Bilge Keel - Rolling Chock installation

[ksanders]

Here is how the fins look today.

All that is left to do is some minor faring, sanding and apply bottom paint

We'll be launching late this week.

 

[Comodave]

Looking good.

 

[Southern Boater]

The downside of the chocks is that on some installations, when heading into a sizable chop, there are occasional loud BANG sounds, like a small explosion. I suspect this is due to a pocket of air being trapped as the hull drops down off a wave. This is just a guess.

A friend had roll chocks on a Selene that he purchased and had them removed because he did not like that sound.

That bang sound, as you say, can occur with any hard chine boat when the sea is more than 30-ish degrees to your heading and the waves above a certain height and speed through the water.

 

[mvweebles]

Bulbous bows are prown to bangs. Scared the bejesus out of me first time it happened. Sounded like a stevedore with a 9-lb hammer. I thought we hit something and started pulling up hatch covers.

Occasionally get some noise from stabilizer fins, but nothing like the bulbous bow. Will be interested if anything more than minor annoyance.

Peter

 

[rslifkin]

I wouldn't expect it to be anything worse than the occasional thump that happens on a hull with down turned hard chines forward.

 

[Ka_sea_ta]

Looks great Kevin, but don't you think the Mexican courteous flag in the first picture is a little overkill

 

[ksanders]

Looks great Kevin, but don't you think the Mexican courteous flag in the first picture is a little overkill

That is really a great flag photo!!!

That flag, flying on the Malicon in Ensenada is the largest Mexican flag in existance.

It is truly a sight to behold in person

 

[Marco Flamingo]

While not quite a "bang," but I do seem to get more ocassional "slaps" against the hull. I just assumed that was caused by the the anti-roll bag making the hull less respondent to the swell/chop.

I'll post a separate thread about my anti-roll bag construction, etc. For some reason my ancient CPU, which has all my pictures on it, didn't fire back up correctly when I returned home. Maybe it's because I'm still running Widows 3.2. Just kidding, but it is way out of date. I have to wade through a bunch of notices to "update" every time I use it. Time to go computer shopping.

 

[dannc]

Wow!!!

Please tell more about your anti roll bag!

I remember your posting about it a bit, but do not know how to search well

Kasten mentions anti rolling tanks, Roll Attenuation and Bilge Keels, to help stabilize a boat. The anti rolling bag is a very interesting, quick, removable, and cheap approach.

The following is most of what is on the page regarding anti roll tanks but other options are discussed on the link. Also, combining a couple methods works better than one.

* Passive Anti-Roll Tanks: According to published research in Marine Technology, in some sea conditions, with optimized tank / vessel design, roll reductions in both amplitude and acceleration on the order of 50% to 60% have been documented. In other sea conditions, the percentage of roll reduction appears to vary considerably. Vessel speed does not appear to be important to roll damping benefit. There does not seem to be any negative effect on vessel speed or efficiency, except of course for the added displacement required to carry the extra deadweight of the tank contents. Anti-roll tanks seem to vary in size from around 1.5% to around 2.5% of a vessel's displacement. If located higher, the overall weight may be able to be less, since the tank will have a greater effect due to being farther from the vessel's center of gravity. Similarly, if the tank is able to be the full width of the vessel, its effect appears to be greater and there may be the potential for a reduction in tank weight. Space requirements are very difficult for small pleasure vessels (say below 60 feet). Possible undesirable effects on stability, depending on the vessel (large free surface effect). Very unlikely as a retro-fit. Possibly noisy. Relatively complex to design correctly (therefore relatively expensive to design). Relatively inexpensive to build. Relatively simple in use.

Anti Rolling Tanks

On vessels above, say, 60 feet it is possible that the use of anti-roll tanks may be preferred over the use of paravanes, primarily due to the large forces involved in terms of being able to easily handle the paravane rig. Anti-roll tanks operate by allowing water to slosh (passive type) or by pumping water (active type) from side to side out of sync with the wave induced roll of the ship. There are several different styles of each. Anti-roll tanks must be designed carefully, sized right, tuned to the ship, and then tweaked to match the anticipated conditions.

For vessels below around 60 feet LOA, the space, weight and stability requirements of anti-roll tanks may prove to be prohibitive. For example, a 50,000 pound boat would need around a half ton of water in an anti-roll tank located at least as high as deck level. For supply vessels, research vessels or fishing vessels, all of which spend some amount of time at sea while not making any headway, anti-roll tanks can make a lot of sense. For example, per published data in Marine Technology, the combination of anti-roll tanks and bilge keels have been shown to be capable of reducing roll amplitude and accelerations by as much as 90% in some sea conditions.

In spite of their potential benefits, as a retro-fit anti-roll tanks are a very unlikely solution. During new construction however, there may possibly be justification for their use, since they can then be more gracefully incorporated into the design.

Later,
Dan

 

[Marco Flamingo]

Wow!!!

Please tell more about your anti roll bag!

I just started a thread about my anti-roll bag experiment.

 

[ksanders]

The bilge keel addition is done finally!

They are bottom painting tomorrow. Launch on Wednesday

 

[Comodave]

Good luck!

 

[Bmarler]

Those are substantial. Really nicely done too. I hope you get good results with them.

 

[ofer]

these are certainly heavy-duty way more robust than the ones i see on commercial fisherman.

looks good

 

[ksanders]

Well, the bilge keels are installed, and I am super happy with the results.

In my first sea trial I noticed a huge increase in comfort in a beam sea.

