Build time 40ft catamaran

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

  1. bluebox3000
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    bluebox3000 Junior Member

    On the weight issue I'm trying to compare plywood vs foam. Overall it look like I need somewhere around 2500 sq. ft. of panels and using 9mm okoume or meranti plywood with 6 oz fiberglass on one side and stringers the average panel weight without paint will come in at around 1.5 lbs. perhaps a little more.

    One reference (cant find it again) compares 9mm plywood to 3/4 in foam with 32 oz fiberglass. Such a panel would weigh in around 1.2 lbs sq.ft, really not that different from plywood and uses a lot of epoxy. West System however specifies a typical 3/4 in foam to have 12 oz cloth so it would weigh in at around 1/2 lbs per sq. ft. That is of cause a huge weight saving on 2500 sq ft of panels.

    So on 3/4 in foam what is closer to the norm, 12 oz or 32 oz?
  2. WestVanHan
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    WestVanHan Not a Senior Member

    I can think of the two (and only IIRC) builders of larger cats who posted here,who both ran into $$ troubles.

    One still wandering about Australia (and waiting for Armageddon) in an uncomplete boat,trying to sell it for half the $400k he has into it.
    And the other ditched by his supporting wife who had enough of it-last I heard he was living in a van in Walmart parking lots in Florida.
  3. groper
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    groper Senior Member

    dont forget our member 44c - also posts here, finished his a couple years ago after 3 years building and is happily cruising around australia right now... Very nice boat, goes well and wouldnt have trouble selling it for over $300k...

    Bluebox - different designers spec different laminates, based on how much arse covering is required. For professional charter use, you will find a heavier laminate like the 32oz which the nut job "catbuilder" (referred to by WVH above) had specced on his 46fter by Kurt Hughes. Most of the fast australian designs for private use much lighter laminates, more like 15-20oz over most areas using foam core. Balsa core more like 15oz over most areas. Of course, there is extra reinforcement below the waterline...

    A 40ft sandwich boat will be alot lighter than a typical ply boat... the performance and resale will be more than the increased material cost.

    WVH - Masalia paid people to build his boat - thats what it cost so much, if he did it himself he would have been into it for a tad over $100k...
  4. Corley
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    Corley epoxy coated

  5. rob denney
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    rob denney Senior Member

    Thanks for that, Corley. A great site, 3 of the 4 builders of the unstayed wing mast cats are there, with lots of information.

    Last edited: Feb 23, 2014
  6. Richard Woods
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    Richard Woods Woods Designs

    I have been quiet on this forum for a few days. That's because we've been down on our Skoota powercat, and yesterday I was racing a half tonner (and yes, it was snowing).

    Catsketcher says I can speak for myself. But why should I have to? And why on earth would I make things up? I've been a full time multihull designer for nearly 40 years, and previously spent three years at college studying yacht design, not a different engineering discipline.

    One definition of a professional is someone who gets paid to do something. Another would be that it is someone with integrity.

    Unlike most designers I don't have a "real' job, nor do I sell boat building materials to supplement my income. I am afraid I don't know how many plans I've sold, I lost count years ago, but it has to be between 2000 and 2500.

    Rob says I only know how to build wood boats. He should check my website before writing stuff like that, as it's all documented there. In fact the biggest wood hulled boat I have ever built was the 25ft Gwahir, which was launched in 1983. I saw it a couple of years ago, still going strong, despite being built in unsheathed 4mm ply.

    The last cruising boat I built was the 32ft foam sandwich Eclipse. A few years earlier I built the 28ft Gypsy. That had flat panel foam sandwich hulls as I thought that was the cheapest/quickest/easiest method. The largest boat I've built (with my ex wife) was the 35ft foam sandwich Banshee. I cannot remember the exact hours, but we started in January 1986 and were sailing it in July that year, even though we built a foam sandwich 24ft Strider at the same time, and of course still had the designer's "day job". The topsides and decks of the Banshee were all single curvature, so too was the Eclipse (apart from the cabin roof)

    Our Banshee went to the Southampton Boat Show and was filmed, and then used as a floating interview room by the BBC so it was a finished boat, not an empty shell. The next year we won the Azores and Back 2 handed race and the following year the Yachting Monthly triangle race (other Banshees were second and fourth). The second Banshee built was the first catamaran ever to finish the Fastnet Race.

