Trailerable Multihulls

Discussion in 'Multihulls' started by JCD, Mar 4, 2008.

  1. JCD
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    JCD Follow the Bubbles!

    Hello all...

    Just want to kick this around a bit and see what happens since I have found myself pretty busy but with time to read.

    Which is the smallest size multihull that you would consider for "offshore" cruising and why or why not?

    Here is a start.
    http://www.smallsailboats.co.uk/weblinks/multihulls.htm

    Any thoughts?

    J:cool:
     
  2. tspeer
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    tspeer Senior Member

    Chris White's criteria for an offshore trimaran is a minimum of 40 ft and 100,000 ft-lb of righting moment.

    Ian Farrier recommends the F33 as the smallest of his designs suitable for offshore. The F36/C36 is the smallest of his designs that are really intended for offshore.
     
  3. JCD
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    JCD Follow the Bubbles!

    Hello Tom,

    Thanks for the info.
    Okay...so we have at least 33 feet and 100K#'s of righting moment called out by 2 top caliber designers.

    Now, all possible things considered, comfort, safety, stores, displacement etc., what would be considered the outmost smallest trailerable multi you would consider for offshore cruising, assuming that it can be classified as offshore capable, singlehanded or, possibly a mate.

    J:cool:
     
  4. terhohalme
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    terhohalme BEng Boat Technology

    Simplified from ISO standard 12217-2, In catecory B (offshore):

    1.75 * m * (LH * BCB)^0.5 > 15000

    where m is light loaded mass (kg), LH is length of hull (m) and BCB is beam between centres of bouyancy of outer hulls (m).
     
  5. JCD
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    JCD Follow the Bubbles!

    Terhohalme,

    Excellent post. This now gives us a wide range of LOA, BM and Displacement that we can work within for even the advent minimalist. We will definitely come back to this and thank you for sharing it. Now, more specifically, what would be the smallest offshore multihull you would accept as a cruiser. Take all other things being equal and remember that not always will a trip be of such length out at sea that stores will exceed the weight of a whale. What size do you believe would be minimum for you and possibly a mate? I'm trying to hone in on a LOA range.

    Also, if I may, did you choose cat B because it is the minimum as requested or for some other reason?

    Thanks
    J:cool:
     
  6. terhohalme
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    terhohalme BEng Boat Technology

    Cat A is for ocean and the minimum size against breaking wawes is 40000 for this category. The equation varies slightly, if LH/BCB ratio is not "normal", for catamarans 2.2 - 3.2 and for trimarans 1.1 - 1.6. See standard.

    I am building now catharsis 26, the smallest (cheapest) I concluded for cruising. It is for coastal cruising on Baltic Sea, catecory C. Make it a little heavier, and you'll have an offshore cruiser...
     
  7. Richard Woods
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    Richard Woods Woods Designs

    I have been the multihull representative on the ISO stability committee for about 15 years. The stability formula is very simple but seems to work very well. In general boats over 9m will get into category B and those over 11m in Category A. We consider that Category B boats are seaworthy enough for average sailors to use for trade wind ocean sailing, Category A boats are go anywhere boats, eg Cape Horn to windward etc.

    Having said that we are currently modifying the standard slightly, to include a “bare-poles” factor and also to try to indicate which multihulls are susceptible to pitch poling.

    Now to get back to the topic being discussed. I'm not quite sure what you are after. At one point you ask what is the smallest boat suitable for ocean cruising. Elsewhere you say what is the smallest "trailable" boat , something quite different.

    Although one of my 9m Skuas has crossed the Atlantic, the smallest of my designs I consider suitable for comfortable ocean cruising is my 28ft Gypsy. One sailed Panama to Tahiti last year, another is currently en route to Hawaii.

    The key word in the previous paragraph is “comfortable’

    A number of beach cats have made ocean crossings, the latest in 10 days. A Brazilian is currently sailing round the world in one (there is a youtube video of him leaving Brazil). Another sailed to Antartica.

    Personally I’d be happy living on board a Gypsy (and have done so in the past). I’d only live on a small open deck boat if the land disappeared (as in Waterworld). That doesn’t mean a small boat isn’t seaworthy, just uncomfortable and miserable. You have to be very tough (and probably French) to sail a beach cat overnight.

    Finally don't forget that the first catamaran to sail round Cape Horn was a 30 ft Oceanic, sailed by the inexperienced Rosie and Colin Swale, with their two small children on board.

    See more on Gypsy and Skua and all my designs at
    www.sailingcatamarans.com

    Good sailing, whatever size boat you have

    Richard Woods of Woods Designs
     
  8. JCD
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    JCD Follow the Bubbles!

    Hello Terhohalme...

    Thanks again. I didn't disclose it earlier, but I also had decided that a 26 footer with a 13 foot beam displacing 3500# would meet the criteria you quoted. I did some more calculating and was able to bring that down to 24 feet.

