Colvin Gazelle

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  • 19 Nov 2018 01:08
    Reply # 6913264 on 6879165

    David Tyler makes a very good point about available sections for mast yard etc. The hurricane rated flag poles seem like a very appropriate solution for the masts and most aluminium sections come in 5 or 6 meter lengths so anything over that require splicing or wooden extensions socketed into the aluminium.

    On Arcadian we had a 700 sq ft main and a 500 sq ft foresail. Most of the troubles came from the mainsail with numerous broken battens, it was also hard work getting the sail up, even with an electric winch and four part halyard.  For this reason I would tend to recommend a ketch rig with a mainsail of 450 to 500 sq ft and a mizzen of 300 to 350 sq ft. This would move the center of effort of the sailplan slightly forward from David Tyler's plan but leaving the mast positions as he suggests. It would mean a mainsail with a higher aspect ratio but still achievable.

    All the best with the project, David Webb.

  • 18 Nov 2018 22:18
    Reply # 6913156 on 6912836
    Anonymous wrote:

    Max, the Gazelle is a good sailing boat as is, but lacks the drive upwind to push through any appreciable sea state. Tweaking the sail design to get more power close hauled would do wonders for performance offshore. Sailing this boat is all about balance, with two mast it's quite easy to keep her dialed in. One can even get half a panel reefing using the lazy jacks pick up (or not) the outboard end of the sail. My complaint against the jib is having to go out on the sprit to furl it in heavy weather. 

    Arne,  the jib is essential for balance. Could it be replaced by a raked forward junk sail in the bow? I don't know how to figure if it would get that sail far enough forward to balance.


    Thanks for all these responses, Dave, David and Arne.

    I'm not allergic to a jib, especially if it can be rigged in such a way as to not require a trip to the bowsprit, using a block at the end of the bowsprit, or a roller-furler.

    Seems like there's no way to spread as much sail area as low-down without using the jib.

    It might ultimately be a good idea to make radical changes to the rig, but one might first try using cambered sails of roughly the same area as the original rig, on the original masts, with the jib.

    I rather enjoyed sewing up sails for my first Gazelle, even if I never got to use them, so I wouldn't mind sewing up a more conservative rig experiment before moving on to major surgery. If I can reuse some of the battens and change none of the standing rigging, even better.

    Last modified: 18 Nov 2018 22:34 | Anonymous member
  • 18 Nov 2018 20:27
    Reply # 6912991 on 6912984
    Anonymous member (Administrator)

    David wrote:


    Practicalities matter. Where is one going to get hold of a mast to hang your 71.8 sqm sail on. Where, in N America, is such a mast to be found?

    That sounds as the biggest challenge, and that's why I have suggested the 61.5sqm alternative, or something in between.

    However, there are other materials, Oregon Pine, for instance. Both Samson in Stavanger, and Peregrine in Greifswald, Germany have been rigged with wooden masts.

    Arne

    PS: Come to think of it. I struggle with believing that there are not 6m sections available of sufficient diameter in the US. One can of course build a mast from 2-3 sections, as others  (Jami Jokinen for instance) have done.

    Last modified: 18 Nov 2018 20:56 | Anonymous member (Administrator)
  • 18 Nov 2018 20:13
    Reply # 6912984 on 6912910
    Arne wrote:
    David wrote:

    Arne,

    I know that a 10in dia mast will carry a 55 sqm sail, because I've been there and done that. I don't know whether it will carry a 71.8 sqm sail from personal experience, so I don't feel it wise for me to recommend doing that, and I would have my doubts about it. These flagpoles go down to a diameter at the top that I consider too small for a mast, and the top few metres need to be trimmed off. So a 50ft flagpole gives you a 44ft mast at best.


    Sorry, mate, but you have been there and done that in a lighter boat than the Gazelle. It is not the sail area which breaks masts, but mainly the righting moment (plus pitching) of the vessel. The Gazelle, being about twice the displacement of Tystie, will probably put a lot more strain on the mast even when the sail area is the same. This is because the Gazelle would stand up to the sail longer than the smaller vessel.

    A

    Colvin's original Gazelle: 18000 lbs, 8.2 tonnes, about the same as Tystie.
    Later builds: 24000 lbs, 10.1 tonnes, a little more, but not twice the displacement.
    Both light draught chine hulls, so not too dissimilar. 

    Practicalities matter. Where is one going to get hold of a mast to hang your 71.8 sqm sail on. Where, in N America, is such a mast to be found?

  • 18 Nov 2018 19:05
    Reply # 6912910 on 6912730
    Anonymous member (Administrator)
    Anonymous wrote:

    Arne,

    I know that a 10in dia mast will carry a 55 sqm sail, because I've been there and done that. I don't know whether it will carry a 71.8 sqm sail from personal experience, so I don't feel it wise for me to recommend doing that, and I would have my doubts about it. These flagpoles go down to a diameter at the top that I consider too small for a mast, and the top few metres need to be trimmed off. So a 50ft flagpole gives you a 44ft mast at best.


