Loose lower shrouds

Oct 30, 2019
64
I had been think about the complaints some have had with the cabin top
raising up on top of the bulkhead at the mast on either side. St.
Brendon had had a problem with her Bulkhead. Some have had problems with
the bulkhead beam bending down under the mast. I have sugested at least
once that in the modern practice of tightening the shrouds banjo tight
we might be excedding the strain the designers intended over a long
period of time and that this presuure may have slowly damaged the wood.
Concidering these boats were designed in the sixties more in the
tradition of 1950's wooden boats Than the modern wide racer cruiser some
of which I am told have a downward pressure on the mast of 10,000 lbs.
When you concider the lower shrouds at the angle they pull are trying to
squeeze the hull and cabin in. I think it has cause the cabin top to
bend upward under the load. I have had a couple of wooden boats over the
years that the shrouds had to be kept fairly loose on.
I loosened the shrouds on my Vega until there was almost no load on
the lowers except when sailing. I watch the mast especially when sailing
reef in about 25 knots of wind. It bent slightly. I couldn't tell any
difference in the way she beat to windward or how close she sailed. I
don't think I will ever tighten them again and I know I would keep them
loose if I were going to sea. I think she was designed to be sailed that
way. I just can't imagine being at sea for a month in bad weather
knowing the bulkhead was under an extremely heavy load along with all
the other loads are wringing and twisting her.
I would suggest that most of you should give this some thought and
even give it a try. If you are going to race you can tighten them for
racing and loosen again when setting at the dock. If you mark the
turnbuckles it would only take a few minutes to readjust the rig for
racing. Think about this Doug
 
Dec 2, 2000
34
I also have followed the discussions of the failure of the main beam and cabin top problems. Looking in the files there is an excellent article in the file: VegaRigTune.txt
4 KB pjacobs55 Dec 19, 2007 :How to tension the Vega rigging. There are many resources available but just for the challenge:
A quick calculation which is made easy with the on line calculators, Bolt Torque, Axial Clamp Force, Bolt Diameter Calculator | Engineers Edge| www.engineersedge.com, that a .25 inch diameter screw will exert 1000 Lbs of axial force when 48 inch pounds of torque is applied. That is approximately 5 pounds of force at the end of a 10 inch long screw driver turning the turn buckle. Because it is a turnbuckle and has two screws the force has to be cut in half so the 1000 lbs becomes 500 lbs. There are six shrouds and two stays. Eight time 500 lbs gives 4000 lbs. If you get exuberant and really crank you can see how fast the load will go up to 10,000 lbs

We have owned Vegabond since 1973 and, knock on wood, there is no problem with the cabin top or the main beam. The rig is tuned so the stays and masthead shrouds are tight. The forward lower shrouds are snug and put a little bow in the mast when the backstay is tensioned. The aft lowers are brought up so there is no slack.

And as the comments from Steve in the original article state the position of the mast fore and aft will affect the weather helm. Rake the mast aft and you will increase the "weather helm". Position the mast forward and you will create a "lee helm". The result is noticeable even with the limited amount of adjustment available in the standard turnbuckles.

I look forward to hear other opinions and comments.

Jim
Vegabond 1870
Wickford, RI