Moving boom blocks

Discussion in 'Sunfish Talk' started by fbjru, May 8, 2010.

  1. fbjru

    fbjru Member

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    My Racelite boom blocks have seen better days and need replacement. One of them has developed a flat spot even though it spins fine.

    Anyway since i am going to have to pull rivets to replace the blocks, i may consider moving them.

    Two questions:
    I know that it is legal to move the boom blocks, and I have heard that some people move them. Has anyone found a location that is better? What are the benefits of this move?

    What type of blocks should i use in replacement?
     
  2. beldar boathead

    beldar boathead Well-Known Member

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    If you are going to race your boat the only legal blocks are racelites. I have no idea if moving the blocks helps with performance it seems unlikely. BB
     
  3. Wavedancer

    Wavedancer Upside down? Staff Member

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    Basically, I wouldn't put additional holes in the boom. As BB already wrote, any effect of changing the location would be minor, if not nil. And yes (I just checked the rules), if you want to be 'class legal', one has to use builder-supplied blocks. But I believe I once read that the various builders didn't all use the same blocks over time...

    Just My Humble Opinion, of course...
     
  4. fbjru

    fbjru Member

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    I have finally found two previous threads on this forum that discuss moving the blocks. These answer most of my questions

    http://www.sunfishforum.com/showthread.php?t=25973

    http://www.sunfishforum.com/showthread.php?t=25561

    The current location of mine (67", 126") differ very little from the recommended, so I probably wont be moving them. I may try to find a different strap to attach them though. My current strap is a very shallow U which causes the block to chafe and damage the boom. Newer booms have straps with a much deeper U, which solves this problem. The trick will be finding straps with holes that are the same distance apart as what I currently have. Also it is recommended to through bolt these instead of riveting. I may consider doing that.

    To my knowledge BB is right and the only blocks ever sold with the sunfish were racelites. There have been some differences though. It is recommended that swivel blocks are used rather than the type that do not swivel.
     
  5. NightSailor

    NightSailor Captain

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    I don't like the idea of through bolts, although it seems popular. They add weight and worse, a snag point on top of the boom.

    On one of my booms I have bails with two rivet/bolt holes on each side--four total. I would consider putting on bails with four rivets if you are concerned about these ripping out in a race. I've been looking for these for a while and have been unable to find any since my last purchase many years ago. They are out there. And it would be worth searching for them rather than using through-bolts.

    BTW, I've never had one of these single or double riveted bails pull out. However I do replace anything that looks corroded or weak with fresh rivets.
     
  6. fbjru

    fbjru Member

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    Im back and forth on this. Rivets that have failed are likely old and corroded. Though I'm not so concerned about the weight of through bolts, they do make a snag point, and another thing for the sail the get cut on. Also, how much do you think additional holes weaken the boom?

    Another idea that has just crossed my mind is using several very tight wraps of spectra as an attachment point. This would have the advantage of being easily moved to experiment with block location.

    Such a small easy job, but I have to make some decisions. Why is this bothering me so much?
     
  7. Wayne

    Wayne Member Emeritus

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    Fortunately you have much latitude while still conforming to the rules for Class event participation.
    ISCA CLASS RULES
    3.5.5 The boom block eye straps may be replaced with any type of straps.


    There are so may options it’ll make your head spin, just let your Google do the walking.



    I tend to side with not through-bolting. The practice was dropped at the manufacturing level long long. . . long ago.

    Why not just use Stainless Steel pop-rivets? I’ve been using them for over twenty years now and haven’t had one fail. (I do dry and seal my spars).

    My oldest rivet connections aren’t even silicone filmed to guard against dissimilar metals corrosion (think about all the SS fittings on all the boats, not just Sunfish, over the past half century) In salt water you may see a little. With gross neglect of rinsing, maybe significant, but with prudent care, hardly at all.


    Much higher probability than new rivets failing.



    That would be a good way to test locations, but I think BB is correct, you’ll find the blocks are already at a good all-around location.

    . . . and, heck, for test purposes with such short line length, you could tie up the blocks using my grandma’s old clothes line and if a good hitch is tied well they won’t wander. :rolleyes:

    .
     
