Mast advice needed pls

[Fanie]

Hi guys,

I found someone who has a mast lying around their place. I haven't seen it yet, but will probably in a day or so. I have to make this person an offer if I can use it. All I know is that it's more than 10m, alluminium and is oval.

I will need a mast to use on my 10m cat. So I will either have to buy one, use a street lamp pole like Manie wants to do or make one myself.

My question to you guys are, if it is of suitable length, what do one have to look out for ? I know nothing about masts, so your advice will be valued.

Thanks in advance.

[Richard Woods]

Fractional rig or masthead? Tapered? Spreaders? Rigging (standing and running)? Keel stepped or deck stepped? Sail track ( bolt rope or slides - what size)? Gooseneck?

In general multihull masts are bigger than monohull masts for the same size boat and rig area.

Hope this helps

Richard Woods of Woods Designs

www.sailingcatamarans.com

[Fanie]

Is language like that allowed on a forum ? Sorry Richard, I have no clue what the difference is between all those....er... words are.

Ok, where can I get to see what the difference is between all those things, please ?

Geeze, it's only a mast I'm after.

[Trevlyns]

Here, let me have a go Fanie!

Masthead/fractional is the position of the jib stay on the mast - right at the top (masthead) or lower down - fractional. The spreaders "spread" the shrouds from the top of the mast to their mountings on the port and starboard side of the boat. Keel or deck stepped - where the mast base will be mounted - in your case, the deck I would think. Sail track - how the main sail attaches to the mast - boltrope is set into the mainsail tack and threaded in a channel on the mast and slides are plastic slides fitted to the sail which run in a track on the mast. The gooseneck is the attachment of the boom to the mast.

I just wanted to help out with the terminology, mate - Richard is vastly more experienced in multi's than I am!

[Nordic Cat]

Fanie, take some pictures of the mast,post them here. Measure the outer dimensions of the mast, and the shape. Measure the thickness of the tube. Note where the ropes that hold the mast up are and how many.
Measure the boom length and dimensions, and height from the bottom of the boom to the bottom of the mast.

Then come back for help...

regards

Alan

As you live where you do, make sure you get the length as well as the height of the mast. ( remembered an old van d' Merve joke!)

[Fanie]

Mmmm yes Alan, that would depend on if you want lenth and not height then In this case I want to go for height though...

The way I planned my mast setup is an aft mast, with two stays, one aft to port and the other aft to starboard, the main sail is like a jib and the headstay doubles as the third stay. I would probably add another 'jib' to support the bigger one. You all saw the 'aft mast' by Brian Eiland... so I would like to sort of copy that idea for a sail setup and was what I played with on the tri to see how it worked.

The question then would be, would I need a special type of mast ? It seems the down force on the mast head would be the biggest force to take into account.

If need be I could add two more aft stays lower at the same height as the 2nd jib to support the mast, but in general I want to keep the rigging as simple as possible.

[RHough]

Until you have some idea of what the size and configuration of the rig is, you cannot begin to select the mast.

I suppose you could get a mast, calculate what size rig and boat it is suitable for and then design the boat under it, but that would be backwards to an extreme degree.

A mast section for a 10M boat will probably be 13-15M long. The cost will be in the $2000-3000 range for a bare tube.

It sounds like you are very far from needing a mast.

[Butch .H]

Fanie I have a mast for you if you are interested brand new 11 m

Regards
Butch

[Fanie]

I was rather hoping you guys could provide me with some specifics of the mast I would need.

Mr Hough, the mast I estimated to have is 15m, would give me about 50m sailing area.

Thanks Butch, 11 m would be too short, but do e-mail me what you want for it pls... thanks.

[RHough]

Originally Posted by Fanie

I was rather hoping you guys could provide me with some specifics of the mast I would need.

Mr Hough, the mast I estimated to have is 15m, would give me about 50m sailing area.

