Raking masts

[Rum_Pirate]

Just saw a bald headed schooner eg

Not the one I saw

in the harbour, with significantly raked masts.

Unfortunately I did not have my camera.

What happens if you rake masts?

How far back can you rake them before it it ceases to give any advantage?

 

[KellysEye]

We've seen a couple of schooners with mast rake the same as in the picture. We managed to talk to one of the owners and his was a replica of an American civil war blockade runner, which obviously needed to be fast. The design though was originally French. I doubt you could rake the masts further. They are pretty, they look like they are doing 10 knots when tied to the dock.

 

[Bajansailor]

The Pride of Baltimore is a classic American schooner with very raked masts - more about her here at http://www.pride2.org/history/ogp.php

Raked masts do look very elegant for sure.
However I think the main reason for raking the masts aft is to do away with the need for running backstays - the further aft they are raked, the more aft support they get from the side stays.
There is a limit of course, and one disadvantage is that the mainsheet cannot be eased out very far on a run. But schooners never fare very well on a run, and are probably more efficient tacking downwind on broad reaches.

 

[Poignard]

Thread drift:

Why have schooner-rigged yachts always been so much more popular in the USA than in Europe?

 

[johnalison]

Why have schooner-rigged yachts always been so much more popular in the USA than in Europe?

Maybe it's that the prevailing winds give them mostly reaches, whereas we English have to beat up & down the Channel.

 

[cliffordpope]

All down to design. For some reason schooners have more aft rake. Masts sometimes rake forwards.

 

[jamesjermain]

I'd quite like an informative answer on this. Is it just a style thing when it comes to schooners, or is there a quantifiable performance or handling advantage?

In general terms rake is used to adjust the balance of the centre of effort and the centre of lateral resistance and should not be confused with mast bend which, although it can have the same effect, is more to do with flattening and depowering the sail in stronger winds.

On some boats rake is introduced because the designer got his sums wrong and on others, such as catamarans, the mast has to be stepped on a major structural cross beam which may not be in the optimum postion for sail balance.

There must be a point beyond which you have to say - 'Nah! this is rediculous' - and get the boat rerigged with a new mast step but I don't know what it is. Within reason though, you just have to experiment with inducing rake until you get the balance right with the right amount of weight in the helm and the right agility in the tack, the right stability down wind etc.

 

[SAWDOC]

Mast Rake in my experience increases weather helm on a bermudan rig by moving the driving force/centre of effort aft. excessive rake leads to excessive weather helm. Schooner rig is a different kettle of fish.

 

[VO5]

Why have schooner-rigged yachts always been so much more popular in the USA than in Europe?

It may probably be rooted in traditional values, since the American Civil War, in the same way that the Dutch have their Kwaks, Poons and Botters, though an awful lot of work they must be to maintain as well.

 

[boatmike]

James, you got the answer from Bejan:

However I think the main reason for raking the masts aft is to do away with the need for running backstays - the further aft they are raked, the more aft support they get from the side stays.
There is a limit of course, and one disadvantage is that the mainsheet cannot be eased out very far on a run. But schooners never fare very well on a run, and are probably more efficient tacking downwind on broad reaches.

I would add the obvious, that backstays of any kind are almost impossible on a schooner rigs foremast. That means the normal static load must be taken by the stays with the downhaul contributing when the sail is working. As a side issue the rake allows the stays to be cleared more easily when the main is full downwind but as Bejan says their main "talent" is sailing close to the wind and tacking easily up a channel. Rarely would you sail dead downwind.

 

[Poignard]

Quote from "Yacht Designing and Planning" by Howard I. Chapelle, published by Norton.

"Rake of Masts

In regard to the rake of masts, it is thought desirable to rake the masts somewhat in nearly all types of rig. The rake may be very great, without harm. The extreme rake, in Bugeys' masts, is a present day example [written in 1936]. Rake increases the efficiency of of the jib-headed or leg-of-mutton sail in windward sailing, it is claimed, due to the increase in leading edge that is possible without an increase in the total height of the rig. Excess rake, however, creates a tendency for the booms to swing inboard when running in light weather, which many consider undesirable."

 

[snowleopard]

Having the luff of the sail angled should in theory give a small amount of lift to the sails which should improve performance.

John Leather's book Gaff Rig has very little to say on the subject, mainly what was fashionable in different areas. The NE states went in for very pronounced rakes and no topmasts but whether it produced real speed or just made them look fast is questionable.

Here is a replica of America (of Cup fame)

 

[lw395]

A raked mast should be a bit more efficient to windward.
This particularly true when the jib does not overlap much.
Or in a single sail rig, eg. Contender where it's worth raking the mast and moving the board back to the limits allowed.
Interesting to read Frank Bethwaite's High Performance Sailing, some good points about gaff rigs from a development perspective.

 

[john_morris_uk]

A raked mast should be a bit more efficient to windward.

BUT WHY?

Its what all the books say but (and as James says) can we have some authoritative source or justification? Personally I am not content with quoting a text book on design from 1936 or whatever - research has moved on since then.

(Once upon a time for example, a spinnaker was considered as a sort of parachute to 'catch the wind'. Its now known that wind across the sail - even of a spinnaker - is what produces the most driving force.)

