10ft fibreglass rowing boat seems too heavy?

Discussion in 'Boat Design' started by valvebounce, Jun 27, 2022.

  1. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    I have a 10ft rowing boat project on the go. On the water it planes easily with a 6hp Evinrude or is effortless to row.Out of the water it seems about 1/3 of it's weight too heavy.
    The gunnels are timber fibreglassed over,the seat is a full partition from hull to the top of the seat,(9" wide) There is a similar seat at the stern.
    I am thinking that the timber is waterlogged.With the curve on the gunnels,they are about 11 ft long and 2.5" square.The seat is a frame of 3"x2" boxed in with ply.
    I'm thinking about replacing the gunnels with 2.5" square pvc pipe and replacing the seats with simple 1.5" x 9" timber.
    The boat is a project,and I'm in no rush.
    Any ideas?
     
  2. Tiny Turnip
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    Tiny Turnip Senior Member

    If you popped it on a weigh bridge (on trailer - empty trailer) the actual weight would give a helpful comparison. Plus a photo or two. I'd be cautious about pvc - I think there will be issues with getting sufficient adhesion with either epoxy or polyester to adhere, but others here will know the details of this.
     
  3. valvebounce
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    valvebounce Senior Member

    Thanks for your reply.
    The unfortunate thing is,I have yet to alter a bigger boat trailer to a suitable size to take the rowing boat.
    So getting it to a weighbridge is not possible.
    What I intend to do is cut one side of the fibreglass on the gunnels,(outer face) and remove the timber,which will leave a three sided box section empty,then fit a suitable size square section pvc tube in the gap.That will just leave one face to fibreglass over.
    I can bend the pvc tube with a heatgun to suit the shape of the gunnels.I want to avoid using timber,which may yet again get waterlogged.
    The boat needs quite a bit of tlc because the previous owner used some unsuitable materials for his alterations.
    Here's a couple of pics
     

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  4. philSweet
    Joined: May 2008
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    philSweet Senior Member

    If choppergunned, it should probably weigh about 110 pounds. That's a bit of a heavy layup, but that's probably why it's still in existence. If a hand layup, it should be a few pounds lighter. The mid seat is usually a U shape over plywood top tabbed to the hull at the edges. I made the verticals a bit over 1/8 thick of chop when knocking out 10' Dooley Dinghies (Glander boatworks). The back seat is ususally an L shape over plywood top tabbed at all edges. There may be a bow seat also. It may have foam in these closed compartments. That is where the weight will be. Poke an inspection hole into the seat compartments, and remove and replace any old foam.
     
  5. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    My guess is that the boat was a bit over-built and a view of the inside might confirm the suspicion.A seat box framed with 3"X2" just has to be rather excessive and something about an inch square would have been quite sufficient.Those hefty bilge keels look a bit larger than they need to be as well.The advice to check the inside of the tanks is well worth following and I hope that all enclosed tanks have bungs to allow for drainage.You might like to hold on the square PVC gunwales until you are quite sure you will be able to wrap glass around the section.Do you have any experience of applying glass?
     
  6. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    I think the boat was 'overbuilt'like you said.The central bilge keel is empty and runs from bow to stern.The two outers have timber in them,and rust spots are appearing where they have been bolted in from the outside of the hull.I intend using a thread extractor to remove the bolts because they are not needed.
    I've done some fibreglassing,and I'm pretty confident at doing the gunwales.The boat is very stable and it handles well on the water.I've customised aluminium oars to fit,and it gets on the plane easily with the 6hp Evinrude.
     
  7. valvebounce
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    valvebounce Senior Member

    Yep,you are right,it was heavily built.There is a front middle and stern seat,the foam in them was waterlogged.I intend removing all three and using plain planking with nothing underneath.(sanded and polished)
     
  8. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Those full length strakes alongside the keel could be reduced significantly to cut some drag and weight.
    They may be responsible for allowing this displacement hull to plane by trapping water flow under the bottom.
    If they were sleeker, thinner and restricted to the stern third of the length, they’d do just as well, maybe better.
    Seats/flotation chambers could be easily made of fiberglass with no wood by laminating over temporary melamine molds.
     
  9. Peter Belenky
    Joined: Mar 2009
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    Peter Belenky New Member

    The boat is functional but too heavy. No doubt, there are ways to lighten it, but will the resulting increase in value be enough to compensate you for the time and materials? Not being a show-stopping classic, it may not be worth the effort.
     
  10. valvebounce
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    valvebounce Senior Member

    Good idea with the fibreglass boxes for seats,they would probably be useful as flotation chambers.
    Those big strakes give the boat excellent stability when not under way.They stop the rolling action.(rolling stabilisers)
    When the boat planes, and is trimmed,the boat stays quite flat,and does not 'dig in'at the stern.
     
  11. valvebounce
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    valvebounce Senior Member

    The value is not important,and it's a flight of fancy project.There's something about the boat that I have taken a shine to.
    I have a Broom (british) speedboat that I have converted for sea fishing,but I am getting a bit long in the tooth to handle launching it.
    The rowing boat will be a way to get me on the rivers.
     
  12. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    I REALLY doubt that the strakes have much effect on stability, especially when not under way.
    Their purpose is much more likely to protect the boats bottom.
    They need repair and/or replacement. I’d pull them off, putty the holes and give it a trial without them.
     

  13. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    I appreciate your ideas,and thanks,but,have you ever thought why yachts have deep keels,and ships have stabilisers?
    The strakes are part of the fibreglass hull,they have not been added onto the original hull,so removing them would be a big job.
    The central strake/keel,is totally empty,and there is a long slot in the base of the boat on the inside.
    When I had the shortshaft 6hp Evinrude on the boat,I thought the bottom strake might cause the flow of water to cause problems because it is below the cavitation plate,but it wasn't a problem.Obviously,it's a rowing boat,not designed for an outboard.I toyed with the idea of lowering the transom,but scrapped the idea because the boat would be liable to flooding in a following sea.Also,if I throttle of too quickly,the boat would pitch forward,then pitch back,and a lower transom might cause the stern to dip under the water.
    My problem is the excess weight when moving it about when it's off the trailer.
     
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