I have probably missed the specifics of the design that would enable an estimate of what sort of mast your boat might need. The compression loads on an aftmast rig will be higher than for a more conventional rig. This is something I am looking into. My feeling at this point is that a section that is sized for a larger mono, say in the 20M size range, cut down to the length you need might provide the section strength you are looking for. The good thing about that is that a mast off a bigger boat that has been broken at the deck will be too short for use on a mono (or way too heavy) and might be a bargain way to get the heavy section your boat will probably need. Just general comments here made with no knowledge of the design specifics.

[Paul B]

Originally Posted by Richard Woods

Fractional rig or masthead? Tapered? Spreaders? Rigging (standing and running)? Keel stepped or deck stepped? Sail track ( bolt rope or slides - what size)? Gooseneck?

In general multihull masts are bigger than monohull masts for the same size boat and rig area.

Hope this helps

Richard Woods of Woods Designs

www.sailingcatamarans.com

Originally Posted by Fanie

Is language like that allowed on a forum ? Sorry Richard, I have no clue what the difference is between all those....er... words are.

Ok, where can I get to see what the difference is between all those things, please ?

Geeze, it's only a mast I'm after.

Should be pretty obvious here that someone is just "taking the piss" as you Poms like to say.

Why reply to someone who is claiming to be designing something, yet claims to not know the basics?

[Fanie]

RHough, it seems I may not get a chance to look at the mast before next week... lets wait till then and see what's cooking

I have already done calculations on the compression the mast (and beam) would have to be able to endure... it rather scary

Since I plan to use more than one 'jib', and add a lower set of stays it may help rigiting the mast lower down some. You are right, the down force could be bigger than with a bermuda rig, although keep in mind the sail tends to lift while the bermuda pushes down... so it may well even out to about the same for the same sail size. I don't know the bermuda setup, only what I have done so far on a smaller scale. I'm sure if I see the mast I would have a good idea.

Paul, pls contribute positively. I'm no design expert or claim to have nearly as much experience wrt sailing as any of you. I just know what I want and that is what I'm going for.

Unfortunately I do not have the time to make a study of all the different mast shapes and types, strengths and whatever goes with it since I have already decided what sail setup I'll be using.

Unfortunately I don't know anyone using that aft mast setup on this size boat so it is new to me and very little else available on it. So if you know something about it, let's have it.

[Petros]

Sizing a mast is a pretty complicated analysis procedure. There are a lot of variables in terms of rigging, sail size and shape, stay and spreader placement, etc.

I can not resist a good deal, this is what I would suggest: if it is an exceptional deal, and it about the right length, just buy it and there is one of three ways you can deal with it:

1. When you work out all of the other design details of your rig and sail plan, take it to an marine engineer or NA to work out the loads on the mast and work up a rigging plan to keep the loads within the limits to your particular mast. For example, by adding extra stays or spreaders you can make the same size mast carry the extra design loads. Of course the analysis may reveal that you already have enough strength in the mast you purchased and do not need to add the extra rigging to strengthen it.

2. Skip the analysis and just find a similar size boat with a similar size mast and copy the rig plan (adding extra strength where it will not add much cost where possible). And then just hope it works our fine in all of the conditions you will be sailing it. This is not as risky as it might sound, safety factors and typically conservative design standards usually give you plenty of excess strength where you will not likely ever have an issue with it (of course I would always make sure to reef early too, just in case).

3. Do the analysis to the requirements of your specific rig design as in option one, and if the mast is not usable (and it can not be reinforced), then find a marine supplier that has used masts and rigging assemblies. Use the mast you bought cheap to work out a trade (or partial trade) for one that you can use from the dealer. IF you get it inexpensive enough you can always look for someone that wants it and will pay more for it than you did.

Good luck

[Fanie]

Thanks Petros,

Your option 1 is about what I hope for - to use the mast if it is strong enough although it may have been originally designed for another type of setup than mine.

[Landlubber]

Fanie,

First things first, do you have a sail plan, after all, the mast is only there to hold up the sails....
There are things like Cof E for the sail plan that determine the length of the mast and where to put it, surely you are following some sort of plan, not just expecting to "go buy a stick and put it up"......and hope for the best.

If you fail to plan, you plan to fail......I have a lot of trouble reading this post, sorry mate, but you seriously need to sit down for a few minutes at least to get what you need sorted out.