making a boat longer

Discussion in 'Fiberglass and Composite Boat Building' started by brokensheer, Apr 30, 2012.

  1. brokensheer
    Joined: Jun 2009
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    Location: So. Md

    brokensheer Senior Member

    I have a mold for a 23' boat, I am thinking about building a 25'. my thoughts are to in the mold build a section from the transom forward say about three feet., pull it and then glass a section from the bow back almost to the transom. in the areas of the joint leave the glass light so I can add the additional when the two parts are joined. any thoughts?
  2. keysdisease
    Joined: Mar 2006
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    Location: South Florida USA

    keysdisease Senior Member

    any thoughts?

    Build a 23 ft boat. What you are thinking of is WAY too involved for the return of a 2ft longer boat, not to mention the problems associated with two secondary bonds holding your boat together.


  3. midnitmike
    Joined: Apr 2012
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    Location: Haines and Juneau

    midnitmike Senior Member

    Stretching boats

    Although I'm new to this forum I'm not new to the idea of stretching boats, having done two or three jobs much like you're proposing. Having the mold makes this project not only practical but should produce a satisfactory result.

    Here are a couple of tricks that can make the job easier.

    1) When laying up the first transom section hold back each succesive lay-up 3" to 6". This will allow you to bond in the transom using ever wider lay-ups thereby increasing your bond surface area.

    2) Use this same lay-up schedule at the stern of your larger forward section.

    3) Depending on the hull design you may need to cut along the chine line in order to smooth out the transition between the two pieces.

    4) Blocking and realigning the two hull sections can be difficult...take your time and measure everything!

    5) Consider saving one or two lay-ups for the newly stretched boat as a final tie in over the whole thing.

    6) For me the hardest part has always been dealing with the gelcoat cosmetics at the joint. This should be at least slightly less difficult for you since you'll have the the correct gelcoat and pieces of the same age and weathering.

    Good Luck!

  4. iceboater
    Joined: Jan 2011
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    Location: Iceland

    iceboater Junior Member

    This is an easy task since you have the mold. When you mask of the bow, do it with straight lines if you can and before you demold the bow, make measurements from the transom of the mold, to the masking tape.
    When you mask of the transom for gelcoating, you put the masking tape 2´ from the transom and use the same points for measure.
    I leave the skin coat about 11/2" from the joint and next layer about 8", then each layer after that 4".
    In your case I would lay up the transom in as few layer as possible and demold it same day and join it to the bow and start the same day to layup the parts. Just be careful to not put many layers at a time by the thin joining area, becouse of little heat dispensing. The few layers on the transom also help if you need to cut it up, so it will join better. I would use vinyl ester for the joining. The best way to line up and hold the joint parts together is to use plywood strips and glue them with heat gun on the outside. They have incredible hold and are easy to remove.


    Attached Files:

  5. oops!
    Joined: Oct 2007
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    Location: kelowna bc

    oops! Junior Member

    i did it.......without the mold.

    took a 19 and made it a 25.

    the google hull extension in progress with pics.

    i documnented the entire process.....complete with pics and laminate schedules....materials....ect.

    the boat is now straight.....stiff ....and fast.....

    i love it

    good luck
  6. brokensheer
    Joined: Jun 2009
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    Location: So. Md

    brokensheer Senior Member

    thanks for the info! m Ooops great link !
  7. benglish300
    Joined: Jan 2012
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    Location: New England

    benglish300 Junior Member

    This is a very common thing in downeast Maine for commercial fishing boats. 2 feet can make all the difference sometimes when in need of bait or fish holds below deck. If any advice is needed, id recommend H&H Marine in Stuben Maine. These guys are pros at extending hulls and decks for that matter and a friendly place.
  8. rawleyjerel@yah
    Joined: Apr 2012
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    Location: United States

    rawleyjerel@yah Junior Member

    hi im jerry ive been a boat builder for 20 years,what your suggesting will work but you must be very careful!! when ive done this in the past i made sure to leave my part seems to stagger outwards by four inch staggers.depending on your laminate layup ie chop,woven roving or stitchmat stagger each layer back four inches from your seam. if lets say you have four layers in the build youll lay a 8 inch strip followed by a 16 inch layer and so on.. your final layer should be a 1708 dbm or a 1808 0/90 to cover a foot past your last layer on the seam outward toward your bow and transom, and then i suggest to cover entire hull with a 1.5 ounce mat. this will ensure tesile and sheer strength for your hull when under significant stress while underway whether motor or sail.the hard part is the gel work to be done on the outside seam lol.good luck with this venture and if theres any questions you may have my user name is my email feel free to ask!!
  9. tunnels

    tunnels Previous Member

    If its just a couple of feet then make the boat and cut it and fix mdf board with a waxed shiny finish across the part to be joined gel coats it and lay up and stagger all the glass 200 mm on all the joins . the mdf will pull and fair the panels each side !! so not so bad to do !!
    I Added a meter into a short fat little power boat once and screwed the mdf to each panel after spilting it a way down the chine so the panels would bend and conform to there new shape better . Built in all the new stringers, floors and deck etc and when was bogged ,sanded ,primed and painter it was like it grew there .
    The boat was 1000 times better with the extra metre in length added . :p:):D:p
  10. brokensheer
    Joined: Jun 2009
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    Location: So. Md

    brokensheer Senior Member

    Thanks again guys, I think this project is going to happen, I have the 23' mold and I will make sure I place the joint in the easiest location to fair! and or keep the boat so.

    Again Thanks to all !

  11. tunnels

    tunnels Previous Member

    Adding to a existing hull isnt difficult and the size of the boat dosent really matter !!
    A well known power boat manufacturing company in New Zealand has a 55 foot mould and just stretchs it out to 65 foot and longer by adding premade bits from the mould !! they been doing this for years !! and possibly are still doing the same thing !! You cant believe the amount of bog thats use to Fair then up which adds lots of weight to the finished boat weight . There theory is just add bigger motors and if its still dosent plane properly put even bigger ones in !! what the hell !!. :eek:
    Its the same company that backed up a concrete truck to trim the boat once !!
    I only stayed at this place for a short time , Was just a fill in job till my regular work picked up !;)
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