Build Upside-Down or Right-Side Up?

Discussion in 'Boatbuilding' started by zstine, Feb 21, 2023.

  1. zstine
    Joined: Sep 2013
    Posts: 141
    Likes: 18, Points: 18, Legacy Rep: 10
    Location: New Jersey

    zstine Senior Member

    I'm planning the build of a 25ft canal/lake cruiser (pic attached) and am trying to come up with the build sequence. It is a displacement hull and has 3 developed "planks" per side (7mm plywood) to be assembled in a stitch-n-glue manner with 3 molds, plus the transom to help define the shape. All frame shapes (8 frames in all) are predetermined, not templated from the skin shape after gluing as Gougeon Bro's describe.

    So what are the pros and cons of building upside down vs right side up? Typically small stitch-n-glue boats are built upright, which allows for 'heavy' fillets in the concave chines. The heavy fillets allow for a good amount of rounding of the chines prior to glassing the exterior. However, a beam of 8.5 ft will make filleting and laying glass inside the hull a literal pain in the back. So, doing it upside-down over the frames, like a plywood over frame construction, is possible, but I don't know if that's easier.?

    Anyway, what do you all think about the build sequence? What if I just fillet and glass the 2 planks along the keel first, upright, then I should be able to walk on that to make the rest of the glassing easier. But that also means a lot of secondary bonds and sanding... idk?
     

    Attached Files:

    fallguy likes this.
  2. wet feet
    Joined: Nov 2004
    Posts: 1,432
    Likes: 453, Points: 83, Legacy Rep: 124
    Location: East Anglia,England

    wet feet Senior Member

    Have you considered building right way up,with external frames holding the shape?Thats how some OK's were built in the 1960's and it worked well.Once the internal bonding is complete you can deal with the outside.
     
  3. zstine
    Joined: Sep 2013
    Posts: 141
    Likes: 18, Points: 18, Legacy Rep: 10
    Location: New Jersey

    zstine Senior Member

    yes, that's one of the options; upright with external female molds. The main difficulty I see in upright construction is that the gluing/filleting of joints is going to be difficult, ditto laying down the fiberglass. It will require me to lean over the hull and reach inside, or perhaps build some scaffold that allows access into the middle of the boat (not sure how). I'm fairly certain that I can't walk on 7mm plywood until after the fiberglass is down and cured. So all that work has to be done leaning over the boat which is 8.5 ft wide. But even with it's difficulties, it may be better than building upside-down...?
     
  4. wet feet
    Joined: Nov 2004
    Posts: 1,432
    Likes: 453, Points: 83, Legacy Rep: 124
    Location: East Anglia,England

    wet feet Senior Member

    Without knowing what you weigh,and how much experience you might have of turning hulls over,it isn't easy to offer suggestions.I don't see any reason why the external frames shouldn't have something like a 1 1/2!X1" stringer let in to make damage more difficult to create.Then there is the alternative of building upside down and having to get across the bottom panel to the keel,opposite direction but same physical challenge.
     
  5. fallguy
    Joined: Dec 2016
    Posts: 7,707
    Likes: 1,708, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I am a contributor on boat builder central and about 95% of s/g boats there are built upside down. Many are taken all the way to finished paint before flipping to avoid multiple flips. Nearly 100% of the builds there are s/g with only 2 in the last year foam and one aluminum.

    Upside down is the best. Things like the sides opening can introduce hook to the bottom; less important for you, but something you can avoid easily with the hull upside down.

    All of this and I built my foam boat rightside up and flipped it twice for each hull, so my bias is not towards upside down, but the only way I would do it.
     
    rwatson likes this.
  6. fallguy
    Joined: Dec 2016
    Posts: 7,707
    Likes: 1,708, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    For monocoque construction, laying the glass in the bottom can be done off the roll. So, you cut the glass to fit and then roll onto a 3-4" tube. You use a lot of sharpie references on hull and glass to keep length and location p-s correct. You enter the boat with the roll and laminate as you go, 2' at a time, working back to dry boat until you get to the end.

    For the sides, you can tip the boat on her side.

    There are a lot of tricks to make it easier.

    I also recommend precoating the wood before laminating. Depending on the schedule, it may be done a day early if you can drape the cloth or same day if you are rolling glass off tubes. It is especially important for light wovens like 6oz.

    Join bbc and get lotsa free help.

    Light wovens and biaxials lay very differently, so the approach depends on the glass schedule.
     
    Last edited: Feb 21, 2023
  7. zstine
    Joined: Sep 2013
    Posts: 141
    Likes: 18, Points: 18, Legacy Rep: 10
    Location: New Jersey

    zstine Senior Member

    thanks, wet feet. I'm ~190lbs and the boats I have flipped (a few) have been trivial, no more than 20ft and under ~800lbs. yes, I could support the hull better. Being a stitch n glue, I was planning minimal support. Just enough to keep it up off the ground and 'check' the shape, not to force it in a shape like ply over frame. While its possible to do that, I think i'd have to add several stringers and several molds/frames to support walking on the hull before glassing. would be a lot of extra work. Upside-down it will be about 5ft high at the highest point. But unlike right-side up, you can lean against the hull to reach the keel.

    Hey Fallguy, I have built s/g upside-down. I like that frames can be used as molds and placed properly on a strongback. And you don't need to make female molds, which saves a bit of time and cost. There's a few drawbacks. Like the glue joint is just the thickness of the ply, so you can't round and fair the chine as much as having a thick fillet on the inside, allowing you to sand nearly through the plywood without concern... Maybe this is not a big deal. I'm not designing a race boat.
    Putting her on her side is a great idea. I only have 8 ft ceilings, so I can't get her 90 deg, but likely far enough to make doing the interior work a lot easier. I will have to move the boat outside the shop to flip her. so the 1 flip for upside-down start has an advantage of saving a flip there, but I don't think flipping the boat is going to be that big of a deal..

    hhmmm.. thanks guys.
     
    bajansailor likes this.
  8. rwatson
    Joined: Aug 2007
    Posts: 6,170
    Likes: 498, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    Fallguys comments are spot on.
    For my part, any S&G boat I build from now on will be on a strongback on a Rotisserie.
    To avoid Epoxy and Paint runs, and for ease of fairing ( which there is lots of in S&G) fitting out etc, being able to rotate on demand, especially in a smaller shop, is the ultimate in time and effort in building.
    S&G is supposed to be "self fairing", but its surprising how much manipulation you end up needing to do, especially if you didn't have the panels C&C cut.
    My tip is to use fairly stiff wire for the joins, so that not only can you pull them tighter, but also force them inwards etc.
     
    Last edited: Feb 22, 2023
    bajansailor and fallguy like this.
  9. BlueBell
    Joined: May 2017
    Posts: 2,722
    Likes: 988, Points: 113
    Location: Victoria BC Canada

    BlueBell . . . _ _ _ . . . _ _ _

    I haven't read any of this thread.

    Zstine,

    When I built my houseboat (25' x 10') -similar to your design, I built the hull upside down in a shop, rolled it outside, flipped it with a two hoist crane, rolled it back in and built the cabin (17'x9').
     
    fallguy likes this.

  10. voodoochile
    Joined: Nov 2009
    Posts: 57
    Likes: 53, Points: 18, Legacy Rep: 10
    Location: Macau SAR

    voodoochile Junior Member

    upside down
    just having gravity doing the work for you when it comes to laminate is reason enough.
    25 feet isnt that big aniway. 6 guys should do it
    reverse, rinse and repeat on the inside and boom, new boat!
    looks like a cool project.
     
    fallguy likes this.
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.