Mast Base Oriantation

Hello
I was looking at two catamaran plan and i saw that the Mast Base is not flat , there is 1 degrees going down to the front


https://drive.google.com/file/d/0B2Cwu0IkTCvtTHpEX1loYjZTTms/view?usp=sharing


Is somebody can explaim me why
Is that common ?

thank you

 

It is usually for water drainage. Sometimes that is also to induce bending to flatten the sail when the wind picks up and increases compression loads.

 

Ok for the water drainage
But is the mast is pointed 1 degree forward ?
for me il will put more 1 degree backward ?

did they cut the mast to make back the orientation as wanted
Or the mast have follow the Mast Base orientation ?
or can you use the mast shoe to change orientation

cat does not have back backstay

Hope i am clear
thank you

 

40 feet cruising cat

 

I don´t understand what you mean by orientation.

 

Hello
see picture on the right
if i put 1 degree on the mast base, the mast orientation will go forward (direction of Arrow) (saw two catamaran like this)

https://drive.google.com/file/d/0B2Cwu0IkTCvtdVJPN1hidHZQb2c/view?usp=sharing

Sorry with my english is not that clear

On this other cat see pic the mast base is backward

https://drive.google.com/file/d/0B2Cwu0IkTCvtX1UwOUplZFh3aTQ/view?usp=sharing

I can understand more this type of configuration


but why you will want to put 1 degrees to oriant the mast forward ?
It look verry ugly if the mast pointing forward
is the Shrouds help , to get it backward , to bend the mast backward ?

Thank to helping me to understand

 

The rigging controls the rake of the mast, not the mast step.

 

Probably a fixed non rotating mast, locking the mast to a certain position is a bit of a no for me as very often with real life sail CE's you need to be able to cant the mast forward or back to get the correct loading on the centre board and rudder once the boat is built and has begun its first sail trials.

 

http://www.boatdesign.net/forums/at...529-mast-base-laminate-concerns-mast-base.jpg

and what about this one ?

can somebody explein

The base making 4 degrees rake
plus you have to add 2 degrees from the shroud

How to decide , design , to select the rake on the mast on a 40 feet catamaran

Can i design mine with base 1 degrees forward (see this picture, begining of the forum)
with no problem , the fine tune the rake mast with no problem
Must be Ok because saw two cat bluild like this

phill

 

Mast rake prediction is not a very accurate science, it depends on many parameters. You need som tuning after sea trials ! so it is better to anticipate the possibility to change your mast rake within a sufficient range !

 

Mast base doesn't matter

Gday Phil

I wouldn't worry at all about the mast base. You will rake the mast forward and back with the stays/shrouds.

Very few masts rake forwards - I can't think of any stayed boats on the water with such masts, rake is always aft. (Etchells and Stars often let their masts fall forwards on square runs but on the mooring or upwind the masts are raked aft.) Some junk ketches have the fore mast raked forward.

The centre of effort of the rig has to be located near the centre of lateral resistance of the boat. Then you have to work out a black art called LEAD. On monos, lead helps with getting balance when heeled. On multis, lead is more problematic, some designs have none.

Build the mast base flat. The boat will pitch up and down anyway and even getting a cat to sit exactly flat on its lines is pretty near impossible. 1 degree will probably not be enough slope to overcome water's adhesion to surfaces, it sounds a bit silly to me.

cheers

Phil