So walk me through the in-mast furling mainsail

[David B]

Originally Posted by 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.

All my thoughts too - then we got a boat with Selden IMF.

Would not be without it now - take it from one who tried it and was converted!

[David B]

Originally Posted by thinwater

I love them. Or rather I love passing boats that have them.

Like this you mean?

https://youtu.be/L3f6REPF2RE?t=980

Any faster in that wind, and I'd need a fizz boat.
Just so easy - leaves more time to savour the joy of sailing.

[SteveSadler]

I've sailed 15k miles on slab reefing boats and 17K on my own in mast furler. The answer is clear, in mast furling is as simple as your headsails furler. But I didn't get a trial sail when I bought it so I made every mistake in the book. Then I read the directions! It's so simple and easy if you follow the DIRECTIONS! Now when my wife is on watch and sees a substantial squall closing in, she reefs without me and carries on. Oh it's blowing 40? I'll just roll it all up! I just sleep thru it. Yes you lose the roach area, so if you're beer can racing you lose the edge. But as a cruiser I could care less, I have a code 0 for light days.

[Dockhead]

Originally Posted by markiobe

I've never used one but they make my eyes bleed when looking at them.

The operative phrase being "I've never used one" -- I had similar prejudices before spending a few thousand miles with a properly sorted Selden in-mast furling system. They are mostly wrong.

Originally Posted by markiobe

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.

Furling mains furl the same as furling headsails, which are just as 3D. It is true that furling mains are cut somewhat flatter than full batten ones typically are, but that does not produce a "horrible shape". It means that they have less power in that particular wind range where you need an extra fat shape, which may or may not be a problem depending on where and how you sail. Flatter cut mainsails are MORE efficient in stronger wind, which can be a big advantage in latitudes where there is a lot of wind (probably one reason why in-mast furling is so popular in Northern Europe).

Originally Posted by markiobe

- 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.

You are completely confusing two different concepts here, center of effort and center of mass. Weight has nothing to do with center of effort. More weight aloft does have some disadvantages, but more heeling moment is not one of them -- the weight is balanced with more weight in the keel, and heeling behavior is the same.

Originally Posted by markiobe

- 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.

You have it backwards. More weight aloft produces BETTER, not worse motion. Why some sailors used to hang sandbags in the rigging to improve motion. More weight aloft requires more weight in the keel to balance it, and that's a disadvantage -- the boat weighs a bit more and that will take a bit off speed. But motion is better.

Originally Posted by markiobe

- 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)

You presume wrong on all counts. Vertical battens work well. For best possible shape, I would prefer long horizontal battens which smooth the whole shape of the sail, but vertical battens do the most important job of keeping the leech in shape, and are not a "kludge" at all.

Some "horrible" in-mast furling mainsail shape:

Originally Posted by markiobe

- 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.

Extra drag of the larger mast is definitely a disadvantage of in-mast furling. It is however only incrementally worse, not even really noticeable.

Originally Posted by markiobe

- 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.

You haven't been paying attention. A long list of advantages of in-mast furling were listed above; convenience is not the only and not even the main one. And you greatly exaggerate the negatives.

In-mast furling has some significant disadvantages, and the main one is lack of roach, which is a significant performance hit compared to roachy full batten mainsails. It is this, and not any kind of nonexistent "horrible shape", which is the main performance difference between in-mast furling mains and full batten ones. Except that not all full batten mains are roachy -- not everyone needs this advantage. Compared to a non-roachy full batten mainsail, any performance hit from in-mast furling is small to non-existent.

I wouldn't choose in-mast furling for mild latitudes, and especially not for smaller boats or casual coastal sailing like what many people do. But for offshore work in stormy higher latitudes (I've been to Northern Greenland with my in-mast furling boat, and crossed the North Sea something like 12 times), the advantages of in-mast furling become quite persuasive. In gnarly big sea conditions, in-mast furling is a Godsend. In very windy weather, like what we have up here in these latitudes quite often, there is no performance disadvantage, and on the contrary, since you have much better control over sail area with in-mast furling, doing much more active management of sail area, this can be a profound performance advantage.

My next boat will be custom built (I hope), and at the moment I'm thinking it will not have in-mast furling. I'm thinking a ketch rig to make the sails more manageable in size (the boat will be about 65'), and full batten main and mizzen. I might give single line reefing another shot (had a very bad experience the first time around). But I have not definitely decided yet. This boat will be metal and will be purpose built for high latitudes. In-mast furling has really big advantages for that use case so I haven't yet excluded it.

[Dockhead]

Originally Posted by David B

Like this you mean?

https://youtu.be/L3f6REPF2RE?t=980

Any faster in that wind, and I'd need a fizz boat.
Just so easy - leaves more time to savour the joy of sailing.

Well, Thinwater has an ultralight performance cat. He'll be passing ALL of us. I doubt if he notices any difference between the full batten and in-mast monos he blows the doors off of.