 

[john_morris_uk]

Mast Rake in my experience increases weather helm on a bermudan rig by moving the driving force/centre of effort aft. excessive rake leads to excessive weather helm. Schooner rig is a different kettle of fish.

WHY? Raking the mast back on any boat moves the centre of effort further back and induces less lee helm/more weather helm.

Bermudean or Schooner - it surely makes no difference - masts raked aft - centre of effort goes aft

 

[cliffordpope]

Discussion here:

http://www.boatdesign.net/forums/boat-design/rake-masts-14741.html

I repeat, masts sometimes rake forwards, but not usually as far as in junks.

 

[lw395]

BUT WHY?

Its what all the books say but (and as James says) can we have some authoritative source or justification? Personally I am not content with quoting a text book on design from 1936 or whatever - research has moved on since then.

Bethwaite's book is one starting point, but many authors have summarised the influence of planform on aerofoil efficiency.
Crudely, sail outlines that cause pressure gradients along the wing with a component at right angles to the 'desired' direction of airflow, promote inefficient flow.
An elliptical planform is often held to be ideal (e.g. spitfire wing, who mentioned 1936?), but a triangle or rhombus with a sloped leading edge can be better than a vertical leading edge.
Also applies to keels, and lots of people understand (and explain) it better than me!

 

[Roberto]

What happens if you rake masts?

How far back can you rake them before it it ceases to give any advantage?

I don't know about schooners mast rake, but on modern racing yachts one of the reasons often invoked (apart from hull balance, sail shape, etc) for rake is the decrease of induced resistance in medium winds, when the boat is fully powered.

In basic terms, when a boat has reached its maximum desirable heel angle, you cannot increase sail lift any more (otherwise it would heel more), so one way to increase boat speed is to reduce total resistance.

One component of sail resistance is vortex drag, vortex drag is dependent on span length (actually is it squared ? I'll check): now think about two extremes, one upright sail has a span long like the luff, if one could rake the mast back enough it might get a span long like the leech --> there is an increase in span length, hence a reduction in vortex drag, hence a (possible) increase in boat speed.

Not saying it explains it all, but IMHO is one of the several factor to be take into account.



I must have a reference somewhere I'll try to dig it out

 

[boatmike]

Too much generalisation here. Yes raking a mast will move the centre of effort aft and make the boat more "windward", It will also cause the steering to get a lot heavier! The question is not what happens when you rake an existing mast it is why a vessel should be designed with high mast rake. There was indeed a feeling at one time that this made for a longer leading edge without a higher mast and therefore made for a more efficient rig. With the advent of aluminium masts and bermudan rigs though this became irrelevant. In fact the sail plan MUST be arranged so that the combined centre of effort is in the correct relationship to the dynamic centre of the hull (usually just aft of it) regardless of the mast rake. Whatever the original rake was, moving it forward or back will help balance the sail plan until a correct balance is reached. This ain't why the old fast schooners (especially the Cape Cod schooners) were designed that way though. The reason was purely that without high mast rake, and no backstay the whole damn thing would have fallen down otherwise! Look again at the photo of the "America" and you will see that there was no way that big main boom would permit a standing aft stay. Running stays could indeed be used (and sometimes were on downwind runs) but would need swapping over on every tack. Short tacking up a river, or indeed racing would not permit such. Hence high rake and swept shrouds.

 

[lw395]

Too much generalisation here. Yes raking a mast will move the centre of effort aft and make the boat more "windward", It will also cause the steering to get a lot heavier! The question is not what happens when you rake an existing mast it is why a vessel should be designed with high mast rake. There was indeed a feeling at one time that this made for a longer leading edge without a higher mast and therefore made for a more efficient rig. With the advent of aluminium masts and bermudan rigs though this became irrelevant. In fact the sail plan MUST be arranged so that the combined centre of effort is in the correct relationship to the dynamic centre of the hull (usually just aft of it) regardless of the mast rake. Whatever the original rake was, moving it forward or back will help balance the sail plan until a correct balance is reached. This ain't why the old fast schooners (especially the Cape Cod schooners) were designed that way though. The reason was purely that without high mast rake, and no backstay the whole damn thing would have fallen down otherwise! Look again at the photo of the "America" and you will see that there was no way that big main boom would permit a standing aft stay. Running stays could indeed be used (and sometimes were on downwind runs) but would need swapping over on every tack. Short tacking up a river, or indeed racing would not permit such. Hence high rake and swept shrouds.

Sweeping the shrouds back acts as a backstay, and stops the boom going out.
That's much the same regardless of rake.
Plenty of British fore and aft rigs had upright masts and booms extending over the stern.
I suspect the schooners evolved through a development process, what was fast locally got copied and taken further.
There may have been other influences such as availability of the right timber and a history of smaller boats with rake, such as 'cat' rigs.
Also perhaps fashion was as important then as now in determining what an owner would commission?
I've used running backstays short-tacking up the non-tidal Thames, racing in an A-rater. It's what the third man is for!
Although with many rigs you only need the runners down wind, as the leach tension does the job upwind.