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Thread: Keyhaven Skiff Build

  1. #1
    Join Date
    Aug 2018
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    Prince Frederick, MD USA
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    19

    Default Keyhaven Skiff Build

    I decided this past year to build the Keyhaven Skiff. I started the build in July, and I plan to finish this Spring when the weather improves. This thread will document the progress to date and then continue with the build progress.

    Background - This is my first boat build, but I have experience with other construction/build techniques. I also have many years of boating experience including power boats, canoeing, whitewater kayaking, and to a lesser extent, small sailboats.

    Why the Keyhaven Skiff - I have always like being on the water in small boats. After moving to Calvert County, MD, I realized that my canoes are not the ideal watercraft given that there is more open water (Patuxent River and various tributaries) and longer distances to cover. After reading about the larger semi-planing hulls, I became very interested in the possibility of a small boat that will reach twice hull speed without planing so that I could cover longer distances without skipping/bouncing across the water. I did not find many options for small semi-planing hulls, and the Keyhaven specifications were impressive to me. Jurgen Sass, http://sassdesign.net/, designed the Keyhaven Skiff and he was kind enough to share his CAD design (not a set of plans) with me.

    Early build - First, I had to move through a small learning curve to generate the lofting tables. Second, I reviewed several similar boats to determine a reasonable bill of materials. After careful consideration of the lively plywood debates on the forums, the fact that I am a first time builder, it is a small boat, the cost, and that this the first build of this design, I chose not to build with marine grade plywood. The hull was constructed with Ultraply XL 5.2 mm underlayment with marine-grade adhesive. This plywood proved to be virtually void free, and has 3 significant veneers with 2 ultra thin exterior veneers. I would later realize that this plywood has some glue voids, and I may later regret this decision. With that being said, I would consider this plywood again for non-critical applications. For the bottom I needed a stiffer material, and I choose Georgia Pacific 1/4" Plytanium BCX with waterproof glue. This plywood is riddled with voids, and I would not recommend it. In my case, the bottom of the Keyhaven Skiff is flat with a gradual rocker, and I covered the bottom with 4 oz cloth on the inside, and 6 oz cloth on the outside. Both types of plywood were $16 to $17 a sheet versus 6 mm Okoume at $90 a sheet, and the build requires 7.5 sheets. I also built a jig for my DeWalt track saw that made the scarfing process rather easy.
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  2. #2
    Join Date
    Aug 2018
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    Prince Frederick, MD USA
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    19

    Default Re: Keyhaven Skiff Build

    I preferred to use a mold/template process, but I did not think that I had the right information to build the external templates. I pushed forward with a stitch and glue approach, but I quickly realized that the flat bottom with double chine and longitudinal bulkheads made this approach difficult at best. Jurgen pointed me in the right direction to pull the external template information from the CAD model in DELFTship. The mold/template process really improved my confidence that the final product would match the CAD model. Originally, I increased the top and bottom strake dimensions by the thickness of the material to match the inside of the hull to the zero thickness CAD model. Moving to an external template approach required the removal of that material (or adjustment of the templates) to match the outside of the hull to the CAD design. This post lofting process introduced some additional error. I was also very careful to level the mold, which made a level and laser level very useful throughout the build process in the mold.
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    Last edited by Penobscot17; 12-24-2019 at 06:22 AM.

  3. #3
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    Aug 2018
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    Prince Frederick, MD USA
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    19

    Default Re: Keyhaven Skiff Build

    In the final design, the longitudinal bulkheads provide a great deal of strength via the closed structural member that is nearly the length of the boat, and they provide buoyancy in a great location to help maintain stability of a swamped boat. The downside is the joint is placed at the intersection of the bottom and the strake, creating a three way joint. I decided to finish the bottom/strake joint independent of the longitudinal bulkhead to ensure that it is strong (epoxy fillet with triple fiberglass tape), and then cut approximately the thickness of the joint off of the bulkhead piece. I am interested in feedback in this approach. I found that the interior bulkheads did not seem to match the exterior hull dimensions. I verified the CAD measurements three times using two methods, and came up with the same result. New pieces were cut to fit. The exterior topsides were installed with some trimming of the strake panels to improve the fit (part of the error from re-cutting the strakes). I was concerned about the Ultraply XL plywood fracturing (it seems to be more brittle than other plywood), so I added a significant number of small frame members. I am interested in feedback if this is deemed as necessary, especially in the case of using 6 mm marine plywood. I scarfed and pre-cut the interior topsides based on the CAD design at the same time I cut all of the plywood panels. Given variations in the actual size based on the zero thickness in the CAD design and the actual height of the longitudinal bulkhead, this proved to be a mistake. I scraped that piece, and found that it was easy to measure and cut the interior topsides to the actual dimensions. It was also during this process that I realized that my strake/exterior topside chine was not as fair as I had thought. In hindsight, I should of been more prudent about the space between the mold templates during the exterior topside gluing step (false sense of confidence). I added white die to the epoxy to lighten up the internal compartments, however, it appears that not enough die was added to the mix. The inwale was constructed of two layers of 5/16" x 1.5" pine. The transom above the interior topsides was constructed of 1 5/16th inch fir (probably slightly over built).
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  4. #4
    Join Date
    Jul 2010
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    northeast Ohio
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    2,417

