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New Sails Dimension Discovery

Oct 29, 2016
1,743
Hunter 41 DS Port Huron
I am having new sails made for our Sapphire and stopped by the loft to see how things were going this week. The owner and I went over the mainsail 3d graphic of which they send to their panel cutting machine (like a CNC machine), during that conversation he mentioned a peculiarity in the dimensions of my old sail and the Sailboat data sight (as well as a couple of other sites including the sail pattern software), seems my old sails luff is almost 4' shorter than the sail pattern that he is building the sail from. He was making adjustments to match the old sail and wanted to inform me of this difference.
Now the Sapphire is a 2007 model year and when purchasing this boat no mention was made on the change to mast height, I know there is no recourse with the previous owner (purchased the Sapphire in Sept 2016) and to be honest I really don't think the PO even knew there was an adjustment made to the mast height. The PO purchased the Sapphire in its second year of life (originally named Windsong) from the original owner in Massachusetts who I am told didn't use her as evident by the less than 50 hours on the clock.
The only reason I could think of for shortening the mast would be to ensure bridge clearance. I have asked the race committee to make adjustments to the boats rating based on the sail area reduction, we will see in the spring was the response I received.
 
Jan 11, 2014
7,634
Sabre 362 113 Fair Haven, NY
An interesting mystery! Sailboat Data shows the Hunter 41 DS with a fractional rig, does Sapphire have a fractional rig? Is the headsail also smaller?
 
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Oct 29, 2016
1,743
Hunter 41 DS Port Huron
@dlochner as pictured here not near and fractional as sailboat data show it the luff of our Sapphire is P=46.8' not the P=50.67 as it should be for a furling rig, for a loss of 38 ft2 of sail area. The jib measured as indicated in sailboat data and hunters owners manual.
Sapphire S.jpg
 
Jan 11, 2014
7,634
Sabre 362 113 Fair Haven, NY
The in mast furling may be your answer. With a fractional rig, it easy to bend the top of the mast back. Inducing that bend might interfere with furling. The solution was to make a shorter mast with a masthead rig. Is the boom longer? If so, it might have been lengthened to get the same sail area.
 
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
@dlochner the sails foot dimension is 19.5 as stated on sailboat data site and the Hunter manual. I guess your reasoning as it relates to the furling system is plausible, sacrificing 7.6% of the mainsail area to allow ease of furling operation, does that sound reasonable, I am not sure.
 
Jan 11, 2014
7,634
Sabre 362 113 Fair Haven, NY
Perhaps you could contact the furler manufacturer and ask.

The 7.6% sounds like a lot. however that would only make a difference in light air and the reduced sail area may make the boat faster as there would be less heeling force in a stronger breeze. Once the winds became strong enough to reef, that 7.6% doesn't matter, in fact, it may delay reefing a little bit. So, overall it probably doesn't make much difference, unless you are racing PHRF with a rating based on the standard fractional rig.

Not to induce too much thread drift, but the biggest flaw in PHRF is that ratings are based on classes of boats and not how how an individual skipper sails his boat. It is like getting a golf handicap based on the brand of clubs you use. But that is another rant. :biggrin:
 
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
@dlochner I have come to the same conclusion as it relates to boat performance related to the mainsail area reduction, especially since the area reduction diminishes towards the center of effort. I am still reefing the main when it starts to blow over 18 especially if its gusting and as we know that when the winds picks up there are always gusts.
As for the rating methodology you may have a point but it is a different game which involve far more moving parts.
 
May 17, 2004
3,374
Beneteau Oceanis 37 LE Havre de Grace
It is an interesting puzzle. Looking online for other pictures of 41 DS's I did see one or two that look nearly masthead rigged like the picture you showed, so it may be original and not custom. I also found an ad for a 41DS Spinnaker that said it was for the roller furling main, so maybe the rig is designed differently for that. I've found that sailboatdata doesn't always completely capture every OEM configuration.

Beneteau does manage to put roller furling mains on fractional rigs, but they are usually higher fractions than Hunter, and they're not B&R rigs, so maybe that makes a difference.

Are those full height vertical battens in the picture you showed? That's a good way to help manage the amount of sail area lost in roller furling mains.
 
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
Yes the vertical battens (1/4" dia carbon fiber rods) do help keep the sail shape. The new sail will have (4) battens along the leech vertically oriented as opposed to the full length battens shown in the photograph. The sail loft has indicated that there will be a couple things that come out of this change, improved leech edge stiffness and it should help mitigate any furling issues caused by the full length batten, we will see.
 
Jan 11, 2014
7,634
Sabre 362 113 Fair Haven, NY
As I think about this some more, the bigger loss of sail area is not from the shorter luff, but from the flatter roach on the mainsail. The big advantage to a B & R rig is it allows for a large roach which increases the driving force of the mainsail. The in mast furler does not allow for the larger roach.

Where's @Jackdaw? He'll have a better understanding of this.
 
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
@dlochner The attached certainly shows the main with a great deal of roach, but it also appears there is a lot more bend in the mast, more than a furling system could deal with, so I would guess the depicted is a standard rig.
hunter_41 Roach.jpg
 
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Nov 8, 2010
11,385
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Interesting stuff!
Its clear the the RF main version uses a mast that has been shortened above the hounds, reducing mainsail area while leaving jib area the same. If is by far the cheaper way to do this, but it robs the RF rig of sail area.

I think the key is the B&R rig, which will add a fair amount of pre-bend in the static 7/8ths mast setup when setup with the proper rig tuning to support the larger mainsail. This amount of pre-bend will give the roller furler main fits, so they cut most most the mast above the hounds off, which creates a 9/10 (or maybe even more) rig which combined with the smaller mainsail would not require as aggressive a rig tune, resulting in a straighter mast.

