22' rowing shell design

Discussion in 'Boat Design' started by sfranklin, Dec 12, 2011.

  1. sfranklin
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    sfranklin Junior Member

    I'm looking for a rowing shell design file [.dxf or AutoCAD would work] for a hull which is about 22' LOA and 20" beam. This shell will use drop-in sliding rigger. Thanks for any designs or links you can provide.
     
  2. upchurchmr
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    upchurchmr Senior Member

    clcboats.com has a shell, I don't remember the exact length, I think it is 24" wide.

    Have you looked at the woodenboat.com in the plans for the Kingfisher, possibly one other one also.

    I've seen others in the forums, but don't remember the specifics. have you searched this forum, and the woodenboat.com forum?

    If you are willing to do some design modification yourself one of the longer, narrower kayaks could be modified to meet your needs. Basically the limit I have seen is about 20' and 21 or 22" beam at guilemot.com or clcboats.com. I don't think pygmyboats has something that long. Nick Schade at guilemot.com has a book that suggests some of his kayaks can be streatched by just making a bigger space between each station.

    I don't think these guys provide computer files. Paper is what I got at laughingloon.com for a North Star - 18' 4".

    Marc
     
  3. sfranklin
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    sfranklin Junior Member

    Thanks, Marc — Sorry for the delay, but I am trying to navigate this site. Appreciate your info. I have seen the Kingfisher which looks very similar to what I have in mind.

    Also checked out laughingloon - nice boats and plans. Rob Macks has skills and the willingness to share.

    Did you get full size hull station patterns to use? How easy was it?
     
  4. upchurchmr
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    upchurchmr Senior Member

    Sfranklin,

    I did get full size hull station patterns. One thing I didn't realize when I bought the plans - there were multiple stations overlayed in the same sheet. Since I wanted to cut out a full pattern for each station I had to make 3 copies per sheet. A relatively small price compared to the overall project, but a surprise (I kept the original sheets intact, in case I had a problem). One problem with Rob's plans was that there was no waterline for each section. This made it hard to rig the sections vertically. A friend is making another designers boat which has waterlines drawn, he lined up his frames quick and relatively easy.

    Another issue for me was that the frames were at ~22" spacing, the strips were suppose to be 3/16" thick. This made it easy to build in non fair lines - I had to fix two places and accepted others that were close. I asked for 12" spacing section cuts and was unable to get them. Next time I will take the lines, put them into a 3D drafting system (computer) and cut my own sections. Office Depot where I had the copies made can take files from a memory stick. The thin strips and wide spacing caused no end of problems for me, possibly since this was my first build for strip planking.

    The North Star design also had a very difficult bow and stern, I'll never do that again.

    The plans were less than helpfull for some issues in spite of the very thick set of directions. They also jumped around and were not clear on what should be done next. Again, a problem for a first time build.

    Several things were dead on for suggestions. The need to get every strip clamped accurately in place before gluing (every strip needs to match the adjacent height) and the use of a heat gun to make the strips fit without pressure works great if you spend the time to learn.

    One useful lesson learned was the use of a hand scraper to level the inside of the boat (another designer). One thing not to forget is making sure the width at the shear of the hull needs to match the width of the deck before glassing the inside - that was a bad mistake on my part.

    The last sugestion for any strip panked boat is to cut all the strips to thickness at the same time. Make lots of extra. If you don't and need more, make them slightly thicker, fit them in so the inside surface is flush. The inside is much more difficult to smooth than the outside.

    I used staples, not hot glue to position the strips while gluing, I recommend staples at every strip, every station. I had some bumps from trying to use less staples. I did try hot glue but it let go within a day if I had to delay the next strip.

    Way more than you asked, but I can't help hoping you will have less trouble what ever you build.

    Have fun,

    Marc
     
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  5. sfranklin
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    sfranklin Junior Member

    That's a lot of info, Marc -

    It's always interesting to see how plans are executed by those of us who are not full-time boatbuilders. There is usually some adjustment for people who work with 1] limited space 2] limited tools/equipment 3] limited personnel i.e. yourself.

