Trimaran - tacking probelm

[Sailingpeanut]

Hi,
I own a Skip Johnson design 36' Seawings Trimaran. I do have a fixed keel and am not sure if that is the reason why I cannot tack without backstaying the jib.
So I'm thinking about cutting off the keel leaving just a bit to protect the rudder and install either leeboards or daggerboards in the amas.
She's amazingly fast for being designed as a cruising boat but the draft and the tacking thing bothers me a bit.

I am not into racing and she is fast enough already, so I'd prefer an easy rugged solution.

Question: Has anybody experience with this ? How to find the position for the boards in the amas ? How big should the boards be (roughly) ? What kind of forces (roughly) need the board mountings support ? Pivoting leeboards versus daggerboards ?

thanks in advance,
Olaf

[catsketcher]

Hello Olaf,

I am not sure that cutting off the keel will necessarily make your tri tack better. I would gather that the keel is not long in chord (from the front to back) I would guess it is about 1.2 - 1.8 metres from front to back and about 0.8 metres deep. If this is the case it may not have much to do with your tacking problem, in fact cutting off the keel may make the problem worse.

I haven't had this problem on my own boats but I have owned and sailed a few different multis. Some tack really well and others much less so.

First to tack your rudder has to work really well at high angles of attack. It should have a good 0012 or similar section and be quite large. On a 36 footer I would expect the rudder to be about 1 metre deep with a chord of at least 35cm. If someone has cut down your rudder it will be overloaded at high angles of attack and stall so it won't work well at turning. Your keel is quite important here. It will act as a pivot for the rudder to turn around, but without the keel it won't work well.

The rudder should be as far away from the keel as possible (usually) to give the greatest torque when the rudder applies a load. If you have an underslung rudder of small area you may like to consider a kick up rudder of much larger proportions. These are very common in modern cats with swim steps and work very well.

I am great fan of large appendages on multihulls. Multis are light and have lots of windage. To have them work well at low speeds they need foils of large area or the foils work poorly. This is one reason why many multis are poor at manouvring at low speeds.

The best multis at tacking that I know - Farrier's F series tris have large foils with great separation and efficient shapes. If you try to follow them you would go in the right direction.

cheers

Phil Thompson

[ron17571]

Anouther thought is how your mast is raked?good luck!

[Delane]

Hello,

This is a fool proof technique I've used on Catamarans forever. The same should hold true with your Tri. First insure your at the highest angle to the wind before beginning the tack. As you start, move the rudder steady and smooth through a full swing and hold as you also break loose the main sheet. This allows the boat to pivot through the forces on the main and allows the aposing forces to move the bow threw the eye with a little back wind action. Then release the jib and sheet it in first initially and then the main last. Think it through and give it a try.

Delane

[podboat]

Hi Olaf,
I owned a Cross 46 trimaran with cruising keel that also had issues tacking and going up wind. I removed the keel and installed daggerboards in the hulls, and the boat really came alive. This is really a long story but I'll try to briefly outline the results:

Originally the boat would tack through 105-110 degrees in 10 knots of wind. The boat was very unforgiving when going up wind. The boat would be making 5 knots untill you would point just a degree or two too high and suddenly the boat speed would decrease to 2.5 knots (or less) and the boat would start to slip sideways... basically all lift from the keel gave way suddenly. It would then take a minute or two to get the speed back to 5 knots by bearing off. When tacking, all boat speed would be lost when crossing the eye of the wind. At the end of the tack, the boat was basically sliding sideways dead in the water, and took quite a bit of time and bearing off to get the speed up so that we could start sailing upwind again. Also, when motoring in a tight harbor, it was very difficult to make a sharp turn. I would need to use the prop and repeatly back down, to get the boat to turn a tight corner.

With daggerboards the boat was a whole new experience. She would sail upwind at 6 knots in 10 knots of wind and tack through 95 degrees. She was a lot more forgiving going upwind and you could pinch without losing all speed. She would keep half of her speed through a tack, came about quickly, and came back up to speed quickly. In a harbor she could make sharp turns without backing down (yes, even with the daggerboards in the amas and not inline with the rudder). We reduced our draft from 4.5 feet to 3 feet with the boards up. It also gave the boat a lot more adjustability when sailing off the wind or in a storm offshore. With my experience, I would do it again on a similar boat.

