Fibreglass hull extension

Discussion in 'Fiberglass and Composite Boat Building' started by Reefrunner, Feb 19, 2019.

  1. Reefrunner
    Joined: Feb 2019
    Posts: 12
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    Location: Australia

    Reefrunner Junior Member

    G'day.

    First time poster, Had a few questions for the gurusg here.

    I have a Carribbean reef runner i wish to extend. I have a pretty good knowledge of fibreglass from previous projects and working with a shipright for some time awhile ago.

    I know I'll be told to source another hull of suitible dimensions, but this hull in particular holds a kind of sentimental value.

    I'm in Australia but I shall try to convert units roughly into USA talk.

    I wish to extend the hull 1.5 Meters (5 ish foot) at the transom, I intend on building a splash well and converting to outboards at the same time.

    I have gutted the hull in questiin already, and ground out about 3/8 (10mm);of dry and poorly laid original glass.

    I intend on relaminating the entire hull to a thickness of 1" (25mm) utilising CSM, woven and Double bias.

    My question is when I re laminate the entire hull, I intend on running the laminations into the extension mould at the same time. Will this give the boat ultimate strength? Will their be anything else required?

    I have built hollow glass stringers already at a thickness of 8mm so far. I intend on glassing them down and over to a total of 12mm thick steingers. The stringers are 6" wide across the top.

    I also plan on running webs outboard of the stringers at intervals of 450mm centres.

    Once the boat is to a float stage. I intend to take the boat to the water and load it up to determine steering positions, built in eskys, fuel tanks etc. and engine weights.

    Basically I'm worried about the strength at the join for the extension.
    I was hoping that a re laminated hull laid into the extension would give back to original type hull strength.

    Cheers.
     
  2. JamesG123
    Joined: Mar 2015
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    Location: Columbus, GA

    JamesG123 Senior Member

    You're going to add glass layers to the entire hull?

    What is the requirement for doing this and thickening, strengthening the entire hull to such a degree?

    You're planning on cutting the transom off and reattaching it to the extension?
     
  3. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    You should know what is required from your past experience, to get the joint right, it does sound you are going a bit overboard with the material thicknesses, possibly. Have you got the old hull in a good cradle, to support it properly ? I am familiar with the boat, 5 feet is a lot of extension.
     
  4. Reefrunner
    Joined: Feb 2019
    Posts: 12
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    Location: Australia

    Reefrunner Junior Member

    G'day James.

    Yes I intend to build the complete hull up as iveI had to grind so much away.

    I like to over engineer things to a high degree to last. I also fish all sorts of weather and would prefer not to have any doubts in my mind.

    I'm planning on cutting the xompletc transom out, as when I do the extension, I intend to build a splashwell for an outboard mount. ( Currently stern drive)


    Mr efficiency,

    The hull is well supported, I want to get plenty of strength back into the hull, more then factory if possible.

    While I have a good amount of fibreglass experience, I never attempted a whole hull extension. I've built a fair few 3/4 pods in the past, but they have all been bolted as well as glassed.

    I just want to be sure I haven't overlooked anything and I will not run into any major issues after I've started.

    Cheers.
     
  5. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    $64 question is what happens in a seaway, you might find it behaves differently to what you expect, especially downhill. make sure you don't inadvertently build any hook into that extension. Where will the boat be used ?
     
  6. Reefrunner
    Joined: Feb 2019
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    Location: Australia

    Reefrunner Junior Member

    Indeed that's a worry. A risk I'm willing to take. No hook will be built in... At this stage... Ha.

    Boat used within the reef systems of the east coast of Qld.
     
  7. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    To expect to get any reasonable answers , you need to start by laying out all available information about your project.
    You have stated the length of the proposed extension, but not the length , beam, type of hull, original power, proposed power, thickness of original layup of the original hull, proposed use, etc.
    Some pictures would be very informative too.
    So far, I’m guessing that you’re talking about a fairly small craft, so for starters, a 1” thick layup will put it in the submarine class!
     
  8. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I think they are around 22 feet, a deepish vee hull.

    REEF.jpg
     
  9. Reefrunner
    Joined: Feb 2019
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    Location: Australia

    Reefrunner Junior Member

    G'day, kapnD.


    As per Mr efficiency,

    The hull is the same as his picture. 22ft long, 2.54m beam. And a fairly steep deadrise.

    Original hull was around 8mm thick, however I've taken that down to an average of 2 mm due to dry and delaminating glass.

    The original powerplant was a MerCruiser 350 chev style. I plan on repowering with outboards. I had planned to get the boat to the float stage then simulate weight as to wether I go twins or single screw in order to get the best balance. I intend on a 700l fuel tank also. The boats to be used for extended trips fishing.

    I like to have them built heavy down low, the last 5.4m I buikt brand new out of a mould was 27mm thick, and it rode super quiet and beautifully, we did another build of a lighter build quality and it was lacking ride and noise levels like the first one.

    Cheers.
     
  10. Reefrunner
    Joined: Feb 2019
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    Location: Australia

    Reefrunner Junior Member

    I read somewhere these are a flop of a Bertram 20. Although I haven't been able to measure one up yo compare.
     
  11. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    No, quite different to the Bertram 20. The Reef Runner goes back to the 70's and it appears a few are being converted to outboard, can't remember too many being outboard powered originally. I'm amazed you are sanding so much glass out, surely that isn't needed ? Your boat is disappearing !
     
  12. trip the light fandango
    Joined: Apr 2018
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    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    I'm an amateur who is also adding, cutting shutting older fibreglass hulls, my stuff is more beach cat orientated though, different stresses.. When I look at this proposal the new overall length is beginning to look a bit too skinny. Out riding fillets that increase the beam and extend forward say 1 1/2 metres along the water line tapering out to add an increased width of maybe 250mm to 300mm would make the warning bells settle a little for mine. The added strength down low would also make me feel a little better. The weight of the motors hanging off the new transom is obviously a main concern. There's not much use in bracing it way more than the rest of the boat but some extra is peace of mind. When you said you cut back weakened original matt it explains why your beefing up the glass so much to me, but it also made me question the original hulls integrity too. The increase in twist needs some triangle shapes built in with or diagonally across your stringers, I think, just my 2 bobs worth, an interesting project. Hopefully you have provided the pros with just enough info to respond. One thing work with standard resins avoid epoxy , you can use it as a waterproof seal if it's going to be moored.It may need extra strong backs,in case its thinking about buckling, but they can't be in the way of the glassing,,hmm. cheers
     
  13. Reefrunner
    Joined: Feb 2019
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    Location: Australia

    Reefrunner Junior Member

    Mr efficiency,

    I spoke to a few guys on some reef runner pages that have done restos, seems to be the common practice of grinding all the dry glass out. I've never seen such dryness and delamination in any brand of hull.

    They do a newer reef runner npw that's exclusively outboard, however I believe they took 2deg of deadrise out, and also pulled the sides in anot, apart from that the hull is the same according to Carribbean.
     
  14. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Sounds odd to me, is there woven rovings in there ?
     

  15. Reefrunner
    Joined: Feb 2019
    Posts: 12
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    Location: Australia

    Reefrunner Junior Member

    Some hulls allegedly. Mine not that I've ground out.
     
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