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Thread: Rig Conversion Advice for Gunter-rigged Boat

  1. #1
    Join Date
    Sep 2013
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    Default Rig Conversion Advice for Gunter-rigged Boat

    Hello,

    Please accept my apology in advance for this post, if too scandalous! When I signed up for an account, I was intending to build a stitch-and-glue kit. In the end, I bought a GRP open boat needing a little renovation. It's a "Tern II", as built in the UK by the Falmouth Packet Co, probably around 1994. Whilst GRP and not wood, I do "sense" this it to have a wooden boat mentality!

    I'm hoping to receive advice regarding the benefits and practicality of making a straightforward conversion to a balanced lug rig, without having to move the mast position. The reason for my query is that I am lucky enough to be able to moor the boat immediately in front of our house, in The Netherlands. There are low bridges to escape from the town, but a nice area for sailing a few miles away. The current rig has wire stays with turnbuckles. My thought behind having a balanced lug rig is to have an unstayed mast and quicker set for when only able to sail for a few hours, especially if single-handed - I would motor out of town and then moor up to step the mast. I shall insert some links to an illustration and photos to demonstrate the sail plan and mast step.



    https://lh3.googleusercontent.com/-s...h640-p-rw/Tern
    %2BII%2Bside%2Bview%2Billustration.jpg

    Looking forward to some helpful advice, even if the result should be that I should make no changes!

    Thanks and regards, Adrian.
    Attached Images Attached Images
    Last edited by adrianr; 05-16-2017 at 04:24 AM. Reason: URL to external image

  2. #2
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    Sep 2013
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    7

    Default Re: Rig Conversion Advice for Gunter-rigged Boat

    Interior view.



    https://lh3.googleusercontent.com/-t...%2Binboard.jpg

    Other photos, of my boat:-



    https://lh3.googleusercontent.com/-_...44721large.jpg



    https://lh3.googleusercontent.com/-Z...w/P1070381.jpg



    https://lh3.googleusercontent.com/-w...w/IMG_0024.JPG

    The boat has the following details:-

    LOA 18ft 5in
    LWL 15ft 1in
    Beam 6ft 5in
    Draft 1ft 4in
    Sail area 110 sq ft
    Disp 1100 lb
    Ballast 285 lb
    Attached Images Attached Images
    Last edited by adrianr; 05-16-2017 at 04:26 AM. Reason: Replaced micro photos with URLs

  3. #3
    Join Date
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    Walney, near Cumbria UK
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    Default Re: Rig Conversion Advice for Gunter-rigged Boat

    Hi, welcome to the forum.
    Read the FAQ page about posting images, this is the relevant bit, and will show you how to post legible images.:
    POSTING PICTURES
    Control yourself. Avoid posting BIG pictures. Keep them 500 pixels wide OR LESS. That way the dial-up folks aren't bogged-down, and the width doesn't make the page hard to read in a standard sized window. If you don't have Photoshop, try the freebie from gimp.org. We do NOT host your images. You need to have a place like Flickr, Imagestation, Photobucket, DropBox, or one of the free other hosting outfits... or your own site. Per Thorne's 'How-to', here's how to post photos on this forum:



    ...FIRST - Don't attach photos. Only a tiny version will display.
    ...SECOND - Post the photos on the web. Use your own website or a free image hosting service like www.flickr.com, picasaweb.google.com, picturetrail, photobucket, etc. Images posted on Facebook must be set to "Public" access via the Edit option, not limited to "Friends".

    ...THIRD - Once posted on the web, right-click the photo to "Copy Image Location", or drag the photo to another browser window, then copy the image URL (web address) which will end in ".jpg". You can test by pasting the photo URL into the location field (http://* ) of a web browser and see if the photo displays. Remember that this process will not work for photos located just on your computer, on members-only Yahoo groups, or on Facebook unless set to "Public" view. (In Flickr - You usually have to first click the photo to bring up the black-framed viewer, then click the "View All Sizes" link near the top right. Then you can get the image URL by right-clicking the image. Alternately you can go to the Actions menu on the upper left, then select "View All Sizes".

    ...FOURTH - DO THIS EVERY TIME TO POST IMAGES IN THREADS: A. In any "Reply" window you can click the "insert image" icon --> a little yellow square icon with a dot at each corner, a tiny tree in the center. Depending on browser version and Reply/Edit status, this may bring up a simple window with a field to paste the URL into, or the "Add an Image" window described below.
    B. If the window titled "Add an Image" comes up, click the "From URL" tab, paste the URL of the photo in the field, deselect the box for "Retrieve remote file and reference locally", then click the "INSERT IMAGE" button. The Forum software will resize some large images, so look at your post to see the actual displayed images.


    You can change the rig and keep the mast in the same place, probably.
    First off, calculate the centre of effort of the existing rig.

    The CoE of each triangle is where the lines from the mid length of an edge to the opposite corner cross. It will also be 1/3 of the way along the line, by way of double checking. Then join the two centres with a line and work out the two areas. the total CoE will lie along that line in proportion to the areas at a distance closest to the biggest sail.

