Ski Boat Stringer/Sole Replacement

Discussion in 'Fiberglass and Composite Boat Building' started by rickr, Dec 18, 2007.

  1. rickr
    Joined: Dec 2007
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    Location: TN

    rickr Junior Member

    I am removing the water soaked foam and replacing all the wood (stringers, floors, sole, rudder and swim platform bracing).

    I plan on using ;
    Douglas Fir (Stringers)
    A/C plywood
    US Composites Epoxy
    Cab o sil
    1708

    THANKS to all the reasearch I have done on the "Boat Design Forums"

    Deck is pulled
    Hull is braced
    I am removing one stringer at a time

    Now the fun begins:p

    What is the best tool for grinding the old Kevlar/fiberglasss to level the area of the new stingers??????? What kind of sandpaper and backing??????
    I am using the DA w/40 grit but it is making a HUGE mess in the garage :(
    So I was thinking of trying the 7" buffer if a backing plate will fit on it?

    Tools available (I have air);

    DA (air)
    4.25" angle grinder
    Die Grinder (air)
    Angle Die grinder (air)
    Large (7") Milwaukee buffer

    THANKS!
     

    Attached Files:

  2. grantn
    Joined: Dec 2007
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    grantn Junior Member

    all of the above!

    well except the buffer.

    harbor freight sells a good 7" grinder and an accessory backing pad. the whole set up cost me around $55. get plenty of abrasive discs.

    norton also sell a great flapper disk. the 40 grit makes QUICK work of fiberglass grinding. available at home depot.

    http://www.nortonconsumer.com/Data/..._line_edit.asp?ele_ch_id=L0000000000000002588

    for the record.........

    THEY'RE ALL GOING TO MAKE A MESS!
     
  3. tuantom
    Joined: Jan 2005
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    tuantom Senior Member

    I performed a similar operation on my boat this past summer and into this spring. I used a my sawz-all wherever I could to help keep the itching powder to a minimum - the longer blades work well. I also used a 4" grinder with the guard removed and a flapper disk (most versatile), and to a lesser extent a Milwaukee 7" grinder with a 40 grit disk.

    I also used US Composites and was pretty happy w/ them.

    What's the condition of the foam? Is it absorbing water? Mine did - lots of it.
     
  4. rickr
    Joined: Dec 2007
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    Location: TN

    rickr Junior Member

    MY GARAGE WILL NEVER BE THE SAME, THESE AIR TOOLS ARE MAKIING A MESS! :p

    grantn
    This is the type buffer I have (see pic) do you think that would work like an 7" angle grinder? It is low RPM (1750) and might keep the dust down ("The Boss's" black car is getting dusty BUT it is her boat;) ). I'll go by Lowes and the local paint supply and look for some grinding discs and flapper discs.


    trantom
    Half the hull produced 4 bags of water soaked foam, well over 100lbs:(
    Most all of the sole and stringer wood was wet. Sole and about 10% of the stringers were soft.
    +1 on the sawzall, I'm using an Xtreme brand "Demolition and Rescue" blade (long and thin) from Home Depot that works great.

    When I start with the glass what is the best way to keep the tools (rollers,squeegee...) clean? If I soak them in a bucket of acetone will the epoxy soften and come off?
     

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  5. grantn
    Joined: Dec 2007
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    Location: New Orleans

    grantn Junior Member

    the buffer would work in a pinch but you would want something with more speed. you would end up with less dust in the air but not less dust if you get the drift. i'm in the process of rebuilding a 25' mako and so far have vacuumed up at least 50 lbs. of dust. not including what has ended up all over the neighborhood, car, house, etc.

    http://www.classicmako.com/forum/topic.asp?TOPIC_ID=18771

    i took almost 200 lbs of wet foam just out of the tank area.
     
  6. rickr
    Joined: Dec 2007
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    Location: TN

    rickr Junior Member

    grantn
    Mako looks like a BIG project! Our grouper boat is a 24 WA Sportcraft that is going to need a new tank and transom soon:(

    Using 1708 and US Composites Epoxy, what is the best way to lay up the stringers on the Supra ? I was planning on bedding the stringers w/thick epoxie/cab-o-sil with a fileted edge, coat the wood with a thin layer of epoxy, lay the 1708 on the stringers dry and rolling the resin on with a 3/8" foam roller??????

    What do you use to clean the epoxy off your tools?
     
