Building an in-boom furler

[mastreb]

Hey Guys,

Obelix suggested I start a new forum thread on building DIY in-boom furlers for the Mac. So this is it. Firstly, you should google the CDI MR2 mainsail furling system and decide whether that complete system is not a better bet for you. For those who rarely trailer, it's a pre-fab system that would be easy to install on a Mac. However, it will dramatically complicate trailering, which this boom furling system is designed to keep very simple and easy.

What I'd proposed is using a piece of aluminum C-channel extrusion as a boom, with a typical furler located inside the channel such that the benefits of a rigid, non-rotating boom are preserved and roller furling is possible.

It's pretty clear how this would work. I'll talk the system aft from the mast to the boom-end.

0) Obtain a loose-footed, bolt-roped mainsail of lightweight cloth having #6 luff tape installed. Converting an existing older mainsail is a good idea. Tightly roll this sail from the foot to the head, and note the maximum width of the tightly rolled bundle forward.

1) The mast is prepared with a Spin-lock bolt-rope feeder above the bolt-rope feed slot to ensure proper feeding. These work great, I had one on my boat until I went with track.

2) The stock gooseneck assembly is used, except that the tack ring bolt is replaced with a swivel shackle, allowing the furling line to rotate.

3) Obtain an 11" long extrusion of aluminum C-channel according to these specifications:

Length: 11"
width & height: From measurement in step 0.
wall thickness: 0.12 or greater (likely you will not be able to obtain this thin of C-channel)
Material: 6063-T6 aluminum alloy with 202 R1 anodization

3) A single extrusion of aluminum C-Channel is drilled such that a nylock bolt will pass through the gooseneck hole, thus connecting the C-channel to the gooseneck in exactly the same manner as the existing boom is connected. Now the C-channel is rigged as a boom.

4) As near as practical to the bottom edge of the boom, and at the same lengths rearward as on the original boom, drill holes for the vang bail and mainsheet bails, and install.

5) Obtain roller furling luff extrusion part CDI LFF2 http://www.mauriprosailing.com/us/product/CDILFF2.html. Cut to 10'6".

6) Install the furling luff extrusion onto the foot of the mainsail. Shackle the tack of the mainsail to the swivel shackle above the gooseneck at the mast base. Using a small length of rope, tie the clew of the mainsail to the furler extrusion base drum (the black portion at the end of the extrusion) using a soft-shackle knot.

7) Drill two holes midway high near the end of the boom for passing a nylock bolt through. Affix a swivel shackle to a bolt through and nylock this. Fix the end of the furling extrusion drum to this swivel shackle. Drill holes for another bolt near the top of the extrusion for the outhaul.

Affix a flying shackle block to the clew of the mainsail using another swivel shackle (such that the swivel shackle is between the clew and the block). Tie the outhaul to the top bolt at the end of the extrusion using a bowline knot, pass this through the flying shackle cam-cleat block at the mainsheet clew, and bring the outhaul to the back of the boom.

9) The outhaul will need to be turned back forward with check blocks, which may or may not be possible to do inside the boom. Budget two cheeck-blocks, one at the aft end of the boom and one at the forward end, to take the outhaul forward to the mast and then back to the cockpit. The best possible mounting should be determined at installation.

10) Install and tension the mainsail with the outhaul. Determine where the drum portion of the luff extrusion lies in the C-channel. This should be at 10' 9" back on the C-channel. At this point drill a 1/4" hole centered on the bottom of the C-channel. Bolt a thru-deck block at this point to turn the furling line forward. At the forward bottom of the boom (routing through the mainsheet and vang bails) mount a turning block to lead the furling line down the mast. At the mast base, bolt a shackle block to the mast slot to turn the furling line back to the cockpit. Finish by mounting a cleat or cam-cleat at the cabin top as per your preference, or using the existing winches and cleats.

The rolling boom is now complete. By slacking the outhaul slightly and loosing the main halyard, and then hauling on the furling line, the furling extrusion will twist the mainsail into the boom.

