Build time 40ft catamaran

Discussion in 'Multihulls' started by bluebox3000, Jan 8, 2014.

  1. John Perry
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    John Perry Senior Member

    I realize that is is possible to reinforce apertures in foam sandwich using a 'rope' of unidirectional, for example by digging out the core around the aperture and feeding resin impregnated 'rope' between the two skins. This looks to be a good way to finish off the edge and provide some strengthening, you need to do something to seal the core anyway, but I am not sure that on its own it is the optimum way to mitigate the stresses around a large aperture caused by torsion on the hulls.

    When I did my analysis I looked at having strengthening only near the edge of the hatch but from memory I found that for best effect I also needed strengthening extending some way from the hatch.

    The first figure below shows the kind of hatch I analysed - see to the right of the right hand green man in the first pic. The actual hatch covers (non-structural of course) are in two pieces and are shown closed, when open they would drop down below the aperture. This is quite a big opening cutting into both the roof (deck) and the inner side of the hull structure.

    (I am sure you won't like the look of the old fashioned chain plates and some other features in this picture - at that time I was thinking in terms of plywood/timber construction, I might be more likely to think composites today and reading these kind of messages might have some influence on that!)

    Anyway, the second picture shows what I ended up with after some FEA analysis. It was cutting into the roof (deck) that was the problem, the corners at the bottom of the aperture didn't look too much of a problem so they stayed as 90 degree sharp corners. I rounded off the corners in the roof cutout giving an almost semicircular cut - that helped a lot but stresses under hull torsion still looked significant. I then looked at reinforcing just the edge of the aperture but that did not seem to work all that well. What I ended up with is shown in the second picture that shows the roof structure panel looking up from underneath. There are two extra layers of plywood extending some way from the actual aperture. Maybe they could have been 'feathered' into the main panel by making one of the extra layers a bit smaller than the other.

    I am not claiming that this is a fully optimized solution but this investigation did suggest to me that one might need more than just reinforcement of the periphery of a large hatch opening. Say for simplicity that you have a rectangular hatch aperture with rounded corners. Reinforcing just the periphery stops the length of the aperture perimeter changing much but it may not do much to stop the opening changing from rectangular to lozenge shaped, with consequent stress in the skins, when the structure comes under torsion.

    Sorry if I am wandering too much into structural matters when the original topic was build time.

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  2. waikikin
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    waikikin Senior Member

    one thing I've seen in composite race yacht deck laminates is around hatch appetures that some uni fiber "bandages" are laid within the skins, these were at 45 degrees to the radiused corners & tangenting the corner extending some way into the surrounding structure, I imagine these help distribute load/stresses out & around the cut out. Might well be quicker than the rope & have more contact with the rest of the laminate.Or do both as the rope/uni in between the skins effectively acts as a core "close out" at the apeture- another good thing.
  3. John Perry
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    John Perry Senior Member

    Sounds like it could be a good scheme. Not something I have looked into, but if it is being used on race boats someone may already have done some analysis. Also relevant to aircraft etc.
  4. John Perry
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    John Perry Senior Member

    Let me try to bring this thread back from structural analysis to the original question of build time for alternative construction methods. We are discussing mid sized sailing multihulls so the most obvious alternatives are foam sandwich and plywood. Having said that, the 40 foot length that the OP mentions is big for a plywood boat. Perhaps this is simply because plywood is mainly used by home builders and relatively few home builders build boats much above 30 foot? Here is one about 35 foot in plywood, I think it looks quite nice but its a huge boat for most home builders. The pictures show it being built in a factory, few home builders have access to such a facility.

