MERLIN ROCKET FORUM

Topic : sails question

Hello there

I have a Winder MkI Canterbury Tales with a set of Speeds (about 3 years old) and a set of P&B's (about 18 months old).

The Speed Kevlar main is fine for Club sailing but the jib is a bit worn.

The P&B Kevlar main is still in very good condition not used that much and I use this for Opens and important club races.

Question is are diferent manufacturers Main and Jibs matched to each other, or could i quite happily use a Speed Main with a P&B jib or vice versa ?

The speed Jib seems larger than the P&B jib...

Many thank to all who reply.

Ed.


Posted: 30/05/2006 09:18:27
By: EdD
To Clarify (I just re-read my post and it did not make much sense !!)

I would like to use my Speed main and P&B Jib for club racing

and I will use my P&B main for import races - so I need to buy a new Jib, does this have to be a P&B Jib to match the P&B Main ?

Its just I have been given a good price from Speeds for one of their Jibs.

Thanks again

ed


Posted: 30/05/2006 11:02:58
By: EdD
What did


Posted: 30/05/2006 12:02:12
By: Jon
Whoops - wrong thread!


Posted: 30/05/2006 12:02:28
By: Jon
No reason why you can't mix and match, but make sure the jib luff wires are the same length or your calibrations for rake, lowers etc will be messed up.  However, tuning will be a bit harder if you use different kit for club racing.


Posted: 30/05/2006 12:23:14
By: Dave Lee
Selective quotes from Class Rules:

9. (b) Total Sail Area .... shall not exceed 10.20 square metres.

9. (c) .... The measured mainsail area shall not exceed 80% of the Total Sail Area.

9. (d) Maximum Foresail Area is the Total Sail Area less the Mainsail Area.

The message is that to be legal both sails have to be measured together. You therefore cannot mix and match from two different sets.

Sorry.


Posted: 30/05/2006 12:28:39
By: bill
Sorry Bill, this is not right.

Provided that the jib area does not exceed the maximum permitted area for the certified sail plan, you may use whatever jib shape or size you like form whatever manufacturer you like. As Dave points out you would be well advised to check that jib luff wires are the same, but in themselves these are not measured. Dan Alsop, for example, likes his jib luff wire to be several inches longer than the sail luff so that he can have a tie at the top which eliminates the effect of that annoying twist that occurs with some jib luff wires. The rules have no comment on this.

In practical terms, Ed, you can buy your jib from whomsoever you like - you could even make one yourself! All you need to do is to make sure that the slot is perfect by careful setting of the jib cars, the tack tie and the sheet tension.

Good luck,

GGGGGG


Posted: 30/05/2006 13:32:37
By: Chairman GGGGGG
This doesn't make sense to me.  We are talking about area not shape (original point 'the Speed jib looks bigger than the P&B jib')

Well, it could be bigger. Although it may be unlikely, it is possible that a main is cut and measured at less than the optimum 80% and the jib is deliberately cut to take up the rest. For the sake of the argument you could therefore have a main at 75% of the sail area and a jib at 25%. You clearly cannot take the large jib and 'match' it with a different main which has been cut at 80%.

The rules say that the Maximum Foresail Area (which is a function of the Mainsail Area) is to be marked on the boom. It follows that the rules recognise that foresails and mainsails can be different sizes.

So my slightly amended answer will still be, no you cannot just mix and match unless the area of the jib is equal to or less than that permitted by the size of the main.


Posted: 30/05/2006 14:15:35
By: bill
That all make perfect sense to me. many thanks for the quick replies.

The old speed Jib just touches the foredeck along its foot, the newer P&B Jib is a good 2 inches off the foredeck. i am using the same shackle to attach it to the bow plate on each sail.

I will tell my chosen sailmaker how big my P&B main is, and they can make me a new jib to the max allowable area.

As a matter of interest, we are 22 stone all up weight (crew is 8 stone), would the preference be for a relatively larger jib and smaller main, or do the fastest rigs have the largest main allowable with a big roach and a relatively smaller jib to the max allowable area, or is this a trade secret ?

