designing a fast rowboat

Discussion in 'Boat Design' started by nordvindcrew, Oct 13, 2006.

  1. El_Guero

    El_Guero Previous Member

    Rules, them dang rules!

    That is why the Olympics use smooth skin.

    Lapstrake? That is interesting. I was thinking of an automated method, powered by a small engine or motor. But, power boats use small chines to suck the air in.

    Don't need extra engine power for that.
     
  2. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    No, the Olympic rules don't ban clinker (lapstrake) hulls. It's just that nobody thinks they are worth using.
     
  3. keith66
    Joined: Sep 2007
    Posts: 339
    Likes: 25, Points: 28, Legacy Rep: 168
    Location: Essex UK

    keith66 Senior Member

    im curious about the difference between Clinker & smooth & have often wondered if there is a difference. A strange experience a few years ago shows how the lands entrap air. I had sold my old Rye beach boat Billows (21ft) & was delivering her to her new home port with the owner. She had been out of the water some time & was still a bit leaky here & there.
    Sailing on the River Swale in extremely light airs we noticed a strange fizzing noise, Eventually i traced it to a fastening under the floor boards about 6ft frd of the transom. The air was coming up from a leak from entrained air under a land just up from her keel. She was barely making a knot at the time. This boat was always noted for her performance in light airs. Makes me wonder!
     
  4. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    Ay up. :)

    Any progress on this?

    AFAICT from Michlet stunts, once the boat is up around Fn = 0.35 or higher the best results seem to come from having a curve of areas with no hollow aft, and minimal hollow forward. If combined with other sensible restrictions on shape, that seems to do the business.

    Keeping shoulders out of waterlines seems to help too, although those seem to primarily impact resistance at more moderate speeds (causing a resistance hump at around Fn = 0.3).



    I had an idea regarding construction that I think is worth a try. I noticed on your blog that you've rather enjoyed doing a 'pod that didn't rely on heaps of epoxy. I can quite understand that. :D

    I have a love/hate relationship with epoxy, and prefer to minimise its use. I've come to the conclusion that for a combination of ease (and cleanliness) of building and strength/weight ratio clinker ply is probably still the best option.

    I like the way Ruud sets his jigs up, but thought of a possible refinement. I can't see any reason why it wouldn't be possible to cut the jig's stringers where permanent frames will be. That would make getting a finished product quicker and easier.

    The idea goes like this: build the jig as normal, but with a pair of moulds just forward and aft of where you want the permanent frames (spaced according to frame siding).

    Next, stick some gussets (ply or whatever) alongside the stringers, to the pairs of moulds, to lock in fair curvature where you are going to cut the stringers. Now chop the stringers to suit the permanent frames, much like cutting a nesting dinghy in half after it's all stuck together.

    The jig's stringers should keep a fair shape all the way along the boat, and the frames can be laminated up and just dropped into the slots, at which point bevelling the frames using the stringers as guides would be a no-brainer, and very quick.

    Seems to me that if building two or more of the same boat off the same jig, this would be the quickest and easiest way of getting the things finished.
     
  5. DCockey
    Joined: Oct 2009
    Posts: 5,071
    Likes: 550, Points: 113, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Not ready to report any more than I did in post 1644.

    I haven't seen at significant variance from your comments.
     
  6. DCockey
    Joined: Oct 2009
    Posts: 5,071
    Likes: 550, Points: 113, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Why does the jig need stringers if the spacing between molds is sufficiently small?
     
  7. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    Practicality. It's just easier to fair for a start, since fairing fewer stations is always easier. It also means you can clamp the lap easily and consistently over its entire length. This is particularly useful with lightweight planking.

    Doesn't matter so much if you're using 9mm. Makes a big difference if using 4mm or less (which is why Tom Hill started doing it years ago). Ruud obviously finds it very useful even when using 6mm for the Savo's, and he spaces his moulds at 500mm.

    My 2c: the stringers are just worth it. I've seen so many clinker ply boats with unfair laps. Why not make things easy? :)
     
  8. Clinton B Chase
    Joined: Mar 2005
    Posts: 227
    Likes: 2, Points: 18, Legacy Rep: 21
    Location: Saco, ME

    Clinton B Chase Senior Member

    So there is another way to get at fair laps without super close station spacing and that is by using clamping battens on the outside of the laps. This is how I learned following John Brooks' lead (glued-lap guru). This came up recently on my FB page.

    https://www.facebook.com/photo.php?...0201608250840356.1073741825.1600920977&type=1

     
  9. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    Yeah I know about that trick, but if building light you'll probably be best with both inner and outer, just to get good clamping without an insane number of clamps.

    Also, having the stringers on the mould is handy for lining off and for support during bevelling. So, although you can get away without them I see no reason to, as long as you're planning on building a few boats off the same jig. Leaving the stringers out just seems to be a way of making a really good result harder to get.
     