    A bit about my own background. I designed and built a 15 foot monohull sailing boat, completed back in 1978 and this is the boat I have used for nearly all the sailing I have done since then. That boat is a grp sheathed plywood sailing dinghy with a heavy (lead) centreboard. We have a tent cover to provide shelter at night and over the years I have lost count of how many thousands of miles we have sailed it in UK and France, including a number of passages across the English Channel. I have often felt that at some stage I would like to build another boat but the first one I built works well enough that it has been hard to justify building another one. As well as building my own small boat, for about two years of my career I worked in the boat building industry, making carbon fibre spars and also for a time making subassemblies for large sailing yachts. I did enjoy that period, it was great to work with tools after years of sitting in front of a computer, but it was not so good financially and after a couple of years I went back to a 'proper' job. A typical project I was involved in was making a fold down transom door for a large sailing yacht. This was a carbon and foam sandwich construction (vacuum bagged, but not resin infusion) with lots of custom made titanium parts in the folding mechanism and hydraulics. The small firm I worked for at the time did most of the metal work as well as the composites. The thing was something like 20 foot square, so possibly equivalent to building the whole of a small yacht. So my boat building experience includes both stitch and glue plywood and vacuum bagged foam sandwich, but the total experience is much less than that of some of the contributors here.

    When I built my own stitch and glue boat I worked out the shape of the plywood parts using a computer program on a 1970's 'mainframe' computer, then cut out all the plywood with a jigsaw before doing any assembly work. The boat went together pretty quickly, I recall that the assembly of most of the structure using wire ties and temporary wood screws was completed in just one enjoyable afternoon - the rest was mainly painting and fairing. Today I would consider having the plywood pre cut by cnc equipment which would make it even quicker and more accurate. Indeed, when we built the formwork for the large transom door I mentioned above, and various moulds for other composite constructions, we had hundreds of pieces of MDF cut out by a sub-contractor using waterjet cutting and this really speeded up the work. It occured to me at the time that I could build that transom door much quicker with cnc cut plywood than with carbon fibre, but needless to say plywood was not an option for a boat as expensive as the one we were working on.

    I am just thinking about the steps involved with resin infusion, making panels on a table, whilst remembering that I dont actually have any practical experience of it. First you have to build the smooth flat vacuum tight table. Then mark out and cut the foam. Maybe fit high density inserts where heavily loaded fittings will be fixed. Then probably apply some edge treatment to the foam, for example if you are going to join the panels with tape you cut a rebate along the edges, then cut out a piece of thin plastic to fit in that rebate so that the panel stays flat under vacuum. Then you set up the panels in position on the table together with the vacuum 'stack' which consists of several layers that all have to be cut to the right shapes (and much of which will end up in landfill afterwards). Then you set up all the vacuum and resin lines, test the vacuum, possibly fix leaks then finally you can start the infusion. But after doing all that work for every panel, are you any further ahead than the plywood builder at the point when a pile of precut plywood parts is delivered from a cnc cutting company? There are a couple of subsequent things the plywood builder needs to do that do not apply to resin infusion. One is the external sheathing of the whole hull with, typically, 200gsm glass. I didnt find that much of a problem, a single layer of light glass cloth didnt take much longer than a single coat of resin or paint. The other thing is scarfing some of the 8 foot plywood panels to make up the length of the boat. Cutting the scarfs is easy, I have used an electric plane to work on a stack of parts altogether. When I built my small boat I actually glued most of the scarf joints in situ, clamping the joints with a plastic wrapped wood batten each side and screws through all. Only the two highest topside panels were glued off the hull and I think they could also have been done in situ. I see that as a bit of an advantage if you are working alone since you don't have to manipulate any panels longer than 8 foot (or 10 foot if you can get the large sheets). Seems that the builder of a 40 foot resin infused boat may have to manipulate some 40 foot long panels since I think it's hard to get a fair curve if joining the panels in-situ?

    I can see that cnc cutting could be used to cut out the foam for resin infused foam sandwich panels but since edges of these panels would later need to be trimmed to the final size I wonder whether you would be able to keep the original accuracy of the cnc cutting? It is the reliable accuracy of CNC cutting that makes the subsequent assembly so fast. Once you start introducing even tiny errors (perhaps a mm or two) these can build up and cause problems later, as I found with my little boat made from panels hand cut with a jigsaw. I did end up with some unfairness in parts of the hull and on the internal work there was one gap between two panels that I just could not close up so I ended up fitting a 6mm strip of contrasting wood to fill the gap and make a feature of it.

    Several people have said that time building the hull shell is not so important since it is the fitting out that takes most of the time. Well, I would have thought that it is in the fitting out stages that cnc cut plywood panels could actually save the most time. Surely if all the panels for the internal furniture are cut to fit in place without spilling to the hull that will save a lot of time, and if all the cut outs for wiring and plumbing and even the mounting holes for all the fittings have been pre cut in advance that would also save a shed load of time. I think it would be great to just bolt fittings to the boat without having to think about where each one needs to go.

