Hull Extension on 19 foot Stitch and Glue Center Console

Discussion in 'Boatbuilding' started by johnnythefish, Jan 20, 2019.

  1. johnnythefish
    Joined: May 2016
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    Location: E.A.

    johnnythefish Junior Member

    So here is a 19 foot Stitch and Glue Center console that I build from plans by Jacques Mertens (Classic 19 (C19) - Study Plans https://bateau.com/studyplans/C19_study.php?prod=C19).

    Unfortunately, I had some issues with one batch of epoxy resin that never cured. I only discovered this several years after launching. Cut a long story short, I had to gut the inside of her as the layer of biaxial cloth that sheathed the inside of the hull - to which the stringers were bedded - had started to lift off. I was using a very viscous epoxy resin for the inside (as I had run out of the Gurit SP106 that I used on the outside of the hull). This was all that was locally available - and I believe there were batches when we sheathed the inside that were either not mixed properly or the ratio was out. The issue was hidden by the fact that we worked wet on wet and the top layers cured firm and hard and I never noticed that beneath were some batches than stayed uncured for years.

    [​IMG] [​IMG]

    Anyways ... I had always wished that I had built a slightly longer boat. I cannot fault the C19 in any ways as far as "doing what it said it would" on the box. But over time as I became more familiar with boats and what I was using it for, I realized that I should perhaps have gone for a longer, thinner hull... more of a "Panga" than a classic planning hull.

    Much of my time is spent fishing in the boat - trolling lures at 8 kts which is about the worst speed for a hull of this shape in terms of fuel usage.

    I have read what I can on the subject of boats - I thoroughly enjoyed David Gerr's "The Nature of Boats" - but I must say that I start to glaze over when hard-core mathematical formula come out! I have been particularly interested in Tom Lathrops "Bluejacket boats" - and how he went about attempting to achieve a boat that transitioned to the plane nicely, with little hump and minimal change of trim angle. The fact that he does this with a Constant deadrise hull is also interesting.

    Well... I have decided to extend my C19... at the very least I gain more space and a bigger boat and I come out of my gutting process with some semblance of feeling like "oh well ... maybe it was for the best"...

    My hopes are that she will be lighter for her size (I am planning on keeping weight as low as possible) and possibly, I will see some improvement in her "efficiency" at the 8 kt trolling speeds (though I am under no illusions here).

    The designer is happy with a 10% scaling up of his plans from scratch - so that would be about 2 feet - but he also is happy with a bolt on armstrong type bracket... so the optimist in me feels that stretching the hull 4 feet wouldn't be totally unreasonable!! That I believe would make some serious differences to how she would behave - and given that I am sticking with the same engine, fuel quantities, fishing buddies etc, I would have a boat that was relatively much lighter in the water.

    I have cut the transom off ... so there is no going back now...

    [​IMG]

    The extension will be done from the transom end - and as you can see I have cut the hull so that I can add a lower side panel first that follows the hull contours and takes its shape from the topside panel. The stringers will be extended and the existing transom returned but trimmed down to fit the slightly narrower stern created by the slight curve as the hull panels extend back. The hull bottom will then be then cut to fit into this - ensuring I keep everything straight and avoid any hook or rocker, I feel like it should turn out OK!!

    I am planning to add between one and two frames (depending on what final length I decide on). I am also going to add a skeg - as the boat is quite hard to steer at slow speeds and in wind. I will butt join the panel overlaps and have a frame right above this. I will also extend the lifting strakes across the joint. I will keep the lamination schedule the same.

    All the gaps between stringers and frames will be foam filled for added stiffness (and safety reasons).

    I guess the all important question is to all of you who are wiser and more experienced at this than I am .... how many feet should I add on?!!

    Here are some pics of a temporary mock up I made out of plywood... 2 feet and 3 feet shown...

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    [​IMG]

    Part of me feels that adding 4 feet will get me closer to what I want to achieve - but I am worried that at a certain point, I am pushing my luck with the strength of the hull and the scantlings would need to be increased.

    Any thoughts and comments most deeply appreciated!!
     

