Trailer cruiser revisited... as a trimaran

Discussion in 'Projects & Proposals' started by marshmat, Apr 21, 2009.

  1. marshmat
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    marshmat Senior Member

    I now have free time again, for the first time in eight months. Thus, it is project time once again.

    Some of you may recall my last project ( http://www.boatdesign.net/forums/projects-proposals/playing-around-10-m-trailer-cruiser-17597.html ) and I very much appreciate the excellent discussion and heaps of advice that came from that one.

    This is the next stage of that project. The planing monohull hasn't been rejected- it's still in the running. But between the computer simulations and the model tests, I'm not convinced it would run well in the "hump speed" range with the kind of load (1 to 1.5 t of payload) I'm talking about. And the need for a 150 hp engine is a bit off-putting.

    Recently, I've been working on some Godzilla optimizations for a trimaran in this size. It'd be a folding tri, less than 1.5 tonnes on the trailer and capable of carrying 1 to 1.5 t of people and gear. LOA is 8.5 m, beam would be about 4 to 4.6 m with the amas out and less than 2.5 m with them retracted. I know that's a fair bit wider than most power tris, but for a reason- we want a lot of space out on the wings for carrying bulky stuff (kayaks, lumber, trusses, etc.) or playing (fishing, swimming).

    I want this to be a relatively straightforward, quick build, so it's all developable shapes for taped-seam plywood/glass. The shapes are based on Godzilla optimizations, adjusted for developable construction while keeping the sectional area curve, key dimensions and coefficients the same.

    As shown, at 2.5 t total displacement, the drag at 10 m/s (20 kt) is about 3.1 kN. Even with the flattened stern I don't think speeds much higher than this are feasible, but 16 to 20 knots on the top end should be plenty. More importantly, 16 knots loaded down / 20 knots empty would be achievable with a 50-horse outboard, and a very economical cruise at lower speeds should be possible.

    Comments are welcome on any of the following points:
    - Feasibility
    - Folding mechanisms
    - Styling (the blockiness shown here will not survive)
    - Practicality
    - Possible performance issues
    - Anything else you feel is worthy of comment

    Please keep in mind that this is only the 9th iteration of the design, and the first iteration in which the complete tri form is assembled. The intended use is mainly on canals, inland lakes, and the coastal areas of the Great Lakes. Crew would be 2 for a week, or 4 for a weekend.
     

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  2. Fanie
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    Fanie Fanie

    Hi Mars,

    My 2 bits -

    I like the size, 8m500 is a very nice size.

    The length of the ama's also looks good, I don't like these short thingy's they put on some tri's.

    The ama's is too low. I like the extra bouyancy and they can be used to store lots of stuff in which will free hull space up. It will also keep the trampoline up a bit to make for a dryer ride. There seems to be the idea the leeward ama must bury... I say no, keep it up and dry.

    Personally I would look at a 6m BOA on an 8m500 tri. More stability, and more room to move around and space to do stuff on. Never heard anyone say they have too much space, usually not enough.

    I've been playing with the idea of having the fuel, gass bottles in the ama's as well as the batteries. Piping and wiring goes through the beams to the hull, could also save some space in the hull, although I haven't thought this through yet.

    One thing a tri does have a lack of is solid areas one can walk on. Maybe the ama's 'decks' could be widened towards the hulls. I remember seeing a tri that has solids between the hull and ama's, I liked it more than the tramps you cannot fish from properly ;) Even a part solid would be a bonus.

    At 16 knots there won't be much drag from the stern, the hull would just plane over.

    The 2 for a week sounds good, who is she :D
     
  3. Willallison
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    Willallison Senior Member

    I'll be intereseted to see how you manage to squeeze those 2-for-a-week accomodations in. This has always been the problem with small multi's - there simply isn't enough room in the hull volume to move around. And moving all the accomodation onto the bridgedeck makes the boat very high. Having said that, if you can get around that little snag, the gains are definitely there in terms of efficiency and stability - though multi's aren't exact;y renowned for their ability to cope with big variations in payload....
     
  4. Fanie
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    Fanie Fanie

    Eh Will, it is quite possible imo. Why do you think I asked who is she, you gotta think one on top... oh never mind :D

    The place for the pipe berths is where the hull flares wide, and if you make them telescopic or foldable they are away when you are awake, and you bring them out when you want to sleep. I like the foldables since you don't have to waste fishing time putting sleeping bags and blankets away, you just squish them to the side of the hull and you are done.

    The hull is long enough for 4 berths and some storage in that area. If the hull bottom which is flat which I like is around 600 / 700mm wide you can walk there, maybe passing is less comfortable but that depends how big one (or two) is. A standard house door is 800mm wide.

    There is place for a head ahead and a shower unless you plan to keep Wet-Ones for all accasions :D

    What have you in mind for a sail Matt ? There's got to be one.
     
