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Developing the swing rig

I am starting from scratch setting up the rig.  The spars are Sailsetc carbon and the sails are little used Housemartin and they all look fantastic.  All the luffs are tied on and I understand the trend is not for sleeved luffs.  My challenge is, on the IOM, I have precise settings for all rigs and all conditions.  On the Marblehead I have two measurements.  The jib boom on the swing rig should be approx 40mm from the mast and the jib foot approx 10, off the boom.  Other than that, I will be doing all my initial sailing by eye.

The first days friendly racing will be on 10/12/22 at Guildford MRC if there is any wind and we don't freeze.  I did have some commissioning days at Frensham and have been able to balance the boat with the swing rig so I have started the development.   

6/12/22 Racing at Frensham

A perfect day with a perfect 4-8 knot breeze, ideal for tuning and speed comparison.  Fortunately one of our member brought his brand new Grunge to the club with an A rig put together by Robot yachts and a fine piece of machinery it is too.  More on this later.

My A swing rig is simplicity itself and very easy to set up.  I start with the jib luff tension using the bowsie at the head of the sail to the mast and then set the backstay to provide the right mast bend and therefore upper camber in the sail for the conditions.  Next I adjust the jib topping lift so I have about 25mm of twist and that the leech is firm.    If it isn't I apply more luff tension and readjust the leech line.  The foot has approx 10mm depth.  Once the jib is set with the aft side of the boom 40mm from the centre of the mast, I look at the twist in the mainsail and look to have the upper part of the sail parallel to the boom by adjust a bowie that hold the clew down to the boom.  The main foot is set with approx 10-15mm from the side of the boom.  The side of the boom is set 10 -15mm from the centre of the mainsheet post.  Take a final look and then put the boat on the water to see how the rig looks.  I am looking for the right twist with slight give in a breeze but not too much as this will reduce acceleration.

On the water the boat performed perfectly although I did need to rake the swing rig back slightly as the boat had a tendency to bear away.  I won the day although I struggled in two races having picked up two 4 ft reeds which neatly wrapped themselves around the fin.  I was leading both races.

What did I learn today

How a GIZMO works which I explain below.  From what I can see, if the boat is set up correctly on flat water you may not even need the GIZMO

If you set up the boat correctly and sail well, it is possible to be competitive.  How this will translate in real competition who knows.

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I love setting these rigs up.

How does the GIZMO work.  

Whilst I am going to play with my rigs for a few months before I start adding complications, I was very interested to see what the GIZMO does by looking at the rig on a new Grunge from Robot Yachts.  

There are two pictures below showing the sheeting lines for the main and then the jib and I will describe what the GIZMO does to each.  Graham Bantock also has a nice plan showing the layout on the Sailsetc web site.  The GIZMO lever is clearly visible bolted to the base of the mast on the starboard side.  The cord connected to the top end of the Lever is part of the mainsheet.  At the top of the mainsheet post are two plastic balls through which the mainsheet is threaded. When you sheet in, the boom is brought in to the distance of the two balls from the mainsheet post so you cannot oversheet.  If you did not have a GIZMO the story stops here.   But with the GIZMO you sheet in a bit more and you pull the lever in the direction of the mainsheet.  There are 3 cords attached to the other end of the lever.  2 to adjust the main and one to adjust the jib.  Here are the pictures of the GIZMO sheeting arrangement and a video below of the sheet movement caused by the rotation of the lever

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Application of the GIZMO lever tightens the leach of the main slightly at the same times as flattening the foot, at the same time as increasing the cunningham, whilst on the jib, the jib boom is pulled down slightly but the clever bit is as the jib boom is pulled down, the leach line is eased to maintain the same leech twist.  In addition the jib is sheeted in slightly.  So the overall effect of the LAM is to close the main leech, tighten the jib luff and sheet in slightly and I guess you point higher.  Here are two videos that show the LAM in action on land.

Of course the key to effectively use of the GIZMO is setting up the rig in the first place.  Get this wrong and the GIZMO is of no use to you

How do you move the GIZMO using the transmitter.  You can either set a toggle switch to engage the GIZMO or use the fine adjustment.  The only challenge with the fine adjustment is you might forget it is applied or not.  My preference would be for the toggle approach as the GIZMO is either on or off.

