MULTIHULL MONOHULL SURVEY

[Hud3]

Brad,

You sure do have a way with words!

When we bought our Island Packet, five years ago, catamarans weren't even a consideration. I just didn't like the way they looked. Now, after reading your eloquent ode to sailboats of the two-hull persuasion, you have me second-guessing myself. My old prejudices are falling by the wayside.

Seriously, I've learned a lot about the virtues (and vices) of cats in the various discussions here on CF over the last few months. And I've come to appreciate the variety of knowledge and experiences that many of our members bring to the table. Thanks for that, All

[Robertcateran]

The next saga is why someone would prefer a Harrproa over a cat
Robert

[Southern Star]

Thanks for some kind comments - and Hud, your Island Packet is a sensational boat in my opinion. Solid, safe and attractive. As I've already pointed out, if I were to go back to a mono, it would tend to be in a more traditional design, like your own.

Brad

[isbolick]

Brad- Yeah, I was enthusiastically telling my husband about getting a fixer upper and he wasn't feeling the love. I think we are back to playing with the little boat this summer, getting a mono in the 27'-30' range for the next 3-4 years while we save up and make some life changes and then try to get into our 'ultimate boat' around the time my daughter graduates from high school and heads off to college. We can skip around SC-FL and over to Bimini on the mono earning some sailing chops and just doing as much learning and sailing as we can. But we are both really sold on the idea of the cat for our long term cruising.

[Southern Star]

Good plan, Isbolick.

Brad

[jzk]

I want a cat. However, the cat I want is $300,000 (leopard 47). A 38 is 200k. For $150k or so I can get a 2000 Beneteau 50 with 4 cabins and save $150,000. The beneteau 50 is a pretty sweet ride for $150k and includes a generator and airconditioning. What catamaran can be had for $150k that includes a generator and airconditioning?

[BigCat]

Originally Posted by cptnandy

Based solely on my 600+ days sailing a cat in Hawaii, I personally don’t like the pounding of waves on the bridge deck sailing to windward.

Hi, Captain Andy. I, for one, appreciate your sharing your experiences with the forum. I have been looking at the Conser 47 online, and it looks like it's bridgedeck clearance is quite low-maybe 1 1/2', judging by comparing the bridgedeck with the hull line (not the height of the profile, but the line drawn on the profile showing the bottom of the deck structure.) When I compare that height with a berth drawing on the same boat, it is a bit less than 1/4 of a berth legth. That is much less than it should be for a 47' boat, which should have at least 30" of clearance for use at sea. Does your experience of bridgedeck smacking by waves include such experiences on other catamarans? If so, could you tell us which, so that we can try to find out their bridgedeck clearance? Thanks, Tim Dunn aka BigCat

[cptnandy]

Tim,
Most of my time on cats was on the paragon (s), I did however do some sailing on a Gemini (a POS in my opinion) and on another custom 36 foot cat (builder unknown). I suppose that this limited exposure to cats of a “cruising design” has colored my view of them. I did sail some on a 65’ charter cat that had quite a bit of bridge deck clearance, (Marpels design?) cant remember if it had the same problem…
Of course the conditions I was working in off Maui may be a bit rougher than typically at sea ie: short steep waves are the norm often “square” which of course would make more bridge deck freeboard even more important if avoiding the slap is paramount.
Wouldn’t lots of freeboard (required for bridge deck clearance) hurt the overall stability?

[BigCat]

I did the math on the Conser 47, which I posted on this site on the thread where we were discussing the Paragon capsize, and its extreme light weight gave it very low stability. A slightly higher bridgedeck hurts the stability in theory, but the formulas used for calculating sailing catamaran stability don't even look at bridgedeck height.

The components of the formulas in use look at overall weight and beam from the hull centerline to the boat's center or to the other hull's center, the height of the center of the sail area, and the sail area.

I'd say the Paragon went over because it was very, very light-12,000# light ship, apparently, plus whatever was aboard-which was just 11 passengers and whatever the tanks held-probably little more than 2000#. The formula predicted the capsize at something less than 60 knots, so no extradordinary conditions beyond that wind speed were required to capsize it, says the formula.

I sailed to Honolulu from LA in 1971, and the waves in the channel between Oahu and Molokai were so steep that I thought we'd be pooped. They kept the same height as offshore to windward, but lessened their distance from crest to crest amazingly.

[cptnandy]

As I stated a few times the paragon went over due to a combination of wind and wave. While I don’t have the actual stability figures, I think that there must be something off with your calcs or data set as I doubt that the CG would have issued or re-issued the COI and stability letter for the Conser 47’s if they were likely to flip in under 60 knots of wind by the #’s.

Anyway, the seas in the channels build due to the fact that the water rises from around 16000 feet to less than 400 in a very short distance. I drove a 120ft ferry between Maui and Molokai (1.5 years prior to Paragon) and have seen green water over the bow (>10ft freeboard at bow) in that channel due to the steepness of the waves… yuck. Got so bad that we always handed out barf bags and often would have to make all passengers stay seated for the first half of the trip (after that it was down swell).

