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Thread: Catspaw for first build

  1. #1
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    Default Catspaw for first build

    Hello,
    I just started a project I've planned for many years, building a Catspaw dinghy, and I want to briefly introduce myself before I humbly ask for some help. I just turned 60 (so I'm still young enough I hope!) and have been working with wood my entire life, just not curved pieces. I live in the foothills of Virginia, an I have a small cabinet shop which is big enough to build this boat in. I have read and have copies of Greg Rossel's Building Small Boats, Robert Steward's Boat Building Manual, and David McIntosh's How to Build a Wooden Boat, and I have just received Larry Pardey's Classic Boat Construction.

    I have lofted the lines twice now and feel better about what's now drawn, but I'm still a bit unsure of the ends of buttocks lines going from station 8 into the transom (in profile view). They turn considerably more sharp there, but they look fair as far as a longer arc transitioning to a smaller one, though. So my question is, What does this mean as far as building the boat? Will it be difficult to bend the planking in that area? Or is this just another bend in the whole process? I'm anxious to get started, but I also know it's important to get this part right. Or am I overthinking this?

    Also while we are in that area, station 8 intersects part of the transom. I assume I don't need a mold for station 8 then, right?

    Yes, I know, real basic stuff for most of you.

    Thanks in advance, Uwe

  2. #2
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    Default Re: Catspaw for first build

    Looking at the lines plan in WBv26 I don't see a radical bend in the buttocks except the outside buttock that comes to the sheer short of the transom. In any case, the planks do not follow the buttock lines so there is little correspondence between the buttock lines and plank installation. For that, the diagonals tell you more, indeed they govern the lofted shape. You do need the buttock and waterlines to establish the true inside and outside shape of the transom, giving the transom bevels, and the stem rabbet bevels.
    Building the boat for that article it looks like they did not use a mold at st8.
    Last edited by Thad; 05-22-2020 at 03:47 PM.

  3. #3
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    Default Re: Catspaw for first build

    Thanks for the response Thad.

    The lines do look like the drawings, and the transom expansion looks right, so I'll start building.

    What glue would be good for the stem joints? Resorcinol seems recommended a lot in some of my books, but they were printed a while ago. Are there other products that others have experience with? I'll be using white oak.

    I can get Douglas Fir C + better grade from the local lumberyard. Does anyone have thoughts on using this as planking? Some will be sliced and some will be quartersawn as you would assume. I could try to pick through it, or is it that critical on this project?

    I live in Virginia, can anyone recommend a source and a more suitable material?

    Thanks, Uwe

  4. #4
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    Default Re: Catspaw for first build

    I'd talk to John England in Urbanna about cedar for planking. For the backbone joints I'd not think to glue but be sure to install stopwaters at the joints connecting the caulking from side to side.

  5. #5
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    Default Re: Catspaw for first build

    Don't use that fir from your local lumberyard if it is kiln dried. Commercially kiln dried lumber is typically too dry for traditional planking. Douglas Fir was used extensively here in the Pacific Northwest for planking medium and large sized vessels. Different varieties of cedars are used almost exclusively, west or east coast, for planking dinghys and other small craft. Fir is relatively stiff and brittle compared to the cedars. That makes it less compliant for the twists and bends planking a small boat, where steam and moisture are also very important.

  6. #6
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    Default Re: Catspaw for first build

    carvel or lapstrake?

  7. #7
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    Default Re: Catspaw for first build

    Catspaw is carvel.

  8. #8
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    Default Re: Catspaw for first build

    Yes, it will be carvel planked.

    As per Thad's suggestion I contacted John England, and he has some Atlantic White Cedar available that I plan to use.

    I appreciate the input, Eric. As you can see I found the material you suggested. I already bought a few kiln dried boards, so I'll just steam those for experimentational purposes. It never hurts to learn first hand!

    I was reading on the internet that someone was using adhesive on the joints for carvel planking. I have not heard of this before. It seems the wood would need to move somewhat, even though it's a small boat. Any thoughts on this? BTW, this boat will not in the water full time.

    Also, Thad, are you saying to not use any adhesive on the back bone joints? Yes, I would use stopwaters, but could a bit of 5200 or some other adhesive negatively affect the joint? Again, I'm not new to wood working, but I'm new to boat building. So to me any additional strength or a sealer seems like a bonus. Please explain.

