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Thread: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

  1. #1
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    Default Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Hey folks,
    been a while since I last posted here.

    I have a pram dinghy hull I've dragged around for years that I finally want to rig up for sailing.
    It is an odd/unique hull in that it appears to be precisely like a mirror dinghy except that the builder carefully scaled it up (from 10' 10") to 12' 4" LOA.
    This must have been somewhat laborious as as far as I can tell, the mirror plans themselves have never been available?

    here is an old thread when I bought it, with some confusion by me, and some photos in it.
    http://forum.woodenboat.com/showthre...boat-Mirror-12

    Back then after I bought it, I pulled off the rub rails that were cracking, and re-glued, and fixed up all the bubbling seams and everything else that was wrong. It has since been stored under a boat cover and is in perfectly sound condition. Never even been in the water.

    This hull has no daggerboard case installed or slot cut, it is just a bare hull, and came to me without a sailing rig.
    I have since bought a wreck of standard sized mirror dinghy to scrap for its trailer and complete traditional gunter sailing rig, including spinaker, plus rudder and a few other bits.
    Given this is a one of a kind hull that could never be used for mirror class racing or anything, I am not interested in staying traditional with everything or anything in particular.

    I would like to set this up as a sailing/fishing/day cruise boat to use with my daughter, partner, solo and/or friends. I want to set it up for ease of use.
    I am drawn to trying to build a swinging/hinged centreboard rather than the standard daggerboard that would better deal with grounding/retracting in shallow waters, and just because...
    Given my hull is a bit longer than a traditional one, I would assume that the traditional rig will be a little bit underpowered, but I suspect I will be just fine with that.
    I have no mast steps on it yet, but intend to go with the early mirror approach of doing a standard and a forward mast step (forward for sailing with main only).
    I have an old seagull outboard I might use on it first, and if I get too sick of the noise and the oil slick and if I am enjoying the boat enough I might end up buying a very light modern outboard for it.

    Beyond that, I am totally open to suggestions as to what people think I should do with this hull, and or the rig, and hopefully how I might go about designing/positioning a swinging centerboard for it- plus any other suggestions regarding its intended use.

    If anyone needs any actual measurements or detailed photos, just ask, it is about time I had another look under the cover!

    Cheers,
    Hans.
    One path leads to despair and utter hopelessness. The other, to total extinction. Let us pray we have the wisdom to choose correctly.
    Woody Allen

  2. #2
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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Just for starters, i would consider using the seat face as part of an off-set board, though this will need some extra stiffening, it would keep the slot clear of the bottom.

  3. #3
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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    I'd put in the centerboard right about 1' forward of where it goes in the 10'10" design. Cut a slot in the foredeck to give you that double mast step location, but build a temp mast partner and step. Rig the rudder and take it out to see how the sail balance works. If too much lee helm, move the mast aft. If too much weather helm move it forward. Once balanced, finish the mast step and partner. The nice thing about the slot is that it lets you make an angled approach to raising and lowering the mast -- see the many posts here about building mast gates.

    If you can pull the whole foredeck that might work better for the temp step & partner, and you may have to remove it to put the CB case in the right position anyway.
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  4. #4
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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Thought I better have an actual look at the hull after posting that.
    Aside from a fair bit of peeling paint on the internal glass tape seams (tape itself is fine) it is all still in pretty good order. Needs a good scrape and repaint and a few other things.

    I took some measurements again, to be sure.
    LOA is 3750mm (standard mirror is 3300mm, approx 13.5% longer)
    Max Beam is about 1670 (standard mirror is 1390, approx 20% wider- though it has very thick external rubrails)
    everything else looks like traditional mirror details from what I can tell from online pictures.

