Results 1 to 24 of 24

Thread: Cosine Wherry Construction questions

  1. #1
    Join Date
    Nov 2019
    Location
    BERLIN MD
    Posts
    4

    Default Cosine Wherry Construction questions

    Hello all. Been a long time lurker on this site, I have "stolen" many great ideas from its members and I thank everyone for that.

    I am coming to the finish line (at least I think so) on my Cosine Wherry build and have a few questions and would appreciate feedback. Although I am not new to boatbuilding, I've never attempted anything this "lightly" built.

    I bought plans for 14' boat, I stretched it to 15' (discussed this with designer/plan provided prior to doing this) and employed some modern techniques and materials in the build (please don't shoot me for breaking from tradition!).

    Construction: 3/16"-1/4" Paulownia square edge strips (final milling ended up slightly less than 1/4")
    2 layers 9 oz stitched biaxial fabric, peel ply used during lamination (hull to be painted-personal preference) on outside of hull
    2 layers 9 oz "finish cloth", boat cloth?-standard weave inside of hull
    Capped / solid rails. 2-1/4" wide x 1" thick. This was achieved by laminating 3 pieces 1/4" plywood in and out side of hull, then veneered with 1/8" Teak for looks
    Transom is 1/8" teak veneer inside and out with 3/4" divinycell H-80 foam core
    Aft seat is built as airtight flotation chambebr /> Bow deck is extended back 36" and bulkheaded off as airtight flotation chambebr /> Bow deck is 1/8" Teak backed with 1700 stitched biaxial fabric, paulownia scantling underneath for support
    Bulkheads and aft seat are 1/16" Teak veneer with 1/2" carbon-core plastic honeycomb coring, 9 ox stitched cloth on undersides
    Thwarts-will start with center one only, will install second if needed. 1/8" teak on top, 5/8" edge framing, 2 layers 1700 stiched biaxial on undersides. 1" plastic honeycomb core in between

    The plans and instructions leave some things to interpretation and question, so I seek advice from more knowledgeable people.

    Seat Post- Are these structural, or can these be omitted? I like the clean look without them
    Knees on top of seats- Again I like clean look without
    Oarlock location. I will be using "corner mount (?)", angle mount? style. Should these go inside or outside the rail
    My plans seem to indicate floorboards, but nothing is noted or mentioned anywhere about such. Do these boats normally have floorboards?
    Bottom bracing/framing, Again I see something on the plans that "might" be frames, but again no mention of this. Maybe these items are "options" and not required for structural support?

    I want everyone to understand, I have absolutely ZERO experience in a rowboat, so I won't know if the thing is great or a dud- it will be the best I've ever rowed and the worst I've ever rowed. I live on a shallow protected creek and thought this would be a fun project and maybe I'd start rowing for exercise (creek is about 1-1/4" mile long). We don't have any rocks, its a mud and marsh bottom so not worried about damage too much. This will be stored on my dock in Summer, inside stored during Winter.

    Your thoughts, insights, and suggestions are appreciated

  2. #2
    Join Date
    Jun 2000
    Location
    Pleasant Valley NS Canada
    Posts
    21,428

    Default Re: Cosine Wherry Construction questions

    Welcome, gonnabe; I hope that you find your time here productive and pleasurable.

    I don't have any issues with the changes you have made to your boat's construction. I rather like your transom construction - how did you apply bonding pressure to the veneers?

    To your questions:

    Seat post - normally these are structural to support the span of the thin thwart plank. An alternative is to beef up the plank for strength, but rout a cove or chamfer on the underside edges so that the plank looks thin to the casual observer unless he/shee bends down and looks under the plank.

    Knees on top of seats - structurally important because in addition to supporting the thwart, they make a structural 'thwartships beam that reinforces the sheer in resisting bumps as the boat comes alongside a wharf or another boat. Select crotch-grain wood and finish them all pretty-like to reduce the ugly.

    Oarlocks - normally on the inside so they don't fetch up on things like wharfs or expensive yacht topsides.

    Floorboards are good to keep your shoes and pantlegs out of the inevitable bilgewater. They look good, too, I think - one sort of expects to see them there.

    Bottom bracing - I think that the hull, if built properly, doesn't absolutely need them, but being a belt-and-britches kinda guy, I think that they are a good addition, especially if the boat gets hauled up on beaches and sandbars regularly. Besides, they provide a good foundation for floorboards.

    Well, that is my opinionate opinion. But don't take my word as gospel - there are lots of well-experienced small boat guys (and a few girls) here, some of whom may have first-hand experience with a Cosine Wherry. wait to see what a few have to say, and then make a decision based on what they say and what feels right to you.
    Hope for the best, but plan for the worst.

