Multihull Rig tune Question

Rickm505

Rickm505

Active Member
Joined
7 Aug 2005
Messages
54
Location
Florida (ICW), USA
www.catamaransite.com
Hi all,

I'm doing a lot of reading on tuning masthead rigs, as I believe my recently aquired Catalac 8M (catamaran) hasn't been tuned in years. I'm hoping there might be someone on the forum who has had some experience with a Catalac. I'd like to tune the rigging myself, but I haven't found a website which specifically deals with tuning multihull masthead rigs, so I'm slightly concerned about proceeding.

From what I've read it seems that the tuning procedure begins at the dock with the rig slack.

1.) The cap stays are tensioned first and are tightened enough to induce a 6 inch (150mm) aft prebend (10 meter mast). I read that this is done by marking a spot on each hull even with the mast, and using a tape measure attached to the main halyard to insure lateral centering. Measure as I tighten to insure the masthead is centered on the boat. It sounds as if it's possible to turn the mast halyard into a plum bob, and use this to measure the aft bend.

2.)Next the lowers are tightened as tight as possible with a 6" (150mm) spanner/wrench, and double check mast centering.. (question: does this include the inner forestay?)

3.)Next the forestay is tightened enough to control forestay sag (150-200mm)6-8 inches.

4.)Backstays are tightened lightly as not to depower the sails in light wind.

5.) Go for a sail and sail close to the wind. If any slack in the leeward lower shrouds, remove slack. Assume the other tack and do the same.

6.) readjust forestay sag if needed, as noted above.

That seems to be all I've read.... but is it right?

Thanks

Rick in Florida, USA
 
Someone asked this question in relation to Heavenly Twins so as I was in Millbrook next day I put the question to Pip Paterson who now builds the twins. His answer was basically 'adjust it till it looks about right'.

A slightly different problem to yours as the HT has the forestay attached to a bridle rather than a rigid foredeck but I suspect the solution is similar. The big problem with multihulls is that flexing of the structure can put excessive loads on the rig if it's done up too tight, leading to fatigue failure or even a bent mast.

The Catalac is a relatively rigid unit but, given its hull form, it will never perform well to windward so forestay tension is fairly unimportant. The thing you must be sure of is keeping the mast in column on all points of sailing. I think your sequence will do the job, just don't be too enthuiastic with the bottlescrews. Not too sure about pre-bend though.
 
If the rig hasn't been tuned in years, then the first thing to do is determine whether the wire should be replaced. My insurance co allows max 7 years life before any cover of rig is voided.
Next, you need some way of measuring tension - a Loos guage or something similar. Check out the Brion Toss web site for details of how to conduct the tune - I've got his book as well as the rig tune video - both very good.
Lastly, be very careful about taking slack out of leeward wires - very easy to get too much tension and cause a failure.
 
One thing I learnt early on in fiddling with cats (heavy) is that mast integrity is vital. The hull just sits resisting heel so that the mast takes a huge load. Wheras on a lead mine (half boat) the hull heeling provides a resilience to gusts which removes that extras load problem.
So as said keep the mast in column ie straight not necessarily vertical.
I have never subscribed to the need for really tight rigging. It is to me wrong to expect to be able to remove the slack on the lee stays when sailing hard. I just don't believe a hull especially cat can be rigid enough.
Certainly I agree you should consideer replacing stays. They do fail and a failure usually means loss of mast.
On a mast head rig the amount of set back aft of the side stays (chain plates) will determine whether the backstay can dictate the amout of rake. So a large set back means the forestay and cap shrouds will between them set the forestay tension and the rake.( set up with loose backstay initially) If however the cap shrouds are abeam the mast then the cap shrouds have little effect on rake and forestay tension this all being set by the backstay.
The rake of the mast determines the windward or weather helm under GENTLE winds. As soon as the boat heels over the weather helm is produced mostly by assymetrical drag of the hull(s) in the water.
So I reckon the guy who said do it up till it looks right is not far wrong as long as you know what to look for. The only place for a tension gauge is in comparing the tension of the intermediate shrouds to the cap shrouds. Logic would dictate that the tension be somewhat less on the intermediates. But this can be guessed at. The critical part being getting the two intermediates equal as shown by a straight mast. good luck olewill
 
Is this a spoof, I ask myself. Might the next question be about fitting Harken Windward Sheeting Traveller Cars and a Code Zero Assy-Spi?

I recall being told, not a million miles from Mudeford, that the 8M Catalac goes to windward only when the engines are on - and then reluctantly. And that it sails downwind at 4 knots, regardless of which way it is pointed.

