Trailerable Multihulls

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

  1. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Thanks for the concern everyone, about my wide boat :D

    Let me explain what my argument on this is and if you still disagree then I would like to understand the reasoning behind it.

    Assume I have a 10m LOA and 6m wide cat, then it would sail right with a 50m^2 sail - I have compared with all other current cats and the size is moderate. I'm not building a racer so I won't go larger sail area. I have to keep it to a size I can handle as well.

    Now assume the sail area remains as it is, the length is still 10m and the hulls moved further appart, would this begin to create a problem still ? If, why ?

    The force of the wind on this size sail will remain the same when running and when reaching it would just lean less, right ?

    So what I'm saying is if the sail area for a 6m wide cat sails right and you widen the cat then the effect with the same size sail should be about the same, assuming some extra weight has no effect.

    ****

    Regarding the construction of the 8m beams (for the 8m wide version) - I have met a very nice engineer here who's job it is to design fiberglass structural things. Before putting a hand to the beams I will have him confirm what I'm about to do will stand up to the requirements. Sleep sound tonight knowing I'm not putting some lives at risk, I do my homework thoroughly.

    I have two versions of my cat. The one is 8m and the other 6m. I'm aware that the structural demands is considerable more for the 8m, as well as add quite a bit of weight.

    If I can get the 6m version to be spacious enough of course I'll rather build it instead of the 8m.

    ****

    There are some legal requirements around building a boat and putting it on our seas. The plans have to be approved locally so I cannot just build a boat and dunk it on the sea.

    Everything I plan to do gets tested in principle before I do it and I compare to what others have done that has had success with theirs, and also why the unsuccessfull ones were not what they are supposed to be.

    It would probably be easy to just buy plans and put it together, I however have the time (yeah right) to do the research and draw the plans up to a final product before I could start building.

    There are also no other boat like the one I want that is trailable and can be assembled the way I want to do it, getting someone to desigh in for me is going to cost too much. If someone would design something like this for his production then fine, I would gladly work with someone. The question is would there be enough prospective buyers interested in this to make it worth the effort or are there only three of us ?
     
  2. Richard Woods
    Joined: Jun 2006
    Posts: 2,179
    Likes: 145, Points: 63, Legacy Rep: 1244
    Location: UK, USA and Canada

    Richard Woods Woods Designs

    One traditional reason for building narrow multihulls was the width of shed doors (seriously). These days narrow Travelhoist widths can cause problems as in many areas they are only 18-20ft wide. No point in building a boat that cannot be launched or stored ashore.

    Another reason is that wide boats look scarily wide on paper and very wide in the boatyard.

    But they look good on the water.

    About 25 years ago I built an experimental Strider with a 17ft beam (on a 22ft WL). I thought it sailed better than the standard boat. However even though it was an open deck boat it was quite a bit heavier than standard.

    My 10m Eclipse is 6m wide. I wouldn't like to have had it 8m wide. Not just that I'd never have slipped it on the east coast USA (for example) but also it would have been significantly heavier.

    And it would have had more freeboard and cabin camber (unless you like a very boxy looking cabin). I don't know how the interior layout would have worked with an extra 2m of bridgdeck width. Clearly the hulls would have to be much the same size to keep the performance I want.

    So I'd think very seriously about building an over wide boat. I'm sure it would sail OK, but the two important things to consider are shell weight and use of interior space. Then consider the practicalities of mooring/lifting/launching/building a wide boat.

    Hope this helps

    Richard Woods

    www.sailingcatamarans.com
     
  3. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hello Richard,

    Some valued comments there, thanks, and yes it helps a lot.

    I haven't done the interior setup yet. The best thing to do would probably be to do a rough layout and see how space work out. I'm tied up with some things currently but could attend to it in a couple of days or so.

    The only reason for considering a wider boat is that I don't want the cabin crampy, especially in weather where everyone has to stay in or night times socializing.

    The cabin would be the living area where most activities take place so everyone aboard would participate in whatever is about. Galley, lounge, navigation, bar, and not to speak of the fishing stuff that will be prepared in there.

    You'd retire to the hulls to sleep or if you need to do your private stuff.




    BTW, next time you feel the heaving of your boat, do think of us poor souls who don't have ours yet ;) I'm considering some hudraulic cylinders under my bed to simulate that feeling :D
     
  4. JCD
    Joined: Jul 2006
    Posts: 359
    Likes: 3, Points: 0, Legacy Rep: 36
    Location: Coney

    JCD Follow the Bubbles!

    Hello to one and all...

