Something different – furling sails

[Philip LeithParticipant @philipleith92012]

I have a sailing boat and would like to put a furling spinnaker on it, but the price of the top and bottom parts of the system are astronomical (£1500 or so for my size of boat). I'm sure I could produce something as good in the workshop for a fraction of the price. Basically there is a bearing fastened at the top of the sail and a round drum with a bearing at the bottom. A continuous rope goes round this lower drum to allow you to roll up the sail.

There is a 'tension rope' which goes between the two bearings, attached to the front of the sail which rolls the sail up.

You can see this type of system here: http://www.facnor.com/uk/products/asym_spi_furlers/

Producing the elements in 316 stainless steel would not be a problem, but what kind of bearings would be appropriate? There is quite a tension on the sails (halyard – the rope – breaking strain is usually 2500Kg or so). Also, there is always salt spray so bearings would have to be protected or salt resistant.

Any ideas on planning this would be welcome.

Philip

[Philip LeithParticipant @philipleith92012]

[jason udallParticipant @jasonudall57142]

Delrin washer.
Ptfe also works but care since it flows under pressure…
Basically large diameter friction component..reduces pressure and flow.

On a twenty footer I used 30 mm od and ten mm shaft..
Think large headed pin ..washer… cage..
Less than perfect but smaller than original drum and has lasted three seasons…
At halyard end don’t over do it because of bulk at mast head but same form of swivel
…

[Ady1Participant @ady1]

Lignum vitae was used for sternshaft bearings

There are plenty of old lignum bowling ball sets on a well known auction site

Edited By Ady1 on 22/12/2014 11:51:55

[Bob Brown 1Participant @bobbrown1]

Stainless steel angular contact bearings would be my choice, still with seals but if/when water gets in corrosion should be minimal. Need to watch out for galvanic corrosion but if you made the parts out of 316 should not be a problem.

Bob

[Philip LeithParticipant @philipleith92012]

I've never heard for angular contact bearings but note here that they need to be paired because of their geometry:

http://www.nmbtc.com/bearings/angular-contact-ball-bearing/

Is that the case?

[Bob Brown 1Participant @bobbrown1]

They are used in pairs sometimes like tapered roller bearings spaced along a shaft other times back to back as in car wheel bearings. they are designed to take both radial and axial loads bit like this application.

Bob

[Matt DParticipant @mattd]

If I understand it the loads are applied by the halyard and the furling line and that both furling devices can move on their mounts therefore the loads experienced by the bearings are mostly in line loads. Yes, the furling line will apply a side load but it can't be great can it? A well sealed thrust bearing at the top of the sail and annular contact at the bottom? I expect that the sail loading can be pretty high so both bearings will need to carry quite high static loads without coming to harm. Sea water in bearings and grease on sails are both bad and lots of plastics absorb water don't they? Salt can be abrasive so what ever is used (except perhaps for naval bonze) it needs to be sealed well.

[Ady1Participant @ady1]

As the heaviest, most dense, commercially available hardwood Lignum-Vitae is nature’s perfect answer to man’s need of durable bearings. The wood is clearly an anomaly in that it contains a quaic resin bound by an interwoven interlocking grain pattern giving it a combination of enormous compression strength and unmatched lubricity. This combination gives Lignum-Vitae the ability to work flawlessly in extreme conditions underwater for decades under working loads in excess of 10,000 psi. Lignum-Vitae set the standard for nearly every industrial “1^st” in Machinery history. Lignum-Vitae was the first hydro bearing specified by Thomas Edison in 1882. It was the “First Stern Tube Bearing” to make the transatlantic voyage in 1856. Lignum-Vitae was the First Jack Staff bearing in the First Nuclear Submarine (USS Nautilus), Lignum-Vitae was used by to “The Great Eastern in 1856” to lay the first Transatlantic cable. Lignum-Vitae replaced existing Babbitt bearings, and was the first stern tube bearing in 1854. The First Antarctic Voyage by Shakelton, Polar Class Icebreaker (1976) (The largest Non-Nuclear ship operating at the time used lignum-Vitae. With the rich history Lignum-Vitae has enjoyed it is no wonder it remains the longest lasting material today!

**LINK**

[John OlsenParticipant @johnolsen79199]

Ok, well first off I think the sail you are talking about is actually a jib, which is a triangular sail that sets on a stay. I made my own roller furling setup for the jib on a Sunburst, which is a New Zealand dinghy class that carries main, jib, and spinnaker.

The stay that the jib sets on is normally the forestay for the mast. When the breeze gets up, you need to flatten the mainsail and the jib by various means, and that means that you can end up with a fair tension in the stay. It is desirable for the forestay to stay quite straight. In the Sunburst, which is only 11 foot six inches long, the forestay tension can easily reach a ton or so. The bearings have to be able to turn freely under that load. I looked at the commercial offerings and felt they were both too expensive, and not adequate for that sort of load. So I made my own. I don't think plain bearings of any sort are really what is needed here, at least for the thrust load. I made up a pair of units machined from aluminium stock that housed a ball thrust bearing. The lower one was larger and included a reel for the furling line. The furling line doesn't have to be a continuous loop, you can unfurl by pulling on a sheet and use the furling line just to furl. However, it does need to be controlled so that it winds nicely onto the drum. The jib on the Sunburst is small enough that it is never used reefed, but on a larger boat you could cleat the furling line and just use part of the sail.

