Mast setup, pls comment

Discussion in 'Multihulls' started by Fanie, Jul 9, 2008.

  1. Fanie
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    Fanie Fanie

    Hi Everyone,

    Pls comment on the advantages or disadvantages of the attached setup.

    Some notes on this.

    There is a mast on each hull. There is a cross-bar keeping the mast heads at their distance from each other. There are two stays crossing keeping the stays uprightas seen from aft, and one stay from the steps on each mast and the sails stays keep the masts upright from abeam.

    Here are some advantages from my point of view -

    The aft beam does not carry the weight and down force of the mast (if it was in the centre), hence the beams can be made lighter.

    It would be easier to upright the masts, since they cannot swing either way as could be the case with a single mast in the centre.

    The mast sits higher on the hulls than it would be on the beam if it was a single mast. I thus score a bit of mast length (height)

    Q-
    Do I enlarge the sail area effectively on both sails ?

    Can one make way ok with one sail ? ie the other is furled ?

    Would a setup like this have any disadvantages, other than maybe extra costs ?


    Thanks for taking the time out...
     

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  2. rob denney
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    rob denney Senior Member

    G'day,

    Couple of drawbacks:

    Large unsupported length of mast would mean the masts are bigger than normal.
    Additional weight up high
    Additional drag
    Difficult to get to the cross bar for maintenance
    Sail area is in the wrong place(low and forward) for most sailing.
    No sheeting angle on the leeward headsail, particularly when reaching
    Huge sheeting loads
    Huge tension required to keep the forestay straight
    All the loads work backwards. That is, as the breeze increases and nothing is changed, the sails get fuller. What you want is a rig that automatically reduces power in an increasing wind, not decreases it.
    Will need substantial bulkheads under each mast. The hulls may need beefing up to take the larger fore and aft loads.
    Will not sail upwind very well with partially furled headsails.
    Hard work lowering them as the crossbar will see high twisting loads if they are not lowered exactly together, You then have the cross bar sitting 20' off the bows and no easy way to disconnect it.

    Last, but not least. If it is deck stepped, there is nothing stopping the whole lot falling sideways, either as a collapsing paralellogram, or by lifting the windward rig off the deck. The stays must attach to the boat, adding more loads and another strong point.

    This is taking a complex, high effort rig and making it even more complex.

    How could it be improved? Make the masts unstayed, move them forward and replace the headsails with mainsails. This would overcome all the above problems.

    Regards,

    Rob
     
  3. Fanie
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    Fanie Fanie

    Hi Rob,

    Thanks, some valued comments there.

    The reason for using this sail setup is I want the sail setup to remain as simple as possible. Ideally a single sail that can be furled away or deployed easy and quickly.

    Since it is going on a fishing cat, the sail or sails has to be able to furl away asap if you get a fish on, so I'm trying to stay away from a boom (bermuda-like) setup.

    The centre of sail area can be shifted aftward. Ideally the mast should move aftward to about a meter from aft. A second and smaller sail could be used if the wind gets too much ? and could retain the centre of force on the hulls.

    The rig is made trailable, so the masts must be taken down, but they do get bolted down, the parallelogram won't topple over sideways.

    As for the substantial bulkheads under each mast, it is going to be even worse if the mast sits on a crossbeam between the hulls. By adding a substantial beam where the mast sits on, I either have to sacrifice bridgedeck clearance or have a beam to step over when you enter or exit the cabin. Neither is a sacrefice I want to make. As it is now the aft deck and cabin is at the same level.

    What is more desirable - A big sail with lots of area, (would work better when running) or a narrow sail to get more wing (luff) area (less side force when reaching).

    On the little trimaran I built just to test the sail setup I first had an 8 sqm sail. I then increased the sail area to 12sqm, both had the same luff length. Big difference in the force if you hold onto the clew rope. I got the impression I didn't really get more speed from the larger sail area, unless I was running (of course). Unfortunately the wind around here is nothing to brag about...
     
