Re: chainplate bend angles

Fred C

Definitely helps.  I think it will be a good exercise to verify how close the originals are to the calculated values.  I appreciate the trig refresher - its been a long time.

To: "Flicka20@..."
Sent: Saturday, February 16, 2013 3:33 PM
Subject: Re: [Flicka20] chainplate bend angles

Hi Fred:
I would ignore the measurements from the old chainplates, especially because the port and starboard are different. They should be the same.
I would make a good sketch of the mast, including the spreaders. There are different size masts for the Flicka, and also different points where the lowers are attached to the mast, so the best thing is to sketch YOUR mast, and measure the dimensions. Now I would extend the sketch of the mast from the foot to the level of the gunwale, (where the chainplate bend is). (this will add the cabin-top height and the curvature of the deck correction) .When making the sketch for the uppers, they do not go to the top, but to the spreaders, so that has to be sketched like that.
After it's done, calculate the angles using trigonometry.  Add side angle at gunwale.  (Side of the boat to vertical).

For example. (Your mast maybe different).
The drawing I used was for a 29.8 foot Marconi rigging. Most masts are shorter.
From the Flicka drawing: Foot to lowers's attaching point =13.7'
From foot to gunwale attaching point vertically = 2'
Total vertical = 15.7'

from centerline of boat to gunvale attaching point horizontally = 3.85'

arctangent (3.85/15.7) = 13.73 degrees.
Side angle at gunwale (measured on the boat with an angle gauge with level) = 4 degrees (Yours maybe different)

Total bending angle 17.77 , round up to 18 degrees. Not that critical.

The top:

Total vertical to spreader (same as for lower's attaching point) = 15.7'
Horizontal between the gunwale attaching point and the point below the outer end of the spreader = 1.05'
{3.85-2.8} the 2.8 being the corrected length of the 3' spreader

arctangent (1.07/15.7)=3.85 degrees.
Total angle 3.85+4= 7.85  Round up to 8 degrees.

When you give it out for bending, mark the angles very clearly, so they don't bend it something silly, like 90 degrees minus your angle.
Best to also give the shop a piece of aluminum or even a heavy wire to show the correct angle.

I hope this helps.

-Ivan, Sans Souci on the LI  Sound NY

From: fredc_fl
To: Flicka20@...
Sent: Friday, February 15, 2013 12:34 PM
Subject: [Flicka20] chainplate bend angles

I have lowered the mast and removed the chainplates in preparation of having new ones fabricated. I am hoping that someone may have information on the chainplate bends. After removing them I noticed that at least one of the forward lowers were deformed.

This what I measured:

Uppers: 14 degrees.
Aft lowers: 20 degrees.
Fore lowers: 27 degrees (port) and 16 degrees (starboard).

The boat is sloop rigged and I am hoping that someone may have information to verify these measurements especially for the fore lowers.