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Old 09-19-2015, 11:09 AM   #21
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Can anyone think of a positive reason to use trim tabs in following seas or while running an inlet?
As has been posted...Trim for "bow up" in a following sea. Also, trimming in a quartering sea really helps with the ride.
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Old 09-19-2015, 12:08 PM   #22
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The Hatteras has an interesting hull shape

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Originally Posted by Rustybarge View Post
Very interesting; why is the Hatt so good at tracking....what's different about the transom?

I notice there's some deadrise, does this help?





If you look at the LRC hull it has a fairly flat aft section, however the bulk of the hull is very rounded. The flat aft section is large enough to provide primary stability to the hull at rest and to prevent the stern from squatting at hull speed. The large keel and rudders plus the 66,000lbs with fuel probably is as large a component. Active fins help as well. When the following wave lifts the stern boats heel in the opposite direction as the broach, the fins try to correct that heel forcing the boat to try to run straight. Years ago when I raced dingy's we would induce surfing by hiking hard on the top of the wave counteracting the dingy's attempt to broach, the boat would squirt off the top of the wave and plane. These big displacement boats don't plane but the fins act like we did when we were hiking out and keep the boat tracking straight.
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Old 09-19-2015, 12:34 PM   #23
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Steering successfully in a quartering aft sea is simply a matter of timing. The trick is to anticipate the next wave and put the steering correction in before the boat starts to yaw. Then take it out before the boat starts to yaw back the other way. Waiting until something happens to take action will cause you to continuously be behind the curve and you'll be chasing the boat forever.

We learned this early on with our 30,000 pound flat-transomed PNW cabin cruiser and today we find it very easy to maintain a nearly connstant heading even in three and four foot aft quartering seas. It keeps you busy at the wheel but we find it a rather enjoyable challenge. It's all about knowing the reaction characteristics of the boat, understanding its inertia, and timing.

We used to be a bit fearful of aft quartering seas. Today they're just another thing that keeps boating from getting boring.
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Old 09-19-2015, 12:35 PM   #24
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Can anyone think of a positive reason to use trim tabs in following seas or while running an inlet?
In such conditions I'd raise the tabs and forget about them. But I've never had tabs so I may be missing something.
Ther are boats in which raising tabs all the way up leads to other issues, including lack of tracking and/or porpoising even. While this wouldn't likely be an issue in a Hatteras or Bayliner it might in other boats, especially sport or performance boats.
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Old 09-19-2015, 12:41 PM   #25
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Yeah right. Anticipate this:

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Old 09-19-2015, 05:55 PM   #26
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If you look at the LRC hull it has a fairly flat aft section, however the bulk of the hull is very rounded. The flat aft section is large enough to provide primary stability to the hull at rest and to prevent the stern from squatting at hull speed. The large keel and rudders plus the 66,000lbs with fuel probably is as large a component. Active fins help as well. When the following wave lifts the stern boats heel in the opposite direction as the broach, the fins try to correct that heel forcing the boat to try to run straight. Years ago when I raced dingy's we would induce surfing by hiking hard on the top of the wave counteracting the dingy's attempt to broach, the boat would squirt off the top of the wave and plane. These big displacement boats don't plane but the fins act like we did when we were hiking out and keep the boat tracking straight.
Thanks. I hadn't considered the righting actions of the stabs giving directional stability.
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Old 09-20-2015, 05:44 AM   #27
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Something else that occurred to me re tracking.

The keel dosn't extend very far aft and the rudders are rather small. But the sides of the aft quarter between the chines and the water line provide a surface on each side of the boat that probably acts much like the feathers on an arrow. Any yawing would need to overcome the flat submersed hull sides. Also at or near hull speed the returning bow wave will be pushing inboard on both sides of the hull aft. The above combination could result in strong tracking. I might add that lots of other trawlers would benefit from this too. The IG comes to mind.
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Old 09-20-2015, 07:01 AM   #28
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The Corvette 320 manufactured in England, but now owned by Fleming, has a very strange hull shape; its like two canoes glue down each side of the keel.

https://en.m.wikipedia.org/wiki/Corvette_Motoryacht

Its got a good reputation for straight tracking and virtually no roll with 13' beam; surprisingly enough the hull does not suffer from slamming at 20kts.

Is hull design based on dumb luck?

