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

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• 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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