Sheet Loads

[JimC]

Does anyone know if there's a rule of thumb for estimating sheet tensions? I want to know what they would be for a 200 square foot jib so I can choose the appropriate fittings e.g. 25mm or 32mm Barton track etc.

 

[ben tye]

Rope Size

The size of rope on a smallish sail is irrelevant, modern ropes are so strong. A more important factor is what size rope is comfortable to handle. A very small rope will tare your hands to bits. Remember the strength is in the core. I would imagine around 14 mm would be fine.

 

[prv]

The size of rope on a smallish sail is irrelevant, modern ropes are so strong. A more important factor is what size rope is comfortable to handle. A very small rope will tare your hands to bits. Remember the strength is in the core. I would imagine around 14 mm would be fine.

Did you actually read the post? He didn't ask anything about rope.

I've encountered a similar problem choosing parts for a storm forestay - all decent kit has a published safe working load, but it's hard to decide what your minimum SWL for a given rigging assembly ought to be.

Sorry, I have no figures for headsail sheet loads.

Pete

 

[rogerthebodger]

Does anyone know if there's a rule of thumb for estimating sheet tensions? I want to know what they would be for a 200 square foot jib so I can choose the appropriate fittings e.g. 25mm or 32mm Barton track etc.

When I was sizing my bow thruster the Vetus catalogue gave figures for wind load per square meter of the hull/superstructure areas for different wind speeds.

I think this could also be used to estimate the loading on a jib and thus the loading of the rigging and fittings.

The winch manufactures also give load/size estimates for their winches that are used to resist the wind load on the sail rigging.

 

[knuterikt]

Here are some usefull calculators for rig loads
http://www.harken.com/Calculators/

 

[PeterWright]

Speak to a professional!

Try asking your local rigger, then at least give him the opportunity of supplying the kit. If you can get it substantially cheaper elsewhere, then just tell him his prices are not competitive.

For what it's worth, 25mm track will easily handle a 200 sq ft jib, provided you install it with adequate fasteners, i.e. bolts, not screws with penny washers and nuts under the deck.

If the jib is a roller reefer, you might like to think about towable cars.

 

[Tranona]

Information in the Barton catalogue. 24mm track for boats up to 35ft overall. So more than adequate for your requirements.

 

[JimC]

Thanks All. I now Know all I need to know and it's only an hour since I asked the question. Where would we be without the forum?

 

[Pinnacle]

Where would we be without the forum?

Working.

 

[Deleted member 36384]

Sheet Tension Rules of Thumb

A rule of thumb for sheets: -

Sail Area Of Headsail x (Windspeed Squared) x 0.005.

(Length of Mainsail Foot x (mainsail luff Squared) x 0.005 x (wind speed squared )) / Length of mainsail Leach

The above formula is for a mainsail sheet at the end of the boom. Mutiply the answer by 1.25 for 1/5 away from the boom end, 1.33 for 1/4 away and 2 in the middle of the boom.

Dimensions in feet the force in lbs.

The answers from above should be doubled to provide a safety factor as the rule of thumb does not take into account shock loadings.

Source: The Boat Data Handbook, 6th Edition, Ian Nicolson, 2009 Adlard Coles Nautical

From Knuterikt's Post above the link to the Harken site gives: SL = SA x V2 x 0.00431 same dimensions

 

[simonfraser]

Try asking your local rigger, then at least give him the opportunity of supplying the kit. If you can get it substantially cheaper elsewhere, then just tell him his prices are not competitive./QUOTE]

Yeh, right, you would presumably be quite happy to pay the rigger for his time / training / legal implications without purchasing the parts required ?