Dolfi R&S, a rowing/sailing for quiet balads in inland and coastal waters

Discussion in 'Boat Design' started by Dolfiman, Aug 2, 2019.

  1. Dolfiman
    Joined: Aug 2017
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    Location: NICE (France)

    Dolfiman Senior Member

    Dolfi R&S project wants to be part of the rowing & sailing revival, inspired by the classic lines of historical boats, here especially the "Whitehall", for the authentic pleasure of quiet sailings in inland and coastal waters.
    At first, it is the rowing practice for one rower which is targeted, with the possibility of roaming and camping stops on the shore. With a waterline length of 4.35 m and a hull width of 1.34 m at the level of the oar locks, an average speed of 3 to 4 knots by rowing can be targeted on a several hours basis (by flat sea and no or light wind). The standard design includes a fixed seat, but a slide seat option is feasible.
    Thanks to a sail of 5,6 m2 (60 ft, or 7,5 m2 / 80 ft in option) and removable daggerboard and rudder, it is also the possibility to go sailing when weather conditions permit, including upwind although without seeking the same performance as with a dinghy.

    The project is detailed on the principle of a strip-planking construction, with 1/4'' thick Red Cedar slats + external and internal glass resin epoxy stratification, combining lightness, strength, watertightness and easy maintenance, not to mention the aesthetics of such refined building.

    Many thanks in advance for your comments,

    Attached Files:

  2. Squidly-Diddly
    Joined: Sep 2007
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    Location: SF bay

    Squidly-Diddly Senior Member

    I don't think anyone rows for more that few hundred yards without a sliding seat rig these days. Only time people row non-sliding seat is yacht-to-shore dingy, or beat up aluminum boat for sitting and fishing, or LARP on Viking ship or age-of-sail jolly-boat. I'd go with sliding seat as default, since you should be able to easily go to non-sliding but not the other way.

    I'd also build in a provision for using a tiny outboard. Just make it so adding one isn't a problem, to greatly broaden the appeal. There are lots of places where you might want to travel a bit from a launch point to get to the nice area you really want play around in. Like people that will put road bikes on top of cars to drive to the section of road they want to ride their bikes on, but different.
  3. J Smythe
    Joined: Jul 2019
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    Location: USA

    J Smythe Junior Member

    That looks sweet! You could throw a rucksack on that baby, and off you go for a weekend of fishing, hunting, sailing, whatever. Very nice.
  4. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Nice work.

    I'd want a couple of things arranged a bit differently. It looks like the rowing seat is about 10" above the bottom. Won't the oar hands hit the knees at that height? I think the seat needs to be a little higher for a boat this big. My dink has 10" seat height, but it is only 8' and uses 7' oars. I'd also want to have the option of using 9' oars and folding outrigger oarlocks on this boat, so the ergonomics seem slightly cramped.

    Stem piece needs to be thicker. First thing I'm going to do is drill 4 3/8 holes through it. Two for a big U-bolt and two more for a rope handle. Figure about 10 tons load on the U bolt. I've borne this in 1/4" hull.

    Dagger board is a bit small. It seems to be sized the way you size one for a 40 or 50 footer. That doesn't work for little light boats if you have any ambition to tack under sail. I'd allow for 50% more chord. Maybe you won't need all of that, but you will want most of that. It's plenty thick, just needs more chord.

    May as well tie the aft end of the daggerboard case to the seat.

    To build it with strips, you will need two intermediate molds between the permanent frames. I'd just strip build it over all molds, glass the outside, then sand the inside (this is a real pita), then glass inside and add the frames. At 16', I'd be very tempted to use a 3/8 by 2" bilge strip to get me started. And a 3/8 garboard strake wouldn't be a bad idea either.

    It looks like your heeling calcs targeted the wrong center of buoyancy (2.041 vs 2.104 for the level state.) I'd shift some volume so that the trim angle at 20 degrees heel was zero (and not more than 0.1 degree anywhere in between). It's a pretty small shift. But a there's a logic to wineglass sterns. Some people are bound to revise your transom, and those wineglass sterns don't want trim. That aft kink in the 20 degree heeled waterline where it crosses the centerplane - it probably shouldn't be there for this type craft. Also notice the trim changes from pos. to neg. going from 10 to 20 degrees of heel. That is actually a fairly sizable trim change for just a ten degree difference in heel. If you narrowed the hull at the 300 station just a smidgen, making the exit angle steeper, reducing waterline curvature at the 300 station and shifting the inflection point of the waterline forward a bit, I think that would lessen all the trim numbers. <Edit> I just realized the seating positions are probably different for rowing and sailing. That would account for the different lcb's.

