What effect would increasing the sail area have?

[john_morris_uk]

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.

The load on the standing rigging will NOT increase. The only way to increase that (unless you wind up the static rig tension) is to add weight to the keel. Its a common misconception that putting bigger rigging on the boat adds to the loads on the rigging. The only way that it adds load is if you put bigger wire on and pre-tension it to the same % of its breaking strain as the equivalent smaller wire. (Hope you follow that!) The rig tension caused by heeling is entirely dependant initially on the form stability of the hull and at 90 degrees heel by the weight of the keel etc. In fact the maximum tension is achieved well before the 90 degree point on most boats. The height of the mast has no bearing on these figures.

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.

As others have pointed out, the taller mast DOESN'T necessarily mean more roll. As it alters the moment of inertia, it will only alter the natural roll frequency.

A longer boom would certainly be one option to increase sail area.

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.

My thoughts exactly. If the boat is seriously under canvased then a taller mast and bigger rig will help.

However its not the whole story. There's a matter of where the centre of effort is relative to the centre of lateral resistance, and the hull shape and how that centre moves as the boat heels etc. For a considered view of whether the rig will be balanced and make the boat pleasant to sail, you need to do some more calculations (or consult a yacht designer.) For the few hundred £ he/she will charge it might be worth it and it will be a fraction of the cost of the new mast and sails.

The cheapest solution would be to find the original plans and see what the original designer put for a single mast version. Even that might not be perfect as he/she might have designed the boat as under canvased in the first place!

However if the mast is second hand and very cheap, you can do some back of an envelope sums and assuming it looks vaguely ok you could give it a try. Be prepared to experiment with the mast rake etc to get the boat reasonably balanced. The sailmaker should be able to give you some guidance as well.

 

[johnphilip]

OR.........

As you say Lazy Kipper is not intended for windward performance, so looking at where you could improve, do you have a cruising chute? This could make the difference between wallowing and getting somewhere in light and medium breezes.

 

[Otter]

Thanks for the comments so far. To clear up a point, the mast was designed to be where it is, 20 inches aft of the usual CW34 position because it was designed to not have a mizzen, that was a later and ill thought through attempt by a previous owner to add more sail area.

We have a chute but the problem with our shortish main mast is the chute is the same area as a 31 foot boat and we're 35. The same would be true of a genneker type, the genoa is one area to look at it's only a 110% but going to 130% wouldn't add much plus it's newish and that seems like a lot of effort for what I'd assumed would be a small increase - am I wrong?

Going back to a furling genneker on a bowsprit - size wise would that be about a sort if 150% genoa size? And would the sailcloth be intermediate weight between a genoa cruising weight and spinnaker cloth?

Another option would be to convert to cutter which the plans for the boat may suggest was intended (there were only two of these variants built) would the extra sail area help?

Thanks.

 

[NUTMEG]

I have seen pics of a CW that was/is gaff cutter rigged with a bowsprit and looks very pretty.

 

[john_morris_uk]

Thanks for the comments so far. To clear up a point, the mast was designed to be where it is, 20 inches aft of the usual CW34 position because it was designed to not have a mizzen, that was a later and ill thought through attempt by a previous owner to add more sail area.

We have a chute but the problem with our shortish main mast is the chute is the same area as a 31 foot boat and we're 35. The same would be true of a genneker type, the genoa is one area to look at it's only a 110% but going to 130% wouldn't add much plus it's newish and that seems like a lot of effort for what I'd assumed would be a small increase - am I wrong?

Going back to a furling genneker on a bowsprit - size wise would that be about a sort if 150% genoa size? And would the sailcloth be intermediate weight between a genoa cruising weight and spinnaker cloth?

Another option would be to convert to cutter which the plans for the boat may suggest was intended (there were only two of these variants built) would the extra sail area help?

Thanks.

The best person to discuss sailcloth weight with is the sailmaker… I've always discussed with them and taken their advice and I've never been disappointed. (Just use a reliable one that you can actually talk to; not one over the internet from distant lands?)

 

[geem]

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

That's an interesting one. We have a heavy mast. There are a number of similar sized yachts next to us in the marina. When the lifeboat goes out they make lots of wake. It knocks the boats around in the marina. We roll very slowly compared to the boats next to us. We roll the same distance but we do less rolls and we stop rolling in the same time as the other boats. So it does have a dampening effect because we do not roll as much for the same wave as similar boats.

 

[geem]

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.

On my last boat the mast was 18% taller than standard and this gave us 15% more sail area. In light wind the boat flew compared to a standard rigged boat.

 

[DoubleEnder]

I'd keep the current main mast, ditch the mizzen, add a short bowsprit and a furling headsail on a new stay to the end of the bowsprit. Much less messing about, simple, less cost, no second hand gear, only one new piece of standing rigging, net weight change nil (ish), more sail area forward of CLR, less weather helm. Good chance to think through new improved anchor arrangements (stowage, rollers etc).

Maybe some lee helm eek! so do a few sums. It is quite easy to calculate CLR and COE, but worth getting a pro eg good sailmaker to go through it with you. Pay him/her for a half a day's work. And they could advise on size cut and weight of the new sail.

You might miss the mizzen though, it can be a good place for antennae etc

 

[JumbleDuck]

That's an interesting one. We have a heavy mast. There are a number of similar sized yachts next to us in the marina. When the lifeboat goes out they make lots of wake. It knocks the boats around in the marina. We roll very slowly compared to the boats next to us. We roll the same distance but we do less rolls and we stop rolling in the same time as the other boats. So it does have a dampening effect because we do not roll as much for the same wave as similar boats.

The underwater profile of your boat will be much more important in determining damping. "Similar sized" isn't enough.

 

[Otter]

The existing mast is 1970's and very heavy for its profile, the new mast at 20% taller will probably weight 10% less.

The Bowsprit idea is growing on me, there's an existing 26 inch bowsprit platform thing and it would be easy to bolt on the fittings for a retractable bowsprit. I can vaguely see a plan emerging: Fit a retractable bowsprit with furling genneker but keep the mizzen, the big foresail countering the mizzen, that way I gain more sail area. It's an idea to talk to the riggers and sailmaker about. I get your point about actually paying for advice, it alters the dynamic from sales pitch to professional advice.

 

[JumbleDuck]

TThe rig tension caused by heeling is entirely dependant initially on the form stability of the hull and at 90 degrees heel by the weight of the keel etc. In fact the maximum tension is achieved well before the 90 degree point on most boats. The height of the mast has no bearing on these figures.

That's only true for static heeling, and even then it's only partially true. Yes, for a given angle of heel the rig forces on the hull depend on the hull's stability (form and pendulum) but equally for a given angle of heel the rig forces on the mast depend on the mast's mass and centre of gravity, both of which are likely to depend on height.

Dynamically the effect of the mast configuration - mass, cog and radius of gyration - are extremely important, as anyone who has been on a sailing boat with and without its mast (or with the mast up and down) knows, and the forces involved reach the hull through the rigging.

 

[robmcg]

There is a CW34 in our yard that was converted from a ketch to a cutter by the very knowledgable owner. It included moving the mast aft and resiting the chain plates (which you wouldn't need to do by the sounds of it). The result was the vessel sailed quicker and pointed higher. I may be inclined to look at the cutter route, given your mast location. Would make an interesting project BTW.

Rob

 

[Otter]

Hi Rob, if I pm you my contact details, could you pass them on to the owner via the yard? He sounds very worthwhile talking to!

 

[geem]

The underwater profile of your boat will be much more important in determining damping. "Similar sized" isn't enough.

I know its a complicated subject but the modern yachts along side us are all relatively flat hull shapes, eg Sweden yachts 42, Bavaria 46, Dufour 380, Moody 44. Our boat is 44ft ketch with a 58ft main mast weighing 400kg with the rigging. We have 6 ton of lead in a 7 ft deep keel but slack bilges so little form stability from hull shape alone.

 

[Lakesailor]

Whilst liking your Youtube compilation I did find myself being drawn to some of the underwater profiles in the Danish sailing video alongside

 

[Otter]

Long chat with Mike at North Sails today, very helpful chap. He said similar to some of the comments, suggested we take off the genoa and replace it with a 180% reaching genoa in a sailcloth a bit lighter than the current genoa. I could then have the existing genoa cut down and fitted as a staysail. The reaching genoa will fly from 50 degrees through to about 140 degrees and drop the main and run with it. It will fly happily up to F6 and will fit the existing harken roller reefing gear, after a F6 we'd be using the staysail with the benefits of inboard sail area. All this will increase our sail area by 30% instead of the 20% we'd get with a new mast and that doesn't include the staysail if it can be flown cutter rigged at the same time.

All in all it was a useful discussion and thanks for the comments on here nudging me that way. Other suggestions welcome.