New Adventures! - 1st time building a boat - Quattro 16

Discussion in 'Multihulls' started by danboyk, Sep 10, 2010.

  1. SoCal Ken
    Joined: Jan 2011
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    Location: Southern California

    SoCal Ken New Member

    Response to Ray's post: Congrats on a very nice looking boat. You may have several things working in your favor - hull bends don't look too significant & your ply is birch, not Douglas Fir, which is what's available here in SoCal (if not using marine grade & 1/4" being the thinnest generally available, unless you go do Luan "doorskin"). Less familiar with Birch ply, but Doug Fir is know for checking horribly after a few years, which is what starts the problems. My kayaks lasted about 3 years (left outside also) before the problems became very obvous. You also don't specify what thickness of ply you're using & what thickness is called for by the designer. Quattro 16 (and the CLC kayaks) is/are designed for 4 mm ply; 1/4" douglas fir equates to 6 mm. Trying to bend 3-layer, 6 mm ply around bends designed for 5-layer, 4 mm ply was probably doomed from the start. You make a good point about using the ply thickness called for by the designer. My point is simply, for me, I will never build another boat without using marine grade ply. I'm still of the opinion the additiional cost is only a small fraction of your overall expense in time and money. I'd like the quattro I'm building to last more than just 5-6 years. Thanks for the input and I wish you well on your projects.
     
  2. rayaldridge
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    rayaldridge Senior Member

    Thanks, Ken. I must admit to being the designer. Slider was drawn to use 1/4" ply, which is approximately what the underlayment is (actual 5.5 mm).

    A lot of builders have used this stuff, and it seems to be lasting well. I'd be surprised if it were unavailable in CA. Still, if your budget can cover marine ply, it is of course superior.

    By the way, I was astonished at how well the Multiply bent around tight curves. My cockpit coamings on Slider were built from two layers of the stuff.

    [​IMG]

    This is where I might expect to get some delamination, were that going to happen, since I neglected to glass these coamings, and the paint tends to wear off them pretty rapidly, exposing the end grain. But so far, there is no sign of any trouble.
     
  3. ThomD
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    ThomD Senior Member

    Awhile back I built a boat for which the specified material for the main hull was luan doorskins. The designer was so (rightfully) complimentary about doorskins, and said so many nice things about them, that when I got to the part about stressforming my amas, I completely missed the fact i was supposed to use 1088 ply for them. 4mm doorskins are a lot rattier than 3mm doorskins, but some careful building later, I got the boat together, and she is still going strong 20 years later. What happens is that if your boat calls for complete encapsulation, at least externally, you can get away with plywood that doesn't even have marine glue, but that is certainly a bad choice. But any old crap with outdoor glue that is completely encapsulated will hold up for ever. The key phrase is the whole complete encapsulation, and also the competent detailing. Detailing is never covered in depth in the plans, and is what you learn while repairing boats that have fallen apart, so it's a painful outlook for the beginner.

    By the way, while people go off the reservation plans wise on a lot of things, with multihulls one of the stupider substitutions to make if to switch in a heavier material.

    I don't know about the present subject, but most boats have very few numbers associated with them. Designers just wing it. The dirt has poured out of some well known studios recently, and it turns out a lot of these guys didn't even do basic hydro. Oops. In other words, business as usual for the last 5000 years. I've been keeping track, I know the guys who don't engineer the structure, didn't do weight budgets, and didn't do hydro. John Marples who is one of the good guys and also an engineer, once said (I have this second hand) something to the effect that you could very nearly sheet a multihull in toilet paper, for the loads the sheeting comes under.

    Here is my little boat, you can see what a trip to HD will do for you here, well OK we didn't have HD at the time, but that kind of place...

    http://www.youtube.com/watch?v=BnLmKXY-FCg&feature=related
     
  4. rayaldridge
    Joined: Jun 2006
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    rayaldridge Senior Member

    Thom-- very nice boat!

    You're right about winging it-- that's a time-honored tradition for us folks who really don't know what we're doing. I lifted Slider's beam scantlings from Thomas Firth Jones' Weekender, figuring that the latter was bigger, heavier, and had more sail area, so I'd be safe. Now I know a little about cantilever beam analysis, so I can do a better job, but however much you know about a subject, there are still some leaps of faith involved, at least if you're trying to break a little new ground.

    I'm pretty sure Slider would have been fine skinned in 3 mm ply, and with less massive frames, but as a beginner, I tended to always pick the stronger alternative. I'm kind of glad I did that now, since I feel less anxiety about those who are building the boat.

    The other issue here is cost. Slider was drawn to give someone who was willing to do a little scrounging a way to build a handy little cat for a couple thousand dollars. Jim Brown's (and Marples) new design for recycled beach cat rigs, the Seaclipper 20, appears drawn to use inexpensive materials, and as a consequence seems heavier than it really needs to be, if cost and time were less important.

    Anyway, it's a wonderfully complicated subject. As an easily bored person, I welcome this complexity. It means I'll be dead long before I risk running out of new stuff to learn.
     
  5. ThomD
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    ThomD Senior Member

    Thanks Ray.

    Just to be clear, I am in favour of following plans, I'm just saying normally the designs have a less NASA like root than one might think. Beams are a good example. Before the internet, it took a long time to get exposure to beam scantling, at least for the land lubber. Over times I got a peek, as the mysteries unfolded. It was fun to discovered the apparent origins of the progression in these designs. They appeared to be all derived from the solid beams of earlier designs. Then in turn designers would evolve these solid wood design, and running through the numbers later there would be a direct fit.
     
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  6. rayaldridge
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    rayaldridge Senior Member

    Thom, I finally found something I could disagree with you about. I looked at the other video of your tri, Ghosting with Bad Sails.

    http://www.youtube.com/user/Proaconstructor#p/a/u/1/Rrt459Gj0Ck

    I wouldn't call that ghosting, though your boat is undoubtedly going faster than Slider would in a similar light breeze.

    Now, this is ghosting:

    http://www.youtube.com/user/knobmaker#p/a/u/0/-HUajvGd5Yg

    Took me from morning to the middle of the afternoon to make the 18 miles between Ft. Walton and Navarre Beach.
     

  7. ThomD
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    ThomD Senior Member

    I did have a good sail this year in zero wind. One of my daughters was able to swim around us, and yet, for the most part we kept moving. Lot's of fun in some perverse way. It is fun, even sometimes in heavier winds to have the boat balanced so that the amas don't hardly touch the water, and one feels like some kind of master Australian 18 sailor, all the while knowing that without the amas one would loose focus and ditch the boat. You boat was doing nicely, particularly with your Bimini up. What keeps our exercises in low wind interesting is that we don't have an outboard, since it was stolen even before we launched the boat for the first time. Some day we will get stranded, but for now we have been lucky.
     
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