    The hull plywood appears to be bang-on the normal odd mirror dinghy thickness of 4.6mm.
    One path leads to despair and utter hopelessness. The other, to total extinction. Let us pray we have the wisdom to choose correctly.
    Woody Allen

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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Just a comment about the length, there is a French design ( name doesn't come to mind, more coffee needed ;o) ) that looks very like the Mirror, but is bigger.
    A2

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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Thanks skaraborgcraft,

    I was assuming the seat would come completely out and then figure out something else to build around it (hopefully in a good rowing position) once the centerboard was built.

    Thanks Thorne,
    It has been quite a while since I've been comfortable with boat lingo, but I think I understood all that. I am searching and reading to get a good picture in my head of what you mean.
    The foredeck is quite large and at the very least I wouldn't mind removing the section above that open stowage locker area. That would help open up some room to build the centerboard case and enable me to build a strong mast step.

    Here is a diagram of the normal mirror mast steps (I seem to be having more problems than I used to in posting images here)

    http://www.ukmirrorsailing.com/image...s/plate_52.jpg


    A2, I'll hit the google to look for that french dinghy
    One path leads to despair and utter hopelessness. The other, to total extinction. Let us pray we have the wisdom to choose correctly.
    Woody Allen

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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Quote Originally Posted by Andrew2 View Post
    Just a comment about the length, there is a French design ( name doesn't come to mind, more coffee needed ;o) ) that looks very like the Mirror, but is bigger.
    A2

    There is the French Caravelle ( designed by Jean - Jacques Herbulot in 1952 ) , but it`s bigger at 15.09 ft or 4.6 m.











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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.



    Drawing shows a dagger board too , unfortunately .

    https://www.google.com.au/url?sa=i&s...43659294460123
    Last edited by beam reach; 11-30-2018 at 05:20 AM.

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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.



    Somewhat confusing , this one has a swinging board ?

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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Nice find, Beam Reach, that's it.

  11. #11
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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Yep, boat lingo can be confusing. In effect I'm suggesting that you build and install the CB first, then fab up a temp mast step (on the bottom) and partner (at the gunwales) and test to find the best sail balance. I'm sure with a lot of measuring and Nautical mathematics you could find the best location, but I find it easier to just test the boat in the real world with real people in it, then finish the mast position(s). It might be easier to just bite the bullet and plan on sailing with main and jib all the time, so you'd only need one mast step/partner.

    The slot and gate setup is handy for stepping / unstepping the mast while in the water -- for low bridges, for example. But for a rig that size you can just pull the mast straight up and out, so no real need for the slot & gate. And with stays you're less likely to be pulling the rig anyway.
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  12. #12
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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Quote Originally Posted by beam reach View Post


    Somewhat confusing , this one has a swinging board ?
    Wiki says that the Caravelle originally had a daggerboard, then changed to a centreboard after 1965.

  13. #13
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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Quote Originally Posted by hansp77 View Post
    I have since bought a wreck of standard sized mirror dinghy to scrap for its trailer and complete traditional gunter sailing rig, including spinaker, plus rudder and a few other bits.
    Given this is a one of a kind hull that could never be used for mirror class racing or anything, I am not interested in staying traditional with everything or anything in particular.

    I would like to set this up as a sailing/fishing/day cruise boat to use with my daughter, partner, solo and/or friends. I want to set it up for ease of use.


    Cheers,
    Hans.
    Quote Originally Posted by Thorne View Post
    Yep, boat lingo can be confusing. In effect I'm suggesting that you build and install the CB first, then fab up a temp mast step (on the bottom) and partner (at the gunwales) and test to find the best sail balance. I'm sure with a lot of measuring and Nautical mathematics you could find the best location, but I find it easier to just test the boat in the real world with real people in it, then finish the mast position(s). It might be easier to just bite the bullet and plan on sailing with main and jib all the time, so you'd only need one mast step/partner.

    The slot and gate setup is handy for stepping / unstepping the mast while in the water -- for low bridges, for example. But for a rig that size you can just pull the mast straight up and out, so no real need for the slot & gate. And with stays you're less likely to be pulling the rig anyway.
    He has the mast which is deck stepped.
    It really is quite difficult to build an ugly wooden boat.

