Hints and Tips



German mainsheet retrofit

Updated - Detail of a conversion on a Sun Odyssey 39i


Newer Jeanneau's like the Sun Odyssey 409 are fitted as standard with a "German Admiral's Cup style" mainsheet system. The benefits of this is that the helmsman has full control of the sail without leaving either wheel, this is great both for tweaking the sail trim when the cockpit is full of guests, and also if the wind gusts up so that the mainsheet needs dumping to avoid rounding up.


An earlier hints and tips article provides an overview of the system and shows the conversion to a German mainsheet on a SO36i


The following photos and notes of retrofitting the system on my SO39i will hopefully help others who want to do something similar.


UPDATE I have also added at the end of this article, some additional images of another installation on a SO39i performance, that has some neater solutions to my own. More on this conversion is at this Jeanneau Owners Forum thread by Element.


The original 39i mainsheet layout shown in the following four images;

First stage was to remove the existing double Harken turning blocks - note the salt build up.....

The pads were cleaned then a pair of double Spinlock XTS clutches were bolted on - the picture on the right shows the mounting within the locker - four new holes were drilled and the units bolted with M8 bolts with nylock nuts fitted with large backing washers. Rather than use filler I opted to simply fill the two exposed holes with cheesehead machine screws.


Spinlock do not recommend clutches being used to lead rope at angles beyond 10 degrees, so the fitting is slightly compromised here - it is OK on the starboard winch, but the lead for the port winch as shown below is more acute. Nonetheless by bisecting the angle I have ended up with around a 15 degree bend and the clutches are symmetrically positioned on both port and starboard. I am reasonably confident this is fully strong enough. Whilst making a large stainless plate with a lead bulls eye would also work, in my view that would be more unsightly and probably unnecessary. (PS Even after 6 seasons use, no sign of stress or excess wear).


The next task was to provide anchorages at the inboard end of the boom (in my case a Selden) for the new blocks. As there was a spare alloy pin on the fitting simply by slightly enlarging one hole I was able to fit an M8 stud right through the boom, with lock nuts and eyebolt ends.



Next was the most difficult part, providing the turning blocks on the side deck. I wanted the installation to be as neat as possible and to avoid trip hazards, but if the turning blocks are mounted too far inboard they, or the mainsheets, will rub onto the coachroof moulding. Harken parts were outrageously expensive, so I opted for a pair of Barton size 7 turning stand-up blocks, these are well made and came with delrin bearings.


The best location for them seemed to be just aft of the main shrouds and forward of the genoa track, this area has smooth fibreglass and does not have the balsa core that is further out under the main sidedeck. The joinery at this point is effectively a single plank with internal handrail, just held with self-tapping screws, and with an extra pair of hands was not difficult to lower out of the way. The photo above shows the main shroud base and (slightly in the dark) - the Genoa track bolts. The square piece of timber is used to support the cover piece and I had to cut about 100cm off to allow access to the new bolts. Note that the 2 outboard holes continue the line of the genoa track. The Prism process moulded deck is only about 10cm thick at this point.


Four large washers with chrome nuts - which can hardly be seen, once the main joinery is re-assembled as they are covered by the internal handrail. (With hindsight, would be better with a larger backing plate, I have a slight stress crack on one side after 5 seasons, the Barton blocks have worked very well).


I had two 30cm spacers made of white acetyl turned by a local engineer to lift the blocks up to a clearance height.



The completed set-up is largely self explanatory but points to note - the 30cm spacers may have been better if they were around 50cm, as although the mainsheet does clear the coachroof when fully tightened, as the boom is let out it does just rub slightly - I have put some stainless wear pads to stop any permanent damage to the fibreglass, rather than now refit longer bolts and a thicker spacer.


The XAS clutches do slightly overhang the moulding at the leading edge - but they are very well secured, so I think this is only a cosmetic issue. Alternatives such as bespoke additional fibreglass or stainless pads are options , but in my view that would be both expensive and more unsightly that simply leaving the slight overhang.


I used 40m of new mainsheet - which was a slight over estimate - but I wanted to be on the safe side...., the rope I used was a 12.7cm (US 1/2in) from Barry Edwards "Boatropes" on ebay who I have used several times and find not only very competitive but also knowledgeable and very helpful.


Before the conversion I had to periodically re-glue the odd letter from the raised Jeanneau logo when they became detached - I am expecting this will be more of a problem now as the mainsheet runs very close to the lettering, if so I will remove them entirely and replace with a vinyl boat name graphic.


An unexpected outcome is that a spare clutch is available on the coachroof, which I am using for a spare main halyard - having replaced the original topping lift with an upgraded and longer rope.


One downside may be having surplus rope tails around the helms, so I had a pair of halyard bags made to attach to the guardrails made by Quantum sails to my spec, the base is made of mesh so any water/rain drains, and wide velcro flaps to fit the guardwires.



I made one mistake in leading the mainsheet - for ease I had threaded the mainsheets through the genoa cars to keep them tidy - silly mistake, what I now realise is obvious is that when the genoa is loaded up the sheave in the car will not turn, so the mainsheet then gets abraded if it is pulled.


So I have made the above "cheap" fix, I will see how it goes for the rest of the season, alternatives are to bolt bulls eyes, but I am trying to avoid too many additional holes in the deck, or possibly another genoa car - but they are well over £100 each. As is largely self explanatory, I replaced the standard track end stop bolt with a 8mm eyebolt that I had shortened and fitted a couple of nylon 8mm spacers (from Ebay) partially for appearance and to ensure the genoa sheet did not snag. (Still working fine..)


Overall the cost in 2012 was around £650, which has proved to have been money well spent.....


UPDATED images below from conversion on SO39i performance Element:

Overview of system with blocks installed at the front end of the boom:


The turning block on deck is just too low to have a straight line from the boom, so a metal strip is placed to protect the gelcoat


The mainsheet is led aft trough two small tube fairleads


Harken double turning blocks with jammers


Small bag to store surplus mainsheet


More on this conversion is at this Jeanneau Owners Forum thread by Element.


Malcolm - Serica SO39i