SeaCraft project boat restoration (25' seafari)

Discussion in 'Powerboats' started by flyingfrizzle, Jan 8, 2015.

  1. flyingfrizzle
    Joined: Jan 2015
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    flyingfrizzle Junior Member

    Just starting on a simple restore on this 1975 SeaCraft Seafari. I have several older SeaCraft hulls from the late 60's and 70's and have done some restores on a few of them and some other boats in the past but not a professional by any means. The hull at had needs a new transom and some bulk heads changed/added. The fuel hatch needs to be recored and a new tank installed. The boat had twin mercury 470's (inline 4 cyl'd) originally but I will be converting it to a outboard hull and using twin 200 efi Mercury outboards to repower the hull.

    Here is a few PIC's:
    20140614_135309.jpg
     
  2. flyingfrizzle
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    flyingfrizzle Junior Member

    Here is the old transom (wood ply is completely rotted out):
    restore 3.jpg

    restore  1.jpg

    I cut the old inner skin out and worked on getting the old ply removed:

    restore 5.jpg

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  3. flyingfrizzle
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    flyingfrizzle Junior Member

    I purchased two pieces of 3/4" Douglas Fir marine grade AB ply and cut them to match the rear of the hull and fitted them in place:

    attachment113.jpg

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  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The key to getting a good transom out of this is the interlaminate bond and the core's tabbing to the hull shell. It appears you've ground away all the previous tabbing, so you'll have to bulk up new, once the core is bonded to the external skin.
     
  5. steve123
    Joined: Dec 2014
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    steve123 Junior Member

    Bed the ply to transom with structural bonding paste, cut relief holes in ply about 1"dia at random to allow air out and paste when sqeezed into place.
    Dont be mean with the paste or you will end up with voids.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    If the plywood pieces to the core are put together with a rolling action, you don't need air release holes, which just promote rot eventually. When you assemble the core, start in the center, with 3/4" strips of wood spaced at the edges, holding and separating the plywood. Start in the center and work outward, in circular pattern, driving the temporary fasteners, to hold the core pieces until the goo cures. As you get close to the edges, pull out the 3/4" wood strips and continue screwing it down. This will force any trapped air to escape along the edges. When cured, remove the fasteners and fill the holes.
     
  7. flyingfrizzle
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    flyingfrizzle Junior Member

    I have used vinyl ester resin to hot coat the rear of the core section with thinned resin with styrene and also added a layer of csm just to fully seal the wood ply off so that if I do get a void by chance there is no way for the ply to soak up water. I fell like the thinned VE resin absorbs better than epoxy so I used that for the hot coat but will be bonding it in with thickened epoxy. I plan on using a trowel with 1/4"notched teeth to spread the paste across the old skin and then like mention slide the vee section in first and roll it to the skin trying to get all the air to escape out while applying pressure. I have 4) homemade c-clamps that have 4' throats made in them that have two clamping bolts on each one that I will use to clamp it in place with while it sets up to prevent drilling holes in the ply. (I don't want to break threw the hot coated section with the csm). Once I get that set up I was going to pull some filets in the corners and then laminate the front side with pre cut 1708 cloth with tabbing ears made in to the cloth as one continuous piece. The first having 4" tabbing ears the second 6"ears and the third having 8" ears. I may need to add some additional tabbing after this to the core but not sure how much additional is needed after the first three over lapping sections that will be part of the inner skin. I 45 angled the top of the core and rounded the edges so the upper cloth would roll over the ply edge easier on the top of the ply rounded the back edges so it would lay flat against the old skin before I hot coated the back. Im not sure if I forgotten anything but thanks for the help guys and any additional feedback is appreciated moving forward. I want to get it right the first time!

    A picture of the core hot coated on the back, I used a infusion resin for its thin viscosity and also added some styrene to thin it a little more so it would wick in to the wood well. I applied it cold in my shop to give the resin some more time to soak in and then after an hour of soak time I brought the temp in the shop from the 40's to 95 degrees and it kicked of quickly after the temp started rising. Then let it stay at 95 for 10 hours over night.:
    transom core.jpg
     
  8. flyingfrizzle
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    flyingfrizzle Junior Member

    I haven't got the transom core installed yet due to the cold weather, but I have started making my outboard bracket for mounting up twin 2.5 mercury 200 hp outboards. I started out with melamine for making my mold. I cut the bracket to have a large floatation tub 60" wide and 24" deep. The bottom will vee will match the hull deadrise and mount 2" higher than the keel. The tub will be built on a 12 degree angle to match the lay back of the transom and it will also have a 10 degree angle up to the motor mount on the bottom to allow for the rise of the water off the transom. It will have a swim platform that will be 72" wide by 24". I will be laying it up with Vinyl ester resin and 1708 biax and csm. The motor mount will have marine ply for compression strength and the swim platform and the stringers will be core cell. Here are a few pictures:

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    !1.jpg

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  9. flyingfrizzle
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    flyingfrizzle Junior Member