But with all that said, you will be putting loads on the boat that it was not originally designed for. Here you will really want to do the math and be conservative. Consult a naval architect- one who really knows multihulls. In our case our daggerboards were 75% of the area of our original keel. They were designed to be used in tandem, sharing the loads while sailing. They also pierced the deck while fully deployed to help transfer the loads to an already stout piece of the boat. Their cases where well tied into bulkeads in the amas and where designed to take many times the breaking strength of the daggerboard in an impact or offshore storm.

I hope this helps you in your decision.... I could ramble on about this topic for days. I'm curious what your keel looks like... What is its length, depth, thickness, and cross section/shape?

[thom wessels]

I have a 39' Horstman TriStar, (have owned 3 TriStars - love 'em) which are designed with ama daggerboards.

I too, don't care for the long 'Cross type' keels, plus the additional draft they bring. I decided on Horstman's TriStar design partly because of the adjustability of his daggerboards.

Olaf, Re; your having to help your boat tack, you may still need to backwind the jib just for a second to tack. This will assure follow through. It should be a smooth, quick process. Since multihulls are free of all that 'monohull mass' to carry them through, this is a common way to complete the tack.

Thom

[parry]

If you have a storm jib I would try tacking with that before loping off parts of your boat. I have a tri and in high winds have to be careful in how I tack running a full jib. Not that I would say to run a storm jib all the time but it may take you down a different path if you can simply make adjustments to your rigging or the few hundred dollars to recut your current jib. Im not sure what rig configuration your running but I find this escpecially true for mast head rigs.

Originally Posted by catsketcher;

Hello Olaf,

I am not sure that cutting off the keel will necessarily make your tri tack better. I would gather that the keel is not long in chord (from the front to back) I would guess it is about 1.2 - 1.8 metres from front to back and about 0.8 metres deep. If this is the case it may not have much to do with your tacking problem, in fact cutting off the keel may make the problem worse.

I haven't had this problem on my own boats but I have owned and sailed a few different multis. Some tack really well and others much less so.

First to tack your rudder has to work really well at high angles of attack. It should have a good 0012 or similar section and be quite large. On a 36 footer I would expect the rudder to be about 1 metre deep with a chord of at least 35cm. If someone has cut down your rudder it will be overloaded at high angles of attack and stall so it won't work well at turning. Your keel is quite important here. It will act as a pivot for the rudder to turn around, but without the keel it won't work well.

The rudder should be as far away from the keel as possible (usually) to give the greatest torque when the rudder applies a load. If you have an underslung rudder of small area you may like to consider a kick up rudder of much larger proportions. These are very common in modern cats with swim steps and work very well.

I am great fan of large appendages on multihulls. Multis are light and have lots of windage. To have them work well at low speeds they need foils of large area or the foils work poorly. This is one reason why many multis are poor at manouvring at low speeds.

The best multis at tacking that I know - Farrier's F series tris have large foils with great separation and efficient shapes. If you try to follow them you would go in the right direction.

cheers

Phil Thompson

Nice post Phil, good advice

[Meanz Beanz]

Originally Posted by Delane

Hello,

This is a fool proof technique I've used on Catamarans forever. The same should hold true with your Tri. First insure your at the highest angle to the wind before beginning the tack. As you start, move the rudder steady and smooth through a full swing and hold as you also break loose the main sheet. This allows the boat to pivot through the forces on the main and allows the aposing forces to move the bow threw the eye with a little back wind action. Then release the jib and sheet it in first initially and then the main last. Think it through and give it a try.

Delane

My guess is that this is correct.

The problem is that multis do not have the same momentum through tacks as a mono because they are much lighter. The tendency is for a multi to skid to a halt through the tack. At this point the mainsail tends to push the boat back up into the wind and is the major steering force as the rudder has become ineffective at low or no speed. Hence releasing the main a foot or two and making sure that the jib is drawing before the mainsail is reset makes a world of difference. As well as this it pays to find the tacking arc that will help maintain as much boat speed as possible through the turn.

This is my experience anyway and I started out with a similar issue, now we tack the boat easily first time every time.