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Thread: Keyhaven Skiff Plans

  1. #1
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    Default Keyhaven Skiff Plans

    Are there plans for the Jurgen Sass Keyhaven Skiff? I do not see contact information or much of anything on the internet.

    http://sassdesign.net/Keyhaven%20Ski...ht%20skiff.pdf

    In any event, are there any other options out there for a small semi-displacement hull? Preferably a small skiff or wider canoe (about 16' and two people) that exceeds displacement speeds (maybe 9 kts) with a small outboard (5Hp maximum) without planing (lots of chop and boat wakes around here)? Twice displacement speed without planing would be a worthwhile build. Use is for exploring and fishing in the upper tidal Patuxent River or other small tributaries near the Chesapeake Bay.

  2. #2
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    Default Re: Keyhaven Skiff Plans

    sass@sassdesign.net

  3. #3
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    Default Re: Keyhaven Skiff Plans

    Thanks, not sure how I missed that other than too many hours in a row reading boat threads... It does not sound like Jurgen is going to send me the plans because it is my first build. Are there any comparable options? Why are there not more offerings with similar characteristics? Is there something inherently undesirable or difficult with this hull design?

  4. #4
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    Default Re: Keyhaven Skiff Plans

    A design exercise that is close to your requirements:










  5. #5
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    Default Re: Keyhaven Skiff Plans

    Oooh nice......sorta Flint inspired...or was it Fleet?
    Paul Fisher has some motor canoes, but i think they will be planing by the time they reach that speed.

  6. #6
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    Default Re: Keyhaven Skiff Plans

    Great looking boat, is that a planing hull?

    The good news is that Jurgen has shared his Keyhaven Skiff plans with me. Now I understand his reluctance to share with a first timer, I am starting with the CAD design in DELFTship. It appears that I can select the unfold view in DELFTship to determine the lofting data. I just wish there was a metric to English conversion button, I might have to buy a metric tape measure! Any suggestions on the material selection for the bottom panels? It is a maximum of 13" wide, so 9mm ply might be adequate? The overall displacement is 646 pounds. Based on similar sized S&G skiffs, I suspect the hull weight will be in the 150 to 200 pound range.

  7. #7
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    Default Re: Keyhaven Skiff Plans

    Stanley makes a 26 foot tape, metric on one side, inch on the other. No need to do conversions or "understand" metric.

  8. #8
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    Default Re: Keyhaven Skiff Plans

    The scantlings and number and place of additional stiffening structures (which seem to be not in the plans yet) is strongly depending on which weight you will put into that hull, and which outboard power you will use. Think about it. Are 2.3 hp sufficient or do you have the desire for more power? What are you doing if you find out that the "various calculations" that assume a maximum speed of 9 mph do not materialize?
    Mostly empirical experience with german "Wellenbinder" boats has shown that it is possible to damage the structure of a light boat with higher outboard power, and have revealed a number of stress points that are likely to break first.
    I have built very light planing sailing canoes, and have occasionally reached a velocity somewhat close to 9 mph. Sailing these boats has given me a good insight into wave impact that should be considered.
    Yes, to keep this boat light (which is important, because it looses most of its fun if it is not), I think it would a good idea to think about wood composite (plywood - glass or carbon), re-inforced where necessary. S&G is a good starting point.

    That said, a prototype that will flex its body until first cracks will appear can be repaired and re-inforced with glass and epoxy when the damage becomes apparent. Personally, I think an ultra-light boat of that type that will need some additional stiffening after ist first months of service is still much more useful than an overbuilt boat with heavy scantlings.

  9. #9
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    Default Re: Keyhaven Skiff Plans

    Found the imperial units setting, although the lofting math will likely be easier in mm so I might still buy that metric tape measure. I am not planning to overpower, but I will still build for about 5 Hp. I expect that the longitudinal floatation that forms a closed triangular shape most of the length of the hull will be very strong. I will likely add an additional bulkhead/storage area near the middle of the boat between the floatation chambers to strengthen for transverse loads. First I need to determine the placement given a single person and a two person configuration with proper trim. I like the original plan for a movable seat across the floatation tanks, although a seat back is a must. I might add a 3/4" overhang to the interior topsides to provide a lip to clamp the movable seats. Then the trim will be adjustable.

    My son and I experimented with two layers of 6oz fiberglass on 1/2" foam sheathing. Although it was very strong for uniform loads, I am not convinced that the foam itself is strong enough for point loads. It seems to tear/crush easily internally, and then the fiberglass shape is compromised. I thought about laminating the foam to luan (save weight and money), but the panels would likely not bend well to achieve the desired shapes in the hull, and there is an extra step. I plan to build with plywood for all hull structural components.

  10. #10
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    Default Re: Keyhaven Skiff Plans

    Talking about interior and seat positions, it might be a good time now to discuss stability issues. The seat position looks very high. Given that this hull shape has not much form stability, I wonder whether she will be tippy, epecially with that outboard on the transom. Could you tell us about the width of the hull and the width of the waterline?

    You are mentioning a two person configuration. That boat has been designed primarily for solo use. A passenger will make her significantly slower, and could alter the wave response in a way that the boat might be swamped easier. It would be a good idea to look at the freeboard now, midships, in the single and in the two person configuration.

