[krisscross]

So I'm modifying this 22 foot mast to be used on my catamaran (Solcat 18) because the original mast is too big and heavy for one person to raise (I'm almost always sailing solo). This smaller mast cast came from Islands 17 dinghy and had one set of spreaders which are fairly swept back. The original spreaders were fairly lightweight aluminum pipe, there was only one left, and in poor shape, so I have to make new ones.
My questions are:

Is it OK to get rid of the spreaders?

My gut feeling is 'no'. But they are swept back so much that going downwind they will be seriously interfering with the sail, likely to the point of rubbing the crap out of it. So the next question is:

Should I change the spreader sweep, and to what extent?

Because my cat has a 1.5 feet wider beam than the boat from which the mast came, I have to make the spreaders longer (which makes them interfere with the sail that much more). I'm making the spreaders out of aluminum rod, about the same diameter as the original aluminum pipe. I have the rods already so it is not a matter of cost, but maybe that is not the best material? So the last question:

Is aluminum rod a good choice for these spreaders?

Thanks for your help!

 

[christian.hess]

yeah good choice on material but some pics or diagrams would be great...

I dont think you will HAVE to make the spreaders that much longer...

is it not possible to modify the sweep of the spreaders?

 

[krisscross]

Yes, it is possible to modify the sweep and placement of the spreaders, I'm just not sure what would be a best way to do it. The original mast and boat here: ISLANDS 17 sailboat specifications and details on sailboatdata.com
This is the boat I'm modifying:
SOL CAT 18 sailboat specifications and details on sailboatdata.com

I could move them up and change the angle a bit to make it work with the geometry of the rig. That is my gut feeling about it.

 

[christian.hess]

any real life pics?

I can see the stays are angle back quote a bit from the mast on the 17,

what I would do is try to emulate the angles found on that boat since your are using that mast...with maybe slightly less sweep...

does the forestay attachment look the same, or better put will the angle off the luff be the same?

try to keep the same gemoetries or it might put too much strain in places that mast wasnt designed to

for exampe is the spreader height remaining the same?

 

[christian.hess]

the cat has no spreaders I see now my bad...but I see the angle of the stays is similar if not more on the cat...just from looking at the diagrams...

mast height slightly less with the new mast right? how much shorter?(this could be important for going spreaderless, just maybe)

 

[svHyLyte]

Considering the sail area of the Islands 17 (135 SF) compare with the Sol Cat (220 SF) changing the rig will dramatically reduce the performance capability of the Sol Cat (by about 39%). It would be wiser for you to learn how to use a gin-pole to assist your mast raising which, with that could be accomplished with a relatively small 2 or 3 part tackle.

 

[appick]

When I had my solcat 18, and I was by myself I found the easiest way to rig the mast was this. Take the cat off the trailer and put it on the beach. With a 2x4 cut to the right length at your feet, flip the cat on its side 90 degrees and wedge in 2x4. Walk around other side and lift mast into place using its weight to wedge it onto the mast base. Then connect your wires. I'm 6'2" tall and could easily reach the upper shrouds to connect the pins but it might be different for you.

As was said earlier a gin pole would be the "proper" solution to be used while on the trailer. It makes it handier as there isn't always a nice soft beach nearby. I just never spent the time to make one when I owned my cat. You could make one out of wood with a few relatively cheap fittings to attach it to the mast. No need for stainless as it'd just be used for rigging the mast then stored on the trailer.

 

[appick]

I'd stick with the original mast as well before switching to a different one. The other mast may be built lighter but it'd might not be up the task strength wise for the cat. Keep in mind the solcats were designed for racing/ performance. So if they have a heavy mast it's probably for a reason.

Or maybe that reason was just to simplify the rig and not have spreaders... Either way I'd not use solid rod for the spreaders, considering you want to keep the weight aloft to a minimum. Whats the saying every pound aloft is like loosing 10lb off the keel. (Then again I guess you don't have a keel to worry about ) I'd use a pipe before solid rod.

 

[christian.hess]

I beleive kriss cross already considered that on another thread...a while back

he has this mast and is asking about this mast

I remember comenting on that other thread too...there are benefits to a shorter, lighter mast for a solo cat sailor...

cheers

 

[krisscross]

I'm planning to use smaller sails, of course, and I'm not that concerned with speed. The smaller mast is SO MUCH easier to rig by myself, so it is very tempting to modify. I am sailing on inland lakes so beach rigging is not an option. I have to launch from the trailer. I would love to try the idea of flipping the cat on the side and rigging the mast that way, but that is not an option right now. I'm not worried about the weight gain from solid spreaders as the new mast is a lot lighter. My primary concern is rig strength (do not want to get dismasted in a blow) and mast stability. And of course I don't want to make a hole in the main by one of those spreaders.

