Masthead gennaker for fractional rig

Im thinking of adding a gennaker with a diy carbon bowsprit to my fractionally rigged quarter tonner for light airs. This is not for racing, just to put in some miles single-handing. The current rig is prob ely 70s, thick sectioned alloy, holding well. I'm wondering if I would need to alter the standing rigging (ie add further backstays in addition to the current one)? thanks

 

My son and i did this about 5 yrs ago on a 24ft uldb which i designed, built and launched 25yrs ago. The boat was designed to use a soling rig (lots of cheap,lightly used sails available in olympic runup years). The mast is light and heavily tapered above the hounds so we added a set of jumpers angled aft which does the job of keeping the top of the mast from snapping off. The halyard exited the mast just above the forestay in the original location through a harken exit box which we swapped out for a double sheave version which allowed us to run the halyard up the face of the mast to a hanging block at the masthead. We bought the sprit, i dont remember the length but it cantilevers 5ft and exits through the bow just below the forestay on center and articulates about 15 Degrees each side. The asym is from a Melges 24 and is about 250 square ft bigger than the Soling sail. Overall its been a great improvement, we will be upsizing the backstay this winter just because its time to replace all the standing rigging anyway.

Steve.

 

A simple system to add a sail is to use your spinnaker halyard to raise a block with a new halyard .

The bottom of the block will hoist a stay for the sail to be hanked to.

This is frequently used by folks that want 2 headsails for long downwind runs , as its cheap and works .

 

The Hobie 33 used a masthead spinnaker on a fractional rig. Google Hobie 33 and you get to the owners website. Also some of the Wylie Hark Farm's in So Cal added masthead spinnakers for light airs. A friend of mine did this and I don't remember him having any problems or that he added any jumper stays to support the mast. Good luck with your project.

 

The H33's kite is above the hounds, but not quite masthead. Sort of in between, like my boat. The H33 rig was originally designed for this.

The Hawkfarms had jumpers already.

 

You won't need any more backstays, but you might need some help athwartships if you plan to do any tight reaching or get caught out in a big breeze. It all depends on how long your unsupported section is, what the moments are, and how you use the sail.

Your jumpers don't have to go backward since you already have a backstay. They need to support the rig sideways. So they can go to the side or even forward 30 degrees or so. My boat uses an Etchells rig with the spinnaker hounds about 5 feet above the headstay. It has jumpers added to help support the rig when reaching (and when flogging in a knockdown).

 

thanks

thanks everyone for replies. The athwartships reinforcement makes a lot of sense. Maybe a single 4 mm dyneema line that can switch sides might work. Would it need to be secured at the mast head, or could I use a running line like a topping lift?

 

Angle would likely be too flat to be effective. Depending on the strength of the existing mast this could be a significant mod. You should really think about installing jumpers as Paul mentioned. The downside of doing it wrong is the mast might break so it's no place to skimp.

 

Thaks for that

if I was going to add jumpers, is that something that needs a professional rigger to do, or can I get an estimate of angle for the jumpers, take them from mast head down to x point on mast, and use say dyneema 4mm? I'd like to keep it as light as possible, maybe even shape the jumpers from carbon fibre.
any help much appreciated.

 

The jumpers should go somewhere close to the existing hounds (just above) to ensure the upper shrouds take the load they impart.

They should be long enough so the angle of the wire fron the top of the mast is at least 11 degrees from the mast wall.

You will have to take a look at the way your boat is set up and make sure you dead end the wire in a position so that it's run does not interfere with the sheeting of any of your headsails.

If you already like the mast bend you have upwind it would be best if the struts had no forward angle and were simply straight out from the side of the mast.

 

I did something similar to what you are planning on my boat, had to move the shrouds higher to support mast. I have a very beefy mast section as well. To do the bowsprit on the cheap I bought a piece of scrap aluminum pipe, about 2.5 inches diameter and it has been lashed on the bow working beautifully for the last 10,000 miles using a 30 ft luff asym. Works great and very easy to undo the lashings when I need to shorten the boat to fit in a slip. The pipe is about 6 ft long and hangs over the bow a bit over 2 ft. Cost about $7.