What effect would increasing the sail area have?

[Colvic Watson]

To cut a long story short, the previous owner of Lazy Kipper changed the sail plan from a sloop to a ketch, for lots of reasons this was a bad idea, the main reason is that the mast was designed to be 20 inches aft of a standard CW34 because there was no mizzen. Because the centre of effort is so much further back, the mizzen adds nothing to forward momentum because it's trying to round up the boat and the weather helm increases and slows us down on anything broader than a broad-beat.

Solution may be to ditch the mizzen mast all together and I've been offered a bigger used main mast at a good price, it will increase the sail area of the main and genoa by exactly 20% - how much effect might that have? Bearing in mind we don't bother sailing on passages below a F4, if we're not on passage we still sail OK in a F3, just not very fast! We're a long keel heavy displacement boat but what we want to do is sail faster and motor less, we've never reefed below a F7 because we don't need to, there isn't enough sail to justify it and she don't heel much. Will it be it a simple 20% increase in speed? I'm not sure.

 

[dovekie]

I hope wiser folk add to this reply. If the replacement mast adds 20% sail area it is taller presumably? So the centre of effort of the new bigger sails will be higher, at least when unreefed. So more heeling force, for the keel and hullshape to oppose, in a given wind, so more heel. That may not matter given what you describe. But there is the potential for greater loads on the standing rigging and it's hull attachments. It would also lessen the angle at which the boat would lose righting moment altogether and turn turtle. If you currently don't reef until F7 presumably you feel the current rig is seriously underpowered, can you get hold of the original drawings to see the designed mast height? A final thought is that without the mizzen, the amount of weather helm will drop - you presumably want to keep some weather helm . As for how much faster you'll go in a given wind, I've no idea.

 

[silver-fox]

My thoughts are that your proposed change would improve light wind sailing, probably mean that you have to reef earlier, and it would also move forward the centre of effort. All of which you have indicated you would like to achieve.

Given that you are disposing of the mizzen and all its rigging, there is unlikely to be much of a nett change to weight aloft and hence your CoG/stability/AVS.

The stress on the rigging isn't going to change much either as this is largely determined by the boats stiffness and the ability to resist healing in any given wind as this is the self limiting factor.

So, assuming there is no significant increase in mast weight (beyond what might be proportionally expected by the taller mast) and the fact that you can currently hold full sail in an F7, and the boat is stiff and stable with its present rig, its a change I would certainly consider. That said I would be inclined to run your plans past a local rigger to check that he doesn't foresee any practical problems before proceeding.

 

[lpdsn]

One effect to consider is that the taller rig will increase the moment of inertia of the boat, which means you'll roll a bit more. This will increase the forces on the rig and keel too.

That said, I suspect your keel and rig aren't finely engineered and that you have quite a margin of safety. If, on the other hand, you were some ULDB carbon-fibre racer you'd want to be talking to the designer.

Your alternative to a taller rig to increase sail area is a longer boom. Obviously high aspect sails are crucial to your performance in windward leeward races, however I suspect that isn't something you care much about. Lower aspect sails are good when it comes to reaching.

 

[Colvic Watson]

Is there a smarter way of increasing sail area then? Bearing in mind we don't do closer than 50 degrees and no real desire to, and we put our first reef in at 25knots, what are the alternatives to a taller mast? Extending the boom isn't possible because of the back stays.

 

[lpdsn]

Is there a smarter way of increasing sail area then?

Roach?

 

[Colvic Watson]

Do you mean recut the sails?

 

[Lakesailor]

Surely the aspect ratio of the new sail will be the deciding factor. If you have taller mast you don't have to use all the extra height. A longer boom with a main to suit will keep the centre of effort lower at the expense of moving it slightly aft. Look at the dinghy in my avatar. It has a low-aspect rig. A lot of sail to move a clinker dinghy, but it didn't heel much as the centre of effort was relatively low.
I would have thought a good sailmaker would have a programme on his computer to work those things out easily.

 

[30boat]

One effect to consider is that the taller rig will increase the moment of inertia of the boat, which means you'll roll a bit more. This will increase the forces on the rig and keel too.

That said, I suspect your keel and rig aren't finely engineered and that you have quite a margin of safety. If, on the other hand, you were some ULDB carbon-fibre racer you'd want to be talking to the designer.

Your alternative to a taller rig to increase sail area is a longer boom. Obviously high aspect sails are crucial to your performance in windward leeward races, however I suspect that isn't something you care much about. Lower aspect sails are good when it comes to reaching.

