Advice on Fibreglass boat building

Discussion in 'Fiberglass and Composite Boat Building' started by goboatingnow, Oct 19, 2008.

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    FAST FRED Senior Member

    "as to foam core , I had been siding towards say cedar core, but could you reccomnend any online sources or books on foam core and whats the most common type of foam being used now."

    Airex although expensive is still the choice of most of the CG and lifesaving and Pilot boats built in eueo land .

    It takes a hell of a beating and is repairable .They have a builders manual.

    The biggest "hassle" with what used to be called Franz Mass construction , core over a male plug is surface finish.

    It takes mucho man hours IF you want a fantastic yacht finish.
    Mass would build #1 in Airex and then pull a mold from the hull. Of course his plug raced better than the solid glass heavier and less stiff customer boats.

    Either a relaxation in "perfection" or a source of inexpensive marginally skilled (but willing) labor to long board the boat would work.

    Simple marine paint is far easier to patch up (after a docking spectacular) compared to gelcoat or 2 part polly.We have used Toplac with good results

    Our more rapid fairing technique was to long board with machine floor sanding paper glued on. Silicon carbide is a better abrasive than the more common aluminum oxide , so much faster.
    Dont panic , it looks like rocks glued on a hunk of cardboard 14 or 20 grit , but does a good rapid job.

    Advantage of ANY foam core is stiffer , usually lighter , quieter , and insulated , a great help to any cruiser.

  2. keesdisease
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    keesdisease New Member

    just two cents from abroad...... Why would you bother making molds for one off pieces, I read earlier on that you are not skilled with wood so I would suggest using foam for such items and glassing the inside and or out as deemed necessary. As far as cabinetry and such go what a lot of the one off custom builders are doing here is having the pieces made out of house by cabinet makers from the design of the architect. These pieces are made a little bit long or tall then trimmed to fit to the boat sides or what have you, custom builders are now even getting the jigs for the house and the flybridge cut on CNC and now they have curves on both axis', there is a jig cutter here on the east coast that charges about 100 US per foot. Hope this helps with your endeavor, I am building a 29' fishing boat cold mold and I say go for it as there is nothing like the satisfaction from doing so,,,bloody knuckles and all:D
  3. robherc
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    robherc Designer/Hobbyist


    Actually (& I just re-read his initial post), he said he is fairly competent with woodwork, I.E. he's good enough to build his own mold. Your suggestion still sounds like a great way to save yourself some work to me though! :)
  4. gouloozeyachts
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    gouloozeyachts Junior Member

    B 40 ft GA 1.doc

    We locally advertised: ‘moulds for hire’, starting some 24 years ago and a few weeks ago our first client hired our mould for a rowing dinghy exactly how he wanted it. Maybe he brought us some luck.

    I built a 40 ft cold-moulded ply yacht for personal use quite some time ago and took a female mould of it. Our cold moulded yachts are good performers. Neal Petersen’s 11,2 mtr yacht is an example by finalizing the single-handed yacht race around the world. He lengthened herself to 12,2 mtr for qualifying purposes. Cold-moulded ply however lost some of its glory to more modern building materials special in the speed, and stiffness departments. It strengths and integrity however remains superior.

    The 40 ft mould was gathering dust because of my adversity against foam cores and even high-tech ones such as Nomex. (I still don’t know why) Because of a streak in my nature of never giving-up I started thinking and being an average person it indeed took me quite some time to find the (for me) ultimate solution.. Here it follows:

    The hull’s outer skin will be supported / strengthened with (pre-fab) GRP ribs across. They are hollow and their cross-section is a parallelogram. They are starting points of a complete enclosed honeycomb skin structure. Other parts are GRP channels laid toe-down, lengthwise between- and connected to the U-ribs. All members are glassed against the inside of the outer skin. Such a core has anti-delaminating properties, something which other cores (such as foam or even Nomex’ fail to have.