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Old 09-20-2015, 10:24 AM   #29
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No it's certianly not dumb luck. Some creative designer just had the guts to get out of the box. And it's not new. Just new with this size and type of boat. Many sit-on-top kayaks employ the same hull displayed in the Corvette.
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Old 09-20-2015, 10:43 AM   #30
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Many sit-on-top kayaks employ the same hull displayed in the Corvette.
My son paddled from Nice in France to Rome in Italy in a sea kayak in some very variable weather; always felt the kayak was capable of taking everything in its stride.

IMO most boats are seaworthy, but the handling chararistics can vary enormously .

Even modern trawler designs like the Beneteau swift 34' suffer from ' bow steer' in a following sea, according to a MBM test I read; and Beneteau even advertised in the mag so it must have been quite bad to warrent a mention. ( now defunct).

Someone on the mbm forum is refitting a Corvette 320 , so I will ask about sea handling in a following sea....
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Old 09-20-2015, 10:51 AM   #31
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This is how the RNLI sorted the problem of getting a lifeboat to track straight in a following sea; it took 8 years of research!




It looks a bit like the fins on a surfboard! Not unlike the entry/stern sections on the Hatt 48 LRC.
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Old 09-20-2015, 11:13 AM   #32
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interesting jet power

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This is how the RNLI sorted the problem of getting a lifeboat to track straight in a following sea; it took 8 years of research!




It looks a bit like the fins on a surfboard! Not unlike the entry/stern sections on the Hatt 48 LRC.
Being jet powered it has it own set of slow speed tracking issues. I imagine large power plants and plenty of speed.
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Old 09-20-2015, 11:18 AM   #33
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Sure but the good thing that those Fins do w basic tracking turns into a bad thing at times while broaching. The stern moves sideways quickly and the drag of the slab side of the hull between the WL and the chines or the even lower fins tend to or do cause capsizing. It's usually called chine tripping and a double chine is seen as a good solution to that problem. Double chine hulls are often or usually called Sampan hulls. Small racing outboards of the 50's w "anti tripping chines" are an excellent example.

Speaking of Sampan hulls I'd propose that the classic GB's would benefit from a double chine. One could make the hull even wider and reduce the power needed for propulsion.
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Old 09-20-2015, 11:37 AM   #34
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Sure but the good thing that those Fins do w basic tracking turns into a bad thing at times while broaching. The stern moves sideways quickly and the drag of the slab side of the hull between the WL and the chines or the even lower fins tend to or do cause capsizing. It's usually called chine tripping and a double chine is seen as a good solution to that problem. Double chine hulls are often or usually called Sampan hulls. Small racing outboards of the 50's w "anti tripping chines" are an excellent example.

Speaking of Sampan hulls I'd propose that the classic GB's would benefit from a double chine. One could make the hull even wider and reduce the power needed for propulsion.
Im No NA, but having a guess: lol....

The wave energy from behind tries to push the hull sideways. The boat naturally rolls as its breaching towards the side which is closest to the actual wave face.

A big keel/skeg will get pushed sideways by all that wave energy causing a broach.

Maybe The little fins act like fins on a surf board, only helping to keep the boat straight when its hurtling down the back of a wave. I can't see how they could stop broaching?

But..
the lifeboat has virtually no draft, so maybe that's what stops it being pushed sideways; there's not enough hull underneath the waterline to get pushed about.
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Old 09-20-2015, 11:59 AM   #35
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Many sit-on-top kayaks employ the same hull displayed in the Corvette.
My wife's Hobie Revolution looks like the that!
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Old 09-20-2015, 12:01 PM   #36
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Just by looking at the lines of the Hatteras it appears to have a few differences than most power boats.

the thin bow entry with a thin middle
decent sized rudders for a twin
cut away after section of the keel
sloping hull sides aft vs the normal slab sides of a semi displacement boat
the combination of rudders/props being far aft and outboard
the apparent aft cg/ce of the boat due to house and mechanical location
and they probably have a powerful steering system.

all the factors more than likely add up to a great handling boat.. they have always been a favorite of mine.. now if I could find a well kept one with Luggers vs the D.D. 4-53's and get the Admiral on board to go cruising again...
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Old 09-20-2015, 12:06 PM   #37
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There seems to be only one handling characteristic of my Halvorsen that I dislike. It is when I find myself in quartering seas. They lift up a corner of the transom and with the semi displacement deep forefoot she will catch an upcoming wave at an angle creating bow steer.
As people have already mentioned, when the waves are from directly astern the trick is to match your speed to that of the waves and settle into the trough for a smooth ride.

