Boat extension question..

Discussion in 'Fiberglass and Composite Boat Building' started by Wingman, Feb 12, 2010.

  1. Wingman
    Joined: Feb 2010
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    Wingman New Member

    Not sure if this is in the right place but, I thought I would start here. I have read many posts and threads looking for information and have not found anything to answer my questions about fiberglass boat construction. I am hoping somebody could point me in the right direction or tell me if it’s possible or not.

    I am wondering if it is possible to stretch/lengthen the hull length of a fiberglass boat without terribly upsetting the characteristics of how the boat performs in the water. Referring to center of gravity, buoyancy stability, etc, etc... Is there a formula that is used to determine what the beam needs to be in relation to the length or are there other factors that are looked at?

    For example, I have an old 24’ Sea Ray boat (8’ beam) project that I really like and would like to look at options for lengthening it. I originally purchased it with the intentions of using it as a weekend fishing boat but, now I am thinking that I would like to do some traveling with it. It does not have a head/shower, or kitchen. It’s just a basic fishing boat with a tiny flybridge.

    I have asked a couple of people and the response I get is “if ya want more room get a bigger boat” I looked at the next model up and it starts getting into traffic law problems, meaning it’s too wide. Yes, I can get permits, hang the “wide load” banners, put flags at every corner and get my routes approved and plan for only traveling on certain days but, it seems like such a hassle.

    I like the thought of the street legal width and want to stay with the trailer boat but want something with more room or length without being worried about stability problems. Does that make sense? Any thoughts?
  2. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    It is a lot of work but it can be done. Is this an outdrive unit? How much longer do you want it to be? Can you post some pictures of the bottom of the boat both inside and outside plus the transom? Do you know the year of the boat?
  3. Hunter25
    Joined: Mar 2006
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    Hunter25 Senior Member

    There is more to this thing then making a 24' boat a 28' boat. A 28' boat has a thicker hull, bigger hull strengthing componites, larger everyhting. If you add a piece to the back by the time you smooth it in, the transom might be too narrow and the rest of the hull will be still the thickness of a 24' boat. You could cut the boat in the middle and add a center piece but you have the same problems. The free board is lower on a 24' boat then a 28', lots of problems I can see. I sure you can do it but a lot of work. I can not see how you would keep the centers of buoyancy, gravity, etc. in the same places.
  4. Obsession
    Joined: Jan 2010
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    Location: Chicago, IL, USA

    Obsession Junior Member

    I have seen pictures of stretching 80 to 110 foot boats a bit, but the percentage of the overall isn't huge and the budget is not tight. I can't remember ever hearing of someone stretching a production boat (where the next model up is also available on the used market.) There have to be larger boats which are still trailerable unless you're really attached to this boat. From a practical sense, the scope of this job seems massive and you end up with an unproven boat that likely has equal or less resale value than what you have now. I admire your courage, and don't mean to be negative, but I warn you the job will be 10x harder than you anticipate and can easily end up costing more than buying a new boat when it's all said and done. Search far and wide first, unless you really love this specific boat.
  5. alan white
    Joined: Mar 2007
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    alan white Senior Member

    Obsession is right. Start with a boat that is closer to your trailering dimension goals, whatever length you can manage to find (26 ft x 8.5 ft maybe), and hopefully it has a layput needing little if any modifications.
    The job you propose to do is indeed massive and not only that, should only be done by someone who has a lot of experience in glass work, not to mention the design considerations.
    Just making what you've got into a cruiser is a giant task, worth 20k-30k maybe, to have it done.
  6. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Wingman, look how Bayliner make their boats look longer. They do not add an inch to the hull, but instead bolt on a flashy extension with one or two steps leading to a large platform.
    It is thin walled, just strong enough to carry the weight of the people on the platform and needs not be watertight.

    If you add an extension all the way to the bottom, it complicates your project enormously: propulsion, buoyancy, water intrusion to name a few.
    I added 1 ft to my boat and already look at a totally different waterline, rain and dirt collecting on deck corners and the kitchen sink having the drain hole on the wrong side now. My project concerned new propulsion, so I needed a 1 ft longer engine bay, so I had no real choice.
  7. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    If your boat has an inboard engine and outdrive. You could remove same, patch and stiffen the transom and mount a large outboard engine bracket to the transom that will handle your HP needs. This way you pick up at least 3' x 32" wide on your rear deck. Sell the engine and outdrive and pick up a good outboard engine. Much simpler plan then adding to the whole hull.
  8. Wingman
    Joined: Feb 2010
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    Wingman New Member

    Thanks guys,

    I appreciate the feed back. I’m not looking at the responses as being negative. I just wanted truth in opinions and ideas. As we all know, ideas or projects get started in our mind and sometimes bouncing it off of other people brings out other things to consider or different ways of looking at it.

    I like the looks of the older Sea Rays and was hoping to stay with the hull I have. I know it would be a huge job and as with most projects the time and money spent are usually more than planned on.

    At this point, I think I will keep it simple and continue looking for something closer to the legal specs.
  9. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Hi Wingman,

    As much as it would be really nice to be able to "just add a few feet" to our boats when they get too small.... the friends you've already talked to, and the forum members who have replied above, are right.

    We all get attached to our boats; sadly, there comes a time when the one we have just isn't the right boat anymore. If the required modifications are so extensive as to involve lengthening the hull, it's time to look for a new boat. Unless it is perfectly engineered and perfectly executed, such a modification is likely to completely destroy the boat's resale value and may seriously compromise its performance and safety.

    Fortunately, there are quite a lot of boats out there with a bit more room than your 24' and that are still trailerable without special permits. Most production builders assume that anything over 26' or so will live in a marina slip, but there is still a pretty good selection of boats up to 30', going back quite a few years, that would suit your needs.
  10. tunnels

    tunnels Previous Member

    So you want to make a small boat big ! Forget it you will always have just that a small / big boat! . Like has already been said theres the other things that go with the add on . You change one part of a boat and lots of other things change with it . Balance is one thing . the ride is another and the loadings on the join are something else!! Because of the added length it will ride the waves differantly .
    We have a company here that has a 55 ft mould and they have been pulling and making 65 and up to 70 footers and it has finally caught up with what they have been doing .One has started to come apart at the join up . The bigger boats take on a canoe look and are not good sea boats , because they dont have the beam to carry the weight of a 70 foot with all the rubbish that goes into them .
    I have added one meter to a 5.5 metre power boat but it was very Beamy for its length anyway to start off with so made this boat into a good all rounder .
    Buy the size of boat you need .The exspense of doing the add on can and will run way over budget so plan well and double what ever cost you see on paper because that will be more realistic of what you will end up with !. :p

  11. TollyWally
    Joined: Mar 2005
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    TollyWally Senior Member

    While I concurr with the thoughts as to whether or not this is a good idea for you. I've seen many fiberglass fishing boats in the 32 to 45 foot range stretched 3 to 6 feet and fished on one of them. Most of the time the rudder and wheel are left where they are. Tanks and holds are manipulated to balance trim. Larger steel boats are lengthened and widened almost routinely.

    On the other hand I know of one stretched boat back in the day that disappeared during a halibut opening. No distress call, no debris was ever found.
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