Proa Self Steering? AD-Scull? Sheet to Tiller? Lets see...

Discussion in 'Multihulls' started by rael dobkins, Apr 2, 2022.

  1. rael dobkins
    Joined: Jul 2015
    Posts: 163
    Likes: 57, Points: 28, Legacy Rep: 16
    Location: Bulgaria

    rael dobkins Dreams come True, But only to Dreamers...

    Shunting Proas don't have a fixed stern. Rudders must be raised or moved after every shunt.
    This VIDEO explains pros and cons of the various systems, why I don't like them and how I plan to modify the AD-Scull for sheet to tiller...
    Finally, the Build, 4th Proa from Balkan Shipyards, where we're at, what we use and why.... Keep Shunting, Balkan Shipyards

    SolGato likes this.
  2. Robert Biegler
    Joined: Jun 2017
    Posts: 169
    Likes: 90, Points: 38
    Location: Trondheim

    Robert Biegler Senior Member

    The rotation axis for your sheet to tiller self-steering is horizontal, so if the rudder is parallel to the longitudinal axis, that rotation does not change that angle. But if there is leeway, then the effective angle of attack decreases, I think, proportional to the cosine of the angle to the vertical. And the immersion of the foil also decreases as the angle deviates from vertical. So I can see how that part works.

    Your setup differs from those I have seen (mostly in books, and one on an Yngling keelboat) in that you are likely to have higher loads on the tiller and lower loads on your junk rig sheet. Do you already have plans how to compensate for that, or will you work that out once you are on the water?
  3. rael dobkins
    Joined: Jul 2015
    Posts: 163
    Likes: 57, Points: 28, Legacy Rep: 16
    Location: Bulgaria

    rael dobkins Dreams come True, But only to Dreamers...

    My blocks connect to the boat with carabiners, so if there's a cam cleat on the double block, the whole block gets unhooked from deck, I pull the sheet through and cleat it with the cam cleat on the block, now block is hanging in the air closer to the sail. A line gets fixed to the carabiner at the bottom of the block, then through a block on deck at the other side of the tiller, now back to it. This way I'm eliminating the block and tackle and the full sail is directly pulling the scull. The bungy cords will be very long, I plan on mounting them to the boat far from the tiller, I want to be able to have a long cord that will stretch easily.

    The objective, full pull of sail. Meaning: eliminating the 2:1 purchase of the junk sheet.
    Stretchy long bungy cords mounted to boat via mobile cleats, like jib block tracks for example. This way the long cord will offer minimal resistance to the sheet pulling the oar, since short cords are hard to stretch... As wind builds car moves on track closer to tiller, shortening the working cord making it harder to stretch, at a certain point more cords are added, but I feel a very long cord (1 meter) is a good start...

    Those are the rough plans, I'm expecting a hard learning curve... Yet who knows, sometimes expecting the worse, could have surprising results....

    Keep Shunting, Balkan Shipyards.
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