Storm sail dimensions?

[Seaslug Caravan]

Ok Madwand can you frame your question more clearly.

A/ are you saying you want a genuine STORM JIB.

B/ You want to know the exact measurement of said sail. ie luff 'leach' foot.

C/ you don't understand where the % figure comes from.

or D/ you require a smaller headsail for stronger winds and not a STORM JIB at all.

??
Storm force..... 48 to 63 knots

[UNCIVILIZED]

I'm not sure if this will help, but below is a quick way to get a ballpark idea of how large a sail should be for your boat based on a given wind strength.

You can do the math in order to optimize the size of the sail to best match up with the winds it'll commonly be used in. Which is a good way to figure out how large the sail should actually be if you don't have the performance of sisterships with small jibs to compare her to.
It's also wise to discuss sail sizes with your sailmaker, who'll likely have a database of info on sail sizes & combinations for heaps of similar boats. Which will help in removing most of the guess work from sail sizing.

In general terms, sit down & figure out how big your current jib is. Where it's center of effort is. And what wind strength it works best in, without the boat being overpowered, or underpowered.

Also ask yourself how many/what size reefs you take in the conditions that you're trying to re-tune your sail plan for. And how well your boat goes to weather in such conditions, including if she's tender, in terms of heeling, or if she gets overpowered easily in puffs, or when the wind speed climbs by 20%. Plus, what kind of leeway she makes, & how well she does punching through head seas.

Looking at all of this, you'll then do the math in order to figure out how many square feet the jib should be as compared to some of your other jibs, based on wind force vs. sail area.
Force measured in lbs, Sail Area in square feet, Wind Speed in knots
Force = Sail Area x Wind Speed squared x 0.00432

You'll want to take this number, & use it along with the location of the sail's center of effort (to include the CE's height about WL) in order to calculate the sail's heeling force. Which in simplest terms equals Force x Height of CE

Armed with this number for the force needed to heel your boat, you can then approximate the size of your high wind jib, based on various sizes for it using the wind strength that you want to use it in. Factoring in the height of this sail's CE.

This is where the factors about how your boat handles in a breeze come into play. Since if she's stiff, upwind, & doesn't make much leeway, then you'll likely want to error a bit on the large size for this new jib so that you have a bit of extra power to punch through seas when going upwind.
Or, if your boat is tender upwind, then you'll perhaps err on the small side in terms of area. With how much you reef, & how well the boat sails when reefed, also being taken into account.

Hopefully this makes sense in the above description. As it's tougher to type up the explanation then it is to figure out sail sizes.

Ah, one other factor to think about is that if it's truly nasty out, then you'll want the sail to be elevated off of the deck a bit so that it doesn't often get struck by waves coming over the bow.
And if it's a jib for true heavy weather, then you'll want the entire sail & it's CE to be high enough so that when you're in the trough of a wave, the sail is up high enough so that it still captures enough wind to keep the boat driving forward. As if you become underpowered in the troughs, you'll not make any progress to windward.

[Pete7]

Originally Posted by Madwand

So your Mast is 5 feet shorter than mine, and Seaslug said I would want a 50 square foot storm sail?

I think Jim and Uncivilized summed it up rather nicely

Don't forget your Cal 30 has the tall mast rig not a standard rig, which would be 41 feet.

CATALINA 30 MKII sailboat specifications and details on sailboatdata.com

Our 75 ft2 storm jib is for clawing off a lee shore in a storm, heaven help us if we ever end up in that situation. The storm jib came with the boat when new and I think it has only been flown twice in calm conditions. It's very heavy cloth with hanks on a separate halyard and very high clewed so it doesn't get caught by green water on the deck. I doubt it will ever be used in anger and so lives in the bow lockers.

The smaller 80% jib is far more likely to be used as we replaced the elderly Genoa last year and I would rather not trash the new one with excessive winds. If I blow out the 80% its replaceable without tears.

Pete

[Madwand]

Originally Posted by Seaslug Caravan

Ok Madwand can you frame your question more clearly.

A/ are you saying you want a genuine STORM JIB.

B/ You want to know the exact measurement of said sail. ie luff 'leach' foot.

C/ you don't understand where the % figure comes from.

or D/ you require a smaller headsail for stronger winds and not a STORM JIB at all.

Yes

??
Storm force..... 48 to 63 knots

a. No. But I'd like one that has a sleeve to go over the headsail. Not likely to find that used, though.

c. No, how to get 35% of my I, J numbers. Just doing 35% of a 43 foot I doesn't give me the answer.

[Madwand]

Originally Posted by UNCIVILIZED

I'm not sure if this will help, but below is a quick way to get a ballpark idea of how large a sail should be for your boat based on a given wind strength.

You can do the math....

I'll have to sail the boat a few years to figure out the answers to all those questions, and I'll get back to you.

