Running rigging - foot blocks

[impulsive19]

I am setting up a new running rigging deck plan and have many questions....I'll post them individually to stay on topic.


The boat is a heavy deep displacement monohull set up as a sloop with twin furled headsails - genoa and solent.


First question is: I'm coming off of a 1 1/2 inch track thru a twin sheet car with the genoa sheet to a 2 speed sf primary. Do I have to turn the genoa sheet thru a foot block aft of the primary - or can I lead directly to the winch?


The boat is center cockpit with a 12 inch step up deck aft - so not much room (maybe 3 feet) to step up aft of the winch. Is this enough distance if it is preferred to turn the sheet thru a foot block?


Thanks in advance for your thoughts....

[nuku34]

Hello to the OP (original poster),
A picture is worth a thousand words....I kind of understand your problem, but hard to visualize the geometry without a photo. Put a tape measure in it to give us some idea of the dimensions.
A foot block AFT of the winch might be useful to get the lead into the winch drum aligned properly height wise, but if the sheet leads into the winch drum from a position forward of the winch at the proper angle, it is not necessary. The sheet obviously has to enter the drum angling up from whatever block it comes from or you get over rides.

Since it seems like your winch is a foot higher than the genoa track, you'll need to somehow get the sheet over that step before it either goes straight to the winch or a foot block.
The downsides of the foot block, is that your are adding another source of friction, and that expensive block and its mounting has to be very strong since the load on it is doubled.

[OzDean]

Hello Impulsive, yes you can go straight from the jib car track to your winch but its not recommended for a couple of reasons 1) angle from car to winch will change as you move the car fwd and aft, and 2) the angle from the jib clew to the car means there is an upwards force component on the car and therefore the track, best not to keep the sheet exit aft from the car parallel to the deck so as to limit the upwards force. Therefore there should be a guiding or turning block aft of the car. Most yachts have a guiding block fwd of the winch and close to the deck so as to maintain the correct entry angle to the winch drum. However, some will prefer a block aft of the winch as this becomes a turning block and reduces the load on the winch. Such turning bocks are pretty hefty as they take a large load. If you type this phrase "jib sheet aft turning block to reduce the load on winch" you will see a few pictures.

[nuku34]

With respect to OzDean:
As I understand the forces involved in tackle systems, a turning block will not reduce the load on the winch. Its still just a 1 to 1 system. All it will do is make the load pull the winch aft rather than forward.
To visualize my meaning, imagine lifting a 1 kg weight straight UP off the ground by hand. Then attach a line to the weight, run the line through a (turning) block suspended above your head and down to your hand. Pull DOWN to lift the 1kg weight. You sill pull 1kg , just the direction changes. A 2 to 1 tackle will halve the force at the expense of doubling the amount of line you need to pull.

[SailingHarmonie]

Originally Posted by nuku34

With respect to OzDean:
As I understand the forces involved in tackle systems, a turning block will not reduce the load on the winch. Its still just a 1 to 1 system. All it will do is make the load pull the winch aft rather than forward.

This is correct. A turning block will not change the load on the winch.

You want to be sure that the line’s approach to the winch drum is within the spec for the winch, and stays consistent. That can be done with a block in front, or behind, the winch whatever is consistent with a fair lead, and with keeping the line out of the most common deck passage routes taken by the crew. Dealing with the changing position of the jib car can be trivial, or complex depending on the geometry involved.

[Bowdrie]

Virtually any headsail is going to create an upward load on the car, the load changing with the included angle between entry and exit from the car.
Be careful with turning blocks, don't ever get yourself within/between the entry/exit parts of the line.
The load on a turning block can be huge, it can be up to double the sheet load.

[impulsive19]

Thanks guys - I'm having trouble getting the pictures I uploaded to my 'pictures - alblums' from my profile to this thread.
Perhaps they can be viewed there...


As I understand the loads - one can assume approx 8,000 lbs coming off a large genoa. The recommended angle off the jib car to the winch is < 15 degrees - (which I have).
The load off the turning block would at least double in a 180 degree turn. The Andersen 68 ST I am using is rated at approx. 4000 lb working load.


I know that spinnakers / gennakers / etc. are typically turned well aft of the primary winch.


The concerns for my deck plan are:


1) The primary(s) will be located alongside of my center cockpit in a critical traffic area - narrow deck space that includes ingress and egress from the cockpit and dock.
2) The primary(s) will be located within 48 inches of a 10" step up to the aft deck


The forward deck plane coming off the genoa track and car - line line up well with a fair lead to the primary(s). Locating a large turning block in the 48 inches aft of the winch and before the 10 inch deck step up seems like a stretch.

[nuku34]

To the OP:
You say:
"The load off the turning block would at least double in a 180 degree turn".
I think you mean "the load ON the turning block"

The sheet load to the winch will still be max 8,000 lbs. Your #68 should be able to handle that load

ok.


Re your spinnaker sheeting problem, Yes, spinnakers and gennakers usually sheet to a turning block on the aft quarter, so you are going to have a difficult route to get from there to your primaries which are 10'' lower. You could mount a custom made fixed block on top of the step and another one on the deck just in front of the step. The sheet would run over the upper block and under the lower block and then to the winch. That will add a lot of extra friction, but I see no other way to do it.