If one wants to sail any faster, get a 10M Catalac. That's good for 5 knots downwind. /forums/images/graemlins/wink.gif
 
Mr. bilbobaggins, Pointing isn't the object (or the point (excuse the pun)). My boat does quiet well, but thank you very much for your concern!! (smile).

William, you make a very good point as the boat has one pair of uppers, and one pair of lower stays (single spreader) and in fact they are abeam of the mast. From what I've read, tension on the baby stay is used to induce the pre bend. I was planning on leaving the mast vertical (no rake) and utilize only the pre bend.

Rick, I of course have a Loos gauge, but frankly, in the procedure I've outlined, I don't see a place to actually use it!!

Rick in Florida, USA
 
Rick, you are trying to turn a carthorse into a racer! With a mast of this height and stiffness extreme mast bend is not usually required and the sails are probably cut with this in mind. Also on a cat the shrouds do not need to be so tight to resist side to side movement as they do on a monohull due to it's beam.
Start by getting the rig set roughly right but slack. Concentrate on getting the mast vertical by taking a halyard to one gunwale and then the other first but leave the shrouds fairly slack. Then adjust forestay and backstays to get mast vertical fore and aft but don't wind them up tight. On a catalac a builders spirit level is good enough for this. Inner forestay should be slack at this point. Then tension forestay and backstays equally making sure that if you have twin backstays you don't pull the mast off to one side. Then tension the lowers including the inner forestay and lower shrouds and sight up the mast to ensure the shrouds are equal and the sail track is straight. Then tension the backstays to bring the forestay up to tension. You should aim to get the forestay pretty tight as this is important for windward performance ( Catalacs are never good to windward so you need all the power you can find!) At this point you will induce a very small bend in the mast. When you are finished the forestay, inner forestay and backstays should be pretty tight but the upper and lower shrouds less so. Leave it like that and invest the rest of your time in changing the engine oil, filters etc. You will need the engine for going to windward anyway.......
 
I have a 9m Catalac.

before you start to tighten your rigging, make sure that the mast is fully into the tabernacle - preferably using a long bolt through the base of the mast into the tabernacle through the stainless tube used to fit the mast lowering rig.

You cant put the tensions on a caterlac that you would expect on a mono, and in any case the sails are not cut to allow any real windward progression - recomendation is normally to change genoa for the smaller jib, and this allows tighter pointing (cause of the cut)

I tighten my rigging up to a point where it feels about right - but making sure that the mast is upright and vertical. I then go for a sail and check that I am achieving the same speed on each tack, and look at the slack in the lee rigging. I then tighten up to eradicate the slack - but make sure that I maintain the mast straight.

The catalac rigging recommendation from their site is:
<span style="color:blue"> 1 : For the best results the boat should be checked that it is trimmed level and square.

2 : If it is possible at the time, Shrouds and Stays ( Pairs ) should be checked that they are of equal length.

3 : Open all Bottle Screws to Equal amount of threads both ends.

4 : Hand tighten bottlescrews, pairs require equal turns.

5 : Get close to the bottom of the mast sail track, and look up see if track is running straight.

6 : Now set up the Main Halyard as a Plum Bob. Depending on the present position of the mast this may be forward or aft of the tabernacle ?

7 : Check the position of the mast, is it forward, backward and /or sideways?

8 : Keeping a check of settings, make adjustments of an equal nature to achieve your required position, possibly vertical or up to 5 degree’s backwards, keeping regular checks up the mast sail track. Depending on your own personal requirements.

9 : When satisfied tension bottlescrews an extra half to one turn and lock off and/or secure with split pins.

10: The inner forestay should not be over tightened.

11: Test Sail and check tensions but don’t make adjustments under sail wait till you are back in. You will probably need to tension some more but don't over do it.

</span>
 
Catalacs can sail although progression to windward is hard work. Progression against wind and tide is really hard work.

I have completeted the round the island in 10.5 hrs although most of that time was spent on the needles to st cats leg where it was against wind and tide.

They do need a bit of wind to move with at least 1 kt extra from 15 kt apparent to 18 kt apparent. and I dont normally reef until at least 25 kt apparent when going to windward.

The hull form does not like the solent chop and this will kill any boat speed unless there is enough wind to enable you to make headway.

I have achieved 10kts with the apparent wind at 45 degrees - but was pressing a bit too hard! Given the right conditions these boats will surprise you!
 
First, I would like to thank all who responded. This is my first catamaran, and I certainly don’t want to make a mistake.

I saw those tuning notes on one of the Catalac sites, but kept on searching for a better procedure because I felt they were a little vague, especially concerning the baby stay.

