12ft skiffs develop a new boom vang setup

Originally posted by JimC Originally posted by Granite stump... I do not think works unless you have shrouds going to the spreader roots Which it has, being based on an R rig.

I know, but shrouds going to spreader roots are quite long compared to lowers going to goosneck

Putting the mast of the stump complicates the whole lower mast bend and I do not think works unless you have shrouds going to the spreader roots

I bet you would be supprised how much the stump on your old boat moves about under kicker loads, it could even be more than an equivalent hogg stepped mast. thanks to loosing the stiffness of the mast at goosneck level.

Having lowers is also usefull to allow you to tune the bend in the lower mast.

Originally posted by JimC OK, Disadvantages of the compression vang. Bear in mind that not all of these apply to every boat and the extent to which these are issues varies from boat to boat. Sailboat design is always a compromise, and doubtless there are situations where the compression vang is the best solution. On a one design many of the disadvantages are irrelevant as all boats are the same. 1) Mast is pushed forward by the vang well above the gooseneck. This will require either staying or else a very stiff mast section. On a tension kicker the gooseneck can be off the mast, and thus the forward push taken out of the mast. In any case if the gooseneck require staying then the stays are much shorter and create less drag. 2) The compression strut affects airflow round the sail reducing power and creating drag. Even the Bethwaite dual luff setup (illegal on most classes) is a compromise and is also a pain to rig. 3) The arrangements nevcessary to stop the vang pushing the boom off the gooseneck are a nuisance 4) Its possible to arrange mast support with a tension kicker so that lowers are unnecessary, for instance with the mast stump used by some 12s and Cherubs, or the gooseneck on the front bulkhead like Moths. This reduces drag still more and makes it easier for the crew to position in front of the shrouds. For balance, the chief advantages include room under the boom the boom can be as low as desired no concerns about clearance for the kicker in internal layout. RS300 is an example where the advantages probably outweigh the disadvantages, as the bend issues are less of a concern on an unstayed spar, and the very low boom with its aerodynamic advantages is made practical.

Jim,

We use the GNAV on the MPS and I don't see any disadvantage; it allows the goosneck to be at deck level which a a great advantage.

Also you only need to move a very small amount of rope to change the kicker from full on to full off which is a big advantage in a short handed boat.

Rick

OK, Disadvantages of the compression vang. Bear in mind that not all of these apply to every boat and the extent to which these are issues varies from boat to boat. Sailboat design is always a compromise, and doubtless there are situations where the compression vang is the best solution. On a one design many of the disadvantages are irrelevant as all boats are the same.

1) Mast is pushed forward by the vang well above the gooseneck. This will require either staying or else a very stiff mast section. On a tension kicker the gooseneck can be off the mast, and thus the forward push taken out of the mast. In any case if the gooseneck require staying then the stays are much shorter and create less drag.

2) The compression strut affects airflow round the sail reducing power and creating drag. Even the Bethwaite dual luff setup (illegal on most classes) is a compromise and is also a pain to rig.

3) The arrangements nevcessary to stop the vang pushing the boom off the gooseneck are a nuisance

4) Its possible to arrange mast support with a tension kicker so that lowers are unnecessary, for instance with the mast stump used by some 12s and Cherubs, or the gooseneck on the front bulkhead like Moths. This reduces drag still more and makes it easier for the crew to position in front of the shrouds.

For balance, the chief advantages include
room under the boom
the boom can be as low as desired
no concerns about clearance for the kicker in internal layout.

RS300 is an example where the advantages probably outweigh the disadvantages, as the bend issues are less of a concern on an unstayed spar, and the very low boom with its aerodynamic advantages is made practical.

Edited by JimC

just for the techno-freaks this is what happens to all the loads compared to a normal kicker...