  7. grantn
    Joined: Dec 2007
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    grantn Junior Member

    i would start here rick: http://www.yachtsurvey.com/HullFailP2.htm

    david pascoe does a good job of explaining why NOT to bond the stringer cores to the hull. the wooden cores in the stringer of my mako were NOT bonded to the hull. that being said here's where i'm going with mine.

    after fitting the stringer core shim the core with 1/8" luan strips 1" wide x 6 or so inches long (anything 1/8" thick will work, i just happen to have a ton of it laying around) set the strips under the stringer crossways to get it up off of the hull. put 3 or 4 six inch long fillets from the stringer to the hull on both sides to 'tack' the stringer in place. let it cure, remove the shims then fillet the entire length of the exposed core. make sure you have the core mounted perpendicular to the hull before tacking. eddie ring has a real good explanation with pictures of this procedure on the mako site under his 21b project.

    i have also see stringer mounting where a structural foam (divynicel, airex, etc) was cut with a cove bit and the core bullnosed and set in the foam. this piece acted as the fillet for the glass layup and a cushion between the hull and the core. some good shots of that here: http://www.buildinggalene.com/

    click on progress, then click on bulheads. picture 7.

    in your case since you are replacing the entire stringer determine the height of the sole and build the stringers to that height. add 'bulkheads' to build a 'grid' system and attach the sole to the grid. this way you have the sole supported fully by the vertical bracing (stingers and bulkheads) instead of using foam to support the sole as was probably done by the factory. in addition to strenghtening the hull of the boat it also preserves the integrity of the floatation foam as now you don't have the sole crushing it, which is what causes it to hold water.

    as far as the layup 4 layers of the 1708 should be perfect. it will give you approximately 1/4" of glass over the core. in my mako they laid the glass over the square cut ends of the boards. this created air gaps between the wood and the glass. i would run the boards through a round over bit to round the ends over and make the glass turn much smoother. remember to make each layer progressively longer where it meets the hull. 1 to 2 inches of overlap on each progressive layer should be fine. if you're doing the work by yourself i would lay a sheet of visqueen or plastic in the boat and wet the cloth first. some of the bends the cloth makes on stringers and the areas you have to get into make it very difficult to get the proper amount of resin into. by wetting it out first you're sure to have a more consitent glass to resin ratio. if you can find a partner in crime (in my case i taught the 'boss' how to mix resin and wet out fabric) have them wet out the pieces while you fit and roll. wetting out the wood BEFORE applying any cloth is standard operating procedure. this prevents the dry wood from wicking resin from the cloth creating a dry bond. if you really want to get adventurous, vacuum bagging would be the way to go (you still have to do the layup but you come out with virtually zero air pockets and a closer to ideal resin/cloth ratio).

    i've heard many different explanataions as to 1708 being 45/45 bias and 1808 being 0/90 bias, but i've heard of both weights sold in both biases. that being said the point of this is IDEALLY when laying up structural components the greatest strength or resistance to flex is acheived by alternating layers of 45/45 biax with 0/90 bias. this keeps the strands from 'stacking up' in one direction creating the strength (resistance to bending) along only one axis. this can be achieved with either one or the other by alternating cutting the material on a different bias but can also be very wasteful and create many more seams. on the other hand laying up the stringers with a straight 45/45 bias cloth will still get the job done. just something i wanted to mention for future planning.

    as far as laying it up. 1/4" nap mohair rollers will do the trick (3/8 will work, it just sucks up a lot of resin). acetone or mineral spirits clean up tools nicely. i usually soak paint rollers and fiberglass rollers in acetone for a day to loosen up hardened epoxy. use vinegar to get any uncured epoxy off of your skin. recommendations are to let it dry and peel it off but i don't think i can be sticky THAT long. best bet is to use protective suits to keep it off yourself in the first place. i have become sensitized to epoxy and now break out in a rash every time i use it. from now on it will be tyvek even when laying up. you'd be amazed where epoxy ends up getting on you.

    i have used us composites epoxy on my 25 exclusively. on my 230wa i started with west system but couldn't justify the expense and switched to us composites. i've been very happy with us composites epoxy (which by the way is made by epon, www.epon.com) and you can't beat the price or customer service. i also use them for smaller orders of cloth. for larger orders of cloth and coosa i have an advanced plastics branch nearby.
     
  8. AroMarine
    Joined: Jul 2005
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    AroMarine Junior Member

    Your 4.5" grinder is the most versatile. A masonry wheel available at almost any hardware store and a diamond cutting disc usually available from Home D or Lowes and 5" 36 grit grinding discs with appropriate fiber backing disk. These will get what the sawzall misses and the prep sanding and grinding will go much faster than DA. Also 7" grinding discs will speed things up. The faster to get the grinding done the better.
     
