Trimaran with accomodation in the amas

Discussion in 'Multihulls' started by eiasu, Nov 23, 2012.

  1. eiasu
    Joined: Nov 2011
    Posts: 74
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: novutopia, Germany

    eiasu Junior Member

    the tristar performance could be compared with a lagoon 410 for example?
    impossible questions .... mhhhhh
     
  2. cavalier mk2
    Joined: Mar 2010
    Posts: 2,123
    Likes: 55, Points: 48, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    Compare the sail area to displacement ratios and look at the hull windage.

    I looked at the specs for the Cross 52R Crusader, good for 300+ mile days, but it is a boat compared to the ships you are looking at. Here is a comparison with the Cross 52 cruising trimaran with all the comforts.

    Cross 52R Cross52

    length 52' length 52'4

    waterline 45, 9" waterline 47'

    overall beam 32' overall beam 28' 10"

    draft 6' 2" draft 4' 8"

    sail area 100% FT 1125 sq feet SA 1050 sq feet

    Displacement 14,000-15000 pounds disp. 30,000 pounds

    Easy to see what will be faster and what will carry more.
     
  3. Richard Woods
    Joined: Jun 2006
    Posts: 2,208
    Likes: 166, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    I'm sorry I still don't think the cost savings are there

    A typical 45ft catamaran will have three shrouds and two diamonds. So 5 wires and 10 ends to terminate

    A Tiki 46 has 9 wires, so 18 ends to terminate. Two mast steps not one, two mainsails that need reef points, not one. Two mainsheet systems, not one. Nine chainplates not three. Many big charter boats only have one sheet winch and have really cut down on deck gear. You don't have to build a Wharram to make your own mast.

    I bet if you did a real, detailed costing you'd find little saving. And I bet you'll find that Lagoon and other big yards have done such a costing and gone for the cheapest option.

    Lagoon are big enough to change public opinion to, eg gaff sails, if they thought they'd make more money that way. After all they have made people think that vertical windows are the way to go

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  4. rberrey
    Joined: Oct 2010
    Posts: 457
    Likes: 20, Points: 18, Legacy Rep: 112
    Location: AL gulf coast

    rberrey Senior Member

    I did material , sails , mast , power , stove , ect. estimates for my build and would tend to agree with Richard to a point. Price is by the pound, but what you build with, the sail plan , power unit , and fit out will determain the final cost. A 50' boat can be built for less money by the pound if they use the same interior fit out that I might use in my 31' boat , ( stove , porta pot, ect. ). In that respect I would agree with Cav. Apples for apples. Rick
     
  5. cavalier mk2
    Joined: Mar 2010
    Posts: 2,123
    Likes: 55, Points: 48, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    Well from a hull standpoint all the Pahi has is a bunk level platform and a floor level platform in the hulls. Nothing easier or faster to build, huge savings in labor, the furnishings are cushions and fun trips getting hangings etc.......

    The masts are commercial round extrusions, 2 are cheaper than 1 spar extrusion. Sails cost by the square foot largely, dacron is fine for the Pahi and here are savings again as they don't need battens, luff cars etc....

    I like them apples.......
     
  6. oceancruiser

    oceancruiser Previous Member

    You don"t happen to know what year this wooden vessel was built and whether by a boat yard or home build. The price seems ridiculously high.

    The design it self by age only warrants a maximum figure $90,000 in my book or even less. He talks about all the dry rot he could find was replaced- Home builder - It beggs the question what about all the dry rot he did not find.

    If it has got heaps more dry rot to be found and was originally built over 26 years ago then the true value is second hand hard fittings prices only.
     
  7. Sand crab
    Joined: Feb 2011
    Posts: 92
    Likes: 3, Points: 0, Legacy Rep: 23
    Location: Montana

    Sand crab Junior Member

    I don't know anymore about the 50' Horstman tri than what was in the ad. I was thinking that it would be worth considerably less, also. It was just.... interesting.
     