  8. NightSailor

    NightSailor Captain

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    Here is an example of the four (4) rivet eye straps. Shaeffer makes them. I found the inner two rivet holes lined up exactly with the existing holes on my Sunfish Boom. I didn't think two more 1/8" holes would weaken the boom any, while doubling the fastners made me a bit more confident in heavy air.

    [​IMG]
     
  9. Zeppo

    Zeppo Member

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    Your idea of lashing the blocks on is a good one, it allows you to re-position the block and if replaced occasionally the lashings will not break. (The lashing of various blocks on all sizes of high performance keel boats is quite common). Regarding the position of the block, efficiency puts it as close to being directly above the mainsheet block as possible.
     
  10. fbjru

    fbjru Member

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    All done. I couldn't decide whether to through bolt or rivet, so i did neither. It sound's like science fiction, but it is possible to bolt through one side of the boom, leaving the nut inside.

    I used the method cgates used in the thread below:

    http://www.sunfishforum.com/showthread.php?t=27290

    I am still baffled by the string method that is used with the kit aps sells. I have worked that one out in my head, and still have no idea how that works. If anyone does know, please share.
     
  11. fbjru

    fbjru Member

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    So I thought I would add a little update to this topic.

    Like I said, i reattached my boom blocks and am quite happy, but I had another problem arise.

    The rivets failed and pulled out on my practice set of spars. Luckily, it was the rear block, and it turns out you can sail in using your main sheet hanger as a block to limp home.

    The problem was more of a mast corrosion problem than a rivet problem. So now the holes where a bit big and nasty. I devised a new way to mount blocks (or cleats for that matter) that works very well and makes for a strong connection.

    Pictures would make this easier, but use your imagination. Cut out a rectangular piece of aluminum flashing or similar material as sort of a backing plate. Bend the piece against the spar to round it. Now drill two holes in it and attach the strap with screws washers and nuts to the flashing as if it where the boom. Now the fun part. Get a $5 tube of kneed-able epoxy (think Billy Maze and Mighty Putty). Cut off a piece, kneed it, and spread a one thick amount on the back of the flashing surrounding the two nuts. Once the putty dries the screws can be backed out leaving a perfect backing. The putty is not structural, it just acts as a "wrench" to hold the nuts tight. Now, open up your spar, get a long stick, tape the backing to the stick, shove it down the spar, line up the holes and screw on the strap. It's very strong because its backed with washers and if ever you want to get it off it's an easy unscrew.

    FYI

    Don't buy the kid aps sells. I learned the secret and am not impressed. I stumbled across directions at my club. It says, in my words to:

    feed string down into the hole and out the end up the mast
    tape the string to the end screws with scotch tape
    pull the string back through spar so the head is inside
    thread the washers and nuts on the bolts
    hold the free end of the bolt with vice grips and tighten the nut with a wrench
    use a saw to cut the end of the bolt off when done
     
  12. rmwmmw

    rmwmmw New Member

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    All this discussion has caught me in the middle of checking out my boat for the NA's. Good review for me of the what's, why's and how's of my boat's setup.

    I had previously bolted the boom bails (only thru the bottom side of the tube, not the top). After thinking about it a little more, I decided to reverse the situation. I use padeyes on top of the boom and suspend the boom blocks from there. .

    a. The padeyes are small, lightweight, low profile (doesn't interfere with the sail), take very little stress, and install with aluminum rivets and 5200.
    b. I use an upper spar in place of the lower, so there are NO holes in bottom of my boom (where the greatest tension stress is located). I certaily don't worry about padeyes pulling out. The stress is taken up by the entire boom section. I'm good as long as I inspect and replace the lines when needed. Three years now, lots of use and no line wear.
    c. The boom blocks do not apply torsion stress the to tube at all, such as when reaching or downwind.

    As to location: Yes, the aft block location DOES make a difference. The effect is similar to a Jens rig, only for the lower aft portion of the sail vice the upper half. I tried the aft boom block much farther forward - about a whole "segment" - forward of the next sail tie. This was about 117".

    a. The lower aft portion of the sail "breathed" a little better in blow. The boom (from the boom bail to the aft tip) flexes a little more to leeward in the puffs. Goodness knows, the lower leach of the sail hooks around to weather badly enough.
    b. The main flattens out just a little more effectively when the mainsheet is cranked in.

