Aftmast rigs???

Discussion in 'Sailboats' started by jdardozzi, May 28, 2002.

  1. brian eiland
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    brian eiland Senior Member

    .
    Hopefully I can get them to join in the conversation.
     
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  2. brian eiland
    Joined: Jun 2002
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    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Running Off in Storm Conditions

    Dear Mike,
    Don’t get me wrong Mike, I can fully appreciate your concerns for where the drag center is on my bare poled mast-aft rig, particularly in storm conditions. And you have brought this issue several times before, so I thought I would reply in greater length….pardon the length.

    Let me begin by asking where those drag centers might be for a conventional ketch or yawl rig under bare poles?? I venture to guess they are at least as far aft as the one for my single-masted ketch. So I might ask, are you saying those conventional yawls and ketches are unsafe in running conditions?

    I spent 3 days in a very heavy Atlantic winter storm one time sailing out of the Chesapeake Bay down to St Thomas. I was onboard my 47’ wood ketch with two other gentleman. Fortunately we got out pass the majority of the north flowing Gulf Stream before this strong northerly hit us. We did a lot of surfing towards Bermuda in waves that towered over our mast, but fortunately were long in scope. We decreased sail down to just the little cutter-rigged staysail jib, which kept us moving along at a good clip to be just slower than the waves, but not too slow to be crested by the next oncoming one. This small jib was up front pulling us along, but occasionally would jibe over due to our tendency to broach from one side to the other as we raced down the face of the wave to bury our long bowsprit into the back-side of the previous wave.

    Now one would suppose that this little jib up forward would ‘pull’ or push us along by the front of the vessel in a straight line running with the sea. But in fact the MUCH bigger influence was the fact that the circular motion of the water at the crest of a wave is exactly opposite that circular motion at the trough of the wave. This factor far outweighs the center of drag and/or center of effort of the rig in determining your straight-line progress ‘running’ down the seaway in a storm. Regardless of what side that jib was on the boat wanted to veer off to either side even while the wind pushed us downhill.

    At one point I decided that this continuous jibe-ing of that small staysail was going to destroy that sail and make it unusable for the remainder of the trip. Besides, surely the wind was blowing strong enough for us to continue under bare poles. So I decided to go up on the bow and take that sail down (got buried under the sea a few times as we punched our nose into the backside of a few waves). Now we are under bare poles and the boat slows down. BUT it slows just a little too much! Now the crest of the wave behind us breaks over the aft cockpit before pushing us off on the next sleigh ride down the face of the wave. This got to a very wet situation for the helmsman, as well as for my brand new diesel engine located under the hatch in the floor of the cockpit. I decided that it was worth sacrificing that jib sail for my new diesel engine!

    Now there were 3 guys onboard, so we split the steering duties into 3 hour shifts….and you had to pay attention for all of those 3 hours to not broach over sideways to the sea. We did this for what seems like 48 hours. Had I been alone, I would never have lasted that long…or even half that long. Remember I had no auto-pilot or self steering gear, and in fact I doubt it could have handled that situation.

    Eventually I decided to employ another tactic so we could get some rest. I decided to turn back into the remains of the storm (not as much wind, but big seas remaining). I hoisted my reefed mizzen and back-sheeted the small jib we had been flying. Now the mizzen attempted to point us up into the wind, but the jib prevented it from fully happening. We rode approx 60 degrees to the wind and waves in a very comfortable manner. We got that much needed rest.

    Based upon that experience I can say without a doubt, that I would much rather have the bow of my vessels pointed toward the storm (the big waves), particularly if I am shorthanded, or expecting the storm to last more than 6-8 hours. There is no way I can last much longer than this at one watch, without becoming exhausted enough to make a mistake in steering. I am firmly convinced that I would much prefer a parachute anchor properly deployed from the bow of the vessel in a sever storm. If I start out running with the storm, it becomes that much more problematic to turn back into the bigger conditions and readjust……just my assessment for what its worth. I think I even started a subject thread on parachute anchoring??

    Under bare poles and no engine I’ve got NO maneuverability control whether monohull or multihull. I believe this is likely the reason most vessels have opted for a storm tri-sail. I would also. I’d fly a small one that zips over the roller-furled staysail (mainstaysail as I refer to my cutter rigged inner headsail). And I’d be prepared to partially unfurl a little bit of that mizzen. And note both of these ‘storm’ configurations would/could be low center of effort sail area deployment configurations..

