extending a mast

grafozz

grafozz

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i am fitting a 500mm section to my mast to raise the boom so as to be able to fit a bimini under the boom . i have chosen this method so i dont lose sail area by re-cutting the foot . any tips on securing the new section ? there is no "sleeve " available for this job .
 
Re: extending a mast

I was going to ask if you had calculated the effect on stability of raising the CG of the rig by that distance then I saw it's a cat but presumably it means a whole new set of standing rigging.

I can't think of a way of doing it that would be strong enough.
 
Isn't it easier to raise the boom and buy a big sexy fat top mainsail to make up for the loss of sail area?
 
You're fitting a bimini and you're worried about a small loss of sail area in the main in what is clearly not a racing machine.
So you're undertaking the massive task of extending your mast....
Meaning of course that all the standing rigging will need replacing or (gulp) extending, and your spreaders may now be in the wrong place and subject to some strange angles.
And of course that your Genoa will now be too short for your new forestay, so will either be suspended quite strangely in mid air, or will no longer reach the top of the mast and so lose the slot at the top.
To say nothing of the probable strength of your DIY mast extension.

Are you entirely sure you've thought this through?
 
Re: extending a mast

well all you should do is ether shorten the boom which i did , no loss of speed or anything eles or move it up a bit and shorten main any of these will solve your problem with out to much coast to you or anychanges in boat per formance dave
 
I <suppose> you could get a 500mm alloy post welded up with flanges thus creating a new mast footplate 500mm higher off the deck,then add wire strops to bridge the standing rigging,then add to the genoa foot then,hopefully enjoy the new walkabout covered cockpit.
Would it not be easier to simply sit down in the bimini'd cockpit ?
 
It's certainly possible, all sorts of mast get joined. I can sympathasize with the desire not to reduce sail area, a lot of cruising boats could do with a bit more imho, they might motor a bit less then!
You might want some extra lower shrouds to take the forces from the gooseneck.
I suspect we may have found the limits of what the forum can do for you here! It is possible, but you need to either design it properly, make it somewhat on the heavy side, or as has been alluded to, be prepared for it to break!
Some more info about size of boat, dimensions of mast would be of interest.
I'm surprised if a sleeve cannot be made to fit either inside or outside. A major question is 'was the orignal mast design generous, or only just strong enough?'
Or as blueboatman suggests raise the heel of the mast, maybe on a tabernacle type of mount?
I suppose it comes down to economics but its all possible.
Don't give up yet!
 
thanks iw 95 , good to hear a positive outlook ! its a z spars 600 e section with the in mast furling tube , a very strong section . i have a new fully battened main which i do not want to re- cut as there are limited facilities here in the ionian .
 
Why not cut the head of the main instead. That's what I did to get a bit more head room under our boom. Only lost about 0.2m2 of sail and alot cheaper and probably safer than messing with the mast. Surely adding to the top of the mast will be costly and add to weight up there, that, on top of raising all that sail up too, might prove unstable?
 
All quips and jokes asside, PLEASE get a good rigger to have a look at it before you do anything, you may be doing things to the rig that you haven't appreciated, especially regarding the spreader angles.
 
[ QUOTE ]
its a fractional rig ,the jib will remain in position ,and by fitting the extension at the top of the mast -no re- rigging !

[/ QUOTE ]
Hi Graham,

my guess is that when you lift the mainsail by 50 cm and the jib remains on the old level - that part of the mainsail looses the slot effect, worse performance in that area as a result - I'd leave the mast extension and cut the 50 cm of the top of the mainsail and keep the performance on the same level.

best luck what ever your decision will be !
 
Below the boom you might get away with a simple butt weld as the section is mainly in compression. If the addition is at the top , sleeving may be also required to deal with the more complex loadings.
The safest thing is probably to raise the boom and recut the main. 500mm seems a lot!!! I would go for the minimum to give clearance for your head and the boom.
 
well the facts are , i,m 6 ft 4 " and i need to fit a bimini under the boom , it only just clears my head now so needs to go up some . looking at it today , the crane has been fitted with 2 cutouts ,80mm deep fore and aft into the masthead , so now looking at fitting extra section at the foot and adding extensions to the cap and lower shrouds , and forestay ,and welding the new section is a good idea ,can do . the main is new and my location makes it more difficult for serious sail work. the new main was made too short by jeckells and after they re- made it it was too long !! so a bit shy of re- cutting mainsails at present !
 
[ QUOTE ]
well the facts are , i,m 6 ft 4 " and i need to fit a bimini under the boom , it only just clears my head now so needs to go up some . looking at it today , the crane has been fitted with 2 cutouts ,80mm deep fore and aft into the masthead , so now looking at fitting extra section at the foot and adding extensions to the cap and lower shrouds , and forestay ,and welding the new section is a good idea ,can do . the main is new and my location makes it more difficult for serious sail work. the new main was made too short by jeckells and after they re- made it it was too long !! so a bit shy of re- cutting mainsails at present !

[/ QUOTE ]
If your spreaders are at all swept back you will get some strange angles if you extend the mast, funny angles at spreaders are a really common cause of mast-fallingitis.

I'll just repeat my "this is a seriously bad idea" statement of above and slope off shaking my head wistfully.
 
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