Building Methods

Derek Kelsall has been building cruising cats and small cats using flat finished pre-fab panels for years, with the stringers attached.

http://www.kelsall.com/methods.html

He used to use plywood, but now favours foam panel

 

My question was a sailboat of approx 8m and i will add to that, say 5m to 9m just to widen the field a bit more.

I do appreciate the comments on smaller builds such as a kayak, but when you start looking around at the many boats (sail and power) that are built SNG you start wondering why not even more?

What worries me is that there are many "newbies" that haven't got experience and are looking at an endless list of "free" plans, and i think that most of us will agree that 99% of those plans are outdated and hopelessly insufficient for a beginner to build without assistance. One of the mayor problems in the current economy, is for ANY designer to prepare a complete NEW set of plans for a beginner is virtually impossible, as it wont pay. Designers simply cannot make a decent living out of selling plans. When you draw as much as i do on CAD you will soon realise that the prices quoted for plans are generally cheap. Therefore the plans that a beginner should look at are those which have good support online. Unfortunately our popular designers are not spring chikens anymore either and the good designs out there are also a couple of years old already. When you look at the ease with which a HUGE build such as Mas's dream cat http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-40.html is coming together and when you look at the endless stream of SNG projects out there, you start realising that many of the current designs on the market today, should be converted / redrawn as female / basket mould type of SNG / taped seam types of builds. There are many of the popular designs out there that lend themselves to this kind of build method.

I have spent DAYS (100's hours) on FREESHIP looking at and comparing resistance values of round bilge designs VS hard chine boats and please believe me that a hard chine - 5 or 6 panel has so little resistance more that for cruising / club racing it makes absolutely no difference.

I am now on my 5 th build (#five) and i have had the good fortune to spend time in some boat yards with very competent builders working with all materials, GRP, steel, wood - and i can assure you that SNG in a basket is fast and economical and light. I know that some folks regard Epoxy and Marine ply as expensive and problematic (toxic) but it gives a strong and very light build. I am also convinced that for the home builder Epoxy and ply SNG is actually cheaper. One point that i MUST STRESS is that i do not favour ANY build method above the other, if you can prove that YOUR method is faster i will change over tomorrow, but that remains to be seen.

I also would like to see some of the more recent designs REDRAWN and re-engineered where the internals and "furniture" etc. is part and parcel of the "honeycomb" structure as per Oram, as a "basket" female mould type of build. Flat panels SNG. For me there are nice designs out there, but the skin over frame just doesn't do it anymore. The big CATs are fantastic in expensive balsa laminates, pre cut panels. Simple cut out and glue together, but if you dont live in that country you simply cant afford it. Unfortunately there is not enough of that type of build research going on for cruising mono's. The world is cat mad and yet the monos have plenty to offer, show me where can you see a MONO build similar to Mas's cat.

anywaaaaaay enjoy your day, supper time here, hot and dusty, Sydney is covered in dust and so is Pretoria, damn why is the sea so flippen far

 

And just as an after thought

here is my "dream boat"

the ultimate live aboard for 2 world cruiser, small enough, light, fast in moderate winds, Honda fourstroke 20 hp outboard, NO TV and other fancy ****

but it has to be built as SNG in a basket, Epoxy over ply hard chine

 

Yes no doubt about it.

The basket is wasteful.
Sanding the fillets to a nice finish is a pain.
It`s slow, dirty, tedious work.
Careful masking , taping and laying of fillets will help a great deal, BUT.....

Sam Devlins boats have nice clean interiors.
he`s a pro in every sense of the word , yet I bet that he does not enjoy the huge amount of fairing and sanding it takes to produce a highly finished product ( which ) his boats are.

It is light as you say.

Absolutely.As above.

All in all Manie I think your`e right about what you say.

The fairing is still a pain. Take a look here , at the work involved just fairing some steps :http://www.mahnamahna.com.au/May 2009.html

As far as Mas and his Oram ......the boat does go together relatively fast , the panels are obviously a perfect fit .
Lovely boat , good choice.

But I think you will find that to finish that boat to the standard it deserves , there is a huge amount of fairing and finishing yet to be done.

 

Sydney`s dust......It`s moved to where Mas is building ...last night.

 

Interesting thread. I looked into a lot of different boat building methods, they all had some disadvantages. Stitch methods leave all those little holes with bits of copper wire, and then there’s all the sanding of the epoxy fillets. The finished boat shape magnifies any errors in the lofted plank developments and cutting, and the individual planks are flimsy.

