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Old 14-07-2017, 10:48   #91
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Re: No love for trimarans - why?

Most trimarans do fly the windward ama starting in light winds and low heel angles., At 3-4 degrees ours is out of the water. Some boats like Pivers and some of the Tristars should really be considered 3 hulled catamarans as nothing will get the windward ama clear do to hull depth and over all beam. I saw a guy in a boatyard desperately trying to mod his Piver so it would fly a hull, he thought something was wrong compared to new boats but all 3 in is what it was designed for.

With max stability on our boat close to 30 degrees I set a cruising redline of around 10 degrees heel for big safety margins and easy working.

More rounded V ama shapes give a much softer ride and reduce shock loads over the full shaped ultra high buoyancy amas that racers tended to. Of course racing tends to set fashions whether or not they are best for other purposes like cruising.

On the beam on to wave impacts it makes sense to go high or low on the course to take them at a angle. If the rhumb line has to be made a daggerboard boat can pull it up to get leeway, by pointing above the course you'll soften the impacts while keeping your desired direction.

Smaller rigs for cruising make sense to me, some of Newick's plans showed 3 rigs. Full on wingmast for racing, hot conventional mast rig for performance, schooner/ketch for cruising to keep sail area but lower the center of effort and split the sails up for less strain and easier handling.
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Old 14-07-2017, 14:17   #92
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Re: No love for trimarans - why?

Gregg,

Hortsman trimarans are probably best thought of as a catamaran with a center hull and not really what a modern designer would think of as a trimaran. I know it's a strange way to look at it conceptually since it quite clearly has three hulls, but bare with me a moment.

Modern trimarans are designed around a positive dihedral angle, basically if you measure the angle between the main hull and the amas the amas are not on the same plane, if the boat is perfectly level the amas are lifted 8-10 degrees above level. This means that when sailing the windward ama is almost always out of the water, in fact on most modern trimarans it is next to impossible to even motor without one of the amas out of the water.

Flying the main hull btw is something reserved for only racers and the truly crazy. No cruising tri should ever fly the main hull, and many simply cannot. The leeward ama simply does not have enough buoyancy, instead the leeward hull just sinks deeper and deeper and the main hull starts to drag. This is by design, to keep the boat from flipping.

Your boat by comparison has either zero or almost zero dihedral. This means that your main hull and windward ama will start to fly at almost the same time (remember what I just said about flying the main hull?).

The Hortsman's really are much more like overwide catamarans than they are like trimarans. Good boats, but almost in a design class by themselves.

Below you can see a modern cruising trimaran the Rapido 60 beating in about 5kn of breeze. As you can see even in very moderate conditions the windward ama is still flying free of the water. But note, due to your extreme width for a boat your size the loads are going to be massive due to the very high static RM. Even compared to a normal tri your size the loads are going to be higer so sizing blocks and gear need to take that into account.

The shock loading the PBMaise discusses above is true, but only really for the Hortsman type trimarans. Those with a more pronounced dihedral simply don't experience this. The windward ama is always clear of the water, and so it's just the two hulls that are immersed. In fact this is a large part of why you would want a larger angle in the first place, the larger it is the higher the windward ama flys, the downside is lost RM and more onboard heel, since the boat will almost always be heeled over at exactly the dihedral angle. More than 10% gets uncomfortable, less than 5% leads to ama slamming, so there is a pretty narrow range that most (non-race) boats fall into.

As for big rigs... there is nothing like sail area in light wind, and knowing how to reef for bigger breeze. It's a lot harder to add mast height down the road. But a well designed trimaran doesn't need a small rig to be safe, it just needs a skipper who knows when to reef her.
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Old 14-07-2017, 20:17   #93
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Re: No love for trimarans - why?

The dihedral angle can be misleading as it is the main hull and ama keel and center of buoyancy angles you need to look at. Many cruising tris were in fact designed with straight beams to the amas which were set higher relative to the main hull for dihedral. Accommodations and build simplicity are the reasons . Dihedral but straight arms.

For cruising you really want amas that are immersed at least a few inches to avoid the dreaded anchor teeter totter. When the amas just kiss the surface any ripple will start a oscillation around the center hull with each ama bouncing off the water in turns. People with these boats tend to put weight to one side at anchor.

Reefing in time is the key to safety but a tall mast will contribute to boat motion, pitching etc..., in heavy seas. The current round the world record holder IDEC actually went with a shorter mast to maximize effectiveness in the anticipated conditions.
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Old 15-07-2017, 05:59   #94
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Interesting Points Cav - Re: No love for trimarans - why?

Quote:
Originally Posted by Cavalier MK2 View Post
Most trimarans do fly the windward ama starting in light winds and low heel angles., At 3-4 degrees ours is out of the water. Some boats like Pivers and some of the Tristars should really be considered 3 hulled catamarans as nothing will get the windward ama clear do to hull depth and over all beam. I saw a guy in a boatyard desperately trying to mod his Piver so it would fly a hull, he thought something was wrong compared to new boats but all 3 in is what it was designed for.

With max stability on our boat close to 30 degrees I set a cruising redline of around 10 degrees heel for big safety margins and easy working.

More rounded V ama shapes give a much softer ride and reduce shock loads over the full shaped ultra high buoyancy amas that racers tended to. Of course racing tends to set fashions whether or not they are best for other purposes like cruising.

On the beam on to wave impacts it makes sense to go high or low on the course to take them at a angle. If the rhumb line has to be made a daggerboard boat can pull it up to get leeway, by pointing above the course you'll soften the impacts while keeping your desired direction.