This explains why my sailmaker told me he didn't have time to do the math...

[Madwand]

Originally Posted by Pete7

I think Jim and Uncivilized summed it up rather nicely

Don't forget your Cal 30 has the tall mast rig not a standard rig, which would be 41 feet.

CATALINA 30 MKII sailboat specifications and details on sailboatdata.com

Our 75 ft2 storm jib is for clawing off a lee shore in a storm, heaven help us if we ever end up in that situation. The storm jib came with the boat when new and I think it has only been flown twice in calm conditions. It's very heavy cloth with hanks on a separate halyard and very high clewed so it doesn't get caught by green water on the deck. I doubt it will ever be used in anger and so lives in the bow lockers.

The smaller 80% jib is far more likely to be used as we replaced the elderly Genoa last year and I would rather not trash the new one with excessive winds. If I blow out the 80% its replaceable without tears.

Pete

At the bottom of that page, it says
TALL RIG:
I: 43.00'/13.11m
J: 13.16'/4.01m
P: 37.00'/11.28m
E: 12.00'/3.66m
Sail Area(100%): 504.94 ft2/46.91 m2

[Pete7]

I thought 35% was for a storm jib, but not sure this is what you actually need.

If the sail is going to be new I watched my sail maker play around with a software program which worked it all out for him. It looked like one of the CAD programs. By moving the Clew position he could alter the shape and still maintain the sail area etc. I asked that the sail not touch or rub on the pullpit and he achieved this.

If the sail is going to be second hand then I don't think you can be too choosy. If you know the measurements of your current Genoa then you can work our its area. Playing around with some graph paper will give you approximately the size you need to go shopping and that is probably good enough for a second hand sail.

Pete

[Pete7]

Originally Posted by Madwand

At the bottom of that page, it says
TALL RIG:
I: 43.00'/13.11m
J: 13.16'/4.01m
P: 37.00'/11.28m
E: 12.00'/3.66m
Sail Area(100%): 504.94 ft2/46.91 m2

Exactly, you have an optional tall rig for sailing in light wind areas. Bet they supplied the standard rig on yachts in the PNW. Your looking for sails for use out of the calm summer season so perhaps base the numbers on the standard rig Cal 30.

Pete

[Madwand]

Originally Posted by Pete7

I thought 35% was for a storm jib, but not sure this is what you actually need.

If the sail is going to be new I watched my sail maker play around with a software program which worked it all out for him. It looked like one of the CAD programs. By moving the Clew position he could alter the shape and still maintain the sail area etc. I asked that the sail not touch or rub on the pullpit and he achieved this.

If the sail is going to be second hand then I don't think you can be too choosy. If you know the measurements of your current Genoa then you can work our its area. Playing around with some graph paper will give you approximately the size you need to go shopping and that is probably good enough for a second hand sail.

Pete

35% is what my sailmaker told me a storm jib should be, he also didn't tell me what those numbers should be since he said he didn't have time to do the math. The sail I asked him about was a storm jib for the guy selling it.

I would like a 90% for general use in the winter.

I would like a storm sail for if the sh*t hit the fan.

I still don't know how to do the math. I majored in a particular degree in college because it only had two maths...I wouldn't be particular at all if I knew the numbers for a 90% sail.

[Seaslug Caravan]

1/2 J x I x 35%

0.35 is 35% if your calculator doesn't have a % function

What about a used hank on jib and a new wrappy bit?

[Madwand]

Originally Posted by Seaslug Caravan

1/2 J x I x 35%

What about a used hank on jib and a new wrappy bit?

That would be fantastic if such a thing existed on the used sail market. Actually, seems the only way to go, because when you need it, you can't be lowering and raising furling sails.

[Seaslug Caravan]

I notice some of the race rules use 5% of I^2 as a storm jib size.

Good luck with that size ,plus the trisail in 63 knots on a 30 footer.

I'm not convinced that wrappy bit is going to slide up OR down in 63 knots.

I'd need some convincing that "THAT" whole shooting match isn't a WAFTAM.

[Pete7]

there is, but its in the UK, actually about 2 miles from me:

Storm Jib Luff Sleeve | eBay

[Madwand]

Originally Posted by Seaslug Caravan

I notice some of the race rules use 5% of I^2 as a storm jib size.

Good luck with that size ,plus the trisail in 63 knots on a 30 footer.

Yeah, they probably know what they are doing.

[Pete7]

Originally Posted by Seaslug Caravan

I notice some of the race rules use 5% of I^2 as a storm jib size.

Good luck with that size ,plus the trisail in 63 knots on a 30 footer.

The only use for sails of that size in a storm will be to attach sheets to the corners and chuck them out the back of the boat as a drogue.

Okay its late here in England time for bed.

Pete