Framed methods increase the weight compared to monocoque construction. I love the look of glued lapstrake and strip-planked boats but I resent the material cost and effort that goes into any kind of mold that doesn’t form part of the finished product. As my boats are slowly getting bigger (there must be a medical name for that) the handling problems of rollovers are becoming more apparent.

For some years I have worked with prefab flat panels - similar to Boat Fan. I found it was ideally suited to smaller boats, and I am looking into how to adapt it for the larger craft that my medical condition requires me to build. Presently I glue chine logs and inwales to the sheer planks while flat, makes ‘em tougher and easier to handle. Flat bottomed boats are very quick with this method. For five-plank construction I also add chine logs to the bottom plank, attach it to the stem(s) and a mold or two, then plane the edges to fit the bilge planks, which are simply cut to fit. Errors in developments are not very important, very little waste, and I can use cheaper glue for all the joints except the last ones, for bilge planks, which are the only ones exposed to water.

Adding internal construction seems a bit of a hassle. Getting a good fit inside an existing body is more difficult, access can be a problem, and I find fitting a bent panel between bulkheads with really tight joints all round can be a real challenge. More skill needed here than building the basic hull.

Therefore I am working on adapting the prefab method to a larger boat with interior construction such as a cockpit. Briefly, I am thinking of building the cockpit and buoyancy tanks first, using those as a mold around which to bend the hull planks.. It seems to eliminate many of the difficulties and objections I have with other methods. I am also looking at rounded bilges instead of hard chine; these will be cross-planked in a lightweight lumber. No doubt it will be a learning experience just like all the other boats were ...

I must just add this: having a live and accessible designer is a huge advantage especially if you are using a different or unusual construction method.

 

I`m trying to visualize this ...are you saying you " cross plank " in the traditional sense , how the original sharpies were built , ( planking the bottom across the beam ) ? but " bending" the planks in a curve ?

http://dieselducks.com/Woodducks/bottomplanks.jpg

You could strip plank the curve at the bilge I guess :

http://www.westsystem.com/ss/assets.../_resampled/ResizedImage360302-sharpie8a2.jpg

 

http://www.google.com.au/url?sa=t&s...g_HoCA&usg=AFQjCNFLlvsMam-Js8HGZNvm8KfVn376Lg

Take a look Manie ......may be of interest , check out the construction .........

May be possible to adapt to SNG .

 

I have no idea what you are talking about here. The internal frame can also become the furniture and fittings. You build the internal frame and it becomes part of the structure, adding strength, so the skin material is lighter. You do not have a lot of fillets to sand, in fact you do not have to glass the inside at all, just seal and paint it. All the fiberglass prep is done on the outside. But I have built without any skin plywood or fiberglass at all, the skin is heavy polyester fabric with polyeurathane sealant supported by stingers. With an external frame/mold it becomes scrap when you are done with it. All the stitching and glueing and fillet sanding of SNG is very tedious and time consuming, there is no equivalent for SOF.

You are the one lacking experience here, I have built using all three methods. A skin on frame kayak or sailing dingy takes about one third the amount of hours to build, and half the materials, than either stitch and glue or strip built. You also appear to think that strip built is interchangeable with Skin-on-frame, totally different method, different structual design, different process.

 

Agreed Petros , I think you pointed out the major disadvantages of SNG.

The thing I DO like about SNG s the nice radiused clean corners.
Too much horrible , dusty , tedious sanding for me afraid .....

 

No all SOG designs leave all the the framing inside the fininshed boat - there can be a lot of temporary inserts.

Even so, you have to build a very complex and awkward "skeleton" to support the relatively lighter skin.

Much of the skeleton serves no purpose than hold the skin apart, and take up room - as you say yourself.

It is crazy to stick the strength in the internal frame, and leave the bit holding the water out thin. It is much better to maximise the skin strength, because thats what keeps the water out.

Thats why cars no longer have chassis - much more efficiency of materials and labour.

If you use peel ply in SNG, that sanding is very much reduced. With SOG you have all the little angles in the interior that are hard to finish (even with only painting), have taken a long time to cut and assemble, sharp angles to capture grit and water, and as you say yourself - take up room

True there is sanding to do, but that bit of sanding is offset with the much more complex framing and internals (stringers and bulkeads) required for SOF. The other benefit of having fibreglass on the inside as well as out, is extra strength, requiring less framing and furniture, but mostly, better weather protection.

For small boats with only paint on the interior, the plywood is far more prone to degradation from moisture.

