Im building my own cedarstrip row boat,need help with info

Discussion in 'Boatbuilding' started by irish guy1888, Jan 5, 2012.

  1. irish guy1888
    Joined: Oct 2011
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    irish guy1888 New Member

    *****dont know if this is in the right section, if so can a mod move for me please******

    Ive been drawing a few sketches on graph paper the last few days and ive came up with a 12ft row boat but im stuck on a few things and dont really want to commit trying to build one untill ive all the proper info incase i make a balls of it.

    Im wanting to know can i make the cedar strips thicker than whats used on canoes just to give it that wee bit more strength. Im thinking of using teh method gill gillpatrick uses when building his canoes with having some cut outs of ply wood and bend the strips of cedar around these and join with wood glue. Ill be sealing with epoxy resin and 2 layers of strong fiberglass.

    Im only at the desgiun stage but im finding it abit difficult as i think i should be using 3d diagrams instead of 2d which im currently doing. My boat is 12ft long and 500mm high and will have a curve at the front and back of the boat but i dont know how much of a curve to put on it. When i draw my boat on paper, i have a straight line where my gun whales go , is this ok to do or will i have to have the same curve as i have on the bottom. Ill try and get a picture up of what im talking about so yous can see the plans ive drew.

    Any help would be great because ive got the itch to build something else after succesfully building a plywood canoe last year.

    Here is a sketch of what im thinking of starting soon. If anyone can point out any mistakes or if you know of any changes that i can make so i can make a better boat,it would be great if you could point them out to me.

    Is there anyone on this forum who can put my measurements into their computer and check to see if everything will work out for me and this boat will float properly. I dont have the softwear or even know where to start to figer it all out. Just curious incase someone on here can do it all in a matter of minutes for me.
  2. irish guy1888
    Joined: Oct 2011
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    irish guy1888 New Member

    Is there any reason why i cant copy and paste my pictures into this thread.
  3. Boat Design Net Moderator
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    Boat Design Net Moderator Moderator

    Welcome to the forum.
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  4. cthippo
    Joined: Sep 2010
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    Location: Bellingham WA

    cthippo Senior Member

    First off, welcome aboard!

    You can, but you don't gain anything by it except weight. Cedar strip is a composite construction method with a wood layer sandwiched between two layers of fiberglass. There is an ongoing debate on this forum about how much of the strength comes from the wood and how much from the glass, but adding greatly to the thickness of either just adds weight and cost. Despite what it seems like when you're building it, the finished boat is really strong. On my current build I used a variety of wood cut into 1/4" thick strips and while it was pretty floppy and fragile until the first layer of glass went on, the finished hull is very rigid.

    Here is a link for Freeship which is a pretty good program for boat design. I've used it to design several kayaks including the cedar strip one I'm building now.

    For what you're doing it's pretty safe to just eyeball it and if it looks right it will probably row fine. I suggest rowing as many boats as you can beg, borrow, or steal and see what features you like and which you can't stand.
  5. alan white
    Joined: Mar 2007
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    alan white Senior Member

    I believe the thicker wood can add a lot of stiffness but the question is how much stiffness is really needed or even desirable.
    Too much stiffness can cause the hull to be damaged in cases where it otherwise would have flexed (e.g., when sliding over a submerged rock).
    This is why an egg is damaged if you drop it on a hard surface but a skinned hard-boiled egg would be unharmed.
    You get something like four times the stiffness by increasing the core thickness by double.
    Strength is not just derived from stiffness but from a host of factors such as would help a boat to survive in real world conditions. Those who have gone before you know from experience that you cannot just double every material that contributes to strength. What happens is you will lose some important attributes such as light weight and maneuverability and handiness, plus economy of build and ease of storage and transport.
    your questions indicate you need to learn quite a bit about boat design. You asked about the curve of the sheer. The sheerline has absolutely nothing to do with the bottom profile. For the most part, the sheer is critical to aesthetics and also to reduce windage in the middle of the boat.
    If a sheer looks right it probably is.
    I would encourage you to continue with design but realize, your firest boat should be designed by a recognized designer. You are years away from knowing enough to confidently design your own boat. This is nothing to be ashamed of. Designing a boat properly is no different than a lot of other skills like an orthodontist requires, for example. But of course nobody would make their kid's braces, and especially not "extra strong" ones if they could copy the construction of normal braces from plans.
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Irish, let see if I have this right. You want to design your own boat, but lack the hydrodynamic understanding. This understanding isn't software related BTW. You want to develop the build scantlings, but haven't formulated up the appropriate structural considerations. And lastly, you're interested in a hybrid build method based on a preconceived but not verified need, for additional strength/stiffness.

    First off, I have to say, yes, all this is very possible. If you have the skills, experience and fortitude to follow this through, sure you can do it. Judging by your initial post, I'd have to say you have none of the skills, understanding or practical experience to make this a reasonable and successful project. This isn't meant as an insult, but just an observation (abet a frank one) to what you've admitted.

    The wisest among us, would best advise you to by a set of plans. Get them from a living, well noted designer and try to adhere to them as best as you can. Changing things in small craft, without understanding and experience, usually just leads to a boat that doesn't do what you'd hoped, most often from excessive weight or worse altered hull shapes, that kill the boat's abilities underway.

    There are hundreds of 12' row boat designs to choose from, many are strip planked. Select one you like, build to the plans and save you inventiveness for the next build, when you have a better handle on things. As to the design aspects, unless you're willing to adsorb several large texts and some serious studying, then leave this as well, for a time when you have a far greater understanding, of the physics and engineering involved.
  7. ancient kayaker
    Joined: Aug 2006
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    ancient kayaker aka Terry Haines

    Rowboat sketches from Song of the Paddle Forum -

  8. hoytedow
    Joined: Sep 2009
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    hoytedow Carbon Based Life Form

    Here are the others from Song of the Paddle Forum:

    Attached Files:

  9. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The stations as drawn are not too useful. They should have a common centerline so they are superimposed. That is the standard method.
  10. ancient kayaker
    Joined: Aug 2006
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    I think it would be simpler if you took the canoe design and just scaled it to the beam and height that you needed. I did that with one of my own design files in FreeShip. Here's the original canoe (Rushton's Wee Lassie) and the scaled up rowboat (1.14X, 1.6Y, 2Y). The stems need to be lowered a bit but it looks like a good place to start.

    Attached Files:

    1 person likes this.

  11. ancient kayaker
    Joined: Aug 2006
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    I took another look at this FreeShip file and I discovered that I can select just the points I want to lower, at the stem, using the scaling tool. This flattened the sheerline in profile in a single step. I lengthened the 12' long hull by 20% then lopped off the stern at the 12' station to create a transom which I raised above the 500 lb displacement waterline leaving a small skeg. I also reduced the width of the sheer strake slightly although the plank widths need more work.

    This is the result. It illustrates the power of FreeShip and looks like a pretty and handy little rowboat to me. I have attached the FreeShip file in case anyone wishes to scrutinize it further . . .

    Attached Files:

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