Sorry if this has been done to death in the past, but I am new to the class and finding my way.

Many thanks

Ed Dixon
3582


Posted: 30/05/2006 14:33:21
By: EdD
Most sail plans are now total sail area 9.96 sqm, with the main being 7.16 and the jib 2.8. This has evolved over the years to give arguably the best all round balance, performance and flexibility.

It is not at all uncommon for 2.8sqm jibs to actually measure to 2.78, the smallest I can recall was 2.76sqm (which should have been sold at a discount to reflect the saving on the cloth...). The measured area does not include any foot round, so one 2.8 sqm jib might be a real deck sweeper with a low cut clew and a long leech, while another might have a high cut clew, and a relatively straight foot. Both legal, both the 'same' size, but will look radically different, even 'larger'.

Ed, at 22 st, which is optimum weight for the boat, I would say stick with the 'known' formula until you have a real reason to want to branch out....

GGGGGGGGGG


Posted: 30/05/2006 16:02:33
By: Chairman GGGGGG
Many thanks Graham


Posted: 30/05/2006 16:15:44
By: EdD
"Most sail plans are now total sail area 9.96 sqm, with the main being 7.16 and the jib 2.8. This has evolved over the years to give arguably the best all round balance, performance and flexibility."

If the max allowable sail area is 10.20 sqm, then why are we only using 9.96sqm ?

Surely this is a loss of power that would give an advantage in lighter winds, and we could rake to dump some of the power in the heavier stuff ?

Any idea why we are not using the maximum allowable area ?, is there anyone in the fleet doing well that is using 10.20sqm ?


Posted: 31/05/2006 10:57:34
By: newbie
What is the 'maximum jib area?'


Posted: 31/05/2006 15:43:41
By: The Judge
The maximum sail area is calculated from the length of the luff of the main sail.

The maximum jib area is max sail area less main sail area.

For the formula see the rules - a copy can be found on the RYA web site


Posted: 31/05/2006 16:00:34
By: Observer
Judge, according to the Rules, there is no such term.  

The Maximum Foresail Area is the Total Sail Area (10.20 sq m) less the Mainsail Area (which is derived from the measurements taken along the spars between the bands). Since the Mainsail Area cannot exceed 80% of the TSA, the MFA will never be less than 20% of the TSA.

The Actual Foresail Area cannot exceed the MFA and is derived from measuring the jib in accordance with the formula given.

If your boat has been correctly measured and marked, then the maximum size of jib you can have is the figure painted on the boom.


Posted: 31/05/2006 16:15:02
By: bill
I'm not sure but I don't think that the question has been answered why does everyone use a sail area of 9.96 when the maximum allowed is 10.2.


Posted: 31/05/2006 17:09:38
By: David 3150
I suspect it is because the rule is more complex than max 10.2 sq meters but includes the luff length of the mainsail, so I guess that to meet the 80% 20% rule and get the right aspect ratio something must give. But I can't be bothered to do all the maths to work it out in detail.

TOTAL SAIL AREA in square metres is:
13.80 – (0.60 x (L + 0.680)
but shall not exceed 10.20 square metres.

take a look at the rules from link below

http://www.rya.org.uk/NR/rdonlyres/18AA0447-9BD0-45AC-905D-2C2008CE08D9/0/ClassRulesMerlin.pdf

Posted: 31/05/2006 17:53:19
By: Alan F
Sorry again, Bill, I am not usually reckoned to be pedantic but you last post is not right.

The total sail area for a rig is calculated from the L measurement, between the bands on the mast. For a 5720mm L measurement the Total Sail Area will be 9.96 sqm. It is from this total that the division of area between the main and jib is calculated. Therefore the max Main area could be 7.97sqm, which would leave a jib of 1.99sqm - roughly two thirds the size of a current 'standard' jib. This would contribute virtually nothing to the jib's important role of creating the 'slot'.

To make the jib large enough to be efficient, and to keep the mainsail proportional, the sailmakers arrived at the compromise situation I described earlier.