    I have no doubt that foam sandwich can save weight over plywood and I am about half way to being a convert for that reason alone. I am surprised that two professionals (Rob here is one, the other, well easy to guess who I mean) who are strong advocates of resin infusion and sandwich seem to emphasise ease and speed of construction even ahead of weight saving, long term durablity, resale value etc.

    Groper can make a 40 foot infused sandwich panel in one morning. At that rate of progress it does start to look attractive from the point of build time as well as lightness. On the other hand, other home builders have found infusion rather more time consuming. I looked at the thread here 'Infusion Plan' where a first time resin infusion builder seems to have had a quite difficult learning experience, but got there eventually with advice from Groper and other experts.

    Problem I have is that since I took early retirement we have been away for about half each year, mostly sailing but also travelling by other means. With the normal things that everyone has to do, I haven't found much time for boat designing let alone building. Nice problem to have eh? I still want to build another boat at some stage, but due to lack of time it might have to be a smaller boat than I showed in recent pictures on this thread. Hence my interest in discussing build times with people who have used the various alternative construction methods.
  5. bluebox3000
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    bluebox3000 Junior Member

    I'm really in a hot/cold state of mind when it comes to the foam infusion. Really like the table infusion method and I believe it can save a lot of time, both in construction as well as fairing and finishing. A couple of issues;

    1. The Kelsall method uses gelcoat on table first for smooth finish. Is that necessary if one is going to paint with epoxy paint and is using epoxy resin? And/or what are other benefits?

    2. Foam vs Nida-core/Plascore. Nida-core/Plascore make special infusion panels that look very interesting and they claim it will make a stiffer panels than foam as well a being lighter. Some say not to use them below the waterline. How about a hybrid with Nida-core/Plascore for decks, bulkheads and superstructure and foam for hull bottoms and sides.
  6. scape
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    scape Junior Member

    great looking build, have any more info? I don't want to interrupt the flow on this thread but couldn't find a way to PM you :-\
  7. groper
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    groper Senior Member

    Gel coat is for use with PE or VE resins... Although there is now epoxy compatible gel coats on the market in a very recent development. If you make a really nice table, it's worth the effort as one side of the panel is then completely finished. One regret I have is not making a really nice perfect table, if I do it again I would do it this way...

    There is a build on DIY yachts dot com called "finally does it" . I suggest you take a look as its a CNC cut premade plascore panel kit assembly of a 40ft cruising cat. This guy also lives near me so I've seen it in person. It's about the same as building in foam core, all the processes are the same although we both agree that foam is a little easier and friendlier to work with.

    You can buy pre made panels or infuse them yourself, like I said before it's just another money for time trade. Making your own panels costs less money but more of your time to do it.

    John perry, I had a lot of foam CNC cut before I infused it as a large panel. The time saved was minimal because infusing complex shaped parts is difficult as a beginner. Later, I found it quicker to simply infuse a large flat rectangular panel, done in a single morning, then chop it up into smaller panels I needed with a circular saw. If I was to build again, I would use premade panels that were CNC cut for all of the intricate details such as the internal furniture and the bulkheads. The larger panels such as the decks, bridgdeck floors and top sides etc I would infuse them myself again on a gelcoated table so that all the deck hardware reinforcements are pre placed before infusion and the large panels are very time efficient to make. Small panels are not time efficient with infusion.

    In a good design, most if not all of the internal furniture is structural. It provides stiffeners for the top sides, bridge deck floors, and added athwart ships strength just like the main crossbeams. For this reason I wouldn't consider a bolt together ply interior otherwise the entire shell needs to be built stronger, heavier, more expensive...
  8. groper
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    groper Senior Member

    Only this scape,

    As a relevance to this thread, the recessed edges of the panels have been taped together and bogged over to finish flush in a single "wet on wet" process...