    Catharsis is a damn fine vessel. How far along are you with her? I would be very interested in following her progress.

    I'm on a mission. Stand by for further disclosure.

    J:cool:
     
  9. JCD
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    JCD Follow the Bubbles!

    Hello Mr. Woods,

    Thank you for taking the time to share your experience and knowlege. I apologize if I caused any confusion. My initial post made reference to "trailerable" and any future posts will be in reference to trailerable.

    What I'm after is this. It is my belief that a gap may exist in "Offshore" trailerable multihulls. In other words, I don't believe that there is any catamaran design currently existing which has been designed to be "offshore" capable, whether Cat A or B, while also being trailerable. This is of course in my limited knowlege. Further, those that are considered trailerable and offshore capable are huge and expensive and leave out a large number of the "minimalist" multihull cruisers that may not want to haul the condo around while cruising or have to walk a mile to relieve the bladder. You are absolutely right. The key word is comfortable. I know that I would need some minimal comfort.

    Yes...there have been several vessels that have crossed oceans and kudos to them for doing so. But they were not designed as offshore capable and having done so was taking a risk. Also, hats off to the designers for those designs that had the vision to know that someone may try it and designed them accordingly.

    So, bottom line is that I intend to attempt to design an "offshore" trailerable catamaran, by offshore design criteria, at the smallest "comfortable" size possible. No, not by the broker criteria of "the larger the better". I do however believe that a Cat A design may be near impossible for the minimalist approach to a multihull but I'm not at this time excluding it until all attempts have been exhausted.

    Okay...the Gypsy is 28' so now we have another length to add to the list.

    If I may... do you know if the Oceanic was trailerable or designed for offshore use?

    Thanks

    J:cool:
     
  10. Richard Woods
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    Richard Woods Woods Designs

    A Category A boat will weigh about 4T, 9000lbs, and be about 11m, 35ft long. That may be trailable in the US, but isn't normally considered trailable elsewhere. Even if you are in the US I'd be tempted to get a smaller car and put the money into a bigger boat (but maybe I'm biased, as I haven't owned a car for 6 years)

    I'm sure you can do a search for Rosie Swale and the Oceanic. She wrote two best sellers which I expect you can find on Amazon. The Oceanic was designed by Bill O'Brien in the 1960's and was something like a 9m Catalac.

    Personally I wouldn't sail an Oceanic offshore, never mind round the world.

    A Skua was sailed across the Atlantic to the Caribbean from Germany in 2002/3. I sailed it in the Grenadines, you can see more on my website, as ever.

    www.sailingcatamarans.com

    Speaking personally, again, I'd prefer to live on a catamaran with at least a cuddy, better still a full bridgedeck cabin, rather than an open deck boat. I have lived on board all three types during the last 30 years. Maybe that is my problem, I am too old for only a basic standard of living. Having said that, we did spend 2 months living on board our Merlin last year.

    Best wishes

    Richard Woods of Woods Designs
     
  11. JCD
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    JCD Follow the Bubbles!

    Hello Richard,

    My Green Lantern came in at a little over 3.22 Tons and 34'. That was long time in the making but all the calculations point to a very lively Cat A catamaran. I'm not of the opinion that a trailerable is anything that can be trailered. Shoot...I'm licensed to trailer "triples" behind a tractor for a 90' length. For me, trailerable should be a design that you can trailer in your vehicle, without having to buy a vehicle or trailer to fit the boat and, you must do it fairly simple and safely and it has to fit on the road without permits. That means 8'6" in the US.

    Six years is a long time to go without a car IMHO. I guess I can, but not yet. Maybe once I'm on the water forever.;) No need to research Swale or the Oceanic as the question has been answered...it is not trailerable.

    Trust me when I say that I visit it often as I do many other respected designers. I am always looking to see what is newly developing. Many times, I go for a refresher or a quick "recliner sail".

    I believe that we are of like mind when it comes to this point. I believe myself capable of enduring some hardship and enjoying it fairly well on an open deck boat, but a bridgedeck cabin is always nice to have. That being said, I know that there are many that don't mind donning foul weather gear instead of sitting in a dry cabin.

    So...are you aware of any trailerable catamarans that are designed for offshore duty and if you are, which is the design? Do you think that a market exists for such a concept?

    I believe that those minimalist owners will more than likely remain inshore for a large percentage of their ownership, but wouldn't it be nice to know that they can go offshore with confidence in knowing that the design is offshore capable? Lower maintenance and expenses notwhitstanding?

    Thanks,

    J:cool:
     
  12. Richard Woods
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    Richard Woods Woods Designs

    I think it is worth clarifying what is meant by offshore cruising.

    Sailing from Alaska to Seattle is not an offshore cruise, it isn’t even coastal. Rather it is inshore, which is why the most popular boats in the Pacific North West are kayaks.