To address the point why doesn't anyone use the full 10.2 sqm. To arrive at this max area you would need a luff length (L) of about 5.3m, which is 420mm lower than the current L. While this may be good on the sea, when it comes to river sailing, the extra height is usually reckoned to be beneficial, hence the trade off. The 10.2sqm is a notional figure, and by trial and error, has become irrelevent to most sail plans. However, if you only sailed on the sea, there is nothing to stop you designing a rig to these dimensions if you felt it would give you an edge. That is one of the beauties of the Merlin Rocket!

GGGGGGGGG


Posted: 31/05/2006 18:13:01
By: What language..
I am surprised Ancient Geek has not answered this one.  Put simply, in old money, you can have a 22ft 6in high rig of 100 sq ft or a 20ft rig of 110 sq ft, or anything in between.In other words you can sacrifice sail area for height. After years of trisl and error the current "standard" was reached. Hope this answers your question Bill.


Posted: 31/05/2006 23:36:53
By: JC
JC, I didn't think I had any questions, but now that I have .........

Chairman, you've been at this for years, and I am a newcomer, so thank you very much for your patience. Please treat this as a daft laddie question (neither the first nor the last).

The rule (9.c) clearly states that the mainsail area is calculated from luff and foot measurement of the spars between the appropriate bands. There is no mention in the rules of the mainsail area being measured from the actual sail.

The MFA is derived from the TSA less the MA as measured in 9c (Rule 9d). Again no mention of the actual sail sizes. The MFA is marked on the boom. The AFA (first mention of a real sail) cannot exceed the MFA (Rule 9e).

So far so good. The issue therefore moves to the location of the bands. Height bands on the mast are clearly defined. The boom band on the other hand is not. I assume therefore (bad idea in rules to have assumptions) that the aft boom band is painted to match the actual measured mainsail.

As soon as that aft band appears on the boom you have a MFA which must be marked on the boom and which cannot be exceeded. Therefore you cannot have a jib which exceeds the marked MFA. Which was my point.

As you pointed out, strict application of the rules could result in a large main and a very small jib.

Well Ed initally asked whether he could mix and match. Surely the answer has to be as I gave it, 'not if the jib area exceeds the marked MFA', otherwise you could keep the large mainsail and add a larger jib

Where have I gone wrong?


Posted: 01/06/2006 09:03:41
By: bill
Perhaps as an old man I might be permitted to help. (Or further confuse!)
1. The rules permit (The MR is a restricted class and thus flexible.) a variation in "rig height" from (in old money) 22'6" down to 20' above the sheer line to the underside of the top black band.
2.Percieved wisdom is that the best trade off between sail area, aerodynamic efficiency and power is 21'-21'6"
3.This gives you your total permitted sail area.
4. Because of the "half height rule" there is an increase in free area the shorter the maximum mainsail foot is permitted to be.
5. You now need to "design" your sail plan.
6. Thus within reason a larger jib and a taller rig will decrease the mainsail foot and your free area.
7. Again the 60 years od accumulated experience, and wisdom suggests a 21'- 21'6" height rig with a jib area of (Old money again!)31-33 sq ft or thereabouts.
8. In the old days when boats usually only had one set of sails the practice was the jib was measured and this fixed the sail plan as set down on the certificate, which explains why old pictures show very few mains out to the black band. Because a "suit of sails" as provided with a new boat were made at the same time.
9. The reason for the area of the jib being on the main boom is that it is also marked on the forsail by the measurer when he measures the sail, and it provides an ad-hoc check that all est in ordnung and bigger jibs have not been substituted.
10. The Boom black band is measured from the rear of the luff groove of the mast or its extension if the luff groove extends aft from the mast.
It does help if you try to think of the intent of the rules and the priciple of trade off between rig height and sail area.
Extremme low rigs have never seemed especially sucessful and they are ugly too!


