So walk me through the in-mast furling mainsail

[Dockhead]

Originally Posted by Muaddib1116

That definitely is the biggest risk/fear with IMF, but he did a lot of things wrong. Aside from having a crazy boom angle and letting the sail flap around when furling, he indicates that at some point he accidentally released the halyard tension. What's also crazy to me, is that he turned into the wind to furl the main (this is something a few people in this thread have also mentioned doing). I don't know if that's wrong, per se, but it seems to me that it's much easier and you get a much tighter wrap, if you furl the sail with some wind in it to control it's shape and tension as it enters the slot. This is something I came to well before I even took ownership of my boat, after reading a lot about IMF. Even when furling a genoa, using the sheet to maintain some wind in the sail makes it easier to furl, compared to pointing up wind and letting the genoa flap about. It only ever seemed to make sense to point into the wind to reef/drop a slab reefed main. It even seems like it would be advantageous to have some wind in the sail when furling an IBF sail, but I don't know enough about that.

This makes me really glad that my boat came with a batten-less mainsail as my first IMF system. It is surely much more forgiving. Perhaps after a few years of experience, when it's time to replace my main, I'll go for a vertically battened laminated main. Perhaps not.

Yeah, I think that kind of cluster fumble is not uncommon when people are first learning how to use in mast furling. I had a very similar experience in my first year with in-mast furling. I learned a lot from that case and never experienced a serious jam again.

One really serious misunderstanding about in mast furling that people have (who don't know the system) is that it's some of dumb simple system. It on the contrary requires significant skill.

What I hope that guy learned:

1. Boom angle is critical. If you have the boom angle wrong, the sail will not wrap smoothly at one end or another, usually the top. Which is the correct angle depends on the cut of the sail, but normally it should be exactly horizontal.

2. Do NOT head up to furl. Opposite of slab reefing. You need some wind in the sail for smooth furling; you do NOT want to furl with the sail luffing. Not too much wind in the sail, not too little -- the sail should be depowered by slacking the main sheet (with vang on to control boom angle) but not so much that the sail is flapping. Same with pulling the sail out. You want some wind in the sail when it's coming out.

3. Keep just a bit of outhaul tension on, but just a bit -- just enough to keep folds out of the sail and no more. Don't overdo it.

4. When rolling the sail out, it can be good to roll out the furler as you are putting on outhaul. Counterintuitively, you want the roll inside the mast to be slightly loose. But only slightly, if the roll loosens and expands to fill the mast, you will have problems.

5. Feel what's going on when you're furling in and STOP if something is not going smoothly. You CAN feel it, and if you stop right away, you cannot have a bad jam, even if you make some mistake. I think this is probably the most important point. And the reason why most owners of in mast furling boats end up having exactly one jam is that once you've felt that happen even once, you just never do it again.

6. Do not accidentally let the halyard off In general with in mast furling, you never touch the halyard except to adjust luff tension.

7. This is optional, but for easier furling, do it on a starboard tack (Selden; others may be the other way). The sail then goes straight onto the foil, rather than getting turned by the slot. Reduces effort by about one half.

All this gets to be second nature with a certain amount of experience.

[DMF Sailing]

Originally Posted by mglonnro

Here's a video with some IMF challenges on a new Hanse 418. Elvstrøm sail, Seldén furler.

I love the honesty of this guy, and his willingness to make his misfortune a learning module for others

[mglonnro]

Originally Posted by DMF Sailing

I love the honesty of this guy, and his willingness to make his misfortune a learning module for others

I agree!

(He is a Hanse owner, of course, so it comes naturally )

[chrisr]

Originally Posted by Hoodsail

Somewhat still on topic - with in mast furling do you still carrry a try-sail for heavy weather? Or is it redundant given the ability to shorten sail into the mast? Thinking to qualify for offshore races, Newport to Bermuda or Marion to Bermuda. thnks

in australia to qualify for cat 1 i believe that the boat would still need to carry a trysail...and more importantly be able to set such a sail even with the mainsail rolled up. this could be quite complicated eg a track on the mast, another halyard etc.

other countries may have different rules

cheers,

[Dockhead]

Originally Posted by chrisr

in australia to qualify for cat 1 i believe that the boat would still need to carry a trysail...and more importantly be able to set such a sail even with the mainsail rolled up. this could be quite complicated eg a track on the mast, another halyard etc.

other countries may have different rules

cheers,

I have a spare main halyard and a trisail track on my Selden mast; I am pretty sure that all Selden in-mast furling masts have that.


