How much tabbing for my new transom?

Discussion in 'Boat Design' started by helluvaboater, Feb 14, 2016.

  1. helluvaboater
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    helluvaboater Junior Member

    My boat is a 27 foot express cruiser with an 8 foot beam. The boat will weigh roughly 7000lbs when fully loaded and will be powered with a single screw Cummins 6BT 210HP with a ZF-63 IV 1.56 ratio v-drive.

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    I hired a guy who got my transom halfway installed. I wasn't happy with the quality of work, so I decided to finish it myself.

    http://fiberglassin.com/pics/20151201_123619.jpg

    http://fiberglassin.com/pics/2016-02-06/20160206_134859.jpg

    The transom is made of 3 layers of 1/2 marine plywood. I am currently repowering the boat so I have the whole back 8 feet of the boat gutted. The tabbing on the interior of the transom looks very thin and dinky. I want to add more thickness.

    I have 100 yards of 1.5oz mat and 60 yards of 18 oz woven roving so I will be using those along with VE resin.

    How many layers of tabbing should there be to connect the inside of the transom to the side and bottom of the hull? How far should those layers extend?
     
    Last edited: Feb 14, 2016
  2. ondarvr
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    ondarvr Senior Member

    i assume you meant 1.5 oz mat.

    24oz roving is better than 18, but if that's what you have just use it.

    First, how much material is on there now, looking thin and dinky is something we can't measure. Since you don't have twin 300's on a bracket hanging off the back, you don't need a heavy thick laminate, what's on there now could be fine.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Use a minimum of 6 layers of 18 ounce, staggering the overlaps progressively from bottom top. This is what would be done for an outboard transom, As mentioned, your V drive doesn't need this much, so 3 layers of 18 will do, but it would be nice to have it stiff enough, so that when you sell it and someone wants to hang a couple of Black Maxes on it's butt, the tabbing will be sufficient.
     
  4. philSweet
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    philSweet Senior Member

    OP, please delete, resize, and repost your picture, or post it as an attachment so the thread remains readable.

    Following on with PAR's schedule, I would cut my 6 pieces of 18oz stuff crosswise and at an angle. Say a foot of slant across a 50" cloth. I'd cut them about 14" wide. I'd mark lines starting 3" from the transom and every 2" after that forward along the hull. I'd place the first piece on the 3" line and have 11" on the transom. The next piece goes on the 5" line and has 9"on the transom. Continue until the last piece which starts 11" forwards and has 3" on the transom. Fill all the weave with resin. If you want to fair this in afterwards, build up the feathered areas with putty and sand the putty. Don't sand the resin or the glass.
     
  5. helluvaboater
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    helluvaboater Junior Member

    Here's a few more pics...

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    I'm gonna say there's 1 layer of biaxial 1308 and a few layers of 1.5 oz mat holding it right now.

    Par, since I have to do a layer of 1.5oz mat between each layer of 18 oz roving, you are saying do...

    mat
    roving
    mat
    roving
    mat
    roving
    mat
    roving
    mat
    roving
    mat
    roving

    ... If I need to have at least 6 layers of roving. Right?

    How far should these pieces extend onto the sides of the hull and the transom? A foot?

    So can I cut pieces, say 12 inches by 24 inches and lay them across the inside corners?
     
  6. helluvaboater
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    helluvaboater Junior Member

    I forgot to mention....

    Before all this, the boat had capsized and the transom broke out when it beat on the rocks for a few hours. We removed all the delamination and rebuilt the upper aft edge of the hull since that chipped away too. The bottom of the hull was OK. Here are some pics of the boat right after I bought it:

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    Taking all this into consideration, I think the sides of the hull needs to be thickened before I tab the transom in. There only looks to be a couple layers of mat connecting everything together...

    [​IMG]
     
  7. PAR
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    PAR Yacht Designer/Builder

    You always alternate mat and roving layers, to get a good tooth (bond), regardless of the schedule, with vinyl and polyester.

    Fill the major dings, divots and gouges on the hull sides. Fillet or foam the corners and apply some 1708, mat down and use this as the base for the subsequent bulk up and tabbing. If using cloth or roving, cut it on the bias, as Phil mentioned, to orient the fibers more favorably. Stagger as suggested, until you've got the thickness you want. Again the big to small approuch and if you need to, use this first layer to bulk up hull side thickness if desired and save some effort. Personally, I don't think you needs anywhere near the extra reinforcement you've shown with the red square, but if it makes you feel better, a single layer of 1708 in this area will firm it up a bit. This area will get considerably stiffer once the corner tabbing is finished. As to the size of the pieces, well it's tough to tell from these images (a scale thing) but use common sense. A typical transom corner tab, for an outboard power of this size might has as have as a 12" bottom layer, using the 25% rule. What this means is as described by Phil above - 25% of the layer goes over the intersection, the rest laying on one of the pieces. So the first piece would have 9" on the hull side, with 3" rounding the corner and up onto the transom. The next piece would be opposite of this with 9" on the transom and a 3" section rounding the corner and landing on the hull side. This is your base (big) layer and subsequent layers, use a similar schedule and overlap. For the extra reinforcement areas, I'd treat them separately, before tabbing in the transom, but there's no reason you can't do it all at once too.
     