The bearings were standard off the shelf items, protected by a standard lip type oil seal. You can improve these seals for salt water use by taking out the tensioning spring and replacing it with a 1/16" cord O ring of the right length. That way it will not rust. I relied on this and the bearings being packed with grease and never had any trouble. The boat is still in use by relatives after over twenty years so it all worked out fine. As far as I can recall I didn't provide any bearing other than the thrust bearing. The oil seal and the hole in the end locate the moving part enough, as any radial loads are negligible compared to the end load.

If you are dealing with a spinnaker, then what you need is a self launching spinnaker pole. The windward corner of the spinnaker is poled out by a pole that seats against the mast. When you gybe, the pole needs to be retrieved, moved across the bow to the new upwind side, and relaunched. There are a number of ways of doing this, some of them quite dangerous for the crew member involved, who is working on a small wet space…and boats that are running downwind do not need extra weight up front. Especially a small dinghy that is planing. (Guess how I know this!)

So what I came up with is a self launching pole. The spinnaker pole has to be large enough in diameter to accommodate two spinnaker lines and a bungee rubber. Ideally some light plastic tube would be fitted internally to separate them as otherwise they may be inclined to bind on each other. A single sheeve is fitted into the boom about the length of the pole back from the gooseneck. A length of bungee rubber runs from the forward end of the spinnaker pole, out the aft end, into the sheeve and forward up the length of the boom inside. When the pole is not in use this pulls it back to lie alongside the boom. There is also a line from each corner of the spinnaker to the forward end of the pole. These proceed through the pole, out the aft end, and forward to a double sheeve on the mast at the point where the pole would normally seat. From there they proceed aft to some convenient point where they can be cleated. Each lower corner of the spinnaker also has the conventional sheet, leading to a cleating point aft.

OK, so the pole when not in use lies on one side of the sail next to the boom. When it is desired to launch the spinnaker, the line that attaches to what is going to be the upwind corner of the spinnaker is pulled. As the tension comes on, the corner of the sail will be pulled up against the forward end of the pole, and then the pole will be pulled out against the tension of the bungee, until the aft end of the pole is up against the mast. The spinnaker can then be launched from a chute by pulling on the halyard. In order to gybe, the pole outhaul is released, the pole retracts to beside the boom, and after the boom has gone across, the other outhaul can be pulled in to set the pole on the other side. All sounds a bit complex, but this setup allowed me to operate the spinnaker single handed in heavy conditions, eg enough to make the dinghy plane. Actually it was more awkward in light conditions, when the friction in the various runs tended to make things hang up. But then in light conditions you can get away with going forward to sort things out.

John

[Philip LeithParticipant @philipleith92012]

You are perhaps mixing up reefing around a forestay and furling a spinnaker. Your pole idea works on dinghys but not on large boats. What kind of thrust bearing were you using, though?

[OuBallieParticipant @ouballie]

I thought I was finished with boats after serving my time with the SAN.

Need to somehow re-attach the busted handle on a cooking pot lid for 'her indoors', as she is preparing for the marathon that happens every Christmas.

Geoff – I'll be on short rations if I don't succeed

[Russell EberhardtParticipant @russelleberhardt48058]

I'd be inclined to look for ceramic or hybrid bearings. It doesn't matter how well you protect them salt water will get in.

Stainless steel doesn't perform too well in a salt water environment, I had to replace about two thousand stainless steel screws in my teak decking, many of which had almost completely rusted away. It's OK where it gets to the air but not if it can be submerged in trapped water.

Russell.

[Neil WyattModerator @neilwyatt]

> Need to somehow re-attach the busted handle on a cooking pot lid for 'her indoors', as she is preparing for the marathon that happens every Christmas.

Sounds like job for Lignum vitae!

Neil

[Bob Brown 1Participant @bobbrown1]

Posted by Russell Eberhardt on 23/12/2014 10:10:37:

Stainless steel doesn't perform too well in a salt water environment,

Russell.

Wood corrodes metals, and not all stainless steels are suitable for a marine environment also mixing metals is also not good but it depends on where they sit on the galvanic scale. Fixing aluminium with stainless fasteners or galvanised with stainless steel is asking for problems.

Bob

[OuBallieParticipant @ouballie]

Indeed Neil.

Would have looked for some to make a new handle, but perseverance paid off.

After a couple of false starts it's now fixed.

Geoff – Full rations now I expect

[Speedy Builder5Participant @speedybuilder5]

Cooking pots etc. Make small handles in stainless steel strips and ask your friendly garage / body shop to spot weld them back on for you. Might even get a chockie biscuit for your labours.

[OuBallieParticipant @ouballie]

The round plastic handle was fastened to a screw protruding through the centre of a glass lid, the boss that had the M5 female insert having sheared off.

Tried some of that macho primate glue, but that was as good as the skin on rice pud, so drilled through the broken off part and handle, tapped M5 then used the tried and tested method of screw and nut.

No doubt the head of the screw, on the inside of the lid, will rust, so have planned on stocking up with brass or stainless just in case.

For some reason I either cannot find any brass screws, or I've never had any.

Geoff – No doubt the former, so I will find them after ordering

[Ian S CParticipant @iansc]

316 stainless for the screw in the pot lid, and for the boat fittings, 316 is the best for general marine work, and would work ok in the environment in a pot.

Ian S C

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