 

[krisscross]

I was thinking long and hard about building a gin pole for the original mast, but raising mast that way is still a 2 man operation. The original mast is about 4.5 feet longer than the mast I want to use. And I can raise that mast by myself in just a couple of minutes.

 

[christian.hess]

yeah I dont see where you gain any wieght by going sold bar versus pipe, for one you are using a shorter lighter mast...so its a very hard argument against what you already have not to mention cost savings

can you find any pics of the 2 boats for example looking at the mast from the stern, then a real life profile pic?

that way you can compare stay angles, forestay height and angle and if and where you can tie in your spreaders and at what angle ideally

good luck!

 

[krisscross]

Good idea, Christian. I will look on line for that.

 

[VallelyJ]

Brion Toss's book, The Rigger's Apprentice, has the kind of info on mast/spreader/shroud angle geometry you are asking about. It's very straightforward and will help you to minimize the guesswork on something that is pretty crucial to your boat.
John V.

 

[Stumble]

Keep the bigger mast and instal a mast hinge and gin pole. I can put up the rig on my Corsair 750 in about 30 minutes solo.

If you go with a smaller mast, you have more issues than just spreader angles. You also need to address the extra righting moment of the multihull. Figure the RM on the cat is probably 10 times what the dinghy was, which means you need a much stronger rig to carry the same sail area since the boat won't heel to dump air.

This is doable, though I wouldn't advise it, but you need to run the numbers to make sure the new mast can handle the load.

 

[krisscross]

If you go with a smaller mast, you have more issues than just spreader angles. You also need to address the extra righting moment of the multihull. Figure the RM on the cat is probably 10 times what the dinghy was, which means you need a much stronger rig to carry the same sail area since the boat won't heel to dump air.

This is doable, though I wouldn't advise it, but you need to run the numbers to make sure the new mast can handle the load.

Good point, something I thought about. I was planning to dump air through a more conservative sail trim. I am using the same size shrouds as the big mast had, so they should be strong enough. Most of the time I sail in relatively light air anyway. There are some strong gusts now and then but these can be managed by spilling the air from the main. My jib is rather small.

What would be the initial signs that the rig is not strong enough for the amount of sail I carry? Spreaders bending?

 

[krisscross]

Brion Toss's book, The Rigger's Apprentice, has the kind of info on mast/spreader/shroud angle geometry you are asking about. It's very straightforward and will help you to minimize the guesswork on something that is pretty crucial to your boat.
John V.

Thanks, John. I will definitely get that book. Sounds like a good one to have anyway.

 

[Stumble]

Good point, something I thought about. I was planning to dump air through a more conservative sail trim. I am using the same size shrouds as the big mast had, so they should be strong enough. Most of the time I sail in relatively light air anyway. There are some strong gusts now and then but these can be managed by spilling the air from the main. My jib is rather small.

What would be the initial signs that the rig is not strong enough for the amount of sail I carry? Spreaders bending?

With the larger shrouds the first sign will probably be a mast snapping in half.

Mast design is tricky and I don't pretend to know it well, but multihull masts are massively oversized compared to a monohull. My 24' tri has the same mast profile as my 38' mono for instance. I think you better bet is to investigate a better way to step the mast instead of a lighter one.

 

[SloopJonB]

The purpose of spreaders is to reduce the compression load on the mast by widening the angle of the stays to the masthead. Any cat is wider than a mono so simply running the shrouds out to the hulls should give you plenty of angle without spreaders.

Can't run an overlapping gennie that way though.

Or am I missing something here?

 

[krisscross]

Mast design is tricky and I don't pretend to know it well, but multihull masts are massively oversized compared to a monohull. My 24' tri has the same mast profile as my 38' mono for instance. I think you better bet is to investigate a better way to step the mast instead of a lighter one.

I think they are oversized because they usually carry an insane amount of canvass in order to be competitive in races. I'm hoping that carrying less sail will still give me decent recreational performance and not fold the mast. But I guess I will find out soon enough. I made the spreaders yesterday and will be ready for hoisting sail on a dry run very soon.