    Yes, primarily plywood (okoume) would be also my preferred option.

    Axel

  11. #11
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    Default Re: Keyhaven Skiff Plans

    Quote Originally Posted by Penobscot17 View Post
    Found the imperial units setting, although the lofting math will likely be easier in mm so I might still buy that metric tape measure. I am not planning to overpower, but I will still build for about 5 Hp. I expect that the longitudinal floatation that forms a closed triangular shape most of the length of the hull will be very strong. I will likely add an additional bulkhead/storage area near the middle of the boat between the floatation chambers to strengthen for transverse loads. First I need to determine the placement given a single person and a two person configuration with proper trim. I like the original plan for a movable seat across the floatation tanks, although a seat back is a must. I might add a 3/4" overhang to the interior topsides to provide a lip to clamp the movable seats. Then the trim will be adjustable.

    My son and I experimented with two layers of 6oz fiberglass on 1/2" foam sheathing. Although it was very strong for uniform loads, I am not convinced that the foam itself is strong enough for point loads. It seems to tear/crush easily internally, and then the fiberglass shape is compromised. I thought about laminating the foam to luan (save weight and money), but the panels would likely not bend well to achieve the desired shapes in the hull, and there is an extra step. I plan to build with plywood for all hull structural components.
    Deviating a bit from the wooden ethos of the forum,what density foam were you using?I would have thought that a PVC foam of at least 85Kg/cu.metre would be a good starting point.Point loads might still be an issue if you don't take a bit of care,but on a sandy coast and with a good trailer,it should have a good chance.

  12. #12
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    Default Re: Keyhaven Skiff Plans

    The foam was EPS (Scrap Greenguard Insulation Sheathing). I was looking at cheap building materials for non-structural pieces. I did not look at PVC foam.

    The beam is about 48" and at the DWL is about 37". The seat is about 7.5" above the DWL. Midship freeboard is about 13" above the DWL at a displacement of 646 pounds. With a 200 pound hull (should be lighter than that) and a 40 pound engine (most small outboards are 10 pounds heavier than the Honda), that leaves 400 pounds to spare. That should be adequate for two people and minimal gear. I also just realized that the bottom panels are actually a single flat panel about 26" wide that was cut down the centerline and on opposite sides in the un-folded view. I think that rules out 6mm for the bottom. As compared to many years of canoeing and kayaking, I suspect the primary stability will be reasonable with good secondary stability. It is likely a necessary compromise for a low power, semi-planing monohull.

  13. #13
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    Default Re: Keyhaven Skiff Plans

    Yes, very similar to a canoe, overall. The high position of the outboard will add some instability. I think you will change the seat position deep between the benches, 10 cm lower as they are now, after the first capsize. That would also center the passengers on the centerline.
    Getting in and out on a high dock might need some practice.

    The bottom is prone to oilcanning, regardless whether it is 6 or 9 mm. Think I would not rule out 6 mm, sheathed with 160 g/m2 glass on both sides, but would certainly add some stringers.

  14. #14
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    Default Re: Keyhaven Skiff Plans

    What cross section and spacing of stringers do you recommend? I would like a flatter cross section to reduce the floor clutter. I am planning to use 6 oz cloth and I will figure out the seating during the build process.

    For the transom, it is 6.5" between the top of the aft deck and the top of the transom. What thickness of solid wood is recommended to mount a maximum of 5 Hp? The transom is also 16.7" above the trailing edge of the skiff. Is that a short shaft or long shaft outboard?

  15. #15
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    Default Re: Keyhaven Skiff Plans

    Think you need a boatbuilder now, with some experience in building similar ultralight craft, to look over the design and advise you on scantlings and building details. Most well-established scantlings and building technologies for wooden runabouts will work as well, but will result in a heavy overbuilt boat.

    Transoms for ultralight boats can be made from 6 mm ply, re-inforced with a "T"-structure of slabs of solid clear wood, well anchored behind the benches. With a 5 hp, you will need to add several staggered layers of glass on stress points and seams. I think a knee between transom and bottom and knees between transom and sides will be useful.

    Thinking about your bottom, the goal is not to make that completely stiff. Plywood sheathed with glass can take some oilcanning. The seams should be engineered in a way to dampen vibration, so they won't develop cracks. Depending on the assembly angle of the planks, these connections are engineered with the size of their fillets and the staggering of several layers of glass strips over the seams. Stringers are mainly used to limit excessive vibration to such an extent that the seams can handle that, and to absorb wave impact and trailer impact.
    Plywood scantlings and glass sheathing should be designed with occasional punctual impact resistance in mind, i.e. on a beach, depending much on how you use her.
    Last edited by canoe_sailor; 09-10-2018 at 11:21 AM.

  16. #16
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    Default Re: Keyhaven Skiff Plans

    I appreciate the concerns, but I also believe the glass is half full. It is a non-planning hull with longitudinal bulkheads along the floor with a topside interior deck that ties the transom into the sides and the longitudinal bulkheads. With a standard schedule of taped seams and a layer of cloth on the outside, I believe the hull is well constructed for the intended loads. There are a few more details that are not specified in the CAD model for the transom that I will determine. Most likely solid wood across the top of the transom and maybe a tie in along the floor to the longitudinal bulkheads.

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