Rudder shape and Size?

Discussion in 'Multihulls' started by soulofasailor, Dec 19, 2012.

  1. cavalier mk2
    Joined: Mar 2010
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    cavalier mk2 Senior Member

    You might try raking the mast aft to compensate. If the previous owner didn't have problems it might be the rig set up. Raking aft reduces lee helm and helps keep the bows up.
     
  2. Phil Locker
    Joined: Oct 2004
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    Phil Locker Junior Member

    Its not that simple

    With all respect, if you are asking that question, then you probably don't have the knowledge to successfully build a new set of rudders for this boat.

    You may be surprised to see the loads generated at 14 knots - they're very high.

    We have an online calculator here:
    http://www.fastcomposites.ca/site/marine/design-tips-fabrication-overview/helpful-calculations/

    Scroll down to the calculator for "calculate lift"

    Pick a Coefficient of Lift of maybe 1.0 (rudder hard over), a rudder size of say 200 sq inches (guess from looking at yours), a velocity of 14 knots and you'll see a side load from lift of 770 lbs. It takes more than a simple shaped wood rudder to handle that... you need to look at a composite construction of core + skins...

    Cheers
    Phil
     
  3. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    I assume this is a cat, if the dagger boards ? are not down the bow will want to follow the wind like you say and you will only have the rudders to keep you going ahead and not into the wind. The harder the wind pushes the more the hulls will point downwind. The dagger boards are the hull's pivot in the water around which the hulls rotate.

    The heavy steering could be caused by the rudders lifting while you sail, so instead of the rudders balancing vertical around the pivot in the housing they lift up towards the rear and multiply the steering force multiple times. Make sure they remain vertical all the time.

    If the dagger boards are down then steering is simply a matter of trimming the angle to the wind, there should be little force even when you tack. The hulls should rotate around the dagger boards effortlessly because the dagger boards take all the side force, and being balanced, the rudders simply swing the stern around the dagger boards. The dagger boards shape is designed to "fly" into the wind and tend to keep you in a straight line instead of being pushed downwind.

    Why don't you post a picture of the whole boat ? What is it ?
     
  4. soulofasailor
    Joined: Nov 2011
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    soulofasailor Junior Member

  5. soulofasailor
    Joined: Nov 2011
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    soulofasailor Junior Member

  6. Fanie
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    Fanie Fanie

    Ok I can tell right of that that music you play aboard is going to make the winds, the water and all the other gods very angry ! What is on top of the mast ? A sub woofer ?! No wonder... the boat is trying to escape !

    :D

    The only time you can sail with the boards out is when you run (sail downwind) and when you beach in the shallows (better remember).

    You want them in all the way or they won't work right. When they're out you remove the hulls pivots and the wind will of course slide you sideways, it makes a big difference.

    I don't think there is anything wrong with the rig (maybe those speakers :rolleyes:).
    You must listen to the wind and the water and the rig squeaking instead...

    I watched the vids now... ok what was the problem again... ?
     
  7. caiman
    Joined: Dec 2008
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    caiman Junior Member

    Why are your sails so 'baggy' between each batten-on the jib and on the main(the tack of which is down to the black band)?Are you 'honking' the halyards up tight enough?Are the halyards made out of rope which is stretching when there is a bit of 'weight' of wind in the sails?
    Nice boat.Hope you get sorted.
    Cheers
     
  8. Petros
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    Petros Senior Member

    I see a number of things wrong on your video, one already mentioned is your rig is all out of adjustment. You need to find some instructions on tuning your rig, making all the adjustments to get all the puckers and wrinkles out of it, and to trim it so it is balanced. It appears you do not know what all the various adjustments do, you either need to find a book on the subjects (I know there are some good ones out there for Hobie cats, which have similar rigs) or find someone that knows about adjusting a fully battened sloop rig like yours.

    The other is the dagger boards, both should be down the same amount. There is a stupid idea out there by some beach cat owners that holding one up reduces drag, but it causes asymmetric drag that is larger than the drag of the one dagger board, and it also increases the tiller loads and trim drag of the hull. In most cases both should be down all the way, the boat was designed to sail that way and it will never balance with one up and one down. Who ever told you that have one up was a good idea did not understand how sail boats work.

    When in very light wind, and going down wind, it would be acceptable to raise them up part way by equal amounts to reduce drag, never all the way or you will loose rudder control.

    If your sails are so stretched out and out of shape there is no way to get all the puckers and wrinkles out, than it is time for new sails. those will increase your speed noticably (espcially once they area all trimmed properly), and perhaps solve some of the issues with the tiller loads as well. But you really can not address the tiller load issue until you get the boat sorted out so it is sailing the way it was designed. If you mess with the rudder without properly adjusting your sail trim, than you will be chasing your tail with changes. Each thing you change on the boat affects everything else, get it into proper trim first, and than look at what adjustments you can make to fix the tiller loads.

    I suspect once you learn how to adjust the rig properly, and put both dagger boards down, most of the complaints about the tiller loads will be resolved.
     
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  9. soulofasailor
    Joined: Nov 2011
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    soulofasailor Junior Member

    COOL thanks for all the HELP here! so the ONE BIG thing i am doing this YEAR is getting NEW sails! They should be almost done, im getting a Square Top main and a New Jib.. for 1200 bucks. It was a December special! I cant wait, i hear alot of stories of how new sails made boats like new again! Last year was my first year with the boat and with all the trimming i have done and things those sails would look like i haven't done anything! I have had her out in 20 plus winds with those sails too . It made for a hairy sail but since i am on a small lake we would get great big puffs and then Die or slow down, so i have not had her in a constant Blow yet, on a good day a H18 couldn't catch me, it was so crazy that day H16 were bouncing when trying to right them! I just want to be able to fly a HULL! and be under control..