Posted: 01/06/2006 11:10:20
By: Rigger Mortis
I'm a simple guy and I like simple concepts.  I am new to the game and I found this thread enlightening, but a bit confusing. If I have understood it correctly, this is what I conclude.

1. The total maximum sail area is NOT a constant, but is determined by the luff length. The shorter the luff, the larger the maximum area. But in any case it cannot exceed 10.2 sq meters
2. The maximum permissible ratio between main sail area and jib sail area is also a constant and is fixed at 0.8
3. The maximum rig height is fixed at 22'6"

Then,
4. The jib area is measured, which thus determines a maximum area of the main permitted
5. The rig height is measured which then refines the requirement for maximum mainsail area and thus the maximum permitted foot length is calculated, which is marked on the boom. There are rules concerning the length of the top batton etc, but they don't affect the overall sail area.

But,
6. Experience has determined that the optimum rig height does not allow for the maximum permitted area (see 1. above)
7. Experience has also determined that the optimum jib size is almost always bigger than the mimumum permitted of 20% of the total

So the foot length of the main is made as long as possble to comply with the maximum total area requirment (remember point one above). Is this correct?

This means that if you fit a new jib that is bigger than your old one, you will almost certainly break the rules. Otherwise, your old one was too small!!


Posted: 01/06/2006 13:12:36
By: Mark Rahn
Very few sails measure on limit, and if you order a new sail you will specify the measurements, Luff - Leech - cross (Luff to clew) and probably foot too, so you really shouldn't have a problem if you are buying 2nd hand then jibs are realtively simple within limits to downsize.
1-3 correct
4 Only historically, modern stable sailcloths enable more precise sailmaking means you probably; or your builder or designer does for you; design a rig and give the dimensions to the sailmaker of your choice; who should be capable of getting very close indeed.
5. Once again you choose it's pretty simple to get the mast right and the rest follows.
6-7. more or less!
With us so far..
Good luck.


Posted: 01/06/2006 15:31:40
By: Rigger Mortis
On point 3 not quite depending on the era.  The early boats - like Kate (1)and Iska (6) and Terrapin (36) the masts are still 25ft  Mine (111) on the other hand has either been chopped off or damaged and is 21ft 6in tall and has sails made to match the rig.  Those masts are actually rotating masts!! Oh - the joys of a development class.


Posted: 01/06/2006 15:40:51
By: Garry R
Exceptions (Almost.)prove the rule! 
Of course the older boats 25' will be different but perhaps the application of rules is not quite as stringent more in the spirit; for instance; is no - 1 Kate at Merlin Rocket at all? Being a prototype, the first Merlin Rocket (2) is in the Maritime Museum at Falmouth, pictures on this web site I think.


Posted: 01/06/2006 15:56:42
By: Rigger Mortis
Bill,

We are in absolute agreement that you cannot use a jib that exceeds the maximum permitted on the certificate. Where you were erroneous is in suggesting that Ed can't substitute a new jib for an old one, and that the suit must be measured together, and in a later post that the foresail area was derived from the notional maximum of 10.2 sqm.

The F (foot measurement or boom band dimension, shortly to be renamed the 'Outer Limit Mark, but that is a different story) is used to calculate the certified area of the mainsail, and the controlling half and three quarter heights.

When measuring a MR mainsail the only measurements taken are half height, three quarter height, and position of the battens (plus logo reinforcement etc). We do not measure luff and foot, relying on users not pulling them beyond the Limit Marks.

Hope this sorts the matter - this has been great, people are not usually interested in measurement matters!

GGGGGGG


Posted: 01/06/2006 16:32:47
By: Chairman GGGGGGG
Just reading the very first bit of all this - Ed, I'm very surprises that your P&B jib is well clear of the foredeck - mine certainly isn't and it shouldn't be!  It may be worth having a little look at the seizings at the top and bottom, or giving Tom a ring if it's not obvious.  As I understand it, the whole point of the lens foot design is that it just sits on top of the deck upwind to prevent distortion of the flow at the bottom of the slot, although I may well be wrong!


