Home Frequently Asked Race Recaps Videos Specs Repairs Jn18 Group

Johnson 18 Repairs and Maintenance

Jn18 Repairs

A dingey sportboat sailing community

Some repairs are straight forward, others are a little more tricky. We've seen or heard about most things you'll want to fix, so read on to benefit from those who have gone before.
Please visit the Johnson 18 One Design if there's a topic we haven't covered or if you need more information on something we have.


Sails wear out. It's a fact of life. You can patch them, repair them, or replace them.

  • Patch
    • Main: You may want some spreader patches for the main depending on how you trim downwind.
    • Jib:
    • Spinnaker: Mostly for accidents launching or dousing the spinnaker. Sail tape does the job.
  • Repair - No advice; in my experience sewing sails back together yourself is not a multi-outingsolution.


  • Mast
    • Spar
      • New spars are tough to get your hands on, a new extrusion is pricey.
      • Best bet is to repair the one you've got. Atlantic Spars in Annapolis has straightened a bent mast.
    • Bottom Bracket
    • Spreaders
      • Spreader Tips/Angle
      • Spreaders can corrode from normal wear or flex because of abnormal use
      • can have them duplicated whenreplacingthe shrouds

  • Forestay
    • Keep the wire from your old jib to use as a forestay if you store your boat with the mast up!
    • Furler Drum

  • Shrouds
    • Uppers
    • Lowers
    • Triangle Bungee
      • An optional section of bungee cordtied across the shrouds at the top of the lower shrouds will help with spinnaker launches. The spinnaker head has a tendency to wedge between the shrouds and mast if the hoist is faster than the tack line in. This can damage the kite, put it in the water (going shrimping!), and just isn't fast. The bungee should keep most launches from getting jammed; it can still need help but won't be nearly as hard to get loose.
      • Bungee shown in green on lowers shown in red

  • Boom
    • "We just broke one of our boats' boom during a capsize. It clearly broke directly over the rivet holes for one of the mainsheet blocks. Other than that the boom is in good condition."

    • I knew someone who repaired a break like that one with a wooden plug inside theboom. But it wasn't pretty (or lightweight)! For a replacement extrusion, you might try asking Jason Brown at White Bear Boatworks about what size you'd need.
    • The boom failed there because that is (other than the gooseneck) the most loaded point (especially being mid-boom sheeted). There have been some dynamics involved where the boom was in compression with a solid object at that same moment, I don't know if that occurred or not, but it is no surprise that is where it failed. A repair, unless sleeve inside the extrusion will not be a safe repair.
    • I would buy a new boom section and move all the hardware. I'd start by checking the dimensions of your existing boom and then I would check the website for Dwyer Mast. Seems to me the have a similar or exact section

  • Outhaul
    • I broke the outhaul on Wednesday night. Not too bad considering the line is original from 1995.
      I tried to tug it tighter, since the foot was flogging a bit and just snapped it outside the boom luckily.
      I took the boom off and tried to figure how to run it since I didn't know what purchase was inside.
      ~5^3 skipper

    • Supplies:
      1. A replacement bolt for the mast end plug, since the bolt was fairly corroded.
      2. A new 4mm replacement outhaul line (15 feet) out of the sale bucket at APS ( I think it may be 5mm line, but 4 will work fine and holds in the cleat without issue)
      3. A feeder/messenger line ( I had 18 feet which was plenty- by about 5 feet or so)
    • Tape the feeder line to the bitter end so you can ease enough to put the floating block out the end of the boom. This allows you to tie the new outhaul line on.
    • You don't need to remove the mast end toggle to replace the outhaul line (that the pin fits through to attach it to the mast),
      but if you do you can inspect where the outhaul runs when it goes into the boom. Get that bolt out without drilling after some WD-40 and pounding it backwards with a smaller bolt:
    • The second photo shows the fixed block bolted/screwed inside the boom where the outhaul line turns at the mast end (blurry edges are the outside of the plug still in the boom with the toggle removed.)
    • Tape the new line to the broken outhaul line with electrical tape and ease it through by pulling out the sail/clue end cable that lays inside the boom until you get the moving block out the stern end of the boom.
    • This is what the assembly looks like (with cable crimped after it was threaded through the sheave; so if you want to replace the cable you'll need to be able to crimp it AFTER you run it through the sheave):
    • So as you can see the old line is white and the new blue line has run through this block.
    • To to have enough line to get to the butt end of the blue line you had to keep pulling, so tape a red messenger line to the other end of the new blue outhaul line:
    • Untape and tie the new outhaul line to the block, then just put the block back into the boom and pull it all back snug being careful to not unstick/separate the messenger from the new line until it's back out of the pinch cleat near the mast end of the boom... easy!

