Yes, any block can be used as long as the amount of blocks used for the purchase system dont exceed 5 counting the traveler blocks, mainsheet block, and the boom blocks. If you want a good ratchet, get a ronstan orbit
No Janson, it is NOT legal to change the traveller block or boom blocks - these have to be builder supplied blocks (either the old design or the new design, not any other design). The only block of the mainsheet system that it is legal to change is the mainsheet block itself i.e. the ratchet block attached to the deck just behind the daggerboard.
136831 - If the rules don't say that you can change it then you can't.
I dunno, GML. The class magazine for Lasers clearly advertises new Harken blocks on page 7 of the Summer 2011 issue. These may be the 'new design' you speak of.. but it's obvious that you can change out your blocks, traveler and boom included, with 'approved' Harken blocks... (surprised me, actually) So the answer is not a firm NO, but instead a 'yes, as long as you continue to follow class rules and use approved parts' .
I think 136831 just needs to grab his class magazine ( I'm sure he/she is a member ) and make sure they order the correct replacement Harken block.
Janson, you did imply this by your statement above.
As has been pointed out you can only use builder approved/supplied blocks for the 2 blocks on the boom and the traveller block assembly.
You are free to use any flavour of mainsheet block that you want though.
With regards to the new 'harken' blocks most of the top guys do not use these and stick with the older Holt blocks. This is because the Harken block have a tendancy to clip inboard on the traveller when you are going upwind. You can counter this by using more kicker but this is obviously not optimal (sometimes a bit too much friction is useful).
My 2p is that I have the new harken blocks throughout on my boat, they are great aside from the creeping inboard. As the lake I sail on is quite small and the water is generally flat this really does not make much difference.
I understand If my post was a little bit misleading. I was saying that you cant use other blocks on the boom or the traveler to upgrade the purchase system so trimming is easier, i assume most people know they can't replace the traveler and boom blocks. Sorry for the misunderstanding..
The "new upgrade" traveler blocks also have the added benefit of not snapping or breaking after a lot of use under high stress. My own traveler blocks (the old holt ones) broke just before the start of the first race of North Americans, costing me my drop and keeping me out of top 10 at the regatta (no redress for gear that was yours). That was the second set I have had that has broken in the last 4-5 years.
There was clearly a defect with those second ones (the first were just old) because the metal hooks inside of where I taped the blocks together was just shattered, and all I did was trim to closehauled and they broke. I think the newer Harken ones are probably the more reliable. I haven't heard of any breaking yet.
That's the first time I've heard of the through riveted Holt Allan traveller blocks failing. When they were only screwed they used to fail all the time, hence why the first thing you used to do was to through bolt them.
It wasn't the blocks themselves, but the hook joining them together. I'm not sure what that part of the block is made of but I don't think its a very reliable material. Or maybe it is and having 2 sets of broken blocks is like lightning striking twice...
I was thinking about writing Holt Allen about it after the second time but decided that a ten dollar block wasn't worth it.