Questions about stitch and glue...

[Mark42]

I see that most stitch & glue boat plans call for 1/4" marine plywood and a few layers of fiberglass on the outside and one or two on the in side. How much strength is the 1/4" ply contributing? Would any other material that absorbs the resin work? What if plywood is covered in plastic drop cloth and used as a "mold" and multiple layers of fiberglass to 1/4 or 3/8 or 1/2" thick? Would that be as strong? Just trying to avoid having wood in the hull because I don't want water soaked core if the hull is damaged when I hit a rock or something (and I know that will eventually happen). I see that my MFG is solid fiberglass hull only about 3/8" thick. I know it was made in a pressure mold, so hand laid should be thicker for the same strength?<br /><br />Not ever having done fiberglass layup on plywood before, I am slightly leary of the thought.

 

[crab bait]

Re: Questions about stitch and glue...

most i see is 3/8's..<br /><br />you can do what you like.. but the designers know what they are doing.. <br /><br />as per addin' fiberglass thickness,,, weight, weight an more weight..can't make it bullet-proof.. <br /><br />contact plan company an ask..<br /><br />a S & G boat is stronger then any bar-none 'cept for steel & weld..

 

[Rudderman]

Re: Questions about stitch and glue...

I would imagine that the plywood is providing most of the structural strength and that the fibreglass is just providing a waterproof covering and a more scratch resistant surface than paint. On most of the plywood boat plans I've seen, they emphasise that adding extra layers of fibreglass on top of plywood in the hope of strengthening up a badly made hull will not work.

 

[rogerwa]

Re: Questions about stitch and glue...

You can use a foam core in a fiberglass sandwich. With the plywood everything is covered with epoxy and if glassed shoud be impervious to a breach. I have even seen people integrating kevlar or carbon fiber but this has been regarded as overkill.<br /><br />Not all boats use 1/4". Some use a combination of thicknesses depending on the portion of the hull.<br /><br />I am building a S&G canoe in my garage and I have absolutely no issue with the rigidity or durabliltiy of the PW in this application. I am not even glassing the outside.<br /><br />I am gluing and taping the seams and I have to tell you this thing is rock solid and is quite a bit lighter than comparable sized canoes. This weight relationship applies to the larger boats as well. This translates into less HP and better MPG.<br /><br />Checkout this site for more info and a discussion board on S&G construction.<br /> http://www.boatplans-online.com/index.php <br /><br />Here is a link to my canoe assembly from start to finish.<br /> http://forums.bateau2.com/gallery/thumbnails.php?album=193

 

[prockvoan]

Re: Questions about stitch and glue...

What size boat you are looking to build?Here in Louisiana,one would never build a boat of wood,then come back in put fiberglass on the inside and out!By doing that,the wood will rot in no time.Wood has to breath,cut and dry,thats all there is to it!Don't know were you getting your info,but I think you need to do some more reserch into boat building.<br /> I myself built my first boat,a 14' pirouge( for ya'll yanks,a canoe) when I was 12 years old,its still around.Been building them from wood till about 15 years ago.The cost of wood compare to fiberglass compare to Alum,I would go with Alum.<br /> What type of boat you planning on building?

 

[rogerwa]

Re: Questions about stitch and glue...

Production FG boats have been using wood cores for years.. So long as you encapsulate the wood entirely, you won't have rot. <br /><br />The S&G method totally encapsulates the wood. There are several amateur boatbuilding sites and production firms that use this method. If you breach the glass and resin, then you will get rot.<br /><br />Its a good thing I don't live in La..

 

[petrolhead]

Re: Questions about stitch and glue...

Several of us here have built plywood Glen-L designs and epoxy encapsulated them, if you go to the Glen-L site you'll find many people restoring old Glen-L boats that have been encapsulated and they haven't rotted away. Encapsulation is the method Glen-L recommend, they are professionals who have been in the business since the early 1950s, I think they've probably done a fair bit of research into boatbuilding in the past 50 years. <br />And they are far from being the only ones who use this method, there are many professionals who use encapsulated wood in one way or another, if not for the whole boat then at least for stringers, roofs etc... They only rot when the water gets in, provided the encapsulation is complete they last just fine.<br />My father-in-law's boat needed a new cabin roof last year, it was a balsa end grain core encapsulated in glass, the core had rotted in places but only where some fool had drilled into the roof to attach something and failed to seal the holes! Where the core was still sealed the wood was as good as new, this is a 30 year old boat, and balsa is not noted for good rot resistance!

 

[Mark42]

Re: Questions about stitch and glue...

Wow! Thanks for all the input. You all have given me a lot to think about. Regarding the type of boat, what I am trying to do is build or modify a boat that will meet my families needs:<br /><br />- V-birth bed/table combo. <br />- Full stall head with portable toilet.<br />- 2 foot of counter/galley space to make lunches and keep cold foods, sink and 5 gallons fresh water supply.<br />- Helm inside with bench seating for 2.<br />- Seating for 6 adults. <br />- 6 foot headroom in all areas except v-birth where 4" would be acceptable.<br />- Full "hard" enclosure, not canvas. <br />- Sun deck on top.<br />- Permenant fuel tanks.. 50 gal?<br />- Now the hard part... Make it all fit in 19' and cruise at 25mph with 70hp o/b. Maybe use transom bracket to offset o/b and regain motor well space. <br /><br />I'm thinking of a floating camper to go out for the day, visit secluded areas, have all the food and drink needed, protection from sun and wind, place to take care of young kids without having sand all over the place. I remember how much space there was in that little camper that sat on the back of my Dad's pickup. Had kitchen, full enclosed toilet, slept 4 adults, TV, stereo, etc.<br /><br />Don't really need an open cockpit. Although I am trying to think of an easy way to enclose the back of the boat with removable plastic panels sort of like storm windows. Want to have a full rigid roof from stem to stern. Maybe with ladder access to roof but that means more structure support and therefore more weight. I want it to be an economy machine, not a luxury high speed cruiser with high operating expenses (gas).<br /><br />I am working on some drawings based on modifications of some Glen-l and boatplans-online.com. I usually do a lot of planning and cost estimating on any project I do to keep surprises to a minimum and to decide if it is feasable. So... I have a lot of research to do. If I were to build from scratch by modifying existing plans, I would get the OK from the plan designers on my modifications before doing anything. It would be cheaper and quicker to buy a used bow rider or cuddy cabin and modify it.<br /><br />Anyway, I am now rambling.<br /><br />Thanks again for your interest.<br /><br />Mark.<br /><br />Ps, I am in no hurry, I have the Niagara to use all next season!

 

[CalicoKid]

Re: Questions about stitch and glue...

It is not the plywood alone that gives strength and it is not the fiberglass alone that gives strength. It is the combination of the materials laminated together. Actually, epoxy penetrates wood so deeply that it becomes a matrix, a singular structure made of multiple materials posessing different attributes. Racing sailboats have been returning to wood and epoxy/fiberglass (or carbon) hulls because the wood handles repeated stress loading so well and holds tight to the epoxy better than other materials like straight glass cloth or carbon cloth, which eventually "loosen up" in the epoxy on a nearly microscopic level after being through stressful load cycles. This never leads to hull failure but after several races a hull can lose some of its initial stiffness. Of course these are ultra-light boats that are not tolerant of any loss of rigidity because it could mean losing tenths of seconds in a race. A homebuilt cruiser is going to be totally overbuilt compared with a racing sailboat and the above is merely trivia beyond the point that wood, epoxy and fiberglass make a hell of a sturdy boat.

 

[crab bait]

Re: Questions about stitch and glue...

the downfall of S & G is that it can't/shouldn't/good luck in findin' plans of a boat over 20 ft.. more like 18 ft. .. <br /><br />over that,, it's conventional frame build up construction..<br /><br />PETRO is sooo right.. glen-l is the poop..<br /><br />and an encapsulated wood hull (UN-BREACHED) is/well be an heirloom..<br /><br />an slapping ' chauk/silicone' on an hole IS NOT a proper seal..

 

[lark2004]

Re: Questions about stitch and glue...

ya, crabs right there, If you get a breach, sand it back, let it dry then re-apply the glass(if needed) and epoxy,<br /><br />Do it right, do it once!

 

[AG]

Re: Questions about stitch and glue...

Go to www.devlinboat.com (I think I have it right)... They specialize in S&G. I built a 16.5 footer, I live in New England where the water and temperatures are pretty interesting. My boat is tough as nails, I love S&G.

 

[geezOREGON]

Re: Questions about stitch and glue...

The Gougeon Brothers (West System epoxy) have books about doing what you are proposing (wood frame used as mold for fiberglass layup). The book on vacuum bagging is probably the one you want. I got mine at Armchair Sailor in Seattle. They are online. Your local marine store may have copies as well.<br /><br />Basically, you build your wooden mold, cover it with plastic, lay your fiberglass blanket and epoxy, cover with a bag, and use a vacuum to suck out the air so ambient air pressure evenly holds the epoxy/fiberglass to the wooden mold while it cures.<br /><br />I agree with a prior poster that plywood stitch and goo is probably not the approach you want to use for the size of boat you want. You will need framing for a boat that size. Stitch and goo is nice for avoiding putting much framing into a relatively small boat.