Pitching in heavier seas

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jim
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Pitching in heavier seas

Post by jim »

Bill Parlatore raves about the sea keeping of the new Shannon SRD in the February 2005 Passagemaker magazine. Walter Schulz, the builder of the Shannon, claims that power catamarans pound when the seas pick up. My only PDQ experince has been in calm water off southwest Florida. Is his description inaccurate? Would a stern hydrofoil reduce pitching or would it lead to submarining at the bottom of a steep wave? Thanks, Jim
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Mishigas
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Post by Mishigas »

Jim, I think no one knows much about the stern hydrofoil to really make any first hand comments. I also read the article in Passagemaker and alway kind of chuckle when I hear negative comments regarding a Catamaran's seakeeeping ability. What the writer should have said is that ANY boat can pound you if the seas get nasty enough. I don't yet have any rough water experience on my own Powercat (mine is still in production) but in researching Catamarans in general and going out many times on a friends cat (not a PDQ), I think the pitch / roll / ride are exceptional and that's why I am putting my boating interest into a new PDQ. The debate regarding Cats vs Mono's have been discussed in many other web forums and it is always an interesting read. Anyway, I am truly looking forward to cruising in our new PDQ Powercat and when she begins to pound, I'll just slow her down a bit and perhaps change the angle of approach...Oh, I did read somewhere else in this forum about these boats in extreme conditions and the opinions are that these cats can take a beating and get you to your destination safe and sound. Just my 2 cents...(american)... Sandy K.
"Mishigas Hull 68"
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Pitching in heavier seas

Post by Sno' Dog »

Hydrofoils can be placed between the hulls on a powercat so as not to increase draft which makes their use as performance enhancers potentially very appealing, although I doubt that most cruisers would consider the small gain worth the extra cost.

There was an interesting article in Power & Motoryacht magazine (June 2004) comparing two identical powercats, one with hydrofoils the other without. The article is availble on the web at: http://www.powerandmotoryacht.com/boatt ... auticblue/

Their conclusion was that the addition of foils did indeed improve performance at the top end -- it increased top speed of these big 46-footers from 21 knots to 28 knots. But at lower speeds (below 15 knots) the foils added drag and actually decreased performance.

So, unless you're considering the 25-knot, 125-hp "Sport" model PDQ (I just made that up), you probably won't benefit from added hydrofoils. Also, I doubt that the type tested on the Nautic Blue powercats would have much effect on pitching characteristics -- which was the original question. For that, I suspect adding some long, wave piercing bows would have a more beneficial effect, but I doubt that most coastal cruisers would want to be saddled with them. (PDQ, especially the Sunsail charter versions, seem to have enough trouble just keeping those little spray rails around the bow intact).

Finally, the tendency to pound is closely related to bridge deck clearance. For it's size, the 34 Powercat has high clearance, but obviously once the limit is reached, some pounding will occur.

Now, you've got four cents,
Henry
(Future owner of 34 Powercat "Sno'Dog")
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Pounding

Post by Rejoice »

We enjoyed about 3 hours of 6 to 8s, with some 8 to 10s, when crossing Lake Erie. The waves were very steep and close together. The MV/34 did pound if we tried to take the seas head on, but did much better when we angled across the waves, rolling one sponson over the crest followed by the other. Still got some pounding as the waves were erratic and came from different directions, but the ride was significantly better with the angled approach.
Anne & Dave Mensel
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Gadzooks!
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Post by Gadzooks! »

Yes, catamarans pound. The bridgedeck makes it inevitable. (I suppose a trampoline forward would reduce foredeck pounding but perhaps at the expense of increasing windshield pounding!) Also, by watching the deck bounce at the base of our MV34 dinette table, I know there is pounding further aft as well.

And they pitch. The displacement carried to the extreme aft end generates a lot of lift, so a sea has a lot of leverage to push the stern up and the bow down. The fine entry at the bows means an oncoming sea will begin to lift the boat relatively far aft, so pitch is exaggerated, analogous to a short-wheelbase car. And the relatively light overall displacement makes for more pitch, as well.

Our worst experience was on the Chesapeake, from Solomons MD to Glouchester Point VA, in headwinds up to 30 kt. Seas were 6-7 feet, worst in confused, directionless seas around headlands. Sometimes had to slow to 4 or 5 kts. Not dangerous, just uncomfortable and noisy. Still made the 70 miles in 8 or 9 hours. Learned the inside helm and the portside "piano bar" are definitely the place to be in seas. (Crew went to sleep on the "couch"). Would not have wanted to be on the flybridge.
Mebs and Wally Gilliam
Gadzooks! MV34 #33
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Pitching in heavier seas

Post by Stray Cat »

Admiral Candy and I have taken Stray Cat (MV34 hull 12) over the Columbia bar and up the Washington coast to and from Puget Sound a couple of times now, in pretty bumpy water without problems (not counting me breaking a couple of ribs when we were rammed at the dock in Astoria -- another story).

Seas and swells are worst as you approach the turn into the Straits of Juan de Fuca, and we usually find seas in the 4 to 8 foot range and long swells upwards of 20 feet. Always a nice chilly and wet NW wind too, in the 15 to 25 kt range.

We also had a loooooong day of Lake Erie's finest when on our first day boating without our training skipper we took five day old Small Craft Warnings chop right astern on our run from Buffalo to Cleaveland. Wicked short steep stuff in the six or eight foot range, with some 15's. Hobby horsing can really throw you around, with these slender bows, but keeping a good watch for the big waves and tinkering with the angle you take them at will keep the violent pitching to a minimum. Hobby horse pitching is a resonance thing, all you need to do to escape it is to turn or change speed to break the rhythm.

The boat takes bumpy water quite safely, and yes the bridge section does pound sometimes. Sounds like somebody kicked the underside of the table. No harm is done, and if you are willing to make a trade off for comfort in place of economical courses, you can usually stop the pounding by taking the offending waves at a broader angle.

The long period deep water ocean swells can be taken right on the beam with amazing results. You look out the side window, and there is a solid cliff of water bearing right down on you, you can't see the top! The boat slowly rolls a tiny amount and you get an elevator ride to the top and back down, then before you know it there is a solid cliff of water retreating on the other side, and you look around eagerly for the next one.

Wally and Mebs are absolutely right, the lower helm station and the Admiral's lounge are the places to be in crummy westher -- of any sort. Warm and dry, great visibility and control, and as close as possible to the center of gravity -- and hence the pivot point of the boat's motion. Close to the galley too.

Spray over the bow in bumpy water is among the issues I want to tackle next. I have repeatedly chewed up the little low mounted spray rails as mentioned in one of your other replies, and am contemplating having robust stainless rails attached at a significant angle and well above the present frozen silly putty ones. These rails will form a substantially wider 'fin' on the inside faces of the bows, and will be angled to provide a lifting nudge when they do submerge. I'll keep ya posted....
Candy Chapman and Gary Bell in Stray Cat, MV34 hull 12
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