    Your comment about having the sections in 22" centers did seem quite odd - I've seen hull sections for large boats [over 40'] which are on 24" centers. But I would expect that on these smaller boats, one would definitely want
    12" centers to define the rapidly-changing hull shape accurately.

    As you mentioned, you could bring these into a CAD program and make some intermediate stations, but these might not be accurate. Unless you had some kind of algorithm for amidships-to-stern and amidships-to-bow, the interpolation might be only a rough 50% approximation between the adjacent stations. I would be concerned about this approach without first creating these additional sections and viewing them in a 3D model or at least creating a scale model.

    It seems that unless you're building a guide boat or a canoe, the distance from bow to max beam is usually greater than distance from max beam to stern, but that's just my limited observation.

    I didn't quite understand your comment about needing the waterline markings for the sections. Never having built a boat, I need to learn how this figures into the build sequence. I'd planned on building hull sections out of plywood to be spaced at 12" centers, on a 4" x 4" full length beam.

    Had seen that technique used for an 18' Herreshoff-style dory. There was a preliminary photo which showed all sections in place on the backbone; scrap strips were tacked on temporarily to give a visual of the hull. Looked kind of like my 'wire frame' CAD drawings.

    Here's a few questions:

    You advice about cutting plenty of strips makes sense; were you able to start from well-planed planks, then rip to 3/16" strips? Did you use a shaper for bead & cove? What width strips would you recommend for a 20' boat? Do you use any kind of cedar, or is there another type of wood which wouldn't be extremely expensive? Do you place the staples just shy of being flush so you can pull them later? Do you leave the ribs in afterward?

    My workspace and tools are limited, but I have use of a nice 44" x 64" plotter, so I can render any design imaginable. I guess that hull sections [for most shallow hull designs] up to a 60" beam could be drawn at 100%. Beyond that, I could tile the drawing and render the parts at 100% with register marks for mating the pieces together. This CAD program is nice because it allows you to turn the image in 3D space to view different aspects of the design. But it's not as robust as SolidWorks.

    If you have a design you're working on and need to have a CAD file rendered, let me know, perhaps I could provide line drawings of the sections at 100%.
     
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  6. messabout
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    messabout Senior Member

    If you are going to do a strip built boat, then get Ted Moores book; Canoecraft. It is a gold mine of information and hints that will help keep you out of the moaning chair. Also The Geougeon Brothers on Boat Building is a valuable reference. They describe strip building in one of the sections. They have many suggestions such as using a piece of popsicle stick under the staple. That makes the staple easy to extract and assures that you do not damage the wood fibers. Simple suggestions like that are well worth the price of the books.

    Most of the experienced strip builders specify elmers yellow glue or the original titebond but not titebond II. Either of these can be dispensed easily and accurately by using a syringe. The syringe helps you judge whether or not you are using too much or not enough glue on a strip of known length.

    The biggest hassel of a stripper is ripping all those damned strips and then having to rout them for the cove and bead edges. You can spend many hours and make a mountain of sawdust when preparing strips. In the end, if you ever get to the end, you have a marvelous structure that is worthy of all the work that you have lavished.
     
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  7. upchurchmr
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    upchurchmr Senior Member

    sfranklin,

    About the Cad system, I work in aerospace and we use Catia. I would be able to bring in the sections and the ends and then recreate the surface intended by the design. That way I would have a complete 3D surface which could be cut anywhere I want to make new sections. Thanks for the offer, with a little bit of relearning I can do it myself. I have been out of directly doing the design for several years.

    When we do an aircraft design everything is related to a waterline. That is one reference that stays constant. When you are trying to locate the sections on your 4 x 4 beam (I used a 2 x 4 per Nick Schade's book) the accurately located waterline for each individual section allows you locate everything in height. Rob Macks used a straight line which was located off the actual boat forms then you measured to the peak of the deck. This introduces an additional measurement to get right, which in my case caused me a lot of innacuracy.

    "I didn't quite understand your comment about needing the waterline markings for the sections. Never having built a boat, I need to learn how this figures into the build sequence. I'd planned on building hull sections out of plywood to be spaced at 12" centers, on a 4" x 4" full length beam." Somehow you have to place the sections vertically so they are all in the same relationship as the designer wanted. Neither the top centerline, the bottom centerline or the shear line was straight in my case.