    The first cruising boat I built, in 1979, was the 30ft Cockleshell Hero and guess what - it had flat panel grp hulls, not plywood ones.

    I also know a bit about Ikea as my niece is an Ikea designer. If you really want to build a light fast simple boat then you shouldn't be thinking about doors at all, you need to change your mind set. And as everyone who has built a boat, whether in aluminium ply or foam sandwich, knows, it is the interior that takes the time, not the hull shell.

    Probably the main reason NOT to buy a used boat, or any production boat for that matter, is because it is a mass market boat, thus not necessarily the boat you really want. People still build wood boats because they like wood, just look at the Wooden Boat forum to see how enthusiastic they are. My Skoota 28 is a plywood boat because the builder was a high class woodworker, not a laminator, and he didn't want to work in foam and glass.

    But none of that is what this post is about. I emailed a customer who is having a Transit 38 built in the UK right now on a sort of MIY scheme. He is a doctor and lives 400 miles from the boat. So he doesn't see it often, nor does much work on it - except I know he applied the coppercoat antifouling. Instead he employs sub contract laminators and wood workers to build the boat and rents a shed. He will be launching this spring. When I last saw him he was fitting his central heating system that will heat the whole boat, not just the saloon, so it isn't a simple fitout.

    I quote from his email of 2 days ago

    "There is quite a bit yet to do and significant expenditure remains. If I had been in a position to do the boat myself it would have been rather more basic as I do not have the builders degree of skill and expertise, so I would have limited the sophistication of the fit out. It would have taken me much longer. The total spend to date is @GBP129K. I am going to have to do my very best to get launched for @175K which was my total budget. The original quote to me for a complete boat, (including engine, rig, sails, electronics and complete internal fit out) was £158,775."

    At today's rate that's about USD 200,000 spent so far and a predicted total of USD280,000, the original quote being USD254000. That includes the VAT (sales tax) of 20% on all materials, but not labour. Obviously if the owner had done more work himself the cost would have been much less.

    And of course he got the interior and fit out that he wanted, not what some boatyard thought he would like. The deck gear is all Harken, the spars and sails are UK sourced, not Chinese cheapies.

    The Transit is a faster boat than a equivalent Fountaine Pajot, with a larger more comfortable interior and is better built. I can say that with confidence as in October I sailed a 38ft FP Athena in Greece and then a few weeks later I sailed a Transit 38 in the Bahamas, so the Athena experience was fresh in my mind.

    That Transit was built in the USA using hull and deck mouldings sent out from the UK in two containers. No doubt other potential builders could do the same.

    Richard Woods of Woods Designs
  7. Baltic Bandit

    Baltic Bandit Previous Member

    IOW that's not a "closed" price... that's a biased estimate of what you believe it should be worth. Kinda the point I was making
  8. groper
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    groper Senior Member

    Congratulations Baltic Bandit, you the first privileged member to make my "ignore" list, you should feel proud... Everything you post in any thread is inflammatory and im tired of seeing it...

    Cya mate...
  9. rob denney
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    rob denney Senior Member

    Sorry about my last post, was meant to go on the biplane rigs thread.

    Groper, DGreenwood and others have said it better than I can.

    Aluminium is a great material. Tougher than glass or wood in coral reef encounters, easy to build with if the cutting is done by cnc and you can use a tig or mig welder (very easy to learn, and like infusion, mistakes are pretty obvious and easy to fix) and does not need painting or fairing, which is a huge saving. I have not tried rolled alloy, but flat sheet boats look pretty good. Downside is corrosion if you are not aware of the possibilities, and insulation, which can be a pain. I have not done the cost numbers for a while, but Peter Kerr at Lizard Cats on the Sunshine Coast has been building them for decades, so it can't be too far out of the ballpark. Weight wise, the cut off with infused foam is probably closer to 60', but vs ply it is probably not far off 40.

