Question about sails that came with my boat

Scott T-Bird · Mar 16, 2015

I would go on-line and search Bacon's (or similar sail consignment shop) for a used jib if you want to economize. Otherwise, shop for a new sail. The 170 genny is probably too large for everyday use and trying to retrofit a mainsail is just too much trouble to be worth it ... especially if it is as old as you think. Reefing the 170 (if you purchase a reefing furler) will result in a lousy shape if you reef all the way down to 110 or so. For a few hundred bucks you can probably find a perfectly good used sail that you can use for the majority of your sailing. Then take the 170 out when the breeze is suitable so you don't rapidly destroy its shape by flying it when the wind is too strong for its purpose..

Charlie Jones s/v Tehani · Mar 16, 2015

I agree with Scott on the jib.. Also, on the mainsail question- no- the two sails are cut totally differently. It could probably be done, but would result in a crappy sail.

Oh, and that bolt rope was undoubtedly dacron, not cotton

Ken Cross · Mar 16, 2015

It kind of depends on where you live and what the normal winds are. If you typically have light winds, I'd raise the big one. You can always roll it up and motor in.

I never liked changing sails on a furler. Having said that I love the convenience of just rolling it out. I tend to go a bit smaller jib size, and then if I really need so I can roll some up to reef it. As a cruiser it seems to work well for us.
Ken

caguy · Mar 16, 2015

Don't throw away that furled or give up on it just yet. It will serve you well in light wind and if the winds pipe up to 15-25 its you will have more wind and sail than you need even if the shape is less than optimal. On the Mac25 and on the Cat27 I sail up to 15kts with a 150 Genoa. I wish that I had had one on the Mac25, my PVC furler worked well but was a PITA to take down for trailering.

Calif. Ted · Mar 16, 2015

Here are the sailplan measurements as listed on Sailrite's database.
http://sailritesails.com/ShowAd.aspx?id=4321&SourceID=%200%20&BoatName=O'DAY+22+(OLD)+1979+AND+PRIOR
I'd measure the foot of that 170 to make sure it's really that big and if it's on a furler why not try it out, apparently the previous owner thought it was a good idea.
I suggest measuring because the foot of a 150 would be 14.5 feet and that's quite a bit for a 22' boat.

Scott T-Bird · Mar 16, 2015

The leach is going to tell you how high the clew is. If the leach is significantly shorter than the luff, then the clew is very high, like a "yankee" cut. If the leach is about the same length as the luff, it is a "deck sweeper". Personally, I prefer a lower clew for better performance but many like a higher clew for visibility under the sail.

Technically, the dimension of the foot relative to the "J" dimension isn't the overlap percentage. You must determine the dimension of a line from the clew to the luff of a line perpendicular to the luff to determine how far the overlap is relative to "J". That's a shape that is relative to the length of the leech and the foot.

If you are given the dimensions of the luff, leech, & foot, you can use geometry to figure out how high the clew is and the overlap in percentage. Or if you know the luff, leach and overlap, you can alternatively determine the foot and draw a picture to describe the sail.

The belly is going to be determined by the sag in the forestay, which is based on a specific tension for a specific wind strength (generally speaking). Sails will be cut for a "normal" condition. When the wind strengthens, you want to reduce sag with backstay tension because if you don't the belly in the sail will become excessive. If you can't tension the backstay, then the alternative is to reduce sail area (or struggle with excessive sag on a larger sail). Basically, sails are not really cut for more or less "belly". They are cut for the sag of the forestay under "normal" circumstance.

Joe · Mar 16, 2015

The foot dimension has nothing to do with sail size. As you all know, sail size is expressed as a percentage relationship between the area of the head sail and the area of the boat's fore triangle.

The sail's sq ft area is measured geometrically, using the luff (L) as the base of the triangle and a line perpendicular to the luff (LP) as the height measurement. The boat's fore triangle area uses the "J" and the "I" dimensions.... "J" is foredeck length from stemhead to mast base, "I" is the hoist, or distance from mast base to halyard block on mast.

so: Sail Size = Sail area / Fore deck area

where sail area = 1/2 L x LP and Fore deck area = 1/2 I x J

this relationship can be further simplified by comparing the sail's "LP" with the boat's "J" .... since they both represent the height of two triangles that share a common side (luff and forestay).

Thus: Sail Size = LP / J

Note that a 100 percent jib, where the LP and J are the same, will still have some overlap....... depending on where the clew is cut. A non overlapping sail would most likely have an LP somewhat less than the J ..... or a size less than 100 percent.

If you experiment with triangle shapes laid over a drawing of your boat's foredeck.... you can see that the sail's leech (trailing edge) length has a huge effect on where the LP intersects the luff..... So the LP and foot are often very different lengths. The leech dimension essentially determines the "cut" of the headsail.... as Scott mentioned it directly affects how high the clew will be above the deck.