    Thanks, Uwe

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    Default Re: Catspaw for first build

    Thanks - that would be my assumption. Although I thought occasionally builders went lapstrake. Incidentally, is it exactly the same design as the Columbia tender?
    Every couple of seasons a catspaw comes in to the shop for some TLC. Built by the clients father, not a bad job, kind of a nice story. The owner finds a berth for it on the lake in the summer which reduces the soaking up headache.
    Come to think of it, I probably have the catspaw publication.
    E

  10. #10
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    Default Re: Catspaw for first build

    Quote Originally Posted by urumohr View Post
    Yes, it will be carvel planked.

    As per Thad's suggestion I contacted John England, and he has some Atlantic White Cedar available that I plan to use.

    I appreciate the input, Eric. As you can see I found the material you suggested. I already bought a few kiln dried boards, so I'll just steam those for experimentational purposes. It never hurts to learn first hand!

    I was reading on the internet that someone was using adhesive on the joints for carvel planking. I have not heard of this before. It seems the wood would need to move somewhat, even though it's a small boat. Any thoughts on this? BTW, this boat will not in the water full time.

    Also, Thad, are you saying to not use any adhesive on the back bone joints? Yes, I would use stopwaters, but could a bit of 5200 or some other adhesive negatively affect the joint? Again, I'm not new to wood working, but I'm new to boat building. So to me any additional strength or a sealer seems like a bonus. Please explain.

    Thanks, Uwe
    To be honest, I stay away from oak except for steam bent ribs and sometimes rubrails. I find that it is not a particularly stable wood, obviously most especially flat sawn (and not particularly varnish friendly). In a boat the size of a catspaw, with wood that I feel is dimensionally stable and glues well, I will bond some backbone parts with epoxy, other parts with Boatlife.

    Epoxy and Oak not so much. I remember trying to deal with straight up tradiitonal whitehall, oak backbone. I did not build it. Neither I, nor anyone else could make it stop leaking and weeping. I don't know exactly what the problem was, but it was another thing that put me off oak.

    But seeing as you have oak - yes stopwaters. Seal the living daylight out of the faying surfaces, in fact all surfaces. You could use an oil based traditional bedding compound in the joint, dolfinite or Interlux boatyard bedding compound. Problem with that stuff is that it tends to go on and on bleeding. Over a very long period of time it will dry out. I would NOT use 5200. But I might use boatlife, or one of the sikas.

    Very happy you have a line on cedar.

    edit to add - quick answer is no you are not using adhesive in carvel plank seams.
    Last edited by Eric Hvalsoe; 05-23-2020 at 09:20 PM.

  11. #11
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    Default Re: Catspaw for first build

    From what I know it's the same design as the Columbia tender except an additional 10% increase in size. The first bit of literature on it I received was entitled "How to build the Catspaw Dinghy" by Joel White from WoodenBoat Books. Greg Rossel's "Building Small Boats" refers to it throughout his book.

    What is the "soaking up headache" you are referring to?

  12. #12
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    Default Re: Catspaw for first build

    It's a carvel hull - depending on your skill, quality of materials, and how you use the boat, quite likely there will be times it needs to soak up to become watertight.
    But you already knew that - right...?

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    Default Re: Catspaw for first build

    WoodenBoat also sold paper patterns of molds, stem and transom, in the past, and maybe they still do. It would save you time, doubts and you could start almost immediately with the fun. The boat has been built so often that it might be possible these molds and patterns are still around to pass on to a new builder. Frank
    www.oarandsail.nl

  14. #14
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    Default Re: Catspaw for first build

    In this case it is not a kit (far as I know). Patterns mean squat without the loft. Working from someone else's loft is a mistake. That generates all kinds of doubts.

  15. #15
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    Default Re: Catspaw for first build

    Uwe - I'm finishing up my Columbia model dinghy, which is what the Catspaw was derived from. It's my first build as well. I'd echo nearly everything Eric said in post #10.