Note that this furler does not include a wire stay, relying instead on the tension of the mainsail foot bolt rope. This should work just fine. Also, I have not included any kind of spool retaining ends on the furler. These will likely be necessary, and will have to be fashioned specifically for the luff extrusion, which I've not seen and can't specify. Alternatively, you could fit an entire CDI MR2010 drum assembly into the extrusion, but I don't think that's necessary at all.

Anyway, those are just my thoughts. The purpose of this thread is to discuss this as a possible solution. I wanted to be sure that this can dismount just as easily as the current boom, taking the boom, furling assembly, and mainsail away in one step. It can lie inside the boat on the cabin sole to port for trailering, and should be simple to maneuver into that location. I would strongly recommend using it with a topping lift due to the weight of the system. I would also recommend affixing some sort of padding on the boom end and corners to make them safer.

Matt

[Obelix]

Just roughly looked at weight numbers. if we use a 5" square C-channel .25" thick (1 square foot of .25 aluminum sheet is about 3.55lbs), the channel itself would already come in at about 45 lbs.
Adding the furler and the sail would make it a pretty heavy boom, developing lots of momentum in a wild jibe.
I wonder how heavy commercial in-boom furler are?

Obelix

[mastreb]

Just roughly looked at weight numbers. if we use a 5" square C-channel .25" thick (1 square foot of .25 aluminum sheet is about 3.55lbs), the channel itself would already come in at about 45 lbs.
Adding the furler and the sail would make it a pretty heavy boom, developing lots of momentum in a wild jibe.
I wonder how heavy commercial in-boom furler are?

Obelix

Yep. A boom that heavy would need to be rigged with a preventer or double main sheet system to prevent gybes.

That said, I'm pretty sure this can be done at 4" width (having rolled my mainsail on its boom), and the extrusion does not need to be 4" high--it need only be 2" high to support all the necessary through-bolts. That extrusion, in .125" thickness (sufficient) is 1.16 lbs./foot or about 13 lbs. for the boom. The only trick will be finding it in an 11" length.

[Catigale]

You can sail this for at least a year until Software finishes beta for OS2 Warp is released, followed by WIN 2000, then OSX drivers. Finally WiN10 is released and then the furler steals your credit cards

I'm a confirmed trailer sailor so in boom furling doesn't make sense for me but this is great stuff and even sounds manageable on our boats if something jams up.

[DaveC426913]

The only trick will be finding it in an 11" length.

Great for the 1/12th scale prototype but you might want to scale that up for the real thing.



Spinal Tap visits Stonehenge.

[bobbob]

I have the CDI MR2 mainsail furling system - in what way do you think it complicates trailering? When I trailer I only have to unhook it from the boom and make sure its supported along the length of the mast (similar to the jib furler) so that it doesnt kink. In fact, the jib furler is more difficult to manage because it sticks out past the end of the boat, and I have to lash a pole (usually the MRS pole) extending past the end of the boat to support it.

[BOAT]

I don't like the standard mainsail furling systems because they compromise the shape of the sail. The sail battens are all screwed up and the sail is cut to be wound up from top to bottom and makes for a lousy shape.

Rolling up the sail from the foot to the top is much better because it does not require any shape alteration to the main sail at all or the sail battens.

All the boats I have seen with a roller furling main that rolls into the boom have all had a carbon fiber boom. I assume the weight is an issue.

The booms that I saw were on 44 foot boats and larger - they were very wide at the point where they met the mast to accommodate the very large and bulky roll you get on that part of the sail when it's all rolled up. The ones I saw were electric - but that's a bad option for us because we could rip up a sail.

I would not even use a regular spindle furler with a rope to rotate it - I would just have a crank on the end of the boom or a place to insert a crank. Again - all to save on weight, and to eliminate the problems I saw with the existing boom furler (a zillion ropes to rig and pulling this and that back an forth when it jamms - a real pain - a simple crank eliminates all that rigging).. I think weight is key. It's gotta be VERY VERY light.

I will see if I can get a picture of the booms I saw on the big boats - they were shaped like a V "tub" like thing so the sail would fit in. Our main sails would not fit in a small C channel - it's gonna require something at least 8 to 12 inches wide at the end near the mast. Either a molded fiberglass tub with a metal rod inside or a carbon fiber thing or some other gadget. It's possible. Maybe a suber lightweight tub with a hollow carbon fiber rod on the inside that rotates - not sure - it's doable. Would need to fab up a mock up in wood first to see what shapes work.