On the contrary.A higher heavier mast wil dampen roll not increase it.It will decrease the stability of the boat because of the higher weight aloft but probably not by much.The sail area won't increase by 20% if the mast height increases by 20% if the boom length is kept the same.You'll get a more effective foil for windward work and if overpressed you just reef a bit earlier.I think it's a valid idea.

 

[mrming]

Do you mean recut the sails?

I think he probably means a new main with a larger roach. The boat looks very lightly canvassed so I don't think that would make a significant difference.

If this was me I would engage a yacht designer / NA - preferably the original design firm is they are still in business.

It could be cheaper in the long run to have someone do the right maths in relation to stability and also the extra loads transferred to the hull as a result of a larger / heavier rig with more sail area. I suspect that speculation that boat is over-engineered and could handle a 20% taller rig is correct, but I would want to know for sure before messing with the boat. After all, had the previous owner done that, you wouldn't now have the problem of an unbalanced rig.

 

[JumbleDuck]

To cut a long story short, the previous owner of Lazy Kipper changed the sail plan from a sloop to a ketch ... I've been offered a bigger used main mast at a good price, it will increase the sail area of the main and genoa by exactly 20% - how much effect might that have?

How close would that bring you to the standard sail plan? I'm presuming that the main mast and sail were reduced in size when she was beketched (ketchified?).

 

[Colvic Watson]

Standard sail plan was added to by the mizzen, the mast is original.

 

[mrming]

Is it an option to move the main mast forward 20 inches to it's intended position?

 

[lpdsn]

On the contrary.A higher heavier mast wil dampen roll not increase it..

It will increase the period of the roll, but it certainly won't dampen it.

 

[JumbleDuck]

It will increase the period of the roll, but it certainly won't dampen it.

A bored modeller writes:

The standard form of equation for a mass-spring-damper system is

y" + 2 z w_n y' + w_n² y = 0

where w_n is the undamped natural frequency, w_n² = k/m (spring constant/mass), z is the damping factor and 2 z w_n = c/m (damping ratio/mass).

Rearrange and you get that z = c / 2 sqrt (k m). Unfortunately, increasing the mast length will change c, k and m. It will increase c very slightly, because there will be increased air resistance to the mast and sail moving about, but that's probably a small effect compared to the water damping the keel(s) and hull, so it's probably safe to ignore. k is the ratio of restoring torque to rotation (the pendulum stability) and a taller mast will reduce that slightly. m in this case is the moment of inertia in roll, and that will increase significantly.

So, all in all I reckon that c will stay the same, k will go down slightly, m will go up significantly and therefore the damping factor z = c / 2 sqrt (k m) will go down a bit. In other words, from a given initial roll it will take longer for the oscillations to die out. So I'm agreeing. Now, has my bloody program compiled yet?

 

[lpdsn]

I probably have that in a text book somewhere, but it'll be in a cardboard box in the spare bedroom. Glad to hear your maths agrees with my intuitive understanding.

 

[JumbleDuck]

I probably have that in a text book somewhere, but it'll be in a cardboard box in the spare bedroom. Glad to hear your maths agrees with my intuitive understanding.

I know which I'd trust more. (Hint: not my maths, particularly at this time of night.)

 

[30boat]

Ok so the period will be longer but there will be more resistance to start the roll .It is better to have a mast than no mast at all.When a boat is dismasted the rolling is very quick and the range short.If there's enough stability to take a heavier mast the rolling motion will be slower (less unpleasant) but the range of the motion will be larger.

 

[William_H]

You will be getting in to a lot more costs in changing the mast. I would suggest that the sail area could be imcreased easily.
As said a new mainsail with more roach and perhaps longer in the boom. The backstay concern can be helped by fitting a crane to the backstay attachment at mast top so moving backstays further back. You may also do well with a bigger genoa or use of a genacker or code 0 type of additional sail up front.
Regarding your concerns about un ballanced rig I don't think thse effects are as dramatic as theory might suggest. After alll most boats can sail OK on mainsail alone or genoa alone and that is a dramatic unballance from design.
A taller mainsail will improve light weather performance and especially windward sailing but you say you are not interested in going to windward so much.
I imagine OP is just cogitating about possibilities. He should remember it is nice to have a boat which will not need reefing if the wind comes up a bit. Even ifhe uses the motor a bit more than others. good luck olewill

 

[Iliade]

What about a, perhaps folding, bowsprit and turn her into a cutter? Cheapest option of all to try plus no sail becomes any larger and hence more difficult to control in a blow.