    - Goop, not glue, in the backbone joints. I used Boatlife Lifecaulk, but if I were to do it again I would seal the wood with shellac then bed the joint in Dolfinite. I switched part way through my build because I don't like waiting for Boatlife to cure.
    - I've had mixed experiences with white oak. I laminated a white oak stem and stem cap using GFlex and had no issues. Steam bent ribs were no issues either, not a single broken one. But bending the keel from unseasoned white oak and getting it not to bow out as it dried was a horror story. Make sure you have plenty of bracing and clamps to set and keep it to the correct shape.
    - You may already know this, but I'll share because you mentioned concern about sharp bends in the ends of some lines. When you're lofting any line, do NOT adjust the batten beyond the ends of the line. How do I know? I put a nail in after the transom to make my apex line fair, but it actually produced too sharp a curve (even though it was a fair line). I should have made the batten fair by adjusting a point at station 7 or 6, not by creating an imaginary point extending past the end of the boat.

  16. #16
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    Default Re: Catspaw for first build

    I often divide the tee shaped keel structure into two parts. The top of the T might be called the apron, the bottom of the T the keel. Avoids the somewhat arduous talk of chopping the rabbit out of a larger timber - and having to find an appropriate larger timber in the first place. The middle line separates the constituent parts on the loft. After getting out the two parts you are able to easily bevel them separately, the rabbet is formed when the apron and keel come together on the set up. In my case usually screwed and glued.

  17. #17
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    Default Re: Catspaw for first build

    Eric Hvalsoe wrote: It's a carvel hull - depending on your skill, quality of materials, and how you use the boat, quite likely there will be times it needs to soak up to become watertight.
    But you already knew that - right...?



    I get the fact that wood swells when it gets wet, but am curious how this pertains to the various joints on a wooden boat.

    So for planking, when a I/2" cedar planks touches another plank for a 1/4" or less (leaving a slight bevel for cotton), does the cotton keep moisture there to help the wood stay swollen? Or does the cotton need another product on top of it to complete the Joint?

    And for the planking attaches to the back bone, that's just a tight fit with no adhesive or sealant, right? So, the two woods (white oak and cedar) just needs to swell to keep water out?

    And for assembling the backbone, one generally uses no adhesive, dolfinite or some kind of sealant maybe, and of course stopwaters, correct? You said to seal the living daylight out of the white oak backbone faying surfaces in particular. This would make the wood at the joint not be able to swell, which is confusing to me. Wouldn't one want the wood to swell (which the wood won't be able to if sealed) to make a tighter joint when wet?

    Again, I not new to working with wood, but I am new to boat building, so I apologize for these basic questions. I want to be clear on this type of info before I get too far into this project.

    Thanks, Uwe

  18. #18
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    Default Re: Catspaw for first build

    Quote Originally Posted by FF View Post
    WoodenBoat also sold paper patterns of molds, stem and transom, in the past, and maybe they still do. It would save you time, doubts and you could start almost immediately with the fun. The boat has been built so often that it might be possible these molds and patterns are still around to pass on to a new builder. Frank
    www.oarandsail.nl
    Thanks for the suggestion, but I don't want to miss out on any of whole boatbuilding experience, lofting included.

    And also, as Eric said, I may be building to mistake made by others. Of course I can make them myself too!

  19. #19
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    Default Re: Catspaw for first build

    For me, finding the timber is part of the fun, as is cutting rabbets. I like well fit faying surfaces bolted together around stopwater locations, with the joint dry for the tightest fit possible and knowing that the different parts will swell on their own. (There is (virtually) no coating that will keep water from passing through.) I like coating all parts with raw linseed oil, which is absorbed.

  20. #20
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    Default Re: Catspaw for first build

    Quote Originally Posted by ptscho View Post
    Uwe - I'm finishing up my Columbia model dinghy, which is what the Catspaw was derived from. It's my first build as well. I'd echo nearly everything Eric said in post #10.

    - Goop, not glue, in the backbone joints. I used Boatlife Lifecaulk, but if I were to do it again I would seal the wood with shellac then bed the joint in Dolfinite. I switched part way through my build because I don't like waiting for Boatlife to cure.
    - I've had mixed experiences with white oak. I laminated a white oak stem and stem cap using GFlex and had no issues. Steam bent ribs were no issues either, not a single broken one. But bending the keel from unseasoned white oak and getting it not to bow out as it dried was a horror story. Make sure you have plenty of bracing and clamps to set and keep it to the correct shape.
    - You may already know this, but I'll share because you mentioned concern about sharp bends in the ends of some lines. When you're lofting any line, do NOT adjust the batten beyond the ends of the line. How do I know? I put a nail in after the transom to make my apex line fair, but it actually produced too sharp a curve (even though it was a fair line). I should have made the batten fair by adjusting a point at station 7 or 6, not by creating an imaginary point extending past the end of the boat.
    ptscho,

    I remember station 8 being very close to the transom, and in order to get to the other stations it required a bit sharper of a curve. It still looked fair, so I plan to go with it. There won't be a mold at station 8 and that helped me to decide. Is this what you are talking about and does this sound familiar?