Here is one of the best made ones out there:

https://youtu.be/PNVHaSUbcjg

This video is a good primer on what it's like to make one as they go through the manufacturing process. I like the system, but it's way way too heavy for our boats.

[bobbob]

I've been thinking of getting a new main sail with vertical battens to allow for a positive roach, but for sure it's a compromise. That being said, I can't count the number of times someone has come over to ask about my main sail furler - mostly walking away saying that they have to get one

[paul I]

I will see if I can get a picture of the booms I saw on the big boats - they were shaped like a V "tub" like thing so the sail would fit in. Our main sails would not fit in a small C channel - it's gonna require something at least 8 to 12 inches wide at the end near the mast. Either a molded fiberglass tub with a metal rod inside or a carbon fiber thing or some other gadget. It's possible. Maybe a suber lightweight tub with a hollow carbon fiber rod on the inside that rotates - not sure - it's doable. Would need to fab up a mock up in wood first to see what shapes work.

Why would it even require a fully cast channel? Think of a piece of nearly flat stock to serve as the bottom with several smallish vertical arms attached to it to make a cradle type of mechanism. The weight would be reduced substantially.

[BOAT]

Yes,

There are a lot of ideas like that out there like the LeisureFurl and also the Furlboom:

http://www.furlboom.com/descript.htm

The "tub" for the sail is a feature of the LeisureFurl - but ALL of these are for boats over 35 feet:



One time when I was at mastrebs house he showed me a piece of hollow carbon fiber that was only about 2 inches wide and was the same length at our aluminum boom. The weight in my hand felt like i was holding something made of paper - it was as light as a long piece of Styrofoam, but as strong as our stock boom. The only issue about the CF "boom" that mastreb showed me was that it had a bit too much 'flex' in it - but! I think that CF piece might be a good start for a FURLER. That thing was so light and strong you could wrap your mainsail around it and wind it right up.

[Jimmyt]

I have the 'stock' furling boom, and I love the furling main. Not crazy about the look of it, though. The one in your pic above is beautiful. I'm sure you and Mastreb will have it scaled down to Mac size soon. I was thinking I might try a redesign using a structural boom, some actual bearings (rear bearing on mine is a cable thru nylon bushing); and a light weight furling tube. I was thinking a fiberglass cover to house the whole business - allowing my next sail to omit the heavy cover border that's necessary for the open furler.

[mastreb]

BOAT you can have that tube if you want to work on a furler.

[bobbob]

mastreb, I'm still really curious what problems you see with trailering with the CDI main furler - perhaps there is something I haven't considered.

[BOAT]

mastreb, I'm still really curious what problems you see with trailering with the CDI main furler - perhaps there is something I haven't considered.

It's not JUST trailering if it's a mast furl.

Mast furls vs Boom furls:

Boom is lower and weight distribution is better
Sail Shape is poor on mast furler (20% decrease in performance!)
Booms have less reef line clutter

And this from Practical Sailor:

“There are other plusses—freedom from reefing-line clutter, variable sizing potential, automatic sail-covering, and the ability to retain your original spar, to name a few—but to us the most telling difference is safety: If an in-mast furler jams it's probable that someone will need to go aloft to free it. Until then, you'll be stuck with a hoisted mainsail in what may be exactly the wrong conditions.
A jam in the boom can be addressed from on deck. If all else fails, just drop the sail as you would a normal main and furl it on the boom instead of inside”

[bobbob]

There is no question there are sail shape tradeoffs. I don't understand your other two points:

Boom is lower and weight distribution is better - ???
Booms have less reef line clutter - There is very little clutter to the CDI main sail furler. The unfurling line runs along the length of the boom, down the mast and then can be run aft. The furling line runs partially along the boom, down the mast and then can be run aft.

With respect to jamming, this is not a consideration because it's not an in-mast furler. I see very little possibility that the CDI furler can jam.

But the original post was very specific that this furler dramatically complicates trailering, and I just don't have that experience at all.