    I would not try to change the geometry of the hull from the designer, so I did not worry about where the max beam was, I just matched Macks plans. Different boats have it fwd, aft, or right in the middle.

    Well planed planks.... Well my planer was busted at the time. So I cut oversized thickness, full width of the boards (Home Depot the best I could find, mostly 8'). Then I cut the width 3/4". Then I used finger boards to cut to the final thickness. This was the result of several mistakes and turned out to be the way for me to get uniform strips.

    I used square edge strips (no cove and bead) and hand planed to get the rolling bevel. Just throw away anything you get wrong and do it again. I have a setup for cove and bead and did it on a couple of catamaran row boats, but I found the square edges to be easier overall.

    My cedar was hand picked at Lowes and Home depot, butt joined on the mold to get the 18' lengths necessary. I also used Poplar to get as white as I could to make a specific pattern. The cedar was choosen to be as dark as possible which was hard to find, and probably very excessive. The cedar gets relatively dark with epoxy unless you find the very blond stuff. I also considered basswood which was cheap, very even grained, available in long large clear timbers, but has virtually no grain for visual interest - it is also relatively light. In the middle of my build I was given a log of cottonwood, which was very light, not available commercially usually and has a twisted grain I am not sure you could use. If I had a lot of money I would use Mahogany, but it would make a relatively heavy boat. It looks beautiful in a hull under glass and epoxy.

    I followed several suggestions to staple thru a piece of plastic to help remove the staples, you still need to be carefull in cedar, it dents easily. Popular is much tougher and will swell back out if you wet it, even staple holes essentially dissapear. Not so with Cedar - but I don't really care.

    My kayak sections are 21 x 13 maximum so your plotter will work easily with a similar boat. I would suggest NC cut sections, it is well worth the cost if your designer offers them, especially for a first build.

    I certainly agree with Ted Moore, the Gougeons, and particularly Nick Shades book. Each book has some points well worth knowing, but there are a thousand ways to succeed.

    Messabout is right about the hassle of the strips, but check out buying them and you will make your own unless you own Fort Knox. This is one reason I suggest cutting everything at once with everything going thru the same setup in the same sequence. For me it was mindless, repetative but required good attention, fingerboards, a respirator (cedar affects me badly, but poplar does not), and hearing protection.

    Well I guess my friends are right, I like to hear myself talk. I probably should have written my own book.

    One thing I suggest is to make a "nose" or the first 4 feet of a boat (any boat) to get some first hand understanding before you mess up the actual boat. Actually I did two, and planked each side differently to see the pattern I wanted. Still made lots of mistakes - just not as bad.

    Good luck

    Marc
     
  8. sfranklin
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    sfranklin Junior Member

    Ok, Marc, you've given me a lot to think about and study - appreciate all the references.

    One thing that will take some understanding is the waterline. I know that each section has a vertical reference to all the others which should not change. I guess that the waterline would still be a reference whether it was rendered on an empty boat or one that was overloaded.

    What I remember from study generally, is how a volume of water needs to be displaced so flotation can occur - to pinpoint that in a construction plan is my mystery.

    Looking at many of Chapelle's well-detailed hull plans is a great learning opportunity, so the LWL and other measurements are fairly clear.

    Would like to check Catia, although it's probably out of my range. No doubt it's the 800 pound gorilla of multi-faceted 3D design. I've been able to get a demo version of SolidWorks, but a fully functioning seat is pretty expensive. The exception is to get a 'student' license which I can obtain by taking a CAD course at the local community college.

    Using ArtiosCAD [packaging software] I created what could only be considered a scratchpad demo of hull sections. I'm working with flat planes, so it's impossible to create curves required for the hull. All I've been able to do is arrange the hull sections into the correct hull shape.

    That was achieved by using a flat plane for the deck as the long./hor. reference point, then attaching the hull sections to it. I output a .dxf of the hull sections, then a 3D .pdf of the assembled boat. For this 2D app, 3D is at the edge of its capability, so I really need something to start out in 3D. However, station shape geometry is quite simple to modify and plot.