    If you build it with an itinerant's help (and/or cost your hours at the same rate), the overall cost will be far less than a pro who has to pay more for build labour, office labour, factory overheads, profit, warranty, govt imposts, etc. Thus, your cost will be less for the same quality job. Therefore, a possible lower selling price is not a bigger loss as you start from a lower base. Plus all the other benefits from earlier posts.

    CC would be a lot of work (mould prep, bending/spiling panels, difficulty of making edge joins/bulkhead landings/etc. Cylinder Moulding would be easier, but the laminate won't compound, so would need some experimentation. Solid foam bows would help a lot. We are building lee hulls from simple mdf moulds with filletted corners which means only 2 joins and compound curve chines and deck edges.

    My materials costs are just that. The other stuff (plans, shed, tools, etc) is too hard to quantify on a general basis, but should be done by anyone considering building. On the subject of tools, $1,000 will get everything you need from Bunnings/Walmart for a ply or an infused boat. Cost of fitout is also impossible to quantify generally, but again, doing so is essential before you start. There is no boat related reason why the costs should not be calculated very accurately before you start. Done thoroughly, there will be no surprises.

    Sorry about the units.
    Most 12m cats use 15mm foam with 600 glass outside, 400 inside. Infusion uses about half the weight of glass in resin, plus .2 kgs per side to fill the foam. Infused, this weighs ~3.1 kgs/sq m, total. The same as a sq m of 9mm gaboon, before it gets at least half as much weight again added in resin, glass, filler, frames and stringers plus all the filletting and tabbing.

    The weight will be ~775 kgs/1,700 lbs infused, or ~1,200 kgs/2,550 lbs in ply. The foam boat will have vastly bigger panels as it is much stiffer. Not sure how many 40' cruising cats are built with 9mm instead of 12.

    What I said (post #70) was " Richard and Peter are both experienced ply builders" If this is not true, I apologise to anyone who was misled.

    You talk about how many foam boats you have built, don't mention how many of them were infused?

    Good advice about your web page, thanks. I visited, put "infusion" in the Search box and it came up with one hit where it said:

    "The newest construction technique is to use resin infusion. I am not going to say any more about it here. In part because I feel that if you need to know the basics about it then probably you should chose an easier building system. In other words, it is for experienced builders.

    Using a vacuum does suck up some of the resin and remove most of the little air bubbles. That makes a stronger, lighter laminate but to be honest I don't think the savings really amount to very much and are only important on a racing boat. And the bond is still only on the surface of each foam skin.

    Instead of using a vacuum bag, I prefer using "contour foam" or scored foam (on a male mould), which is like end grain balsa in the sense that it is cut into small squares (about 11/2") and stuck to a thin glass backing."
    end quote

    Given the number of total novices infusing successfully and the ease with which they do it, these quotes are why I don't think you are qualified to discuss the differences between ply and infused flat panels, or for that matter foam construction at all as your preferred method has been superceded (several years ago) by lengthwise and width wise foam strip.

    It is also a diabolical way to build a boat, not least because you have to build 2 hulls, the first one being a throw away mould.
    Non vac bagged contoured core is responsible for almost as many boat problems as plywood. For those tempted to try it, Don't. Wetting out foam by hand cannot fill all the open bubbles in the surface (the same as bog does not fill screw holes in ply when it is screeded over them) so the bond (which is the weakest part of the sandwich) is even weaker. Using bog without prewetting the foam will be considerably worse.

    Infusion removes all the air before wetting out, so the bond is 100%. Vacuum should remove all the air, but often doesn't due to insufficient gel time or thick laminates.