Sometimes though, like when conditions are getting worse and it's time to hide in a protected bay, you have to move downwind diagonally across the direction of the waves, which is what your question is about, right?

We live at the head of a narrow 60 mile mountainous channel which funnels the winds, so have a bit of experience with this.

We stay in the trough and turn to take the waves on a slight angle, but not so far that there is a danger of going out of control and taking waves over the side. Speeding up slightly is needed to stay in the trough.

If it turns out the comfortable angle to the waves isn't enough to get us to the protected bay, instead of increasing the angle and risking broaching we'll wait for a flat section in the waves, then make a fast turn into the waves and take them diagonally on the bow until at a better angle for another downwind shot at it.

Just some thoughts from a relative rookie...
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Old 09-20-2015, 12:37 PM   #38
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In wind driven large quartering seas we have noticed this in our Bayliner as well. In large rollers, it is not so bad, but when the wind stacks the waves is when there is an issue.

What I found, (except for avoidance) is to hand steer in these conditions. As Marin indicated the autopilot only knows about what is happening, and tries to correct for it. As humans we have the ability to anticipate, and we can swing the rudder to pre-steer making for a much more pleasant ride.

My autopilot has a option of a joy stick or knob for steering. I was thinking about buying one of them and experimenting with it.
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Old 09-20-2015, 01:33 PM   #39
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Sure but the good thing that those Fins do w basic tracking turns into a bad thing at times while broaching. The stern moves sideways quickly and the drag of the slab side of the hull between the WL and the chines or the even lower fins tend to or do cause capsizing. It's usually called chine tripping and a double chine is seen as a good solution to that problem. Double chine hulls are often or usually called Sampan hulls. Small racing outboards of the 50's w "anti tripping chines" are an excellent example.

Speaking of Sampan hulls I'd propose that the classic GB's would benefit from a double chine. One could make the hull even wider and reduce the power needed for propulsion.
A photo of an Ed Monk designed Ocean Alexander hull. The boat cruises on the "inner" hull width/chine at slow speeds. When it begins to squat with application of higher power, the outer width provides additional lift. Moonen has employed the same design concept on at least one of their current "efficient" (their word) hull designs. OA also pointed out in their literature that the double chine functionally acts to "soften" the hard chine in operation. This particular hull is exceptionally efficient both at hull speed +, and in the trans "hump" to low semiplaning speed range. It also has a very nice roll characteristic that is somewhere between a hard chine and a rolled chine. While it experiences the typical quartering seas steer issue....the relatively large rudders and a pretty smart and quick W-H (Will Hamm) autopilot go a long way toward mitigating the phenomena. So, here's a hull with some genuine engineering applied to the efficiency aspect of design. When you read an OA ad that says engineering and performance are their overriding design objectives, they aren't blowing smoke.

Agree that GB and most other SD hulls could benefit from the double chine...but they're plenty wide...actually too wide to begin with. Going inward from the current width would make more sense from an efficiency perspective.




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Old 09-20-2015, 03:19 PM   #40
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Semi,
Yes the rudders do look bigger than on the Hatt.
As to double chine the OA pictured is not what I had in mind but very similar. A much wider flat between the bottom and the topsides as found on the Payson "Diablo" skiff. Would have the dynamics of a much narrower boat. The more I think about it the more I can't understand why it's not common. There are reasons of course and it's probably not just because no one has thought out of the box. But that's always a remote posibility. Kinda like a prospector finding the mother lode but I suspect most good NA's probably get well known by designing convential hulls.

I agree w Kevin and Marin that anticipation is the name of the game on following seas and in other circumstances like plunging into a strong side current.

HOLLYWOOD,
The Hatt is a very popular and respected boat. And got there by being a very good design.

Rusty Barge,
Thanks so much for the very interesting link.
What is puzzling to me is how the exit lines at the aft end of the bulge would not be enough drag to prevent the boat from getting anywhere near 20 knots. The abrupt termination of the bulge would be too much drag .. IMO. But appearently it's not. However if shown the lines beforehand I would have said the speed would be limited to 13 or 14 knots.
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