    You can also tell via the shadow lines on the panels, that they are dead fair... which is one of the best features of vacuum or press laminated sandwich panel building compared to plywood - which always has warps and bumps no matter how good the quality of the ply...
  9. nimblemotors
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    nimblemotors Senior Member

    As I ran into this excellent website again, I thought it would be worth posting,
    3500 hours to build a 32ft Woods Gypsy, well documented details.
    What I wanted to point out is one view here, just roughly 300 hours to BUILD just the two hulls, then 675 hours fairing and painting.
    What I get from this, design a boat so it doesn't need painting.
  10. ThomD
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    ThomD Senior Member

    It is dead nice and you should be proud, but I don't see that as fairer than ply. I have seen plenty of ply boats that look great. My own looks fair. I used the worst imaginable ply on the amas, actual crap, and it still looks good 25 years on. I did not spend as much time as some do fairing the deck radius, but that was a conscious decision. I also awlgripped right over the raw wood epoxy, no primers.

    I would do a better job, that was before I did a seminar with Jim and Steve Brown. Towards the end of the seminar, the 23' foot boat was mostly done. They got to the shop about an hour early and between the two of them scraped and ground the boat, everything but the keels, which were already done. Two guys, one hour. The boat looked great. Brown boats are known to look great. Russ is famous for it. It isn't magic, I now know how, but it is something I learned after my project. Maybe that is the real magic of the KSS method. A lot of people take a seminar. If I had taken a seminar before I did my boat, rather than after, I would have been a lot further ahead.

    Ply boat finishing is basically like drywall. Drywall walls are not fair in the boat sense. But they would be if the panels were the length of the walls, or scarphed togethe, :)r. A lot of very picky people have hugely expensive homes the walls of which are all drywalled. Drywall can be done very quickly if you know the method. It can also be done without sanding, if you want to. The trick in drywall to getting heavily radiused fair corners is to use bullnose molding, which is a trick the Gougeons have used on ply boats. The problem is where do you learn how to do this stuff. Russ Brown has a book out, but I haven't read my copy yet. One of the most important parts of clean work is learning what steps to do in what order, at a time. One of the problems I had with my radius's was the order in which I used the tape and the cloth. My method seemed to make sense, but it turned out to be wrong. Also, one of my problems was getting rid of trace surface blemishes, or the lines around a patch of 410. Turned out to be easy if one used epoxy primer.
  11. jamez
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    jamez Senior Member

    The Hennigans were an inspiration to me in my early days of interest in multis. The Gypsy is a great design and it was on my possible list for some time.

    It would have been helpful if they had generally separated fairing time - ie. the time spent achieving a paintable surface - from the painting itself. In a couple of places they have, but when I look at the table and see 114 hours to fair the forward beam I can't help wondering how they were going about it.

    Assuming of course the basic frames/stringer structure is true and fair to begin with, a properly set up ply hull should not require any large area panel fairing. The only 'fairing' on my boat amounted to filling screw holes, and around localised areas like bow caps (and a couple of electric plane accidents) before glassing. I never used a long board on it.

    IMO it is a waste of time trying to make a sheet ply boat look like its been popped out of a mold. Whatever you do it will still have corners. Incidently Jim Brown wrote a thoughtful piece about levels of finish in Searunner Construction. Brown advocated a 'work boat' approach to finishing pleasure boats as one way of keeping cost/time under control. That doesn't mean poorly finished, but adequately finished for purpose.

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  12. ThomD
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    ThomD Senior Member

    I would agree it is sometimes cheaper. If I was redoing my small tri main hull the skin, which is what we are talking about, would be 6 sheets of plywood, at 15 dollars each, or 90 dollars (81 US). I would need deck clamp stock, and 4 oz glass on the outside, and 3 coats of epoxy on the inside. Just stipulating that your hull is better in every way. I've none the less been perfectly happy with the boat all these years, now about 25. I only have had one major problem, and that was due to water coming into a hatch, that due to personal issue I never got redone for a few years, so it did rot. Foam is way better when stuff like divorce, injury, or illness strikes. It can take care of itself. I had to rip off the rear deck. But when I got around to it, it was a pleasant job that took an afternoon, and then a few minutes here and there to get all the little steps like glassing, and painting done.