    It is good to see a little progress...even if it is still open to discussion.
    The scantlings for the TR27B have been calculated...well, as far as I can go thus far, which is the hull.

    Please take note that there is the basic call out for a quick and easy skin lay-up of unidirectional and then there is the recommended callout, (recommended by me).

    I will attach them so if anyone would like to study them for comment without coming back here they can do so. As always, your candor and advice is welcome along with any comments or questions.

    Thanks
    J:cool:
     

    Attached Files:

  5. Richard Woods
    Joined: Jun 2006
    Posts: 2,179
    Likes: 145, Points: 63, Legacy Rep: 1244
    Location: UK, USA and Canada

    Richard Woods Woods Designs

    Interesting...

    I assume the decks are completely flat and horizontal

    It would be useful for those of us who aren't US citizens to have a metric TR27B scantling list

    Richard Woods

    www.sailingcatamarans.com
     
  6. JCD
    Joined: Jul 2006
    Posts: 359
    Likes: 3, Points: 0, Legacy Rep: 36
    Location: Coney

    JCD Follow the Bubbles!

    Hello Richard,
    Thanks for the view.;)

    The decks are flat and horizontal except for a very small slope at the cuddy sole to shed water aft and in the pits to shed water outboard, but they are generally horizontal.

    I will convert and provide a scantling list in metric for your review and for the community at my earliest convenience tomorrow. If I'm sleepless, I will do it tonight. I suppose that I should be providing both moving forward?

    Coversion was not that hard, so here it is as an edit to the post.

    Thanks
    J:cool:
     

    Attached Files:

    Last edited: May 14, 2008
  7. JCD
    Joined: Jul 2006
    Posts: 359
    Likes: 3, Points: 0, Legacy Rep: 36
    Location: Coney

    JCD Follow the Bubbles!

    Hello Fanie,

    Thanks for the post. This will in no way be helpful for the TR27B however. The TR27B must be KISS, KISS, KISS.

    It appears that you are going to provide quite a big amount of information. It may be a good idea to post it in a separate thread so that it is all in one place and it doesn't confuse the direction of this thread. Let me know what you name the thread so I can follow your progress.

    Thanks
    J:cool:
     
  8. JCD
    Joined: Jul 2006
    Posts: 359
    Likes: 3, Points: 0, Legacy Rep: 36
    Location: Coney

    JCD Follow the Bubbles!

    Hello Fanie,

    Wow. The moderators are watchful...and fast.:eek:

    I got the email but I don't see the post.
    Don't take offense and there is no need need to apologize as I don't believe you have been offensive. There has been no inconvenience. I definitely understand how the name of the thread could be deceiving that it's about "trailerable multihulls." It is, but then it kind of became more specific about the TR27B. I guess it is I who should apologize to you for that and I do.

    I just want to make sure that this thread and your thread gets the attention they deserve. It would be a disservice to the community members if they read through 20 pages in a thread to find out it is not what they were interested in contributing to or that they lost their train of thought because the direction in the threads change.

    I'll look for your thread because as I said before, I would like to follow the progress since they are very much related and you have already begun to work on scaled models of the system.

    Thanks
    J:cool:
     
  9. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hi J,

    No offense taken and no appologies please.

    I should have read the threads before posting, I wasn't aware that I was imposing on something that was in the making. I'll post my progress in the boxy fisher thread which will be more appropriate.

    When I get time I'll read through the posts to catch up on what has been developing...
     
  10. Richard Atkin
    Joined: Jul 2007
    Posts: 579
    Likes: 18, Points: 0, Legacy Rep: 219
    Location: Wellington, New Zealand

    Richard Atkin atn_atkin@hotmail.com

    Hi J
    I'll post updates on the beachcat-cruiser in my own thread. Thanks. It'll be a while before I have something better to look at. I was inspired by that little cat Perry sent me. A smaller cat might be an option for me if the Atcat 28 proves to be too impractical. I've discovered quite a few problems with beach and marina regulations in LA and Catalina Island. Not as loose as New Zealand :)

    Fanie
    A few things I've read on the internet:
    Generally speaking, when the length is twice the width, you will get the best handling, but not quite the best speed. Slightly more width than 50% will let you put more power in the sails, but there is some compromise on overall handling. I cant remember the exact reasons why (I'm a lazy reader). I think it has something to do with one hull acting as a horizontal lever when the other one is slowing down. I think there are other reasons too. If you want a really stable boat, then you should stick to the old rule of length = twice the width...(according to what I read anyway).

    Cheers
    (I should try climbing over someone's wife......)
     
