Proline 15'6 Jet Boat to Outboard Conversion.

Discussion in 'Boat Design' started by lowkeyfilmz, Feb 20, 2015.

  1. lowkeyfilmz
    Joined: Feb 2015
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United States

    lowkeyfilmz Junior Member

    Like many others before me the mid 90's jet boats powered by Chrysler's Finest the 90-115hp Mercury/Force Sportjet have become yard art with no other useful purpose.
    [​IMG]

    After neglecting her for a couple of years and almost turning her bow into a tiki bar I've decided to turn her back into a super skinny water fishing machine.

    Like many others before me the mid 90's jet boats powered by Chrysler's Finest the 90-115hp Mercury/Force Sportjet have become yard art with no other useful purpose.

    After neglecting her for a couple of years and almost turning her bow into a tiki bar I've decided to turn her back into a super skinny water fishing machine.

    My main motivation is that she floated in 4" of water with 2 + gear + motor + 10G Gas+ dog.

    The plan is:
    Pull the motor and housing
    Fill the hole with 3/4" Starboard, heavy mesh and resin top and bottom in 2-4 heavy coats.
    [​IMG]
    Reinforce Transom with Starboard, mesh and resin in 3-5 Heavy Coats, and a couple Stainless 1/4" L brackets tied to where powerhead previously lived. (Stringers)
    Install Jackplate and new motor, then rigging
    Gelcoat Transom, and create Storage / head / cabin in the old engine bay. (It's Huge)

    The Questions:
    Can I just fill the hole top side and leave the cavity below? (I'm thinking it will decrease my draft and is allot less work) {I've seen twin screws with a similar cavity just before the shafts, it's less pronounced and I'm sure engineered properly}
    [​IMG]
    Will Mesh and Glass over/under 3/4" board to transom be strong enough for a 50-70hp, or should I look more towards a different direction?
    POWER: The previous motor was a 90hp jet, I've seen 1 similar conversion with a custom transom outboard bracket and an 85 on it. I want light and like the rest of us as fast as reliably possible.

    My main motivation is that she floated in 4" of water with 2 + gear + motor + 10G Gas+ dog.

    The plan is:
    Pull the motor and housing
    Fill the hole with 3/4" Starboard glued in from bottom, heavy mesh and resin top and bottom in 2-4 heavy coats.
    Reinforce Transom with Starboard, mesh and resin in 3-5 Heavy Coats, and a couple Stainless 1/4" L brackets tied to where powerhead previously lived. (Stringers)
    Install Jackplate and new motor, then rigging
    Gelcoat Transom, and create Storage / head / cabin in the old engine bay. (It's Huge)

    The Questions:
    Can I just fill the hole top side and leave the cavity below? (I'm thinking it will decrease my draft and is allot less work) {I've seen twin screws with a similar cavity just before the shafts, it's less pronounced and I'm sure engineered properly}
    Will Mesh and Glass over/under 3/4" board to inside transom be strong enough for a 50-70hp, or should I look more towards a different direction?
    POWER: Rated for a 90jet I want light and reliable so I'm thinking 50hp Carborated Yamaha or 07+ Yamaha fourstroke 70+

    [​IMG]
     
  2. lowkeyfilmz
    Joined: Feb 2015
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United States

    lowkeyfilmz Junior Member

    I know the tunnel may create issues but I wanted to talk to some folks more knowledgeable than myself about what specific challenges it would pose and why. (my thoughts are it would decrease draft and help to offset weight as waterline was raised in that portion)

    If improbable what would be the best way to glass in the entire cavity?

    I was thinking I would cut out the entire compartment topside, make templates, cut 1/2" or 3/16" starboard to snug fit, grind mating surfaces, marine epoxy glue in pieces to fit then mat and glass top and bottom, then gelcoat.

    What would be a good thickness to use? Marine quality wood, regular wood or starboard? From the hip how many hours to tackle something like this? (just hull modifications)

    I'm no expert but I have at least 150 hours working with glass, gelcoat mat etc...
     
  3. gonzo
    Joined: Aug 2002
    Posts: 14,569
    Likes: 689, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    You could save yourself a lot of work by using the powerhead of your outboard and attaching it to the jet. It will also keep the skinny water capabilities.
     
  4. ondarvr
    Joined: Dec 2005
    Posts: 2,385
    Likes: 278, Points: 83, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    If you plan to use Starboard as a core, or part of the structure, don't, the bond will be poor, it can work as mold surface though.
     
  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,065
    Likes: 640, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I can't quite get a complete picture of what you are doing here, but if you think you can mount an outboard behind that tunnel, up high to allow low draft, I don't think it will work too well, and go horribly awry when you try to turn the boat. What is the width of the gap ?
     
  6. lowkeyfilmz
    Joined: Feb 2015
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United States

    lowkeyfilmz Junior Member

    Gap where nozzle used to be is 13.5" thanks in advance for any help. Having trouble finding any info on this.
     
  7. gonzo
    Joined: Aug 2002
    Posts: 14,569
    Likes: 689, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    If you are set on using an outboard, the repair is really simple. Screw plywood in the bottom gap and the transom. Fiberglass inside and out.
     
  8. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,065
    Likes: 640, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    What gonzo says is likely the best fix, I can't see it being feasible to retain your previous jet-power draft, with an outboard, the "tunnel" is too small. Also, the disappearance of bottom surface area back there, could cause squat and/or porpoising.
     
  9. lowkeyfilmz
    Joined: Feb 2015
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United States

    lowkeyfilmz Junior Member

    Thanks guys, the purposing and chine walking was pretty bad before the trim tabs so I will make up some marine 3/4 plywood using the acetone resin then resin method then cut snug plugs recess screwed in there with 5200 or expoxy on the edges then glass and mat the entire topside and bottom side then gelcoat. (I will also fill the hole topside in the same manner as an added insurance)

    I have a huge piece of 1/4" starboard I was think about using to reinforce the transom wall to wall and glass over it then big pieces to act as washers behind the jackplate.
    (Along with the big stainless L brackets for added support)

    Would I be better served with 3/4" wood here?
     
  10. gonzo
    Joined: Aug 2002
    Posts: 14,569
    Likes: 689, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Resin won't adhere to starboard. Basically, nothing does. If you are using a core, plywood is a good choice. The standard thickness for a transom is about 1 3/4"
     
  11. TANSL
    Joined: Sep 2011
    Posts: 6,238
    Likes: 301, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    There is not a standard thickness for the transom. Naturally, the transom thickness depends, inter alia, on the engine power. Another thing would have no logic.
     
    Last edited: Feb 22, 2015
  12. gonzo
    Joined: Aug 2002
    Posts: 14,569
    Likes: 689, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Wrong. All outboards have brackets designed for a standard transom thickness. They usually accommodate up to 2" or so.
     
  13. lowkeyfilmz
    Joined: Feb 2015
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United States

    lowkeyfilmz Junior Member

    Made some progress today.

    Stripped out all the hardware
    Completed a bulk of the prep
    Cut and water proofed plugs.
    (3/4" PT plywood with 2 coats of 4-1 > 3-1 acetone / resin & 1 coat 1-1.)
    [​IMG]

    [​IMG]

    [​IMG]
     
  14. ondarvr
    Joined: Dec 2005
    Posts: 2,385
    Likes: 278, Points: 83, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    Don't thin the resin.
     

  15. gonzo
    Joined: Aug 2002
    Posts: 14,569
    Likes: 689, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Ditto
     
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.