  • Spinnaker Pole
    • Yes, the carbon pole can break!
    • Years of stress add up, unfortunately this is a part that doesn't lend itself to being repaired very well and probably will need to be replaced. We've had good results with Forte Carbon in CT building a custom pole using the existing fittings.
    • BIG note on replacing this is the POLE OUT LINE! DO NOT let it retract into the tube as you remove the pole! Tape an extension line onto it that will run through the blocks. Here's some advice if it gets away from you: Bow Sprit Launching Line Question
      • Forte carbon (in Connecticut) built me a pole using my then existing fittings (same tack cap and blocks in the butt end). (in November 2008) here's my post from 2010 about logistics of replacing it...big issue is the extension line... you need to make sure to tape a long extension on the tail end before you pull the pole out!

      • "New pole is in! Ordered it from Offshore Spars, they have a really cool production process, they hand lay pre-preg Carbon, vacuum bag it, then heat cure it in a pressurized oven. Should hold up well!"

  • Blocks & Cleats
    • Backing washers
      • It seems some bolts and washers on some Johnson 18's aren't stainless. We have yet to devise a pattern on where they are used.
      • I recently added a swivel extension for the main sheet. When I went to remove the screws of the aft-most main block on the spine, they were frozen to what I assume is an embedded aluminum plate as there were no nuts. 3 out of four broke on attempting to gently remove them. I took a while to get them off and the holes cleared. I wound up through-bolting them while worrying about centerboard clearance. I think it worked out in the end but I had about for hours into that (4 screws). I removed the two main sheet cam-cleats on the tanks only to find completely rusted out backing washers that crumbled when turning the screws. My pole and tack cam-cleats were pretty beat,with a broken spring in one, and would re-engage in the douse. I took these off for service and they too were backed with crumbling steel washers. As I look over the boat, most of the hardware shows signs of rust at the fasteners.
      • I just found a rusted nut inside the mast on #181, built by JBW. It was on the back of the vang turning block, and it was regular steel. The other nut was stainless, so it looks like it was just a mistake. I haven't seen any rusted hardware on my boat, #132. But I have found a lot of galvanic corrosion in the backing plates like you did. It looks like JBW used thick aluminum plates glassed into the deck during layup. They were drilled and tapped for stainless bolts, which now have completely galled threads on my boat after 22 years. I broke off several . bolts while removing the spin halyard cleat and the spin pole tube flange. I drilled out the bolts and re-tapped the holes, but what a PAIN! I broke 6 drill bits on 5 bolts...
    • Rudder
    • Tiller Extension
    • Centerboard
    • Hiking Straps
    • Spinnaker Bag
      • The blocks are attached to the bolts in the hull with small eyestraps - something like this: APS item: RWO R2849

Running Rigging

We're talking lines and whatnot, head up to hardware for advice on standing rigging.

  • General Rigging Instructions
  • Main Halyard

  • Spinnaker Halyard

  • Centerboard

  • Pole lines

  • Jib furler line
    • Probably the easiest is to use about 12 feet of wire (like bailing wire), stiff enough to be able to push it. Run it through the bow well to the stern, taping the new line (about 18' is about right for the line length- get a couple more feet to be safe- or more if you've got it run farther aft) to the end of the wire, when you can get a hold of the wire, gently pull the whole thing through from the cockpit until you get your line.

  • Vang

  • Cunningham

Hull Damage

  • Bow Eye

  • Topsides

  • Cockpit

  • Bottom


  • Spinnaker Pole Tube
    • If you've got a substantial amount of water in your hull after sailing in waves, chances are good that the bow end connection to your spinnaker pole tube is loose. Water should be pouring out the diamond into the cockpit when water enters the tube, but if the tube slides backward it goes straight below decks instead.

  • Centerboard Gap
    • The board is flanked by gaskets on either side that help to keep water out. Replacing them can help keep water away from the seam between upper and lower hull pieces.
    • Not entirely sure I bet it was like this: gasket-for-centerboard

  • Plugs
    • Sailing without your plugs in is slow and that's a fact.


  • Cover
    • Zipper
    • Bungees
    • Canvas
    • Clips

  • Trailer
    • Bunks
    • Tires
    • Hubs
    • Frame
    • Winch
    • Lights
    • Hitch
    • Dolly Wheel

  • Modifications
    • Trapeze
      • Although it is controversial in a one design class, almost every boat I know in the SF Bay Area has been converted to trapeze for the crew. We typically sail in 20-25 knots in the summer months and unless you have a couple of really weighty crew, you cannot possibly hold the boat down when going to windward in those conditions without a trapeze. With the trapeze the boat is really fun. For a couple of seasons I had a very athletic 220lb 6 ft crew and we had a blast on San Francisco Bay in summer afternoon conditions. We were able to hold the asymetric spinnaker on tight reaches and really fly, passing 49ers. Going downwind in waves the J18s full bow prevents it from nosediving and, as a result, you can go deeper than the skiffs in heavy breeze and big waves which is a big help in 30 knot puffs.
    • I-14 Mast
      • One friend, Mark Briner, has rigged an International 14 mast with a big roach and larger jib. The result is the boat planes far sooner but in 20-30 knots the roach falls away and reduces overpowering.
    • Kite launch tube