View Full Version : Scantlings for plywood fishing boat

10-30-2013, 05:31 AM
I am somewhat confused by the information at hand, as the examples I looked at varies wildly.

The boat (nothing exotic ) under discussion is roughly:
LOA 15'
Beam 6'
Deep V (17 degree deadrise at transom)
Center console
Power by 30hp 2-stroke outboard

What is the typical plywood thickness for this type of craft?
( I am of course going to glass the outside and tape the inside. 6 ounce fabric seems standard for glassing, but I think it is a bit light.
I want to go with a 450g/sqm, which is roughly 13 ounce per sq yard, (a woven roving which is cheap as chips, and of course implies more fairing and sanding to make the structure of the weave disappear.))

10-30-2013, 05:53 AM
Just a guess.

9mm bottom panels

6mm side panels

24 inch frame spacing. 9mm ply

2 longitudinals 12 inch centerline offset. 9mm ply

12 oz 45 45 biax eglass taped seams...one layer outside, 2 layer inside

12 oz 45 45 biax eglass inside and outside skin

structural 12mm plywood cockpit sole, epoxyed to frame floors and longitudinal, bonded around perimeter with one layer
12oz biax eglass tape

transoms are normally 3x12mm ply for small craft

sheer clamp timber or ply is structural

10-31-2013, 12:38 AM
That sounds just about in line with what I was thinking. I was going to see if there is a weight advantage to decreasing the frame spacing, and making the cockpit sole 9 instead of 12.
And that middle panel of the transom sandwich begs to be replaced by a softwood core of pine, with a skin of 6mm ply on either side, but probably rather 9mm. And glassed into the boat with nice large radius cotton flock filled epoxy and three plies of 12 oz biax.

10-31-2013, 02:18 AM
When you add frames you add epoxy. Expensive and also added weight. 12mm okume is a light weight cost effective sole.

A cored transom needs proper detailing and requires that you use best practice for the rest of the boats service life. A solid rot resistant marine marine ply is best.

to save weight you might substitue 9oz biax for 12oz. Difficult to find. Refered to as DB090.

try http://www.fiberglasssupply.com/Product_Catalog/Reinforcements/Knitted_Fabrics/knitted_fabrics.html

the faster the skiff the more hull pounding loads. Be wise when you propose scantlings