Bear in mind, if the GIZMO is applied with a large amount of movement on the lever there will be a force applied to the winch and this will burn up battery power.


What might need doing on my boat.  

The immediate things on the current rig are to lower the Jib boom to get the jib closer to the deck

The first outing against competition at Abbey Meads lake

I always thought this would not be an easy entry into the Marblehead class with oldish sails and rig.  Today we sailed in near calm conditions and discovered three immediate problems with the swing rig.  Firstly it would not swing easily and for the first few races I was sailing downwind with the sails stuck as though on a beat.  Second the jib thought it would be fun to maintain a central position in the light breeze and lastly the main remained inverted after a tack if there was little or no wind.  When the wind was up, 4 knots or so the boat took off and I could race competitively.  As soon as the wind died the boat stopped.  I liked it to being in a boxing match with one hand tied behind your back

Results were poor and I retired from the first two races as I could not run downwind with the boom out.  I can sort the jib out but believe I may need a light wind rig If I am to sail in these conditions competitively.

My thanks to Roger an Peter Stollery for organising/setting up and packing up and Hugh McAdoo for acting as race officer.  It was a great day with relatively warm sunshine.

At home I got my thinking cap on and took a close look at the mast bearings on and under the deck. I removed the additional cord at the bottom bearing and cleaned the bearings adding some PTFE spray which has no residue and will not attract dirt or dust. The mast is now rotating freely.


The jib requires a bit more work. Like an IOM I believe a straight boom should sort the problem and will allow me to lower and adjust the jib height a little as well as moving the end point of the jib boom closer to the sheet fairlead which gives more precise sheeting.


Here is a picture of the current jib configuration..

Screenshot 2022-12-14 at 11.23_edited.jpg

I have a couple of bits of IOM spars to play with. I will use a straight piece of 11mm tube as a yard from the gooseneck and use 10mm lightweight jib boom. Without a Gizmo the rigging is so simple and I will continue with the grommet for sheeting until I eventually fit a Gizmo and replace the booms with carbon. The jib clew will be tied down and a bowsie run to the end of the boom to adjust the foot.


What I cannot cure is the mainsail inverting when I tack the boat in calm conditions. The cloth is too stiff and there is too much luff curve. I could apply massive prebend but this will tighten the jib luff and reduce the ability for the jib boom to swing freely. The only cure is a lightweight rig. I will save that one for later


Another annoying issue is the mainsheet post is glued in. There is a tube that runs from the deck to the floor which fits a Sailsetc mainsheet post nicely. When I drilled it out, there was an inch of a sailsetc mainsheet post and then an inch and a half of another post. Anyway its all out now and I can fit a new post and be able to adjust the height of the post which is key for the B and C rigs as the booms are higher.


Finally got round to reprogramming the RMG Smartwinch to increase the range of the sheet movement so I can get the main boom at 90 degrees to the centreline of the boat.  Here is the link to the programming guide on RMG Web site

As an aside, the boat came with an unused 2018 set of BG sails for the swing rig so I will get them measured and try them out.


There are a couple of events in January/february where I can get a better understanding of how the boat goes.


Lastly I weighed the various components of the boat to see how I stood against the current thinking.


  • Swing rig 356gm (OK I think as there is no data. Could use lighter cloth)

  • Hull 924gm (Recommended 900 -1000gms. New Pro boats 800-900gms)

  • Fin/bulb 3.618kg (3.2-3.4kg is recommended so I may have the opportuntiy to lose 200gms but I will wait until I have race data before making any adjustments here.

  • Total 4.898kg (recomendation is 4.5 to 4.8 so I am within this range if I lighten the fin


Thats it for now. Lots sorted. I guess that is life with a new second hand boat as you work it up for competitive sailing. Waiting for the bits from Sailsetc to complete the changes and then it is off to Chipstead in January. My schedule will be going up on the results page.  There are only 12 Marblehead events so progress and learning might be a bit slow.

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