  5. Willallison
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    Willallison Senior Member

    I fear you may be disappointed Fanie.... Matt lurks on the dark side with me;)

    No arguing about whether it's possible to fit the accomodations in.... Just a question of whether it results in so much compromise that the gain in efficiency over a similar sized mono makes it worthwhile....
     
  6. marshmat
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    marshmat Senior Member

    Could probably slap a mast on her, yes.... unfortunately that would make many of the canals and lock systems around here virtually inaccessible. I might include fittings for a kite, though.

    I'm thinking of a convertible cockpit seating area / dinette / double berth for the flared part, with a windscreen and small hardtop immediately forward of this at the helm.... the amas would fold in and under for trailering (I'm working on the 4-bar linkage to do that, they definitely fit quite well but the linkage is a bit tricky).

    I've done 5 people / 5 weeks in a tent trailer, and several camping trips in my 5-metre Bolger Diablo (using a shore-based tent for sleeping). So we're quite fine with tight quarters.

    An earlier series of attempts with a catamaran led to disappointment accommodation-wise; the hulls just couldn't be made wide enough to fit bunks without compromising the efficiency that made the cat attractive. I think with the folding tri, I can pull it off.

    Fanie, I like the idea of getting a bit of solid decking instead of just trampoline. The trick would be to get it to fold with the amas, but it would definitely be a huge advantage when it comes time to haul stuff (or partiers).
     
  7. Fanie
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    Fanie Fanie

    On the cat, Matt :D I don't see how you couldn't fit the accomodations. You should look at making the cat foldable as well, something like I'm doing and cat2fold already did. Means your hulls can be around 1.2m wide each and still trailer legally. The folding beams on an 8m cat is going to be considerably less than an a larger cat 10m or longer.

    Want to reconsider ? The only drawback the folding cat have is you cannot add a single outboard, you have to go double, but the advantages are numerous over a tri.

    On the tri you could look at widening the aft beam to make a solid area. I have no idea what your folding system is going to look like though. If you are going to fold a narrow beam you can probably just as well fold a wide one.

    As for adding or not adding a sail, imo it's not even a question. It's half the fun on either... just motoring is fun for just a short while but it gets boring quickly, sailing is quiet, you keep buzy, it's fun, less expensive... and you can go non stop and not worry about fuel any other than your own.

    Have a look at the sail setup I used for the little tri, easier than that you can't get, any one even a novice can sail it.
     
  8. marshmat
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    marshmat Senior Member

    Fanie:

    Like so, only folding?
    I rather liked the performance simulations of this design (2.5 tonnes at 20 knots with only 2.5 kN drag, so twin 20-25hp outboards). Never thought about making it fold, though. The hulls are quite narrow and, as drawn, the overall beam was trailerable. Flaring out the hulls top provide enough space in there for a few bunks resulted in the hull centrelines being too close for the stability I'm after, and any increase in the waterplane beam- only 67 cm- increases the drag noticeably.
    I will take another run at that one with folding beams. The bridgedeck cabin would have to be scrapped but since the hulls could then be widened more above the waterline, it might work....

    As much as I like sailing, a mast would be rather difficult here unless it can be folded and re-stepped by one person in a minute or two. There are just too many low bridges in my preferred cruising grounds.
     

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  9. Fanie
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    Fanie Fanie

    I disagree with your weight on this size boat, unless that's everything... the bare boat should weigh less.

    That's the idea. The beams fold into cavities in the hull sides, so the two hulls sit side by side. To launch they are floated apart and the deck is folded over the area from beam to beam. This keeps the hulls from overtaking one another and is the tennis court I mean deck area.

    A hull that is 8m500 long and 1m200 wide and say 1m500 high is quite a big hull. They seem narrow but they will float with a few people on them. You should have at least 8 tonnes or more of floatation per hull, draft around 300mm. A normal double bed is only a few mm off on 1m200, you can check...

    You're not really limited by the BOA, the decks can also be 1,2m each if there's 2 per hull you'll end up with a 8m500 LOA cat that has a BOA of around 7m200 :D

    The very first cat I drawed was this size, and that was before I knew about cat2fold and that it was illegal to make a cat that wide :rolleyes: I still like the idea though... Tri's can be square, why not cats :D

    With two 40's it will fly, two 28's or 30's is plenty and even 2 x 15's is good enough.
    You can add two shorter stand alone masts ie 10m each and still have a large sail area, again more manageable than one huge sail.

    The initial 'cabin' I designed was a canvas tent, but tents are cold, noisey in wind and hot in the sun. I later tried to design a foldable cabin, but actually making it would be something else. The current design for my cat is a cabin trailered on a second trailer, we are always going with more than one vehicle anyway so.

