23ft mast or 19ft

KILLER.BEE

Hi all very new to sailing
I am looking for some advice for my 19ft manta i got it about a year ago and its was a project it came with a broken mast:( that i hear its not a great idea to fix as its spilt in two and then i got my hands on a 23ft mast rigging and all ..so
can i use the 23ft mast or will i have to cut it to the same length as the old broken mast of 19ft any help would be great

fergal.b

I'm no sailor but I think it would be ok to use a slightly bigger mast as long as you don't use an oversized sail the extra 4 foot of mast wouldn't weigh that much and shouldn't effect the balance of the boat much.


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noby

If it came with stays then at least you won't have to get a new set as the originals will be too short. Other than that I see no issue.

pedroeibar1

The Manta is not dissimilar to a Leisure 17. The latter came with two mast sizes, Lake Rig (6.6m) and Sea Rig (6.1m). I think 23 feet (7m) is borderline, and I'd be happier with taking out the saw. Remember also that the insurers will ask you when was the rigging renewed, so the cost of new stays, shrouds etc will not be a wasted exercise. Also your sails will be smaller=cheaper.

HeidiHeidi

I won't pretend to be an expert on this - but instinct would tell me that if you have a 4-ft higher mast (+20%), then you're going to have similarly larger sails (or not far off) - do you not run the risk of being wildly over-canvassed?

Or else having very odd-shaped sails if you try to compensate for the extra height?

Do you still have the original boom?

I'm hoping someone who actaully knows these things can answer, as I'm interested to know if I'm miles wide of the mark (pardon the pun )

noby

HeidiHeidi wrote: »

I won't pretend to be an expert on this - but instinct would tell me that if you have a 4-ft higher mast (+20%), then you're going to have similarly larger sails (or not far off) - do you not run the risk of being wildly over-canvassed?

I was going on the assumption that the OP has the original sails.
I wouldn't recommend over-canvassing. And actually, thinking about it more, while there would be no problem using a longer mast, considering the OP is a beginner I would be inclined to cut the mast to the original length. If the stays that came with it are in good condition it's only a matter of shortening the stays and getting new fittings put on.

pedroeibar1

HeidiHeidi wrote: »

... I'm interested to know if I'm miles wide of the mark (pardon the pun )

There is some serious math involved in this topic. Mast height and position is calculated by the sail plan rather than the other way around, and, roughly speaking, it is based on the relationship between the “Combined centre of effort” (CoE) i.e. the position of the total power between the two sails (main & jib/genny) and the centre of lateral resistance of the hull, giving a figure called the “lead”. There are no exact rules on “lead” – it can vary by up to 30% on most rigs, but get it wrong and the boats handling will be seriously affected e.g. over-canvassing of main would give huge weather helm.

In layman’s terms the mast height/sail plan also has to take into account several factors that make up the “righting moment”. That is the critical figure and is based on the relationship between the mast height, the width of the boat’s beam, the weight + length of keel, and where the weight is on the keel (fin or twin or bilge or torpedo) Obviously a chunk of weight on the base of a fin keel (i.e. torpedo keel) will have a greater righting moment than a keel which will have its weight evenly distributed, so there is about a 10% difference. The lower the ballastweight is carried on the keel, the greater the righting moment so the taller a mast can be.

OP’s boat has a stubby keel (designed as a trailer sailer) so it is too short to prevent leeway and therefore compensated for by a drop centreboard. As a result the main weight is higher rather than lower on the keel. With a 23 foot mast and the old sails, there will be an extra 4 foot of mast doing nothing and in the wrong place, because as soon as the boat begins to heel over the fulcrum effect is introduced. She also will have a tendency to roll in light airs and particularly downwind if the plate is pulled up. If he buys a new main with 23 ft. luff and uses the old genny, the boat will probably handle like a cow because the CoE will be in the” wrong” place. That’s why I suggested taking out the saw; I’d be surprised if the mast break could be sleeved successfully, but that might be another option.

That "hit the mark" for you Heidi?

HeidiHeidi

pedroeibar1 wrote: »

There is some serious math involved in this topic. Mast height and position is calculated by the sail plan rather than the other way around, and, roughly speaking, it is based on the relationship between the “Combined centre of effort” (CoE) i.e. the position of the total power between the two sails (main & jib/genny) and the centre of lateral resistance of the hull, giving a figure called the “lead”. There are no exact rules on “lead” – it can vary by up to 30% on most rigs, but get it wrong and the boats handling will be seriously affected e.g. over-canvassing of main would give huge weather helm.

In layman’s terms the mast height/sail plan also has to take into account several factors that make up the “righting moment”. That is the critical figure and is based on the relationship between the mast height, the width of the boat’s beam, the weight + length of keel, and where the weight is on the keel (fin or twin or bilge or torpedo) Obviously a chunk of weight on the base of a fin keel (i.e. torpedo keel) will have a greater righting moment than a keel which will have its weight evenly distributed, so there is about a 10% difference. The lower the ballastweight is carried on the keel, the greater the righting moment so the taller a mast can be.