[bclaude]

My wife and I bought our first yacht in 2003, it was a Hallberg Rassy 48. I had similar concerns as those expressed in this post about in mast furling and Magnus Rassy, the owner of the company convinced me to go for in mast hydraulic furling. We sailed our HR 48 around the world and never looked back, not once did we have issues with our Selden/Furlex system. My big fear was being stuck with my main sail wide open in heavy weather. In reality that never happens. when you begin furling, there is a ton of room for the sail to fit inside the mast, it is only towards the end when most of the sail is in that if the furling was done in a sloppy manner that things could get tight but by then there is no danger as only and hankerchief is left out. If that happens you can just unfurl and start all over, no drama. Being able to have infinite reefing capability is a real plus. Our first sail had full height vertical batons and that turned out to be a headache because if the batons were not parallel to the mast going in , they would damage the sail pockets. When we replaced that first main sail we ordered it with short battens at the top of the sail and that is definitely the better way to go. Our HR was equipped with a hydraulic in mast fuller but a manual haul out. A winch was used to get proper tension in the haul out. On our new boat elected to have a hydraulic haul out in the boom and that turned out to be a mistake. In terms of convenience it is slightly preferable as I can use two fingers to at the same time unfurl my sail and adjust the haul out. In reality, more complication is rarely a plus on a bot and that turns out to be true for this as well. If I had to do it all over again, I would go back to the simpler "manual" haul out.

One of the benefit of hydraulic systems is that above a certain load, the system will slip and the risk of breaking something because of excessive load being applied is minimal. The noise the system makes when you furl and unfurl is a good indication of wether the loads applied are normal. If something gets jammed, the noise pitch changes and you can tell right away. That said in a storm, there is so much wind noise that it is difficult to tell. In those instances it is nice to know that the system will protect itself with the slippage of the hydraulics. Electric furlers have load switches as well that are supposed to achieve the same thing but in reality they are not nearly as reliable and IMHO they are more likely to let a miss use cause some damage.

My wife and I are in the process of completing our second round the world with our new boat. in most instances it is just the two of us on a 58ft yacht. Being able to furl, reef and adjust our sails from the protected cockpit and without risking one of us flying overboard is a mega plus. Do we loose a bit of performance compared to a traditional setup, perhaps but then who cares, we are cruisers and not racers.

As for in boom furling systems, I can see that in theory they may have an advantage. My sense is that they are much more expensive and delicate. I have seen MANY in boom systems being dismantled for repairs in boat yards along with owners waiting for parts for weeks. That never happened to us and I like it that way.

Altogether we have sailed our in mast furling yachts for over 100,000NM in all sorts of weather conditions and we never had any hair raising moments, quite the contrary. I would never go back to a traditional system particularly as the years go by and our agility on deck is not what it used to be.

[Paul_Carroll]

Just to throw it in there, I believe that the unit I used on s/v Delos, an Amel Super Maramu, is a custom Seldon unit made for Amel.

[Muaddib1116]

Originally Posted by Paul_Carroll

Just to throw it in there, I believe that the unit I used on s/v Delos, an Amel Super Maramu, is a custom Seldon unit made for Amel.

That may be true, but I don't think so. The Amel masts and drive units look very different from Selden. It certainly isn't white label. I suppose it's possible that Selden manufactures their IMF system to a totally custom spec, but I was under the impression that Amel did the fabrication themselves.

[mglonnro]

Originally Posted by bclaude

My wife and I bought our first yacht in 2003, it was a Hallberg Rassy 48. I had similar concerns as those expressed in this post about in mast furling and Magnus Rassy, the owner of the company convinced me to go for in mast hydraulic furling. We sailed our HR 48 around the world and never looked back, not once did we have issues with our Selden/Furlex system.

...

Altogether we have sailed our in mast furling yachts for over 100,000NM in all sorts of weather conditions and we never had any hair raising moments, quite the contrary. I would never go back to a traditional system particularly as the years go by and our agility on deck is not what it used to be.

Thank you for your elaborate post!

Regarding the performance issue, the difference would be most evident in light winds, right? Did HR give any quantitative figures for that?

I'm a big believer in the technology, but at the same time, I'm also a big believer in not starting the engine. My biggest fear is that I would loose too much of our low-wind speed.

[Dockhead]

Originally Posted by mglonnro

Thank you for your elaborate post!

Regarding the performance issue, the difference would be most evident in light winds, right? Did HR give any quantitative figures for that?

I'm a big believer in the technology, but at the same time, I'm also a big believer in not starting the engine. My biggest fear is that I would loose too much of our low-wind speed.

If you're considering an HR, I'm not sure it's even possible to buy one without in-mast furling. HR, like other high end Northern European boat builders, are all-in with in-mast furling.

As to light wind performance, it depends on what you're comparing, because neither full batten mains nor in-mast furling mains are all created equal.

The difference will certainly be noticeable if you're comparing a roachy laminate full batten main to any kind of in-mast furling main. A big roach makes a huge difference -- that part of the sail makes a wholly disproportionate amount of power. But how many of you are sailing with big roaches? the difference will be much less if you compare a laminate in-mast furling main with straight luff or slight roach, to an average full batten main with moderate roach. Performance of such an in-mast furling main may be better even in light wind compared to a Dacron full batten main with a couple of seasons on it.

