Determining spreader length/size

[lincolns1st]

As I start laying out the beams to mill for parts, the plans I have don't give any details on the spreaders except location...they don't have the view from the bow. Where can I find the formula to determine the spreader length and sizes?

[Jay Greer]

Here is a point where you might consider research into similar designs ea, sail area and disp. Reviewing designs such as seen in UFFA Fox's Second Book or The Good Boat series by Roger Taylor are excellent sources of information. Info can also be found in "Skene's Elements of Yacht Design". Herreshoff also devoted a chapter to the subject in "The Common Sense of Yacht Design".
Jay

[mmd]

How big is the boat? A sixteen foot dinghy has a lot more tolerance for error than a 40-ft ocean performance cruiser.

[lincolns1st]

Thank you gentlemen, I have ordered Skene's yaght design so I'm glad to see it'll be helpful there. mmd she's a 32'-10" Alden cutter, marconi with a 10'-10" beam. The mast is not going to be original and I'm not sure I'll able to get the height shown on the plans.

[donald branscom]

Thank you gentlemen, I have ordered Skene's yaght design so I'm glad to see it'll be helpful there. mmd she's a 32'-10" Alden cutter, marconi with a 10'-10" beam. The mast is not going to be original and I'm not sure I'll able to get the height shown on the plans.

You have the best book thats for sure. His formulas for masts really work. Not like other books. Real world.
The included angle must be at least 12º That will help determine the position of the spreader.
You need to draw it on a piece of paper from the deck view fore and aft.
Since your beam is 10 feet 10 inches it WILL work.
The spreader goes about 2/3 up the mast.

You can look at some other boats also but make sure to draw it on a piece of paper.
Brent Swain steel boats are about the same LOA and beam and there are many others.
The next decision is wether or not you will have standing rigging that has uppers and lowers that run all the way from the deck to the top of the mast OR if you will split them at the spreader. The best is from deck to top of mast for side stays. Inner forestay for storm tri sail and foward lowers and aft lowers will be needed.
Put the aft lowers about 1 foot aft of the mast and on the cabin sides. Use a piece of string and make sure the sails and running rigging do not run into the lowers.

Also you need to decide if you have a sloop rig the inner forestay will go 2/3 up OR if they will meet the lowers at the spreader position. on the mast.

There is a very good book that explains rigging and it is a book written by the worlds best boat designers. Like McCurdy and Rhodes, Sparman Stevens and others.
The book cover is red white and blue and is paper back size. Can't remember the title but the book goes over each part of a boat and explains the best designs for each part of the boat.

[mmd]

A 33-ft sloop - particularly an Alden - is a reasonably big boat. Not much smaller than Forumite Wilson Fitt's, in which he recently did a solo trans-Atlantic voyage. Therefore, it would behoove one to get this right the first time, before one gets into a situation far from home where even the thought of insufficiency is frightening. With all due respect to the knowlegable and experienced folks who have posted above, it gives me the heebie-jeebies to go about mast design using terms such as "about" and "at least" and "similar". I'd want to do a proper engineering analysis of the mast as a stayed pillar to determine what the static forces are on each component and the mast itself (not really that hard, as it is a rather simple structure, but it requires a scale drawing of the mast & standing rig) and to determine the optimum angles of stays and spreaders. With "hard" numbers in hand, one can then compare these to the same data derived from existing structures and from texts to determine appropriate factors of safety. Then one can apply the safety factors to the results of your custom mast to arrive at mast and rigging scantlings that you can have confidence in.

But that is just my approach, and I am admittedly rather fussy over having hard numbers for boat stuff instead of educated guesses.

BTW, unless the newer editions of Skene's have changed the chapter on rigging, it assumes that your rig will be rather low-tech, so the standing rigging will be over-sized if you use more modern lay stainless or synthetic cables. Just sayin'...

[lincolns1st]

I appreciate your input mmd, I like the substance of my Alden, I do have the sail and spar plan and would like to stay to the original as close as practical for safety and pleasure, very simple plans, but he does leave a bit to the professional builder to figure, of which I am not. For instance the stay sizes. I have lots of time and work to get to in the mean time. I'm hoping to get a close rough idea of the spreader size for milling, I can always glue up.
NS...I'll be up there, some day!

[lincolns1st]

I've been reading Foss's Rigging Apprentice and someone with experience has offered to run some numbers with plans in hand, to determine the spreader construction. I can't wait to do some calculations and see what I have to work with. I think the mast may work without too much alteration.
I have all this info and I'm still waiting for the yard to shrinkwrap the boat-cover so I can start with the deadwood repair! Just got a few inches of snow to clear out! There is of course the small matter of Time!