    As to the "savings not amounting to much weight" and "changing the mindset" by leaving out the internal doors.
    Elsewhere you quote 2:1 resin fibre ratio for hand laminating. With infusion/vac bagging, it is 1:2. That is 4 times as much resin in the boat than if it was infused or bagged. Using Bluebox's 2,500 sq'/230 sq m of material with 400 inside/600 outside, this will be 230 kgs using hand layup (plus 10% wastage according to the Gougeons), plus the bog to (sort of) stick the foam down, plus (a lot of) filling and fairing. Minimum of 300 kgs. If it was infused, it would use about 60, plus maybe 5% waste, with no filling, say 70.
    An infused door and it's surroundings would weigh 5 kgs, take 5 minutes to include in the infusion. You would need 46 of them to make up for the extra resin which adds absolutely nothing to the boat except many hours of extra labour and cost.
    "Change the mindset", indeed!

    I don't see "just being a designer" as a plus. The benefit of being a material salesman, mast manufacturer, boat builder, delivery skipper and paid crew is that I saw what everyone was doing, spoke to and worked with designers, builders, sailors and engineers. This gave me a broader education and a better appreciation of what was good, bad or indifferent than I would have got 40 years ago in boat design school. Maybe the differences in our experience could explain the differences in our design/build approaches?

    What did it cost to ship a set of moulds from the UK to the USA and back again? Did they fit in a container?

  10. cavalier mk2
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    cavalier mk2 Senior Member

    Hello Rob, I did think of cylinder molding too, I like the idea of the solid foam ends. The CC foam all takes the same spile/cut making a easy cnc program or jig cut. With one layer it is vastly simpler than the wood CC layup. A bending jig would take some experimenting but once worked out would be as easy as a toaster but I'm not sure it would be necessary. With a female mold pressure inward on the edges would force the foam into the curve. On a male mold holding the edges down would do the same thing. These procedures should work for either CC or cylinder molding. Depending on the brittleness of the foam, the sheets might need scoring but again a cnc could take the drudgery out of the work. Good to see you working on proas, I've always felt the concept could have advantages.
  11. nimblemotors
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    nimblemotors Senior Member

    This has discussion of different building methods:

    I don't think there is any question that using female molds and resin infusion is the fastest method, it is how every fiberglass production boat is built.

    The question then becomes how can one create a female mold quickly and cheaply.
    One answer is to use it many times so its costs is amortized over each use.
    For a multihull, you can use a hull mold at least twice.

    I would ask/suggest to create half a hull mold and use it four times, but then it requires a hull shape that is symmetric.
    This is how I have done my dinghy cataraman hulls:
    This leads to a question why not a hull shape just a cylinder or rectangle with alterations after molding.
    This is how hull for houseboats are made.
  12. groper
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    groper Senior Member

    Ive often wondered about the feasibility of this method too, infusing in female molds. Having not tried it at full scale, i cant say whether the time to build the mold would be worth it, but ive often thought that it probably is worth it everytime i have to tape and fillet a chine. I did the compound bow areas below the waterline infused in a "temporary mold" - it was ruined after the second hull trying to demold it. It was made cheap and fast - hence it couldnt last.

    There is added cost in building the mold however but i think the time savings could be there, as depsite the time to build the mold, i think it would save more time overall.

    Alot depends on the shape of the boat however, more chines means more joining if flat panels. If less chines, and generally more able to simply fold up the flat panels and bond them together like Rob Denny does, then building molds is a waste of time.

    As to CC and compound curvature surfaces - with foam cores the panels are much stiffer and so are not reliant on the curvature to get the stiffness required. If the panel is very flat and lacks inherrant stiffness, then simply increasing the core thickness is all thats needed. This is far simpler than building compound curves into the boat and all the associated hard work after the fact when it comes to fitting it out later. You cant take this approach with plywood tho, as it just gets too damn heavy if the thickness is increased.
  13. Barra
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    Barra Junior Member

    Compound curvature

    What's all this silly talk about cc not being important?
    One moment we are advocating minimum weight then we are excluding the benifits of shape. When chickens start laying flat pannel eggs then I'm prepared to concede . To me beauty of form is important. Flat panels scream cheap, amateur , and sometimes ugly. One has to be proud of their boat . That's very difficult if the designer has drawn inspiration from a butter box.
    Malcolm tennant used cc beautifully at times.
  14. nimblemotors
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    nimblemotors Senior Member

    And just what are all those chimney's on house as rectangles do they have no sense of beauty? A satellite dish with its lovely compound curves attached to it, now THERE is something to admire. :rolleyes:

    Beauty is building your boat in 6 months, and out watching the sunset,
    not sanding in a shed for 6 months.

