Aftmast rigs???

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

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

    brian eiland Senior Member

    Sketch of Your Rigging Plan

    Hi Mark,
    I've not yet had time to go back thru your postings and look more carefully at your rigging details. Would you perhaps have a little sketch of your rigging plan? It's not always easy to make out in photos.

    And why do you term it a trimaran, as it appears to be a catamaran in the latest photos?
     
  2. brian eiland
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    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

  3. markstrimaran
    Joined: Dec 2014
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    markstrimaran Senior Member

    Rigging sketch

    Just an old school graph paper drawing.
    The black cabin cover kind of blends in with the black trampolines.
    It does have some 18' Sol Cat in it.
    Thanks for taking a look.
     

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  4. tgtony52
    Joined: Aug 2015
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    Location: Tea Gardens, Australia

    tgtony52 ...

    aft mast gaff cutter

    Hi, I'm a newbie here, but have been following various threads for a couple of years, particularly this one on aft mast rigs.

    I have a 24' (7.3m) gaff rigged cutter, a kit boat built in 2002 and have just recently converted it to be aft masted.

    There are various reasons for this, the main being ease of use. On the original setup I found it difficult to manage single handedly the large main with its 5m long boom. However, sailing it with the staysail alone was a lot easier and it still had reasonable performance (5 knots). Fully rigged I have had it over 6.5 knots (hull speed). With the new aft mast rig and just the two new larger foresails I have reached 6.2 knots with less than 15 degrees heel. I have yet to sail it with the new cut down main as well.

    Being a trailer sailer, raising the mast and setting up the rig has to be fast and easy. By moving the mast two metres aft, I can now step it on the cockpit floor immediately above the keel rather than have it hinge on the roof of the cabin. I had to lengthen the mast to achieve this, but I can now pivot it on the back of the cabin. Raising the mast is now simply achieved by standing in the cockpit and pushing down on the foot of the mast until it locks in place on the cockpit floor. I can then rig the side and back stays at my leisure before raising the two roller furling foresails.

    So far I can say that both the setting up and sailing are both much easier and performance has not been compromised at all. I expect to go sailing a lot more frequently now.

    For anyone interested, I am setting up a blog to show in more detail (than I can here) the transition of a very pretty gaff cutter to (I think) just as pretty aft mast gaff cutter.
     

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

    brian eiland Senior Member

    Welcome to the forums Tony.

    Very interesting submission. And you say you have reached 6.2 knots, and yet have not utilized a mainsail yet?

    Going to interested in how your upwind performance is.
     
  6. markstrimaran
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    markstrimaran Senior Member

    marks trimaran video link

    Had it out sailing in steady 9 mph winds. GPS had me going 4.5 mph on a close reach. Still going in easy with my soft mast. Had it on a beam reach for a short duration at about 6.5 mph. My mast head stays are not bullet proof and did not want too brake anything.
    Mast is a little bendy. I am not sure just how far too leeward it can go.
    https://youtu.be/ViYOSpFsZZY
     
  7. tgtony52
    Joined: Aug 2015
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    Location: Tea Gardens, Australia

    tgtony52 ...

    Actually although the boat is 24' long, the waterline length is only 21', so its theoretical hull speed is 6.2 knots as a displacement hull (not 6.5). Its shape is partly planing, so anything over 6.2 knots I see as a bonus. The shape is also single chine so it sails at this speed more or less upright (see attached pic - heel angle only about 15 degrees).
     

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  8. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

    From the looks of your video that is not excess bending. But don't get me wrong I don't want to encourage you to go too far.

    I'm going to assume you have an older Hobie mast of solid alum tube,...not one of the 'comp-tip' ones? (There was a point where hobie became concerned with guys getting electrocuted when rigging there boats near an overhead powerline, so they started making mast with composite tops.)