Smaller rigs for cruising make sense to me, some of Newick's plans showed 3 rigs. Full on wingmast for racing, hot conventional mast rig for performance, schooner/ketch for cruising to keep sail area but lower the center of effort and split the sails up for less strain and easier handling.
Exactly what I thought when these guys were talking about taking waves on the beam and worrying about wobbling and their rigging. Especially when cruising, why not simply steer more into the wave? Of course, wind direction would be a factor and one may not be able to steer to closer to the wind if on a close reach or a tight, delivery schedule.

We found ourselves in a situation like that described above with 2.5' high waves hitting us every 2 seconds or so. I was motoring, but had the genny up a good part of the time as well. Do not understand anything about the hydro-physics of it all, but, the moral of the story is that we steered into the seas and got where we were going a bit later, but in relative comfort and safely.

Encountered similar conditions bare-poled at anchor from ferry wash, and that seemed to stress the rigging a lot more, though, thankfully, for only a few moments.

Of note is that our Nicol amas definitely have a gentle, rounded, V shape and we have no centerboard, so slipping is a problem for us. As you note; the ama shape probably helps smooth our ride a bit in beamy, choppy seas. We have never pushed the 40' boat fast enough to entirely lift an ama for any consistent length of time, and have maxed our speed at just under 9 knots, though I know she will go a lot faster.

Just two cents worth of experience from a relative newbie.

G2L
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Old 15-07-2017, 09:44   #95
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Re: No love for trimarans - why?

Hello G2L, You guys do need to push harder! If you hold on till the windward ama keel is at least clear of the water you'll make less leeway because the lee ama will have a good bite. Get a gauge for heeling and don't reef till you hit 10 degrees. We can break 9 knots to windward in cruising trim in a good breeze.
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Old 17-07-2017, 12:55   #96
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Re: No love for trimarans - why?

Don't reef until you're burying the leeward float!
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Old 17-07-2017, 13:36   #97
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Re: No love for trimarans - why?

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Don't reef until you're burying the leeward float!
I'm chicken, when the windward ama is 1 1/2' clear of the water and the GPS says 17 1/2 knots that's my limit. letting the sheets out some even with a 22 ft beam. Running before the wind it's time to reef if green water is trying to come on the leading ama's deck, that's sliding down 16fters. An SR31.

I still loved my 25' Piver.
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Old 17-07-2017, 14:25   #98
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Re: No love for trimarans - why?

It's pretty hard to bury the lee ama on a wing deck tri at speed as the wing starts to work as a scow. There are horizontal buoyancy reserves working there not to mention the planing area. G2L does have most of the wing deck removed like a Searunner vent wing so it might be possible but we want him to take baby steps here. Remember, If you scare the wife there will be strife!
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Old 17-07-2017, 15:52   #99
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Re: No love for trimarans - why?

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Don't reef until you're burying the leeward float!
Lets all be macho. What could possibly go wrong??

Boat capsizes in Chicago-to-Mackinac race, Coast Guard helps with rescue | MLive.com
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Old 17-07-2017, 17:54   #100
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Re: No love for trimarans - why?

I'm scared now. Me thinks I'll be safest if I just stay tied up to the dock. Better yet, a couch in a house!
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Old 17-07-2017, 18:41   #101
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Re: No love for trimarans - why?

If you look in the gallery on Horstman's website the yellow 27'9" is comfortably flying the windward float in what looks like pretty moderate breeze. Not as high as modern tris but not glued to the water by any means.
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Old 17-07-2017, 21:19   #102
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Re: No love for trimarans - why?

There is a pretty big difference between cruising and racing. Most of the F-boat capsizes are actually pitchpoles when they hit a tall standing wave in heavy winds with the chute up.
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Old 18-07-2017, 10:28   #103
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Re: No love for trimarans - why?

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There is a pretty big difference between cruising and racing. Most of the F-boat capsizes are actually pitchpoles when they hit a tall standing wave in heavy winds with the chute up.
Ya, but those are racers being stupid... I know because I have been one of them (though we have never flipped our Corsair). Any time the leeward float is starting to press down, certainly when you get water on the leeward ama bow deck, it is time to slow down.

Unlike monohulls that typically get rolled by wave induced heel, trimarans are almost always rolled by wind. Almost always downwind with a spinnaker in high winds. Pull the spin down when the wind exceeds 20kn and it's hard to see a cruising trimaran flipping.
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Old 20-07-2017, 07:41   #104
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Re: No love for trimarans - why?

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All of the above. I've owned a Piver and Sunrunner. Speed,the ability to run shallow inlets and sea worthiness are the pluses. However, some common sense is required. Once over they don't come back.
Hi Cadence.
Since you are a Piver-Brown-Marples follower you know that they can be designed to come back.

When properly designed they don't sink and will float upside down on the amas which leaves the main hull high and dry and habitable. No other design measures.

I'll gladly sacrifice space for safety and 200 mile days when I must run and hide. Just keep an eye on the satellite weather map.

My #1 big open water cruising design for a singlehander is a 40ft center cockpit tri cutter. This size can accommodate all the conveniences.

Problems? Yes, slim pickings.

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Old 20-07-2017, 08:03   #105
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Re: No love for trimarans - why?

Foam core 38ft center cockpit open wing cruising trimaran with excellent sails and never started 27hp Yanmar diesel $46k, excellent fiberglass work, built by professional builder for himself.
38x24 Harris trimaran, Wings.
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