    The small gaps between the U-channels, needed for laminating against the skin, will be ‘stuffed’ with PUR foam and the whole inside be ‘glassed’ over

    We started tooling for making the 20 odd mould pairs for laminating the hollow ribs,
    in anticipation of future orders or for when I can afford my own (super) version.
    There remain a few minor problems such as: Do you like my designs and can you come to S.A. as my guest and laminate your hull and deck and how do we overcome possible laborlaw restrictions ?

    Attached Files:

    Last edited: Jan 25, 2009
  5. Sea Jay
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    Sea Jay Doug Brown


    I complete understand your position as I was mulling the very same question a few years back. I concur with the other poster that rehabbing an older boat is a very compelling proposition. I’d even go so far as to say it is likely the best from an economic point of view. I’d also agree with Eric that ply/epoxy is probably the option with the greatest likelihood of success for an amateur builder without metal skills. As a matter of fact, I went pretty far down that road with a Dudley Dix design. (Dudley is a great guy, has excellent designs, and really understands amateur builders). However, having built a ferro-cement trawler years ago, I really didn’t want to start from scratch so my plan was to contract for a bare hull. The quotes weren’t terribly out of line, but were high enough to make me seriously revisit the rehab option. In doing so I was fortunate enough to find a bare hull from a defunct manufacturer which suited my requirements very closely…and so I’m off down this path again.

    Regardless of your decision, I think there is one concept that you need to come to grips with. There is no rational reason to build a boat. Don’t waste any time trying to justify it. A fellow builder, Collin Harty ( said it so eloquently, “The choice to build a boat often does not feel like much of a choice. For us amateur builders, a project of this scale is best understood as a creative act, rather than as a practical solution to a problem. You build because a boat is unavoidably in you.” I smile every time I read those words. Good luck with your project.

  6. gouloozeyachts
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    gouloozeyachts Junior Member

    c16-480 honeycomb hull.jpg

    Hello Goboatingnow,
    We like to expand on our hollow rib / mono-medium honeycomb concept and include a file containing a building sequence simulation.


    Attached Files:

    Last edited: Mar 11, 2009
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    GGODDD New Member

    ello all

  8. old_sailor
    Joined: Aug 2009
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    old_sailor amateur boatbuilder

    I recently completed a Bruce Roberts Spray 40. It took a long time. I agree with all the others that say to buy a used boat and go from there. That said, It took me 11 years, working at a regular job full time. I made a lot of mistakes that this forum might have helped me prevent.
    You can see the history of my project at

    With all the mistakes I made, looking back, I would build a single skin, using a male mold. I would make the mold as fair as possible. There are a lot of books out there, I think that the best is still Ken Hankinson's "Fiberglass Boatbuilding for Amateurs".
    I thing that you are overestimating the amount of work necessary to build the mold for the hull relative to the rest of the work. I also think that you are underestimating the rest of the work. I think that building the deck and cabin structure is more difficult than the hull. For my deck and cabin, I used epoxy glass over strip plank fir. For all of the compound curves, I did not think that sheets of anything would work well. Remember that sheets of material typically only generate conic sections. Foam sheets will distort and come close to the compound curves that are usually found in sailboats.

    Don't underestimate the time required for all of the auxillary equipment! Hugely time consuming unless you go very, very basic.


  9. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Hey GBNow. I hope the comment previously about 'you cant avoid longboarding' isnt totally true, and moulds are truly big timesinks.

    I have spent the last 12 months agonising over a one off 28ft construction project, but I am avoiding strip plank and longboarding as much as possible - especially strip planking!

    I am going to attempt your original idea of a developable surface hull, using full length foam (Airex or similar) panels, initially glassed on one side, so they can be laid like plywood sheets (self fairing) in a female 'basket'.

    Then, once the insides are glassed, compartments fitted - the whole thing is rolled over for a final layer of glass.

    Hopefully, with the judicious use of peel play and a smooth flat melamime table to lay the panels on during layup, the amount of finishing work will be left behind.

    My NA has approved the concept, and it will be built ot full ISO standards, so I am optimistic at this point.

    The concept is similar to the Kelsall technique, for a monohull. The only strip planking is at the bilge turn for market appeal.
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