    Default Re: Keyhaven Skiff Build

    That has come together nicely.

  5. #5
    Join Date
    Apr 2009
    Location
    Mountain lakes of Vermont
    Posts
    15,233

    Default Re: Keyhaven Skiff Build

    You've done a nice job there! Certainly isn't going to sink!
    What size motor goes on the boat?
    I was born on a wooden boat that I built myself.

  6. #6
    Join Date
    Aug 2018
    Location
    Prince Frederick, MD USA
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    19

    Default Re: Keyhaven Skiff Build

    The boat was designed for the 2.3 Hp Honda, but I found a good deal on a 1990 Evinrude 3 Hp.

    It was a bit nerve racking to do so much work on the boat, and to have not seen the bottom with an uninterrupted view. After flipping the hull and inspecting my work: The bottom rocker looked really good, minus a flat spot at the scarf joint that was easily fixed. The bottom chine was good, minus a minor bulge near station 2. The upper chine needed some work, but fortunately, that is above the water line. The hull was sanded and the more significant spots were filled with epoxy and wood flour. The hull was covered with 6 oz cloth overlapping on the bottom panel, and the seams were taped with 4" wide 6 oz cloth. Maybe I should have skipped the extra layer of tape to avoid the extra fill and sanding? I did struggle with achieving a smooth application of the epoxy, and then finally settled on the roll and tip method. I also ran out of epoxy during this step (3 gallons of Raka 127/350). Throughout the build, I was definitely inefficient with the epoxy by applying it excessively or unevenly followed up by lots of sanding. Two layers of 1.5" x 5/16th" wood were used to complete the gunwales. An additional coat of epoxy was added inside and out to seal everything up for a test trial prior to fairing and painting. The boat was built without any metal fasteners until the addition of the screws for the hatch covers. I also plan to add rope for the bow eye and two transom tie downs via 1/2" fiberglass tubes through the hull. The CAD design calls out drain holes on each corner of the transom level with the interior topsides. My interior topsides are sloped upward at each end, so I may skip this detail. In retrospect, I would have leveled the longitudinal bulkheads with my laser level, and then added a slight slope forward of the front bulkhead. This would have been a good reference for proper trim and would make the drains more effective.
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  7. #7
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    Aug 2018
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    Prince Frederick, MD USA
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    Default Re: Keyhaven Skiff Build

    I decided to take the boat for a test trial prior to finishing and painting, especially after seeing the price tag of quality primer and paint. The boat hull is 16'8" with a beam of about 4', and I measured the hull weight at 161 pounds (I need to verify with a better scale). I fitted a 1990 3 HP Evinrude engine that ran great in my garage, but during the trial run under load it was difficult to exceed 1/2 throttle. I also found that I could not properly trim the engine. I measured the transom angle at 9.7 degrees, so it will require some modification. I also brought along buckets of sand/dirt to simulate the weight of a second person and gear. The DWL displacement of the skiff is 660 pounds. The first test was primary and secondary stability to get a feel for the boat. I found that the boat was very stable with loads over the floor (much more than my Old Town Penobscot and Discovery canoes). With me sitting on the side deck of the boat, it certainly leaned over as one might expect, but I was quickly comfortable with the secondary stability. While underway, I moved the center of gravity along the length of the boat, and I found that the trim was not overly sensitive to the speed of the boat. I did finally get the engine to near full throttle (8/9ths) prior to it stalling again, with a displacement of 611 pounds the boat achieved 11 MPH. There is still room for improvement given that the hull was not sanded and painted, the fiberglass tape seems are still showing, the engine needs tuned to reach WOT, the engine trim angle is incorrect, and the boat trim could be further adjusted. Handling was really smooth in all conditions (flat, small waves, both weight configurations, forward and rear trim angles, straight, and turning). I am very impressed with the performance of Jurgen's design and his optimization of all the key characteristics on a small boat, especially considering the power efficiency. I plan to follow through with sanding and painting this Spring when the weather improves.

    The video of the test trial is shown here: https://www.youtube.com/watch?v=7GgBhkDkzmk
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  8. #8
    Join Date
    Jan 2003
    Location
    Southern Maine
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    21,361

    Default Re: Keyhaven Skiff Build

    Nice practical boat. I was expecting a version of the Keyhaven scow when i opened the thread.

  9. #9
    Join Date
    Dec 2012
    Location
    59* 24' N 18* 21' E
    Posts
    36

    Default Re: Keyhaven Skiff Build

    I have changed the Delftship file so that the interior is decoupled from the hull. It should therefore be easier to shape the different parts the next time a boat is built.
    I have received very positive reviews about the seven-meter boat for fisherman in Gambia. That boat has basically the same shape as the Keyhaven Skiff.
    Right now I'm working on a six-meter boat for three person and planing speeds. It will be equipped with an engine of six horsepower and an aft-ship interceptor.

    JS
    www.sassdesign.net
    I'm not lost, I'm just uncertain of my position.
    I'm still confused, but on a higher level

  10. #10
    Join Date
    Oct 2019
    Location
    Ladysmith, BC
    Posts
    6

    Default Re: Keyhaven Skiff Build

    I have been really wanting to see one of these go together, ever since I first saw the origin back in the low power planing boats thread. I was quite disappointed that it didn't proceed at that time; seeing one built is pretty interesting. I am currently exploring the idea of a low-powered, seaworthy skiff for my area (the Gulf Islands of BC, Canada) when I don't want to plow the glass tank around and this is the first time I've seen one of Jurgen Sass' designs built by a home builder, so it's quite illuminating.

    Having a spare 9.9 Merc that doesn't get much use as a kicker on my big boat, I'm more than a little inclined to study his ideas.

    Fantastic looking little skiff; I like the longtitudinal seating layout also.

  11. #11
    Join Date
    Aug 2018
    Location
    Prince Frederick, MD USA
    Posts
    19

    Default Re: Keyhaven Skiff Build

    Sorry for the long time between posts, but a lot of progress has been made...

    I started the project again this past June, including adding the bow and transom rope holes and adjusting the transom angle. A lot of fairing was required (byproduct of re-cutting the panels during the switch from stitch and glue to mold process) and then I followed up with Total Boat topside primer. It took a several weeks to dry, and even then it was very difficult to sand. I thinned the primer paint prior to application to keep the coat thin as suggested. I washed the hull with water and denatured alcohol prior to applying, and it was in the mid 80s with high humidity. I suspect the biggest issue was a reaction of the denatured alcohol with the Raka epoxy (127/350). Does anyone have any guidance on this issue? I then tipped and rolled thinned Total Boat Topsides Paint, but it it was drying too fast to properly tip. Ultimately, the paint did not adhere well to the substrate, and I had to strip the hull back down to the epoxy. That was maddening...
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  12. #12
    Join Date
    Aug 2018
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    Prince Frederick, MD USA
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    Default Re: Keyhaven Skiff Build

    This time I used mineral spirits to clean the hull, and then I primed it again with thinned TB topside primer. It dried quickly and was easy to sand minus about a dozen spots. I stripped those trouble areas back down to the epoxy and followed up with more primer. I followed up with the TB topside paint, but this time I sprayed it. That seemed to work much better in the hot and humid environment. After several coats, I flipped the hull and faired the inside along with adding a front seat. I did not add a rear seat because I want to work out some more details first (remotes for power and steering and trim for 1 vs. 2 people). For the inside of the boat, I switched to the Rustoleum marine primer and paint products. That primer was easier to work with, but I did have a bad sinus reaction to it after sanding when my respirator was unknowingly leaking. That took several weeks to clear...
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  13. #13
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    Aug 2018
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    Prince Frederick, MD USA
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    Default Re: Keyhaven Skiff Build

    I ran a somewhat controlled trial to document the performance. The boat hull weighed in at 179 pounds (includes the hatch assemblies). With a 1990 Evinrude 3hp engine, 7.5x7 propeller (slightly irregular edge), and the equivalent of two adults and gear (592 pounds total displacement), the boat averaged 10 knots. I ran the boat in a slower portion of the river with/against a slow tide and across the current flow in both directions, and the speeds varied from 9.6 to 10.3 knots. The boat rides very soft in the water, it handles great, and it is very capable in rough water (I have been in 3 foot waves with white caps). The boat can be seen in action here - https://www.youtube.com/watch?v=SlVtI0wISZA
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  14. #14
    Join Date
    Oct 2019
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    Ladysmith, BC
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    6

    Default Re: Keyhaven Skiff Build

    Great looking little boat; glad to see one of these get built. I notice fishing gear in the video - how do you find this hullform for fishing out of? That was one concern I had with some of Jurgen's designs - are they stable enough at rest to fish well? This is the first home build I have seen of one of his boats.

  15. #15
    Join Date
    Aug 2018
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    Prince Frederick, MD USA
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    Default Re: Keyhaven Skiff Build

    We fished for two days at Lake Quemahoning, PA with two adults and one 12 year old on board. Although a little crowded, it was stable enough for all of us to stand and cast. The key thing is to stay between the two longitudinal floatation chambers, otherwise it will lean over. Secondary stability is very good for the boat, but not necessarily for a standing person. Stability is far superior to my Discovery 169 canoe, which we also fished out of on the lake that weekend.

  16. #16
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    Oct 2019
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    Ladysmith, BC
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    6

    Default Re: Keyhaven Skiff Build

    Good to hear! If you were in it by yourself, could you sit on one of the floatation chambers to net a fish, do you think?

  17. #17
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    Aug 2018
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    Prince Frederick, MD USA
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    19

    Default Re: Keyhaven Skiff Build

    The picture above shows me sitting on the floatation chamber in calm water. Leaning is probably not an issue, shifting your weight on top of the floatation chamber is probably not a good idea, especially if there are waves. Maybe the bigger factor is the floatation chamber is only 9" wide and the gunnel is maybe 16" above the water. So it is not much of a reach.

  18. #18
    Join Date
    Oct 2019
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    Ladysmith, BC
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    Default Re: Keyhaven Skiff Build

    Derp - my brain must have been out of RAM when I read that post; I didn't register the picture or the link. That looks like a fantastic little boat for low power on relatively protected waters.

  19. #19
    Join Date
    Mar 2017
    Location
    Owings, MD , USA
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    6

    Default Re: Keyhaven Skiff Build

    Howdy from Calvert County , I'm up the road in Owings.

    Great build , I have a great running Mercury 5hp that I've been looking for a project for. The design you chose might be a good choice.

    Have you had it out in the Bay yet or taken it down by Solomons? I usually launch a wood runabout out of Chesapeake Beach but it takes a 25hp to run halfway well in the Bay.

  20. #20
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    Aug 2018
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    Prince Frederick, MD USA
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    Default Re: Keyhaven Skiff Build

    Is your boat finished clear? If so, I might have seen you at Hallowing Point a few years ago. The Bay is a bit much for the Keyhaven, especially now that the water temperatures have dropped into the 50's. This Fall, I have been on most of the tidal Patuxent and on the Potomac a couple of times. I think I spoke to you on Facebook about the 5 hp Mercury. The 3 hp 2 stroke Evinrude that I have is very loud and is only good for about 5 or 6 miles before it needs refueled.

  21. #21
    Join Date
    Aug 2018
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    Prince Frederick, MD USA
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    Default Re: Keyhaven Skiff Build

    Reflecting back to the original intent of this build, I cannot understand the absence of small semi-planing hull designs? On a family outing side by side with my Old Town Discovery 169 canoe similarly loaded and both with trolling motors - both boats were at the same wattage at about 4 mph. However, the canoe power vs speed curve starts to go vertical at that point and the Keyhaven is closer to a linear proportional curve up to 2X hull speed (~11 mph). The Keyhaven significantly outperforms the canoe on power vs speed, seaworthiness including the gentle ride through wakes, stability, comfort, etc. It is not a car topper at 179 pounds and it is not as fast as a planing hull, but I am thoroughly impressed with how well it fills this specific performance void between displacement and planing hulls. If someone has feedback to the contrary for small semi-planing hulls, I am interested to understand. I made some minor modifications to the trolling motor, and the Keyhaven goes 6.4 mph at 760 watts. Not bad for two Walmart batteries and about $400 for the motor setup, and there is a lot of room for improvement with lithium batteries and brushless motors...
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