As others have alluded to, the 7/8 factional is falling out of favor with designers who see 9/10s as having all the benefits of a factional rig with none of the downsides.

hunter_41_ds_photo.jpg
 
Jun 25, 2004
1,108
Corsair F24 Mk1 003 San Francisco Bay, CA
To the OP:
Did you or the sailmaker remove the mainsail and measure the rig? What was the dimension for the max hoist of the mainsail, using the halyard and a tape measure.

To determine the max luff, you have to measure the hoist with a tape. Also, what brand and model is the mast. You need both of those pieces of info to design a sail with the correct luff length. You shouldnt depend on the dimensions of the old sail.

Furling mains must be cut flatter and with smaller roaches than the typical Hunter B&R rig, to reduce the bulk of the furled sail and the risk of jamming. Adding vertical battens helps increase the sail area, but increase the chance of jamming and importance of annual inspection and maintenance. Bulk is a bad thing in a furled mainsail.

Stretching increases the chances of jamming too, so you should buy the lowest stretch sail you can afford. Cruising laminates and molded sail are arguablely worth the extra expense, because stretched out furling mainsails jam much more frequently.

The standard rule of thumb is that a furling mast B&R on a Hunter (at least those with Selden Masts) can't have more than two inches of bend tuned into it, or else it will jam.

Your furling mainsail should entitle you to an adjustment of at least +3 seconds compared to a standard rig mainsail. But ask your local PHRF authority.

Judy B
Sailmaker
 
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Oct 29, 2016
1,743
Hunter 41 DS Port Huron
@DrJudyB I am not a sail maker nor the sail maker son, I am not trying to challenge you, I am just wondering why a sail could not be measured and those dimensions used as the basis for a new build?
The furling mast is by Selden and until toward the end of last season I had no trouble with the system. The mast appears to have at least 5" of bend. I am looking at tightening the lower shrouds to mitigate this issue. I noticed that the lower lee side shroud while sailing is too loose ergo the first step in eliminating what I feel is too much bend in the mast.
 
Jun 25, 2004
1,108
Corsair F24 Mk1 003 San Francisco Bay, CA
@DrJudyB I am not a sail maker nor the sail maker son, I am not trying to challenge you, I am just wondering why a sail could not be measured and those dimensions used as the basis for a new build?
The furling mast is by Selden and until toward the end of last season I had no trouble with the system. The mast appears to have at least 5" of bend. I am looking at tightening the lower shrouds to mitigate this issue. I noticed that the lower lee side shroud while sailing is too loose ergo the first step in eliminating what I feel is too much bend in the mast.

@DayDreamer41
It's far better to measure the rig, to ensure the sail performs properly, than to rely on measuring an old sail.
The previous sail may have been smaller than needed for the rig.
Sail cloth both shrinks and stretches over the life of the sail, depending on the construction of the laminate or weave of the dacron.
The previous sail may have been made to a different purpose than the OEM sail, or specifically for your purposes.
The previous sail may be shorter for who knows what reason.

If your mast is original, you have a Selden F section furling mast, Their eingineers recommend a MAX bend of 0.5% of the Max sail space (usually just a little bigger than the P dimension) for their furling F sections. For a 50.67' max hoist, max bend would be 3".

I would start with a mainsail design for 2" of bend. You can retune the rig and increase it to 3" as the (dacron) sail aged and the draft stretched out or if you wanted a less powerful shape. Putting more bend in the mast will allow yu to flatten the draft.

We want the draft in the mainsail to be shallower than a standard mainsail, so that it rolls up without wrinkles. (For a laminate, the sail designer would account for stretch slightly differently, since laminate shrinks when it's new and it doesn't stretch as much over the long term.)

The max luff for your mast section is measured by attaching a tape measure to the shackle on the bottom of he the upper swivel and hoisting the tape up to max height. Measure down to the attachment point at the bottom of the furler. Subtract 120 mm (4.75") for webbing loops at the head and tack. That's your maximum practical luff length. Selden calls it "Max. sail space" in their technical literature. From a practical point of view, that's your "P" dimensions, because the builder doesn't want to pay for a mast thats longer than it needs to be.

An experienced sailmaker may tweak the dimensions but the maximum dimensions are determined by the manufacturer. The luff (or foot) can be designed shorter, but I would install a pendant at the head so the upper swivel goes to the top of the mast, rather than have the upper swivel significantly lower (because it will chafe on the inside of the extrusion).

Hope this helps,
Judy
 
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capta

.
Jun 4, 2009
4,285
Pearson 530 Admiralty Bay, Bequia SVG
I recently replaced a radial cut IMF main with a standard cut sail, and I believe it was a big mistake. They also put way too much belly in the sail; I agree an IMF main (or mizzen) should be a flatter cut. Next time I will go with both a flatter sail and a radial cut if I outlive this sail.
We had the sailmaker come to the boat and take the dimensions. No computer approximations for us. Since we never race and almost always sail reefed, we did not want battens. Every IMF system I've known that had consistent problems had either a very baggy sail, or battens, sometimes both.
 
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
@DrJudyB thanks for your detail explanation I have sent a note off to the loft to advise that they/I need to get a couple of dimensions from the rig prior to them starting the said. Hopefully we can get this sorted out and sail done by the time I launch next month, the problem being the boat is under canvas and it will be tough to get a measurement, but I think it is possible just a pain as I will have to loosen a bunch of ties unzip the cover at the mast which should give me enough access to run a measurement. I will talk with them about the cut of the sail as it relates to furling, they have mentioned they are well aware of rig prebend and the issues which will cause a furling main to be difficult.