    The sail setup I used works quite well imo. I'm not the sailing expert around here, but I think I got some fair results.
     

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  10. Fanie
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    Fanie Fanie

    Pic 1 there is Dugout, the name I gave the roughly built experimantal little tri. I built it to test the 'aft mast' (stolen from Brian Eiland) and single sail with. The sail furls up in a second and is out of the way. Deploys as easy.

    Pic 2 is where the mast fits in. You clip the sail to the mast head, just push the foot into the slot there, all done at ground level, and push the mast up. This is easy in this case because the mast is only 6m in total which is actually 2 to 3m short of what a single mast should be for this size a tri. On a larger mast I would do this with a gin pole and a winch, just as easy. The slot prevents the mast from swinging in any direction, it can go only up or down. Once up you clip the furler in place and this holds the mast upright.

    Pic 3 is on the Vaal dam. The wife announced 'that boat is following us' and by golly that mono tried to catch us. I was actually just cruising with a slack sail then, soaking it in, he he... some minor adjustments later we were leaving it behind. My sailing area is 12m^2

    LOA 5m500, BOA 4m :D Told you I like square things ;)

    Manie also sailed with me once, you could ask his opinion on it too. He has some dinghy experience so I guess anything ese should feel good :D

    http://www.youtube.com/watch?v=buLlFWcjRUo
     
  11. marshmat
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    marshmat Senior Member

    Thanks for posting the details on "Dugout", Fanie. Your folding system is roughly what I had in mind for my trimaran, although I'd be thinking of a slightly more bulky vaka hull to give some interior room.

    2.5 tonnes is at design displacement for both the cat and the tri versions of what I'm working on now. No more than 1.5 t trailering weight.

    The aft-mast idea looks rather appealing. I saw some of Brian's articles on that a while back, but they were all about very large, sophisticated boats and I didn't really think to extend the concept to a little folder. But an 8 m tall aft-stepped mast should be able to fold forward within the trailering length of an 8 m tri or cat. I don't like the idea of trying to engineer a folding hinge for the cat that would also support a mast step... but one in each hull, now there's an idea... aft-mast bi-plane....

    (Am I crazy yet?)

    More on the cat coming this afternoon....
     
  12. Fanie
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    Fanie Fanie

    A pity he didn't persue it some more. Personally I think there is some real merit in them. A few ovelooked simple trick of which I 'discovered' a few of, adds quite a bit of functionality.

    I also didn't like the idea of the mast on the beams, and you will also have to stay it. The hull provides a very nice guide and support to hold the masts.

    If you consider that I have a small 12m^2 sail on only a 6m mast of which 700mm is in the hull, then if it was a cat there would be 24m^2 on a double setup.

    A single 8m mast is going to give you 18m^2 sailing area. To reach the same sailing area as the 2 x 6m masts you will need a 10m mast...

    A more proprtional mast would be 8m in length, then 2 masts would give a 36m^2 sailing area. I can live with that :D and probably fly a bit with it too :D

    Sorry, I know the stuff on my tri must be boring, it is only an experiment, remember. It's going to be better on the cat tho.

    If there's crazy here then I'm in too...
     
  13. marshmat
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    marshmat Senior Member

    Cats

    36 square metres of sail Fanie.... on a tonne or two of cat, that would certainly tend to move you along. I would think the forestay angle on the aft-mast rig would also tend to encourage the sail to pull upward as well as forward, much like some of the more elaborate spinnaker setups you see on offshore racers.

    See more cat below.... 8 m on the waterline, draught 30 cm at a hair over 2 tonnes, hulls at 4 m centre-centre, and folds down to something that might fit on the trailer. Those hinges will be beasts, though....
     

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  14. Fanie
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    Fanie Fanie

    The forestay angle does make a lot of lift. On the Vaal dam the first day the wind was really up, at one stage I thought it was going to push us over. At no stage did the ama's even looked like it's going to go under.

    That said, one must be carefull that you don't just make lift and no foreward power, it's a cat remember, not a hovercradft :D The longer mast improves this relationship some, modest lift with good foreward force. Sounds like a cam eh ;) It is kinda.

    Brian's drawings all had their masts slanted foreward. It didn't work too well for me. The mast vertical worked best. You can change the cam some more if you keep the foot of the sail stiff so the wind gets dumped aft, makes a heck of a difference in speed as to allow dumping air off the foot. You can also sail higher to wind... and tack very fast. This was when I got the idea that you can actually sail directly to wind without tacking... you would need a wide cat though...

    Do you plan to build this cat or is it just a design thing you're working on ?
     

  15. Fanie
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    Fanie Fanie

    I'm sure you must have seen Orange... that big racing cat. Ever wondered how it can beat those big tri's :D

    Be a sad day when the cats beat the tri's and nobody wants them any more.
     
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