  3. #3
    Join Date
    Sep 2015
    Location
    Viroqua, Wisconsin
    Posts
    189

    Default Re: Cosine Wherry Construction questions

    Sounds well thought-out! Post pics please!

  4. #4
    Join Date
    Apr 2004
    Location
    Pender Harbour BC Canada
    Posts
    101

    Default Re: Cosine Wherry Construction questions

    I've built a few cosine wherries, have never stretched one but have seen some 16 footers on the internet... 15 feet sounds perfect, a bit more room inside and a bit of extra space between rowing stations.
    I think that the seat post and knees tie the gunwales to the keel. Your seat construction sounds like it would be strong enough not to need the support, but I like the idea of that link to the keel. I have started making knees by laminating them over a form, they are probably stronger than cut ones and are less obtrusive. Also, its hard to get stock with the best grain to make sawn ones.
    Best rgds

    Rick
    oysterbayboats.ca

  5. #5
    Join Date
    Nov 2011
    Location
    Salt Spring Island, BC
    Posts
    7,489

    Default Re: Cosine Wherry Construction questions

    Laminated knees will be lighter. You appear to be focused on weight.

  6. #6
    Join Date
    Apr 2010
    Location
    Fairfield, CA
    Posts
    1,963

    Default Re: Cosine Wherry Construction questions

    You had me at "Paulownia". Where did you find this in the US? Any idea how much the finished boat is going to wind up weighing?

    The two cosine wherries I have seen both rowed very well. Go ahead with the inside oarlock mounts to get started, but you might find that folding riggers to increase span to ~60" would let you use longer oars and go a bit faster.

  7. #7
    Join Date
    Sep 2015
    Location
    Viroqua, Wisconsin
    Posts
    189

    Default Re: Cosine Wherry Construction questions

    Pretty light stuff, supposed to be decay-resistant too:

    https://www.wood-database.com/paulownia/

  8. #8
    Join Date
    Apr 2010
    Location
    Fairfield, CA
    Posts
    1,963

    Default Re: Cosine Wherry Construction questions

    Paulownia was not readily available in the US last time I was looking. Really interested in where the OP sourced it. There was supposed to be some plantation grown, otherwise imported. There are some surfboard kits sold using Paulownia.

  9. #9
    Join Date
    Nov 2019
    Location
    BERLIN MD
    Posts
    4

    Default Re: Cosine Wherry Construction questions

    Just checked to be sure.
    site is "clearwoodpaddleboards.com. Still advertising paulownia lumber. I believe it is imported from China- imagine that!

  10. #10
    Join Date
    Apr 2010
    Location
    Fairfield, CA
    Posts
    1,963

    Default Re: Cosine Wherry Construction questions

    Quote Originally Posted by gonnabe View Post
    Just checked to be sure.
    site is "clearwoodpaddleboards.com. Still advertising paulownia lumber. I believe it is imported from China- imagine that!
    Thanks. There is another board shop advertising a lower price for similar 1 x 6 x 8 foot planks, I do not know the quality: http://www.woodsurfboardsupply.com/wood.html
    Probably also China.

  11. #11
    Join Date
    Jul 2002
    Location
    Seattle, WA
    Posts
    9,359

    Default Re: Cosine Wherry Construction questions

    Quote Originally Posted by rgthom View Post
    Thanks. There is another board shop advertising a lower price for similar 1 x 6 x 8 foot planks, I do not know the quality: http://www.woodsurfboardsupply.com/wood.html
    Probably also China.
    I have a closet made of paulownia. Pretty but very, very light; I suspect not strong.

  12. #12
    Join Date
    Apr 2010
    Location
    Fairfield, CA
    Posts
    1,963

    Default Re: Cosine Wherry Construction questions

    It's probably very good for this strip plank boat with glass in and out. Stronger than balsa, which works as a core for glass.

  13. #13
    Join Date
    Aug 2005
    Location
    SF Bay Area- Richmond
    Posts
    16,412

    Default Re: Cosine Wherry Construction questions

    Someone else built my Cosine, but I've replaced the forward and center thwarts, leaving out the rear thwart, as the sternsheets work fine for having someone sit aft.

    No knees on top of the thwarts and they don't seem to need them, even when pulling hard in rough water. I do have the center support posts and with the thin spruce thwarts the supports are needed.

    I'm not a fan of the right-angle oarlock base mounts, vastly prefer the standard oarlock bases set into blocks on top of the gunwales -- and in this case I need the height to let the long spoon oar handles clear my legs.