    Many people would say that sailing 1500 miles from SW England to the Soviet Union is an offshore trip, but I/we did it singlehanded in 24ft catamarans without ever sailing at night. So that was also an inshore, or at best, a coastal trip.

    Sailing from the UK to the Med isn’t offshore cruising, it is coastal.

    Sailing from the PNW to the Panama Canal and from Toronto to Venezuela are both coastal trips.

    To my mind an offshore trip is one where you go hundreds of miles from land. An ocean trip is one where you go thousands of miles from land.

    But of course you can get “ocean” conditions inshore. When the ISO stability group first started discussing seaworthiness we collated the data of wind and wave conditions for the whole of Europe. We found that the worst weather is off the west coast of Ireland. And what are the boats traditionally used there? Open boats made of leather and light enough to carry up the beach, that’s what!

    So it all makes deciding on what is a seaworthy boat rather difficult.

    Deciding what is a good cruising boat is somewhat easier. In simple terms it is a floating cottage. Any boat that you cannot be comfortable living on board is not a real cruising boat. Just because a boat has 4 berths and a cooker that doesn’t make it a cruiser.

    The beach cat sailors who sail across the Atlantic don’t live on board. They get on in the Canaries, sail for 10-15 days and get off in the West Indies. So although they are “offshore” or even “ocean” sailors they aren’t cruising.

    Conversely I have met a lot of “ocean cruisers” who never go anywhere, even though they do live aboard full time.

    There are other requirements for a cruising boat, but living on board in comfort is essential. That is why catamarans make great cruising boats!

    Maybe you disagree with this, but I don’t think we can have a sensible discussion about offshore cruising until we have defined it.

    Maybe time for a new topic??

    Best wishes

    Richard Woods of Woods Designs
     
  13. JCD
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    JCD Follow the Bubbles!

    Hello Richard,

    Thank you again for the visit and contribution.

    I think that this is probably belabored to full extent. As you have denoted, inshore, offshore, coastal and ocean have been clearly identified somewhere and has been generally accepted. There are enforcement agencies, insurance companies etc. that put their own spin on interpreting these distances. Are you coastal because you're in a lagoon on an atoll although it is 1000nm from another land mass?

    You have identified many examples where land is not very far away and this is exactly why I believed that the gap in the trailerable catamaran realm is huge. In all reality, there will be few instances where a cruiser will experience an immensely long and drawn out trip out in the ocean unless it is by choice.

    Me...I don't tend to be so careful with delineating lines of definition. I tend to generalize a bit more to my own liking, but if asked, in my opinion, if you must be self sufficient and there is no way to depend on outside resources for assistance without causing an international rescue incident, then you are bluewater sailing, or in this case ocean sailing. That can be a thousand miles from land or it could be 100 days as long as the above applies. In my area, the tow companies define 50 miles from land offshore and falls under "extended" coverage, but the Coast Guard may say 100 miles.

    This has always thrown me for a loop. I am unaware of any design of any material other than steel for the higher latitudes and no way that a leg should be made through the Northern Passage in anything but steel...but I'll be damned if the Eskimoes haven't been completing those legs for millenia in animal bones for frames and hide for sheathing. I suspect these recommendations may be well advised for insurance purposes.

    I agree but need to point out that the definition of "comfort" will be as varied as the number of skippers. Many times, IMHO, the reality of the definition is lost. Is a 125' megayacht really required for comfort or is it one of those I got more money than you statements? I mean for crying outloud, any one person can only occupy 10 square feet of space at any given moment in time. I do understand go a little bigger be a little more comfortable, but dammmnnn, there is a serious overcompensating illness out in the nautical field.

    I agree emphatically. I am always amazed at how comfortable even the smallest of cats can be made to be. This is yet another reason why I believe that a "reasonable" person with "reasonable" expectations about comfort will view a trailerable catamaran capable of crossing oceans as the best of all worlds. Easy to build. Cheap to build by comparison. Cheaper to maintain. Cheaper costs. Make a crossing if time allows knowing it is designed to do so. Take it home.

    I don't disagree at all...about having a sensible discussion regarding offshore cruising. I am however at a loss in attempting to define offshore cruising because the definitions will be so varied that it may be impossible to do so. For example, the first mate will never board a vessel that has a confined head or lacks a full headroom stand-up shower. Easy for her because she is 5'9" but not so easy for me at 6'1". Me? I can lay on the sole and take a shower.

    I am definitely open to a new topic. How would you pose the topic question? I ask because I am not sure if it may not be better to stick to "empirical" data surrounding comfort, seaworthyness, size, displacement etc., for the concept of a trailerable catamaran rated for bluewater crossings.

