Genoa Winch
Dear friends, I need some techincal advice ( Lars….) on how to calculate and/or modify the actual genoa sheet lay out of my 48’. The problem arises from the fact that two years ago I decided to replace all lewmar winches with new harken self tailing ones. I almost kept the same dimension/specification of the original ones except for the genoa ones for which I wanted to increase the gear ratio to be able to sheet-in easily even with a family crew. The actual ones are the harken 70.2 ST After several races and more that 1.000 miles I still considered them not powerful enough; the effort required is considerable ( genoa is 130%) and after a series of tacks the crew need to recover. Of course I tried it as well and I can tell you that sheeting-in upwind is a serious matter.I then approached Harken again to have some help , and the answer was that this is due to the fact that the genoa sheet ( like in most of the S&S) is first sent back to a big pulley before going to the winch. As per Harken specs http://www.technicalsailing.it/consiglitecnici/PDF/Formule/formule_di_carico.pdf) this means that the load to the pulley is increased of 200% . Harken says that this + 200% is also valid for the winch which therefore looks now undersize.
Do you think this is possible? - it would seem only to add the
friction of the block - nothing like 200% They suggested me that even the new 90.2 st winches would not be enough , and that the only thing t do is to go directly to the winch from the genoa car , bypassing the bigt aft pulley. Do you think that I could face problems on the genoa track ( still the original one) for the increased load? Has anyone experienced and solved the same problem?

Sergio

Clarion of Skye 042/48

Sergio,
someone expert in rigging will give you more technical advices but for what concerns basic physics laws I can assure you that there must have been a serious misunderstanding between you and those people.
If there is no friction, the radial load on the shaft of the big aft block is indeed twice the load along the sheet at the sail but the tangential load at the winch is exactly the load at the sail. Galileo would get very mad if someone asserts differently.
Friction complicates matters. The strong radial load on the shaft of the big aft block may affect its turning friction and change the load at the winch of any kind of amount depending on the bearing quality. I insist, any amount: from few per cent up to infinite. Even Galileo would not be able to give a number if he does not check the bearing!
If I were you I would first try to lower the turning friction of the sheet block and of the big aft block before considering to change the winch.
In my case, for example, one big aft block has almost seized so the increase in load is close to infinite. I am planning to dismantle them in the next months but I wonder if originally they were made with ball bearings or not.

Daniel, 411-004

Dear Daniel, thank you for your very professional answer. If I understand well the load on the winch is the same either if the line is coming from the aft block or from the genoa car ( direct). The difference stays only in the friction in the aft block which could influence the load on the line.
If you agrre I would like to forward your comments to harken Italy to have their reply.
As far as I know the two aft blocks do not have any inside bearing, and it looks quite difficult to install new ones . The only option could be to have two custom blocks made to fit , even if I honestly don't know how and where to order them.
I will try to add two "temporary" harken 100mm air magic blocks to see how it works.
Thank you again for your help

Sergio Clarion of Skye 042/48

Dear Sergio and Daniel

I would agree with Harken's advice to go straight to the winch in order to avoid the additional friction in the turning block. This can usually be arranged by adding a sheet car near the aft end of the genoa track, and leading the sheet through this car to the winch. The additional car probably can have lower strength as the sheet deflection angle is usually smaller.

This works right away on stbd side, as the sheet is meeting the winch drum on the outside, but on port side it may be tight. A lead block further outboard may help.

The original turning blocks have plain bearings. Harken roller bearing blocks are not intended for the highest loads, the rollers flatten, but this depends on how big sheave diameter can be used. For restricted diameters there are also Harken High-Load sheaves available, and they have plain bearings.

Best regards

Lars

Lars, thank you for your kind answer. Do you hink that going directly to the winch will have any impact of the genoa track? would it be strong enough for the extra load (? assuming there will be an extra load)

Sergio Clarion of Skye 48/042

Sergio

Provided the additional sheet car is a foot or more from the ordinary car, and the angle to the winch not too steep the loads are low and not of concern

Lars