weight aloft

[mariner2k]

I've created a pattern for a bronze alloy mast cap for my new mast. But the guestamate on the weight was about 25-30 lbs. I made it a bit thick for overkill strength, but ultimately thought it necessary to reduce the thickness and weight, which I've done. I know that weight aloft effects the performance/ righting moment of the boat, but how much? I'm happy with the pattern now but I am still curious. The boat is 47' loa with a 55' mainmast.

[Brion Toss]

Hi,
Go sailing in the steadiest breeze you can find. While on the wind, measure your angle of heel, and of rudder, then hoist a weight equal to that of your new fitting to the masthead. Use a carefully-tended downhaul. Recheck that heel angle, recheck that rudder angle. At the weights and distances you are talking about, this will probably have an effect roughly equivalent to having a large person camped on the leeward rail. It will mean reefing that much sooner, spilling that much more coffee, steering that much harder.
You might then want to look up the origin of the term "overkill," and think about whether that is a useful term here. Base your scantlings on load-times-safety-factor.
Fair leads,
Brion Toss

[allene]

Originally Posted by mariner2k

I've created a pattern for a bronze alloy mast cap for my new mast. But the guestamate on the weight was about 25-30 lbs. I made it a bit thick for overkill strength, but ultimately thought it necessary to reduce the thickness and weight, which I've done. I know that weight aloft effects the performance/ righting moment of the boat, but how much? I'm happy with the pattern now but I am still curious. The boat is 47' loa with a 55' mainmast.

Assume a 30 degree heel then roughly the weight aloft will be about half as important as weight on the rail -- scaled by the distance away from the boat pivot point. 25 pounds up 60 feet is about 750 foot pounds. Weight on the rail might be 6 feet out and is about 85% effective at 30 degrees so to get 750 foot pounds at 6 feet is about 150 pounds, just as Brion said.

Allen
L-36.com

[mariner2k]

I've managed to trim the new mast cap weight/design down to around 16 lbs. Plus the new mast is lighter so I'm expecting the will be little differerece if not even favorable over the old rig. I'm very anxious to find out but I'm still a good month from stepping the new mast.