Mast Rotation Systems

[i_mac]

Hi All

Most multis use a spanner under the boom to control mast rotation - simple and easy.

But... I am rebuilding a 26ft 80's tri that has an arm in front of the mast to control rotation - there is no space behind because the boom is right at deck level.

The advantage is a positive tension to keep the mast rotated or over-rotated, the big disadvantage is the need to tack/gybe the mast manually. Some MOD 70s (Argo, Race For Water, maybe others) use a spanner / arm in front of the mast. Does anyone know if they have a system to tack/gybe the mast automatically or is it manual.

Any sketches welcome.

thanks

 

[Russell Brown]

Some people use an arm pointing aft with just an adjustable restrainer led to the boom to control rotation. I like that method, but may still need something (besides compression at the gooseneck) to induce rotation.

 

[i_mac]

Thanks Russell.

What you suggest is the easiest / most obvious option but there isn't a lot of space to fit it in as the gooseneck is right at deck level, plus all the halyards and cunno come in right there - even more crowded if we have a reef in. The mast has a forward facing arm built into it already as per the picture.

With the system we have, before a tack or a gybe we have to release the rotation line then pull the new side on manually after the manoeuvre - easy to overlook with a crew of just 4 - one steering, one managing runners and the main, one managing the kite and one doing all the rest.

Cheers

 

[patzefran]

If you have enough compression on the gooseneck, induced by aft location of the mainsheet attachment on the boom, and use two lines acting leeward on forward rotation arm to control rotation,
there is (theoretically, at hope !) no need to tune the rotation lines when tacking.

 

[Russell Brown]

If you figure out a better way, I'd like to know about it. My G-32 had 3 control lines, one to center the mast and two side to side. If you forgot to release before gybing, the spreader would poke through the main. That boat also had water ballast controls and a tacking bowsprit to add to the gybing checklist.

 

[Blueknarr]

Forgive my crude drawing

The geometry has to be spot on and would be difficult to determine.
- Counter crossing red and blue lines of equal static length should auto tack and jibe the mast.
- The green line would allow for mast rotation tuning by allowing the red/blue turning blocks to move in/out board.
- Force required to rotate mast must also be considered.