modifying a sharpie into a slight v bottom very small trimaran

Discussion in 'Boat Design' started by shmuelbrody, May 5, 2013.

  1. shmuelbrody
    Joined: May 2013
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    Location: israel

    shmuelbrody Junior Member

    i am new to this forum so please excuse me for knowing very little about boats

    i built a 4 meter sharpie called summer breeze

    it was a mistake
    as the only water in israel is the dead sea
    the mediteranian
    and the sea of galalee

    she is flat bottomed and although i have not sailed it
    i am sure that she will pound badly in rough water
    which is what we have
    not high waves but
    with wave and some white tops

    so i want to change her desigh to a slight v design with a dead rise
    of about 12 degrees and add two pontoons to make a tiny trimaran

    the reason for this is i like the space of the boat and i dont want to sit
    on a trampeline

    beside i feel that the added floats will add stability in the ocean

    i am not concerned about speed
    something like 5 to 10 knots would be fine

    adding a second bottom would be easy
    and the floats are not much different from building the sharpie

    should the dead rise be constant
    or become more acute toward the bow

    should it flatten at the stern

    if you think that i am crazy
    i have heard that before
    thanks ahead of time

    i know a little about the water as i spent 8 years in the coast guard reserve
    in the states
    between 59 and 66

    thanks again shmuel
  2. troy2000
    Joined: Nov 2009
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    troy2000 Senior Member

    I think you should at least try the boat out, before you cavalierly dismiss its performance. It might surprise you. Sharpies sail heeled, which means that you'd effectively be sailing a vee-bottomed boat most of the time.
  3. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    If you can get an 11 ft sailing boat to 'pound' you are a better sailor than most.

    As per the previous post, you might like to actually try it, and not rely on the demons in your head.

    It seem your initial goal was to save money by using two sheets of plywood - so you cant expect superb performance if you are budget bound.

    You would be far better off building a new, properly designed multihull than trying to modify this hull.
  4. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Shmuel; As noted above, you should use the boat a few times before you condemn it. As Troy has said, sharpies are sailed heeled. When they are heeled they will not pound any more than a vee bottom, perhaps even less

    Routine heel angle is about ten to twelve degrees but most sharpies will tolerate more. Too much heel and you will probably be reminded by increasing weather helm. It is not uncommon to heel them artificially (deliberately) on down wind legs. You can crash into a power boat wake with impunity if you do it correctly. On a little boat like that you are going to shift your weight a lot in order to take full advantage of the wind and waves and the versatility of the shaprie design. Heeling the sharpie reduces the wetted surface and also narrows the waterline, both of which contributes to performance.

    Pounding is a subjective term anyway. Your small boat is not likely ever to pound to the extent that your dentition is at risk. One more thing, even converted to a trimaran, you need not anticipate speed that approaches ten knots. Five knots for a 4 meter boat is about the upper limit of realistic expectation unless you are sailing offwind in a half gale. There are certain hot rod sharpie designs, usually longer than 4 meters, that will plane readily. These almost always have a very small quarter beam buttock run angle. In that case you might approach ten knots while planeing.
  5. shmuelbrody
    Joined: May 2013
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    Location: israel

    shmuelbrody Junior Member

    thanks a lot
    all your answers are thoughful and nice to read
    please forgive an old man (73)
    the boat is not really finished though your answers are putting me back on path

    a few comments to the above
    as to the word cavalierly dismiss
    i would like to change it to
    mistakenly or unknowingly or wrongly
    but troy's comment had me upset for several days.

    i still have to put the mast and the rudder and the skeg on
    but all the parts are made

    i was not trying to save money
    at all as i spent 3500 sheckels (1000 dollars) on the boat
    things are not cheap in israel as they are in the states
    and i live on a very very small pension

    the boat was made small so that it could be car topped

    it is impossible for you to understand what it is to live here
    you cant just hook up a large car to a trailer to pull a trailer
    you have to have a 7 ton truck

    there is a 100% tax on cars here
    a 15000 dollar car in the states costs
    30000 here
    gas is 8 dollars a gallon

    the average israeli works 10 hours a day
    6 days a week
    and makes 1500 dollars a month

    and to get the license for the truck
    you have to take a 30 hour driving course
    even if you have a regular one
    and no one passes on the first test
    usually 3
    so its 90 hours of instruction at an unbelievable price

