Why are GRP gaffer masts usually wooden?

[Greenheart]

Very basic question, which I apologise for giving no forethought at all.

Cornish Crabbers, Cape Cutter, Heard 28, Memory 19, lots more, all built mainly in glassfibre but all (or almost all?) have wood masts.

They're very attractive, but is that the main reason for choosing a wood mast rather than metal, like nearly all boats that aren't retro-styled?

Is the use of wood for spars, a decision made by the heart and regretted by the head? Or is wood genuinely as good, or even better, than alloy?
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[Egret]

Maybe something to do with the kind of point loading from a gaff jaw which might be at various levels or that a suitable round aluminium section just isn't available - someone from one of the builders or mast manufacturers will no doubt respond.

 

[Tranona]

Yes, there are no off the shelf aluminium masts available although some boats have used carbon masts. For straight pole masts on smallish gaff rigs wood is still cheap and easy to make plus in tune with the ethos of the boats.

 

[Aquaboy]

Surely its about looks, the boat has a traditional/retro design and an alloy mast would look out of place.

 

[Tranona]

Crabbers offered Bermudan rigged versions with alloy masts on some of their models.

 

[Laminar Flow]

Thomas Colvin, USA, designed many traditionally rigged vessels using aluminium pipe for the spars. This material is readily available in various diametres and can be easily sleeved to lengthen.
By cutting darts and welding these up, the spar may be tapered as well.

A great many of the Dutch traditional craft use steel pipe for their masts, as do most of the traditional square rigged ships these days. Both lighter and stronger than wood in the larger sizes.

 

[wombat88]

A friend bought alloy lampposts for his 40ft junk rugged ketch. Light, already tapered etc. 25 years later and they are still fine.

 

[AntarcticPilot]

A friend bought alloy lampposts for his 40ft junk rugged ketch. Light, already tapered etc. 25 years later and they are still fine.

Roger Taylor's MingMing used an alloy lamppost for the junk rig.

 

[Greenheart]

Lamp posts are a nice economical idea! I suppose a small gaffer (or junk) sailplan is adaptable to any form of support - no need for a sail track or flexibility that can be controlled by shroud tension...although I don't pretend to know much about them.

Somewhere I read of some Crabbers using carbon fibre masts. It mightn't be their natural style, but I suppose they reduce weight aloft.

Perhaps they were only the Bermudan rigged versions?

 

[AntarcticPilot]

Lamp posts are a nice economical idea! I suppose a small gaffer (or junk) sailplan is adaptable to any form of support - no need for a sail track or flexibility that can be controlled by shroud tension...although I don't pretend to know much about them.

Somewhere I read of some Crabbers using carbon fibre masts. It mightn't be their natural style, but I suppose they reduce weight aloft.

Perhaps they were only the Bermudan rigged versions?

I think that junk masts must be keel stepped (or equivalent) because shrouds would interfere with the sail.

 

[wombat88]

I notice 'Bay Raider' have carbon masts. At first I thought this a bit over the top but then their masts are longer (bermudan) than a normal gaff and would be heavy if in wood. I guess the weight saving really counts if you are a single handed trailer sailer.

 

[Greenheart]

Carbon fibre seems miraculous. I suppose the parts that are subject to continuous localised stress and abrasion can be reinforced for durability, without increasing the spar's overall weight to anything close to wood or alloy.

 

[wombat88]

Although carbon fibre seems miraculous, especially for dinghies, doe it have a problem with UV?

 

[Laminar Flow]

I think that junk masts must be keel stepped (or equivalent) because shrouds would interfere with the sail.

More correctly: junk masts tend to be free standing and these are almost always keel stepped. Not withstanding, most of Tom Colvin's junk rigged boats had supported masts, i.e. they had shrouds. For example his Gazelle model and even his true junk hull types.

The problem with carbon fibre masts is that they are extremely sensitive to impact loading and should not be drilled for attaching hardware etc. It is the resin that is u.v. sensitive.

 

[Greenheart]

The problem with carbon fibre masts is that they are extremely sensitive to impact loading...

I suppose a carbon-masted gaffer would benefit from equally light carbon gaff and boom, too.

It wouldn't seem clever to save weight on the mast then send up a hefty wooden gaff.

My query is based on the possible (highly unlikely) re-rigging of a late-20th-century sloop, using a retro two-masted sailplan. So the natural choice of wooden spars would likely be lots heavier than the standard yacht's alloy mast. Even alloy masts, plus gaff, would be heavy.

Carbon, though... The masts will likely cost more than the yacht.
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[DownWest]

I suppose a carbon-masted gaffer would benefit from equally light carbon gaff and boom, too.

It wouldn't seem clever to save weight on the mast then send up a hefty wooden gaff.

My query is based on the possible (highly unlikely) re-rigging of a late-20th-century sloop, using a retro two-masted sailplan. So the natural choice of wooden spars would likely be lots heavier than the standard yacht's alloy mast. Even alloy masts, plus gaff, would be heavy.

Carbon, though... The masts will likely cost more than the yacht.
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You might look into wood using the 'Birdsmouth' tecnique. Makes a lighter mast by being hollow (basicly the wood in the middle of a solid mast is non structural)
I have built several and it is quite easy and satisfying. Certainly 'looks right' on a trad rig.
Friend with a heavy gaff ketch, used engineered beams (laminates) after his first set of grown trees had rot problems.

 

[Laminar Flow]

A hollow wooden spar needs to be 20% greater in diametre than a solid one, with a 20% wall thickness, for the same strength. It will weigh about half of the solid version.

Engineered laminates are considerably heavier than the grown timbers usually used for mast construction. They don't exactly give them away either.

 

[MisterBaxter]

You might look into wood using the 'Birdsmouth' tecnique. Makes a lighter mast by being hollow (basicly the wood in the middle of a solid mast is non structural)
I have built several and it is quite easy and satisfying. Certainly 'looks right' on a trad rig.
Friend with a heavy gaff ketch, used engineered beams (laminates) after his first set of grown trees had rot problems.

I've often wondered - how do you build in taper with the birdsmouth technique?

 

[Keith 66]

I've often wondered - how do you build in taper with the birdsmouth technique?

Just taper the back flat of each stave slightly & you get a cumulative degree of taper for the whole lot as they come together. My son & i recently made a 7m birdsmouth spar 150mm dia in the centre tapered a bit at each end.
The critical thing with birdsmouth spars is getting the angles accurately cut, they have to be spot on.
An 8 stave mast is common as you just need an equal 45 degree cut each side, if you have odd staves it gets worse.
With our spar making an 8 stave spar we didnt have enough timber as the baulk of spruce was an odd size that didnt divvy up right. But if we made the staves smaller it worked as a 10 stave spar, this mean different angles each side of the cut, we had to be bloody careful assembling it & a dry run was done first!