The importance....

[John Nantz]

Donalex - Really Impressive!

I can imagine you would have made someone a good lab partner in school!So, you must have your own lathe with a bin of scrap metal to be able to turn these sheaves?Shame on any boating magazine which couldn't find a way to publish this valuable information. Heck, they could have done it in a two-part series or a pull-out special.Okay, onward. Just happened to have a few three-year old lines laying around - that was very opportune. Most magazine test articles would have used new lines and left one to guess what happened when they aged so your test is really more practical and therefore valuable. That's a good observation about the lubricant being gone, too. What's a "roller sheave" and "plain bearing"? Would a plain bearing be like what I have with a nylon sheave and a stainless pin through it?Question: How is the "% Lifting Power Loss" calculated?Oh, and with regard to the two pence, darn it, I forgot what they called them so thanks for the spelling.

 

[Don12364]

Me - Yet Again

John,A 'plain bearing' sheave just has a simple bush running on a plain metal shaft. Some older bushes were brass or sintered bronze on stainless shafts. These carry great loads and are much better in this respect than ball or roller bearings. Newer sheaves are made of plastic or have plastic bushes. These deform so don't carry extreme loads as well.Roller bearings are just that. Whereas a ball bearing has balls running in a race, a roller bearing has rollers. ie. small round parallel sided items like on a conveyor. The difference is that ball bearings only run on the minute contact points where the balls touch the inner and outer races - low friction but are thus NOT good load carriers, particularly if the balls are made of plastic. The roller types have 'rollers' and these have long contact lines between roller and race so carry greater loads.Bicycle wheels run on ball bearings but automobile wheels almost always use rollers.Having said this all blocks should carry the loads they are designed for without failure - but at how much friction?Lifting Power Loss:- If one has a four part tackle, ie. four sheaves, two forming a block at the top and two forming a second block at the bottom. Then, if these were perfectly frictionless and the rope also had no internal friction, the tackle would lift FOUR times the pull on the tail rope. 100 lb pull gives 400 lb lifting force.Now allow for friction in the rope and the lifting force (sorry I used 'Power' incorrectly) and this will be reduced by the percentage shown in my graph.Thus 75mm (3") diameter blocks with low stretch halyard will loose 35% of this theoretical force so one may only expect 65% remaining; and 65% of 400 lb gives 260 lb.That's not the whole story because each sheave will loose a further, say 2.5% if a 'good' ball type or 11% if a plain bearing.This extra friction means the ball block setup will now only lift 90% (.975 to fourth power = .90) of the previous load or 235 lb.For the plain bearing blocks the comparative figure is (.98 to fourth power = .63) and the lift is now only 163 lb ......and you were expecting 400 lb.I said it gets technical!The secret is to always use the largest sheaves in comparison to the rope diameter. To their credit the sheave makers do tell us this but we ignore it in the interests of cost and weight.

 

[John Nantz]

By Jove, I think I'm gettin' it!

The sheaves on my boat I think are just the plain bearing type without any bushing so this is probably the worst case for loss, bearing wise. Then the next characteristic is sheave diameter and mine is probably close to the 50mm diameter which has about double the loss as the larger sheave in your test. So, just by changing sheave diameters to a larger one would reduce loss significantly. In addition to changing the sheaves to ones with roller bearings and a larger diameter, going to a stronger but smaller halyard will help. Unfortunately, at somewhere around 130 to 140 feet this can get expensive really quick. Wonder what I could use my old halyard for?Well, when I get home I'll sit down and try figuring out some options. Now that we know the factors that influence or contribute to loss then perhaps an interesting approach would be to do a cost-benefit analysis of each change: bearing type, bearing size, line type & size, etc. There's nothing like having good facts and figures.Thanks for your great input Donalex!

 

[RickS]

Outhaul line

I understand the importance of a high quality low stretch halyard. Is it just a important to have a similiar line used for the mainsail outhaul, ie StaSet or a line with less stretch?

 

[Alan]

Rick

Stretch is less of an issue with your outhaul, but efficiency is. Smaller line sizes produce less friction, but are not as strong as larger line. High tech line can be smaller and as strong or stronger than the larger line and have the added benefit of much less turning friction. As you add 'parts' to your outhaul purchase the friction becomes multiplied therefore anything you can do to minimize friction is to your benefit.I upgraded my outhaul arrangement to a 6:1 internal system with spectra line. It is extremely powerful and easy to operate.

 

[RickS]

Alan - line size

Alan, the luff and foot of the main on our Peterson 34 are approx 41.5 and 11 feet, respectively. I was planning on using two fiddle blocks inside the boom, a turning block at the end of the boom and bottom of the boom, a jam clean and bullet block outside on the bottom of the boom. I was planning on using 3/8" line for strength and handling comfort. Would you suggest an alternative size line?