But I've never known anyone who carried a trisail on a boat with this system unless they were required to because of racing rules. You can roll these down to just a little scrap and it works well as a storm sail.


My boat likewise has a self-tacking staysail cut of heavy cloth and set on a heavy duty furler, a Furlex S400 which is the same furler used by the principle headsail. It is specifically designed to be used as a storm jib and works really well in that role. And it's really good that the whole rig is self-tacking when in storm configuration -- one less thing to worry about when you're battling a storm.

[edexter]

Our little Rhodes 22 has in-mast furling main and a giant 170 furling genoa. Being the Chicken of the Sea, and having a centerboard lifting keel, not some large ballasted keel, I really like being able to shrink our sails but keep them balanced when the wind picks up. We're not racers, just poke around the upper Chesapeake mostly on the weekends, so we go out even if it's small craft warnings because we want to go out when we can, and being able to balance the thing without standing on my ear or having to try to reef something quickly while avoiding traffic is handy and safer - just pull on the line over my head, and in she goes.

[markiobe]

I've never used one but they make my eyes bleed when looking at them. In no particular order:

- you cannot get a nice sail shape that will furl properly so you have to compromise on the shape which means you need more area for a given amount of power, horribly inefficient. Remember a sail is (should be!) a 3D shape and you're asking it to furl as if it were 2D. It's acceptable in headsails as the furling allows some more space but still isn't ideal.

- one of the reasons to reef is to reduce weight up high to bring the whole c/e of the sail plan down thus reducing heeling moment. Mast furling keeps that weight up high reducing the advantage you're getting by reducing sail.

- tons more weight as, I don't know the stats, but the furling system must double the mast weight up high? And this is even when not furled, making the boat's motion worse ALL the time.

- horizontal battens help maintain a good sail shape, I can only presume that vertical battens are a very poor attempt to try to maintain leech shape, but they seem like a total kludge. The issue is that you probably need something to try to prevent leech flap because of the crappy sail shape required by the furling system in the first place (first point)

- in addition to weight, the mast also has to be of a much bigger diameter affecting drag but also airflow over the mainsail. Round masts are bad for airflow anyway, increasing the diameter deliberately just seems like madness. Again the result would be a need to increase sail area for a given power requirement, a lot of which is doing nothing but adding drag therefore more heeling moment, less propulsion.

- the purported advantage appears to be convenience and literally NOTHING else. However that assumes it works perfectly all the time. When was the last time that anything on a boat worked perfectly all the time? Good luck trying to fix a jam at the top of the 18m mast in a big sea with too much sail up...

It seems to be a 'convenience trumps everything' approach which totally tramples all over the idea of a good sail shape, weight distribution, drag etc. etc. I totally get the need for compromise, we're not sailing racers after all. However IMO this is waayyyy too far over the convenience end, as the negatives are simply massive.

[twohapence]

I had in boom furling and it was hateful. Slow to reef and significant effort to wind the sail in and out.


I've used in mast furling. It was convenient but the sail shape was awful and there was no roach. However I sat and watched someone spend three hours trying to get a jammed main out of the slot. Happily they were able to get into port to do this - it wouldn't have been easy at sea and could have been downright dangerous.


Yes, I know. It all works perfectly if you RTFM. I still prefer the simplicity of slab reefing. It's quick, easy, and there's precious little to go wrong. KISS!

[charliepsycho]

I have in-mast furling on my Calisto 385. Once you get used to it, then it is fine.

We got the sail jammed in the mast within the first week of ownership as newbies, basically it was all wrinkled up, once we realised this we watched it in and out. We keep a little tension on the out-haul and have never had a problem since.

In terms of sail area, we just have a taller mast (most furling systems just have a bigger sail to compensate for the loss of roach)

This is not a race boat, it's a cruiser. Convenience and storage space are the priorities!

Fair winds...
...(c)

[Paul_Carroll]

I was never a fan, for all of the varied reasons mentioned previously. However, after crossing an ocean on Delos, I can definitely see the advantages. It really is an important safety device for the short-handed cruising boat. The ability to quickly, easily, and safely reef (or un-reef) sail from the cockpit is worth all the hassles. On a night watch there is never the question of "Do I wake the crew to help shorten sail, or hope that this is just a brief gusty moment and it will pass in a few minutes?" All too often that proves to be just the beginning of the wind really picking up and by the time you do decide to wake the crew, things are MUCH rougher.
As a mechanical engineer, what impressed me about the furler on Delos was that it was robust, almost to the point of ridiculousness, and the slot on the mast was HUGE, and the clearance between the furled sail and the mast substantial. Also, all the motors and gearbox were external, so could be easily accessed and serviced by the average cruiser. This system is custom build for Amel. My personal preference would be for a similarly robust in-boom furler, just for the better sail shape possible. There are many systems out there that present a very clean and tidy appearance, but are a plain nightmare if ANYTHING should go wrong. And it does. At night. When the wind is howling. And there is a reef under your lee....

