Results 1 to 6 of 6

Thread: UHMW spray skirt

  1. #1
    New member
    Join Date
    May 2009
    Posts
    2

    Default UHMW spray skirt

    I have read all the threads about catarafts with motors and the difficult with getting them on step. Would anyone who has solved this be willing to share some close up pictures of their design? I have a pretty good idea of dynamics but with the cost of UHMW I would like to get it right the first time. Pics would be greatly appreciated.

  2. #2
    Member
    Join Date
    Aug 2006
    Location
    Anchorage
    Posts
    1,449

    Default

    Problems with getting on step can be solved with larger motors and lower pitched props. I would usually struggle getting an Aire Cougar up with a 30hp, and that was with no more than 2-3 people and no gear. Then I bought the lowest pitched prop I could find (I think it was 13" bronze or brass) and had it beat down the the next flatter size at a prop shop. (Think "lower gear") No problems after that; it would get right up. I probably lost a little speed, but couldn't tell much from driving it. Getting you UHMW down low would probably make getting on step easier though.

    Defeating the spray problem is the bigger issue. If I was going to do this again I think I would start by gluing on a flap to the sides of the tubes, right down the middle or a little lower. Maybe 6" wide and the whole length of the tubes. Then I would lay the UHMW, or even plywood, on top of that. You need to find a water tight way of attaching the flap and UHMW together or water will blow right through it. There is a lot of pressure right there. On my quad tubed raft the water would also blow through between the tube pairs. Everybody got soaked! I once used a system of tarps to keep the spray below deck, but then I still had water blowing around the outside of the tubes near the front of the raft and flying back to the middle, so we still got soaked. I think you are on the right track with the UHMW, but getting it attached right is the key to the spray issue.

    But I have to admit, playing around with it was a lot of fun.

    And then there is the cavitation issue.

    Good luck. You'll need it.

  3. #3
    webmaster Michael Strahan's Avatar
    Join Date
    Apr 1999
    Location
    Anchorage, Alaska
    Posts
    5,765

    Default

    Quote Originally Posted by Jim Strutz View Post
    Problems with getting on step can be solved with larger motors and lower pitched props. I would usually struggle getting an Aire Cougar up with a 30hp, and that was with no more than 2-3 people and no gear. Then I bought the lowest pitched prop I could find (I think it was 13" bronze or brass) and had it beat down the the next flatter size at a prop shop. (Think "lower gear") No problems after that; it would get right up. I probably lost a little speed, but couldn't tell much from driving it. Getting you UHMW down low would probably make getting on step easier though.

    Defeating the spray problem is the bigger issue. If I was going to do this again I think I would start by gluing on a flap to the sides of the tubes, right down the middle or a little lower. Maybe 6" wide and the whole length of the tubes. Then I would lay the UHMW, or even plywood, on top of that. You need to find a water tight way of attaching the flap and UHMW together or water will blow right through it. There is a lot of pressure right there. On my quad tubed raft the water would also blow through between the tube pairs. Everybody got soaked! I once used a system of tarps to keep the spray below deck, but then I still had water blowing around the outside of the tubes near the front of the raft and flying back to the middle, so we still got soaked. I think you are on the right track with the UHMW, but getting it attached right is the key to the spray issue.

    But I have to admit, playing around with it was a lot of fun.

    And then there is the cavitation issue.

    Good luck. You'll need it.
    Jim,

    It appears that we traveled similar paths. I spent a lot of time with this too, but I was a volunteer with the now-defunct "Wild Alaska Rivers Company". A great solution would be a grommetted and welded PVC flange along the inside edges of both tubes. The UHMW would lace to this. You'd still have to do something to keep water from squirting through the grommet holes, but that's not hard. Even better would be a contoured inflatable lace-on floor. But nobody wants to spend the R&D money on it (yet). Controlling the cavitation is only a matter of mashing the air out of that center rooster tail and creating a firm plate just in front of the lower unit so you have a good stream of water to grab. Somebody's gonna do it.

    Mike
    LOST CREEK COMPANY: Specializing in Alaska hunt consultation and planning for do-it-yourself hunts, fully outfitted hunts, and guided hunts.
    CLICK HERE to send me a private message.
    Web Address: http://alaskaoutdoorssupersite.com/hunt-planner/
    Mob: 1 (907) 229-4501
    "Dream big, and dare to fail." -Norman Vaughan
    "I have climbed my mountain, but I must still live my life." - Tenzig Norgay

  4. #4
    New member
    Join Date
    May 2009
    Posts
    2

    Default

    Thank you both for your input you guys have hit the nail on the head. I have been trying to perfect my rig for 2 years lots of trial and error. I have controlled the spray from between the tubes and aluminum floor by taking a 8 foot roll of L shaped garage door seal long side down between the tube and floor top held in place from top of floor with aluminum strip screwed down with sheetmetal screws. Works due to force of water pushing up against tube under power holding it tight against tube. Lot of trial and error as far as positioning to get it right. I keep hearing about UHMW spray skirts and was wanted some pics to better visulize one installed. My solution was cheap 99% effective. Still playing with planing hull design. I am pretty close to nailing this too. Right now I am using 1/2 marine plywood under aluminum floor notched and slid under forward bar and attached at rear with straps and cinched up against transom at the proper measurement for the longshaft motor (So basically it slides in the front and hangs down at back at an angle) quick and easy to remove Lots of trial and error as well. Had to take the flex out under power with support between plywood and floor. I think its close but again was looking for design pics to see if there was something better before I buy UHMW and do same. Still cavitates a bit with heavier load and certain water conditions. Jim I too have played with prop pitch as well. Spent alot of money on props for sure. Currently run a 20Hp Honda with dolfin attached on my 16 foot cat might need a 30Hp to move it better. I believe welding pvc flap to tubes like you said would work with spray as well. I think the air floor is the ultimute idea if positioned properly. I will post pics of my designs this spring. Mike and Jim I appreciate all your previous posts about these topics it really helped getting me oh so close to the perfect rig. I am still looking for pics of others current designs maybe together we can solve this fun but frustrating quest for the dry utility/sport cat.

  5. #5
    webmaster Michael Strahan's Avatar
    Join Date
    Apr 1999
    Location
    Anchorage, Alaska
    Posts
    5,765

    Default

    If someone can master this and do it the right way, we'll have an 18' jet boat that fits inside a Super Cub. Imagine the possibilities!

    -Mike
    LOST CREEK COMPANY: Specializing in Alaska hunt consultation and planning for do-it-yourself hunts, fully outfitted hunts, and guided hunts.
    CLICK HERE to send me a private message.
    Web Address: http://alaskaoutdoorssupersite.com/hunt-planner/
    Mob: 1 (907) 229-4501
    "Dream big, and dare to fail." -Norman Vaughan
    "I have climbed my mountain, but I must still live my life." - Tenzig Norgay

  6. #6
    Member IndyCzar's Avatar
    Join Date
    Feb 2009
    Location
    Just 55 miles north of ANC ... on the lake
    Posts
    351

    Default

    I guess I missed this discussion the last couple weeks...I will get some pictures out of my winter project...I can't comment on the results until the water softens up...but I am cautiously optimistic that the boat will get up on the plane and keep the water off the occupants...I'll try and get some pictures together this week...

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •