BYYB Forums

Say, Paul,

I noticed in your study plan for Discrete that you include a drawing of a dumb sheave.  I didn't quite understand what that was all about so I did a little research.  I started carving one out this morning and have a question.  I read that the whole idea is to take some of the pressure off your hand while holding a sheet by not having a free wheeling sheave in there.  I am wondering if I could also carve the opening so that it will slightly pinch the sheet while it is under tension, but have the hole large enough that the sheet will run freely once it is let to fly? 

My idea is to use the dumb sheave as the final block in my main sheet assembly on the weekender.  The main sheet will run forward to the dumb sheave which will be at the current spot on the boom and hang to hand the same as it does now.  Just forward of that I want to mount a clam cleat to hold the sheet when I need a free hand all the while being such that a quick downward tug on the sheet will let the whole works fly.  This will come in handy when I want to hold the boom tight in the middle at the dock or on  the hook.  I am going to try this.  I just wonder if making the hole into a slight vee shape will be a bad thing.

Al

A dumb sheave is one that can't take a hint, no matter how obvious it might be, pretty much like my ex-wife.

A dump sheave is a beehole that's loose. On small boats, you often don't need a block, just a hole. An example might be a peak halyard. A hole is cut in the mast, generously radiused and waxed. This is a beehole and the line just runs through it to change direction. If greased or well waxed they work fine, though a lot more friction than a regular block. Friction can be your friend at times, but mostly you don't want much. On modern boats, there's not a lot of need for a dumb sheave.

For your sheet block, I'd recommend a ratcheting block or a swiveling cam cleat instead. A dumb sheave, as you've described will not work well, especially in light winds, where the friction will prevent the sheet from paying out as you ease. With sheets, you want really free running lines and some sort of control (cleat, cam cleat, ratcheting block, etc.) at the end. This way you can trim or ease at will, with little resistance and dog it down when permissible. Most will tell you to never cleat a sheet, but hell, you got to get up and grab a beer sometimes, so you need a way to dog a line down. I sail with cleated (cam cleats) sheets all the time, but this is casual sailing, not racing nor in a hot rod. My hot rod (15' mono that does 20 MPH), you can't cleat anything, because one little gust and you're talking to yourself, in an unflattering fashion while swimming around. Casual sailing is very different, you're laid back, maybe the sails are drawing within 80% of max efficiency, the dog on the bow barking at the passing ducks, is causing too much windage to really point well, the beer cooler is on the wrong seat to be effective as ballast, etc.

All this said, I do make blocks that look like a dumb sheave or an old school wooden block, but I substitute a ball bearing block inside, often with a some stainless strap too, for strength. You can use a regular sheave, which doesn't have bearing, just a machined hole for a shaft, but man ball bearing sheaves run like you can't imagine, compaired to a regular sheave.

Getting back to your question, if you have a dumb sheave block and let go a sheet, so it can run, it'll just cause the line to ball up as it enters the block, making for a tangled mess. You can do this, but you have to feed or guide the line through so it does "run free", but is a little more controlled. If you want a little friction, make the sheet have an "unfair" lead to your hand, like pulling it over a combing or something.

Dumb sheaves work on flag halyards and other light load control lines, like things that don't get used much on each outing. A topping lift, outhaul sheave, a gaff vang, etc. all all places these do work well, if you just want simple and no moving parts to break.

It would be possible to make a dumb sheave that also acted like a "jam cleat" One side of the block would be well rounded over, while the other side would have a V shaped groove, so you could jam the line to slow it's run or actually cleat the line. Getting the V shape right will take some experimenting, but it might work. I make custom blocks like this all the time. On the same drawing you're looking at is a "reefing" cleat. I place these on the boom, so I can rig up a tackle for putting in a reef. It serves as part of the tackle and as the cleat, all in one, relatively simple piece. The way it works is you have an eye strap on one side of the boom, directly under the reef crinkle and this line is tied to the eye strap. The line goes up and through the reef cringle, then down around the sheave, so you can pull the reef down to the boom. When it's there, you just wrap the line around the whole shooting match and it self cleats.

When I am beating to windward in my CP 16, I will pretty much always cleat the main sheet and forget about it.  When I tack I lay the tiller over and leave the jib alone until the bow has come through the eye of the wind and then let the jib sheet fly.  Once the main has filled I center the tiller and set the jib.  This is so much easier than tacking the weekender that I want to see if I can get away with it on that boat.  I recognize that I need to be able to let the main out at a seconds notice, so I also want to be able to let it go with a simple tug.  On long tacks in a fresh breeze my sheet hand gets tired and I find myself looking for some way to let go of it for a while.  Also, when I anchor, I want to center the boom and get it out of my way and solid.  That is the reason that I want to add a cleat to my boom. 

The dumb sheave according to my research was touted as a way to save on my hand on long tacks.  However I believe you about the jamming so maybe I will leave this alone.  I have had some trouble with my jib halyard twisting when it goes through the blocks that lead it back to the cockpit, and that is a real pain also.  I find myself not wanting to take the weekender out on days when it is just going to be tug of war between myself and the main sheet.  Blame my hands not the boat.  I enjoy sailing the weekender more than any of my other boats, so this is a problem.  I will look into the ratcheting blocks.  Besides, yesterday I lost that darn dumb block twice while working on it.  For some reason it simply vanishes when I put it down.  Who would have thought that teak could be so invisible. 

Al

Maybe not as dumb a block as you thought?

HA!!!  I found that little bastard and painted it.  It's not gonna hide on me anymore.

Al

Just to clarify,

I sent a pic of the rough block that I made.  It has a 1/2 inch hole in it to accommodate a 3/8 inch sheet.  When I tested it, I couldn't tell if it was easier to keep tension on it than a regular block would have been, but the line ran through it really well even if I whiplashed it.  I don't know if I will actually use it as a main sail sheet, but I think I will make a few more as spares that I can keep in my ditty bag just in case.  Seeing as how it is a solid block, it should stand up to a knocking in the bag with no harm.  I can see using it as a downhaul block or turning block in an emergency jury rig, or a snatch block if I cut it in half and use a pin to close it. 

I tell ya, rigging these boats is to me the most interesting part about them.

Al

So, I've been wishing I had a couple snatch blocks to play with when I am wrestling with sail shape, but haven't seen a workable wooden model.  I can't say for sure, but the block I made today might be the solution.  I already made a dumb sheave block for the main sheet.  It was a short hop to making this snatch block.  All I had to do was cut a slot into one cheek.  The slot in the cheek that allows for the line to be inserted is just wide enough to force 1/4 inch line through it, but shouldn't let it easily slip back out from the sheave.  I also adjusted the strop such that under pressure it will angle away from the slot, making it doubly hard for the line to escape. 

I envision using this mostly for barber haulers if I decide to get fancy, or as emergency rigging in case something breaks.  Because it is a solid block of wood it should take quite a beating without breaking apart like the last time I tried this.  My previous block had a plastic sheave in it which left me with a weak cheek that did in fact break right away. 

This little guy was kind of a head scratcher, but in the end pretty easy to make.  I am looking forward to trying it out to see how tough it is. 

Al

Some ideas.





I've often thought a small wooden "gate" could be used, to close and open access to the sheave. A simple toggle on a pin or maybe a sliding door sort of deal, to make the snatch feature. The block shown first, is about as simple as it gets and the toggle isn't under much load, so it doesn't need to be very big.