  4. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    http://www.schionningdesigns.com.au/www/page.cfm?pageID=271

    Shorter masts (divided sail area), simpler & lighter handling, unstayed keel stepped but offset, Schionning provides plans/instructions for the amateur to construct, you might be able to buy them separately but you would have to adapt them.

    The con here is some question about heavy air handling issues (turning the boat through the wind), yet to be resolved as I understand it.
     
  5. Fanie
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    Fanie Fanie

    Hi Meanz,

    Nice link, thanks, I'm going to check it out now.

    Could you pls explain ?
     
  6. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    Flat out now, I will find it later... its was on that other cat design thread (JCD?) I think... search Radical Bay 8000
     
  7. Fanie
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    Fanie Fanie

    Thanks Meanz... just got an idea.

    If I make a cavity in each hull where the masts sits in, this could make the masts easier to put up as well. No stays except the one, so the mast is thus free-standing. Will have to be fairly rigit to handle the forces though. Think it will hold ?
     

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  8. rob denney
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    rob denney Senior Member

     
  9. Fanie
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    Fanie Fanie

    Thanks Rob !

    Give me a bit of time to ponder all this.

    Regards
    Fanie
     
  10. Fanie
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    Fanie Fanie

    I like the Radical Bay as per Beanz's link. The 2 masts are smaller and easier to handle, centre of sail force is low, which I also like a lot. I also like the no rigging, it is simple which I also like.

    This still leaves me with the problem of how do I get the masts up and down, and when you fish how do you get rid of the sails quickly.

    On the jib you pull a rope and the sail is furled. Takes about a second to do...
     
  11. Butch .H
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    Butch .H Senior Member

    Fanie I still have that 11m mast if you are interested
     
  12. rob denney
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    rob denney Senior Member

    G'day,

    Why get rid of the sails? Presumably you want the boat to stop quietly and without hassle? Releasing the main sheet(s) so the mainsail(s) weathercock(s) and the boat stops will do this much quicker and with no chance of a balls up (furler lines jamming, junping off the furler, needing to be winched in a blow) than furling the jib. Add to this the ease of sailing unstayed main only rigs compared to fighting flogging genoas at each hoist, tack or wind increase and it is a far more sensible solution.

    Stepping/unstepping unstayed masts is very simple.

    You have a small hatch in the deck next to the mast and a mast step next to the regular mast step. Calculate the height of the mast centre of gravity above the keel and get a piece of alloy or steel tube that is the same length plus the distance between the mast bearings plus 0.3m/1'. Call this a gin pole.

    Attach a block and tackle to one end and place the other end through the deck hatch and into the second mast step. Attach the other end of the block and tackle to a strop around the mast at it's centre fo gravity. Hoist on the block and tackle and lift the mast to the top of the gin pole. Grab the heel of the mast and pull it down till the mast is vertical. Lower the mast into the bearing and down to the step. Remove the strop and the gin pole. Unstepping is the reverse. With cradles that sit on the deck, the mast can be lowered into it's traiering position. There are no stayed rigs that can be raised and lowered as quickly, or as safely as this. as this.

    Arrange the boom properly and it and the sail are permanently attached to the boat so do not have to be removed for trailering and need no vang so are trimmed solely by the mainsheet..

    Radical Bay rigs are a step in the right direction, but bent masts are hard to build (and to trail) and have halyard problems. They also have engineering difficulties, as evidenced by one of the original RB's breaking.

    regards,

    Rob
     
  13. Fanie
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    Fanie Fanie

    Hi Rob,

    Releasing the main is fine if you catch certain fish. If you get one of the more sporty fish on you want to get rid of the sails and go to the motors, and trust me there is not much time. A nice size saily or a bluefin will quickly rid you of your expensive braid, somehow these fish goes on to the next continent when they're hooked and they are in a hurry. Those booms are going to cause a lot of trouble if there is a sail on it and you try to maneuver after a fish :D

    I haven't delt with large jib sails, the sail on the little tri is only 15m^2, but it furls away in a second, and it takes the same time to get it going again. I never had it malfunction in any way. If I can find a way of making the mast for it work then that is what I would like to have. It is a one person operation and really very easy to do.

