Replace ply stringers with fibreglass system

Discussion in 'Fiberglass and Composite Boat Building' started by Carpenter Matt, Jul 10, 2018.

  1. Carpenter Matt
    Joined: Jul 2018
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    Location: Tasmania, Australia

    Carpenter Matt New Member

    hi people,
    I’m rebuilding a 4.45M speedboat and I’m turning it in to a centre console boat for fly fishing, the plan is a to do a full width pod extension of about 400mm replace all the rotten stringers, transom and floor the stringers are currently 18mm plywood glassed over but I would like to replace them with a fibreglass stringer system but I’m not sure how thick the walls of the new stringers have to be, my hull is a Haines hunter vi46 built through the 70’s and 80’s then the moulds were used by a company called formula they made the formula 15 and they used a full fibreglass foam filled stringer system in there design, I have some pictures of the stringer system they use but no dimensions of finished glass thickness, hull thickness and actual dimensions of the grid this aside I would like to design my own stringer system with bulk heads where I want them so I’m hoping someone can point me in the right direction as in thickness of stringer grid before I pop it out of the mould what the hull thickness should be before I glass the new stringer system in what should the finished thickness of the sidewalls and top of the truncated v design be what kind of layup I need to follow.

    Any guidance would be greatly appreciated
    ,cheers,

    Matt
     
  2. redreuben
    Joined: Jan 2009
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    Location: Beaconsfield Western Australia

    redreuben redreuben

    To save making moulds etc I would look at using 50mm sheets of polyeurethane as your stringers and frames. Mark out where frames are going, glass in 20mm pvc pipe as limber holes, install polyurethane frames, round off the top edges so glass will wrap over and cove edges where joins to hull. Glass.
    Hard to say sight unseen but probably 600csm with a 600 wr ought to do it wrap glass over top from each side so top has double layer. Grind back limber hole pipes to frame glass, make sure you leave enough glass over pipe to maintain seal. Bond in floor.
     
  3. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    Year's ago I did a similar job on a restoration of a somewhat larger boat. I'll post a couple of links to the old threads on this site that may give you some insight as to what you are facing. As you read through the posts keep in mind that I used 17/08 biaxle mat for the layup. If I was to do it again I would use cloth and/or roving. The 17/08 mat works but isn't necessary for this project and soaks up more resin than is needed.

    stringers https://www.boatdesign.net/threads/stringers.22134/page-2
    Bulkhead Connection - Cored Construction https://www.boatdesign.net/threads/bulkhead-connection-cored-construction.23883/
    Yet another Stringer Post! https://www.boatdesign.net/threads/yet-another-stringer-post.28361/
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Pop what out of the mould ? Have you already made some kind of mould for your stringer/bulkhead grid ? This is a terrific little boat, probably the best of its kind. When you say you are doing a full width hull extension, are you meaning an extension of the boat that contacts the water underway, or not ? Either way, it will affect the dynamics of the boat.
     
  5. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Your best bet is to leave the stringers hollow and drill limber holes as needed for water flow.

    1708 is a good product, roving will work if that's what you have, cloth is worthless in this application.

    1708 or any other stitched or woven combo fabric will use about the same amount of resin, the difference is that with the two products combined it appears to be more resin. CSM is in the 30-35 % (70%+/- resin) glass range and woven or stitched products will be closer to 50% glass, combine them as one product and they use the same amount of resin, it may be a bit more difficult to wet out the glass though.

    As for thickness, 5-6mm would be fine for the stringers. The stringer grid is made a bit thinner, placed in the hull and glassed over to bring it to full thickness. Hull thickness should be fine as is.
     
    Last edited: Jul 10, 2018
  6. Carpenter Matt
    Joined: Jul 2018
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    Location: Tasmania, Australia

    Carpenter Matt New Member

    Yes the extension will follow the shape of the hull, I’m extending the hull because they are prone to take water in over the stern and tis will allow me to make use of the whole deck space, yes I’m going to make a mould for my stringer grid out of kitchen white board once the extension is done so the stringers will run in to the extension
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    I would not be inclined to alter that hull like that, unless you have knowledge of others that have done a similar thing, successfully. It becomes a different boat, and the existing one is very well regarded, as about as good as it gets in the size range. As you know, there have been several builders who have "adopted" that hull, and I am not aware of any hull extensions with them.
     