    My first thought was to try to find out if any existing trailerable catamaran design came off the board designed to be offshore capable, in any category. As much as I looked, I didn't find any. Ergo the gap. A huge gap as there must be an incredible number of avid catamaraners that would love a rated trailerable that isn't a trimaran or monohull or difficult to handle due to size or displacement.

    Then, my next logical step was to get a "generally accepted" idea of minimum size for a comfortable trailerable catamaran and so far it is between 24 feet and 3500# to 33 feet and 100K# of righting moment. I find the 33' and the 100K#RM a little high and getting up there with the big boys which should really be waterlocked.

    My current thinking is trying to establish how much stores (consumable displacement) would be needed for the longest possible distance (assuming there is no shorter distance to the same destination) so that a skipper and mate can get there in whatever amount of time is required to get there, (plus some leeway for light winds) in a seaworthy, trailerable catamaran designed to be bluewater capable right from the board, in reasonable comfort, safely.

    Do you, as a designer agree that the concept may merit further development or do you believe it may be futile to continue on with what may appear to be smoking mirrors? I'm forging ahead anyway and will surrender after I have failed and not before. I would just like to hear your opinion which may carry more years experience than my own.

    Thanks,

    J:cool:
     
  14. JCD
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    JCD Follow the Bubbles!

    Ahhhh...its good to have some time off to play...:D

    I took the Green Lantern hull and reworked the shapes and then scaled it to a nice 26 footer. I was going to go to 28 and probably it would be nice but, I believe many will be comfortable in a nice 26 footer with 4 feet of main hull beam and a beam overall of 17 feet.

    She looks quite nice with the humpback toward the stern and reduced forward profile. Besides scaling for the 10:1 Lwl beam and the Loa, the underwater areas have been kept the same as the Green Lantern in order to preserve what I believe to be an excellent underbody. She is looking sleek topsides and slippery below the waterline and about 25% of her hulls will provide headroom of 6'.

    Anybody think it should be a little smaller or bigger? I personally think 27' is my top end. I'm thinking about folding the beams vertically at the centerline with pinned beams in the hull for pivoting upwards. Any thoughts on this would be appreciated.

    Here are some preliminaries according to my spreadsheet. The 57,500#RM is for full displacement of 4,400# as is the 22,201 figure for Offshore rating. She appears to be a bit overpowered and I think 300 to 325 sq.' for the sail would be nice.

    Design length 26
    Length over all 26
    Design beam 4
    Beam over all 17
    Design draft 1.011
    Sail Area 350
    Displaced volume 54.6
    Displacement 1.5625
    Total length of submerged body 25.126
    Total beam of submerged body 15.502

    RM = 45,500 / 57,200#

    SA/D 22.30874
    LWL/BWL 10.04237
    Windage % of LOA 19.19%

    Bruce # 1.181827
    RPI 1.203679
    Stability # 1.01849
    Stability Speed To Lift Hull 17.59469
    Reef (Knots) 14.95549
    Clearance 2.25
    Lowest Bridgedeck Clearance 2.1

    D/LWL Ratio 112.5705
    Speed Knots 9.114858
    Velocity Ratio 1.570854
    PIC 0.792559
    Base Speed 8.499108
    Texel 110.6782
    Texel K = 0.385353
    Stability Capsize 2.509653
    B/T Ratio 2.474777
    BCL/LWL 0.517392
    Offshore CatB > 15000 17662
    22201

    All thoughts are welcome. I'll try to get a picture up tomorrow.

    J:cool:
     

  15. JCD
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    JCD Follow the Bubbles!

    Folding Beam Challenges

    Hello all...

    Much along the lines of the trailerable offshore catamaran, I have been playing a bit with AutoCad and have come-up with an articulating folding beam for the design. I figured that if I can't get this to work...then it's all over.

    The centerline to centerline beam will be 13 feet and I assume that the hull pivoting pins will be on or about that distance. The hull beam is approximately 3 to 4 feet providing at least a 2 foot bury for the hull box.

    A centerline sleeve would also need to be designed to capture the beams at the centerline and it would slide outboard when readying for folding. The centerline pivoting pins would be recessed into the beam and it would all fit in the sleeve. The plate for the pins would be as high as the inside of the sleeve to provide support for the beam juncture when in tension or compression so that it doesnt flex.

    What kind of challenges can I expect to encounter in getting this designed to perform as required? Do I have to solve for the beams in cantilever and then solve for the box and sleeve based on the same loads for a simply supported beam at those critical points(box, sleeve etc)?

    I know that the hull pivot pin will cause the hulls to swing in or out when afloat, so the folding will not be executed on the water. It will have to be executed on a trailer that slides open to accept the 13' beam and then slide back when the beams are being folded to deliver an 8' beam with both hulls side to side.

    I also attached a picture of a very modified Green Lantern Hull for the trailerable. Everything is still very rough.

    Thanks
    J:cool:
     

    Attached Files:

    Last edited: Mar 9, 2008
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