    I got the mold put together and started laying it up. I made the front so that it has a 1/4" set back on the top 4" of the front so that when I bond the swim platform to it they will end up even on the mounting surface. You can see this in the last post pictures. I also used clay in the corners for the tub radius edges. I started out with 10 mils of gel coat with the corners thicker so I can lightly sand them smooth. Then I laid 4 layers of csm to prevent print threw and to get the base to start layering on. After that I got several layers of 1708 in and tabbed the edges over 4" onto the next sided when installing the cloth. added 4" biax tape in the corners for extra strength. I dropped several layers of csm on the back ear for the transom to bond to. I skimmed thickened resin with a notched trowel to the surface and bedded the core down into it. The core was two 3/4" marine plys bonded together with two layers of 1708 between them. It was hot coated with thinned resin as well. Once that sat up the front will be gassed with a few layers and then the stringers installed. Right now I have got about a 1/2" of glass in the rear of the mold behind the core for the back section that the motor will hang on. The front of the core will get at least 1/4" of glass. The back corners are 3/4" thick and the sides and front of the mold are laid up 3/8" thick. So over all the flotation box will be 3/8" thick with 1/2" on the rear motor mount with the core plus the 1/4" on front of the core. Like said all corners are built up to 3/4" thick and then I will add two stringers center of each outboard. They will have two layers of 1708 on them then tabbed in will to the box front and rear. The front of the bracket will threw bolt to the back of the boat transom.

    My main Question is how is my lay up schedule? Did I over do it? Need more? I can add more at this point but not take off accurse. The outboards will weigh 850 lbs and push the 25' hull around 60 mph or so in moderate to ruff conditions at times. I built it based on the lay up schedule from other fiberglass motor brackets that are produced by a manufacturing company. I also compared the thickness to one that I own that was built by an factory supplier as well. I just want to keep it light as I can but don't want to compromise safety or have it crack and start to fail. The ones I am building off of are a bit narrower but built about the same. Let me know what you think on the construction....

    Here are a few pics so far:

    20150215_175907.jpg

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    20150215_175911.jpg
     
  10. flyingfrizzle
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    flyingfrizzle Junior Member

    Here is that last one I built, just to get an idea on what the final product I am building will look like. It will be much larger than this on that is on a 20' single outboard hull. Swim platform will be the same size but much more larger floatation tub under it plus the wider mounting tab for twins:

    #4.jpg

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    01-20sceptre.jpg

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  11. helluvaboater
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    helluvaboater Junior Member

    Did you ever finish this? How much tabbing did you do from the inner transom wall to the inside of the hull? I am currently doing this on my 28 foot boat.
     
  12. flyingfrizzle
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    flyingfrizzle Junior Member

    I haven't finished this yet. I got side tracked with my drag car. Once it warms up I plan on getting back going on it. Far as tabbing, I like to pull a nice filet in the corners before I tab it to the sides. I try to cut the cloth wide so the tabs stay connected to the center section. Almost like ears off of it. I do add aditional tabbing on top of this as well. I will start with large strips and lap it 2" on both sides then 4" both sides then 6" both sides then 8" both sides. Gradually larger each time. Both sides and the bottom and around the stringers where they meet. Don't want a hard 90 but a smooth transition that curves over the filet. Make sure the top of the core gets coverd also. Many seacraft hulls rot from the top of the transom down due to the ply ends wick water down it when not coverd by glass. I 45 the top so the cloth can form the corner and seal the top up. I got pics of the small hull online and will try to add some of the bigger hull.
     
  13. kapnD
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    kapnD Senior Member

    I would recommend you start with your widest tab, and lay the narrower ones atop that, hopefully in a continuous layup.
     
  14. flyingfrizzle
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    flyingfrizzle Junior Member

    I have done it both ways, smaller to large and large to small. Also read lots of debate over which way is better. Larger to smaller will keep the fibers laying strighter without stepping down. Inside corners I usally do smaller to larger and out side corners larger to smaller. If you get a good filet you can do it with the larger first and it the orientation of the fibers will be better. If you start smaller on a tighter inside cornner then work up on that lesser radius filet the smaller pieces will build the filet out so the larger ones lay nicer. I would be curious to which way yields more strength in a given type of inside corner joint.

    Also I agree wet on wet continuous lay ups are much stronger too.
     

  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A wet on wet, compaired to dry then wet will be the same strength, assuming both have the same resin to fiber ratio. The dry method is a whole lot neater.

    The big to small stack or tabbing is slightly stronger, because the fibers lay down better and if there's fairing involved, the big to small method minimizes fiber cutting when fairing. You'll use less filler too. The attached image physically shows why you stack from big to little. It doesn't matter if it's an inside corner or not. The little to big stack will have voids and get fibers cut during fairing, or you'll just need lots more compound to smooth it out. I know there seems a big debate on this, but there's no real debate among truly experienced laminate designers, just old school laminators who think they're doing it right, when in fact they're too old to change their flawed methods.
     

    Attached Files:

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