BYYB Forums

anyone ever mount the stays on the deck instead of the plate on the side of the hull system?

I don't know of anyone that's done this to a Stevenson design, though some of the less popular designs may have just this feature.

I use this method frequently to get a better sheeting angle, but this is typically on rigs that can benefit from tighter sheeting angles. As a rule, most gaffers don't point well enough to warrant this feature.

Lastly, you need at least a 10 degree angle for the shrouds to hold the mast up without a set of spreaders and lots of wire tension. If you degrees the angle below 10 degrees the load increase exponentially.

Greetings Bob,

Like Paul says ...

(10-03-2011, 11:10 PM)Paul Riccelli PE,NA link Wrote: [ -> ]Lastly, you need at least a 10 degree angle for the shrouds to hold the mast up without a set of spreaders and lots of wire tension. If you degrees the angle below 10 degrees the load increase exponentially.

I did that calculation once, and the answer is ....


Reading right from the materials list, the mast is made up of a 47" stub and an 11' 2" folding mast, which total 181 inches. Subtract from that 6" down from the top for the eye bolt location, and subtract 20" to reach the deck height, and the stayed mast length from deck to eyebolt becomes 155 inches. The front shroud location is in line with the front joint in the deck, and we know that the front decking triangle was cut from a single 48" wide sheet of plywood. Add to that the two little filler triangles and the deck width becomes 50". Half of that is 25". Our rigging triangle is now 25" wide, and 155" tall. The tangent is 25/155, or .1613, so taking the arctan(.1613) in degrees reveals that the shroud angle is already very tight at 9.16 degrees for the front shroud. A tape measure reveals the rear shroud is 36" from the mast, so degrees(arctan(36/155)) = 13.8 degrees. And even these angles are optimistic as they do not account for the thickness of the mast and the size of the eyebolt which will reduce the 25" base by a few inches. Adding a spreader plate to the top of the mast to keep the shrouds clear of the gaff as some have done makes this even worse, maybe 8 and 12 degrees for front and rear shrouds.

I will not bore you with the calculations, but the righting moment of a Weekender hull with two adults sitting on the windward rail at 28 degrees of heel tops out at about 1,400 lbs. That means that each of the shroud lower attachments better be able to support 1,400 lbs. I feel pretty confident about attaching 1,400 lbs to the hull sides through stainless steel chain plates with backing blocks and through bolts and loading the plywood along its length with the deck/hull joint providing lateral support to keep everything aligned under compression. If you move this attachment point to the deck, the load will now be a tension load perpendicular to the plywood deck trying to pull everything apart, and I doubt that there is enough structure there to take the load.

Cheers,
Tom

Ok that answers that thanks guys!

Not so fast.  I did it on my Weekender.  I put U-bolts thru the side decks with a spruce backer board under the deck to spread the load.  It has worked fine for ten years.

Bill

Yep, you can use a backing plate of reasonable size and it should spread the loads well enough. Fortunately, the Weekender rigging loads are quite modest.

Wire strengths for shrouds should be twice the full up displacement, plus a safety margin. In a rough patch and heavy lump of sea, you can "fall on your beam ends" and easily double the shroud loads. Fortunately, (again) most don't take their boats out in these type of conditions.

cool! i like that idea, since i'm building a wooden mast, i'm using 2 stays on each side, any idea how far for and aft of the mast i should position them? i was thinking the "U" bolt idea as well, with a backer board as large as possible

Bob I forget what you are building.  Weekender?  Are you putting in a hinged tabernacle?   My unsolicited take on this is two fold.  A: you are giving up rig strength for potential simplicity to build.  B: you are inducing two major safety issues.  If your stays or eyebolts give way the gate hinge is all that holds the rigging.  You are also creating falling hazard on a already narrow deck.  I will not even mention the 4 holes in a horizontal surface.

Superskipjack with a hinged mast

The hinge IS NOT STRONG ENOUGH TO HOLD THE MAST UP for any longer than it takes to attach the stays and shrouds properly.

Mike