How to determine the boom angle for in-mast furling

[suiramor]

I have replaced the topping lift but forgot to mark off its setting for the correct boom angle to facilitate easy furling. I know the angle is critical but do not know how to determine it now. Is it trial and error, to see when the furling/unfurling is easy or is there some scientific method of doing that?

[sailingabe41ds]

I do not know the answer to that even if I have had an in mast furler for 20 years. I just let the mainsheet out and let the boom flop a little while furling in and out and it appears to work for me. If I tried to keep the boom 90 degrees to the mast it may rub on my canvas so I keep it just above so that the end of the boom clears does not destroy rubbing on the canvas over my cockpit.
Not sure if that helps....hope someone has a more scientific or practical explanation specific to your boat.

abe

[Uncle Bob]

Originally Posted by suiramor

I have replaced the topping lift but forgot to mark off its setting for the correct boom angle to facilitate easy furling. I know the angle is critical but do not know how to determine it now. Is it trial and error, to see when the furling/unfurling is easy or is there some scientific method of doing that?

Hi, if it is a leisure furl boom furler I believe that the angle needed is 88 deg, I find that it is easy to get close and if the sail tends to creep forward then it is a tad low, if it tends to move aft it is high, does take a little trial and error but marking the line when you find the sweet spot makes it easy.

[Na Mara]

For me with my selden in mast it’s about 90 degrees. You are meant to play the topping lift and bang for optimum performance and then return it to that before furling but I don’t bother as the vang and topping lift are at the mast. Instead I have the vang set so the boom won’t go less than 90 degrees to the mast and the topping lift set so the main can be flattened with the mainsheet. Apart from the boom being low over the cockpit at anchor this works for me, as I never feel the need to power up in light conditions by raising the boom but I do feel the need to power down in fresh conditions by flattening the main, particularly with apparent wind forward of the beam.

[EmeraldCoastSailor]

On my Beneteau it is critical to let the boom be mostly free, under some control via mainsheet so it isn't wildly swinging, but definitely loose enough to allow for the boom to rise up as sail comes out. Vang has to be fully released. In other words, no where near 90 degrees. The outhaul and furling line are the only lines that are tight during unfurling. My topping lift is only there for steadying the boom when tensioned against the mainsheet when not sailing; it isn't really needed and is no factor when unfurling and furling. I use my topping lift to get hoisted up the mast when inspection time comes around.

[sail sfbay]

Who is the in-mast furler manufacturer? My Selden in-mast boom angle is close to 90 degrees to the mast and works fine.

[SailingMed]

Originally Posted by sailingabe41ds

I do not know the answer to that even if I have had an in mast furler for 20 years. I just let the mainsheet out and let the boom flop a little while furling in and out and it appears to work for me.
abe

Exactly! Same thing that EmeraldCoastSailor mentioned too. Ease the mainsheet out a little bit and the sail, while furling, will do the rest. The mainsail will pull the boom upwards and not the other way round.

[sailcrazy]

The boom angle is critical for an in-boom furler, but I do not believe it is some important for an in-mast unit. Our in-mast furler , vintage 1989, does not specify an angle. The M/S clew is loose; the outhall runs from the moveable boom car, to the block in the sail, to a loose block on top of the car, to the boom end. The sail can move to whatever angle it wants, and so it goes in/out at whatever angle it needs to. We eyeball an approx 90*, and use it! So far, after 22 years on this boat, not an issue. We do not, however, try to furl the M/S when it's under load, especially on a downwind run.

[Redline452]

The boom on my SO45.2 rides fairly high when the mainsail is unfurled, and is held up by the rigid / sprung vang when furled - never measured but I’d guess 10-15 degrees above horizontal. The topping lift; initially only tied to the boom to keep it from slapping the mast, is now used as a hoist for the long wire HF antenna.

There is a label by the furling line stopper saying “release vang before furling”, which lets the boom rise up, generally about parallel to the foot of the sail as it furls.

tl/dr: just set the topping lift so it doesn’t interfere with the sail while sailing, and holds the boom up when furled. Fine tune after a couple of outings then leave it wherever.
N

[Paul Carey]

I recall repplying to similar query before , but here we again ,we specified a furling main in 2005 on our new Broadblue 385 with Z Spar mast & boom ,, this was problamatic from get go & many opinions were sought , the O/E sail manufacturer was adamant their fit was correct & Z spars also were adamant but a lot more helpfull , I suspect that both were owed money by BB whom subsequently went under , i.e. ' we were not heir customer ' We eventually had Marmaris UK sail franchisee ; ' Selma ' make a new sail & the fit / operation was perfect ,,providing you always kept boom to mast angle at right angle = 90 degree ,, over the last 3 year years we have owned in England a 1977 Catalac 8 metre fitted with a from new ? Colnbrook (they are long gone ) bolt on back of mast reefing this works very well with a verticle battened sail , provided of course you operate at 90 degrees ,, so thats your reply = 90 degrees always .....

[A la carte]

I've enjoyed success with trial and error on my boom fuller. Just a thought: Would a Digital Electronic Level and Angle Gauge prove helpful? If the boat is still, you could place the gauge on the mast and then place on the boom and it will give you the precise angle.

Several digital angle gauges are on Amazon for $20 - $25.

[suiramor]

Thank you all! I will go with the relax all but furling and outhaul lines approach. (It is a Beneteau 46 with z-spar mast). Yes, I did notice that all articles about importance of the angle referenced boom furlers so that where I probably got my concern. Thanks again!

[Martkimwat]

Originally Posted by A la carte

I've enjoyed success with trial and error on my boom fuller. Just a thought: Would a Digital Electronic Level and Angle Gauge prove helpful? If the boat is still, you could place the gauge on the mast and then place on the boom and it will give you the precise angle.

Several digital angle gauges are on Amazon for $20 - $25.

The critical angle is between the boom and mast, not boom and boat. I would use a large protractor to ascertain initial angle making allowance for whether the required angle is greater or lesser than 90º (usually lesser than)adjusting a boom strut or topping lift to hold the boom at the correct angle and then in the case of the topping lift, marking it at the correct position. (for the purposes of ascertaining angular different from 90º the 1 in 60 rule is quite accurate enough for the few degrees difference.)

[NolaSailor]

I've had a Selden in mast furling system for a couple of years. I haven't found that the exact boom angle is crucial. Like others I have just fooled around to be sure the boom's not touching my Bimini and gone sailing.
best of luck!

[A la carte]

Originally Posted by Martkimwat

The critical angle is between the boom and mast, not boom and boat. I would use a large protractor to ascertain initial angle making allowance for whether the required angle is greater or lesser than 90º (usually lesser than)adjusting a boom strut or topping lift to hold the boom at the correct angle and then in the case of the topping lift, marking it at the correct position. (for the purposes of ascertaining angular different from 90º the 1 in 60 rule is quite accurate enough for the few degrees difference.)

Yes, you are correct, between boom and mast. A large protractor could certainly work. The digital angle measuring tool must have some sort of an internal plumb bob. You place it on one surface and set that as zero, then you place it on the next surface and it measures the angle for you. They're very precise and easy to use. I've used them to set a precise 15° angle on an ice resurfacer blade... Takes about 30 seconds... great tool.

Again, I've enjoyed success with adjusting the topping lift by watching how my sail furls so, the protractor and digital angle measuring tool are probably overkill but, the digital tool might prove helpful and easy if someone needs precision.