    With both the H-16's and particularly the later 18's the sailors could put a LOT of downhaul pressure on the mainsail, then when the mast was over-rotated the mast tube would assume a nice even bow shape that was effectively 'flattening' the mainsail shape. So you see these mast can take some bending loads.
    I was trying to find some illustrations/photos of these conditions for you. I tried googling 'mast bend on Hobie 16'.
    https://www.google.com/search?q=mast+bend+on+hobie+16&ie=utf-8&oe=utf-8
    You might try some similar wording and look thru some of the images for a 'feeling' of how far you might go. There is no quantitative manner to explain your situation,...just trail and error as you are doing.

    Maybe try 'mast bend tuning'

    Am I to assume that both of your backstays are attached to some sort of big tube sticking out the back, that is in turn cantilevered/welded to a plate on your transom? No other rigging is attached to that 'stern pulpit' ? If so its going to be tough to get real good headstay tensions,...but the again you don't really need that in this low-tech experiment of yours.
     
  9. brian eiland
    Joined: Jun 2002
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    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Glad you brought that up, as I was thinking you might be near hull speed on that size mono. ;)

    One item you might keep in mind as you try to add that 'third sail' (the old mainsail) back into the equation. Look what Arvel Gentry wrote about those inner staysails,...attached PDF
     

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  10. tgtony52
    Joined: Aug 2015
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    Location: Tea Gardens, Australia

    tgtony52 ...

    Interesting article, thanks Brian. The situation with my rig is slightly different. Both my foresails are close together and do interact, but they are both significantly forward of the main (i.e. no overlap as in the article). I don't think putting the mainsail on should impact on, or be impacted by the foresails to as great an extent as if they all overlapped. The main benefits of the main will be to reduce drag induced by the mast, add some power and look good (love a gaff rig).

    By the way, when sailing with the boomed staysail only, the boat has a slight weather helm, which rather (pleasantly) surprised me.
     
  11. markstrimaran
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    markstrimaran Senior Member

    mast bend

    Thanks for the links Brian.
    Well been reading some. I gather that the hobie cat mast can safely bend about 2 feet to leeward without being damaged. Basically the shape of a bow with the middle to leeward. So as long as the mast step holds and the mast head shroud holds.
    I think as long as I deploy the 190sqft Genoa well pointed down wind. Then build some boat speed before a beam reach I will be safe.
    When I noticed my problem I just raised the sail and had very little speed. Later when I took the video. It does not look too be serious.
    Have favorable winds this week so 8 miles of beam reach
     
  12. markstrimaran
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    Location: usa

    markstrimaran Senior Member

    back stay and jib stay

    I think it is over kill, but if I hooked the back stay and the jib stay to a crane I could hoist the boat with these two points.
     
  13. tgtony52
    Joined: Aug 2015
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    Location: Tea Gardens, Australia

    tgtony52 ...

    Went sailing yesterday. Finally had a chance to put up the gaff mainsail in about 12knots of wind. We reached a maximum speed of 6.5 knots so there doesn't seem to be any drop off in performance with the aft mast rig setup.

    I have put a video of sailing at around 5.5 knots up on my blog at http://aftmastgaffcutter.com/sailing/. I'll have to find someone to take a picture of the boat who is not on the boat.
     
  14. brian eiland
    Joined: Jun 2002
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    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Wind Tunnel & CFD Investigations of Aftmast Rig

    I had forgotten about this research paper link that was made quite some time ago (2013). I seem to recall I had a hard time printing it out. And that old link from above is no longer valid.

    But just this morning I was provided with a new link to that research paper, and was able to print it out. I'm reading with interest.....:!:
    http://www.researchgate.net/profile/Ignazio_Maria_Viola/publication/262797205_Wind_tunnel_and_CFD_investigation_of_unconventional_rigs/links/00b495396bce8e7348000000.pdf
     

  15. tgtony52
    Joined: Aug 2015
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    Location: Tea Gardens, Australia

    tgtony52 ...

    A very interesting article Brian. Thank you for bringing it back.:)
     
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