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  14. #14
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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    It might be worth looking at a Heron for inspiration.

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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.



    Looking at the relationship between the mast and daggerboard in the original boat, and considering that the rudder is now further back, I would set the mast step so that the forestay and shrouds fit, then build the case so that it extends right up to the bulkhead. Then trial fit the cb so that it is where the original dagger board was in relation to the mast. With the rudder further back, you may find that you need to move the CB forward for balance. By extending the CB case forward, you can move the board and its pivot forward if you find that you need to.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
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  16. #16
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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Did the Miracle make any kind of impression in the Antipodes?Designed by Jack Holt,small bow transom and pivoting centreboard while not being too heavy.Like many boats of the type they could originally only be had as kits so as far as I know there aren't plans.


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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Quote Originally Posted by John Meachen View Post
    Did the Miracle make any kind of impression in the Antipodes?Designed by Jack Holt,small bow transom and pivoting centreboard while not being too heavy.Like many boats of the type they could originally only be had as kits so as far as I know there aren't plans.

    Part of the same family. Mirror nespaper sponsored both Mirror and MIRacle IIRC.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Quote Originally Posted by Peerie Maa View Post
    Part of the same family. Mirror nespaper sponsored both Mirror and MIRacle IIRC.

    They never really took off here in OZ ...unlike the Mirror.

  19. #19
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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Quote Originally Posted by Peerie Maa View Post

    Looking at the relationship between the mast and daggerboard in the original boat, and considering that the rudder is now further back, I would set the mast step so that the forestay and shrouds fit, then build the case so that it extends right up to the bulkhead. Then trial fit the cb so that it is where the original dagger board was in relation to the mast. With the rudder further back, you may find that you need to move the CB forward for balance. By extending the CB case forward, you can move the board and its pivot forward if you find that you need to.
    Although the seat and deck and bulkheads and stuff on my hull appear to be scaled the same as a normal mirror hull, I would like to have a good look over a normal mirror and do some measuring and drawings for comparison, to see where everything relates to eachother on both hulls. I just remembered a good friend has a standard mirror sitting in his shed, not far away, so I've just called and booked that in.

    Regarding the daggerboard position, do you mean extending the case up to the first open bulkhead, or up under the deck and mast steps there to the second sealed bulkhead?
    Either way it should help give a bit of strength to the deck mast steps.

    Regarding the forestay and shrouds, I have no fittings nor timber glued in as chainplates or anything, so I will probably need to figure the locations and start there.

    Cheers,
    One path leads to despair and utter hopelessness. The other, to total extinction. Let us pray we have the wisdom to choose correctly.
    Woody Allen

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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    Quote Originally Posted by hansp77 View Post
    Although the seat and deck and bulkheads and stuff on my hull appear to be scaled the same as a normal mirror hull, I would like to have a good look over a normal mirror and do some measuring and drawings for comparison, to see where everything relates to eachother on both hulls. I just remembered a good friend has a standard mirror sitting in his shed, not far away, so I've just called and booked that in.

    Regarding the daggerboard position, do you mean extending the case up to the first open bulkhead, or up under the deck and mast steps there to the second sealed bulkhead?
    Either way it should help give a bit of strength to the deck mast steps.

    Regarding the forestay and shrouds, I have no fittings nor timber glued in as chainplates or anything, so I will probably need to figure the locations and start there.

    Cheers,
    CB case up to that first open bulkhead.
    As to the mast position and rigging. You suggest that you have the mast, and the shrouds & forestay. You will probably want to attach the forestay to the bow transom, as that is stronger in tension. So unless you change the wires for longer, that fixes the mast step and shroud plates position.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Swinging centreboard design suggestions for a scaled up 12' 4" mirror dinghy.

    I would temporarily clamp a leeboard to the rail to find the balance , and then place/size the centre case & board accordingly.

    Fit CB case up to that first open bulkhead like you said Nick.. mast and shrouds as before.


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