  10. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

  11. rowerwet
    Joined: Nov 2011
    Posts: 21
    Likes: 1, Points: 3, Legacy Rep: 18
    Location: Merrimack Valley

    rowerwet Junior Member

    no the saco, I got on the turnpike at the Biddeford exit. I live a couple states away now, I hope to see you at a race in the future, (planning my build for this winter now)
    anybody think the Michelak RB42 a very fast design? I've never seen one to know how it rows, I've had the plans for years.
     
  12. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    Some people probably think the RB42 is a very fast design. Others may not. They may even know why they think this. If you'd like to know for yourself, the best thing is to do a comparison that takes account of the relevant features.
     
  13. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    Been thinking about oars. Obviously I'm silly enough to make my own, so the question is how to go about it. I've made oars before (8 foot, laminated shafts, with Macon blades) but want to try something a bit different this time.

    Now before anyone starts up about the Legend Of Theophilus Brackett, Greatest Doryman of All Time, and how he used to be able to get his Banks dory planing upwind in a gale, while using ten foot solid ash oars with blades 4 feet long and 2 inches wide, and used to do this while carrying a load consisting of 500 pounds of dead cod, the madam of the local brothel, and her pet Pomeranian, all because he was initiated into the Secret Brotherhood of Magical Dory Strokers Who Shall Be Revered Forever, I must point out that I do not consider this relevant.

    I would also particularly appreciate it if nobody speculated as to exactly how said doryman was planning on entertaining himself with 500 pounds of dead cod, the madam of the local brothel, and her pet Pomeranian. That would be far too much information.

    What I'm interested in (at the moment) are comparatively low freeboard boats used in fairly flat water. So, I'm thinking of trying a pair of home made hatchet blades, using a wood/carbon fibre mix.

    I've been reading up on blade construction over at Gaco and his method seems simple, and the results are apparently both light and durable. The layup is this:

    218g/m (6oz) carbon fibre cloth.

    2mm. coremat (aka sphericore or upica).

    225g/m (3/4 oz.) chopped strand mat.

    136g/m (4oz.) woven rovings.

    He's using a combination of CSM and glass roving on the back face of the blades, which is not ideal for weight. Also, while the blades themselves only weigh 200 grams they still have to be bogged and glassed to the oar shafts, which will add more weight (and more work).

    The 3mm plywood I'm using for planking has a density of around 440kg/m3, which means it has much the same weight for a given area as 2mm Coremat (once the Coremat is impregnated with resin). Being 3mm instead of 2mm it will make for a stiffer blade for the same weight, so it seems like it would make a suitable core as long as it'll take the shape required.

    After looking around the Dreher and Concept2 sites it seems that good hatchet blades have little or no vertical curvature. I think they'd probably work just as well if only curved horizontally, which means the plywood core wouldn't have to take compound curvature. This should make construction easier.

    So, after all that, the plan is to just bend and glue the plywood to a shaft that is shaped so it wont require any bog (carving funny shapes out of softwood doesn't bug me) and then laminate one layer of 6oz carbon cloth to front and back faces (going over the shaft on the back face, of course). Seems to me this should be adequately strong and stiff, not difficult to do, and should give the best strength/weight and stiffness/weight, all things considered.

    Can anyone see any possible problems with this cunning plot?
     
  14. Clinton B Chase
    Joined: Mar 2005
    Posts: 227
    Likes: 2, Points: 18, Legacy Rep: 21
    Location: Saco, ME

    Clinton B Chase Senior Member

    This is pretty much what I've settled on, laminated ply and if I want the blades stiffer I laminate CF on there. Light stuff. I teach this method and the oar blades are strong and stiff.

    I do vacuum bag the lams of ply over a form though....rather than using the loom itself.

    What's happenin' in rowboat design world? I'm distracted with a sailing dinghy right now....look fwd getting back to the rowboats. I am finishing a ST Lawrence R. Skiff in the shop.
     

  15. Jon A
    Joined: Jun 2013
    Posts: 25
    Likes: 1, Points: 0, Legacy Rep: 13
    Location: Bourne, Ma

    Jon A Junior Member

    Well, I've got the Series III version of the Monument River Wherry underway. This may be a little backed off from an all out racer. I has 3 planks to a side in an effort to smooth out some of the harsher angles of the Series II boat which has 2 but it will be a little beamier at the waterline. I want it to row as a single or double and I want it to have a little more initial stability, a little more utilitarian. Racing is not my only objective now, the engine is too old to be really competitive. But I will try to build it as light as possible, maybe 80 lbs finished. Don't want to finish at the back of the pack either!
    lofted from a 1/2 model, it took a long time to get the design worked out. I think there was/is a bit of arrogance on my part to think I know enough to do this. What has happened is that I got the stations set up on my strongback and the garboards started and didn't like the way it was turning out. Back to the lofting and tweaking things and carving off the stations here and there. Let it set for a bit and then some more little changes. Not the way to build a boat! I am finally going forward again, the garboards are on and I am fitting the middle planks.
    I'm a lot smarter than I was 4 months ago and the next one will go a little better!
    Happy Holidays all,
    Jon
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.