  8. mcarling
    Joined: Dec 2012
    Posts: 23
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: changes weekly

    mcarling Junior Member

    I frequently hear or read the advice (including in this thread), that heavy items should be located in the vaka, not in the amas. I've never seen an explanation of why.

    Assuming that we've talking about shifting weight from the vaka to the two amas equally (not creating a port/starboard imbalance) and not changing the overall weight, then I can see two things that change:
    1. the stresses on the aka/hull joints change, and
    2. the polar moment of inertia about the boat's longitudinal axis increases.

    Are there any other effects?

    1. Unless the weight shift is large compared to the strength of the aka/hull joints, such a weight shift is not going to break anything.
    2. Increasing the polar moment of inertia will make the boat less responsive (more stable). In other words, it should handle more like a bigger boat, which may or may not be desirable.

    Is there anything else going on when one moves weight from the vaka to the amas? Have I overlooked anything?
     
  9. prograd
    Joined: Oct 2012
    Posts: 35
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: nime

    prograd Junior Member

    Maybe slightly lower righting moment?
     
  10. mcarling
    Joined: Dec 2012
    Posts: 23
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: changes weekly

    mcarling Junior Member

    I believe shifting mass from the vaka to the amas (divided equally) has no effect on the righting moment if the mass remains at the same height. If the mass were to be higher in the amas than it was in the vaka, then the righting moment would be (probably negligibly) reduced. Correct?
     
  11. rberrey
    Joined: Oct 2010
    Posts: 457
    Likes: 20, Points: 18, Legacy Rep: 112
    Location: AL gulf coast

    rberrey Senior Member

    From one of Ed Horstmans books, (This designer's view, and it never entered my mind to consider anything else for a tri-star trimaran, is that if you want to carry all your payload (useful load ) in the two amas that is fine with me, as long as you do not exceed the boat's useful load as stated above and do not place all the load in one ama so the boat is out of trim.) ( How can this be substantiated:Well in the design and stress analysis performed on the trimaran's connecting beams you will find that half of the useful load thet you will put in the individual ama, plus the ama structural weight itself will not add up in total weight or even be close to the force ( weight) you will use to calculate the stress of these connecting beams. If a trimaran will not carry half of its useful load in the amas it is not a seaworthy trimaran. ) Ed's view. Rick
     
  12. mcarling
    Joined: Dec 2012
    Posts: 23
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: changes weekly

    mcarling Junior Member

    Thanks Rick. That is consistent with my intuition. I was uncomfortable repeatedly reading advice that was inconsistent with my intuition.
     
  13. Richard Woods
    Joined: Jun 2006
    Posts: 2,208
    Likes: 166, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    The crossbeam strength shouldn't be a problem. That is because they should be designed according to the total displacement of the outrigger, not its weight. You don't want the crossbeam breaking if the outrigger submerges!

    More of a problem is that the "snap roll" effect, which I discussed earlier, will be greater. Similar to increasing pitching when there is excess weight in the bow/stern of a boat

    Its generally best to try to centralise weight

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  14. mcarling
    Joined: Dec 2012
    Posts: 23
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: changes weekly

    mcarling Junior Member

    Thanks Richard Woods, but may I ask you to clarify? Do you mean that moving weight from the vaka to the amas increases the tendency of a trimaran to "snap roll"? Or do you mean that heavy objects in an ama subjected to the forces of a "snap roll" might cause problems and could be difficult to secure? It seems like you mean the former, but I would like to be sure.
     

  15. cavalier mk2
    Joined: Mar 2010
    Posts: 2,123
    Likes: 55, Points: 48, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    Like a tightrope pole weight in the amas actually slows the roll. The conservative viewpoint is that if the ama is thrown past a certain point by a wave the added mass will tend to keep going. In practice weight stored in the amas of the very small trimaran Klis made it more stable. It is easy to test by sailing. Past a certain point I think more waves would get on deck and the underwing would slap more.
     
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.