Build time 40ft catamaran

Sorry David, it just proves that you are a larger than life character

Like most designers working in plywood I try to minimise waste (which in itself is a design limitation). So for example, I might adjust the freeboard slightly or the cabin side height so that two can be cut from one sheet of ply. I also mesh bulkheads together to optimise sheet use, see attachment

And when I am building my own boats I try very hard not to waste money!!

Sure, when you cut out a bunk locker top the scrap becomes the lid (and that is one place where ply is quicker than foam, you don't need to fill and seal the edges) but when you cut out windows where can you use the scrap? At that stage in the build you have already built much of the boat. Obviously at the cutting out bulkhead stage you can use the scrap foam elsewhere, but look at the attachment, where would you use you the ply scrap?

Apart from being easier, fitting a deck panel in one piece ensures it's a fair camber. So what happens to the hatch cut outs? It isn't really practical to extend the ply to make the hatch itself. But you can do it in foam

I have built a number of foam sandwich boats and also ply boats. There is always more waste with ply.

I am always nervous about people getting CNC cut panels on big boats. If a boatbuilder joins two panels with even a 2mm gap you'd consider it shoddy work. But I doubt if a CAD designed CNC cut 40ft x 6ft panel can be mated to another one by a home builder with gaps less than that. Never mind the problem that a home builder will have in moving those panels when working alone

For that is one difference between a home builder and a professional boatyard. Home builders have plenty of free time. In boat yards the materials are cheap, it's the labour that's expensive. And most boatyards have lifting equipment and other workers to help move things around

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

I was trying to steer this discussion towards a comparison of build times for different construction techniques since that is what the OP was originally interested in. I am sure Richard W. is right about there being more wastage of plywood than of foam core, but that is something that comes into a comparison of material costs, it's not relevant to comparison of build times. In any case, if we are going to start comparing material wastage for the different construction methods, I would have thought that plywood beats foam core overall. There may be minimal wastage of foam but there is wastage of lots of vacuum infusion (or vacuum bagging) consumables. Just looking at this video http://www.easycomposites.co.uk/Cat...Infusion-for-Cosmetic-Carbon-Fibre-Parts.aspx I am struck by the amount and variety of man made plastics materials that end up in land fill rather than becoming part of the final product. Presumably, the reduced wastage with foam is only possible by cutting up all the little spare bits and butt jointing them back together. Perhaps there is scope for doing a bit of extra scarf jointing to save some of the wastage with plywood - for example a rectangular frame with a hole in the middle could be two L shapes that might 'nest' a bit better? I have found scarfing plywood not too difficult. I think Richard is indicating that plywood wastage is likely to be about 15% - that is 5% in bits too small to be anything but fire kindling and 10% in bits that might just be worth keeping for some future project. (his ten sheets out of one hundred) I take that to mean that you need to allow an extra 15% on the cost of plywood to allow for wastage - so its still plenty cheaper than materials for a foam core build. No argument about the weight or resale value though!

Groper, I am very, very impressed that you can make a 40ft x 6ft panel in a morning. I am sure I couldnt even mark out the shape working from a dimensioned drawing in that time! The possibility of buying premade and even pre-cut foam sandwich panels is certainly interesting, indeed, didn't you get your main bulkheads made that way for your current project? However, the last time I briefly looked into this, the prices seemed way high. Maybe I was considering the wrong type of company for the work (it might have been an aerospace company rather than a boat industry company). I would be interested in any pointers to a suitable panel manufacturer in the UK, I expect others here would be too.

Presumably, premade panels are not going to give you the material saving that Richard W. is talking about since the manufacturer will start by making a rectangular panel skinned both sides all over. Then, if you ask him to do the cutting, he will cut your shapes from that rectangle wasting not only foam but also the skin materials attached to the foam. Same is true if you do the cutting yourself.

Continuing with the pre-made panel theme, once you are at the stage that your premade foam cored panels have been delivered cut to final shape you are at the same point that the plywood builder is when the plywood is cut and scarfed (but well down financially I think, also you have some huge panels to handle, a problem for many home builders, as mentioned by Richard in his post above). We are talking about flat panels that will need to be sprung to shape then joined along longitudinal seams to form a hull. With foam core I think we have to maintain the strength of both skins across the joints, say by fairly heavy taping inside and out. I am not too much worried about lumpy finish inside the hull, but I have seen that taping on the outside of a hull can look really ugly unless there is a lot of bogging and fairing to hide it - surely that wipes out much of the advantage gained by transferring a smooth surface from the mold table. Alternatively, you could mold accurately fitting flanges along the mating panel edges (loads of work I think), or rebate the foam to recess the external tapes (neither of these two options possible with premade panels I think). What do Groper and the other experts prefer? My non-expert thought would be to limit precut panels to internal flat structure and infuse my own skin panels with rebates where external tapes will lie, but if these rebates are to be on the smooth table side I am not sure that would be so easy.

