Mast modification question (spreaders)

[HoneyRyder]

Originally Posted by Bor the Wolf

Just make sure the spreaders aren't pulling the mast. The whole idea is that the spreaders pushes the mast straight. The leeward spreader does little or nothing because the leeward shroud looses a lot, if not all of its tension. That means the windward shroud and spreader are the only controls that push the mast straight.

Obviously, when the shrouds are pulling the spreaders away from the mast and the leeward shroud looses its tension, the windward shroud and spreader will have trouble controlling the mast.

You can have some angle between mast and shrouds as long as the spreaders keep pushing the mast. But you may have to increase shroud tension to create the same forces on the mast/spreader as with parallel shrouds. If not you have two choices, either get longer spreaders of move the chain plates inward.

BTW Proctor, now Seldén, still sells spare spreaders for almost all of its masts, but second hand spreaders from another brand should work too.

Great point about tightening the shroud tension. I was always amazed at the tension on the shrouds on my G-cat (catamaran), which were sited very wide at the base and away from the mast.

I will check with a rigger too before I decide what to do. But I'm really hoping I can site the chainplates on the hull rather than inside on the deck. Much easier, much prettier, and much more convenient, in terms of walkways, etc.

Thanks for your help.

[Stumble]

Big picture nothing you are suggesting is a problem. Thespecifics can get tricky.

1) longer spreaders are actually desirable, they reduce shroud loads by widening the shroud base. But it makes spreader attachment a little trickier because the shrouds need to be angled up a little bit more. The one issue is the spreaders need to be just a touch narrower than the chainplate base to ensure the lower shroud isn't pulling in onthe leeward side when the boat heels over. It does funky stuff to the rig.

2) sweeping the shrouds aft also requires a new spreader bases, but is actually preferred in this situation. Again it allows a wider spreader base, and reduces loads on the shrouds. If you sweep them back far enough you can get away with no backstay which has other desirable advantages, like a big roach main.

3) the problem with all of the above is you need to know where the chainplates are on the boat. These aren't just hardpoints, they need to be structural elements of the hull, and adding them afterwords can be a royal pain if it is possible at all. Since the hull was originally designed as a sailboat I assume there are appropriate chainplate locations already and I would really advise using those if at all possible.


All of this boils down to yes it is possible, it's actually pretty easy, but you need a good rigger to help walk you thru it. For detailed advice I would really recommend reading Brion Toss' 'The complete Riggers Apprentice'. It goes thru all the calculations you will need to do to pull this off safely.

[foufou]

Not all rigs have spreaders in compression. I sailed a dinghy that had spreaders in tension. In that design the spreaders act as a lower shroud without a lower coming from its mast side

[tinkrman69]

As has been mentioned the shroud below the spreader might angle away from the mast. Your attention should be the angles at the point where the shroud meets the spreader. The upper section won't be a problem as it will be 40 to 60 degrees in relation to the spreader, the lower section should be less than 90 degrees to the spreader. Either angling the spreader up, relocating the deck attachments or both. I would suggest an angle of at least 85 degrees

I doubt your racing so keep it simple with one set of spreaders at around 2/ 3rd up the mast

you say it's a sailing hull turned motor boat....was the ballast kept in tact.?

[skipper53]

This is definitely a naval,architect/sailboat designer questio . A good designer swill have the skills and experience to get this done right the first time.

[HoneyRyder]

Originally Posted by Stumble

Big picture nothing you are suggesting is a problem. Thespecifics can get tricky.

1) longer spreaders are actually desirable, they reduce shroud loads by widening the shroud base. But it makes spreader attachment a little trickier because the shrouds need to be angled up a little bit more. The one issue is the spreaders need to be just a touch narrower than the chainplate base to ensure the lower shroud isn't pulling in onthe leeward side when the boat heels over. It does funky stuff to the rig.