    Brian
     
  3. brian eiland
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    brian eiland Senior Member

    I’m not so sure that we are going to be able to put a definitive, quantitative numbers to this issue. As Tom Speer said, “I can understand the desire to simplify sail handling with roller furling staysails”… (all roller furling sails in Brian’s aftmast). These trade offs in terms of handling ease may trump some of the small loses (if any) in performance.

    We will probably have to be content with incremental indicators like this Italian wind tunnel study that show a superiority of the twin overlapping headsail arrangement to that of the single headsail sail, or non-overlapping configurations.

    For the cruising sailor we don’t have to be better performance than the conventional sloop if we offer other attributes such as ease of use, etc
     
  4. Fanie
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    Fanie Fanie

    Thanks Brian !

    I have not considered more than one sail in line, but I do want a sail on each hull and just under five meters apart. Worst performance may be at a beam reach but that is where one have the most performance. Any other position will begin to enhance the performance of having two sails.

    I wonder if Tom Speer ever holidays in SA :D
     
  5. MikeJohns
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    MikeJohns Senior Member


    Brian it does concern me and the obvious answer is that you calculate the drag.

    Actually the schooner rig would have been the more immediately obvious comparison.

    But lets look at a fin keeled lightweight like [Edit] Relentless, and compare the vessel to a similar sloop. There is no conceivable way the centre of effort of Relentless under bare poles is not aft of the CLR under any circumstances.
    The masts are the principle sources of drag and I'd calculate the beam on condition as the pivotal (literally) criteria as to how much lift you'd need to get from the rudder to maintain control when trying to run.

    Look at worst case possibilities. There are scenarios in small vessels where heaving to is not feasible and would lead to the loss of the vessel. Scenarios where taking the seas on the stern quarter and running under full control saves the vessel. Some sloops have reported that after the storm sail blew out that a sail bag lashed to the pulpit rails was enough to counter a dangerous broaching tendency(and that's on a sloop).

    A vessel like Relentless would be very prone to 'weathervaning' unless it could carry some canvas. I suspect that aft mast drag and higher rudder angles for higher L with associated D is one factor that made her a disappointment.

    For your own design that you refer to if you could you point to or post some profile drawings?
     
    Last edited: Oct 25, 2010
  6. Paul B

    Paul B Previous Member

    I don't think Amoco Procyon was originally an aft mast design. Has it been converted?
     

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  7. MikeJohns
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    MikeJohns Senior Member

    Sorry wrong vessel apparently, what was the name of this vessel with the aft mast rig [Edit apparently 'Relentless' thanks Brian ]
     

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  8. Paul B

    Paul B Previous Member

    I don't know. White Elephant might be a descriptive one.
     
  9. Alik
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    Alik Senior Member

    Aft mast rig is just a fetish... I have not noted any real advantages yet excerpt one: the boat (and the owner) always gets a lot of attention in any marina :)
     
  10. Fanie
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    Fanie Fanie

    You either missed a few posts or you are looking to see something else.
    Which advantages is it you are looking for ?

    If these boats and owners gets all the attention then surely there must be a bunch of them around, I'd like to see some of them to get some ideas !

    95% of the boats iin our marina's never go out. All white elephants.
    Maybe it's their sails ?
     
  11. Alik
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    Alik Senior Member

    I am just distinguishing advertised advantages form ones achievable in reality, from my personal experience.
     
  12. brian eiland
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    brian eiland Senior Member

    That boat was named 'Relentless'. Here are some more detailed photos.

    She has since had her rig greatly modified very significantly.
    http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999-8.html#post283505

    In fact there are references to this new rig of hers as a crab claw arrangement. I was going to ask PBmaise if he drew any of his inspiration from the modified Relentless??

    I was NOT impressed with this modification, but then its a lot about being willing and bold enough to experiment.
     
  13. brian eiland
    Joined: Jun 2002
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    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

  14. brian eiland
    Joined: Jun 2002
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    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    I believe Alik is referring to this vessel built over in Thailand. I'm actually a little sceptical about the lack of a resistance element at the attachment point of the inner forestay....in combination with the forward force by the aft raked spreaders.
     

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  15. Alik
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    Alik Senior Member

    So, Mr. Internet Expert is skeptical, besides without seeing the boat and rig drawings. If You have ever been on the boat, You would immediately note pair of lower shrouds. Those hold inner stay attachment point form aft/side. I have read the email You sent to the builder, and told him this is complete ******** :D

    FYI: The top of mast on that boat is bending forward, so the aft-swept spreaders are what is needed. We are engineers here, not amateurs posting unproven concepts in Internet :D
     
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