  8. ondarvr
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    ondarvr Senior Member

    I have no idea of the design of this boat, but pods frequently limit bow rise, which may be good, but can also make the boat run too flat which can increase the wetted surface, possibly creating handling issues and lower the top speed. Raising the pods up slightly can help reduce the affects at speed, but these are trial and error adjustments that need to get dialed in before you anchor the pods in place.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    This is the hull in question, a classic small glass boat, very beamy for the 14'6 length, around 6'8 overall beam, and 5'10 chine beam aft. Around 20 degrees transom deadrise, with wide chine flats. I would not mess with pods on one of these, but that is just me.
    HAINES 146.jpg
     
  10. Carpenter Matt
    Joined: Jul 2018
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    Location: Tasmania, Australia

    Carpenter Matt New Member

    Yes it is a very good point being made about messing with a proven design, especially for a bloke in his backyard with little boat building experience,
     
  11. Carpenter Matt
    Joined: Jul 2018
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    Location: Tasmania, Australia

    Carpenter Matt New Member

    Ok I think I’ll scrap the extension idea, which is not the end of the world and I’ll concentrate my energy on producing a really solid long lasting and structural sound boat because as mentioned there is no better hull for its size hence the reason I would like a glass stringer system because I only have one shot a building a fishing boat that’s why i chose this hull with 3 kids and all the associated bills life brings with it money is not freely available to blow on the rebuild so not having the extension will free up some extra money as well
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    It might work well enough, extending it, depending on what use you want to put it to, and you do gain space, but it is gamble, and a lot of extra work. They are just so good as they are, not to tinker. Jackaroo boats has that boat in a tiller version, and a centre console, might be worth taking a look at the website, to see what they did.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Were you to adopt Redreuben's PU "stringers" (just a former to provide the shape to glass over), I would substitute "hard" PU foam, that being at least 4 lbs/cu ft, the light stuff is not much good.
     
    redreuben likes this.
  14. missinginaction
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    missinginaction Senior Member

    A couple of points. 17/08 mat, as I said, will work but it's an expensive solution and makes a laminate that is heavier than necessary. Bi axle mat was originally developed for use with polyester resins. The mat faced out and prevented print through of the cloth weave into gel coated surfaces. If you're going to use 17/08 make sure that it is compatible with epoxy. The binders in bi axle cloth are not always designed for use with epoxy although this has become less of an issue in recent years as the products have evolved. Stringers have been made with hollow cores (foam used as a former, then dissolved away with a solvent) with fine results.

    When I did mine (they're 10 years old with no issues) I used a layer of lightweight cloth in order to easily position the stringers. Think of tacking them into place. Once that cured overnight I began laying up the 17/08. It took gallons to wet out that mat (the cloth used relatively little). Nevertheless since I used 4 to 6 layers my stringers came out solid but heavier than necessary. Think about it....what gives a laminate it's strength? It's the resin/glass matrix. Large amounts of resin and chopped pieces of fiberglass aren't going to add any strength. Long strands of fiberglass oriented in different directions DO make for a strong structure.

    I'm taking the time to write this so that you won't make the same mistake I did. Learn from my mistake and save yourself some money and weight.

    Before you get started with this project do some research. David Gerrs book The Elements of Boat Strength provides an in depth look at what makes a good laminate and the appropriate use of different materials. Gerr is a well respected naval architect, don't take my word, take his.

    https://www.amazon.com/Elements-Boat-Strength-Builders-Designers/dp/0070231591

    Good luck with your project and BTW, welcome to the forum. Keep us posted on your progress.

    Regards,

    MIA
     
    Last edited: Jul 11, 2018

  15. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    If you're using epoxy you can skip the CSM and use just about any type of glass alone, this cannot be done in typical hand lamination with polyester.

    1708 was not designed to have the CSM side face up for a smoother surface (although it can be used that way), it was designed to increase the interlaminate shear strength when using polyester resins. CSM is required as the first layer, and in between each layer of woven or stitched fabric, so adding a layer of CSM to the 1700 makes it very convenient to use.

    This is why cloth is all but useless when using polyester resin, cloth is such a light fabric that by the time you use enough layers to build the strength needed the added CSM between each layer results in a heavy and thick laminate.

    I'm not aware of any 1708 that's not epoxy compatible, but there's rarely a need for it when using epoxy except for the CSM side up method referred to earlier for a smoother surface and being able to sand on it without damaging the actual glass strands in the 1700 fabric.
     
    Last edited: Jul 11, 2018
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