  9. AroMarine
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    Location: Atlantic City NJ

    AroMarine Junior Member

    Your 4.5" grinder is the most versatile. On mine I keep a diamond blade, available from Home D or Lowes, on one and a thick masonry stone on another. You can also use 5" 36grit grinding disc on them too although I use a seperate 5" sander as it runs a little slower. Also yes you definatly can use your 7" with fiber backers andgrinding discs to make shorter those fun grinding sessions. I prefer the slower speed to that of a grinder
     
  10. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I have a 7" and 10" grinder for the big jobs, but they get in the way of lots of things below decks so the 4" angle grinder is handier in the bilge. A simple pie plate backer and shop vac hook up (don't get fancy, duct tape and cussing can make one) will make the mess more manageable. The reciprocating saw is my most used tool. I have a few offset blades that can cut quite flush with surrounding areas.

    I knew a guy that used a 24" box fan and 24" corrugated tubing (like used on a cloths drier, but huge), which he set up at the mouth of his garage. The 24" tubing went up to the work and drew the dust off real neat. It was pretty cool, but his yard looked like whatever color he was grinding for a week.
     
  11. rickr
    Joined: Dec 2007
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    rickr Junior Member

    THANKS for the replies! Merry Christmas!

    I have had the best luck using my buffer with a 7" pad and a 9" 24 grit disc. Along with my belt sander.
    The DA (air tool) was just making too big a mess :(

    Got the 1st stringer in. It was dificult getting the air out of the 1708 with US Composites Med/Thin @ 65 degrees. but I worked at it and it turned out great.

    Another problem I had was using US Composites Med/Thick with Cab-o-sil (peanut butter thickness) to bed the stringers and create the fillets. At 65 degrees the epoxy was kicking too fast and the fillets were hard and brittle??????

    Any suggestions???????

    From preivious post I have read about the stringer bedding controversy. This hull does not have many hours but it is 20 years old and there are NO stress cracks. It was built with some kind of thin (1/8") core material and Kevlar. SOOOOOO I am bedding the stringers the way it was originally made, but, adding fillets, beveling the wood, using epoxy and 1708.
     

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  12. grantn
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    grantn Junior Member

    looks good! i'm jealous. i spent the entire weekend between rain showers grinding and scarfing the stringers to tie in the transom. you're moving pretty good!

    the 1708 does have a tendency to take a little work to get the air out. i find it is usually caused by the cloth being too wet which is why i suggested wetting it out then laying it up. use a bondo spreader to squeegie out the excess resin. i've found it does take a litte work to get it wetted out well with that epoxy.

    the putty kicking is fairly common. by the time you've mixed the epoxy then worked in the cabosil to get the right consistency, you've pretty much burned up close to 10 minutes if not longer. very much a pia. one suggestion i've seen (tho never tried) is to put the resin in the fridge up until you're ready to use it. this will (in theory) give a little more time before exotherm causes it to kick.
     
  13. rickr
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    rickr Junior Member

    Making a little progress:) Inside stringer was a big job (for me) designing, cutting and assembling. I am trying to figure out what originally was engineering and what was cutting corners.

    Thinking about the next steps:
    For the sole, I was planning on using 3/4 AC coated w/epoxy on all sides then laminating top w/1708, screwing and fastening to the stringers w/Cabosil epoxy mixture. Then tabbing to the hullsides and inside stringer w/fiberglass tape.
    Does this sound like a good plan:confused:

    Does anyone know of an online outlet for rivets? I'll need 100 aluminum 1/4"x1"
     

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  14. grantn
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    grantn Junior Member

    nice clean work there rick! looking good.

    epoxying the plywood is the only way to go. if you want a little more insurance on the bottom side a layer of cloth or mat would be the way to go. the 1708 would be overkill unless you're spanning a distance over 2 or 3 feet with no support. as far as tabbing i would go with strips of the 1708. since it is a structural component you want a little more strength than the cloth tape (unless of course you're using biaxial tape) will provide.

    i have some links for a few fastener distributors but unfortunately they're on my pc at work. i'll try to post them monday.
     

  15. rickr
    Joined: Dec 2007
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    rickr Junior Member

    grantn
    Thanks for the advice, I'll go with the 1708 to tab in the sole. The 1708 will be overkill but I do not want to replace the sole again:rolleyes:

    Tip; I used a disposable pastry bag (pic, Boss says they are available @ Wallyworld) to put a bead down for the filets, worked great!
    Also I used PVC for the drain holes. Drilled hole slightly larger than pipe then heated the PVC to make it flexible and snaped into place.

    Please send the link for rivets.
     

    Attached Files:

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