With plywood you probably don't need to worry about all this since you can get away with heavy internal taping only, (or timber 'chine logs' and such like if you prefer the more traditional approach) the external glass being more or less non structural, its mainly there to give the external coating a bit more abrasion resistance and to help achieve a consistent external coating thickness. You just lay the light glass sheathing over the whole hull once the structural joints have been done from the inside. Since its non-structural, no overlaps/fairing needed in the sheathing - the peel ply comes off leaving the hull nearly ready for first coat of primer. It worked for me on a tiny project - I don't have experience of anything the size Groper is building.

Later in the build you come to all the really fiddly bits - hinged hatches, internal furniture, trimming and edge sealing all the holes you need to cut through bulkheads etc. A friend of mine, after years of hard work, has recently finished building a beautiful 10m catamaran. He tried to do almost everything with foam core (albeit much of the foam was, rather unusually, skinned with thin plywood rather than glass). He kept that up right down to the dividers between the knives, forks and spoons in the cutlery draw, but he told me that it would actually have been quicker to do many of the small fiddly details with just wood/plywood and epoxy.

As for the use of cnc cutting in boat building (with either foam or plywood), my own limited experience suggests that it can save a lot of time. At one point in my varied career I was involved with making some boat sized foam cored carbon fibre structures using moulds built up on a temporary formwork constructed mainly from 12mm mdf. We had lots of pieces of mdf cut out by a local waterjet cutting contractor. That certainly saved time and I think we would have been struggling to achieve the specified tolerances without that help. Making parts to the accuracy that you can expect from computer controlled machinery should eliminate much of the trial and error fitting and refitting that often slows down boat building, particularly in the later fitting out stages. Cutting out the individual trial and error fitting of mating parts was surely one of the cornerstones of Henry Ford's manufacturing philosophy that allowed him to make a thousand vehicles in a day when competitors were struggling to build just a few in a year!

I do hear Groper when he says that those who have tried both plywood and foam core find that build times are not a lot different - not trying to deny that, just understand it. Also hope that this kind of discussion does not excessively distract Groper from his interesting project!

 

Setting up flanges and recesses is very quick and easy on flat table infusions. If you want the recesses on the table side, you first rout out the foam to the desired depth and mark the position on the table. Then put a strip of hard plastic sheet material down on the table in the corresponding location to take up the thickness. I bought a sheet of 2mm PE for this purpose and ripped it into 100mm wide strips. Layup your preform as per normal with the core face down in its correct location.

If you want recesses on the bag side, simply rout them out and layup. The bag will conform down onto everything. Same goes for flush hatch recesses... rout a recess and cut out the deck. Drop the gutter mold into the recess etc.

 

Agreed. Even I can make flanges quickly and they save a HUGE amount of time when joining panels. I first did it in the mid 1990's and was amazed how much quicker it was than trying to fair lumpy outside joints

I also agree foam is easy for flush deck hatches. Apart from not rotting, the other advantage of foam sandwich is that - unlike plywood - it won't distort when damp. Flush ply hatches never work without reinforcing, they will always warp in time

So bottom line, all materials have pros and cons and those tend to cancel out depending on the part of the boat you are making. Foam sandwich cutlery tray!! Crazy! I bet it's heavier than a plastic one. I went on one boat that had a carbon fibre washbasin. It was vacuum bagged and must have taken ages to make. It was not yet fitted so I could weigh it. It weighed more than the plastic one I had just bought from a camping shop for GBP5 (USD7). And mine was white, not carbon black - which seems impractical and must hide dirt I would think?

The only sure way to get a boat on the water quickly is to build a small simple one - as I said at the beginning

Richard Woods

 

This is an interesting conversation. The discussion about full length foam panels brought me to read more upon Kelsall KSS method of infusion on a table. Sounds very interesting and something I would like to explore further. But the table or kit idea brought me to think in a different way about the plywood method. Most builders seem to build one hull first on a strongback with bulkheads and then the other hull. Then turn the hulls around and build the beams to hold them together and then put the saloon/cockpit floor in place etc.

Would it not be easier to start with the bulkheads for both hulls including the beams. Put those on one common strongback for the whole boat, lay up stringers and then plywood sheet the whole thing in one shot and fair and fiberglass it in one session (given the manpower is available)? The hull can then be painted upside down before turning it around to lay down the deck and build the superstructure.

It will be a lot easier to manage helpers if there is a lot of the same work that needs to be done instead of getting people to do the same thing with long periods in between.