    Thanks for the bit on the goop. if I understand correctly there needs to be some movement here. Is that why one doesn't use glue?

    Uwe

  21. #21
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    Default Re: Catspaw for first build

    Quote Originally Posted by Eric Hvalsoe View Post
    I often divide the tee shaped keel structure into two parts. The top of the T might be called the apron, the bottom of the T the keel. Avoids the somewhat arduous talk of chopping the rabbit out of a larger timber - and having to find an appropriate larger timber in the first place. The middle line separates the constituent parts on the loft. After getting out the two parts you are able to easily bevel them separately, the rabbet is formed when the apron and keel come together on the set up. In my case usually screwed and glued.

    Thanks for the tip on making up the keel in two pieces which makes very much sense. This a small timber, so it'll be easy enough to make it out of one piece. I can just run it through the tablesaw twice or use a router to get the rabbet started and finish it with a chisel. Beside I already have the boards.

    I'm still sorting out my plan, and unless there is something terribly wrong with using the white oak that I'm not understanding, then I plan to use it. Earlier you said it's
    not a particularly stable wood. What are some of the problems with using it?
    Is there a more suitable material found in my neck of the woods?


  22. #22
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    Default Re: Catspaw for first build

    ptscho,

    Do you have a thread or blog on your dinghy? I would be interested in seeing it.

  23. #23
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    Default Re: Catspaw for first build

    Quote Originally Posted by urumohr View Post
    ptscho,

    I remember station 8 being very close to the transom, and in order to get to the other stations it required a bit sharper of a curve. It still looked fair, so I plan to go with it. There won't be a mold at station 8 and that helped me to decide. Is this what you are talking about and does this sound familiar?

    Thanks for the bit on the goop. if I understand correctly there needs to be some movement here. Is that why one doesn't use glue?

    Uwe
    I'd agree on skipping station 8. I used it and it was unnecessary.

    If you overbend your batten on the lofting floor between stations 7 and 8 to create a fair curve, then your transom bevels might be off (assuming you cut the rolling bevel on the bench, not as you fit planks). Imagine putting a plank on the boat and running it out past the end of the transom. The plank needs to lie flat on the transom bevel. There's only two screws to hold it in place. Those screws in the edge of the transom won't be able to change the bend of the plank around the molds. They'll only hold the plank against the transom. So picture the same thing with your lofting battens — let any portion of batten extending past the end of the transom run out straight, because there's nothing past the end of the boat to fasten to that will change the bend of a plank.

    There's a better description of this somewhere else I'll the forum that I'll do my best to find and link to you here. You're probably in the clear, I just wanted to point it out in case you were running into the same issue I did since you mentioned sharp bends around the transom.

    ---

    And for glue — yes, that's my understanding. Boats are either bedded and fastened, or glued and glassed, but not both. Mixing tradition and modern construction methods leads to a lot of headaches from what I gather.

    ---

    My build is here: http://forum.woodenboat.com/showthre...t-Tender-Build
    Posts are definitely lagging behind as she's almost finished. I've been hoping to find time to update it, need to do that soon.

  24. #24
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    Default Re: Catspaw for first build

    Paul,

    I was very impressed with your build. Great job! As you can imagine there was a lot of good info there for me. Thanks.

    Your explanation on the planks running to the transom makes sense, and my lofting lines seem proper. I expanded both sides of the transom, and feel good about this all working out. We'll see.

    I have the Joel White booklet "Building the Catspaw Dinghy", and I didn't see a mold for station 8, so I assumed I wouldn't need it. But it's good to know that it's optional.

    Thad,

    Thanks for letting me know about John England. I'm going tomorrow to pick up my cedar!

    Uwe

  25. #25
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    Default Re: Catspaw for first build

    Good man, John. Hello to John and Vera from me.

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