New boom blocks

Thread starter #1
So I purchased a 94 laser in overall great condition and I’m upgrade to new harken blocks on the boom. I drilled them out per directions and noticed that one on the holes looked over size (see photo). I’m planning on cleaning up around the holes but should I just oversize the rivet or relocate the eyestrap over a 1/2” and drill new holes.


Active Member
There's enuf corrosion in both of those holes that I'd look for a way to mount the block in new holes, to guard against the possibility of the rivets tearing out. You could flip the boom end-to-end, roll it 180 degrees, or moving the block a short distance.

I'll leave it to others, to comment on whether moving the block complies with or violates class rules for racing.


Active Member
Throw it away. A newer and better (used) boom won't cost an arm and a leg. But have a close look at the other rivets like the ones in the lower mast where you attach the vang.

When you use rivets, don't be tempted to use the 'normal' ones from your builders' shop. Go out a search for rivets made from the material Monel

Why Monel?
Thread starter #6
A 1994 boom should already have the sleeve, but of course that boom could be much older than the hull (the amount of corrosion would indicate that, too).
Is that the aft or forward block position in the picture?

It’s the forward block.
If this was my boat, I would:

- NOT relocate the holes
- NOT flip the boom
- both of the above can lead to you snapping a boom, which is not fun. I sail my boat quite hard and have broken enough laser masts and booms to not want to do such things again.

- What I would do is, seeing as the end plug has been removed, reinforce the existing holes with one of two things: nice big stainless steel washers (shaped to match the curve of the boom, with lots of anti-corrosion paste) OR insert a short semi-circular aluminum sleeve.
-- Use stainless steel rivets, not aluminum ones (alu ones wear then break quite quickly. Your fitting will become loose and eventually snap off).
-- oversize the larger hole if you want to, or add an external washer there (why not? I don't think anyone will call you out on class rules for that).

Both of these solutions work great. It takes some patience to align everything, but the end result is a boom that's 'as good as new' (structurally anyways). And seeing as it's reinforced from inside, it looks clean and class legal.

The last option is to take a bent/broken top section and sacrifice it to make an entirely new boom.

PS: I just got a new boom with the ball-bearing blocks and they are awesome!!! Useless without the traveler blocks to match them though. I use a thick mainsheet and it runs super-smoothly through the boom blocks, and hits resistance at the traveler. It's annoying in light wind, but no problem when it's blowing. I have a set of traveler blocks on it's way to me now though so happy days.

Send us pictures of your progress and end results!
I know it's tricky, but I would think about through bolting with washers and a good bit of anti galvanic gunk stuff. Cheaper than a new boom.

Steve and Alex


Well-Known Member
The sleeve seems to only fit the first 1/3 of the boom.
Ok, so like myself, you have the short (65 cm) sleeve. The longer 90 cm version, which extends aft of the forward sheet block position was introduced around 1997. Like Emilio just said, just changing to that should be enough for a safe reinstallment of the sheet block in the original place. It would be a lot of work, but less than drilling out every fitting and refitting them all on a flipped boom or a topmast, which have been suggested by some.

That said, I would probably just drill new holes. There is a tolerance of 12 mm for the fitting in question - see the measurement diagram (click the "Mast Top Section, Boom and Foils" tab). I think the original position is in the middle of the range but you'd have to measure it. If the boom then breaks, it would have done so anyway, and regardless of the type of fastenings. And then you buy a new boom (which you of course might do anyway) :rolleyes:



Former ISAF Laser Measurer
Whilst this might change with the introduction of carbon top sections.

My recommendation is never to purchase a boom section, but replace your existing top section which is also probably suffering from corrosion and convert your existing top section into a new boom. That way you effectively end up with two new sections at the cost of one top new top section. The only pieces of the boom I replace is the gooseneck plug and maybe the block hangers.

A 900mm sleeve is a must.


Well-Known Member
A 900mm sleeve is a must.
Alan, do you know if anyone has actually measured how much the boom bends, short vs. long sleeve? (Of course I could go to the club and test it any day, but it would be nice to hear someone else's data, too.)

Make sure that you are looking for a 90 cm sleeve, NOT a 90" sleeve. To install the rivets you need a heavy duty rivet tool. You can get one at Harbor Freight.


Well-Known Member
Would it be legal to use a plastic top to make a boom?
In my opinion it would be illegal. Ask the world measurer.
Isn't this a bit trivial? The builders supply only aluminium booms. It can't be "home-built" of another material, and it doesn't help at all if that material comes from another part of the boat.

How tough is it to get that old one out and get a 90” put in?
Haven't tried it, but I wouldn't be surprised if it turned out to be a lot of work. It depends on how tight the fit is; the old sleeve most likely doesn't just fall out after you've drilled out the vang key fitting rivets. I once replaced a forward boom plug, and it was much harder than expected. There's a reason why the sleeve kit includes a new plug: the old one won't get out alive.

As I said, I would just drill new holes for the forward sheet block within the tolerances, especially when it looks like your home waters aren't that rough ;) If it breaks it breaks, and then you have the options of buying a new boom or making one out of the topmast.