By reading these responses to my post, it seems the consensus is to insure the mast tip is centered on the boat, and avoid over tightening the rig. I had read that mast compression aft (pre bend) was to avoid mast pumping in a seaway. Am I to understand that the 10 meter mast is too short to ‘pump’?
 
No you are quite right Rick, pre tension will stop the pumping, thats why I suggested the sequence of tightening inducing a small bend to the mast. The mast (actually any mast) will oscillate fore and aft as the pressure comes on and off the forestay. A slight amount of bend will stop it going over centre and pumping. It's a bit like putting your foot in the middle of Rolf Harris's wobble board.....
(Thinks....will an American forumite know who Rolf Harris is????) /forums/images/graemlins/smile.gif
 
Catamaran masts are stronger than monos to cope with the extra loads following a sudden gust. My baby stay is almost slack by comparison with the forestay. I used to have a small amount of pre-bend, but that was in order to provide a slightly better shape into an old sail. I now have a behind mast reefing unit, which requires a vertical mast .
 
abt 3".
but I started with zero and adjusted when at sea to suit the sail and get the sail shape I wanted.

I suspect your speedo is reading a tad high to get the speeds you are quoting on your web site. at 15 kts apparent from 45 degrees, I am getting abt 5 kts, and that increases to 6 at abt 18 kts apparent.
Under engine (single 27 hp diesel) I get 7.5 kts when I have a clean bottom. I dont know what engines you have but suspect they are the Yanmar 1GM, so would expect slower speeds (with almost no forward speed above 20-25 kts of headwind)

Higher winds can provide a better speed.

Your speed to windward should be helped by the lack of a wheelhouse, but personally I would much rather have the roof over my head!

The biggest problem with the catalac for cruising is the lack of water - total of 40 gallons (UK) in two tanks does not go very far. Their ability as a sea boat for their size is a big surprise to most people. and their accomodation (especially the 9 metre) will really upset a lot of SWMBOs from half boats.
 
You are welcome Rick, and welcome to the forums by the way! File Rolf Harris under irrelevent facts that you really don't need to know. I would think that to stop mast pumping (assuming it was a problem in the first place) you would need no more than 1" bend in your mast assuming that the mainstays are tight. The degree of mast bend that is right for you will depend on the cut of your sails. Rule is it will make no difference to your genoa or foresails but will flatten the cut of your main. More bend = flatter main (better to windward) Less bend = fuller main (better downwind) Experiment. I would think more than 3" was excessive.
 
If you are crouched tightening the turnbuckle on the port quarter and the starboard hull is getting closer - That's too tight!
 
Talbot... all speeds quoted on my website were done with GPS. I don't have a speedometer on board. As I've mentioned on the site, In 10-15 knots of wind I regularly see 6-7 mph of boat speed (divide by 1.15 for knots). What I didn't mention was that this is on flat water ( I sail on the Intracoastal waterway here in east central Florida). I use the GPS religiously as a speedometer because I've been experimenting with lead positions, outhall tensions, and whatnot, to improve performance. My best point of sailing is a broad reach with the 150 Genoa, and the worst is windward (obviously).

I do have 2 1GM10's with new 13X9 props, and I just had the bottom done in September. She sails with her Transom completely out of the water, but buries it when under diesel power.

It's interesting about the water capacity difference between our boats. I really have no idea how much she can hold because I don't cruise with her. But, I can tell you what I do have. A stainless steel tank in each hull ajacent to the engine, and heading aft. Each tank measures approximately .3 meters by .3 meters (12" by 12") and are about 8 feet (2.3 meters?) long. The broker told me capacity was 80 gallons, but I haven't filled them, so I can't verify this. If you like I can snap a couple of photos this weekend and send them to you.

Mike....Saturday is rig tuning day. 3" aft bend is duly noted. That will be my starting point.

Rick in Florida, USA

http://home.cfl.rr.com/rickm505/
 
Hi
your reference to bend in the mast induced by cap shroud tension concerns me. I have seen 2 catalacs with the cap shrouds attached to the rear attachment points and the lower shroud attached to the attachment in line with the mast. As far as I am aware the correct way to set up the rigging is with the cap shrouds in line with the mast and the lowers to the rear. If you want to induce bend the baby stay will do this. Hope this is helpful.. From my experience the 8M is a little faster and more close winded than the 9M, but does slam a little more in head seas. /forums/images/graemlins/confused.gif
 
My cap stays are in line with the mast and the lowers are slightly aft. I did induce about 25mm aft prebend using the uppers, while all other rigging was slack. I did notice that when I got to the tighten up the furler (only moderately), my aft bend disappeard.

I am puzzled by this

Catalpa_front_marina.jpg
 
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