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Old 06-18-2016, 01:39 PM   #21
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You guys are simply amazing. It's threads like this where you all share your knowledge with each other that make TF a great place to hang out.


Thanks to each of you.
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Old 06-18-2016, 02:03 PM   #22
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Here's a boat that works very well w stabilizers (paravanes).
All the same boat except the last pic .. a Fisher.

Wide flat boats can benefit from stabs also but to a much lesser degree. And the loads on the stabilizers goes way up. Can you imagine a boat in very rough seas w broken stabilizers? Soon the other side would probably break and cables would find the prop.

Thanks Mike,
I got a thanks for this post for post #11 too.
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Old 06-18-2016, 02:34 PM   #23
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Pilot boats need to be able to catch ships. a displacement hull wont do that. they also don't care about range. At speed they do achieve dynamic stability.
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Old 06-18-2016, 02:40 PM   #24
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Quote:
Originally Posted by Nomad Willy View Post
SD hulls are usually too stiff to be a good platform for stabs. Will they work on SD? .. Of course .. but much more effective on a heavy, deep, narrow and round bilge boat.
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SD Hulls are too stiff for stabilizers? Wow. Then I guess planing hulls definitely are? Or aren't? I don't know. Guess we should remove all our stabilizers that we thought were working fine since you've declared they obviously aren't.
Sarcasm aside, I think you misread what Eric said. He certainly did NOT say that stabilizers don't work on SD hulls.

I would think that stabilizers would have a greater effect on a FD hull compared to a SD hull, but then a FD hull will have more roll to begin with. That is not the same as saying that they are ineffective on a SD hull.
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Old 06-18-2016, 02:59 PM   #25
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Having had stabilizers on what some would call an "SD" planing boat (very similar hull form to a Fleming, having seen both on the hard a few yards from each other) I would contend that they actually lend themselves to, and in many ways benefit more from active stabilizers than an FD hull, by the very nature of their "stiff" or "snappy" harder chine hulls. I can say this also having been on stabilized and unstabilized FD hulls. Seaways vary greatly in their composition and severity, so of course one has to generalize some, so no I can't say I have been on all the flavors in all different seaways, but certainly a few where the roll characteristics of the boat were a definite factor.
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Old 06-18-2016, 03:18 PM   #26
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Sarcasm aside, I think you misread what Eric said. He certainly did NOT say that stabilizers don't work on SD hulls.

I would think that stabilizers would have a greater effect on a FD hull compared to a SD hull, but then a FD hull will have more roll to begin with. That is not the same as saying that they are ineffective on a SD hull.
But stabilizers don't lend themselves better to FD. Perhaps if he limits his definition of stabilizers to Paravanes that might be true, I don't know, as I've never seen Paravanes used on other hull forms. But there are many forms of stabilizers for every type boat out there. We have different types on different boats. However, all are very effective.
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Old 06-18-2016, 04:05 PM   #27
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So here comes the total lack of experience guy who has never owned a boat with stabilizers.
But how is a hull design that is stiff going to make stabilizers not effective?

And even dumber question is this.
Unless its really rough would you not pull them up for most cruising to reduce drag, thus increasing fuel range?

I have read a little on them but would think if anything a stiffer hull would be a benefit to the effects of stabilization.
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Old 06-18-2016, 04:12 PM   #28
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Pilot boats need to be able to catch ships. a displacement hull wont do that. they also don't care about range. At speed they do achieve dynamic stability.
In ports around coastal BC, big ships come in very very slowly.
It doesn't require a fast boat to catch them.
I see them coming in so slowly that over shooting them would be more likely than not catching them.
I was padding padding my kayak in a relaxed manner and passed 2 ships coming into the harbor last summer.
They tend to move just fast enough to maintain steerage....maybe a knot or so. I'm 45 and not an Olympic athlete.....if i pass you in my kayak you're barely moving.
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Old 06-18-2016, 04:18 PM   #29
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Gross generalizations tend to be full of gross errors.


Some dwell on what they know and have never expanded much beyond that from what I can see.


Roll reduction is just that...does the stabilizer brain know what type of hull you have? Maybe you program that in much like an autopilot....and it reacts according to what it is programmed for. As to paravanes...most commercial fishing boatd around here whether full or semi displacement are all hard chined.... the results of roll reduction seem to be about the same but hard to measure as hardly one setup is similar enough to another or get 2 out under similar conditions.


NEVER in all my years of pro and amateur boating have I read or heard that stabilizers are more effective on one type of hull or another...unless you of course assume because full displacement hulls will roll farther but slower and more comfy that they are more effective.


But reduction is reduction and if they reduce both hull types to a tolerable level...then what the heck is the discussion over? Semantics?


I agree with Bands post where some view this forum through blinders and spend a lot of time passing info while true, is so limited in scope it is hard not to respond.
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Old 06-18-2016, 07:15 PM   #30
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Most all the time fishermen and native cruisers put the fish over when it gets rough enough so that if it got any worse deploying them could be dangerous. Usually they are not used to cruise with unless they are about to cross bad waters w a sour weather forecast. They usually cost about one knot or a little less .. and run about 15' deep.