2) sweeping the shrouds aft also requires a new spreader bases, but is actually preferred in this situation. Again it allows a wider spreader base, and reduces loads on the shrouds. If you sweep them back far enough you can get away with no backstay which has other desirable advantages, like a big roach main.

3) the problem with all of the above is you need to know where the chainplates are on the boat. These aren't just hardpoints, they need to be structural elements of the hull, and adding them afterwords can be a royal pain if it is possible at all. Since the hull was originally designed as a sailboat I assume there are appropriate chainplate locations already and I would really advise using those if at all possible.


All of this boils down to yes it is possible, it's actually pretty easy, but you need a good rigger to help walk you thru it. For detailed advice I would really recommend reading Brion Toss' 'The complete Riggers Apprentice'. It goes thru all the calculations you will need to do to pull this off safely.

The hull is made of 10mm steel. And I intend to attach the chainplates directly onto the hull. I am confident that it can take the load, as long as I spread it.

It is not my intention to sweep the spreaders aft. The rig was originally designed for use off shore, and appears to be very robust, as is. And, I am happy to use the running backstays for extra support too.

I will ask a rigger for his opinion, once I have a little more info gleaned here and from the good book you have recommended, so many thanks for that advice.

[HoneyRyder]

Originally Posted by tinkrman69

As has been mentioned the shroud below the spreader might angle away from the mast. Your attention should be the angles at the point where the shroud meets the spreader. The upper section won't be a problem as it will be 40 to 60 degrees in relation to the spreader, the lower section should be less than 90 degrees to the spreader. Either angling the spreader up, relocating the deck attachments or both. I would suggest an angle of at least 85 degrees

I doubt your racing so keep it simple with one set of spreaders at around 2/ 3rd up the mast

you say it's a sailing hull turned motor boat....was the ballast kept in tact.?

I am certainly not racing. It is really just a back-up rig to use if the engine fails, or to gain an extra knot or two while under power, or to laze along on a broad reach without the engine.

Yes, the ballast is still there. It was being built as a sailboat, and was then modified by the second owner who converted to a trawler. But the hull shape and ballast means it rolls a lot, and I suspect the rig will alleviate some of the effect (when under power).

I intend to do some long distance voyaging. My fear is that the single engine fails at some point, and instead of a back-up engine, I thought I'd install a rig. I am a sailor, and feel much more comfortable under sail anyway. With this rig and the mizzen, it should give me a second option, in the event of engine failure.

At least, that's the theory.

Thank you for your suggestions.

[HoneyRyder]

Originally Posted by skipper53

This is definitely a naval,architect/sailboat designer questio . A good designer swill have the skills and experience to get this done right the first time.

Yes, for sure.

A naval architect and boat designer suggested the overall concept, it's now just a matter of getting the details done correctly.

Having said that, I've gone for a little more sail area than he suggested, but that can be changed easily.

[georgelieber]

Originally Posted by HoneyRyder

I have 5 tons of ballast in the keel, which makes it roll a lot. I am making a little bet that the addition of the mast will act as a counterweight and reduce the rolling, when I don't have a steadying sail up (due to lack of wind).

Thanks for your help.

Your ballast is not causing the roll. The hull shape is allowing the roll. But, those older and more traditional sailboat hull shapes that tend to roll without sails, are also some of the safest and most seaworthy hull shapes ever built. Our boat is one of these designs and rolls horribly without sails. But she is a dream in heavy weather and can be easily balanced to sail effortlessly in high winds and rough seas.

Without a sail up, the mast alone wont make a big difference in rolling. But, with a sail up (or reefed sail up) and the sail sheeted tight, even when motoring directly into the wind, can make a huge difference in decreasing roll and dramatically increase comfort and safety. Loaded sails (sails with wind on them) will work wonders for resisting rolling and increasing comfort.

