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7000550% heavier.. WAS.. [bolger] Re: Options for ply thickness for similar sharpie construction on simila

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  • Chief Redelk
    Dec 24, 2013
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      Quote..<If you assume that ¼” and 3/8’” plywood have equal densities,
      3/8” weighs 50% more than ¼”. If you assume a straight substitution of
      3/8” for ¼” (with no change in framing), then a hull made if 3/8” will
      weigh 50% more than an identical hull made of ¼”. >

      John, not doubting you but my thinking went like this..

      If a boat would weigh 60 lbs in 1/4 ply it seems 3/8 ply would be
      adding only 1/3 more wood..it should weigh 1/3 more..For example a 90
      lbs boat normally made out of 1/4 built with 3/8 ply should have 30
      lbs more wood added so it seems it would weight 120 lbs built using
      3/8 ply...

      From what I understood in your quote that same boat would weigh 90lbs
      + 45lbs and equal 135lbs. net weight finished..15 lbs more than my
      figures....

      I can see that if we build 1/2 ply instead of 1/4 we should have
      doubled the wood and therefore doubled the net weight.

      But when we change from 1/4 ply to 3/8 ply we did increase our wood
      thickness by 1/3 but how can 1/3 more change the boat to half as much
      again..?..

      Can you explain how you did the math to get 50 percent more weight..

      If I build a small boat in 1/4 and it comes in net weight at 90 lbs
      it's much to heavy for me to handle without a trailer..

      SO IF I build that same boat using 3/8 and it comes in only 1/3
      heavier and rides on a trailer I can live with that and in my mind is
      not a big difference in net boat weight..

      In fact I can live with 50 percent more weight but I am not sure how
      you got that figure.

      I did the math a few different ways and once I got the same figures
      you did. I am not sure what I did to arrive there,, smile..

      If you have the time would you explain your math..I mean how did you
      arrive that 3/8 ply would be 50 percent heavier..?.. Is that just a
      known standard...?

      Thanks, Chief..

      On 12/24/13, John Trussell <jtrussell2@...> wrote:
      > If you assume that ¼” and 3/8’” plywood have equal densities, 3/8” weighs
      > 50% more than ¼”. If you assume a straight substitution of 3/8” for ¼”
      > (with
      > no change in framing), then a hull made if 3/8” will weigh 50% more than an
      > identical hull made of ¼”.
      >
      >
      >
      > There are a variety of ways to address boat weight, strength, and
      > stiffness.
      > Decks which are not intended to support people (such as those on kayaks)
      > can
      > be very thin (and some of these are made of fabric). However, very thin
      > bottoms don’t work very well due to flexibility and lack of durability. The
      > trick is to use thicker stuff where you need it and thinner stuff
      > elsewhere.
      >
      >
      >
      >
      > Another approach is to support relatively thin skins with closely spaced
      > framing. Some examples, such as skin on frame boats are obvious. Others,
      > such as the stringers on cold molded boats, the laps on lapstrake boats, or
      > even the fillets on stitch and glue boats are somewhat less obvious.
      > Another
      > possibility is to box in the space between longitudinal thwarts and the
      > bottom of the boat, creating box girders for torsional stiffness and for
      > adding a longitudinal frame on the bottom.
      >
      >
      >
      > Finally, it is possible to add strength and stiffness to a hull by adding a
      > layer of fiberglass on the outside of the boat. Many strip build boats add
      > a
      > layer of fiberglass on the inside and outside of the boat creating a wood
      > cored fiberglass boat. This can create a very light, strong, and stiff
      > boat.
      >
      >
      >
      >
      > All boats are compromises and one of the areas of compromise is scantlings.
      > Many stitch and glue boats were designed on the premise that they would be
      > built out of readily available, construction grade material and ¼” works
      > pretty well for most small boats. But without constraints dictated by the
      > need to market boat plans, it is likely that many small boats would have
      > heavier bottoms and thinner sides.
      >
      >
      >
      > JohnT
      >
      >
      >
      > _____
      >
      > From: bolger@yahoogroups.com [mailto:bolger@yahoogroups.com] On Behalf Of
      > Chief Redelk
      > Sent: Monday, December 23, 2013 5:40 PM
      > To: bolger@yahoogroups.com
      > Subject: Re: [bolger] Re: Options for ply thickness for similar sharpie
      > construction on simila
      >
      >
      >
      >
      >
      > I made that discovery on small boats too..
      >
      > I am of the opinion that 3/8 plywood is MUCH stiffer than 1/4,
      > stronger and not a lot heavier..
      >
      > I find a full 3/8 plywood deck well supported works well..When I
      > design a deck that will be walked on I think of picture frames or 4
      > sides boxes 12 inches wide by 12 inches long by 3 inches deep..Bracing
      > like that well supported then covered with 3/8 ply is very strong..I
      > think that a brace every 12 inches is my standard.. Ribs once were set
      > that close but on some boats I open them up to 16 inches.. However,
      > Stitch and glue boats don't fit that rule..
      >
      > My next boat will have a 3/8 plywood bottom, 3/8 decks and maybe 3/8
      > all over.. BUT since it's gonna be a 12 feet long scow maybe I will
      > make the sides out of 1/4 ext ply...BUT the fact is I am not sure the
      > weight difference is worth all the trouble of using two thicknesses of
      > plywood..
      >
      > In my mind there are TWO boat options when it comes to materials.. ONE
      > for boats on trailers and the other ONE for boats designed to be
      > LIGHT.. Since I trailer all my boats, just a tad Heavier is not a
      > problem..
      >
      > I am not talking excessively Heavy boats or over built boats.. just
      > boats using 3/8 versus 1/4 plywood..1 inch by 1 inch bracing is good
      > IF it's not hanging in the air..Well braced boats need to be
      > overweight.. Good day, Chief..
      >
      > On 12/23/13, MylesJ. Swift <mswift@...> wrote:
      >> I ended up doubling the ¼ inch bottom and main deck on my Micro. With
      >> four
      >> 200pounds plus guys dancing on the deck it flexed too much for my
      >> comfort.
      >>
      >>
      >>
      >> MylesJ
      >>
      >>
      >
      >
      >
      >
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