cheek blocks: bearings or no bearings

[kentobin]

Rafiki 37: 37 foot cutter, full keel, 13 ton. Similar to Tayana.

As a neophyte on a refit I need to replace 13 cheek blocks used to lead halyards and lines on the cabin to the cockpit. Most of the existing hardware was frozen.

So I went searching on the web and read everything I could find on cheek blocks used as organizers. All the information I kept finding talked about low friction and ball bearings so I purchased aluminum cheek blocks with delrin ball bearing sheaves.

Recently I was doing some more research on blocks and loads and found a blog that stated for static loading on blocks, like halyards, I shouldn't be using a ball bearing sheave because the ball bearings would deform under the constant static load, at least delrin ball bearings will.

Don't remember covering this topic in the Brion's rigging class but that was a year ago and if it's in the The Rigger's Apprentice I didn't even think to look. Sorry Brion. :-)

So anyone with enough knowledge and experience to point me in the right direction?

Thanks in advance.

Ken

[Robbie.g]

i agree, static load [i.e. furler halyard] solid bearings are the go for the type of craft you talk about. This is all about bearing area, and movement, i.e small amount of movement under load, amount of material in contact with the sheave pin.
'Dynamic' blocks i.e. blocks moving under considerable load, i'm thinking genoa cars, pole downhauls etc, should be of the 'ball' bearing variety as the idea is to reduce friction under dynamic load.
As your using the cheek blocks to divert the loads of the halyards to the cockpit jammers [low movement under load] then the need to reduce friction under load is in second place to having good bearing area on the pin is in first. The 'ball' bearing blocks used in static load positions, in my experience, leads to the 2 or 3 'ball' actually in contact with the sheaves pin being crushed. Solid sheaves will also generally last longer with minimal [read no] maintainence.
I would also look at the benefits of deck organisers over multiple cheek blocks; fairer leads to jammers, number of holes/fastening through deck.
You'll find that many, if not all, of the deck organisers use solid acetal sheaves, and us 'ball' bearings are used for sorting side loadings resulting from foul leads.

Hope this helps.

[Brion Toss]

Hi,
I'll just add that this is also an opportunity to reduce loads, and thus friction, by positioning the collectors so that the lines form the most open angle possible. This typically means moving them as far aft as you can. If you calculate the reduction of load, it might even be possible to use a lighter, cheaper block. Further, if the layout allows, put your highest-loaded lines on the inboard sheaves, where there will be less of an angle than outboard.
Fair leads,
Brion Toss

[kentobin]

my conclusion: Brion when you have your rigging class in San Francisco please make time for a survey. :-)

Fair winds and following seas.