SeaCraft project boat restoration (25' seafari)

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

  1. flyingfrizzle
    Joined: Jan 2015
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    Location: Eastern, N.C.

    flyingfrizzle Junior Member

    I understand the deal with the fibers being stronger laid out straighter on a larger to smaller lay up. Without the steps in the fibers it will yield more strength due to they are already pulled tight or laid even. Makes total since. My only thing is when I am doing a transom I like to tab it so that the corners are more curved than using a small filet and 90ing the fabric. I feel like it helps eliminate the hard spots corrected where the cored rear ties to the side of the hull. To do such large filets to make the radius larger it would take a lot of thickened resin and would weigh a ton. I sometimes start with the small 2-4" strips to create the radius I want them just build up off of that. It keeps me from having 2 gallons of thickened resin fileted down each side. This area gets hidden by a liner so there is no need to fair out the area so no worries there. I even cut 2" foam triangular strips to fill the voids in the corners so that I can avoid using so much filet material. I agree with what you said and need to get in the habit of laying it the better way between the two even if it don't add much more strength, it will just be a good habit to form.

    Not to be long winded but a little back ground, I am just a back yard self taught "fiberglass boat builder/restore hobbyist" in my mid 30's. The main reason I posted up here was to take my knowledge to the next level and learn from the people on this site. I am a moderator on the classic seacraft site, a boat rehab site dedicated to that make of classic boats. There is a lot of good information on that site and I have learned a lot there but like you mentioned there can be a lot of guys that have done certain things certain ways for years and can be outdated or under achieved in their skills. Like I said I know more people up hear have engineering degrees and such and have a much more vast knowledge of correct ways of doing things. I would love to better grow my skills in the direction that will be founded on facts vs traditions. I don't see myself as a beginner but feel like I still have a lot to learn and am very willing to listen if any up here care to share.

    One thing that jumped out at me you mention is the wet on wet vs the dry on wet. I can see where you say with the same ratio of glass to resin it will yield the same strength in theory but I just don't see how that is possible when you are bonding to cured lambent. If you were to lay up five layers all wet on wet and vacuum bag it vs doing one at the time after the "green" chemical bond period I would think it would be really hard to get the same glass to resin ratio. Plus I wouldn't think the peel strength of each layer would not be as strong due to the chemical bond would lock the fibers together better than the secondary bond of each layered. I always do a lot of secondary bonds just because I cant do it all in one day or weekend. I always take lots of time to prep and scuff up the surface in between each bond or layer. But I still feel like under twisting and flexing loads the chemical bond will yield more peel strength. If you could explain how they would be the same strength? I may be missing something here.

    I don't have the background in the engineering field so I might not be looking at this right but if you have the time to explain I would love to get a better understanding of the proper methods and better or stronger ways of doing this type of stuff. This is just a hobby for me but I would like to do it to the best of my ability and maximize design and strength on my restores. I work as a electrical control & instrumentation technician and have a fair back ground in industrial mechanical, welding, pipe fitting and such. I don't have not plans to seek a career in the boat building or repair field but just enjoy doing it on the weekends. I have done quite a few projects and restores on small mono fiberglass hulls and have gotten better as time passed. Im all ears if any body has pointers along the way as I proceed on this project once I get back up and working on it...

    Sorry for the long post, just trying to get my background out there and get a chance at furthering my progress in a better manor.
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Let's talk apples and apples. A wet on wet laminate is messy and yep a chemical bond, but so is a wet on dry, assuming the dry is still within it's chemically active window. Yields will be exactly the same, though the dry method is a whole lot neater. Simply put, given the choice, I'll always lay down fabric dry, regardless of the physical condition of the substrate (chemical or mechanical bonding). Working around a project with dripping lengths of fabric, seem counter productive to me, though I know plenty of folks do it.

    As for the bigger to small/small to bigger debate, both will be about the same strength if cloth or mat is used. This is because the individual fibers need to straighten out, before they reach a fully loaded condition and with woven fabrics, many will break, because of the undulating weave, before fully loaded. This isn't true of knitted fabrics, where the strands are directionally laid on top of each other. They take up load almost instantly, so elasticity modulus can more closely match resin type.

    It's when the fabrics are smoothed and faired that the real problems arise. In the previously attached sketch, you can see the small to big fabric stack has much of the top layer ground away, defeating the intended overlap and it's "purchase power" on the underlying laminate. The small to big stack also tends to make more puckers, bubbles, etc., as the progressively larger layers try to ride over the previous layer's lap joints.

    A fillet does help eliminate hard spots, because it "ramps up" to the area, then ramps down and away from the area. This allows load transmissions to pass through, over the increase in density, gradually up, then again gradually back down after the transition or directional change. Attached is a recently posted image of what really happens with a fillet and tabbing. If you take your magic density sensing machine and run along a panel (plywood in this image's case). The abutting element causes a huge, dramatic and sudden increase in density. This is what causes things to break, typically just before or just after this "hard point". This is a stress riser and needs to be avoided. The fillet and tabbing, cause the load to get into (and out of) the abutting element with some cushion, so to speak. If the tabbing isn't there, but a well shaped fillet of appropriate dimensions, the same thing still happens. Tabbing is just an additional purchase on the substrate. In fact, you can skip the fillets altogether if you like, using just the tabbing (many boats are built this way), though practical issues crop up, like getting the tabbing to lay down neatly. This means you can use your aunt Millie's mash potato salad as the fillet material, if it's stiff enough to hold the tabbing in place during the cure. Conversely, on some substrates, you can skip the tabbing and rely on the fillets, again if appropriately shaped.
     

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  3. flyingfrizzle
    Joined: Jan 2015
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    Location: Eastern, N.C.

    flyingfrizzle Junior Member

    Thanks for all the insight. I appreciate you taking a moment to explain some of these methods. I will take some of this into consideration when I get back going on the project. I plan to take many pictures and will post up as I go along so you can see how it comes together. I will be glad to listen to any pointers along the way.

    One thing that I also do when laying up a section that will be faired flat that is not on a molding table that will need to be hand blocked is lay some csm up on the final layer. That gives me something to sand down into. I will use several layers of 1700 biax and then add the cms to the top and that will keep me form getting down into the strands of the biax.

    I mainly use vinyl ester that has a 24 hr "green window" so I try my best to work with in that period if all possible. Vacuum bagging makes several layers easier and less messy plus gets the glass to resin ratio better for me. To lay them by hand will get very messy like you mentioned. I have been trying to mold more parts and build on molding tables to keep the fairing down to a minimum if all possible but it can never be eliminated.

    Look forward to future comments once I am able to post up some progress on the hull.
     
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