Aluminium anchor as main

[FranklinGray]

Originally Posted by thinwater

Are you sure? This suggests that a multi is 3.3 times as wide as a mono. More, yes, but I think perhaps there is a problem with the multihull multipliers. I've measure the load and get about 1/2 of that. Yes, they are wider, but the mast is shorter and they are much lighter. The conventional wisdom is ~ 140-160%.



The mono number is close.

The multi-hull uses width as they generally don't swing. The mono-hull swings so I use 30% of hull length as a general number but you can use more if you want. In my experience, if the wind is not shifty and gusty, one does not swing more than 30 degrees each way in strong winds.

One point I also want to make...I generally add 35 to 50 % of total to it for the mast and rigging. That it is more than you think. On my old Hunter 376, the mast was 54' off the deck and 6" wide. The hull accounted for 55 sq feet and the mast was 27.

The 1.4 is an educated guess to the drag on the wind. A flat square facing the wind is 2.0 and a round pole if I remember rightly is 1.2. A slanted/swinging hull I believe is about 1.4.

[FranklinGray]

Originally Posted by Jim Cate

I ask again: Length and height of what?

Jim

multi-hull it is width and height of the whole boat. You can break it down to hulls and cabin if you want.

Monohull it is 30% of length and height of cabin.

[Jim Cate]

Originally Posted by FranklinGray

multi-hull it is width and height of the whole boat. You can break it down to hulls and cabin if you want.

Monohull it is 30% of length and height of cabin.

OK, thanks for that.

Seems like variability in the size of the rig (as you mention upthread) are pretty significant, and the arbitrary correction factors you apply are, well... arbitrary. Would not including a factor for the rig, using height above the deck and some notion of plan area of mast and rigging be worthwhile?

In the long run, seems like dynamic loading is the important number, and that will be pretty hard to quantify. fun to play around with...

Jim

[FranklinGray]

Originally Posted by Jim Cate

OK, thanks for that.

Would not including a factor for the rig, using height above the deck and some notion of plan area of mast and rigging be worthwhile?


Jim

Yes, when I am looking for good numbers I do a more detailed calculation but usually I just want a good idea of the pull.

Originally Posted by Jim Cate

OK, thanks for that.

In the long run, seems like dynamic loading is the important number, and that will be pretty hard to quantify. fun to play around with...

Jim

The only time I am that concerned, it is when I am worried about hurricanes. During the two hurricanes I have rode out on anchor, there really wasn't much for dynamic forces. Now the mild cyclone I rode out in Tonga, well, that was very gusty and the chop was rough due to the tide going against the wind but I was on a mooring then so not that worried.