    Attached Files:

  2. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    The scantling question can't be answered without a lot more info. You need to show us the starting point structurally, and you need to provide a sketch showing where the center console and other furnishings will end up. You also need to include everything you plan on adding to, or removing from, the old version.

    What did the old boat weigh leaving the dock for a day trip?

    What is the actual motor on your boat, and what was the motor rating of the boat you built (looks like 90/150, but the plans in the link might not be what you built to)?

    Do you plan on changing the motor, or buying longer control cables, or moving the helm to keep all the old controls?

    What was the top speed you could run, and what is the design top speed with the largest rated motor?

    Is there any fiddling with the fuel tank or battery location with the, erm, renovation?

    What was the transom deadrise angle, and what was the deadrise angle 4' in front of the transom? Plans say 12 degrees. Is that at the transom?

    Personally, I don't think there are any insurmountable problems here if you are satisfied with the old powerplant. One feature found in many of the Bluejackets is the tucked-in motor mount. There are a lot of good reasons to do this on your boat. The only reason not to would be if you operate long periods in extreme shallows and need to notch the bottom to reduce draft. Since you mention adding a skeg, I'm guessing this isn't the case. I'd hold off on the skeg until the hull is back in the water and trialed.
     
  3. johnnythefish
    Joined: May 2016
    Posts: 36
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: E.A.

    johnnythefish Junior Member

    Ok - I never weighed it - but I believe the designer said it looked "heavy" the way she sat in the water. He estimated 3000 lbs with everything from a photo. I can believe it if the amount of epoxy was anything to go by!

    The top photo is how she sat ready for a full day on the water.

    Structurally, I had I raised the sole 4omm - by adding this about to all 4 stringers and the frames. She has a 12 degree deadrise at the transom and is a constant deadrise for at least the rear 8 feet.

    The boat has been totally gutted - I am planning to do the extension and then bolt on the 150 HP yamaha 4 stroke which I now own - and then launch the boat.

    I will then move the console, expected fuel loads etc around until she sits right. I am not constrained by this at the moment. So weight and balance shouldn't be an issue. Clean slate to work with regarding controls, console placement, internal lay out etc.

    I previously had a 90 HP FICHT Ram that was perfectly adequate and we did 27 kts top speed with that engine and 2 on board and full fuel. Part of my initial desire to extend was that I felt the new engine would make the boat very stern heavy in addition to the amount of time we all spend at the back of the boat whilst fishing.

    I believe that the boat can take speeds up to 45 mph or so - but to be honest I have no desire to get anywhere near this. When I go fishing I have found about 20 kts to be the upper limit for cruising on most days, and often it is more like 17 kts if the wind picks up. I am not a speed freak and I believe she is a little shallow V-eed to be comfortable at speed in serious waves.

    So strength wise ... the frames and stringers are 40 mm taller than spec and I have glassed them with 4oo gsm bias both sides in addition to the lamination schedule which was 2 layers of 6 inch tape each side.

    It will be foam filled - this is optional - but I believe this adds much rigidity and safety.

    My cleats are 2"x2" cut diagonally instead of 1x1 square.

    It has 4 strakes - which are again optional.

    The console is attached to the seat by a box that is 8 inches tall - ie the captain has to step up on this... the whole think is about 6 feet long... again I think it probably adds quite a bit of stiffness.

    I have attached a few pictures that may help...

    [​IMG] [​IMG] [​IMG]
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Two issues involved here, the structural, which johnny seems to be across, and the hydrodynamic, which probably isn't going to see any drastic issues, although if the boat is inclined to be wet, might get wetter. You might get a small improvement in ride, in some conditions, and I don't expect you will get much improvement with the fast trolling, you are still in the zone where resistance is high.
     

  5. johnnythefish
    Joined: May 2016
    Posts: 36
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: E.A.

    johnnythefish Junior Member

    OK - so no glaringly obvious structural issues?! Boat was never wet so not worried there. At the very least if I get more space out of this I will be happy; I have a feeling it will ride a little better and I am hoping it will be lighter for its size - which in itself will improve relative efficiency - but not expecting miracles...

    lets see what happens!
     
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