Mast heights, boom lengths and aspect ratios

[Allan Jennings]

I am building my boat 53 foot Roberts, the design the end of the boom ends up over the steering wheel. If I lengthen the boom there will be bending moment introduced into the boom and spare length not used. What happens if I increase the length of the foot and shorten the mast to maintian sail area,- do I lose performance? It is not a racing boat so would it really matter? At the moment the aspect ratio of the mainsail is 3:1. With an extended boom it comes down to 2.5:1. Either that or any ideas on the main sheet as i do not want it in the cock pit?

 

[D'ARTOIS]

Why do you want to lengthen the boom? What is the issue?

 

[Allan Jennings]

I need to connect the mainsheet to the boom. The traveller has to go either behind the cock pit in which case the boom isn't long enough or on the coach roof where it is going to be too close to the mast.

 

[panthablue]

Boom length

I had the same dilemma when I built my boat. In the end I opted to have a long boom with the mainsheet traveller at the stern of the cockpit. it works perfectly.

Dissadvanteges - weight of increased length of boom
Advantages
mainsheet traveller is out of the way
Mainsheet can be adjusted by the helmaman just like dinghy sailing
the mainsheet fittings can be lighter because the load is less due to the longer boom length. (force x distance)

Good luck with it

 

[TimClark]

You should be able to put a traveler bar right infront of the wheel that is seat height. That's how it's like on most of the J Boats. Good Luck.

Tim

 

[Vega]

Take a look at this boat. Interesting concept for a cruiser.

http://i19.photobucket.com/albums/b152/vega1954/luffe43ds_7.jpg

 

[panthablue]

My boat is tiller steered

here's a pic.

http://www.combeproducts.com/steersman/Justine2a.JPG

 

[FAST FRED]

From an aerodynamic point you don't figgure aspect ratio by simply dividing boom legnth into sail hoist.

Span (hoist)squared divided by area , with an optimum for a cruiser at 6-1 seems to work well.

The formula works for jibs too.

FAST FRED

 

[MikeJohns]

I need to connect the mainsheet to the boom. The traveller has to go either behind the cock pit in which case the boom isn't long enough or on the coach roof where it is going to be too close to the mast.

What about a combination boom gallows and main sheet track above the cockpit ? With a longer boom you might need a tripping reef in the main to keep the boom end away from the waves in boisterous seas.

 

[Allan Jennings]

What's a tripping reef?

 

[MikeJohns]

A tripping reef is a reef line that extends from the tack to a point several feet above the clew on the leech. Its purpose is to raise the boom end.

 

[HeloDriver]

' tripping reef

More commonly called a 'flattening reef'?

____________
HD

 

[julleras]

Allan:
I would check that by lengthening the boom (and the mainsail, I suppose) you do not diminish too much the lead of the Center of Effort vs the Center of Lateral Plane. You could end up with a LOT of weatherhelm.

Check with the designer.
There's a good discussion in http://boatdesign.net/forums/showthread.php?t=1898&page=

 

[Allan Jennings]

OK So I will keep the original sail plan and just make the boom a little bit longer so the mainsheet drops behind the cock pit seat and fit a tripping reef so that the boom is lifted when heeling in strong winds to stop the boom from dipping in the sea.

The only thing to work out is how much longer do I have to make the boom, does the mainsheet need to drop vertically from the end of the boom when the boom lies on the centre line of the boat or can it be inclined parallel to the topping lift?

 

[sharpii2]

OK So I will keep the original sail plan and just make the boom a little bit longer so the mainsheet drops behind the cock pit seat and fit a tripping reef so that the boom is lifted when heeling in strong winds to stop the boom from dipping in the sea.

The only thing to work out is how much longer do I have to make the boom, does the mainsheet need to drop vertically from the end of the boom when the boom lies on the centre line of the boat or can it be inclined parallel to the topping lift?

The more perpendiculer (vertical) it is the more effective it will be. 10 to 20deg off is not too bad though (98 to 94% effectiveness, respectively).

Bob