If you are doing coastal cruising around the Baltic in a boat under 40', I would try to avoid in-mast furling, if I were you. The big advantages of in-mast furling are seen in offshore sailing. For your kind of sailing I would much prefer a roachy laminate full batten mainsail. Then you can milk the very last bit out of light summer winds and save the diesel.

For that kind of sailing, a nice light wind sail or two is also nice to have -- an assy, or a cruising Code 0, or both.

[nortonscove]

This is obviously an issue that is very polarizing and I doubt it will be changing any minds. Some of the the arguments on both sides have merit at least with the poster.

I'm on the pro side because that is what I have and enjoy. Some of the arguments are borderline laughable. If you think that cost plays a part of the reason companies are installing the system you are obviously not giving much thought to the boats now using inmast almost exclusively. If I'm in the market for a high end world girdling sailboat the least of my concerns would be the tiny fraction more or less incurred by furling type. Add to that the possibility that these boats are being bought by newbies ignorant of the intricacies of sailing and it doesn't pass the sniff test.

I think that you have to accept that things change and these systems are here to stay but you are welcome to keep the one you like based upon your obvious bias or knowledge.

[mglonnro]

Originally Posted by Dockhead

If you're considering an HR, I'm not sure it's even possible to buy one without in-mast furling. HR, like other high end Northern European boat builders, are all-in with in-mast furling.

True. As I quoted on the first page, they themselves say almost all 40ft+ boats are put together with Seldén furling.

Despite your good arguments (in that other thread), I'm still primarily a Hanse fanboy, but they too offer the in-mast furling and practically for the same price as the standard mast.

As to light wind performance, it depends on what you're comparing, because neither full batten mains nor in-mast furling mains are all created equal.

The difference will certainly be noticeable if you're comparing a roachy laminate full batten main to any kind of in-mast furling main. A big roach makes a huge difference -- that part of the sail makes a wholly disproportionate amount of power. But how many of you are sailing with big roaches? the difference will be much less if you compare a laminate in-mast furling main with straight luff or slight roach, to an average full batten main with moderate roach. Performance of such an in-mast furling main may be better even in light wind compared to a Dacron full batten main with a couple of seasons on it.

For the Hanse 458, the standard main is 57.8 m2, and the furling main 54.20 m2 (so ~6% loss there, Quantum composite sail).

If you are doing coastal cruising around the Baltic in a boat under 40', I would try to avoid in-mast furling, if I were you. The big advantages of in-mast furling are seen in offshore sailing. For your kind of sailing I would much prefer a roachy laminate full batten mainsail. Then you can milk the very last bit out of light summer winds and save the diesel.

For that kind of sailing, a nice light wind sail or two is also nice to have -- an assy, or a cruising Code 0, or both.

On our 388 we have a code 0 and love it. For the "next boat", I'd just like to get some idea of that we might be giving up on the light wind side.. I assume it won't be very noticeable in real life, but it would be nice to see some polars etc with some theoretical estimates..

[AiniA]

Let's assume that I go with IMF, what type of anchor would best complement this rig?

[Dockhead]

Originally Posted by mglonnro

True. As I quoted on the first page, they themselves say almost all 40ft+ boats are put together with Seldén furling.

Despite your good arguments (in that other thread), I'm still primarily a Hanse fanboy, but they too offer the in-mast furling and practically for the same price as the standard mast.

For the Hanse 458, the standard main is 57.8 m2, and the furling main 54.20 m2 (so ~6% loss there, Quantum composite sail).

On our 388 we have a code 0 and love it. For the "next boat", I'd just like to get some idea of that we might be giving up on the light wind side.. I assume it won't be very noticeable in real life, but it would be nice to see some polars etc with some theoretical estimates..

An advantage of Hanse is that you actually have a choice, unlike HR (or Oyster, Discovery, Contest, etc.).



A 458 is already big enough that you might consider in-mast.


But if I were knocking around the Baltic in such a boat, I think I'd prefer full batten, and with an electric halyard winch, and lazy jacks. And massive roach, laminate sail.



But if you ever plan to sail out the Kattegut, sail the old Viking routes, hit up Iceland, Faroe Islands, or cross the Atlantic -- that's a different story. In that case, in-mast may be your friend.


That's just my humble opinion. YMMV.

[Dockhead]

Originally Posted by mglonnro

. . . For the "next boat", I'd just like to get some idea of that we might be giving up on the light wind side.. I assume it won't be very noticeable in real life, but it would be nice to see some polars etc with some theoretical estimates..

If you choose a good laminate in-mast furling sail with vertical battens, and straight luff or modest roach, you give up nothing compared to an average full batten main.

But if you want ultimate light wind performance, choose a massive roach laminate full batten mainsail. No in-mast furling sail can match that.

And tip No. 1 -- furling, not furling, whatever system -- just don't ever buy a dacron sail again. That's the single best thing you can do for your sailing performance. And sailing fun.