    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  14. #14
    Join Date
    Jan 2009
    Location
    northwestern Wisconsin
    Posts
    8,041

    Default Re: Cosine Wherry Construction questions

    Quote Originally Posted by mmd View Post
    Floorboards are good to keep your shoes and pantlegs out of the inevitable bilgewater. They look good, too, I think - one sort of expects to see them there.
    mmd knows what he is talking about, and I agree with his take on things. But on the issue of floorboards, my own personal preference runs opposite. I like a nice clean hull without floorboards--it makes it very easy to sponge out the small amount of water you're likely to take on in a sheltered-water rowboat, saves a bit of weight and some work making and fitting them. I didn't install them in my boat (the plans showed them), and haven't missed them yet. Then again, my boat has essentially 7 complete ring frames because of 7 bulkheads at the thwarts/sternsheets, and hanging knees above each, so plenty of structure.

    Now, if the floors are essential structural members, then I'd rather have floorboards than bare floor timbers sticking up. I'd be curious to hear if people think floors could be left out. It sounds like the things you say "might be frames" could actually be floor timbers, but are they really needed in a light strip-built boat? If so, floorboards are probably a good idea.

    Tom
    You don't have to be prepared as long as you're willing to suffer the consequences.

    www.tompamperin.com

  15. #15
    Join Date
    Apr 2004
    Location
    Pender Harbour BC Canada
    Posts
    101

    Default Re: Cosine Wherry Construction questions

    Ive only ever seen one cosine with floorboards. I'm pretty sure that the boat doesn't need frames. I put a bit of anti-skid in the bottom to help getting in and out, and good stretchers for the center rowing position. I too like the clean inside, that can easily be sponged out.

    Rgds

    Rick
    oysterbayboats.ca

  16. #16
    Join Date
    Jun 2000
    Location
    Pleasant Valley NS Canada
    Posts
    21,428

    Default Re: Cosine Wherry Construction questions

    A few follow-up comments, if I may...

    Floorboards are a personal preference - I prefer 'em, but that's just me. But I also believe that the floorboards over the low point of the hull should have a lift-out section for sponging the bilge.

    Frames are certainly not needed in this type & size of construction. Floors are another matter; I like them for the structural strength they impart in a section of the hull that sees a lot of stress, especially if trailered on keel supports or beached often. Not that the boat will break without them, but I believe that the boat will last longer with them. But keep in mind that opinions are like bumholes - everybody has one, and some are smellier than others. I am not to be excluded from that generalization.

    Thorne should certainly be paid attention to, as he has spent a lot of time rowing a Cosine Wherry. I like his oarlock type & placement solution, and will probably emulate them when (if) I ever get my wherry completed. Like him, my boat was built by someone else, a friend whom gifted the uncompleted hull to me a few weeks before he passed. My aversion to external rowlocks and outriggers is probably due to how I mostly use rowboats - to get to and around larger boats, where anything on the outside of the rowboat sheer is a danger to the finishes on bigger boats. As an aside, I really like how Thorne's boat has inwales on spacer blocks - looks good, is light, and strong. Downside is the fussiness of re-painting.
    Hope for the best, but plan for the worst.

  17. #17
    Join Date
    Feb 2015
    Location
    Anacortes, WA
    Posts
    40

    Default Re: Cosine Wherry Construction questions

    I have a standard 14’ Cosine Wherry I built in 2015 and I have several comments to your interesting post.

    First, the standard 14’ Cosine Wherry is an excellent fixed seat rowboat. 14 feet is probably around the minimum end of the length scale for good rowboats and the 15 foot stretched version is probably even better. This rowboat will row so fast and far with moderate effort that I suspect you will find that your 1-1/4 mile creek is too small a pond for it.

    I am curious who the designer is that you are corresponding with and what plans you are using. It is my understanding that the designer of this boat, John Hartsock, has been dead for quite a while. The original design and plans were published in a book entitled Rip, Strip and Row during the 1980s by Bob and Erica Pickett who owned Flounder Bay Boat Lumber in Anacortes Washington. This original design didn’t include floorboards. I don’t know what floorboards would add to the boat except making it harder to get water out. However, I do recommend that the finish in the bottom of the boat contain ground walnut shells or something else to give slip resistance.

