Offsetting the Mast

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  • 07 Oct 2019 09:47
    Reply # 7920778 on 7911165
    Anonymous member (Administrator)

    Offsetting this and that...

    One thing is offsetting the rig. The other thing is offsetting the rudder and centreboard. That can help in tidying up the interior, and allow the outboard engine sit closer to the cl.

    A third way of offsetting is to move the rig aft and use the rudder as a second cb. The Chinese have a lot to teach us in this last respect.


    Below is a rig-and-rudder design for an Albin Vega I have been playing with, lately. Moving the rig aft (and to port) like that would solve quite a few problems (and add a couple as well). I have no plans of taking on such a project – Ingeborg is good enough – but it would be fun to rig a dinghy this way. This would let one move the cb. forward and out of the way, and the sheet would no longer sweep over the crew. The boomkin lets one move the sheet out of the way.

    So many ways of doing things...
    Arne

     


    Last modified: 07 Oct 2019 15:05 | Anonymous member (Administrator)
  • 04 Oct 2019 16:07
    Reply # 7917778 on 7911165

    I had a Bolger Birdwatcher once with a sprit rig offset the entire width of the center walk thru "hatch".  Had no effect on how she sailed it seemed.

    I have often thought about this when considering converting a sloop to schooner junk rig to overcome less than optimal interior mast placement.



  • 03 Oct 2019 08:54
    Reply # 7915765 on 7911165

    Hi David, just a reminder that I offset my mast on Miranda in 2013 when I converted her to AeroJunk. The new mast ended up beside the original but offset about 8” to port. This has not made any practical difference to the boat balance or performance. If you were worried then you could angle the mast to starboard so that the mast centrepoint crossed the centreline. Then effectively the bottom half of the mast would be to port and the top half to starboard. 
    Regards, Paul McKay 

  • 02 Oct 2019 15:25
    Reply # 7914201 on 7911165

    Our first Loose Moose (a Phil Bolger Jessie Cooper design) had both of its masts offset and, while it worked just fine, it did drive various observers to distraction.

    That, said it did teach me an awful lot about how boats actually work and, more importantly, how most of those who criticize seldom know what they're talking about.

  • 02 Oct 2019 11:13
    Reply # 7913912 on 7911165

    Many thanks to everyone who has replied so far.  The general consensus seems to be that it shouldn't cause too many problems to offset the mast a little, maybe up to the diameter of the mast, subject to the shape of the hull and internal structure.  

    As Arne might say, if you really want to know, go and do it!  and report back.

    IF I get a bigger boat and I need to offset the mast to make it work for the accommodation, I certainly will. 

    David D.    

    Last modified: 02 Oct 2019 11:14 | Anonymous member
  • 02 Oct 2019 08:26
    Reply # 7913801 on 7911165
    Anonymous member (Administrator)

    Think practically

    My armchair guess is that masts mostly have been fitted on the centreline for practical reasons.

    Since the majority of rigs in the west were stayed, offsetting the mast would result in much steeper shroud angle (and thus loads) on one side than the other. In addition, the shrouds put extra compression on the mast, and since western boats were built around strong keels, it made sense to step the masts on them.

    On rigs with freestanding masts, one is freer to offset the mast, if needed. Still, many boats have the deepest bury along the centreline, which is desirable.

    Even so, when I look around, at least some (western) mizzens have been stepped more or less off-centre, mainly to avoid the tiller of the transom-hung rudders (Phil Bolger yawls).

    On my last two boats, the rudders sit on the transom. On these, it is logic to put the single JR mast on the CL. This results in offset sails with the sheets landing on the side of the rudder, instead of on top of it. Simple and practical.

    On a flat-bottomed boat, I would not be afraid of offsetting the un-stayed mainmast a good deal to better make it suit the interior or improve deck space. I am not afraid of awkward handling, and the offset weight can be balanced out with batteries, outboard engine, etc.

    However, I don’t seek eccentricity just for the sake of it. The same with the JR itself. I didn’t choose it to stand out from the crowd. The rig ‘chose me’ because it is so good.

    Arne


    Last modified: 02 Oct 2019 14:13 | Anonymous member (Administrator)
  • 02 Oct 2019 05:47
    Reply # 7913615 on 7911282
    Scott wrote:

    "And yes, it is off-centre. This is to allow for a bigger bunk and means that the sail will end up on the centre line. Putting masts on the centreline is an occidental obsession."