    I found this to be a little TOO effective, so I moved the location back some. At 200#, I need all the power I can get. The bail is located in the middle, between sail tie locations with the outhaul at it's fully eased setting. This is about 123".

    a. It allows the lower part of the sail the breath a little better than the stock location.
    b. It never snags a sail tie with the outhaul in any postion.
    c. Not as effective as the 117" position, but a fair compromise.
    d. Requires a few less feet of mainsheet length (unimportant).

    The forward boom block is too far aft on the stock boat. I sail most frequently with the gooseneck at 14 to 16". The fwd boom block location comes into play when you need to really crank the main in tight - almost touching the boom block to the ratchet block. This is where you don't want to see a strange or radical angle between the blocks. Usually this occurs under heavier wind conditions. My boom block is set at about 62", directly over the ratchet block with the gooseneck set at about 18" (see photo). I rarely set the gooseneck at 20" or more. Under these conditions, I don't find my self cranking in the main so much.

    When you link fwd boom block location with gooseneck setting, then everyone's optimum location might be different. I watched Nancy Heffernan (about 110#) at the International Masters get away with a main fully cranked in under winds of about 8 to 10 mph. No way I can do that.

    Bottom line: my blocks are located and attached to minimize axial and rotational forces on the boom at the gooseneck. Keep it simple and minimize chances for failure or undesired consequenced.
     

    Attached Files:

  13. fbjru

    fbjru Member

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    Rick, this idea makes so much sense. All round a good idea.

    Is it legal? You can use any kind of strap so i assume that it is.
     
  14. rmwmmw

    rmwmmw New Member

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    Legal? You bet. All my 'gadgets' have been thru the class measurer's grindstone.
     
  15. winever

    winever Member

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    Rick, thanks for taking time to write all this, BIG help for me. I too am pushing 200 lbs and need power. This is great info. I also am putting together another whole rig for the wife's boat, but want the rig to fit me too for recreational sailing. I was worried about moving the standard block location to a more forward position so I could sit farther forward and tack without ducking the mainsheet so much. Moving the boom block over the mainsheet block will fix this. Like I said BIG thanks. Winever.


     
  16. Wavedancer

    Wavedancer Upside down? Staff Member

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    Winever,
    :confused: If you want to sit further forward (basically a good idea), you will need to duck deeper (with gooseneck settings around 16") :confused:
     
  17. winever

    winever Member

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    WD, thanks for the info, this old body needs help ducking, LOL. BTW, when you say 16" on the gooseneck, are you talking from the tip, or just the aluminum section of the spar. Sorry to ask so bacis a question but I need to know. Thanks, Win ever.
     
  18. Wavedancer

    Wavedancer Upside down? Staff Member

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    Sunfish racers typically measure the distance on the spar itself, and don't include the plastic cap.
    For routine sailing, I have mine set at 16", and move it back to 18" or 20" when the wind pipes up to 15 or more. But I am a light weight (150 lbs), and since you are :) a bit heavier :) you should be able to keep the boat flat in higher winds even with the gooseneck at 16" or so. This assumes you can hike as necessary. I suggest you play with the gooseneck setting and see how it effects your sailing (pleasure). If you want to race, talk to your competitors about this issue as well, or just look at their setups.

    PS: All this info is in the Sunfish bible, and a lot more. If you are serious about racing, you will benefit a great deal from studying this compendium.
     
  19. Sunfish65

    Sunfish65 Member

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    Wondering if I could piggy back on this post. After hastily buying a 70's fish in great condition, I noticed that my lower boom, did not have any sort of blocks. There are single holes at each point drilled right through the boom to the other side. What sort of hardware set-up did the older fishes have? Anyone have a picture, so I can try to piece together some sort of hardware configuration?

    Sunfish65

    P.S. have removed and restored coaming (epoxy and spray paint - Krylon Fusion). Wetsanding the gelcoat with 2000 grit, right now.
     
  20. Wavedancer

    Wavedancer Upside down? Staff Member

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    Unfortunately, our class historian (Wayne) passed away last year, but to my knowledge the two (Racelite) blocks to lead the sheet forward have been on Sunfishes for a long long time.

    If, in fact, those are missing, you will need to re-install them, preferably using the empty spots. See NightSailor's earlier post in this thread for some guidance.

    Good luck!
     

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