Posted: 01/06/2006 16:54:13
By: deepy
Chairman GGGGGG,
There’s something I’m not getting here. You said “When measuring a MR mainsail the only measurements taken are half height, three quarter height, and position of the battens (plus logo reinforcement etc). We do not measure luff and foot, relying on users not pulling them beyond the Limit Marks.”

But the formula for the maximum permitted sail area is:
13.80 – (0.60 x (L + 0.680), where L is the luff length

So how can you NOT measure the luff length?


Posted: 01/06/2006 17:36:41
By: Mark Rahn
Thanks to all for contributing to this thread. I never appreciated the implications !

Just looked at my sails again - here is what I found

Speed Jib measured at 2.79sqm
P&B Jib measured at 2.78sqm

Both Jib luffs are the same length, but the Speed Jib does not have a cunningham cringle, where as the P&B Jib does.

I think I found why the P&B Jib sits higher off the foredeck. The jib is tied at the top and if I lengthen this string then the jib will sit lower down the luff wire whilst still allowing the cunningham to be functional and the foot just sitting nicely on the foredeck.

So as the P&B Jib is not larger than the Speed Jib that I am retiring, then I am OK to swap it out with the newer P&B Jib for club racing, and then I will most likely order a new Jib made to 2.78sqm as my best race Jib to match my P&B Main ....

Again many again thanks to all. I cant believe this question generated such a response, but I am grateful !

ed


Posted: 01/06/2006 18:30:49
By: newbie
By George you've got it!
Do bear in mind as you slack off the luff tension on the jib the sail will get fuller (More flow or depth.)and the point of maximum flow move further aft; thus also tightening the leech - even in extremis causing it to curl back; deflecting the wind in the slot more into the mainsail causing more backwinding of the mainsail. Less of a problem with modern stable sail-cloths though.


Posted: 01/06/2006 19:39:47
By: Rigger Mortis
The limit on luff length is that you do not set it outside the limit marks (Black Bands or outer limit marks.)If it's made with lots of slack it will just look like a sack of 'tatties!
To understand it;if you still do not get it;perhaps GGGG or a measurer could do a demonstration for you on the lawn at the next open meeting or do it for yourself following the measurement directions in the rules and on the form, that might help.


Posted: 01/06/2006 20:04:21
By: Rigger Mortis
Thanks Rigger...

This is the correct answer..

GGGGGGGGG


Posted: 04/06/2006 20:26:09
By: Chairman GGGGGGG
Rigger/ GGGGGGG  
Does this comply?
(Sorry can't do links- look on ebay- merlin rocket)

http://search.ebay.co.uk/search/search.dll?cgiurl=http%3A%2F%2Fcgi.ebay.co.uk%2Fws%2F&fkr=1&from=R8&satitle=merlin+rocket&category0=http://cgi.ebay.co.uk/Merlin-Rocket-14-Sailing-dinghy_W0QQitemZ7246927076QQcategoryZ98955QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


Posted: 04/06/2006 22:47:38
By: GeoffP
Is it time we allowed two rigs for each hull so that you could have a heavy weather rig or a light weather rig? Would it make racing closer and would it make the MR more interesting and fun as well?


Posted: 05/06/2006 12:42:31
By: The Judge
.

http://search.ebay.co.uk/search/search.dll?cgiurl=http%3A%2F%2Fcgi.ebay.co.uk%2Fws%2F&fkr=1&from=R8&satitle=merlin+rocket&category0=http://cgi.ebay.co.uk/Merlin-Rocket-14-Sailing-dinghy_W0QQitemZ7246927076QQcategoryZ98955QQssPageNameZWDVWQQrdZ1QQcmdZViewI

Posted: 05/06/2006 13:25:03
By: Everyone can do links!
No - a river rig, and a sea rig.


Posted: 05/06/2006 13:28:28
By: Mags
Why not? It saves having to have two boats.


Posted: 05/06/2006 14:04:17
By: The Judge
Or one rig.....and two hulls....


Posted: 05/06/2006 17:19:08
By: Mags

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