    Then design your new sail so that its CoE lands in the same place along the waterline.
    For the new sail, divide it up into two triangles and use the same method
    It really is quite difficult to build an ugly wooden boat.

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  4. #4
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    Default Re: Rig Conversion Advice for Gunter-rigged Boat

    Excellent and quick response, thanks, Nick. I shall upload the photos elsewhere, later, and re-edit.

  5. #5
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    Hyannis, MA, USA
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    Default Re: Rig Conversion Advice for Gunter-rigged Boat

    The other thing, which the one photo makes obvious, is that you will need to get very very serious about the mast partners and perhaps beef up the step as well. It might be possible to simply improve the partners with a wider and thicker plank and some knees at each end to spread the stress better. The other alternative is to bring the foredeck right back and build the partners into that structure.

    The hole in the partners looks suitable for an aluminum mast held up by stays. An unstayed mast would be larger.

    You'll want to get the books out and engineer this correctly.

  6. #6
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    Default Re: Rig Conversion Advice for Gunter-rigged Boat

    Morning all, I have edited the two original posts with links to third-party image hosting sites. The photos are now larger and there are a couple of additional ones.

    Over the weekend I'll measure the sails to be able to calculate the CoE for the existing rig as per Nick's very helpful and clear instructions.

    Regarding Ian's very sensible suggestion to properly engineer an alternative solution, I sadly do not have the skills and knowledge to do so - left to me it'd only be a home-improvement DIY approach of what I vaguely judge to be adequate! I'd be interested in offers to then make a PayPal payment to someone who can do that mathematically. Alternatively, I do have a relative who is an experienced offshore structural engineer, who may well have the required competency - I know he has completed some design work for lifeboats.

    I'd appreciate any advice with reference to the suitability and pros/cons for such a modification to my boat:-)

  7. #7
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    Default Re: Rig Conversion Advice for Gunter-rigged Boat

    Quote Originally Posted by adrianr View Post
    Morning all, I have edited the two original posts with links to third-party image hosting sites. The photos are now larger and there are a couple of additional ones.

    Over the weekend I'll measure the sails to be able to calculate the CoE for the existing rig as per Nick's very helpful and clear instructions.

    Regarding Ian's very sensible suggestion to properly engineer an alternative solution, I sadly do not have the skills and knowledge to do so - left to me it'd only be a home-improvement DIY approach of what I vaguely judge to be adequate! I'd be interested in offers to then make a PayPal payment to someone who can do that mathematically. Alternatively, I do have a relative who is an experienced offshore structural engineer, who may well have the required competency - I know he has completed some design work for lifeboats.

    I'd appreciate any advice with reference to the suitability and pros/cons for such a modification to my boat:-)
    You are fortunate. I think that the thwart is simply screwed down to that riser. So you can take it out, make a thicker one, and refit it further forward or aft to help balance the new rig. Reinforce the mast hole with some cleats run forward or aft under the thwart, or make a mast gate like this

    is not too difficult.
    Then you need to tie it into the structure with some standing knees.
    You could saw them out of solid stock, being careful to avoid short grain.

    Or you could get a local fab shop bend some up out or stainless pipe, and flatten and drill the ends to screw to the thwart and coaming
    like these steam bent ones

    but in pipe.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
    The weakness of the web: Anyone can post anything on the web.

  8. #8
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    Default Re: Rig Conversion Advice for Gunter-rigged Boat

    Thanks again, Nick. You are correct, it is screwed in. With your suggested technical approach the modifications are definitely do-able for me. I just need to decide if the end result (i.e. sailing manner) will be good in return for valuable physical benefits of quick and single-handed stepping..!

  9. #9
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    Default Re: Rig Conversion Advice for Gunter-rigged Boat

    Hello forum, putting aside the technical tasks and requirements for this proposed modification, I am still hoping for some advice regarding the pros and cons, and general suitability for my boat, of the change. I do expect that I would achieve the practicalities I'm looking for, for my situation, but how well is it likely to sail? Should I consider a different rig? Thanks in advance...

  10. #10
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    Default Re: Rig Conversion Advice for Gunter-rigged Boat

    Quote Originally Posted by adrianr View Post
    Hello forum, putting aside the technical tasks and requirements for this proposed modification, I am still hoping for some advice regarding the pros and cons, and general suitability for my boat, of the change. I do expect that I would achieve the practicalities I'm looking for, for my situation, but how well is it likely to sail? Should I consider a different rig? Thanks in advance...
    She will sail as well on a reach and running, but less well hard on the wind.

    You can probably arrange to step your existing mast quickly by changing the mast thwart to one with a mast gate, like the one in Peerie Maa (post #7), fitting quick release mechanisms to the shrouds,

    and some mechanism for tensioning the forestay, a small block and tackle on a carabina perhaps.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
    The weakness of the web: Anyone can post anything on the web.

  11. #11
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    Default Re: Rig Conversion Advice for Gunter-rigged Boat

    Very helpful once again, Nick - thanks! I did have that idea in mind as a back-up option in case there should be no choice but to retain the gunter rig, but I'd been expecting to need some expensive-looking Seasure forestay levers or similar, so good to know something simpler could suffice.

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