    Ohhh that thing up top is a FLOAT! I was told to use it since this is my first CATAMARAN! :)
     
  10. Paul B

    Paul B Previous Member

    WOW. I can't believe someone would write this.

    Take a look at the attached photo. These guys must not understand how sailboats work?
     

    Attached Files:

  11. Petros
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    Petros Senior Member

    Paul, those are specially designed racing boats that are flying a hull. Not a typical recreational beach cat.

    Some years ago a friend and I would enter local racers in his than new Hobie 18. We notices a lot of people would pull one dagger board up when going down wind. On the largest West Coast Hobie cat regatta in Newport beach one year I had the following experience; Since we were all in the same type of boat, and we had very light wind, it was hard to get any large advantage in a Marina when going down wind. We did the same thing as everyone else and had one dagger board down and one up when on the down wind leg. But I noticed that with one dagger board up the tiller was off center creating some trim drag from the hull asymmetry. I wanted to try and eliminate the trim drag so I slipped both about half way down by equal amounts. the tiller came back to center and we started creeping a head of the pack of all of the other H18s. Everyone was looking over our boat to see what we were doing differently, no one noticed, everyone else had one dagger board up and one down. We won that leg of this big multiday race (there were over 1800 Hobies in the race, including 14, 16 and the 18) To this day I think no one on that race figured it out. It worked because we reduced the asymmetric drag on the hull.

    I do not know what personal experience you have with such things, but it happened to us.

    The OP's beach cat is very similar in operation to the Hobie, so keeping both dagger boards down would eliminate at least one variable in solving his high tiller force mystery.

    Why don't you suggest something helpful?
     
  12. Paul B

    Paul B Previous Member

    Maybe you can tell us what design differences you would make to differentiate the Board up vs board down? I mean, if eliminating the drag of one board is unsettling things as you suggest, surely eliminating the drag of the board plus the drag of the hull would make things even worse? Or is there some design change you know of that makes up for this? Please enlighten us.

    PS: Randy might disagree about his 21 not being designed as a racing boat that flies a hull.


    I'd love to hear more about this regatta of more than 1800 Hobies sailing "in a marina" in Newport Beach. What year was that? Who was hosting that regatta? Where were you launching from? What part of the harbor were you sailing in? There really isn't a good spot inside the harbor to race cats at all, let alone 1800 of them.

    Considering the speed limit inside Newport Harbor has been 5 mph since before the Hobie 18 came into being it seems a strange place to be racing catamarans that would almost always be exceeding this limit. The Harbor Patrol in Newport has always had a rep for writing speeding tickets at every opportunity. They must have become very rich that weekend.


    I may not be able to match your anecdotal experience of sailing on a Hobie 18 inside Newport Harbor in very light air. I have sailed quite a bit inside in Newport and have noted the local puffs (due to the man made structures that line the bay) can have a huge impact on what boat pulls ahead when sailing down the bay. But I'm sure you took that into consideration in your evaluation.

    I did spend 3 years working at Hobie Cat Long Beach. During that time I prepared hundreds of boats for customers and was the primary sailing instructor. I raced extensively, with a bit of success. So much so that the local fleet made a new rule (aimed directly at me) that banned "professionals" from crewing for customers in the B and C fleets on Thursday nights.


    I believe correcting disinformation is pretty important and helpful to the knowledge base on this forum. Don't you?
     
  13. soulofasailor
    Joined: Nov 2011
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    soulofasailor Junior Member

    Well i will take any input that anyone gives, by watching these AC75 and 45s i was wondering the difference in my hull then theirs! Which i know this answer is theirs are more MONEY! :) But it should be all the same similar ideas and technical in designs. I will try everything that is talked about on here.
     
  14. Petros
    Joined: Oct 2007
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    Petros Senior Member

    Paul,

    the Regatta was in about 1980-81 as I recall, over 30 years ago. It started on the beach, and ended inside the marina, most of the time over the three days it was out in open water. We were heading back at the end of the day going straight down wind inside the marina at the end of the race. There were eight fleets staggering the start over the three days. I do not know what they do now, but that is what happened than.

    look it up for yourself in the Archives: http://www.hcana.hobieclass.com/


    No, you are not being helpful. I have not seen one suggestion from you in your post attacking me that would be helpful to the OP nor the topic of this thread.

    If you want to be helpful, why don't you post useful suggestions from all of your knowledge and experience.
     

  15. Paul B

    Paul B Previous Member

    Didn't seem to find the regatta you mention in the archives you point to. Can you be more specific?


    My most useful suggestion would be to not listen to people who make statement like, "..the boat was designed to sail that way and it will never balance with one up and one down. Who ever told you that have one up was a good idea did not understand how sail boats work."

    I hope everyone notices you have attempted to skirt the questions put to you about the design aspects. So I ask again, what design aspects make a boat work with one board up and one down (or partially down), while another needs both boards down the same amount?

    Let's consider your Hobie 18 experience with the Olympic Class Tornado (pre-spinnaker). Both are symmertical hulled cats of a similar length. Both use symmetrical, vertical boards. Somehow, the best cat sailors in the world, sailing the Tornado, could not figure out your trick. So I guess those guys "don't understand how sail boats work?" Of course you may have an idea of the design differences that makes the trick work on your H18 but nor on the T. So what would that be?

    Of course all the best H18 sailors I know not only pulled the windward board up, but kicked up the windward rudder as well. The H18 mechanism was a big improvement over the H14/H16 mechanism for this. This was also done by Tornado sailors, H16 sailors, Prindle sailors, Nacra Sailors, A-Cat sailors, etc. I guess none of those folks knew/know how sailboats work?
     
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