Since I have a boom in my garage awaiting conversion (Thanks Dan!) I would like to pick your brain a bit. If you have the time, please tell me if I'm making sense here.
Harken carbo blocks and all Ronstan blocks are [censored].... they simply explode in the sort of application.
I've heard people curse Ronstan blocks on this forum before, though I've never seen a failure first hand. Do these blocks really not live up to their SWL ratings? Or do people just not understand that the SWL rating needs to be 2x the line load for a 180 degree turn?
I don't understand why the Harkens would have any trouble in the primary section, where the sheeting forces should be slightly less than in a conventional 8:1 setup. However, they obviously cannot carry the loads in the secondary.
Since the strongest Harken small boat ball bearing traveller car is rated at 1250lbs MWL, I've been assuming main sheet total load does not exceed that. Based on this assumption, the configuration with a cascaded 3:1 primary with 3:1 secondary sees the highest loads: the secondary line has 375lbs of tension, meaning you need a block rated at 750lbs at the front of the boom to carry the 180 degree turn. This is above the SWL of Ronstan and Harken ball bearing blocks, but not above the Karver's.
However, the floating block needs only a 375lb SWL rating, which is well within the 485lb SWL of the economical Harken 2651.
Cascades with a 4:1 secondary see maximum line loads of 300lbs in the secondary, requiring blocks with ratings of at most 600lbs SWL. This falls withing the rating of most of the Ronstan 30mm ball bearing series, so I would expect them to work with a 4:1 secondary. Harken ball bearing blocks cannot handle the loads.
I will take pics of the rear end of the system today and post shortly.
Thanks! Thanks a lot!
Karver blocks are awesome and never stuff up.
That's good to know. Thanks. They are still ball bearing blocks though, which makes we wonder:
What about the Marstrom boom-internal system with needle bearings. Why have I never seen that system actually used (except I have seen the similar system on the Marstrom 20)? It is an option on the Tornado order form.
We use Harken Wire Sheaves in the small rope sections, 980kg working load means they hold together pretty good.
Aren't these plain bearings (not ball bears and not needle bearings)? Don't they turn less freely? Does this seem to be an issue?
Wow: there are lots of questions in my mind. Thanks in advance if you can answer any of them.