    SHELL 22ver7sections.dxf
    SHELL 22VER7SECTIONS.pdf


    When you open the .pdf, click on the ball/arrows [rotate] icon at the left side of the toolbar. Then click anywhere in the workspace to rotate the image.

    Thanks again for your insights - once I get the design right, the rendering in wood will be without too many hiccups. Now I'll have to find some good cedar and get ready for the build.

    -Steve
     

    Attached Files:

  9. upchurchmr
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    upchurchmr Senior Member

    Steve,

    I'll have to figure out how to look at the dxf files at home.

    DWL or waterline is just a reference that the designer "thought" would end up being where the boat floats. He had some exact boat weight and paddler weight, probably with nothing else in the boat.

    The boat will actually float somewhere else but you dont really care.

    For buiding it is just a way to get each section positioned vertically, so they are all the same relative to each other.

    Since the deck is flat (I think) that is all you need. Since the sides are almost flat you might think about making this hull from plywood. Jim Brown (noted multihull designer) originally used plywood using 4 flat surfaces for the outerhulls. At each edge joint he would put a fillet of Epoxy between the two inside surfaces. Then fiberglassed the inside. This sets the joint and the hull shape. He then ground away the outside of the two boards until he got a nice curve. Fiberglass this and you have a similar shape to your bottom to side rounding in the .pdf. This might be very quick/ simple to get substantially the same shape you showed. 1/4" ply would probably be heavier than you need.

    As I see it the bottom is also flat across. I tried to look at the Kingfisher plans, they don't show a section cut, but call it a V-bottomed boat. The Oxford shell from clcboats.com is also v-bottomed. Personally I would probably stick with something that has been shown to work.

    Marc
     
  10. upchurchmr
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    upchurchmr Senior Member

    Steve,

    I think you should consider another option. Lood at the Great Auk at clcboats.com designed by Nick Shade. Shade's book on strip planking states that he has stretched and compressed that particular design from 20' to 14'. The point is that it is a very smooth shape that is not degraded by stretching the boat.

    You could buy the 17' plans (24" wide) respace the stations to get 20 or 22', change the cockpit opening and you have a good, slick round bottomed boat. You might want to install a floor to get the seat height right and make the cockpit self bailing.

    I believe the Oxford Shell is essentially done this way.

    Actually this suggestion is just because I personally like rounded boats rather than plywood.

    Marc
     
  11. sfranklin
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    sfranklin Junior Member

    Marc —

    Appreciate the additional info; yes, the Great Auk has many similarities to shells, in terms of minimized wetted surface and beam width. Although I can appreciate the geometry involved in creating a hull from 4 plywood pieces, my preference is also strip construction. No concessions need to be made for chines if you don't want them.

    I agree with taking a set of plans and stretching them to the desired LOA, rather than reinventing a new untried hull design. Topsides, the Great Auk could easily be modified by
    swapping the traditional cockpit rotunda for the elongated box to accept the rowing rig.

    That being said, it appears that shells generally tend to have more defined chines than kayaks, owing to their primary use for speed and straight-line travel. I'm still reviewing a lot of hull designs to find the best composite of stability and minimized turbulence for inland rowing.

    After seeing some great craftsmanship on strip built canoes and kayaks by a local builder, it still looks to be measurably easier for the novice builder [me] with the visual appeal which is unobtainable with plywood.

    Thanks,

    Steve
     
  12. upchurchmr
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    upchurchmr Senior Member

    Steve,

    I looked at shells before deciding to make a catamaran row boat (the wife wanted stability) and all of the racing ones had no chines, in fact they were so smooth it was hard to really see just what the shape was.

    Let us see what you decide.

    Another left field idea. have you seen the latest Triak design? Going to a monohull with outrigger design gives you the minimum wetted surface area, even more skinny than most of the pure racing sculls. I calculated that an 18' single hull with a round bottom required about 8" width to float on its lines for my 240# body. I believe this would be significantly less wetted surface area, especially if you can balance the boat with the outriggers out of the water.

    My latest fantasy on how to build a really light hull would be to strip plank to the waterline then use skin on frame construction above the waterline. That way all the flow except for waves would be really smooth, the lower weight would fractionally reduce the total wetted surface.