  8. helluvaboater
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    helluvaboater Junior Member

    Thank you for getting back to me so quickly. I was able to get started again based on your previous reply. In the meantime, I was able to kill two birds with one stone by strengthening the side as well as doing some tabbing on the transom.

    I was able to lay 12 layers of mat/roving/mat/roving..... over the top half of the hull wall. It got really hot so I put a fan on it which seemed to cool it down.

    [​IMG]

    [​IMG]

    I did not stagger the pieces this time, although I probably should have since there are now a couple big ridges that I will take care of. In the future I will definitely stagger them. Guess I should have listened to you guys but live and learn.

    I will probably end up doing a few more layers on the transom itself to beef that up some. Looks like it has 2-3 layers of 1308 on the inside and outside. It would be nice lay a few "roll-wide" sheets along the entire inner transom wall (below the waterline) that would overlap my tabs and even onto the sides of the hull a little.... Then it sould be super solid, right?

    Or am I overbuilding it?

    This is my first transom.
     
  9. helluvaboater
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    helluvaboater Junior Member

    How many layers of 18 oz roving and 1.5 oz mat should be on the surfaces of the transom?

    I think there are about 2-3 layers of 1308 on the inside and outside along with and unknown amount of mat.

    I am thinking of sanding it down doing a few more coats along the interior wall.
     
  10. PAR
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    PAR Yacht Designer/Builder

    The laminate thickness should match the thickness of the previous laminate. If you'd like maybe a layer or two more, for a feel good thing, but it doesn't need to be much thicker than what was there previously. If you don't know what this is, drill a core sample and measure it. Of course, you'll need to fill in this hole, but not a big deal, compaired with the rest of this project. Typically on your hull, the laminate is progressively thicker the further down the hull you go. Hull sides are often fairly thin, using the liner and/or deck cap to stiffen things up, once assembled. In fact, you don't want it absolutely rigid when it's done. It should be fairly flexible and easily deflected when you push on the topsides. If it's overly rigid, you just break stuff (other tabbing, partitions, bulkheads, etc.) in a pounding sea.

    You've already been told a minimum of 3 layers of 18 ounces, which would be alternating with mat if not a combo fabric and that if this fabric isn't knitted, should be cut on the bias a bit, to place all the fibers across the joint/corner. We call this a unit, so one unit is a layer of fabric and a layer of mat if applied individually. 3 units is the minimum, but 6 would be appropriate if the boat was to hang outboards. At 6 units and a 1.5" thick transom, you're still HP limited, but someone could bring this up if they want to hang 600 HP of twins on it's butt at another point in it's life.
     
  11. helluvaboater
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    helluvaboater Junior Member

    Thanks Par. So I guess that part of the repair is strong enough.

    How many layers of 18oz roving and 1.5oz mat should I put on the stringers you see in the pics?

    I plan to put two new bulkheads in. How much glass should I put on those?
     
  12. helluvaboater
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    helluvaboater Junior Member

    The new stringers do not have the engine connected to them. They are simply there to strengthen up the hull and run directly above a chine. The Stingers are four inches tall made of 1.75 inch thick microlam lvl and are 86 inches long. You can see them in the pictures they run parallel to the engine stringers which are more centerline. How many layers of Fiberglass should I do on these outside stringers? you can see them in the pictures they run parallel to the engine stringers in the center of the boat but on the outside. How many layers of fiberglass should I do on these outside stringers? I am thinking like 3-4 units of 18oz wr/1.5 mat with a 5 inch overlap on to the hull
     
  13. helluvaboater
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    helluvaboater Junior Member

    How many layers on 18 oz roving / 1.5oz mat on the outer stringers would be normal? No engines connected to them. The stringers run about 1/3 the length of the boat.
     
  14. helluvaboater
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    helluvaboater Junior Member

    Last night, we put 3 units (3 layers 1.5mat/3 layes 18oz roving) along the whole length of the new stringers. These stringers only run 86 inches. The boat is 27 feet long. We are only rebuilding the last 8 feet of the boat. Is 3 units probably enough for these stringers?

    These stringers are just for longitudinal support and not for an engine.

    http://www.fiberglassin.com/pics/20160217_093951.jpg
     

  15. helluvaboater
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    helluvaboater Junior Member

    Last night, we put 3 units (3 layers 1.5mat/3 layes 18oz roving) along the whole length of the new stringers. These stringers only run 86 inches. The boat is 27 feet long. We are only rebuilding the last 8 feet of the boat. Is 3 units probably enough for these stringers?

    These stringers are just for longitudinal support and not for an engine.

    http://www.fiberglassin.com/pics/20160217_093951.jpg
     
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