- Dec 24, 2013Quote..<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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