It is important that the mast location, and sail plan you end up with, is balanced. An unbalanced sail plan will at best turn the helm into a tormenting monster, and at worst screw the whole boat down into the sea. Spend the extra time and money to get the mast in the right location, with an appropriate sail plan, and you will be rewarded with many years of greatly increased comfort and free power.

Don't get discouraged. Do it right and it will make you happy.

[Kokanee]

Great advice above!

Sounds like a nice project. I'm sure you'll be pleasantly surprised at how much stability you will get from the sails in messy water. You'll certainly have enough sail area with that mast plus the mizzen.

Have you considered going gaff rigged?

[TheThunderbird]

I disagree with most comments, and skipped the others....honestly, i disagree with people commenting upon no solid experience, in structural isues.

You must have spreaders working evenly, on a same angle upon the lower/upper portion of the stay.

In order to get that, spreaders are tilted upwards, usually by 1° - 3°- 5° on 1st, 2nd, 3rd spreaders...

You can get them longer (welding) considering the additional stress v eventual strengthening needs (by vents).

If they point slightly astern, follow that vertical plane for installation.

In doubt, ask a rigger, not a forum :-)

[Boston Blackie]

If the cap shroud is in a straight line from the upper spreader to the lower spreader to the new rail chainplate, then I think you could actually eliminate the windage of the lower spreaders.

[StuM]

Originally Posted by Boston Blackie

If the cap shroud is in a straight line from the upper spreader to the lower spreader to the new rail chainplate, then I think you could actually eliminate the windage of the lower spreaders.

If the cap shroud is in a straight line from the upper spreader to the lower spreader to the new rail chainplate,... as soon as their is any side load on the rig, the spreaders will no longer be compression!

[Jim Cate]

Without a sail up, the mast alone wont make a big difference in rolling.

Afraid I disagree with this statement!!! A number of years ago we were dismasted in our previous boat. We "self rescued" by motoring the 100 miles or so into Manly Qld. The motion without the mass of the mast was HORRIBLE. Roll period was much shorter, roll amplitude was much higher. It was a struggle to move about the boat... and this was not in a severe sea state.

I can not guess whether or not you will like the new motion, but it sure as hell will be different!

Jim

[HoneyRyder]

Originally Posted by georgelieber

Your ballast is not causing the roll. The hull shape is allowing the roll. But, those older and more traditional sailboat hull shapes that tend to roll without sails, are also some of the safest and most seaworthy hull shapes ever built. Our boat is one of these designs and rolls horribly without sails. But she is a dream in heavy weather and can be easily balanced to sail effortlessly in high winds and rough seas.

Without a sail up, the mast alone wont make a big difference in rolling. But, with a sail up (or reefed sail up) and the sail sheeted tight, even when motoring directly into the wind, can make a huge difference in decreasing roll and dramatically increase comfort and safety. Loaded sails (sails with wind on them) will work wonders for resisting rolling and increasing comfort.

It is important that the mast location, and sail plan you end up with, is balanced. An unbalanced sail plan will at best turn the helm into a tormenting monster, and at worst screw the whole boat down into the sea. Spend the extra time and money to get the mast in the right location, with an appropriate sail plan, and you will be rewarded with many years of greatly increased comfort and free power.

Don't get discouraged. Do it right and it will make you happy.

Agreed on all points. The mizzen, even though it is only 75 sq ft of sail, makes a huge difference. In a decent breeze it heels a little and all is good.

It was built in Holland, and designed for the North Sea, which has a lot of short steep seas. I've been out in her, crossed the Channel in a 7/8 with zero difficulties or discomfort.

My intention with the cutter ketch rig is to give me a low aspect dispersion of smallish sails that will enable me to modify my sail plan to suit the conditions. I am somewhat limited in terms of where I can put the mast, and other stuff I have read suggests the sail plan is more important than mast location.

Total sail area (main, yankee, staysail, mizzen) is only about 500 sq ft (estimate) and easy to modify, so with a little experimentation in different conditions I hope to get it right.

Thanks for your help.