mast

[joeh]

a friend of mine broke his fractional mast on his 25 foot sloop. now he is looking to replace with a used masthead mast of almost same length but different cross section. does anyone have actual experience or knowledge of this ? what should he be looking out for ?

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[oldharry]

Its reasonably straightforward, but the rigging is a bit different for a masthead rig, and extra chainplates or rigging attachments are needed, and all the shroud attachment points may need to be moved. On the boat I converted the masthead shroud chainplates were set aft of the mast, with a second set of plates for the lowers set fairly close behind that, so that they had to be repositioned for the new rig. Also I had to install a new set of plates forward for the lower fwd shrouds which are not present on fractional rigged boats usually.

Provided moving the plates is practical, its all pretty straightforward.

As to the mast itself, a second hand mast should have all the fittings removed to check for cracks and corrosion, and everything refastened with suitable insulation between stainless and alloy - all pretty straightforward usually unless the mast is in bad shape. in which case you need to reconsider its suitability for the job!

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[snowleopard]

the key dimensions for a mast are expressed as cross-sectional moment of inertia. this is a formula that reduces the diameter and wall thickness to a single figure which is a measure of stiffness (there is one figure for the fore-and-aft stiffness and another for athwartships). you can get these figures from the manufacturers and they will be able to recommend the size of boat and sail area they are suitable for.

the difference in rigging between fractional and masthead on small boats is that the fractional relies on back-swept upper shrouds to stop it falling forwards while the masthead uses the backstay for that purpose. it will probably be necessary to move the cap shroud chainplates forward to level with the mast and possibly beef up the backstay anchorage.

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[Guest]

My 1/4 tonner

at approx 25ft ..... broke the mast with previous owner when sails were increased. So he got a Carter 30 mast and chopped of the bottom section ..... to bring to same height as original ..... that broke as well and so now I have original prototype wood mast, (shortest !), and a carter mast that has a riveted strengthener section at base and up 2 mtrs .....


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
http://groups.yahoo.com/group/gps-navigator/

 

[William_H]

The mast should be fine in the fractional rig arrangenment using existing stay wires spreaders chain plates etc. Assuming the cross section is adequate for stiffness and assuming that the mast does not have too many large holes in the wrong places. I imagine as a mast head rig mast it only had holes midway for spreaders and stay attachment with all exit pulleys at the top. The fact that the original mast was tapered where the replacement is not tapered should not matter, just a little extra weight aloft. The purists may disagree but I imagine you are going for cheapest option. I say go for it looking out for corrosiom etc and fit the components as per the original fractional mast not as it was as a masthead mast. A mast rigger may be willing to advise you on the adequacy of the cross section for the job, He may be willing to taper the mast also but that may not be worth the money. Incidently why did the mast break? I think a statistical register of why masts broke could be really informative. Regards wil

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[joeh]

william
your opinion is certainly different from that of oldharry earlier in the thread.
we suspect the breakage was due to insufficient thread in the deck turnbuckle of the port lower shroud. it worked loose. a month earlier this shroud was shortened to fit a new turnbuckle. the mast snap at deck level and bend at a crazy right angle at the spreaders.


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[William_H]

Hello Joe Old Harry's plan would leave you with a mast head rig while I assumed you would want to keep the same rig just use a mast previously used in a mast head set up. Provided it is long enough to fit the mainsail luff and if not you could lower the gooseneck fitting or reduce the sail size to fit (by a sailmaker) youy should be ok. Attach the forestay at the same height above the deck so that your largest jib will fit and so you canuse the existing stays.
You mention the mast breaking at the deck obviously a keel stepped mast. The local masts here all have a hinge so that mast can be lowered for bridges etc. The keel stepped ones have a cut at 45degrees with a hinge bolt at the front and clamping bolts at the back so that the entire mast is rigid when up and bolted together. This could mean that you could use the old mast bottom section have a longer mast and the advantages of being able to lower the mast yourself easily. This would have to be done by a competent aluminium welder or mast rigger. Just a thought which may be worth the cash. Anyway sorry to hear about the mast loss I am on my 4th mast now (and 2 on a previous boat) so know about the dismay. (the first from fractional spreader attachement failure. The next 2 from collision with marker posts. ( on the previous boat a cat it was just not strong enough) It ain't no fun when it's all around your ears. Regards will

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[joeh]

thanks will
it was a deck step mast. about 2 inches of jagged aluminum was left on deck.
we'll probably reinstall with masthead rig setup but swept back spreaders to retain chainplate deck positions

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