    but please let me get to the meat of my new inquiry
    we want to build a boat multi hull
    that is about 18 feet long
    and near 8 feet wide

    i would like it to have a flat deck that size
    so it is like a nice sailing boat that the family can go on
    9 in the family

    sail not gas boat
    remember 8 dollars a gallon
    and it should break down onto a 8 foot trailer

    remember the above 7 ton truck
    be under 1000 pounds

    mooring at marinas is out of the question
    in order to sail this boat
    either me or my son has to get a skippers license
    for a 7 meter boat
    and it has to be registered with the medina (STATE)
    and pass an inspection from a marine engineer

    in 2010 there was a discussion with a person
    i think john who blanked out people faces
    and was generally unruly about a square boat
    and you guys were great with him

    please help me as i have spent a month on this
    and after reading your responses to him i believe all my work
    was worthless

    i can afford a little for plans but my pension of 300 dollars a month
    cant be streched to far

    although i dont believe there are any plans like this available

    thanks again shmuel
  6. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Hi Shmuel

    Thanks for taking the time to detail your circumstances. It is always interesting to hear how other people live. It does make me appreciate the things I take for granted.

    and you probably have to paint it, and add the fixtures.

    If you have spent $1000 on it already, which is a fair investment, you really should finish the project, and then maybe you could find a buyer.

    Also, even the Mediterranean ocean has calmer days.

    In Australia, a 16ft plywood Kayak will cost about the same as this, so I understand your values.

    So ? That is the reality for lots of places in the world. These are not insurmountable requirements.

    You have built a professionally designed and proven craft, that sails. I cant understand how it can be worthless. I don't know what thread you are referring to, but I dont think you should write off your efforts and investment at this stage.

    Of all the boat plans sold, ~15% get started. Of that 15%, about 3% get finished.

    Sam Devlin said "You really have to hate a boat to finish it".

    So, get on there and join the small percentage of the world population that actually finish their boats.

    You are right, this plan is a stretch of requirements. 9 people on an an 18 foot trimaran, that I guess you need to put on top of your car, is a stretch. They may all just fit, but their safety and comfort in all but very sheltered waters would be doubtful.

    Multihulls do not sail perfectly flat and even and dry, especially in the Mediterranean . They lean a bit, and water goes everywhere. Just because there is acreage for bums, does not mean a good experience for everyone.

    You will have to look seriously at your motives for this idea. Is it because you want to build something useful, or is it because you want to entertain your family ?

    If it is just entertainment for the family, spend the money on days trips on chartered tourist boats. Cheaper, safer and a lot less hassle to organize.

    If you want the building experience, you can always work on someone else's boat as an unpaid helper.

    Have you thought of 5 skin on frame kayaks, with some of them being two person craft for younger members ? They can handle quite choppy conditions and you can still get the family out on the water for fun, with minimum cartage problems.
  7. troy2000
    Joined: Nov 2009
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    troy2000 Senior Member

    I have no idea why my comment would upset you for several days; I was simply trying to give you what I consider good advice. I don't understand why you would invest so much time and money in a boat, then decide it's worthless without ever using it.
    By 'cavalier' I meant your decision struck me as an arbitrary and abrupt one. I wasn't trying to be insulting or dismissive....
  8. shmuelbrody
    Joined: May 2013
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    Location: israel

    shmuelbrody Junior Member

    i am one of the 3% of people that always finish what i start
    so please read this post carefully and design your advise accordingly

    1. thank you troy

    2. not all 9 would not be on the boat at one time
    maybe 3 or 4

    i want to build this boat not someone elses
    i am a wood worker for 60 years and can build any thing
    houses, furniture, so far one boat, and lot of other things

    really the perameters for the boat are not difficult

    the floats can be built whole with bulkhead at the middle
    then cut in half and later attached to the boat with with a connector
    that insures good water flow

    the floats would have 4 connectors instead of the usual 2
    that would put the floats on the 8 foot trailer

    the deck can be made of 4 4 x 8 torsion boxes that would cover
    the deck
    these torsion boxes are about 1 and 1/2 inch thick and would stack on the
    trailer 6 inches high

    please look up torsion boxes on google

    the 4 by 8 floor section would have a 6 inch box on the length of each 8 foot sides of about 6 inches and supported flooring for the 3 feet between them