    If you look at Brian Eiland's articles on the aft mast as well as the one on fishing from a catamaran, that is the thing I'm after. He mentions the advantages there, one of them being able to furl the sail in a second and go to the iron sails right away. He also has an understanding of the requirements if you do fishing from a boat.

    The reason for going for sails instead of just outboards (which is much easier and simpler ;)) is you can sail all day long or trawl up and down a stretch of water day in and day out and it coesn't cost you an arm and a leg for fuel. I also for some strange reason developed a liking for sailing. Kinda the best of two worlds.

    To get back to the unstayed setup. I like it for it's simplicity. Is there a way one can down and up the sails quickly ? I'm thinking in the lines of releasing a line and the sail drops, then pull it up if you want to make way again. Another way could be to pull the boom up against the mast...
     
  14. rob denney
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    rob denney Senior Member

    G'day,
    Ball bearing luff cars will allow the sail to drop in seconds with the opening of a clutch. A wide boom, lazy jacks and or a sail bag to catch the sail and it will be completely out of the way before the jib is furled.

    Open the main sheet clutch (may not be required in medium air), open the halyard clutch and turn on the engines. The sail will out of the way before you get the engines in gear.

    Small furling jibs are pretty easy to furl. Dump the sheet, grab a handful of line and lean back. Even this will be slower than the mainsail. Large ones need the sheet released, then the line winched in while the whole boat is shaken by the flogging sail. It ain't quick, or particularly easy. Get some experience with large furling sails, or talk to someone who has (not someone who is trying to sell them, but someone who has furled a big headsail in a 20 knot breeze). Then talk to someone with ball bearing luff cars and see how quickly and easily the sail comes down when it is pointed into the wind.

    How are you going to lower the mast with a furled headsail attached? They are heavy, relatively rigid and easily bent.

    You will enjoy sailing far more with mainsails than with jibs. Less work, better performance and the harder it blows, the better they work.

    I don't know much about sport fishing (and don't really want to, it seems barbaric to me), but I have done a fair bit of sailing, building and designing. If you want complexity, weight, cost and lousy sailing, then the aft mast/furling headsail rig is definitely the way to go. Brian is a nice guy, who has done a lot for multihulls in his time, but does not believe in the rig sufficiently to build one and I don't think he has managed to sell one in ?? years of trying, so I tend to take his articles with a dose of salt.

    regards,

    Rob
     

  15. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    Hi Rob, thank you for your patience.

    The attached picture was posted in another thread, it looks like an easy way to get a mast up or down.

    The carrs in the mast is something I can do. It seems functional, I will play with the idea a bit, see how and if it can work out on the boat.

    As for fishing being barbaric, I agree but I also disagree. Depends on the the angler. Unfortunately some guys kills everything that crosses their path. As for our crowd, we take special precautions not to harm the fish. Almost all our fish goes back, I'm not scared of catching the same one again ;) We keep some fish for the pan, mostly young ones, the big ones goes back, they know how to make more fish :D

    It is very difficult for a guy to put a big fish back if he hasn't cought anything decent in years of trying, he he, it's like taking his trophy from him - but it becomes easier once you get used to let the big one get away by letting them go. What are you going to do with all the fish any way, one can eat only so much ;) Besides, chickens, sheep, cows, pigs and some fish are meant for eating.

    Fishing for fun is different than fishing for food. I'd rather you don't try, the thrill and excitement of gettig hooked and your skill against the fishes power is very addictive. It's pretty much the same as when you launch the new boat the first time... :D Fishing is like launching the new boat feeling many times a day...

    Getting carried away there. Lemme play with some ideas.

    Thanks.
     

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