Adding a keel to an inflatable

Discussion in 'Boat Design' started by Xyberz, Jul 12, 2016.

  1. Xyberz
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    Xyberz Junior Member

    Please, before any flaming or joking, just humor me as I have a natural curiosity on how this could be done and not if it should or not.

    Is there any easy way to add a keel to an inflatable boat that is pretty much flat bottomed? I've seen "inflatable" keels but not sure how they work or how they would attach to a boat bottom. I understand what a keel is for and what it does for a boat in open waters.

    My idea is to get some hypalon material and make a strip pocket, glue it to the bottom of the inflatable down the middle and put like a PVC tube down. That way it'll be removable when I'm done to deflate the boat. The PVC will be in 2 parts so it's a little more easily transportable using a pipe connector piece, maybe even 3 but we'll see. PVC piping is pretty easy to mold using a heat gun so I can mold it to a more triangular shape it that helps the keep perform any better.

    Also how deep should my keel be, 1", 2"?

    Thanks for any knowledge you guys can share on the subject!
     
  2. Anchovy
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    Anchovy New Member

    The inflatable keel is an air chamber between a wood insert floor and the fabric bottom. It makes it more rigid and gives it a small v shape so it isn't so floppy.
     
  3. Xyberz
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    Xyberz Junior Member

    Yeah, mostly likely won't be going with the air camber keel then since it's pretty much something that is normally already designed into the boat. Since I'm most likely looking at custom work, I think I'm gonna go with my 2nd idea of using PVC and hypalon material to create a pocket for the keel and glue the hypalon to the bottom of my inflatable.
     
  4. DennisRB
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    DennisRB Senior Member

    Why? I don't understand the benefit.
     
  5. messabout
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    messabout Senior Member

    ^ I do not understand the benefit either Xberz. An inflated keel on an inflatable will make the boat less stable, not more. If you are planning to make it a sailboat there might be some very limited advantage. If it is tracking ability that you are considering, then tell us more about the intended use of the boat.
     
  6. Xyberz
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    Xyberz Junior Member

    Isn't a keel intended to help keep the boat from drifting sideways on high winds, cut thru the water better, and overall for stability? It's a flat bottom boat and I wanna use it in the ocean so I don't want high winds to make traveling forward nearly impossible. Also won't it help the boat get on a plane so you can get better speeds and mileage?

    Hopefully I'm understanding why a boat usually has a keel in the first place for.
     
  7. DennisRB
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    DennisRB Senior Member



    Some boats need weighted keels so they don't fall over like sailing monohulls. Other boats need keels/boards as leeway prevention to stop them going sideways due to sailing forces such as sailing dingys and sailing catamarans, and of course the weighted keel in a monohull sailing boat also serves to reduce leeway too.

    Power boats usually do not need keels in the same way as sailing boats do, but many do have some form of a vestigial keel. Particularly slower boats that may be blown off course by a strong crosswind, or motor boats that are expected to have a good range of stability may have weight in the keel. But that sort of keel on a motor boat will just be adding large amount of drag 95% of the time just so it can be useful the remaining 5%, but the SOR of the design means it is required for that 5% or it won't meet stability requirements.

    [​IMG]

    Does your dingy have a wood floor or slats? Perhaps you can shape a PVC conduit with the ends pushed together and put it under the floorboards. It will mimic the design of a real inflatable keel dingy with less than optimal results, but with much better results than dragging tubes of PVC around in the water under the boat.

    Have a look at this one. You can see the inflatable keel which goes under the floor. It's not really a keel at all, but it serves to give the dingy somewhat of a V bottom rather than being totally flat. This increases buoyancy, lifts the bow up, reduces slamming, and adds a small amount of leeway prevention.

    http://www.boatstogo.com/inflatable_boat_AM290.asp

    I have also seen fins glued to the bottom of inflatables which help directional stability and reduce leeway in a cross wind. I imagine they would be damaged easily by groundings.

    [​IMG]
     
  8. Xyberz
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    Xyberz Junior Member

    You know what? My mistake. I feel really stupid haha. I posted about something in a difderent forum and someone responded back with the word keel and I got stuck on that subject for some reason.

    As you may tell, I'm no professional boat designer LoL. I think the effect I'm trying to achieve is a deep V effect that boats have. That'll be the overall design I'm trying to achieve without having to have a permanent hard bottom so the boat continues to be deflatable.

    I know it must be beneficial to have this design on a boat if possible, otherwise it wouldn't be so commonly used right? So basically I want to design the bottom to be somewhat like a rib boat.
     
  9. Wavewacker
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    Wavewacker Senior Member

    You'll need a hard hull for a deep v and your inflatable should be more like a flotation collar, the style of boat you want sounds more like a rescue police boat or a military inflatable, there are several variations but the hulls are not inflated.

    My inflatable kayak has a small rubber keel aft glued on and it's usually tilted off to one side somewhat and doesn't stay straight down, but it makes little difference.

    Are you powering this or trying to sail it? For sailing leeboards might be an option. For power your outboard should do the trick without a keel. :)
     
  10. Xyberz
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    Xyberz Junior Member

    I'll be powering it with a gas outboard. I'm planning to go with either a 3.5hp or 6hp outboard. Does more HP make a difference when it comes to an inflatable boat? Also what about when adding more weight with other people and equipment?

    If it doesn't make a big difference, then I'll save a bunch of money and go with the 3.5hp outboard instead.
     
  11. DennisRB
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    DennisRB Senior Member

    How big is it? With one person you could probably plane with 6hp. With 2 or more people the 6hp won't go much faster than the 3.5hp as you wont get it into a plane.
     

  12. Xyberz
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    Xyberz Junior Member

    Sorry, forgot to mention that. The boat is a 12ft inflatable. So I guess I'll be going with the 3.5hp outboard then. Saves me money! :D
     
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