    Stating that the sail will end up on the centre line I think is in some ways a convenience. Telling someone the sail ends up on the centre makes the interiour sound secondary and is easy to explain without having people shake their heads in wonder. The real reason may very well be it is in the way below.

    It is not off-center. It is off-centre. That is why I could not find it with a search!

    Of course, how else would one spell centre?

    I have no experience with this personally but I have to think that on a small boat like my S2 6.7 it would be a bad idea to have so much weight away from the center. On a larger boat or a schooner, where each mast could be offset the opposite direction, maybe it would work well.

    I think the shape of the hull may have more to do with it (for a freestanding mast). For most hulls the centre or close to it is likely the strongest or at least easiest to strengthen. For something with a flat portion and hard chines (dory or  five sided) the mast step may actually be stronger right at the chine. A twin keel craft might be stronger at a keel. With the schooner, having two masts offset to where (or close to where) the two sails are aligned when sailing to windward on one tack might be troublesome.

    Dave D. wrote:

    In most boats, putting the mast on the centre-line of the boat interferes with the accommodation somewhat, dividing the V-berth or especially, sitting in the middle of the access to same.  More of an issue with a Split Rig or Aero Rig

    By offsetting the mast to one side, more space could be created to one side of the passageway for getting forward.

    I think I have suggested this before... but an upside down Y shaped bottom of the mast could span the passageway.

    More curious than anything else, but thinking towards If I get a larger boat in the future.

    In general the larger boat can afford to have the passageway, hatchway, etc. moved to one side. Note in the reference to Annie's boat already posted, there is already enough room to offset the cabin hatch to accommodate the mast which is only moved over half the width of the mast itself (to put the sail at centre). It is the small boats where inside space is the hardest. Mind you Annie's boat makes interior design in a small boat look much easier than it is.

    [tongue in cheek]An excuse for moving the mast farther off centre might be that the boom and sail lay off to the side and out of the way at anchor. Historically, the mast would be moved to the starboard side as the port side was for docking (so as not to damage the steer board).[/tongue in cheek]

  • 01 Oct 2019 17:42
    Reply # 7912854 on 7911165

    "Occidental Obsession".......... I like that!

    In my opinion weight is not an issue....The weight of the sail and battens and the thrust are almost always offset to one side or the other, so is the offset of the mast itself significant?     Ask Rael ;-)      I've given much consideration to offsetting a mast since originally looking at trimarans where access forward would be nearly impossible without offsetting.     But personally I find symmetry a bit boring anyway.    I've argued with friends about planting shelter-belt trees in straight rows like so many dead soldiers instead of in a wild profusion as nature would do it.   My favorite engines odd fire.... creating an odd and uneven beat........... I rebel against symmetry, uniformity, and sameness........  Probably because I'm an outdoorsman, and  love nature and "God's work", in which symmetry is virtually  nowhere to be found.


                                                                        H.W.

  • 01 Oct 2019 13:53
    Reply # 7911289 on 7911165

    The offset mast in SibLim was designed in from the beginning, to allow for a wider berth.

    When I put the mizzen mast into Tystie, it had to go a little bit to the port side of the centreline, to ease access around it. I never noticed any adverse effects. I'm sure there are other examples, where the mast was offset so that the sail is on the centreline, not the mast, but I can't bring the details to mind.

  • 01 Oct 2019 13:46
    Reply # 7911282 on 7911165

    David D,

    I have been reading and re-reading Annie's blog post titled The Tabernacle, plus DIY composting toilet. I am trying educate myself on how exactly I might build a similar tabernacle.

    I was sure that she mentioned something about the tabernacle not being on the center line. After some unsuccessful searching I read it again more carefully. She wrote the following.

    "And yes, it is off-centre. This is to allow for a bigger bunk and means that the sail will end up on the centre line. Putting masts on the centreline is an occidental obsession."

    It is not off-center. It is off-centre. That is why I could not find it with a search!

    I have no experience with this personally but I have to think that on a small boat like my S2 6.7 it would be a bad idea to have so much weight away from the center. On a larger boat or a schooner, where each mast could be offset the opposite direction, maybe it would work well.

    Scott.

    Last modified: 01 Oct 2019 13:51 | Anonymous member
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