    There's a logic to where the waterline inflection points go on a sailboat. It is a function of vertical cg and the design heel under sail. The idea is to generate the most RM with the least wetted surface area. If the cg is high, when heeled, the bow is on the wrong side generating negative RM. You want to minimize wetted area, displacement, and negative RM; so hollow until the waterline shifts under the heeled ycg. Waterline curvature wants to be proportional to the square of the beam referenced to the ycg. A crew moving to a hiking position radically changes the ideal waterlines for a small sailboat. For a boat optimized for rowing, let it heel before climbing onto the rail.
    Last edited: Aug 3, 2019
  5. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    I went looking for some hulls to compare this with because I thought your bow sections were a bit spoony. I found this wonderful site full of punts and rodneys

    Punts & Rodneys – Boats & Builders

    from their site —

    Notice the first two are old boats and had the wineglass stern. We seem to have forgotten why we put wineglass sterns on these boats for two centuries. They used to be sailed and rowed.

    Jolly boat - Wikipedia

  6. Dolfiman
    Joined: Aug 2017
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    Location: NICE (France)

    Dolfiman Senior Member

    Many thanks all for your likes, developed comments and suggestions. My answers here below and a hull revision attached.

    Ok, you are right. In any case (of client preference), the 2 options should be easily interchangeable and compatible with the daggerboard case.

    I think that the present rear transom design, quasi vertical with an half-beam of 40 cm, allows that easily side (or in place of) the rudder (which is removable anyway, as not necessary for the rowing mode)

    >>> Vertically : the rowing seat is at Z + 23 cm /H0 and the rower feet at Z – 0,09 cm /Ho, that means the seat above the bottom is 32 cm = 12,6''. The oar locks are ~ Z +34 cm , so +11 cm (4, 3'') above the seat.
    >>> In longitudinal (I should draw also this view to complete the ergonomics study), the seat center is at 37 cm (14,6'') of the oar locks, and the rower feet are at around 85 cm (33,5'') of the seat center (rower size depending).
    These figures are from average ones communicated by a friend having a similar boat with a fixed seat. Of course, rower sizes can be very variable, and so do the seat (adjustable position fore/aft), the feet holds also, and if needed the seat can be put few cm higher to cope with the knees height issue.
    >>> In transversal : in standard there will be fixed oar locks at gunwale level (so B 1,34 m) , but I suppose it can be also possible to clamp some removable outriggers in order to enlarge the oar locks width if desire.

    The bow upper end piece is 20 mm thick, it is not sufficient ? Your 10 tons seems a very heavy load case, I would take 1 ton (already 5 times the displacement in charge) in case of a towing occurrence.

    Ok, I changed the root chord from 25 to 35 cm, and the draft from 80 to 85 cm, in the revision attached

    Ok, I understand that what you describe is the usual standard for that type of boat size, the one I suggested is more adapted for a keel boat. Both are compatible with the project present definition I think.

    Ok, you mean some strips thicker (3/8'' instead of 1/4'') at critical locations (low incidence on the hull weight) , or the full planking in 3/8'' ? (>>> that costs +10 kg for the bare hull , 76 kg instead of 66 , 167,5 lbs instead of 145,5).

    it is not a mistake, 2,041 m is the Xg for the reference displacement which includes the 105 kg payload, so resulting from the X position choice for the water reserve (5 kg) and the roaming equipment (20 kg), the rower (80 kg) being on the fixed rowing seat. So, I can move forward the water reserve and roaming equipmement to have exactly Xg = LCB, for example X 330 (behind the mast) for the 5 kg water and X 153 for the 20 kg equipment, then leading to Xg = LCB = 2,105 m.

    I think the answer is mostly in your last remark : here, the rower becoming helmsman makes the trim dependant of his X position when under sail with heel. I did the heel study just to see the main trend, to have an estimation of the RM at 20° (> 0,73 kN.m, of which 63% due to the hiking position of the helmsman sit windward), a look at the waterline shape : I am not worry too much about the aft kink (seems unavoidable with a wine glass stern, when heeled), in a zone where the flow is detached in dynamic.

    Thanks to these hulls finds, very informative. I agree that my bow sections are a bit too spoony, with a max curvature too low, can be too stiff and reactive re. pitch motion on small waves >>> I revised the project hull for more smooth bow sections while maintaining all other features inc. the waterline shape, here attached. I will revise the all brochure on that basis.

    Attached Files:

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