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Old 05-01-2021, 08:02 PM   #1
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Rolling Chocks

One of my long term projects is to work on the roll of my boat. with 6.5 draft round hull and 61 tons displacement, I know she can get to rolling. I tell the passengers how smooth the roll is, but I still would like to dampen it a bit. As a retired Alaska Fisherman we NEVER heard of mechanical stabilizers, fins, not even paravanes except on smaller, under 50' boats.
I drove a 123' hard chine single screw no thruster boat for 30 years in all weathers. We all had had rolling chocks, the whole fleet. In talking to the yard I trust, they said "go big (at least 12") or stay home.
My 1952 William Garden slips through the water with no fuss. HAs anyone in the pleasure boat world added rolling chocks. I have no interest in electrical, mechanical, hydraulic etc. powered systems.

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Old 05-01-2021, 08:11 PM   #2
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I don't have personal experience with them, but out of all of the options for roll reduction, the rolling chocks are likely to produce the smallest effect. It should still be significant if implemented well, but not as much as you could get from fins, paravanes, etc.
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Old 05-01-2021, 08:37 PM   #3
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Quote:
Originally Posted by rslifkin View Post
I don't have personal experience with them, but out of all of the options for roll reduction, the rolling chocks are likely to produce the smallest effect. It should still be significant if implemented well, but not as much as you could get from fins, paravanes, etc.
Yes simplest, no moving parts, no brainer, and least effective..:-)
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Old 05-01-2021, 09:54 PM   #4
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Quote:
Originally Posted by trawlercap View Post



]
On the same website as your bottom pic the version used for timber vessels



https://rlmarine.com.au/stabilisers/
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Old 05-02-2021, 05:44 AM   #5
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what's the reason for the holes in the steel hull photo? Why not just make the strake a little narrower?
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Old 05-02-2021, 07:06 AM   #6
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The goal of the chock is zero resistance to water flowing in the fore-aft direction but then huge turbulence when rolling. So slots, alternating plates, T-end plates, etc are employed to increase this resistance over a flat plate.
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Old 05-02-2021, 07:31 AM   #7
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You have a beautiful trawler!
About chocks, refer again to the 4th edition of Beebe, "Voyaging under power".
Recently, I have reached a company in Canada which recommands dolphin wings or articulated wings, sometimes called batwings.
I didn't go ahead because it was too difficult to imagine and calculate the best design for this back up to my hydarulic stabs. So I went with paravanes...
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Old 05-02-2021, 09:02 AM   #8
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I have no experience with those Articulated wings but would love to see reports on their effectiveness in roll reduction. They seem to be getting more and more popular on commercial fishing vessels.
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Old 05-02-2021, 10:37 AM   #9
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Seems to me that "they" came up with paravanes as a way to improve on the effectiveness of rolling chocks.

The idea being to move the point of force further away from the pivot point.
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Old 05-02-2021, 10:52 AM   #10
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Your chances of getting the improvement you want are many times greater if you get some expert help on the design. By expert, I’m suggesting marine architect, not experienced boat yard guy.

Look up Tim Nolan in Port Townsend (Nolan Marine Design). Being a PNW guy, he has lots of experience with the right kind of boats and conditions. He helped me with a project and I found him to be very smart and very practical. He designs lots of boats from a clean sheet of paper but he also does many mods and improvements.

If he is willing to work on the project, it would be the best money you spent on the entire thing. Give him and call and you will learn something, regardless of whether you decide to use him going forward or not.
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Old 05-02-2021, 12:36 PM   #11
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I have added rolling chocks to my American Tug 34, a very different kind of boat, hard chine semi-displacement hull. I attempted to measure the before and after roll amplitudes and excursions, but that measurement is very difficult to do because finding consistent test conditions is impossible. On my hard chine boat, the roll amplitudes were not that great, at say 12-15 degrees things were flying around the cabin more due to the roll acceleration than the amplitude.

I had Independent Shipwrights from Coombs, BC install the rolling chocks, they have done over 300 installations mostly on fishing boats. The result did not change the roll amplitude very much, but slowed down the acceleration noticeably and the rolling dampens out quicker. I did careful measurements of speed and fuel burn vs. rpm before an after and there was no measurable change. Nor was there a noticeable difference in low or high speed maneuverability. The installer said, "it'll take the snap out of the roll" and that is a good summary.

Though not in the same class as active stabilization, I'd say it was well worth the modest cost, and I'f do it again on a new boat if it didn't have fins.
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Old 05-02-2021, 01:51 PM   #12
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Here’s an interesting design on retractable stabilizing fins.