In short, done right and very carefully, I think they are a HUGE boon to cruising comfort and safety. Done the way most systems are, I wouldn't even take them day sailing.

[Bluechart]

I’ve taught sailing on SF Bay for the past 10 years on a fleet of 6 ~40’ boats with in mast furling. My boat is a Beneteau 49, with in mast furling.

Here is what I’ve learned .

Always make sure you are within 10 degrees of the apparent wind when furling and unfurling. (Set your autopilot to ~5, 8, etc. degrees with engine slow ahead (if that is sufficient for the current wind and sea state ) We’ve had many jams when students furl or unfurl on a reach!

MainSails with battens (usually built in bulk for sailboat manufacturing) frequently have vertical pockets that are NOT parallel to the mast , and cause battens to become twisted, rendering furling with battens impossible. If your battens are bent or twisted, do not use them.

I recently had a new mainsail built, beautiful shape, positive roach, vertical battens (~5’ each) . The only problem I’ve had was trying to furl or unfurl at the dock when the sail was new. We had to leave the harbor, and anchor, to keep the boat head to wind, while installing and playing with the new sail.

As with previous comment, everything should be slack, mainsheet, vang, slight tension on out haul when furling, obviously more when unfurling and setting the out haul.

[Paul Carey]

Have had mast furlers a) from new on our Broadblue 385 with Z-Spar furling system ,, initially it was impossible until origonal supplied mainsail replaced & then fine , provided ALWAYS KEEP BOOM RIGHT ANGLES (90 DEGRESS) TO MAST ..b) Our current much older Catalac was retrofitted by a former owner with a piggyback furler made by 'colnbrook' on back of origonal mast, this has vertical battons in the sail & again the right angle rule applies as well as being sure battons are parrallel to mast, this is made easier by also having a kicker (cunningham ) 'vange' on the boom . it's a peach to operate..On both boats the prime motive was safety with no climbing about on coach roof in rough conditions , all sail managment achieved from cockpit ...

[nortonscove]

Originally Posted by Hoodsail

Somewhat still on topic - with in mast furling do you still carrry a try-sail for heavy weather? Or is it redundant given the ability to shorten sail into the mast? Thinking to qualify for offshore races, Newport to Bermuda or Marion to Bermuda. thnks

I don't. Can't speak for anyone else but I've never felt that need.

[Happ]

Let’s start with the basics of an in mast furling. First there is a specific tack you need to be on when you furl it. Most people don’t know this. On one tack you are rubbing the sail against the side of the luff. The other you are furling the sail in the middle of the luff.

One of the reasons the boat builders use in mast furling is it is cheap! Not much to the mechanism and the sails have no battens. Cheaper to build. The negative is the sails blow the leach out really quickly and you can’t get a lot of shape in the main. This would be my last choice.

An in boom furling system is more expensive. First the main sail is full battened. Costs more. It is highly recommended your main sail halyard winch is electric. This is from the manufacturers. Then the mechanism is more complex. This would be my 2nd choice on a boat 40’ and under. Preferable choice in boats over 45’.

My first choice is the tried and true Slab Reefing. I would add Lazy Jacks to contain the main. I would still have a full batten main built with frictionless rings instead of traditional cringles. I’d go one step farther and have single line reefing. Done right you don’t have to leave the cockpit. My FIRST CHOICE!

[Dockhead]

Originally Posted by Bluechart

. . . Always make sure you are within 10 degrees of the apparent wind when furling and unfurling. (Set your autopilot to ~5, 8, etc. degrees with engine slow ahead (if that is sufficient for the current wind and sea state ) We’ve had many jams when students furl or unfurl on a reach!. . .

Your system may be different from mine, so YMMV, but one of the really killer advantages of MOST (at least) in-mast furling systems in gnarly offshore conditions is the ability to reef or unreef on any point of sail, including DDW, without changing course.


This is a HUGE advantage in big sea conditions.


To reef or furl on a reach, put the vang on, then slack the main sheet until the main is mostly depowered. Then furl. The sail may go onto the spreaders as you let off the outhaul, but if your spreaders are properly prepared this is of no consequence.


This works fine on the favored tack (starboard with Selden) but will also work on the other tack.