Moving along, given the hull or structure is only a small part of the build, where can time savings be had on the internal fittings? Use of panels, fabrics or wallpaper instead of having to spend a lot of time sanding and painting internally? Window and door issues to stay away from? My thought was to purchase all hatches instead of making them out of the cutouts. So the question is more then what to make and what to buy when it comes to the build.

 

I chose to make all my own hatches because to buy them costs about 500 bux each... over 6 hatches that's $3k... same goes for a lot of details like this... you have weigh up whether your time is worth the cost to buy something. It will vary depending on your skills and how much things cost to buy and also how much you earn via your normal line of work. Someone who earns obscene amounts of money will pay for someone else to build the entire boat, whereas a peasant will build every last detail themselves, from cutting the trees to weaving their own ropes...

 

Yes it is, but not every home builder has a big shed near home to work in. Travel time and shed costs are a huge factor for home builders.

Not even all professional builders are able to turn a complete catamaran over inside the shed. You also have to consider workshop door width (usually the biggest problem) and how to get the boat to the water

Again its something you have to weigh up before building. But by and large, the smaller the shed you need, the cheaper the boat project; the more work you can do without going up ladders or onto scaffolding the quicker it is. (That's why I always suggest builders make the cockpit last and use the space as a workshop when fitting out the interior)

I used ebay as my supplier when having our last boat built. Buying new Bomar hatches for USD35 made a lot of sense as we were having a professionally built boat

Even then, its the little details that add to resale. Professionally built hatches will nearly always look better and thus increase the boats value. Same thing with metal masts instead of wood, professionally made cushions rather than make your own etc

And a wallpapered interior will mean you can never sell the boat. Most people use what Cornish boatbuilders call "monkey fur" - sorry too long an explanation

Richard Woods

 

I'd love a link to those hatches for 35usd Richard!

 

Methinks, I must lean towards the peasant end of things.....I never mention money spent because nobody would believe me....To reply to bluebox, some early multihulls were built that way. Jim Brown's pre Searunners come to mind. The down side is the more heavy, large and complicated turning over of the hulls and larger build area required.

On the ply end of things I've found the odd scraps are most often used in interior construction and for making gussets. Bins, shelves, cabinet ends etc.....like many things combining methods and materials where each is most important will likely achieve the fastest and most economical result.

I do think John Perry's observation about waste by products is very relevant. I keep trying to champion renewable resources and minimal waste for boat building. I hate to think of a world where there is no good wood left and foam the only option.

Flanges do make sense, I've got Newick plans for a couple boats where he used this method to advantage.

 

Space is definitely an issue. If I go with the idea of a little smaller boat with a beam of less than 22 feet I can start with building the bulkheads in my garage. Then with some additional hands I can move to a temporary structure in the back yard and complete an enclosed structure in one season before winter sets in. I don't think my neighbors would be very happy to see a big shed stay in my back yard for years. In my neighboring town (where I used to live) residents have to apply for town permit to have pod in their driveway for more than 24 hours....

Hmm.. Monkey fur....

 

Indoor/outdoor carpeting + contact cement. Austin Powers fur-go shag man....

 

True, you can do, but I prefer to make shelves from 4mm ply not 9mm

Also true that there is a lot of waste (and thus cost) when vacuum bagging foam sandwich. But you don't need to, you can use "contour foam" instead

We've had this discussion before many times, I suggest the OP searches this site using my, gropers and cavalier's posts as starters

Also discussed before - one advantage of building in the USA is the ready availability of cheap supplies. Although I do think that shipping a small can of spray adhesive, for example, from Florida to the PNW because it was cheaper than buying it in our local store makes no enviromental sense

Richard Woods

 

OK, go here and compare their fur to what you see on any production boat. This is where Beneteau gets it from!

http://www.monkeysanctuary.org/woolly-monkeys/

Which is about 5 miles from my office

Richard Woods

 

Cheers Richard, my scrap is mostly 6mm which sort of splits the difference though I do use some 4mm. The only thing 9mm are the soles. I'll have to get you onto the Nicol one day, a trimaran fits your everything you need in one hull concept except the wings give you more cabin room for bunks and the guest bunks are in the bow or stern. Probably less private but hippies don't care.

 

While building the boat structure is not a huge part of a build, it is where you must start,
and after spending all the time building that part, you get burned out, and don't finish the rest or at least slow down a lot. What looks like you've done so much, where in fact, visible progress slows down significantly.

The other issue is given the plumbing, electrical, engines, cooling, heaters, showers, washer/dryer, fridge, stove, oven, watermaker, big screen tv, sails, masts, furnishing, etc, take so long,
is just build a boat that doesn't have all that stuff, or at least has it in a way that is much faster to install.

My view is the best way to speed up the processs is a) use female molds, b) do the same things over again, c) have motivated help to keep progress going
and to that end, see www.herding-cats-coop.org