OP’s boat has a stubby keel (designed as a trailer sailer) so it is too short to prevent leeway and therefore compensated for by a drop centreboard. As a result the main weight is higher rather than lower on the keel. With a 23 foot mast and the old sails, there will be an extra 4 foot of mast doing nothing and in the wrong place, because as soon as the boat begins to heel over the fulcrum effect is introduced. She also will have a tendency to roll in light airs and particularly downwind if the plate is pulled up. If he buys a new main with 23 ft. luff and uses the old genny, the boat will probably handle like a cow because the CoE will be in the” wrong” place. That’s why I suggested taking out the saw; I’d be surprised if the mast break could be sleeved successfully, but that might be another option.

That "hit the mark" for you Heidi?

Jaysus, I need another strong coffee after reading that :eek:

I knew there was a lot to it, just didn't know the detail.

Not as simple as "stick up the longer mast, be grand".

pedroeibar1

I think I had about three before I tackled that reply! (but I chickened out on introducing the parallelogram of forces and its effect resulting from the curvature on sails!)


Where,
R = Magnitude of resultant vector
α = Direction of resultant vector
P = Magnitude of vector P
Q = Magnitude of vector Q
θ = Angle between two vectors

Understand that and you'll never look at the luff curve on a genny the same way again!:D

HeidiHeidi

pedroeibar1 wrote: »

I think I had about three before I tackled that reply! (but I chickened out on introducing the parallelogram of forces and its effect resulting from the curvature on sails!)


Where,
R = Magnitude of resultant vector
α = Direction of resultant vector
P = Magnitude of vector P
Q = Magnitude of vector Q
θ = Angle between two vectors

Understand that and you'll never look at the luff curve on a genny the same way again!:D

Ah here :eek:

I did get through honours maths in the Leaving, but that being some time back in the 20th century AD, I'll just have to take your word for the above.

Part of me thinks you're just a good bluffer with a fetish for pretty mathematical symbols though

pedroeibar1

In my schooldays we had no calculators (not invented) and we used a book of log tables. I still have a slide rule (rather dates me, that!) but I don't use it. Fetish?? Let’s not go down that route, Fergal might get worked up or over-excited. :eek:

Bluffing - yes, very important:); the uncle taught me to navigate, his first rule being “learn the poker face.” He says "When people are scared/worried/about to panic and want to know where we are, stab a finger firmly on the chart and confidently say “HERE!” Then, says he, they will bugger off, leave you in peace and you can find out exactly wtf you are!" Always worked, except for once, when I identified (in thick fog) a moored tanker with decklights as the pier in Dunmore East! Morto :o

KILLER.BEE

thanks lads for you feed back and the maths sorry for the late reply i was away in france its a drop keel steel/castiron mix I think ,the 23ft rigging mast and boom are all there and looks good as for the sails the sails are from the 19ft manta mast setup but i hope to get some one to look at them for me and see if there are ok they look in good nic so to saw or not saw

pedroeibar1

Wrong play!

Is this a saw which I see before me,
The handle toward my hand? Come, let me clutch thee.
I have thee not, and yet I see thee still.
Art thou not, fatal vision, sensible
To feeling as to sight? Or art thou but
A ripsaw of the mind, a false creation,
Proceeding from the heat-oppressèd brain?

Just cut!

BrensBenz

pedroeibar1 wrote: »

I think I had about three before I tackled that reply! (but I chickened out on introducing the parallelogram of forces and its effect resulting from the curvature on sails!)


Where,
R = Magnitude of resultant vector
α = Direction of resultant vector
P = Magnitude of vector P
Q = Magnitude of vector Q
θ = Angle between two vectors

Makes (ahem) perfect sense to me!

No sail foot / boom dimensions given but, if more or less equal, I doubt if over-canvas would be a great problem in terms of extra power. But weather / lee helm would. It's not the extra area of sail but the fact that the extra area would (probably - I think - maybe) be forward of the hull's natural pivot point. Even when the sails are matched to the hull, i.e. as the designer intended, moving the butt of its mast slightly forward or aft could give your tiller arm muscles on its muscles.

I doubt if the keel(s) can be moved but if you can move the mast butt forward and aft, you should be able to "tune" its position until she steers easily.

Personally, I'd suck it and see! A "tall" boat is always going to look better than a short boat!

pedroeibar1

BrensBenz wrote: »

Makes (ahem) perfect sense to me!

No sail foot / boom dimensions given but, if more or less equal, I doubt if over-canvas would be a great problem in terms of extra power. But weather / lee helm would. It's not the extra area of sail but the fact that the extra area would (probably - I think - maybe) be forward of the hull's natural pivot point. Even when the sails are matched to the hull, i.e. as the designer intended, moving the butt of its mast slightly forward or aft could give your tiller arm muscles on its muscles.

I doubt if the keel(s) can be moved but if you can move the mast butt forward and aft, you should be able to "tune" its position until she steers easily. Boom length will be governed by the backstay.

Personally, I'd suck it and see! A "tall" boat is always going to look better than a short boat!

pedroeibar1 wrote: »

......... If he buys a new main with 23 ft. luff and uses the old genny, the boat will probably handle like a cow because the CoE will be in the” wrong” place. That’s why I suggested taking out the saw....

It could be tried 'as is' for the rest of this season just to see how it works, but I think it will be back to a shorter mast.;) Boom length will be +/- the same as it is governed by the distance to the backstay (His tiller arm will be a lot stronger and longer , though!)