Kevlar boat plug/mold help

Discussion in 'Boat Design' started by jka251, Feb 15, 2021.

  1. jka251
    Joined: Feb 2021
    Posts: 14
    Likes: 0, Points: 1
    Location: AL

    jka251 Junior Member

    I'm wanting to build a lightweight Kevlar boat for use in lakes and bays. It won't be subject to any severe waves or other abuse. I've built a couple of small boats out of wood but never worked with a mold. I was hoping someone could answer a few questions for me. My understanding of the plug/mold process is: build/shape the mold (I plan on using foam), fair it, sand it, apply some type of primer (?) to the faired&sanded plug, apply gel-coat (?) to the primed plug, apply wax (?) to keep epoxy from sticking to it, apply the Kevlar and epoxy and finally pop the mold out. If I'm missing any steps could someone please set me on the right path.

    -After I shape the mold, what should I use for "fairing" it? A high quality car body filler?

    -Am I thinking correctly in terms with the primer, gel coat and wax? Recommendations for each?

    -How many layers of fiberglass or Kevlar is recommended? And also what type?

    -I'll probably build the bottom hull mold and a top deck mold. What's the best way to join them? Epoxy? Maybe glass the seam?

    -Where's a good source to get all or most of my material?

    I greatly appreciate any help and anything else anybody might could add that I didn't mention.
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,587
    Likes: 810, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    What is causing you to think "Kevlar", for either a mould (damned Australian spelling) or a hull ? It ain't easy to work with.
     
  3. jka251
    Joined: Feb 2021
    Posts: 14
    Likes: 0, Points: 1
    Location: AL

    jka251 Junior Member

    I want it to be lightweight as possible. I'll be sculling it with one arm.
     
  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,587
    Likes: 810, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    But a mould and a boat are two separate things, the mould doesn't need Kevlar, or I am misreading your post. I would say a foam sandwich boat with just glass will suffice and be light enough. Do you have any drawings of the planned boat ?
     
  5. bajansailor
    Joined: Oct 2007
    Posts: 1,738
    Likes: 547, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    JKA, have you got any existing designs in mind that you like, and which it is possible to purchase plans for?
    Or are you in the process of designing it yourself?
    How big will she be?
    Do you have any photos or sketches that you can post here?

    It sounds like you just want to build one boat - if this is the case then you are making a lot of work for yourself re building first a plug, and then taking a mould off the plug, and then using the mould to build the hull for your boat.

    Re wanting the boat to be as lightweight as possible - this is all well and good, but how heavy will you yourself be in comparison to the boat?
    Re sculling with one arm, once you build up some momentum it should then become much easier - I have seen fairly heavy small craft being easily sculled with a long sweep.
     
  6. jka251
    Joined: Feb 2021
    Posts: 14
    Likes: 0, Points: 1
    Location: AL

    jka251 Junior Member

    I guess I misused the terminology. I plan on building a plug out of foam and then making the boat out of Kevlar. I don't really intend to make a "mold" to build multiple boats.


    I'll be designing myself since there aren't really any plans for the style I want. I'm planning on building it 14' to 15'. I don't really have any sketches but if you look at a Bankes' Predator, that's the style I'm going for. There are a few older scull boats built like that.

    Yes, just one boat. I think I may have misspoke earlier. I intend to build the plug and then build one boat. Didn't intend to build a mold for multiple boats.

    I'm about 165lbs. You may be right on building momentum. I just wanted it to be as easy as possible.
     
  7. bajansailor
    Joined: Oct 2007
    Posts: 1,738
    Likes: 547, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Apologies, I should have looked at your previous posts about a sculling boat -
    Help: Scull boat plans for hunting https://www.boatdesign.net/threads/help-scull-boat-plans-for-hunting.65097/

    In this thread you seemed keen on building in plywood - this is quite a major about turn to kevlar / fibreglass now?

    Here is the Bankes Predator -
    Bankes Boats Predator Scull Boat * Sculling Boat https://www.bankesboats.com/predator.htm

    It sounds like you intend to build a male mould (or jig), and then cover it in foam, fibreglass it with kevlar, take it off the jig and then fibreglass the inside?
    Even if you build it with kevlar, I don't think that you will really see much appreciable weight savings vs a plywood epoxy hull.
     