    I suspect that the seat posts are structurally critical to avoid hull flexing where the thwarts attach to the hull, especially if there is any flex at all in those composite thwarts you have built. And I hope that you have or intend to install full length winding stringers inside the hull for the thwarts to ride on instead of just having some kind of short ledgers for each thwart. The original design book, Rip, Strip and Row said that either full length stringers or short ledgers would work. However, I live in Anacortes Washington and I discussed building this rowboat with Bob and Erica Pickett before I got started and they told me to use the full length stringers. They still had the second or third Cosine Wherry built, sitting in their garage, and this boat had thwart ledgers approx. 18” long. The Picketts told me that their earlier message that short ledgers would work had been a mistake and that the hull flexing that resulted (even with seat posts installed) had caused fiberglass delamination on the outside of the hull that had been an ongoing problem on that particular boat. After hearing this, I built mine with the long stringers, like the ones you can see in Thorne’s picture of the inside of his boat. I do have posts below the center of my thwarts but did not install the thwart knees. I haven’t had problems with anything on my boat coming apart.

    If you’d give us a picture of your boat, I’d like to see what that paulownia hull looks like. I used Western Red Cedar, as have most of the people who have built Cosine Wherries that I am aware of.

    As an aside: If I remember this correctly, Erica Pickett told me that Flounder Bay Boat Lumber had been selling kits for building 17’ cedar strip kayaks during the 1980s and, with the inevitable knots in “clear” cedar lumber, they had accumulated a pile of strips too short to go in the 17 foot kayak kits. They wanted a new boat design that would allow them to sell the shorter strips that they had a lot of. They commissioned John Hartsock to come up with a stripper rowboat design that would use shorter strips and what resulted was the Cosine Wherry. By luck or science, the design turned out to be better than anyone expected, including John Hartsock. He really hit it right on this hull design. I have rowed various classic traditional rowboats, Whitehalls, Peapods, etc. that are known to be excellent pulling boats. The excellent classics are typically several feet longer than the Cosine Wherry, which had to use up those short cedar strips after all. Nevertheless, the Cosine Wherry is almost in the league with those classics in being a pleasure to row. And it rides wakes, chop and waves well without water coming into the boat. It is really a fine rowboat. I admired this boat for many years before I lived in a place with room to keep one, allowing me to finally build it.

  18. #18
    Join Date
    Oct 2000
    Location
    Padanaram, MA USA
    Posts
    9,902

    Default Re: Cosine Wherry Construction questions

    Are there photos of this boat?

    What’s it weigh?

  19. #19
    Join Date
    Aug 2005
    Location
    SF Bay Area- Richmond
    Posts
    16,412

    Default Re: Cosine Wherry Construction questions

    Quote Originally Posted by mmd View Post
    A few follow-up comments, if I may...

    Floorboards are a personal preference - I prefer 'em, but that's just me. But I also believe that the floorboards over the low point of the hull should have a lift-out section for sponging the bilge.

    Frames are certainly not needed in this type & size of construction. Floors are another matter; I like them for the structural strength they impart in a section of the hull that sees a lot of stress, especially if trailered on keel supports or beached often. Not that the boat will break without them, but I believe that the boat will last longer with them. But keep in mind that opinions are like bumholes - everybody has one, and some are smellier than others. I am not to be excluded from that generalization.

    Thorne should certainly be paid attention to, as he has spent a lot of time rowing a Cosine Wherry. I like his oarlock type & placement solution, and will probably emulate them when (if) I ever get my wherry completed. Like him, my boat was built by someone else, a friend whom gifted the uncompleted hull to me a few weeks before he passed. My aversion to external rowlocks and outriggers is probably due to how I mostly use rowboats - to get to and around larger boats, where anything on the outside of the rowboat sheer is a danger to the finishes on bigger boats. As an aside, I really like how Thorne's boat has inwales on spacer blocks - looks good, is light, and strong. Downside is the fussiness of re-painting.
    My blushes! I have done a lot of rowing in my Cosine, but may not deserve all that much approval. ;-)

    I do get some flexing of the gunwales when pulling hard, and might suggest adding a small support block epoxied to the hull underneath each gunwale-mounted oarlock. As for the third / aft thwart, the only other Cosine Wherry that I see very often was built by boatbuilder Ken Bechtel in Trinidad, California -- and he also left it out. I think I remember reading here that the boat is too short to really row double, resulting in a lot of pitching, but can't remember more than that -- so that makes even less need for the rear thwart.
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  20. #20
    Join Date
    Nov 2019
    Location
    BERLIN MD
    Posts
    4

    Default Re: Cosine Wherry Construction questions

    The plans were bought (November 2019) from a builder (now retired I believe) in the Pacific MW. He apparently had a friendship with the original designer and built many of these boats. I felt comfortable ordering from him (I am hesitant to mention names as I am unsure the rules on this).
    The reason I am asking my questions here (and the reason I assume the gentleman has retired), is his website notes he has stopped "building" boats but is still offering advice and shop services on limited scale. My several attempts to reach him the past few months have yielded one text message stating he was travelling and had very poor cell service. I hope he is enjoying his retirement and certainly understand his lack of response.
    A few have requested pictures, if someone wants to guide me through the process I will attempt- although I am usually unsuccessful.