Most cruisers and daysailors will prefer a higher cut clew, which provides greater visibility and doesn't trap water if it comes over the deck. Since a low cut clew will be next to impossible to see under, the sailmaker will often sew a window into the sail near the luff.

Joe · Mar 16, 2015

davidmhull said:
Another question is if anyone has ever had a mainsail modified to be a working jib (may be a really stupid question)?

You could take it to a sail loft for their opinion. But I would think you could sell it to help pay for the new headsail. The shape of the main is roughly a right triangle..so ... if you flipped it around backwards, sew hanks on the leech and remove the bold rope from the luff.... it might fit... but please, don't tell anyone you heard that from me.

Charlie Jones s/v Tehani · Mar 16, 2015

Joe said:
You could take it to a sail loft for their opinion. But I would think you could sell it to help pay for the new headsail. The shape of the main is roughly a right triangle..so ... if you flipped it around backwards, sew hanks on the leech and remove the bold rope from the luff.... it might fit... but please, don't tell anyone you heard that from me.

Good lord, what a mess THAT would be.!!!

Charlie Jones s/v Tehani · Mar 17, 2015

I have Genoa from Rolly Tasker, and have been extremely pleased with it. Quality work.

Ron20324 · Mar 17, 2015

Did you look online at Bacon's for what they have?

Scott T-Bird · Mar 17, 2015

Very strange ....

davidmhull said:
Thanks for the explanation of the sail dimensions Joe and Scott. I am still having some trouble finding out what the actual dimensions were for the OEM jib. The chart that Ted referred me too is different then the other dimensions I have seen. I'm not saying it is wrong because I don't know at this point and I do thank you for sending me the reference Ted. Perhaps I am reading it wrong or one chart is for a fractional rig or something. I have included the chart to indicate where I am confused. One source I found indicates that the OEM sail was luff=20.18' leach=18.18' and foot is 9.1'.

None of the used sails are exactly the same as the OEM and the prices are all over the place. Thanks so much for your help guys.

First things first because I find the data to be confusing. Sailrite indicates that you have a masthead rigged boat with "I" dimension of 24.0' Sailboatdata.com shows a 1972 fractional rigged boat with "I" dimension of 22.0'. There also seems to be a 1972 masthead rigged with a "tall mast". The 1973 model is masthead rigged with the dimensions referenced in Sailrite.

You should first verify which one is correct ... I tend to trust Sailboatdata, but I don't know the particulars for your boat. If you have any question, let us know. You may be finding a wide variety of used sails based on these differences. You will have to weed out the choices that don't apply.

Secondly, study the definitions of the P, E, I, J dimensions. They are your rig dimensions, not the sail dimensions, particularly for the head sail. Sailboatdata indicates that your forestay length is 23.42' for fraction rig, 25.63' for masthead rig. This does relate to the luff of the jib or genoa. But remember that the luff of the sail will necessarily be slightly less to accommodate fittings, furlers, etc.

You will find used sails of various luff lengths that will work (all shorter than your forestay length). If you choose a new sail, the manufacturer should have your dimensions to make the luff according to your requirements.

I would not worry too much about the OEM specs for the original sails. If you buy a new sail, the important thing is to have it made to the specifications that you desire. If they have pre-cut sails and all you are doing is specifying the overlap percentage (like 110%, which is typical for an OEM sail), you should be fine as long as you verify the rig dimensions. I'd hate to see a mistake based on the confusing issues that you are noticing.

Look on-line at Sailboatdata.com for your model of O'Day if you have any question about these issues. Plus, there are plenty of O'Day owners in the O'Day forum that should be able to clarify.

Calif. Ted · Mar 17, 2015

Looks like Scott covered it, if unsure the best method is to run a tape measure and see for yourself what you got.
I'd suggest trying the sails you have on a nice day, you can always furl it back in if it presents a problem.

Joe · Mar 17, 2015

Scott's explanation should be really helpful to you....

Throw those charts away that you posted earlier and use your own data. PERIOD. Do your own measuring..... presto! no more confusion.

Go to this site and follow their instructions... http://thesailwarehouse.com/cgi-bin/web_store.cgi?page=storeframe.html&cart_id=

Oday 22 masthead rig... Standard OEM type jib 110% Luff 22.8 Leech 20 LP 9.35 5 oz Dacron OEM quality (lowest) with hanks price is $335

a 150, same quality, will run you $475. Luff 24.25 Leech 23.00 LP 13.50 Cloth weight 4.00 Hanks

Is it clear that the smaller sail has a shorter luff, allowing it to be hoisted a foot or more off the deck for visibility(using a tack pendant), or tacked at deck level and not fully hoisted.... your choice. The 110 working jib has heavier cloth than the lighter weight 150 genoa which is for lighter air.

Question about sails that came with my boat

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