    Our 11' hulls with a 6" beam leave virtually no wake, I have to believe there is no real wave making issues with that length to beam ratio.

    But it wouldn't be a classic shape and would not be proven.

    Good luck

    Marc
     
  13. kfriedman
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    kfriedman Junior Member

    Hello,

    For what its worth, I was looking for plans for a strip build rowing shell too and in the end, just made some.

    About 2 months ago I was given a chance to do some repair work on an old plywood shell and decided that it would be fun to build something similar. While testing the boat up at the local pond, got a chance to see up close and personal the CLC Oxford shell - definitely way to heavy and bulky for what I wanted to build.

    Started playing around with Kayak Foundry from Ross Leidy's Blue Heron site (check this out as it not only calculates a lot of interesting metrics, it also creates the templates for the station forms you will need) - designed 5 sculls until I got close to what I was looking for. My goal was a boat that my daughter could use (she's getting into rowing) and that would fit in my garage to build.

    The design I went with is 25' by 11.6" beam with a planned displacement of 180lbs (assumed boat would weigh 40lbs and rower 140lbs - this was pretty nerve-racking to come up with as who knows what the boat will really weigh and I think my daughter has stopped growing, but..) Water line is 24' 8.5" by 10.8" - this is similar to the measurements on the Pocock racing shell.

    Along the way I found an old post on the guillemot kayak forum from a guy in Australia who had built a strip version of Graham King's Kingfisher - he has some photos out on the web: http://pics.livejournal.com/bruce_moffatt/gallery/00007tqg, that pushed me away from a canvas deck to a hardshell - his email to me indicated that his boat came in at 19Kg with rigging which made me very happy as that's in the ballpark of what I was assuming/guessing. His boat is made with 3mm cedar blinds that he ripped down with a light coat of fiberglass on both sides. This is basically what I plan to do as well.

    If you're interested in the design file I'm using, you can find it on the kayak foundry forum (http://www.blueheronkayaks.com/kayak/index.html) - do a search for rowing shell. My build has the stations at 14" (because I was too lazy to put them at 12" which I now regret because it's easier to find the 1/2 way point in feet...) I'm using 1/8" cedar strips and have 1.6oz cloth for the deck and 2oz cloth for the hull coming. Haven't completely figure out how I'm going to build out the cockpit area yet (it will be a raised area for the seat/tracks with a foot area lower in the boat) but will cross that bridge when I get there. Also have know idea how I'm going to deal with the riggers yet.

    This link will take you to pictures of the build: https://picasaweb.google.com/kfriedmn/Scull6

    As of today I've stripped to the first hard decision point - should I put a strip straight down the middle from the stern, or two strips...

    Look forward to seeing what you end up with.

    Ken
     
  14. upchurchmr
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    upchurchmr Senior Member

    Ken,

    Thanks for the post, at least it will keep Steve from believing my bouyancy calculation for a single hull. I obviously made a significant mistake. Probably it was for 2 hulls, since I had been making a kayak.

    Really nice looking project, I had not seen a shell with a hollow in the bow. The Pocock I saw did not have one. Did you have a rationale you could share?

    Marc
     

  15. kfriedman
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    kfriedman Junior Member

    Marc,

    Just got in from putting two more pieces on the boat. Decided to head from the bow downward with two strips and then start from the stern with 2 strips straight down the middle- probably tomorrow or the next day I will bring the stern and bow back together.

    Not sure what you mean by a hollow? The Kayak Foundry software is really just for kayaks, but I figured that I could use it to get the basic hull work done and then would sort of wing it for the deck. For stripping purposes, I ran the first strips right up to the edge of the form (in most cases where the shear line was) - this fixed the slight inconsistency along the shear.

    My deck plans look something like what can be found out at www.carldouglas.co.uk/images/custom1x_big.jpg. In front of the feet will be a bulkhead forward and the seat will be supported by some type of bulkhead/structure (it will be closed in the footwell area. In order to get to the nuts holding the runners down, I will probably do something like the carl douglas boat and put some type of hatch in.

    I have off till Tuesday so I might get close to done with the hull stripping.

    Ken
     
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