rake of masts

I was looking at pictures of schooners from late 1800's and wondered why they put the masts on an angle. I think they call that the "rake" of the masts.Some schooners had up to seven masts.Any design or function purpose to this practice?

 

Yes, a rake of mast(s) can improve the properties of speed of a boat considerably.

For that same reason they were prohibited by the Racing Councils like RORC
and the like.

Since then, you hardly find this in yachts. Maybe I am mistaken and that lately some rake is introduced again.

Basically, it is for this reason (as I do believe).

 

It's a good question, and I hope someone has a good answer. In recent racing some boats have set up to have a little bit of aft rake going to windward and a little bit of forward rake going downwind. I think this was an innovation of Team New Zealand in the 1995 America's Cup, and on the Jim Taylor 49 Numbers (third Taylor design of that name) that Russell Coutts skippered after winning the Cup.

 

One practical reason to have large rake on a gaff rig is to keep the boom out of the water when reaching. On a vertical mast the angle between the mast and boom is 90deg, the height relative to the deck does not change as the boom is eased. If the mast is raked 10 deg aft, the angle is 80deg. When the boom is eased the end moves up in relation to the deck. With the boom eased 90deg the boom will be at a 10 deg angle from horizontal and less prone to catch waves. The boom would be horizontal when the boat is heeled 10deg. On a vertical (unraked) mast the boom would be angled down equal to the angle of heel.

 

Additionally the leaning aft will help tension the fore stays , a difficult task with rope rigging.

FAST FRED

 

Yet another reason for aft rake is that in heavy weather, boats tend to develop weather helm by virtue of their excessive heel. When the crew reefs the sails, not only does the sail area and the amount of heeling reduce, but the center of effort of the sailplan moves forward on aft-raked masts, thereby further easing the weather helm and making the boat easier to steer.

Eric

 

In my opinion this is probably the main reason, as adapting the number and size of sails to prevailing condition has bigger influence in the moving of the center of effort.

RHough,
I'm not sure about your statement. The kind of attachement of boom to mast in old gaffers allows for the boom to not necesarily keep a 90º angle with mast when opening it. Those rigs have not boom-vangs, so when easing the sheets the booms tend to rise.

 

Agreed, the main reason was most likely rigging with rope.

However, the booms of many gaff rigs are considerably longer than the beam of the boat. The geometry of a heavily raked mast makes it possible to reduce twist without dipping the boom into the water. Thus it makes sense to rake the mast on a low aspect rig with a long boom even though modern rigging does not require the rake to keep headstay tension high.

Vangs were used to reduce/control twist on gaff rigs. The vang was attached to the gaff rather than the boom. On a schooner, the foremast gaff vang leads to the mainmast, the mainmast gaff vang leads to the weather rail aft.

 

I have been searching for recent built gaffers (Other than strict replicas, like America) and found not a single one with raked masts. Do you know of some?
Cheers

P.S. Well yes, there is one designer at least! : Michael Kasten

More P.S : Going on with the search, now I've found several other modern examples...
Could you give me examples (pictures, drawings or the like) of those gaff vangs you mention? (I'm not sure if I'm understanding well the term)

 

Most modern gaffers I've seen don't have low freeboard or booms 2+ times the beam either. If the boom is not long enough or low enough to make contact with the water a concern and the designer has no sense of style ... (just kidding).

The arc the boom travels when the mast is raked is an ancillary benefit. Another ancillary benefit is that when the mast is raked, the gaff naturally wants to seek a midships position when lowering the sails.

To my eye, gaff rigs don't "look" right without some rake, schooners in particular.

Here's a fairly recent design with raked masts. Beam 5, main boom 12.

 

Gaff Vangs

There are several good descriptions if you do a search on "Gaff Vang"

One of the characteristics of gaff rigs is lots of twist when the sail is eased. With no boom vang to pull the boom down and close the leech the head of the sail twists off more than is needed for good trim.

A line lead aft from the end of the gaff keeps the head of a gaff sail from twisting off too much. The angle from the deck is not the best when close hauled (as the vang hauls more down than aft), the gaff vang is more effective on a reach.

The gaff vang tackle is #48 in this illustration.

 

Now I realize, thanks. I didn't know the english word for that is vang. The spanish name is 'osta' and there are two, one on each side of the sail, while the boom vang is called 'trapa' and there is only one per sail. The 'ostas' are also used to guide the perch between the two topping lifts when hoisting. The 'ostas' do not work really as a boom vang does (They are not intended to pull downwards the gaff, but bring it towards the middle), but rather like the 'brazas' (braces).
That's why I was confused.
Cheers.

 

The rake of the masts aft when used with sqare rigs allowed the yards to be braced closer to the wind, because of the backwarded standing rigging, so increasing the winward ability of those ships.

 

Rake will help center a boom, it offers some advantage in aspect ratio and makes it easier to perform slight CE adjustments to balance the yacht. Boom stive (it's relationship with horizontal) can help tremendously with keeping green water from filling the sails, on some points of sail, in certain conditions. Well thought-out, sea going craft have a substantial amount of stive for this reason. Generally, the more springy the sheer, the aesthetic value increases the amount of stive, other then it's practical reason. Many gaffers do carry a boom vang, but it's not the typical arrangement seen on Bermudian rigs. A tackle hanging from the boom, which is attached to the rail or two tackles (one for each tack) fixed on the rails which are attached as needed, are the common ones I've seen.

 

I built this boat and found that the weight of the gaff and the rake of the mast reduced twist. The boom also lifts although I never let the boom out more than about 50deg from cl. It was definately a fair weather sailer. I sailed it on a lake. It planes.
Ill post some photos tomorrow. Biggest wow factor for your dollar.