    I don't agree RI is easier, or really see the point to that. It isn't easier to get started on. If you take a seminar it is something people are enthusiastic about. But that applies to taking seminars on the other methods also. Once one has built a hull or two in any method it ceases to be difficult. The first hull is the rub for amateurs. Everything has the vices of it's virtues, and in this case the virtue is how much happens during infusion. But that intimidates noobies who don't want to make a very stiff and hard to hide piece of garbage their first try. I don't even know if anyone has made that mistake. I know a few people who blew up a test piece. But maybe it has never really happened to those following the plans.

    I wouldn't generally build a ply boat over 32 feet unless it was only one sheet high, or something.
  13. Richard Woods
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    Richard Woods Woods Designs

    I built the prototype Gypsy and had it in the water and sailing in 1000 hours, I don't think it could be built any quicker than that. But it didn't look as good as the Hennigan's Lightwave. I had built boats before and they hadn't.

    Russell Brown is (like his brother) a brilliant boatbuilder, if you haven't read his books you should do so.

    It's the finishing that takes the time, not the structure. Flanges on flat panel foam boats save much more time than one might think. The quickest way to build interiors is by using simple melamine face chipboard/mdf moulds, not by making furniture in individual pieces and then joining them up. Painting the interior takes longer than the outside, so pre-coat the interior panels with tinted epoxy and leave it like that.

    A few years ago we bought a plywood 34ft Romany (big sister to Gypsy). It was built by a chiropractor who, again, had never built a big boat before. He had it sailing in 2300 hours, as did the owner of a 35ft Mira which was later sailed round the world.

    The original builder sold the Romany (not to us) for a lot more than the cost of materials, we sold it for more than we paid for it. The biggest all wood boat I've built was the 25ft Gwahir, built in 1982 from unsheathed 4mm plywood. It was still going strong when I saw it 2 years ago

    Richard Woods of Woods Designs
  14. oldsailor7
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    oldsailor7 Senior Member

    Groper said. Quote :-
    There is no problem with handling loads on thin skinned multis which only have single curvature... There are countless examples of very successful multis which prove it...Quote.

    The Buccaneer 24, 28 and 33 trimarans have thin skinned chine panels which have a subtle three dim curve to them.
    Even on a 52 ft Wharram "Tehini", which we built in 1/2" ply, we were able the include a 1" curve in the 4x8 panels.

  15. John Perry
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    John Perry Senior Member

    Richard, that statement puzzles me, perhaps it is not quite what you meant to say or perhaps I misunderstand. Making a mould for internal furniture using melamine faced chipboard or similar would surely require cutting out and joining about the same number of individual pieces as building the furniture directly with plywood. Any imperfections in a mould get perfectly transferred to the part produced, so to avoid a lot of finishing work later on, the mould would need to be finished to whatever standard you feel is acceptable for your finished furniture. I can see that the melamine will give a nice finish over most of the surface but you would still have to take care of joints and use Upol or similar to make nice fillets in all the corners. So altogether I would have thought that making just the mould for the furniture is about as much work as making the furniture directly from plywood but still leaves you needing to do the actual moulding - so how can that be quicker for a one off build? I would have thought that you would need to be making at least two or three identical parts before making a mould could show a time saving. Then, once you have the mould, how would you do the laminating? If you do it as a solid fibreglass laminate it is surely going to end up significantly heavier than the equivalent in thin plywood. To match or improve on the weight of plywood you need to use lightweight core, so two layers of laminating, probably vacuum bagging, de-coring, filling and fairing at exposed edges - even more work I think?

    I think it is possible to put together lightweight internal boat furniture very quickly from thin (typically 3mm to 6mm) plywood. Once you have the pieces cut out (ideally done by computer controlled equipment) it takes just a few copper wire stitches at strategic points to hold it together, then you paint it all over with epoxy, using the brush bristles to help the epoxy seep into the joints between plywood pieces before giving the wire ties a final twist to close the joints. Once the resin has set, an angle grinder smooths out the wire ties and removes any blobs of resin. The next coat of resin improves the finish and the viscosity of the resin automatically produces little fillets at the joints, adequate for a lightly stressed part, but you could use larger fillets with filler and/or internally glass tape the joints if more strength is needed. Then high build epoxy primer (if you can afford it) and finish paint.

    I expect I am preaching to the converted, I expect there are plenty of people here who have done the kind of thing I describe above, probably with their own variations on the basic technique.
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