  8. jka251
    Joined: Feb 2021
    Posts: 14
    Likes: 0, Points: 1
    Location: AL

    jka251 Junior Member

    No worries. I was going to use plywood and then I got to reading about a guy out in California who builds these style scull boats out of Kevlar. I haven't been able to get in touch with him though. It seems like he's built a couple just for friends. Anyway the boat comes in at around 50lbs and the couple of guys who have them talk like they are very easy to move by yourself and scull. That was my main appeal to using Kevlar.

    And the process you just described sounds like what I was thinking. I just want to make sure I'm taking all the right steps in the right order.

    Banke's is not making the Predator boats right now due to being short-staffed and filling orders for their larger boats.
     
  9. gonzo
    Joined: Aug 2002
    Posts: 15,116
    Likes: 897, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Building on a male mold is not a good method for a light weight small boat. The fairing compound will make it heavy. It is also a lot of work to get a good finish. Foam is a really bad substrate for a mold. The heat and pressure will deform it as you laminate. Building a wooden jig, laying the foam core and then laminating will keep the shape. However, for a kayak the foam core will be too thick and heavy. Also, you need to laminate both sides.
     
  10. jka251
    Joined: Feb 2021
    Posts: 14
    Likes: 0, Points: 1
    Location: AL

    jka251 Junior Member

    Not sure if I understand. I thought the fairing compound was just used on the plug to make it smooth so that when you started laying down your fiberglass there wouldn't be any rough spots? I think I see what you mean about the wood core. I was thinking of cutting some plywood or luan and putting them every 6" or so and using them as a template to cut the foam to the correct shape. I wasn't intending on using any foam for he actual boat unless I'm missing something and I have to use it.
     
  11. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,587
    Likes: 810, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    This does sound like something you could make out of slabs of foam, and glass the whole outside of it, after you shape it to where you like it, like a glorified surfboard. Not going to be subjected to much in the way of rigors, I can't see why it wouldn't work. That other rigmarole is just too much hard work, and forget Kevlar completely.
     
  12. wet feet
    Joined: Nov 2004
    Posts: 649
    Likes: 96, Points: 28, Legacy Rep: 124
    Location: East Anglia,England

    wet feet Senior Member

    I've skimmed through this thread and am still confused.Is the OP intending to make a male former for foam and then glass over the outside of the foam?This used to be a relatively common way to get a one off glass hull.It works a lot less well with Kevlar because of the well known fuzzing problem.Attempting a female mould for a fine ended boat is quite challenging and I would advise against it.I would also advise against using Kevlar anywhere as it has several interesting characteristics;you need special shears to cut it reliably,it doesn't wet out well and trimming or sanding gives a very fuzzy edge.On the other hand it does have good impact resistance if that matters.As with all departures from things we have done previously I would recommend trying to build a scale model first to get some familiarity-maybe a 1/4 scale model would make a nice ornament as well as being good experience.
     
  13. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,587
    Likes: 810, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Some commercial boat made from kevlar gave him that idea, just forget that completely, for best results. I don't know the layout or what configuration he intends, but it seems to me he should use slab foam shaped to his desired form, and glass all over and inside it with a single skin. He says non-rigorous usage. Getting involved in some major exercise seems like making work for himself.
     
  14. wet feet
    Joined: Nov 2004
    Posts: 649
    Likes: 96, Points: 28, Legacy Rep: 124
    Location: East Anglia,England

    wet feet Senior Member

    Your final sentence seems to be a good definition of recreational boatbuilding!I agree that carefully laid foam which is glassed over inside and out would be the simplest way to get afloat.A former covered with battens to stitch the foam over with fishing line used to be the way to go..Once glassed you could make a basic cradle over the surface,turn the thing over and once supported by the cradle,you ucut the fishing line and lifted the former out.A glass skin could soon be added and you almost had a finished hull.
     

  15. gonzo
    Joined: Aug 2002
    Posts: 15,116
    Likes: 897, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    It depends what you mean by finished. The bulk of the labor for a well finished hull goes into fairing and sanding.
     
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.