Stitch and glue versus fiber glass from male plug

I am very thankful for the detailed answer by Ilan Voyager. I will keep looking for epoxy, and Sika indeed is available here, so I will check out the planking method as well.

However, I would like to point out that although I am on a budget, I do not want to compromise safety, and would never glue plywood with polyester. That is not my idea. What I am looking for is a relatively cheap, but SAFE method of construction. And if epoxy can not be found cheaply, then I would rather change the construction system.

As far as traditional fiberglass construction is concerned, I would appreciate any input on the following:

I have a design of a boat which is for stitch and glue construction and the concept of which I like very much (Souriceau, 4.75 m). From the rough drawings I was able to copy the outlines (with an exactitude +- ½ inch, 1 cm) for each bulkhead (a total of 7). I entered this data into free!ship and was able to get the shape very close to the real one.

One problem the design has are the vertical bow and stern shapes in the original design (which are very easy for construction of stitch and glue, but not so for moulding). I pretend to extend the nose and the transom at an angle of about 70 degrees form vertical (this will increase the boat size to about 5.1 m) and carefully modify lines above the waterline so as to get a reasonably flowing lines (the shapes below waterline will be unchanged). I understand that building a separate transom is not as safe as integrate it in the hull, so I prefer to modify it rather than stick to the original vertical transom.

Now the questions – female mould:

Option 1: I simply print out the developed plates (three per side) and cross sections, construct a cradle (with cross sections spaced about 30 cm. apart), buy boards (MDF, plywood), cut them to specs as per freeship coordinates and build the female mould.

Questions:
- Would I be able to get a reasonable fit between the plates and is it possible to fill in the gaps, sand them, or it is not possible to obtain a reasonable result?
- What material would I use, 4 mm MDF? Also, in Chile we have a product which looks like a very hard cardboard covered with a plastic covering on one side, could it be used, since the plastic cover is very smooth and only the seams would be an issue? Plywood is available only from 6 mm. up. No thin plywood.
- Are hard chines OK for fiberglass?

Option 2: I modify the original cross section lines in the following way: I add points so that the cross sections run much smoother (about 7 points per side instead of 4 as they are now) I try to obtain the best fit to the existing points and not to modify the total area (=volume) of the cross section. I develop it in freeship and obtain 6 boards per side, and almost rounded shapes. Then I proceed with building the cradle, etc.

I calculate the hull thickness, stringers, bulkheads according to the book by Dave Gerr, “The elements of strength for builders, designers, and owners”, roughly it is about 5 mm. +-1 for different areas of the hull, stringers sized 60 x 30 mm, etc.

I apply the following coats: gelcoat, vynilester resin with mat 300 grams, and from there on: roving 600, mat 300 with polyester (isoftalic), until obtaining the required thickness. For stringers I use soft pine wood (pinus radiata) covered with vynilester resin and continue covering them to the thickness specified with polyester resin/roving/mat. Few structural bulkheads (3) will be cut out of marine plywood, 9 mm. and glued with epoxy and fiber glass to ringframes (so as to avoid hard spots).

I need to obtain a sturdy boat, not for boat shows, but which can resist hard weather, and a reasonable life.


Am I missing something? Is it feasible what I pretend to do? Can someone correct me if there is anything wrong with the idea?

I think now about building a female mould, not male plug mainly due to the fact that the binding between stringers and reinforcements and the body would be much better since I would be working continuously without waiting for the hull to harden and thus would avoid secondary bonds, as would be the case for male plug. Is this important or rather secondary. I would not care that much for building using male plug (I do not care about cosmetic blemishes which would be the result off working from male plug, but I defintively do not want to compromise the structural integrity).

 

From a structural stand point, it wouldn't be wise to convert a taped seam build (stitch and glue) to GRP. This is simply because the physical properties of plywood and taped seams is dramatically different then these same, relatively flat panels of GRP. It'll oil can like a starved cow and you'll need it to be twice as heavy, just for the same strength.

These are common sense engineering issues and once again it appears you're over reaching or over thinking this set of variables. If you'd like a GRP build, select a GRP design or convert it properly, so you don't have to build a 3,000 pound boat when 1,500 will do.

Lastly, unless you plan on popping dozens of boat hulls out of this mold, forget about making one. Read up on the several one of GRP building methods. You don't need a mold for a GRP one off.

This is where buying an appropriate set of plans pays off Michail. You'll get detailed information about the exact build method you're working with, which will include a laminate schedule that'll keep the boat light as well as strong. On the other hand you can over engineer the crap out of a design, who's design and construction fundamentals you don't fully understand. It's your call . . .

 

I am aware that straight surfaces do not work well with fiberglass.

The problem with male mould is that you work with the insides after it hardens, thus weakening the bonds.

I have seen this article:
http://www.daviscoltd.com/Engineeri...rry/Boat building/Free_Forming_Fiberglass.pdf

and in fact modifying the shapes of a chined boat to fully rounded one would be the next logical step. But I am not sure whether this would be too difficult to accomplish (i.e. cut and bend the boards in a female craddle).

Frankly, there are very few plans which I really liked and which suit me. I was almost prepared to part with some 700 bucks for the Souriceau plans, but after checking epoxy prices and doubtful plywood we have in Chile I had to decide against this building system.

And my general idea is to be on the heavier side, i.e. sacrificy weight but gain strength since obviously I can not calculate exactly the hull

 

Ilan Voyager has made good points.
There is a 16' Kingston Lobster boat, the ANNIE A FULLER, in the Mystic Seaport Small Craft collection that was strip-built in 1872, out of free scrap from a local box factory (I was told that was where the construction technique originated) and all nailed with iron nails. This was a common practice at the time and place for cheap sailing work boats.
The frames are few and far apart and she still has all her shape and is solid and 80% original material.

 

Strip planking has been around longer then 1872. It was a technique used in several areas around the USA and elsewhere.

There are at least a dozen distinctly different strip plank methods, some are little more then carvel with narrow, edge fastened planks, while others are true sandwich composites with a core and loaded skin. Geer's book covers about 6 of them. In fact, the very lightest wooden building method known, is the Lord method of strip planking. Developed by Lindsay Lord, many vessels of substantial size and navy SOR spec have been built. It uses a high modulus sheathing exclusively, on everything, which makes a strong, but slightly flexible structure, that can recover without damage from distortion and load path changes. It's not an inexpensive method, in fact likely one of the most costly, though the wooden core can be a fairly cheap material. In short the "goo factor" is quite high.

There are lots of round bilge designs that can be made as one offs in single skin GRP as well as foam (or other light weight core) sandwich GRP.

Often when your SOR is unique enough or your building preferences are restricted, you have little choice but to bite the bullet and have a conversion preformed or a full up custom design done. A conversion isn't especially expensive, though a custom often can be, depending on needs and requirements of course.

Maybe it would be best if you could specifically state your SOR, item by item and possably several examples of designs that you like and why they don't quite fit your SOR. I think this approach would be more fruitful they debating the merits of each build method and comparing them to what you have available locally. The size range of boat you are looking for is the second largest for all the designs available, si finding suitable set of plans should be doable, once we know what the particulars of the SOR are.

 

What I am looking in a boat design is:

LOA:4.5 - 5.5 m.
Max. beam:2.3
Sail area: 15 m2.
Trailarable weight: Under 750 kg ideally.
Sea going. I live close to Pacific coast in Chile and pretend to sail it there (latitude 40) and down to Cape Horn. This implies stability, rather heavy keel, so centerboard designs are probably not OK unless they are quite heavy.
Cold climate: need a small cocpit and a well protected living area, ideally with steering from inside.
Single-handed sailing or maximum for two persons.
Sleeping: for two persons.
Storage: for medium length trips max. (do not plan to cross the pacific).
However, the local legislation require to carry certain safety equipment, including anchor and raft, etc., so it must have some storage area.
Form design criteria: stability for heavy sea and very strong wind, then (if possible) speed factor due to the small size and low hull speed.
Keel type: for trailer and launching - ideally not fixed, but without sacrificing seagoing capability.

Design and construction criteria: relatively cheap and simple
- if fiberglass, then no core since there are no readily available special core in Chile. Fiberglass is very cheap here.
- if plywood, then: plywood possibly of not good quality and dense (700 kg-m3). No lightweight marine plywood available, no plywood under 6 mm. Epoxy very expensive, so possibly alternative system of joints could be used.
- if wood, very limited type of wood available. Pinus radiata is the stock, and very cheap, but rather low quality. All other woods which are usually specified for building (douglas fir, mahagony, for instance) impossible to find. There are some local noble wood types available, but it is very difficult to know which properties correspond to what type of northern hemisphere. It is probably an art.


Costs and budget:
total about 7000 USD. of which 4000 for sails, spars, and all overdeck hardware, etc. (this cost factor limits the aprox. sail area and I have checked what is available locally in terms of mast, boom blanks, etc. Two mast blank sizes available: 70 mm x 54 mm, 700 USD and 130 mm x 90 mm, 1000 USD). Sails are cheap, since they are sewn locally. Hardware is slightly more expensive than in USA. Special fittings (mast step, conectors) would be fabricated locally. This amount does not include safety and navigational equipment.

That leaves about 3000 USD for the hull.

Time is not considered in the cost.

Best design so far:
Souriceau, but the cost of epoxy alone is 2500 USD.
Paradox - too narrow and too small, also do not like the rig. It will survive any sea it seems, but it is too basic.
TLC 19 - stability issues, may require redesign of keel. Also seems to be specified for core construction method.
There are also several Russian designs I liked, but they all need adaptation (mainly keel). I can post sample plans.

 

Its very time consuming but you may be able to cold mold a yacht with a resorcinol (urea formaldehyde) type glue that may be less expensive in Chile. I've never looked into it much as I've always used epoxy but with this method I've heard expansion and contraction of the exterior veneer due to changing moisture percentages is better tolerated and many boats built this way have a painted exterior without resin and fibreglass and hold up quite well it gives a relatively light weight and strong monocoque structure which may help to keep the boat within the fairly low weight target you want to achieve. The yacht designer can normally look at what local timber species you have available and suggest substitutions.

Cold molding allows you to achieve virtually any hull shape but is very time consuming and requires the construction of a male mold (you can make the mold out of virtually any old wood though).

 

I do incline towards male or female mould in fiberglass...

 

Since polyester is cheap and plywood Expensive in Chile you can still build in stitch and glue but with cored fiberglass panels. A solid glass build would be too heavy but it would not be hard to come up with a cored laminate for a 16ft boat that would be similar in weight to ply. What you would do is build a flat table say 18ft by 4ft and surface it with formica, apply mold release, apply gelcoat and then layup your panels full length, i would probably use coremat for the core, Then build your boat stitch and tape style, just like ply.
Steve.

 

Here is a common SA boatbuilding wood referred to as "Cedro" to the North of you, in Peru (a friend grew up there and told me much about local boat building), used for planking and stringers.
http://www.thewoodexplorer.com/maindata/we827.html

 

A couple of questions-comments:
- the plywood is not expensive, quality and types are limited.
- finding adequate core is another issue, maybe balsawood.
- Polyster - vinylester resins do not bind well with wood, plywood
- "PAR" user suggested that flat panels of fiberglass would have to be heavier than rounded shapes, so what Steven W proposes would suffer the same problem.
- Single skin is obviously heavier, but according to Elements of Boat design, the skin for 16' boat would have to be around 1/2 inch, that would give a total hull weight of about 500 pounds (5 meter - 6 mm. - 220 kg), which is fine for me.
- If I take the idea of Steven W further, I could cut panels of some thin product (MDF, plywood, etc.), put them into a female cradle, and then proceed with building fiberglass layers.
- I suspect any small boat design could be modified to rounder shapes as to be better suited for fiberglass.

WHY NO ONE LIKES SIMPLE SINGLE SKIN FIBERGLASS CONSTRUCTION?

I am missing something out?

 

I've seen masonite used for female molds for fiberglass boats. This was for big sportsfishermen with developable shapes.

 

Simple single skin fiberglass is quite heavy for the relative strength, depends on high fiber/resin ratio for consistency and does not do well in flat unsupported sections.
Early F/G boats like the CAL 40 are still around because they were so overbuilt, being very thick in the stressed places.
Of course a single skin fiberglass boat works. Wooden and wood/glue boats work well too, and are much lighter for the strength.
A single skin, one-off f/g boat is difficult to build well. Here is one method which may work for you.
http://www.glen-l.com/methods/mthdfg31.html

 

That was what I was thinking about.

Exactly, and stitch and glue designs by definition must be developpable. However, what I am not sure about is whether a fiberglass hull be really that much heavier if straight panels are used as compared to rounded shapes?

 

Michail,the problem with single skin fiberglass is weight and lack of stiffness unless you can use lots of compound curvature(a single skin panel of equal stiffness to an adequate plywood panel would be much heavier) which pretty much precludes flat panel builds like stitch and tape construction. However a simple cored panel can be very light and stiff which makes possible these easy build methods with some advantages such as a molded gelcoat finish for much of the surface area eliminating a lot of the hand work involved with painting, low cost of polyester resin, and low maintainance. I agree with Par that a single skin flat panel would need to be heavier than rounded shapes but it is fairly easy to build a cored panel for a 16 ft boat that is close to the weight of plywood without anything exotic involved. You can certainly build a female mold out of sheetgoods for a fully molded hull but you will be stuck with a hullshape that will require either a core or a fair bit of internal stiffening with stringers etc, nothing wrong with chine hull shapes, just better suited to plywood or cored glass construction.
Steve.