75.4% of people make up statistics on the spot.

You have not provided any hard figures. You also combine stitch and glue with strip planking - (they are NOT comparable you know!) How you can say that strip planking has the same build ratio as SNG, just doesnt make sense.

How a ... say .. SNG 16 ft finghy uses less material and is less labour than an equivalent 16ft SOF dinghy , just doesnt compute.

I think someone referred to one of the leading SNG builders on this thread - Sam Devlin. he quotes several examples in his book, of the efficiencies of SNG over SOG, including labour, materials, and superior longevity.

Strip plank *is* Skin on frame - its just that the skin is made up of much smaller pieces.

The similarities are -
Limited access to the interior until rollover
Even more sacrifical frames

But if you want to leave that out, I dont mind for the sake of this discussion.

 

No , it is not.

After the hull is stripped , the exterior is sheathed with glass / epoxy
or dynel or polypropylene cloth. After that it is usually turned and all moulds and temporary frames are removed.
The interior is sanded and sheathed with glass / epoxy .
what you have now is is essentially a monocoque shell .
The skin is largely self supporting.

It is further strengthened by bulkheads , floors , bunk flats , cupboards
( built in furniture ) and decking / superstructure.

-- --- --


A skin on frame is essentally a hull that relies on a combination of sawn or laminated frames and stringers to support the " skin " or planking.

The " skin " ( or ) "planking " only keeps the water out.

It is essentially NOT a monocoque shell like a stripped hull.

The two are in fact fundamentally quite different.

A hull built using stitch and glue construction is by its nature similar to the stripper hull.

Both the strip built hull and the stitch and glue are further strengthened by the addition of bulkheads , furniture etc as mentioned before.

The skin on frame relies on the FRAMES AND STRINGERS to gain it`s strength.
.
The two are worlds apart .

( It was I who mentioned Devlin ).

 

Ok just to answer a couple of questions

The wire holes left behind of SNG on my little chigger drove me nuts, way too much work and even though i had the panels CNC cut, i hated the "wobbly" construction of SNG. I tried different types of wire - all lousy IMHO. Difficult to get in between the wires to fillet, so you end up doing fillets in stages. You cant go near the boat with wet fillets, so you wait. Extra work - extra frustration, lost of sanding. I experimented LOTS on the chigger with holes, wire, layups, sanding methods, sanding machines, epoxys, and everything else. One thing that worked well from day one was "bedding" the furniture and stiffners down onto the skin, this worked very well. No gaps, where water can creep in and rot. Easy to fillet and sand. A clean job.

With the Jarcat hulls AND the basket frame i was in heaven. Just the minimum of screws thru the panels into the frames to hold it in position firmly, and no where near where i was going to fillet. All panels cut by hand jig saw. CNC cutting is very expensive and after riding back and forth and explaining to the CNC folks what i wanted, i realised that i might as well loft and cut myself - IT WORKS. Bedding stiffners and furniture once again easy.

But i was still not happy with my fillets - too much work - NEW EXPERIMENT

http://www.boatdesign.net/forums/boat-building/manies-shiny-dinghy-26675.html

here i realised that filleting is part ART part SCIENCE part experience
make your own tools - filleting is like welding PRACTICE
i now lay a fillet down ONE SHOT - - NO SANDING !!!
mix paste and put in plastic bag
small hole - squeze out like toothpaste carefully, like "welding" into corners
scrape smooth with "putty" knife
wait 2 hours to "tacky"
paint light coat of epoxy - roll out fibre cloth - saturate, work in lightly with paint brush - roll on peelply
next morning JOB DONE - EASY PEASY
light quick sand to clean up only

that is why i built the Portuguese Dinghy, to prove to myself that i can do it,
one shot - easy - clean and fast. I hate doing things over, so i force myself to come up with things that work fast and easy. I dont have help, work alone, and obviously DONT LIKE SANDING

so yes here we are now
the basket holds things firmly and accurately in place
fillets go down easy and fast with the minimum of fuss
install furniture and stiffners and bulkheads
glass inside
roll over - glass outside
sand and paint
get onto the water
drink beer

Oh and by the way folks
the basket for the microcruiser is 99 % finished and ready for ASSEMBLY
keep you posted

 

oh and VERY VERY important

with skin on frame you have a LOTS of screws holding the skin down
they have to be smoothed down and filled, metal expands, bump on surface


with the female mould - basket assembly - NO SCREWS - NOTHING

taped seams - glass inside - glass outside - paint - finished !