Raking the mast

The idea of raking Tammy Norie’s mast forward first came up when I compared Tammy to Fantail several years ago. As far as I can make out, raking Tammy’s mast will have three advantages:

  1. It will help the sail stay out in very light winds — particularly useful when becalmed.
  2. It will cause me to rebuild Tammy’s mast step, which is a known weak point.
  3. It will shift the centre of effort of the sail forward, improving the balance of the boat and reducing weather helm.

I believe I can achieve about 5° forward rake by moving the mast step aft, pivoting the mast within the cone that forms the partners.

IMG_2931
IMG_2932
arctan(10cm/118cm) = 4.8° I believe.

This should being the centre of effort of the sail (shown below) forward by about 3.5m × 10cm/118cm = 30cm.

IMG_2974
Because nobody has done this on a Coromandel and the future sail plan is unclear, I’ve come up with a scheme to make the rake adjustable.

Firstly, here’s s picture of the existing step. I hope you can see why this is inadequate. It’s been replaced on every other Coromandel I’ve seen!

IMGA0198
Here’s a drawing of the mast step that will make raking possible. I’m afraid I’m writing blog articles on my phone recently and so I don’t have my nice diagram software. You will have to make do with a photo of my pencil drawing.

This is basically a rectangular box made of aluminium angle, into which the mast is wedged using hard rubber chocks, and further secured with a retaining pin (to stop the mast wandering or jumping out).

The box is screwed to the laminated wood block that’s already glassed into Tammy’s hull, using large coach screws (hex heads and wood threads).

The mast base can be chocked and pinned at various positions in the box, allowing various angles of rake. Of course this means adjusting the blocks in the mast cone, so it’s not something to do at sea. I tried that (accidentally) once.

To allow for this I need to enlarge the hole in the berth that the mast passes through, making it into a round-ended slot.

IMG_2927
The box could be strengthened in various ways, but I already have 6mm gauge aluminium angle — double the gauge of the mast itself — so it ought to be fine.

Incidentally, the reason that the angle turns inwards is that it’s very hard to get tool access to this area of the boat. I don’t think I will be able to make pilot holes for the coach screws except through the slot for the mast. Having the screws inside also makes them possible to inspect through that same slot.

I hope this will all become a lot clearer when I start doing the work and have some photographs.

In the meantime, is be very interested in criticism or ideas for improvement.

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19 Comments

Filed under A New Rig, 2017-2018, mast, Repairs and Modifications

19 responses to “Raking the mast

  1. Antoine Maartens

    This is the part of your plans where i see most difficulties I fear. Here are my anxieties:

    (1) It will put pressure on the mast cone in a way it was not designed for – it seems to be designed for guiding, not for receiving the forces of the rig;
    (2) It might be very difficult to remove the existing base of the mast – on Siskin these massive bolts are beyond moving. They won’t budge without violence;
    (3) Easy alternatives are available without putting a crucial part of Tammy and therefore Tammy herself in jeopardy.

    Here is one I haven’t seen here yet. Have you tried to move the attachment point of the halyard further up the yard. I was out yesterday and while pondering our discussions and gazing op the rig, this one struck me as another option for moving the whole lot forward quite a bit.

    • I think you point (1) isn’t quite right. When on a run the majority of the force pushing the boat along is transmitted through the front of the mast partners inside the cone. Or are you thinking of something else?

      I’m also concerned about those giant screw heads. That will be the first step, so I’ll find out. I’m going to borrow my dad’s tool that allows quite a lot of violence to be applied!

      • I think I haven’t talked much about is the mast wedges that live inside the cone. I made a set of wedges for Tammy Norie from some soft pine, and I shaped them to fit neatly. They aren’t going to fit properly one the mast is raked. I will probably make some more. It’s another reason that changing the rake isn’t something to do at sea.

        IMGA0193

        I have been wondering about whether there’s a better material for doing this job.

  2. Antoine Maartens

    These look COMPLETELY different from mine. I’ll do some pictures when I get to Siskin again.

  3. Pingback: A New Rig | Tammy Norie

  4. Kurt

    On Antoine’s point 1 – Partner forces – On mehitabel, it’s been clear that pitching forces at the partners are the toughest. Sail drive is light. Boat rolls to ease side forces. You’ll fit the partner wedges well after each rake change (man, you’re ambitious!) so they’ll transfer the force to the deck as well as ever. I do wish there were more ‘meat’ in the plane of the deck. That cone is a bit… unfair. It would have to be a lot more substantial to take strain at the top and be part of the effective mast bury.

    On adjusting sail centre-of-effort – If you have enough halyard drift, the sling point aft and tack parrel eased will take advantage of one junk superiority – sail mobility. You’re obviously intending to play with it.

    On the keels – Coromandel & Corribee bilge keels have very blunt trailing edges. Keel designs are predominantly tapered to thinness aft. I’ve experienced a safe temptation (because minim is far away) to construct a wood & foam aftward extension to each keel, faired in and glassed, a bit silly-looking maybe, but adding lateral area where it would alleviate weather helm.

    On the mast step box – Great idea, and designed for research that we’ll all appreciate! I’ve pictured minim’s new step (inevitable project) and partners too, in laminated timber & epoxy, with a close fit to the circular mast, and thin softwood wedges all around. Wee bit of rake forward, drainage, a pin.

    On much weather helm but also reluctant tacking – hmm… puzzling.

    Cheers,
    Kurt

  5. Sneak preview.
    2017-09-18_09-10-53
    (That isn’t the mast.)

  6. This thread is fascinating even to a non-junk rig sailor… I can’t add any scientific input, but a couple of comments… I was a windsurfer for 15-20 years before I bought my first boat, and on them one of the primary steering methods is to move the CE of the sail forward and backward so I would expect your moving the mast forward to increase the “bearing off”/leeward effect? Will that effect your upwind speed? The only other comment is that every picture of a sampan I’ve seen has a mast rake like that last picture.. :o)

    • Yes exactly. The Coromandel isn’t very well balanced as designed, and needs a bit of “bearing off”. That plus the other two things I mentioned in the original post.
      Tammy Norie drying out in Fareham Creek with her sporty new mast rake.

  7. Pingback: Little jobs roundup, 2017-09 | Tammy Norie

  8. Pingback: A new mast step | Tammy Norie

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