    Hull is to be painted outside (I am priming today), originally wanted to paint a dark color (flag blue) but have decided to paint it white- I don't want the headaches of a dark colored hull. Inside is bright, however the wood is not very clear because of the cloth used. When I ordered cloth the supply house shipped half the cloth "normal" (I explained this was to be a clear finish), the second roll was coated with something that they assured wouldn't affect anything- except to make it stronger-, This turned out to be untrue. The first layer was clear as expected, the second has a bluish-green hue that mutes the woodgrain considerably. It does help knock down the glare - but the wood grain in not nearly as pretty.

    I wanted a lighter colored wood than cedar and paulownia seemed like a "unique"option in many ways. Personally I don't find the grain structure of Paulownia anything more than normal- no remarkable figuring or dramatic growth ring colorations- pretty, but not gourgeous.

    After flipping my boat over yesterday (so I can primer the hullside) I can tell I added considerable weight with rails, seats bulkheads. Certainly noticeably heavier than when I took hull off jig and flipped over to work on insides. I also have everything coated with 4 coats epoxy- epoxy gets heavy quickly.Really cannot offer weight guess, however in the near future I will weigh it and let everyone know. I did weigh the thwarts and those are 6lbs each- definitely lighter than a solid Teak seat would have been, but probably heavier that Paulonia would have been?

    Hope this answers some of your questions and curiousities.

    Thanks

  21. #21
    Join Date
    Aug 2005
    Location
    SF Bay Area- Richmond
    Posts
    16,412

    Default Re: Cosine Wherry Construction questions

    I'm sure it will work out just fine. Overbuilding is more the rule than exception for new builders, and the weight won't matter much unless you plan on cartopping the boat. If possible I'd delay installing the oarlock bases until you can float the boat. Fab up some temp oarlock bases that you can clamp to the gunwales and see how the height of the oar handles works with your legs. I find that I really need a decent cushion to row very far, so that raised the required height of the oarlock base to let the handles clear my legs.

    I also installed a trad-style foot brace for the center thwart, but can use the center thwart to brace my feet when rowing from the forward thwart with a passenger. A section of broom handle with the ends reduced in diameter works well as a crossbar.




    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  22. #22
    Join Date
    Nov 2019
    Location
    BERLIN MD
    Posts
    4

    Default Re: Cosine Wherry Construction questions

    Thorne,
    Interesting footrest- functional and minimal.
    I also like the way the thwart cleats run the length of the boat- looks like it would be a royal pain to fit and install. Do you think it adds much strength to the hull?

  23. #23
    Join Date
    Apr 2004
    Location
    Pender Harbour BC Canada
    Posts
    101

    Default Re: Cosine Wherry Construction questions

    I've always done the full length thwart cleats, the last two boats I got smart and laminated them on the forms after the hull is taken off to finish the inside. Two laminations, epoxied, and it's a lot easier to place them into the hull when the time comes. I epoxy them in place, and it was really hard to bend one piece cleats into place and then clamp them until it cured. I believe that they add to the structure of the boat; gunwales, seat ledgers, thwarts, knees, seat posts and keel all adding together to be stronger than the individual bits.
    The boats are surprisingly strong, I had one boat that was picked off a customers dock by the wind, flew a couple of hundred feet and hit a neighboring dock. It broke a chunk out of the skeg, and popped the glue joint on the rear quarter knees, broke the wood in a couple of the blocks in the inwales and stress marked the glass on both sides of the hull. But is still in use, and looking great.
    Rgds

    Rick
    oysterbayboats.ca

  24. #24
    Join Date
    Feb 2015
    Location
    Anacortes, WA
    Posts
    40

    Default Re: Cosine Wherry Construction questions

    Gonnabe, installing those long thwart cleats was the worst PITA of the whole build for me but I did come up with a way to do it that worked. Private message me if you’d like information about how I went about it. It will probably take a phone call to run it down. It may be that Rick in Pender Harbour would be an even better resource in how to go about this than I am. I have built one Cosine Wherry and Rick has built a bunch of them and may have better ideas and methods on this than I do. Incidentally, I know a guy in WA State who has a Cosine pained white and it looks good.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •