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Thread: Building a skiff

  1. #1
    Site Supporter Maple Syrup Actual's Avatar
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    Aug 2011
    Northern Fur Seal Team Six

    Building a skiff

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    I mess around with boat design a bit. My first boat was of my own design, a sailboat I had almost twenty years ago. Iím not particular about using my own designs, though; the last boat I built was someone elseís design. But sometimes I want some particular thing and I figure I can do it well enough that thereís no point in trying to adapt someone elseís design to my needs.

    I have been wanting a simple skiff for a while, maybe to keep at the cabin, but maybe to use around the islands and keep at home. Something lighter and simpler than the big I/O Double Eagle, which is a tank but not really ideal to fish from: small dance floor, big doghouse. I loved it for crossing the strait but now that Iím mostly just inshore fishing in protected waters, itís a bit cumbersome.

    At first I was going to do a really oddball design; now that I have a kid I donít spend money as freely so I was going to build a skiff that would plane off with my kicker, which Iíd have to re-prop but it would work. Thatís how I got it in my head that Iíd need to do my own design for this one; not too many boats designed to plane with a 9.9 XL shaft motor. So I worked on that design for a while; it would have to be pretty narrow, or else dead flat. It was kind of an interesting exercise but then one day my dad emailed me to see if I wanted his friendís í79 Johnson 20hp. Heíd bought it new and maintained it well and it didnít have a ton of hours, but he hadnít run it in 20 years and was going to scrap it.

    Sure, Iíll take that. 20hp off a two stroke? Way easier to make a good basic skiff thatíll run well with that power. What kind of shape is it in? Well, not many hours on it, but it's 40 years old. The owner maintained it well, I think; I picked it up and looked it over. Grease on all the relevant points. Clean under the cowling. Unbelievably light weight compared to what we're used to now. I remember it being on a 14' aluminum Mirrorcraft we fished out of Bamfield when I was about eight years old.

    So I shelved my 10hp designs which, while kind of interesting, would have been pretty tender to fish from. Now I have an easy task: a skiff without a crazy amount of deadrise, but no need to flatten it completely. As long as itís stable and light, it should be fine. And thenÖthereís my complete inability to leave well enough alone to contend with. So why not complicate things by paying homage to the lines of classic BC commercial salmon trollers? I love the way those double-enders look, with their almost tugboat-like proportions. Naturally this canít be a double ender if I want it to be fast, but still, I could incorporate those workboat lines.

    And if Iím doing that, why not run a fairly plumb bow? I could carry the keel forward a long way, extending the waterline length and increasing the theoretical hull speed, like a Chesapeake deadrise boat. Theyíre a bit sensitive to following seas but Iíll work around it. Get that wave-piercing axe-bit of a forefoot to soak up some chop, should smooth out the ride on an otherwise very shallow-V boat.

    Okay, here we go.

    Step one: get the motor running. Otherwise, the project isnít that viable.

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    I designed a boat and now I'm building it. This is where that's happening:

  2. #2
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    Away, away, away, down.......
    I didnít understand much of the design talk, because a mariner I ainít. But Iím looking foward to this .

    Also, your island posts always make me regret not putting forth more effort with gal I met down here on the other side of the continent whoís family owns a nice place on Denman Island up around your parts.
    "I don't know if it is a placebo effect or not, but I have a growing feeling of well being that comes directly from my instinctual survival drive deep in my belly centerĒ

  3. #3
    Site Supporter Coyotesfan97's Avatar
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    Mar 2011
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    That sounds like a great project. Iím looking forward to this thread.
    The bravest are surely those who have the clearest vision of what is before them, glory and danger alike, and yet notwithstanding, go out to meet it.* Thucydides 471BC

    "Hey! Let's be careful out there." Sgt Phil Esterhaus played by Michael Conrad

  4. #4
    I Demand Pie Lex Luthier's Avatar
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    Feb 2015
    Pig's Eye, MN
    I mostly don't care much for motorized watercraft. But I love boats as a general thing, and the waters in that part of the world in a surprisingly visceral way. Boat design is one of the things I have not yet done in a serious way.
    So, following.

    You had best name the product Alaric's Seahorse...
    Cranky and flatulent.

    "I'm not illiterate! My parents were married."

  5. #5
    Cool! Iíve built a simple stitch & glue canoe, and the design review is one of my favorite features in WoodenBoat. Looking forward to this.

  6. #6
    Site Supporter Maple Syrup Actual's Avatar
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    Aug 2011
    Northern Fur Seal Team Six
    Denman does have a lot going for it. One of my old girlfriends is from there originally, actually.

    A super quick primer on boat shape for anyone interested...

    Boats basically have two speed ranges, displacement, and planing. Displacement is like the fastest speed you could push a smooth, pointy log through the water. Planing is like skipping a rock on the surface. If you've ever gone for a swim, you can probably imagine that it doesn't take much of your strength to push a 500lb log gently through the water. But to skip a 5lb rock would probably take everything you've got in one arm. So planing is much, much faster, but much more power-intensive.

    Typically with boats you have this issue where as you speed up, the boat creates this big wave in front of it, so slowly accelerating takes more and more power and gets less and less efficient as the wave builds in size. At some point, usually around 15mph (13ish knots, boat people still use those in the hope we will be mistaken for airplane people) you need to jump to about 20mph to climb on top of the bow wave. Once you do, the boat flattens out and your fuel consumption drops a bit relative to your speed.

    Displacement speed is basically a function of the length of the boat. There are other factors but basically, the longer a boat is, the faster you can push it through the water before it needs to plane to go any faster. This is really oversimplified and there are a bunch of exceptions but the longer the waterplane, the faster you can gently cruise.

    Planing is more complicated - it's not all that well defined, actually. It relates to generating laminar flow of water off the transom and a bunch of other stuff. But you need the bottom to be fairly parallel surfaces with a hard edge at the stern so the water separates cleanly. This is exactly the opposite of what you want for a displacement hull - that you want to look like a canoe, ideally. Slippery, smooth curves, with minimal disruption at either end. But you can't plane a canoe. The water kind of sucks to the hull and pulls it further down at the back and you end up pointing at the moon.

    Similarly, the more flat transom you have on a powerboat, the more the water kind of sucks the transom down, but once you get enough speed to get that laminar flow off the bottom and the back of the boat is dry, the suction is gone and you're off to the races.

    So there's this mix of compromises you need to make. The skiff I've designed has a pretty deep forefoot and the keel is pulled all the way to the bow so it has as much waterline length as I could give it. The V-shape of the hull is fairly shallow. This makes it easier to get that laminar flow and immerses less of the stern, so it'll plane with less power. Of course, it'll also pound more in rough weather: a really deep V is like diving into water; a flat bottom is like belly flopping. But as long as the hull stays in the water instead of dropping off a wave, it should be all right.

    There are downsides to that particular set of compromises but there always are. In this case the sharp, deep bow means that if I plow it into the back of another wave it'll really want to keep right on going in whatever direction it started. Imagine swinging a pipe through the water: it would change direction easily, compared to swinging a machete, which would take less effort but really want to keep on going in the same direction.

    But this setup should plane with low power, and transition from displacement speed to planing with minimal bow wave, so it ought to just accelerate smoothly to speed without having the awkward "hump" of deep Vs.

    That whole explanation was unplanned and not well organized, but maybe it illustrates a little bit about the design choices I made.
    I designed a boat and now I'm building it. This is where that's happening:

  7. #7
    This is reminding me a lot of the Patrick McManus story Easy Ed.

    Will stay tuned.

  8. #8
    Site Supporter Maple Syrup Actual's Avatar
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    Quote Originally Posted by Dan Lehr View Post
    This is reminding me a lot of the Patrick McManus story Easy Ed.

    Will stay tuned.
    I'm not super familiar with his writing but now of course I'll have to check it out.

    In the meantime...Preliminary steps

    I wired up the garage with a couple of outlets today; there was no power in it at all before. Now there's rudimentary power out there. Good enough for now and even if the motor is junk and the project gets scrapped, itís still worth doing. As is getting that wood stove going.

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    With the wiring in place, the infrared quartz heater is up and running. I then spent some time on the stove, taking it apart a bit and replacing a couple of those fiberglass rope gaskets. Now I have it back together, the gasket adhesive drying. Tomorrow I might have a little fire in it just to see if it's sealed up properly. I guess I'll have to get a section of 6" stovepipe just to test it out. I probably should have bought that today but I didn't know if I'd get this far. If it seems reasonable, I'll pump more furnace cement in all the seams and build some kind of simple chimney, and cut some flashing into the garage roof.

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    The old Johnson is in pretty decent shape, all things considered. It turns over and thereís spark, so probably a carb refresh and an impeller will make it run. I fed in some seafoam to the throttle body just to get the thing lubed up a bit, and pulled her over a few times. Doesnít feel bad. A spritz of seafoam, a pull, a spritz, a pull, repeat for a while. I gave it a hard yank after about 20 minutes and she fired up, running briefly on the naptha in the seafoam, I guess. Okay, pretty encouraging. But no love off the gas tank, so I think the carb rebuild is unavoidable. New kit, plus new water pump with all the bits, and a Johnson gas tank fitting so I donít have to use the ancient metal tank it came with, all in for a little under a hundred bucks from Amazon. Should be here in a few days.

    In the meantime, Iím rendering the skiff design, or at least the panels, in Delftship. The software is a bit glitchy but should be sufficient for this design. Itíll get built in glass-ply-glass composite sandwich, with epoxy resin. Should be very light and strong, although itíll eat a lot of resin. The hull will be ľĒ ply with 12oz biaxial fabric on either side. Iíll try to squeeze it into 10 sheets of ply, and will probably burn 10-12 gallons of epoxy glurping it together. Thatíd put the weight at about 300 pounds.

    I think a 16í skiff around 300lbs should motor along okay with a 20hp two stroke. Of course, I suspect the only difference between the 20, which was a down-regulated Canadian-only motor, and the 35, was the carb. Maybe the intake. And the same skiff with 35 hp will really move.

    And so the project begins.
    I designed a boat and now I'm building it. This is where that's happening:

  9. #9
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    You are going to have a fun time building that boat! I look forward to seeing your progress.

    I've built a couple of very small skiffs for duck hunting and for general putzing around on a pond. There is something very satisfying in building a little boat yourself and putting it in the water.

    Resurrecting the old Johnson outboard will be fun too! Please post plenty of pictures.

  10. #10
    Quote Originally Posted by Maple Syrup Actual View Post
    I wired up the garage with a couple of outlets today; there was no power in it at all before. Now there's rudimentary power out there. Good enough for now and even if the motor is junk and the project gets scrapped, itís still worth doing.
    One thing I learned from my boatbuilding project was that you can't have too much light. If I do another one I'll upgrade the lighting in my workspace before I start building.

    You also can't have too many clamps, but that comes later.....

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