  11. Richard Atkin
    Joined: Jul 2007
    Posts: 579
    Likes: 18, Points: 0, Legacy Rep: 219
    Location: Wellington, New Zealand

    Richard Atkin atn_atkin@hotmail.com

    J,
    to build a real offshore cat:

    It will need to be stable....ok so I guess that means good centre of gravity and length to width ratio....rather than sail area (sail area is adjustable), and good buoyancy

    It will need to have all the safety gear....no-brainer

    The hatches and fittings will all need to be designed well and meet a certain grade.....

    Must be able to sustain human life for extended periods of time...

    And I guess most of all, it must be able to smile while it's having it's *** spanked by mother nature.


    The last point interests me the most. Do you know much about building materials? I like the idea of making the hull's skin extremely resistant to holes and scratches and dents, even if it means adding a lot of weight. Can you give me your opinion on the best way to do this?
     
  12. JCD
    Joined: Jul 2006
    Posts: 359
    Likes: 3, Points: 0, Legacy Rep: 36
    Location: Coney

    JCD Follow the Bubbles!

    Hello Richard,

    Okay. Just to close up my thought on this. The first thing that hit me when I opened up the file was "Hobe Miracle" and you can get one here for less than $3K US. I'm confident that purchasing, shipping it and small modifications to personalize it when you get it will save you a lot of $$$ and grief over building it.

    http://cgi.ebay.com/ebaymotors/Hobi...51851884QQcmdZViewItem?hash=item230251851884&


    Yes to everything. You sure know how to pick difficult questions. The answer for this is so broad I can't even begin to answer it.There are many materials available for marine use and they have certain properties that make them excellent for one use and terrible for another.

    My best advice, and I'm sorry if it answers little, is to design to the ultimate with safety factors incorporated then design for fatigue where needed because it will provide a lighter and less costly structure. This is how I'm doing it for the TR27B. Once you have those values, choose the material that most closely matches your needs or material that you would like or know to use.

    Puncture resistance is easy. Hull skins can be made extremely puncture resistant at little added weight. My recommendation would be Kevlar but it is expensive and needs to be worked a little differently. They use this stuff in Apache helicopters to missile proof the pilot cockpits and gas tanks.

    Avoiding little dents and scratches is asking a lot and I suspect that the only two ways to avoid those is to never use the boat or never let it hit or touch anything. The TR27B will have a rub rail and a keel/stem shoe that is quite massive so that it can take a lot of the trailer contact with the keel and if beached, it will work as a sacrificial element to protect those parts of the hull. I called it out on the scantlings.

    Hope that helps. Someone else may chime in and provide another view.

    Thanks
    J:cool:
     
  13. JCD
    Joined: Jul 2006
    Posts: 359
    Likes: 3, Points: 0, Legacy Rep: 36
    Location: Coney

    JCD Follow the Bubbles!

    Hello Steve,

    I received the package. Thank you very much and thank you for the kind words of encouragement. I couldn't believe the size of that hole at the bow. Unbelievable.

    The article read like only the initial bang, jolt and crunch was stressful to the skipper and then he just took care to keep the water out more for concern of carrying the extra weight than concern for foundering.

    What do you think about the trawler knowing that a collision occured and then just staying out of sight in the fog line just "watching" and not rendering any assistance? I would have waved them off like the skipper did but I would have forgotten about the water and went down below to load the "pirate repelling buckshot". I think it may have been some kind of drug or arms smuggling the way they were running dark. What do you think?

    Thanks for the trailer picture too. I have been giving the whole trailer concept a lot of thought from all the excellent contributions and I think I will rethink it and probably provide a design that will pick her up or splash her while she is folded so that a standard flatbed without all the added costs and complexity of the folding mechanism is eliminated. This now reduces the cost to less than $3KUS without all the hassle of the wide beam at the ramp. Not sure yet.

    Thanks again,
    J:cool:
     
  14. Richard Atkin
    Joined: Jul 2007
    Posts: 579
    Likes: 18, Points: 0, Legacy Rep: 219
    Location: Wellington, New Zealand

    Richard Atkin atn_atkin@hotmail.com

    J,
    yes that helps me a lot!

    Thanks mate :)
     

  15. JCD
    Joined: Jul 2006
    Posts: 359
    Likes: 3, Points: 0, Legacy Rep: 36
    Location: Coney

    JCD Follow the Bubbles!

    Hello Richard,

    Really?:confused:
    Well...okay then. You're welcome.
    I guess I can get it right sometimes.:D

    Thanks
    J:cool:
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.