    The vast majority of catamarans hulls have slab sides and have large amount of windage. This is why I think some people find cats ugly.
    But beauty over time follows function. Wings on racecars were considered hideously ugly until they won all the races...

    This Hughes is essentially slab sides, although broken up.


    The real slab sides of most:



    And one of the few, Shuttleworth 'pregnant' hulls.

  15. John Perry
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    John Perry Senior Member

    I dont think it is a straightforward matter to say whether compound curvature panels can be lighter than single curvature or flat panels and if they can be lighter it is not straightforward to quantify the advantage. The skin panels of a yacht are subject to a variety of different kinds of loading such as:

    1. - Overal bending of the hull due to rig loads and water pressure loading - i.e. the kind of loading that snapped the bow off Pete Goss's 'Team Phillips' catamaran and also broke an America's Cup yacht into two halves.
    2. - Torsional loading - this is particularly important for multihulls that consist of roughly tubular hulls connected by two or more cross beams - when the structure is twisted by wave action combined with rig loads the regions of the hulls between the cross beams are subject to torsion.
    3. - Water pressure loads that can cause 'panting' of hull panels in rough seas
    4. - Concentrated impact loads, for example due to hitting floating or fixed objects
    5. - Loading from fenders when berthed alongside in other than calm conditions.
    6. - Localised loads due to taking the ground - important for multihulls that are intended to be suitable for beaching.
    7. - Localised loads where rigging/engine mounts/foil/rudders are fixed

    For 1 above compound curvature may not have any significant advantage, single curvature panels with only a slight longitudinal curvature (or indeed flat panels) may be just as good. This does however depend on whether failure occurs due to the overal longitudinal stress or due to local buckling of the skin on the compression side of the beam. If local buckling is a problem then compound curvature might be an answer. However, with sandwich construction, an increase in core thickness may also eliminate the problem with little extra weight.

    For 2 above much the same applies as for 1 above, except that local buckling is less likely.

    For 3 above a compound curvature panel may be beneficial, but if the panel is capable of withstanding the various other loads listed then it may well be strong enough to withstand this kind of load regardless of whether it is compound curvature or not. And, as Groper says, a foam sandwich panel can if necessary be strengthened against this kind of loading simply by increasing the core thickness, with very little additional weight (but some additional cost I think ;-)

    For 4 above, if it is a very minor impact then I think the properties of the outer skin of a sandwich construction are what will determine whether the result is a slight scratch or no significant damage. For a slightly greater impact the properties of both skins and the core determine the extent of damage. For a still heavier impact the energy absorbing properties of a larger area of the panel are important and a flat or close to flat single curvature panel may conceivably be better than a compound curvature since it can possibly deflect further before the skins rupture. Taking the example of an egg, it is strong when you squeeze it between soft surfaces such as human fingers, but it is a bit vulnerable to a concentrated impact because the compound curvature skin is so stiff that it can absorb little energy in an impact - not too hard to fracture it with the edge of a spoon. Is it conceivable that the same material as the egg shell in a flat panel could absorb a greater impact energy?

    5 above is a bit like 3, but can possibly be more severe.

    6 can result in high loads but the designer knows where those loads will be imposed so can design for them. This may mean adding something like a grounding strake or external keel to take the load and distribute it through internal bulkheads (say) to the whole structure, in which case it is not so important whether the hull skins are compound curvature or not.

    7 - again the designer knows how these loads will be applied and can design for them regardless of whether the skin is compound curvature or not.

    I agree that aesthetics are important - "the sole purpose of a yacht is to please the owner". Boat design is art as well as engineering. However, I would not say that compound curvature panels necessarily make for a better looking boat. The longitudinal joins between single curvature panels can be arranged to emphasize the sleekness of the craft in a visually attractive way. I dislike the look of many of the most recent motor yachts that are all bulbous compound curvature shapes. This is of course subjective.
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