Stitch and glue versus fiber glass from male plug

I know that this subject may seem to be too common place, but I can not really understand which system for building a relatively small sailboat (5 m / 16 feet) is best.

Yes, I have seen all the benefits of stitch and glue, simplicity, etc. Yes, I have seen all the good points of those advocating it (and selling the plans), like the bateau.com.

The basic question is: are the designs for stitch and glue available on the internet (including those which are not free) really good ones, or they are targeting people who just want to dabble in the construction, not for those who like to sail. Most of the designs I have seen seem to be better suited for small pools, not for sea.

It is also advertized that the quality of stitch and glue materials (plywood) is much less important. Is it really true? The difference in temperature expansion properties would not debilitate the sailboat constructed with this system?

Finally, the sharpie type hulls would not be much inferior in terms of sailability and the resistence (on a weight basis for the same size boat)?

I am not looking for the obvious answers which can be found on many sites, but a kind of "behind the scene" opinion, is it a salesgimmick for do it youselfers or a real building option.

 

The "best" system is the one that allows you to arrive cost and time effectively at the result intended. Stitch and tape systems work well - I've built boats this way, as well as using strongback and stations for different hull types.

Generally, developing molds and plugs is a technique used for people intending to make multiple copies of the hull. You can develop more complex shapes and curves than tortured plywood this way.

I've seen plywood used for very seaworthy boats - right up to competitive Mini-transat designs and beyond. Quality materials help make a quality boat. In modern epoxy construction, the core material isn't as important as the outside layers of glass/carbon/kevlar. Most cored designs are a sandwich where a structural composite is fabricated. Cores can be foam, lightweight cells, plywood, cedar or whatever.

Hope this helps a little. There are a lot of people here that can perhaps explain things in more depth.

--
CutOnce

 

Most of the designers I know try very hard to present plans that address the home builder's needs and inabilities.

Michail, I'm not sure where your concerns come, from but no one is selling plans to get rich, trust me.

Taped seam construction methods are sound and well proven. As are most of the one off single skin and sandwich cored construction techniques.

Material selections are important and using the proper materials is just logical. The only methods that doesn't need really good materials, are those that employ a core, over which a structural 'glass shell is applied. As a rule taped seam builds do need good quality plywood, not cheap stuff. This said if you're building an 8' dinghy, then CDX may be a logical choice, but if you're looking for a preformance oriented planning machine then BS 1088 Ocoume is the only logical way to go.

Once epoxy encapsulated plywood and 'glass fabrics are married together, then there are no differing expansion or contraction issues to worry about.

It might be best if you read up on the techniques and became more familiar with the different build methods.

As to your "sharpie type hull" question, well it's very unrefined, difficult to ascertain what you're implying or asking and has nothing to compare it to. The sharpie hull form (or one of it's many derivatives and cousins) has it's good and bad points to consider. This has only any value when placed against your specific SOR.

 

Here in Chile, we have "marine plywood". It is about twice as expensive as standard plywood of the same thickness (40 USD / standard sheet 9 mm.). However, it is very difficult to check whether this is really high quality stuff.

Imported plywood (Ocume) would be certainly too expensive (about 100 % mark-up compared to US prices) and most certainly not available, so in this case I would be forced to go with traditional fiberglass hull.

So that question could be refrased, is a reasonably good (marine) plywood good enough for stitch and glue, or it is too risky to use?... (for a 16 footer, but for serious weather in Pacific Ocean at latitude 50 south).

As far as sharpie, I meant "not rounded shapes" which generally are throught to work better in pounding seas and also offer slightly less resistence (better streamlined).

 

Not rounded shaped DO pound in seas, more so then rounded shapes. They also DO have more resistance then a similarly shaped round bilge boat.

I don't know what your plywood rating system is like, so it's difficult to answer what you should trust in your country. Log onto plywood sites and look into the grading systems and the physical qualities that make up a good panel. Also use the search tool here and learn about what to look for in a panel. Most of the issues related to poor construction can be easily seen, once you know what to look for.

 

Prob depends on the size of the boat too. I take my s&g outrigger canoe, built of abx fir plywood with hard chine, out in fairly rough conditions all the time. The ply never gives any indication of cracking itself. I have had connection points bend really badly, foil attachment points have broken, and I found some cracks in the tape at some high stressed corners that I didn't reinforce properly. If built correctly, the method is quite strong and theoretically wood is far more fatigue resistant than glass. So for a 16' boat s&g is certainly strong enough.

Some designs pound more than others. Just because ur building in ply doesn't mean you have to build a single chined sharpie. There are lots of two or more chined designs out there.

However if the boat will be left outside on the beach, or on a mooring, glass gives u a feeling of security in that u dont have to worry about rot. You can really abuse a glass boat, far more than a wooden one.

I think the beauty of s&g is it allows u to be out on the water quickly and relatively cheaply. In smaller boasts the advantage in time terms is huge. As boats get bigger though, that advantage of s&g diminishes somewhat, or so I am told...

 

It's important to remember that stitch and glue (S&G) and fiberglass are not mutually exclusive terms. The OP mentioned Bateau.com, which is a good example of a designer who offers both plywood boats held together by S&G joints and cored fiberglass/epoxy composite boats using ply as the core. Plywood makes a marvelous core material for a hull, as long as you are willing to accept the limitations of hard chines and developable shapes. It is very stiff for its weight (unlike glass), cheap (compared to foam core), can be machined with cheap and available tools, and doesn't require a big building site infrastructure even for pretty sizable boats. A ply-cored fiberglass boat is a great system for a new boat builder.

Since ply-cored composite boats are usually built with epoxy and woven or biaxial glass, they actually suffer less than factory polyester boats from problems like waterlogged transoms and osmotic blistering. If built correctly, they also don't have bulkheads pull loose from the hull or oil-canning decks. There is a lot of hidden criticism of amateur builders in some boat building discussions, but I've also seen gorgeous boats built with far more care and craftsmanship than a lot of factory boats. A conscientious amateur never says, "good enough -- I can't see it from my boat."

Take a look at Justin Pipkorn's story of building and sailing Just Right, a Mertens-designed 20-foot sloop. It can also be built as an 18-footer, so it is in your general size range.

I've been following builders' stories on www.bateau2.com off and on for nine years, and I would say that Bateau.com's customers are generally happy with their results. I've built a couple of Mertens' small designs (a dink and a canoe) and both went together without any fuss and worked as designed.

 

If you can buy "marine plywood" made in your country. Ask for a small sample and then boil it for an hour or two then try to seperate the plys. If you cannot then you know you have waterproof glue holding it together which is GOOD. It is called the "boil test".

 

Polyester/vynil ester resins versus epoxy

Have been checking prices for epoxy (120 USD/gallon, not a known brand), more than double than in US. Polyester resins - very cheap (12 USD/gallon), half the price of the US. Vynil ester resins are slightly more expensive.

Is it possible to construct the hull of a boat with polyester-fiber glass, and strengthen it transversally with 9 mm. plywood using epoxy resin as binding agent? The basic problem is that it is very time consuming to do the internal structure in fiberglass, so I am thinking about using the plywoood for the interiors which would also double as structural reinforcement.

 

You can build stitch and glue hulls with polyester resin to save money. Not alot of people doing this these days, but before epoxy became readily available dynamite payson was writing books about it.

 

I'd use vinylester resins in preference to polyester resins the biggest caveat with vinylester is you have to be very observant on correct mixing relative to temperature to get the best results.

Polyester is a valid choice but doesnt adhere anywhere near as well to timber and is not as waterproof as vinylester or epoxy this will lead to your boats structure becoming waterlogged more quickly and allow rot to set in as timber moisture content increases. This is more of a problem if your boat is left permanently immersed.

The cheaper options are workable but you have to accept your boat will have a more limited life. Personally I feel that building a boat is a large investment of emotional and financial resources and I would want it to last but different people have different values.

 

vynilester resins?

Is it really possible to build good quality stitch and glue with vynil resins?

I understood that the only valid material for stitch and glue is epoxy. In Chile 1 kg. of epoxy goes for 30 USD, vynil for 7 USD, and poliester for 3 USD. Now if vynil is reasonably safe for stitch and glue, I would consider it as a good option.

I want a sea going vessel, albeit a small one, but I do not want to compromise safety by using inferior construction techniques - I am not talking about a weekend canoe.

 

What is wrong with wooden boat construction? A lapstrake or carvel boat is very strong, needs no glue and can be made of locally available wood and iron. There are literally thousands of plans from excellent designers to build solid seaworthy proven craft out of boards and nails that last for many years of abuse. Even today these old techniques have great value.
This is especially true in areas where some more modern materials are very expensive and of unknown quality.
Fiberglass gives rot resistance and allows shapes impossible in wood, but consider the trade offs of more expensive, difficult, poisonous etc.
It is only stronger if built up thick and well-engineered, and can fail like any other material if not properly done.
If you must build a one-off fiberglass boat, find a set of plans intended for the method, and don't try to adapt another design.
The traditional Sharpie you mentioned (33' New Haven for example) was built of oak and pine in about 6 days for hull, deck and all spars.
That is 6 days for a shop, so a non-pro could do it in a month? Wood is quick and easy basically if you pick the right design, though I don't think a Sharpie is what you need.

 

The usage of resin would depend on what the plans list as being acceptable I'd use epoxy for filleting and adhesive. There may be an option to sheath the boat with a vinylester or polyester resin, adhesion to wood and shrinkage properties are not as good as epoxy but if your budget dictates it may be an option, on the boats I'm building I'm using epoxy exclusively.

 

Michail, I see you're trying to explore all the options....
First I'm sure that looking well you'll find a suitable epoxy resin for less than 30 bucks a kg.
Ask the epoxy resin providers for pool reparation. The resin used to repair swimming pools is generally good for wood epoxy on small boats as the requisites are almost the same.
Look also for a provider of epoxy for big electrical stuff like trains and metros, they have generally an interesting catalog...sure in you search only in yachting you'll find only overpriced stuff.
For the polyester boat: it's possible to make the bare hull in polyester (even in polyester plates made over a flat smooth long mold and joined like plywood stitch and glue) And add all the stringers and bulkheads in wood glued with epoxy. With some precautions (large light fillets and glass tapes) that works very well. Epoxy glues extremely well on a cured polyester. But polyester never cures correctly on epoxy. The boat will be far heavier than the plywood counterpart.

Peterchech is right; a small boat like a dinghy in stitch and glue which does not stay permanently in the water and is stored correctly indoors in winter can be made in common exterior plywood (but with waterproof gluing) and polyester. There is a preparation of the plywood that insures a "not too bad" (I do not mean very good!!!) gluing and glassing. You'll have to accept that the boat won't last a very long time (let's say 10 years so it will be amortized), and it will be of "inferior quality", I mean it will look a bit crude like a working boat, not a yacht for Yacht Clubs with commodores disguised in admirals. Will be also heavier that the plywood epoxy.
But it's interesting for making a first cheap little boat and learn at the lowest price. If you get the virus of sailing and building it will be time to see for a more complex and nicely finished boat.

Sharpies were made by poor people for poor people and were the best boats you could get for the lowest price. http://en.wikipedia.org/wiki/Sharpie_(boat) will give some clues about the origin and purpose of the sharpies and skiffs. It's a great tradition of working boats.

I have been naval carpenter, so I have some idea about classic boatbuilding. Definitely not for a total beginner, unless he is a good amateur carpenter or cabinetmaker. But Bataan's idea is interesting if you wanted a 33 feet boat; if you find a small shipyard making wooden boats (a lot of fishing boats around the world are made in "classic" wood, because they can be made with local materials, little tooling, can last a long time, and can be repaired) it could be a good project with the help of a naval carpenter. Sharpies are very simple to build. In fact the easiest and simplest classic wooden boat. But it looks for me complicated for a 5 meters boat...but if you find an retired naval carpenter, that can be a lot of fun.

Another system that at least suppresses the worries about plywood quality is strip plank. The method is now associated with epoxy and glass/carbon but primitively it has invented a very long time ago for making small working boats with just soft wood strips, dowels, screws and a router and/or planer for beveling. "Gluing/sealing" can be done with a polyurethane mastic like the Sikaflex (I do not remember the number...241?) that will you find in Chile as it's used in construction. It's rather tedious but you can get any shape at a correct weight. And it's pretty strong. But for sure that's longer to build than stitch and glue and there is a lot of sanding (but on light wood not on bad smelling itchy polyester).
I do not agree with all the assertions but these web pages will give you some ideas. http://www.diy-wood-boat.com/Strip-Planking.html and http://www.sredmond.com/strip_plank.htm .
A small precision, I NEVER use nails in strip planking. It's the best way to ruin the job with splitting and later have oxidation. I've always used dowels, glued or not, oven dried at 5-7% and metal drills same diameter or oversized of 1/10 mm (the advantage of metric...) with 135 to 155 degrees points. Maybe longer -not so much- but no problems and it's stronger.