Here are two videos somewhat demonstrating the differences in a controlled experiment.

This first video was taken the morning I left for the boatyard.

The second video was taken upon my return

The things to take note from the videos...

First the boat is much more difficult to get rolling.

Then the boat experiences almost a 50% reduction in the number of roll cycles.

Also notice a smaller change in the roll period.

 

[Blissboat]

There does appear to be quite an improvement in roll resistance. Your plan works!

 

[Dwk]

You must be thrilled. No question about the positive affect! Interesting testing method.Can’t wait to read the what the naysayers come up with…you can bet some negative comments are coming. Congratulations, interesting thread.

 

[DDW]

Some thread posters want to know: Did they break off when you lifted it in the straps to launch?

 

[SteveK]

Some thread posters want to know: Did they break off when you lifted it in the straps to launch?

Or when you hit the dock

 

[dannc]

Impressive.

Too early to know if fuel burn has increased?

Later,
Dan

 

[Comodave]

Glad you are happy with the result. At the speeds you run at I don’t think you will notice much difference in fuel consumption.

 

[Kit_L]

@Kevin: I look forward very much to your reports once you get underway and encounter real seas. As @Comodave mentions, I too doubt that your fuel burn will be significantly different from before, either, but let's see.

There seems to be no doubt that the vessel is more resistant to rolling, and that the rolls decay faster now. Great work.

 

[Simi 60]

Love seeing results for relatively small coin.

 

[Hippocampus]

Often wondered if antiroll measures are additive or non linear. Things like bilge keels and add a gyro. Or tanks and fins. Or fish and Magnus effect. Would think the active techniques would work less hard and consume less energy even if just additive. . The active techniques would get rid of the portion that the passive techniques don’t control. Any knowledge or experience out there?

 

[Airstream345]

Impressive results and thank you for posting the process and real-world results and evidence of the change in roll resistance.

 

[ksanders]

I forgot to add...

At 1250 RPM I measured 7.1 knots in several directions of travel.

Then I got back and checked my log book.

The last time I bottom painted I measured 7.3 knots at 1300 RPM.

My opinion the speed is extremely close. Close enough to be difficult to measure.

Thanks guys!!!

Oh.. When they lifted the boat they decided to put blocks above and below the bilge keels for the aft strap just to be safe.

The lift was easy peasy and the folks at the boat yard did not think there would be a problem, but they covered their butts anyway.

 

[Jeff F]

Thanks for sharing.

My thought when I saw the pics is that they may change handling and ride quite a bit a higher speeds. I think you've mentioned here before that you speed up sometimes to improve the ride. Their placement will add lift at speed, I would think.

It's all interesting.

 

[DDW]

Different boat, but before I put them on mine I made careful speed and consumption measurements over the full speed range on the way to the yard, also high and low speed turns. Leaving with the chocks I repeated the same tests. There was no measurable difference in any of the above. Fuel/water load and bottom paint condition were identical going and coming.

You probably will have to scrub them more often, they are exposed to sunlight and tend to grow grass and algae quicker.

 

[dannc]

Different boat, but before I put them on mine I made careful speed and consumption measurements over the full speed range on the way to the yard, also high and low speed turns. Leaving with the chocks I repeated the same tests. There was no measurable difference in any of the above. Fuel/water load and bottom paint condition were identical going and coming.

...

Thanks for that information.

I am thinking of a boat that has two engines, primarily to allow the boat to dry out. However, bilge keels can be use to dry out the boat as well as work as a passive stabilizer. The twin engine boat has two rudders, props, and skegs so my guess is that the drag of the bilge keels would be no more than the extra weight of a second engine along with the drag of the extra rudder, prop and skeg.

Thanks,
Dan

 

[dannc]

Often wondered if antiroll measures are additive or non linear. Things like bilge keels and add a gyro. Or tanks and fins. Or fish and Magnus effect. Would think the active techniques would work less hard and consume less energy even if just additive. . The active techniques would get rid of the portion that the passive techniques don’t control. Any knowledge or experience out there?

I think I posted links to Kasten's website earlier in the thread. He mentions that using paravanes and bilge keels is additive. https://www.kastenmarine.com/roll_attenuation.htm

Real World Observations
Most commonly, research groups addressed the requirements of commercial vessels, so tended to make use of anti-rolling tanks in combination with relatively long and shoal "bilge keels" or paravanes in combination with bilge keels. These vessels were relatively larger and heavier than typical "trawler yachts."

Combined Methods
The most effective roll reduction appears to be obtainable when two or more methods are used simultaneously, such as paravanes combined with twin keels, or an anti-rolling tank with either, or say, sails in combination with twin keels, etc. Several of the studies in Marine Technology have been aimed at various combined methods. In all cases reviewed, the tests showed that combining roll attenuation strategies does appear to have a dramatically beneficial effect.

A combination of strategies will therefore offer the greatest benefit aboard trawler yachts. A highly effective strategy for trawler yachts might reasonably be the combined use of a single chine hull form, twin keels, a modest get-home sail rig, and paravanes for possible deployment in some conditions. This combination would offer a high degree of roll attenuation, and would be effective over a wide variety of conditions.

He does not mention gyro scopes and my guess is that the research was done before gyros were available.

Using bilge keels large enough to allow the boat to take the ground, as well as for stabilization, along with a gyro, is an idea I am thinking about. My guess is that the drag of a second rudder, prop, and skeg vs a bilges keels is about the same. The boat in has limited engine room space so having one engine would help that issue and lower costs that could be spend elsewhere.

Later,
Dan