Fixing A Broken Finn Boom -- Part Two

Having completed the internal joining of the two boom halves as shown in Part One,, or are wanting to reinforce a cracked boom, the next step is to add the outer join plates and installing the mainsheet boom hangers.

Scroll down to the bottom of the page to see how to fix a flogged out boom pin hole or corroded outhaul exit block mount.

broken boom repair

From 2mm wall thickness, 100x50mm, aluminium box section cut two 340mm long, 80mm high and 12mm wide L shaped cover plates. If an anodised finish is required, anodise prior to installation.

Mark out the centrelines of the boom hangers on the top of the boom.

Mark out the position of the outer join plates on the boom and prepare the surface of the boom and the inside of the cover plates, with a disc grinder to roughen the surface for the adhesive to bond to.

broken boom repair

As welding would alter the temper of the aluminium and make the boom softer, the inserts and boom sections are glued together using a two pack, Methacrylate type adhesive.

Available in handy 50ml dispensers and mixing nozzles, they are ideal for all manner of fixes, but beware they have a limited working time before they set, so line up, prepare and be ready before commencing gluing operations.

As no great clamping force is required, simply use insulation tape to hold the cover plates in place whilst the adhesive sets. Clean up excess adhesive with thinners before it gels.

broken boom repair

Outer cover plates installed. Sand with 320 grit paper (unless anodised) and polish with scotchbrite pad. If painting, apply two pack vinyl etch primer first after scotchbrite pad cleaning.

Measure up 40mm from the bottom of the cover plate and draw the rivet line for the boom hangers rivet holes. Boom hangers are Ronstan RF0463 units.

broken boom repair

Place the boom hangers on the intersection of the vertical boom hangers centreline (projected from the lines drawn on top of the boom earlier) and the drawn rivet line, drill 5mm holes through the boom hanger and the boom. Useful to open up the boom hangers a bit to make the job easier.

Use insulation tape to act as a corrosion preventing barrier between the aluminium cover plate and stainless steel boom hangers. Pop rivet boom hangers on using monel rivets, then trim insulation tape corrosion barrier.

broken boom repair

With judicial use of a hammer, work the boom hangers into the correct position to the drawn rivet lines on the opposite side of the boom.

Drill boom hangers and boom. Place a layer of insulation tape under the boom hangers and pop rivet on. Trim the insulation tape corrosion barrier.

Dress the boom and go sailing.

If the boom pin hole is flogged out (or as in my case drilled out to take a 20mm pin) and or the outhaul exit block hole corroded beyond redemption, simply replace the channel support bracket inside the boom with a acetal or nylon plastic insert.

Bolt through the two pop rivet holes and for extra strength drill and tap from the top after cutting away the outhaul exit block rubbish.

Drill and tap for the outhaul block saddle on the bottom plus the kicker block bracket on the front (make sure the mounting clears the aft mast face).

Offset the mountings so the ropes don't chafe

For extra strength added two 2.5mm plates inside the boom that stretch past the kicker lever mounting holes to stiffen the boom.

broken boom repair broken boom repair broken boom repair
broken boom repair

If the boom outer end is like a piece of Swiss Cheese, fit an outboard end extension sheave box. Designed to lessen the angle the outhaul enters the boom when the sail is at the boom outer distance mark. Suit all Finn booms (NeedleSpar, Holts, etc.)

Replacement for any existing boom outboard sheave fitting, either on new booms or old.

View V-Tech_352 -- Finn Boom Outboard End Extension information.

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