The reason paravanes are far less effective on SD boats is that when more water is under one side of the hull it causes lift and the boat rolls. Two forces (basically) the lifting force or the righting force created by the boats volume X the distance from CL. With the FD fish boat I showed pics of the lifting force is small but the force necessary to maintain a level boat is easily achieved w paravanes. Lighter weight, smaller poles and rigging can be used. With a wide SD boat like a GB36/42 the righting moment or lifting force w more water under one side is huge. That's why when you step onto a cap rail the GB responds so little you may not even notice it moved. Won't right away on the Dixie (FB) either because of inertia but if you stand on the cap rail in 20 to 40 seconds the boat will roll or list far more than the GB. Look at my post #11 and see Dixie w a pole extended. You can clearly see the list.
To put it another way it's easy for the paravanes to keep Dixie from rolling. But on the GB w the same fish and the same water under one side the extreme flotation on one side of a wide hard chine hull (GB) will force the water to have it's way w the boat. She'll rise to the occasion .. smartly. Paravanes or no. The GB will roll much like it would w/o the paravanes but a somewhat better (less).
Dixie can probably go through big steep waves almost like they wer'nt there w her paravanes deployed.

So is it apparent to all why a wide flattish bottomed boat are not the best choice for paravanes?
You're right BandB I know little about active fin stabilizers and have been referring mostly to paravanes.
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Old 06-18-2016, 07:41 PM   #31
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haven't seen much comment about hull shape.


Round chines combined with deep keel and ballast down low increase the tendency of a hull to remain vertical to the earth and not perpendicular to the water surface. Flatter hulls tend to remain perpendicular to the water surface even when the water surface tilts with waves.




Consider how a flat board will behave in waves vs a partially filled beer bottle. The beer bottle will tend more toward remaining vertical while the flat board will always follow the water surface.


Stability or roll resistances a big factor in being comfortable offshore. sailboats have a tall mast and wind loaded sails further reducing roll.
Interesting, the bottle and board analogy really helped. Thanks!
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Old 06-18-2016, 08:34 PM   #32
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BanB wrote;
"The beer bottle will tend more toward remaining vertical while the flat board will always follow the water surface."

The flat board is like the SD hull and the righting moment will overpower the paravanes resulting in only slightly reduced roll unless the paravanes are extremely over sized.

Yes I like the bottle and board analogy too. It's easy to keep the bottle oriented whereas it takes lots of force to counteract the righting moment (force) of the flat board.
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Old 06-18-2016, 08:50 PM   #33
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So is it apparent to all why a wide flattish bottomed boat are not the best choice for paravanes?
You're right BandB I know little about active fin stabilizers and have been referring mostly to paravanes.
I don't know much about paravanes other than I don't use them. Paravanes are really used by a very small segment of the boating population. There are many reasons not to use them on SD or Planing boats. One is speed. You're not going to want them hanging out if you're going 20 knots. There's also, at least in our area of the country, a strong trending away from them even for FD boats. They were most popular before stabilizer installations became more dependable. In 2004, for the Atlantic Rally, many of the Nordhavn's had fin stabilizers but had trouble with them as Nordhavn hadn't really perfected their systems. Now, fin stabilizers are pretty much trouble free on Nordhavn's, probably less trouble that with Paravanes on a long ocean crossing.

The stabilizer market is still developing too. It was fairly straight forward with Naiad, Quantum, and ABT-Trac having most of the market and very similar approaches, but now Seakeeper is gaining a lot of market with Gyro Stabilizers. Then you also have Sleipner/Side Power with Vector Stabilizers designed for boats between 50 and 70' or so with what they call "modern hull forms" so planing boats. By the design of the curved fin they are more effective. I thought it was probably hype at least to some degree, but after using them a while, I'm very impressed and they do everything they claim.

I don't even attempt to understand the science of Gyro Stabilizers but having tested a Sea Ray with Seakeeper and also been on one Sunkeeper with Seakeeper, I'm impressed with the job they do, just not impressed with the spool time and other factors.

A question about Paravanes. Are the majority of them either DIY or done custom by a yard? Are there no brands that are significant in that market? Or is there a "go to" product out there?
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Old 06-18-2016, 08:51 PM   #34
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BanB wrote;
"The beer bottle will tend more toward remaining vertical while the flat board will always follow the water surface."

.
No, I wrote nothing about beer bottles. I don't even drink beer.
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Old 06-18-2016, 08:53 PM   #35
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Stabiliser paravanes come in different sizes, shapes and hanging styles
to accommodate different hull types and sizes.
They are also hung at various distances out the poles to vary the effectivness
of the fish.

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Old 06-18-2016, 09:02 PM   #36
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Stabiliser paravanes come in different sizes, shapes and hanging styles
to accommodate different hull types and sizes.
They are also hung at various distances out the poles to vary the effectivness
of the fish.

Ted
But no major manufacturer of them? I'm just curious.
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Old 06-18-2016, 09:20 PM   #37
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There is a manufacturer of the fish in Seattle. They also make .. Oh I just remembered the name ... Kholstrand (SP?) they also make hydraulic anchor winches and other related fishing gear.
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Old 06-18-2016, 09:37 PM   #38
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There is a manufacturer of the fish in Seattle. They also make .. Oh I just remembered the name ... Kholstrand (SP?) they also make hydraulic anchor winches and other related fishing gear.
Kolstrand
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Old 06-19-2016, 11:13 AM   #39
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The most high performance blue water ship I know of.

SD, FD or something else?
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Old 06-19-2016, 12:56 PM   #40
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Most of the paravanes I am familiar with are one offs, or custom.

Pros: no holes in boat, no seals to replace, no hydraulics, no electrics, no computers, can be used at anchor, tens of thousands of dollars less than other options.

Cons: lots of manual labor, can't run in shallow water, ugly(opinions vary)

I can't imagine running fish at double digit speeds after watching them work at 6-7 kts. They are extemely effective on our hull.

Having had a SD boat before this one, I don't think they would work as well. That boat would fight the roll until it didnt, aka snap roll (lots of force needed in a short period of time). This boat is very linear in its resistance to roll and recover.
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