    torsion boxes are very light and increadibly strong
    they will not flex under heavy load
    8 of these boxes will support the deck and tie the floats to the deck
    very well making a very strong structure

    the weight of the 4 by 8 foot section with 6 inch torsion box on each side running the length of 8 feet is about 104 pounds that makes the 4 deck components about 413

    you see that as the deck sections are assembled side by side
    each adjacent section has a combined size if 12 inches of torsion box

    so the total torsion box for the deck is 5 1/2 feet of torsion box
    with 12 1/2 feet if supported decking between them

    of course the fore and aft sides of the deck would only have a 6 inch torsion box

    the structure on the deck would be a 6 by 8 or 10 pvc pipe cage that could
    be erected easily and covered with light building wrap to keep out water
    with a inside plywood wall about 4 inches high between the pipes and the wrap
    to act as a shield for water this would be attached to the deck

    the structure for camping and bad weather

    as for a sail i investigates many kinds including airplane wings which i invented
    and then found that it already existed

    chinese sails seemed nice but the poles are heavy and long
    kite sails need constant attention
    i am not happy about the attention that has to be given to regular triangular sails

    so with the triangular mounting for crab claw sails and the fact that they dont
    need a lot of handling these seem best

    how big would this sail need to be

    here are the weights that i calculate for the boat

    413 pounds for the deck
    300 for the floats
    50 for the tent
    50 for the sail

    this makes 813 pounds
    i am sure that another 187 lbs will creep in somewhere

    i want the boat to ride as high above the water as possible and am thinking
    of building floats that will support 4000 to 6ooo lbs of lift

    my original thought was a box 1 1/2 feet wide and 2 feet deep by 18 long
    but you have stated that boxes are not good and have to be pointed and round
    in spots

    what do you think would be the best design for the floats
    can you point one out
    i can pay for plans for this but not too much please

    my son is also wanting this boat and will help with the need cash

    we can get stainless screws and such and super 7 glue
    that will glue anything together
    it was used on the summer breeze and we love it

    i used your dads quote yesterday
    i loved it
    People are always talking about the good old days. But I was there, and I wasn't impressed.
    i was there shmuel
    i am waiting for your reply
    from all of you
    i realize that you guys are the cream of the nautical design world
    and i treasure your response

    thanks again shmuel
    by the way
    yes the summer breeze will be sailing soon
    thanks to you all
  9. upchurchmr
    Joined: Feb 2011
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    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member


    You have a good suggestion from Troy and Rwatson, finish the boat.

    However if you really want a trimaran:

    Consider a Cross 18 trimaran, an older design by a well known designer, able to carry 4 at a little slower speed, relatively simple build, and it folds to less than 8'. I have been considering building one for 30 years, still considering. Probably needs to be on a trailer, but longer than 8'. I have towed a similar weight catamaran for years with a 1500cc car.
    An additional report:

    Another option is even simpler, limited to 2 people, could probably be car topped:
    I have never seen a sailing report on this boat.

    Good luck
  10. shmuelbrody
    Joined: May 2013
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    Location: israel

    shmuelbrody Junior Member

    hey up
    thats a nice boat
    my kid wants a cabin
    but ill show it to him
    but please consider the above boat requirements

    as an aside
    what do you think of building two similar boats like a dory or a punt and
    putting a deck over both of them

    what about the smaller tri
    and building 2 of the main section and decking over both
    please think about it

  11. upchurchmr
    Joined: Feb 2011
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    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member


    If you want a cabin you might try Richard Woods.
    A cabin will be a lot heavier and more expensive boat.
    This boat has a "cuddy" which can be built in a larger size.
    Looks a little way down on the page for "study plan"
    The same web site has multiple catamarans. It would be much better building a proven design rather than hoping something you just put together will work. Torsion boxes are fine for torsion but may not work for bending (the deck) or walking on. Depends upon the design but they are not magic cure alls.

    There are lots of designs for catamarans, have you done an internet search?

    Remember that hulls are only about 40% of the cost and time for a build.

    As I read your requirements you might have a difficult time finding something, especially with a cabin. Do you still need an 8' trailer?

    Multihulls need to be slender to work well. Two relatively wide hulls placed close together (traditional dory's at 8' overall width) will be slow, heavy and not handle well.

    The Woods site mentioned above has boats similar to what you want.
    The Gumprecht trimaran built as two main hulls would probably work, but there is a lot more to think about.
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