulkheads - I do not currently have any watertight bulkheads or compartments. I do have some areas, in the bow for example where I could make a watertight compartment but it then would not be of as much use for anchor and rod storage, etc. Until I eventually decide on cabin arrangements, I do not want to make too many changes in spots which could then change purpose.

    The design can be built with a cabin or Center Console. I may eventually do a small cabin, or more accurately a solid aluminum cabin roof supported by minimal (but still adequate..) sides and posts, windshield(s) and likely a lot of removable Lexan or similar panels to block some wind and weather on the sides when needed, but to be removed and stored when not needed.

    It looks like consensus is not to bother extend the hull. I will (if time permits) build a small swim platform, likely with an outer pipe bent to shape and then filled in with pipe rails or topped with a solid plate and some non-skid. I don't think the small weight of that will throw anything off..

    Attached is a pic of the same design,. albeit stretched to 28', with a similar swim bill-zubko-0031[1].jpg platform. It is raised in the middle, due to his home-made surface drive, which would not be required on mine.
     
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  9. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    Decided to do a simple swim platform about 6" above waterline. Will be well out of water when planing and even when getting on plane as the boat does not go bow-up when getting on plane. Did not have time to used sanding disks/grind or wire wheel today..
     

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  10. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Nice.

    Weld done!
     

  11. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    thanks for the encouragement! Not a pro job, but as an amateur, first time builder, I am happy with it..
     
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