Adding to the bow, technique and materials questions

Discussion in 'Fiberglass and Composite Boat Building' started by leaky, Oct 5, 2010.

  1. leaky
    Joined: Sep 2008
    Posts: 146
    Likes: 5, Points: 18, Legacy Rep: 14
    Location: nh

    leaky Senior Member

    Hi,

    I wasn't sure where to add this post, it's a little more than repair but not quite boat building either. I'm adding to the existing hull from the bow, back about 10 feet, of a 26 ft. walkaround, for the purposes of freeboard.

    The shoebox joint has been taken apart, the liner cut, and the cap lifted off, exposing the bare hull around the inside.

    The mold is going on the outside of the hull and I'll be mostly working from the inside. There's a minimum of 12 exposed inches of bare glass I can prep and lay onto all the way around. The plan is to lay the new hull on, then fillet and glass ribs onto it that extend the full length of the work.

    I've had a few people come down and give me pointers with two different opinions on how to lay it up; one stated just start by laying a full length section of mat from the top of the mold to the bottom of where I prepped, followed by cloth, then mat, etc.. Another stated run the first layer of mat from the top of the mold down a few inches onto the hull, followed by the next layer a few inches lower than the last.. What makes more sense?

    Secondly regarding fiberglass material; is there any downside to using the stitched together cloth+mat for this purpose? (versus a layer of mat, a layer of cloth, etc.. etc..)

    Lastly, I've been split on epoxy versus polyester resin. I've been told polyester will be fine (and alot more practical given the 10+ gallons I'll need, ease of finish work, and ability to use polyester gelcoat). Does this sound correct? I've got some concerns about it cracking/delaminating where the new & old work meet up, although at the same time glassed-in ribs shouldn't allow the structure to flex that way?

    Thanks in advance!
     
  2. cdre
    Joined: Jul 2010
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    Location: Iraq

    cdre Junior Member

    Are you looking at putting the deck cap back on, or going with a rolled gunnel? I'm thinking of doing the same thing, so curious to see if you get some responses.
     
  3. War Whoop
    Joined: Jun 2003
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    Location: Sunny Ft Lauderdale Fla

    War Whoop Senior Member

    Lay it out and grind back from a knife edge you have the room to use a 12:1 or better scarf ratio,Gelcoat the mold piece ,then a check mat across the entire repair and start with a 1708 you need to get the most filament possible across the repair early on and continue building the thickness.A vinlyester could be used here,

    It has twice the strength of a Polyester and is close to a room temperature cure epoxy. Yes the first laminate can go 4" or so down the side then the next a couple inches longer and so on ,you do not want a huge bump, layer it back the longest on top.
     
  4. leaky
    Joined: Sep 2008
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    Location: nh

    leaky Senior Member

    I'm scrapping the old cap all together, mostly for two reasons. One is is it's easier to do my own cap and the second is I didn't like the existing cap because it didn't allow rod holders to be installed.

    I'm also scrapping the bow rail & anchor pulpit. The height of the new hull will alleviate the need for a rail and I never used the anchor pulpit anyway. It also helps save weight. I want negligibly the same weight when finished, so some things need to go.

    The issues are the existing cap comes up about one foot from the hull, but actually angles in, so you have something that restricts vision without actually providing additional hull surface (so it doesn't help prevent waves crashing over the bow but restricts vision as if the hull was 1 foot higher).

    Also, due to the cosmetic styling there's alot of weight added by the cap to accomplish a limited degree of structure. Lastly, I want to add rod holders in the gunnels, so I'm going with a design that permits it. Namely, I'm adding ribs to the inside to support the new hull, which will be fastened to the original deck, and the new cap will fasten to the top of the ribs.

    The new cap is just going to be encapsulated plywood which runs around the upper edge, bolted with brackets to the ribs. A rub rail will be screwed to the cap, extending a bit below it, hiding the edge of the hull.

    The trouble with this design is blending the new & old gunnels together. There's no good way to explain it but basically I've got a method figured out for the two places where new & old will meet, which will be cosmetically sound enough.

    FYI this is a walkaround cuddy. When finished the area in the bow will be similar to a center console, except you will see the actual hull & ribs, those are staying exposed; I'll just roll some gel coat over it.

    The one time I've heard of it being done the original cap was used. It just doesn't make sense in this case.

    Jon
     
  5. leaky
    Joined: Sep 2008
    Posts: 146
    Likes: 5, Points: 18, Legacy Rep: 14
    Location: nh

    leaky Senior Member

    1708, meaning the mat + biaxial stitched together? That's the only way I'm finding 1708 anyway.. Actually I happen to have > 100 lbs of that stuff on a ~52 inch roll leftover from something else..

    Regarding the first layer of mat, and this is assuming what you are recommending is mat + biaxial, I should use a layer of just mat first, then followed by another layer of mat which is included in the mat + biaxial stuff?...

    Or is one layer of mat all that is required to hide the weave?

    Thanks,

    Jon
     

  6. War Whoop
    Joined: Jun 2003
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    Location: Sunny Ft Lauderdale Fla

    War Whoop Senior Member

    Yes Gelcoat then a layer of mat, any would work to hide any print I usually use a 1 Oz,allow it to cure,then the 1708 build up since you have it.Lay paper on the floor in the garage for a cutting table.you should be around .046 laminate thickness per layer of 1708.
     
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