[BigCat]

Originally Posted by cptnandy

As I stated a few times the paragon went over due to a combination of wind and wave. While I don’t have the actual stability figures, I think that there must be something off with your calcs or data set as I doubt that the CG would have issued or re-issued the COI and stability letter for the Conser 47’s if they were likely to flip in under 60 knots of wind by the #’s.

Anyway, the seas in the channels build due to the fact that the water rises from around 16000 feet to less than 400 in a very short distance. I drove a 120ft ferry between Maui and Molokai (1.5 years prior to Paragon) and have seen green water over the bow (>10ft freeboard at bow) in that channel due to the steepness of the waves… yuck. Got so bad that we always handed out barf bags and often would have to make all passengers stay seated for the first half of the trip (after that it was down swell).

I don't share your faith that the Coast Guard expects sailing catamarans to sail without turning over in 60 knots of wind. I can't speak for the Coast Guard, but I can tell you that they were satisfied with masts that were calculated to break with full sail up at a little over 50 knots, in a boat designed for a place where 30 knots are not uncommon.

I can't guarantee that the formulas are correct, but I do know that the usual calculation and its equivalents do indeed predict that the Conser 47, if built to specifications, and loaded with one ton of cargo/passengers, will turn over at a bit less than 60 knots. To learn how to do the math, check stability article Part 1 by Woods Designs

From my website:

The theoretical stability of a catamaran is given in the formula, displacement in pounds x the distance between the centerline of the two hulls in feet x .5 = righting moment in foot pounds. To use my BigCat 65 design as an example, 45,000 x 28 x .5 =630,000 foot pounds (that is, a lever of an amount of feet times an amount of force in pounds.) If considering a capsize from wind force, the theoretical heeling force is the wind pressure x the sail area x the CE (the height from the waterline to the center of your sail area.) Wind pressure can be calculated from Martin's formula, which is windspeed in miles per hour squared x .004= pounds per square foot. So, the heeling (capsize) force for BigCat 65 that generates a theoretical force sufficient to capsize it is: 9.21 pounds x 2400 sq. ft. of sail area x 41 feet (center of sail area above waterline) =630,000 foot pounds. This wind pressure is found at 48 miles per hour, which = 41.7 knots. (One knot equals 1.15155 miles per hour, so divide the mph by 1.15155 to get the knot equivalent to the result of Martin's formula.) So, in flat water, theory predicts the BigCat 65 will capsize at 41.7 knots in calm water if the sails are up and unreefed. This theory applies rather poorly to a biplane rig, which the BigCat 65 design has, because you can't get the full effect of the wind abeam if both sails are up, but it works pretty well for a typical catamaran with a single mast. Obviously, this is all very theoretical, because a capsize is unlikely to occur in calm water, sails are rarely strapped hard amidships in high winds, etc., but it does give one a starting point for considering the forces at work. It does help explain how charter catamarans have capsized by coming out from the lee of islands in strong trade winds with the full mainsail sheeted amidships while under motor, when you consider that gusts are often equal to half again the average wind speed, and that winds will often increase as they funnel through channels between islands, or through gaps in cliffs to windward.

[dana-tenacity]

Originally Posted by Robertcateran

The next saga is why someone would prefer a Harrproa over a cat
Robert

I would, and will if I can arrange the funding.

[cptnandy]

Tim,
You must be assuming FULL SAIL, which of course no one in their right mind would have up in that much wind. I know for a fact that I have sailed that boat in winds approaching 60 knots and not flipped, of course I was reefed… duh!

I could very well be wrong about the stability calcs for Paragon, as I said I don’t have all the data in my possession.

The Coast Guard did not do the stability calcs for Paragon, although they did review and approve them.

And for the record... I don’t place much faith in the Coast Guard for anything, esp. in the last few years. Their mission seems to have changed from one of helping to one of harassing mariners. I have twice (in my 40+years on the water) needed the assistance of the Coat Guard, the first time 20+ years ago they helped; the second (Paragon) they did nothing useful, in fact if anything they screwed up as they were unable to get either their helicopter or their C-130 off the ground to assist in the SAR effort, and didn’t send out their Maui based vessel, even though other boats were looking.
Design wise -- I have on occasion had to explain things to the coast guard inspectors about boat building techniques they were not familiar with / didn’t understand. (vacuum bagging comes to mind). Not to say that there aren’t good folks there, I have meet many excellent Coastguardsmen/women, but like everywhere they too make mistakes.

[BigCat]

Capt. Andy, don't you remember my post? We tried to establish just how much sail area you had up, and what its likely center was. I know you were deeply reefed, and I did the calculations using estimates for your reefed sail area and center of sail area. I am an old yachtie, you know-I have done plenty of 'handing, reefing, and steering.'

Here's the post, at the bottom of the page:

http://www.cruisersforum.com/forums/...tle-429-4.html