    Sorry, mate, but you have been there and done that in a lighter boat than the Gazelle. It is not the sail area which breaks masts, but mainly the righting moment (plus pitching) of the vessel. The Gazelle, being about twice the displacement of Tystie, will probably put a lot more strain on the mast even when the sail area is the same. This is because the Gazelle would stand up to the sail longer than the smaller vessel.

    A

    Last modified: 18 Nov 2018 19:06 | Anonymous member (Administrator)
  • 18 Nov 2018 18:39
    Reply # 6912860 on 6879165
    Anonymous member (Administrator)

    In case reports arrives telling that the Gazelle is tender, here I have reefed away one panel of the same sail. This also lets me shorten the main mast to 12.2m  -  about 1' lower than the main of the Colvin rig. Any mainsail between the big AR=1.90 and the short AR=1.68 can be fitted, so it depends where you are to sail.

    Dave, as long as one brings the CE forward of the Colvin schooner's total CE, I see no reason why a jib should be needed. The mainsail alone will probably give the Gazelle a lee helm until the mizzen is sheeted in. That is the wonderful thing with the yawl: The mainsail is the main engine, while the mizzen is trimmed so the rudder stays close to neutral. The little mizzen thus contributes to the speed as well.

    Now, I am sure David Tyler's rig can be made to work. I am equally sure that the yawls I have drawn can be made to work, so in the end it is more a question of what you prefer. 

    Anyway, good luck!
    Arne



    Last modified: 18 Nov 2018 18:55 | Anonymous member (Administrator)
  • 18 Nov 2018 17:59
    Reply # 6912836 on 6879165

    Max, the Gazelle is a good sailing boat as is, but lacks the drive upwind to push through any appreciable sea state. Tweaking the sail design to get more power close hauled would do wonders for performance offshore. Sailing this boat is all about balance, with two mast it's quite easy to keep her dialed in. One can even get half a panel reefing using the lazy jacks pick up (or not) the outboard end of the sail. My complaint against the jib is having to go out on the sprit to furl it in heavy weather. 

    Arne,  the jib is essential for balance. Could it be replaced by a raked forward junk sail in the bow? I don't know how to figure if it would get that sail far enough forward to balance.

    The mainsail on this boat is a workout to hoist with a four part tackle!  I added rubber hose to the parrels to prevent chafe last year and that has made getting the last two panels up quite difficult with wind in the sail. I can't imagine pulling up a sail twice this size without winches.

    Attached is a drawing from David Chidell of their modification to Tin Hau. This is what I am considering doing to ease the sail handling problems. My concern is that it doesn't look possible to use a four part tackle on it and it may be too hard to sheet in the main in a good breeze.  With a four part going to the euphroe it can take a pretty good pull when the wind is more than 20 knots the way it is rigged now.

    I have seen a picture of a Gazelle ketch rigged, both mast were placed further aft than with the traditional schooner rig.

    Dave

    Last modified: 18 Nov 2018 18:08 | Anonymous member
  • 18 Nov 2018 17:21
    Reply # 6912782 on 6879165

    Arne, when I looked for one of these mast tubes, the last time this subject came up, the wall was 5/16in.

    You're right, Maxime, I'd hesitate to put Arne's tall rig onto this shoal draught boat. The after mast for my rig, though, is the same height as the main mast of the original rig.

    I put the foremast a foot further forward to give more room for the sheeting. I guessed that the engine would dictate the position of the after mast, and left it where it was.

    You could indeed keep the stayed masts, but we who have enjoyed secure and chafe-free unstayed masts would consider it second best. The main mast might be OK for my after sail, leaving the foremast to be bought new and a new step arranged for it. I guess that a triatic stay and forestay would still be needed, so a stayed foremast would have to be higher than an unstayed mast.

  • 18 Nov 2018 16:57
    Reply # 6912759 on 6879165

    Wouldn't those sail plans considerably raise the CE? The Gazelle is quite shoal. I don't know if it can stand up to a tall sail plan.

    Regarding the mast placement, it would be possible to move the foremast placement forward as it falls in a v-berth, but not backward into the cabintop. The cabintop on a Gazelle is plywood, not steel. The aft mast would be possible, but difficult, to move backward, because just aft of its current placement is the engine. So you'd have to build some sort of step bridging the engine (?). Doesn't sound great for engine maintenance, ease of installation, or mast bury (but what do I know?). If you go further aft than the length of an engine it becomes possible again, by building a step that bridges the shaft.

    What could be done with the current masts, keeping the stays and the jib? Or at least with the current mast placements, and keeping the stays and jib? Could you gain a lot by simply changing the sail shape and sheeting method, and adding camber?

    Max

  • 18 Nov 2018 16:49
    Reply # 6912756 on 6879165
    Anonymous member (Administrator)

    The strength of the available mast sections could be a limiting factor. Now I tried a 10" tube with 1/4" wall, and ended up on the weak side with a guessed yield strength of 200MPa. If 3/8" or 10mm wall thickness had been available, I would have felt better.

    Arne

    Last modified: 18 Nov 2018 16:52 | Anonymous member (Administrator)
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