This Aluminum 20’ Passagemaker was in Passagemaker mag.
Notice that the space required for retraction is often available in trawler boats.
I suspect they may be very effective too.
Next to zero drag underway.
Opps .... can someone invert this picture?
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Old 05-02-2021, 06:17 PM   #13
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I have factory installed roping chocks on my soft chined round bilge hull. It still tools significantly at anchor or underway with any significant swell on the beam. Because the dampening effect is so close to the centre of motion, a very large surface area is required to successfully calm the roll.
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Old 05-02-2021, 08:36 PM   #14
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I have seen tiny little rolling chocks and wondered if they would do anything. How big are yours? On my 34', the run about 2/3 of the waterline and are about 10" wide.

On mine, the rock and roll dampens out quicker at anchor, the initial roll from a wake is about the same. For beam seas you need active stabilization - the hull wants to follow the sea surface and I don't see how rolling chocks could help.
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Old 05-03-2021, 04:29 AM   #15
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Several Willard 40s have installed roll chocks. Most were free-hand additions glasses into the hull. All report very similar results as DDW states above on his AT34. They dampen/attenuate the oscillation frequency vs active stabilization that defeats initiation of the roll in the first place. All owners are enthusiastic about the appendages and would install them again given the modest cost.

BTW - the most recent conversion was a W40 that has paravanes. The owner wanted dampening when he conditions did not warrant launching his fish. While not a replacement for paravames, he reports the chocks are useful.

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Old 05-03-2021, 07:55 AM   #16
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Thinking about it, the damping from rolling chocks likely has a similar effect to speeding up in a semi-displacement or planing hull. It's not like active stabilizers that will prevent the roll, but by damping the rolling motion more, it gets more comfortable. Instead of a constant pendulum-like roll back and forth, the boat will simply tilt with the water surface. Taking the momentum out of the roll will reduce the amount of roll a bit, but it also makes the motion less constant and easier to live with.
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Old 05-03-2021, 09:49 AM   #17
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Not sure this will work but look up Project BruPeg on YouTube. Putting wings on a ex commercial trawler.
https://youtu.be/tE-WSLnxMyk?t=1101
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Old 05-03-2021, 10:34 AM   #18
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I have found the best application for those who don’t want the gear and headache or risk of paravanes to be properly designed bilge keels. This is especially true for commercial fish conversions where in yacht trim they are too light to set on their lines and too lively empty. In a seaway the roll down is generally easy enough but can snap back enough to hurt people in the right conditions. When Art Defever was first starting out he was a commercial seiner designer but would, on demand, draw up yachts on traditional work boat lines and/or conversions. Trim ballast was enormous on some of his early designs and conversions.

The West coast small sardine and limit seiners conversions were lead mines but once trimmed off pretty sea-kindly. Bilge keels will slow it down the righting motion enough for most experienced sailors. No bilge keel is going to stop a round bilge displacement-semi displacement hull from rolling so anybody looking for this will be sadly disappointed. They only slow down the motion.

I might add on GRP hulls laminating bilge keels to the hull skin will require sound structural analysis in order to provide adequate internal supporting and good secondary bonding. If the hull skin is sandwich or cored construction the job can get tricky but either way the bilge keel must be sacrificial to the hull skin and yet strong enough to withstand sea conditions and light to moderate impact. I should also say that bilge keels invariably reside in or around machinery and fuel tanks making working access difficult and costly.
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Old 05-03-2021, 10:46 AM   #19
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The rolling chocks on my boat were bonded to the chine, approximately bisecting the angle. No interior work required, they are quite robust and installed in one day. On a wood boat a different prospect, and on a cored round hull too.

The chocks dampen the roll which is important, but they also slow the accelerations in the first and second order ("jerk"). That is actually the thing I think I notice most. They lessen roll excursions only a little, but on my hard chine boat that wasn't really the problem, it was the "snap" back and forth. That is lessened quite noticeably. A round bilged boat may not have as much snap back from the initial roll, so may not help as much.
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Old 05-03-2021, 11:19 AM   #20
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Quote:
Originally Posted by Simi 60 View Post
On the same website as your bottom pic the version used for timber vessels



https://rlmarine.com.au/stabilisers/
I have a very similar timber hull to the one in the picture. 1970 DeFever 50

Is installing the steel rolling chock on a wood boat is as simple as it looks? just fabricate bolt and adhere using 5200 etc.
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