Mast pre bend

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pcatterall

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My sail maker says measure the bend so he can make the new main.
My mate on the boat in Spain says there is non!
The photo I have of the old sail clearly shows a curve up the luff.
The boat is a Neptunian, the back stays have no adjuster.
I thought that some back bend was the norm but have no figures for this boat.
I can make some sort of estimate using the old sail and adjust the stays accordingly or just start again with figures that my friends
on this forum will supply!!

Help please
 
The mast on a Neptunian is a short, stout affair with absolutely no pretence to performance.

'Straight' is the strongest configuration and there is no reason to deviate from that.

With a masthead rig and a deck stepped mast, the only way to induce any bend is with the forward lowers. But why would you bother? KISS!
 
Motor_Sailor said:
With a masthead rig and a deck stepped mast, the only way to induce any bend is with the forward lowers. But why would you bother? KISS!
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Some reasons are to prevent mast panting in stronger winds, to reduce the likelihood of fatigue in the mast, to prevent mast inversion when sailing downwind and to match the cut of the mainsail. I cannot speak for a Neptunian but all of these apply with many masthead yachts.
 
Yes I know what lower shrouds do but my point is, why would you use the forward lowers to induce mast bend in a rig like that on a Neptunian? What would mast bend achieve on a motor sailor?
 
The mainmast (and mizzen) on a Neptunian will almost certainly have zero pre-bend - simple "column" masts. If however you lay the mainsail out flat on the ground there will be a curve in the luff of the sail - this is called "broad seaming" and put there by the sailmaker to make the sailcloth form an aerofoil curve to be more efficient than a dead flat sheet. The amount of this curve varies (becomes more) if the mast has pre-bend. 99.9% sure yours will have none.
 
The extra tension induced in the forestay by the genoa tends to bend the masthead forward slightly. I have found, though that this is a very small thing if your rigging has the correct tension. Setting up with a straight mast should be fine.
 
Motor_Sailor said:
The mast on a Neptunian is a short, stout affair with absolutely no pretence to performance.

'Straight' is the strongest configuration and there is no reason to deviate from that.

With a masthead rig and a deck stepped mast, the only way to induce any bend is with the forward lowers. But why would you bother? KISS!
Click to expand...


Thanks all!! Though I consider the Neptunian to be a cruiser rather than a motor sailor!
 
pcatterall said:
Thanks all!! Though I consider the Neptunian to be a cruiser rather than a motor sailor!
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"Cruiser" is a rather fuzzy term, as you can cruise in all sorts of boats. Better to look at it objectively. Your boat is heavy displacement and lightly canvassed, (SA/Displ 13.77, Displ/L 390). Compare, for example with a similar sized boat that is more sail orientated - Westerly Discus SA/Displ 17.08, Displ/L 293.
 
Tranona said:
"Cruiser" is a rather fuzzy term, as you can cruise in all sorts of boats. Better to look at it objectively. Your boat is heavy displacement and lightly canvassed, (SA/Displ 13.77, Displ/L 390). Compare, for example with a similar sized boat that is more sail orientated - Westerly Discus SA/Displ 17.08, Displ/L 293.
Click to expand...

Are those figures obtained using pounds and square feet ? as I cant replicate them? And anyway what of my ( new) inner fore sail and mizzen stay sail !! ??
 
pcatterall said:
Are those figures obtained using pounds and square feet ?
Click to expand...

The figures for comparison sake, use plain sail and only the 100% fore triangle for headsails, so your inner foresail and mizzen staysail make no difference!

Although the figures are dimensionless, they are derived from the imperial measurement. The displacement is in LongTons for the Displacement / Length Ration and in cubic feet for the SA / Displacement Ratio.
 
Motor_Sailor said:
The figures for comparison sake, use plain sail and only the 100% fore triangle for headsails, so your inner foresail and mizzen staysail make no difference!

Although the figures are dimensionless, they are derived from the imperial measurement. The displacement is in LongTons for the Displacement / Length Ration and in cubic feet for the SA / Displacement Ratio.
Click to expand...

Thanks MS ! so I am stuck with being a duck and can never be a swan?? !!
 
pcatterall said:
My mate on the boat in Spain says there is non! probably right for this boat, easily checked pull the main halyard tight down to goose neck and look up any gap is the mast bend.

The photo I have of the old sail clearly shows a curve up the luff.
The curve in the sail is to give it depth as others have said, so you get a foil not a flat sheet even with a mast that is straight.

The boat is a Neptunian, the back stays have no adjuster.
I thought that some back bend was the norm but have no figures for this boat. I doubt it if it's the original rig.
Sometimes the baby stay can induce a small amount of bend with an adjustable back stay but as others have also said the baby stay on this type of rig mainly stops pumping of the rig in heavy weather.

I can make some sort of estimate using the old sail and adjust the stays accordingly or just start again with figures that my friends
on this forum will supply!!

I'd set up for a straight mast sail cut. But I'd trust the sail maker with that. If he builds it for straight and you can induce a little bend by winding on backstay and baby stay then you'd use that in heavy weather to flatten the main a bit.

Help please
Click to expand...

Hope that helps, much the same as others have said above really.
I've had mains re cut for different masts in dinghies where you can induce massive bend and the normal set up for moderate winds has a lot of bend, so much that you could hardly get the main up the mast when it was straight.
 
pcatterall said:
Are those figures obtained using pounds and square feet ? as I cant replicate them? And anyway what of my ( new) inner fore sail and mizzen stay sail !! ??
Click to expand...

The figures were taken from Sailboat Data so all use the same formula. Yes, they are for comparison. Just to give you an idea of what they mean. A Displ/L over 400 is uncommon, and usually very heavy older boats. Mainstream cruising boats tend to be under 300, and racier ones down near 200. SA/Displ for typical cruising boats is in the 15-18 range and 20 gets you into "exciting" territory.

The trade off of course is the higher your displacement, the more sail area you need, and your boat has the opposite - heavy displacement and limited sail area. Of course this is what the designer intended which is why he specified a large (for the times) engine. While adding extra sails will obviously increase sail power, the short masts and inefficient (relatively) ketch rig will limit this. Does not mean it is a bad cruising boat as you have demonstrated, but you have to accept that your passage times are likely to be longer than a more powerful sailing boat of similar size.
 
ghostlymoron said:
I thought the definition of motor sailer was you have to start the engine to go upwind on a motor sailer.
My recollection of Coral Wind is that she pulls to windward pretty well.
Click to expand...

It is ( as stated) difficult to just stick boats into simple groups. Coral wind has a quite decent turn of speed in fresh winds and approaches hull speed no probs. and with comfort.
In lighter airs she struggles but hopefully the new sails idea will help there.
 
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