Bilge Keel - Rolling Chock installation

[ksanders]

After a lot of time thinking about stabilization, and talking to other owners of my same boat I have decided to add Bilge Keels - Rolling Chocks. I am not sure which is the correct term.

I have reports from several owners of this same boat who have made this modification, and have spoken with one owner at length about the changes he noticed.

His words were that the Bayliner 4788 with it's rounded chines and small keel is like a beach ball in the water. There is nothing to stop the roll. He told me that adding bilge keels changed roll of the boat dramatically, amd made it feel like a whole different boat.

The keels are 24' long by 12" deep. They are made of Coosaboard, a total of 4" at the base and tapering to 2" at the tip.

They start at the aft of the boat, and continue foreward to the point where the hull starts to curve inward. They are being installed at a 45 degree angle and are placed so that they do not extend beyond the hull from a foot above the waterline as to not interfere with docking against a typical floating dock.

Here are some photos of the ongoing work

 

[Taras]

Great idea! Looks like a really good installation! How is it that lifting straps when doing a haul out don't snap them off?

 

[Blissboat]

How is it that lifting straps when doing a haul out don't snap them off?

My question as well.

 

[ksanders]

I had the exact same question regarding the slings.

The front sling is clear of the fins so no problem.

On the rear sling the weight of the boat is carried by the keel. The sling sides keep the boat from tilting.

This is similar to a boat on the hard using jack stands. The jack stands only stabilize the boat.

Other owners of this model boat, and many others report zero issues.

That said the fiberglass will be substantially beefed up in the area of the sling for added strength

 

[dannc]

These articles from Kasten about stabilization might be of interest.

Roll Attenuation and Bilge Keels

* Fixed "Twin" Keels: Depending on the twin keel geometry, per research published in Marine Technology, roll reductions have been observed on the order of 40% to 65%. Deeper keels having greater area provide greater attenuation. Low aspect ratio is considered a benefit due to being able to tolerate larger angles of attack (while rolling) without stalling. Location and geometry have been shown to be quite important for optimum vessel handling and resistance, as noted above. Vessel speed does not appear to be important to roll damping. Twin keels will add some frictional resistance due to increased wetted surface area. Enhanced directional stability, if proportioned correctly. Very unlikely as a retro-fit. Relatively inexpensive. Relatively simple.

* Fixed "Bilge" Keels: Long, low aspect ratio bilge keels, per research published in Marine Technology, have been observed to offer possible roll reductions on the order of 35% to 55%. Vessel speed is not important to roll damping. There is some added frictional resistance due to increased wetted surface area. If proportioned correctly, bilge keels offer enhanced directional stability. Very common as a retro-fit. Relatively inexpensive. Relatively simple to build.

My impression is that most/many people consider fixed bilge keels as rolling chocks but who knows.

https://www.kastenmarine.com/bilge_keels.htm

Later,
Dan

 

[Comodave]

I have seen them called both. There used to be a company that made hard chines that could be added to the Bayliner motoryachts called Underhulls. They went out of business a few years after Bayliner stopped making the motoryachts. I understand that they made a big difference in the rolling of the boats. The rolling chocks will likely make a significant difference too. We were patrolling Americas Cup when it was in San Diego aboard a 4588 Bayliner. It certainly knew how to roll…

 

[Jim Cooper]

I had the exact same question regarding the slings.

The front sling is clear of the fins so no problem.

On the rear sling the weight of the boat is carried by the keel. The sling sides keep the boat from tilting.

This is similar to a boat on the hard using jack stands. The jack stands only stabilize the boat.

Other owners of this model boat, and many others report zero issues.

That said the fiberglass will be substantially beefed up in the area of the sling for added strength

I hear what you're saying about the beefed up section but I would be too scared of it breaking, I would probably cut out a 12" section down to allow the sling to rest inside the pocket. Maybe go down to 4" away from the hull. The bilge keel should be about 3-4" thick in that area and be solid enough for my minds' comfort.

 

[sean9c]

Cool, I love stuff like this. Is it the same guys that did DDW's American Tug?

 

[mvweebles]

I hear what you're saying about the beefed up section but I would be too scared of it breaking, I would probably cut out a 12" section down to allow the sling to rest inside the pocket. Maybe go down to 4" away from the hull. The bilge keel should be about 3-4" thick in that area and be solid enough for my minds' comfort.

A number of Willard 40's have had roll chocks installed. Owners report being satisfied with he results but set the expectation that roll is attenuated vs eliminated. I have heard of no reports of fins being crushed by Travelift slings.

The yard doing Kevin's work has been around for 40-years and is well respected in the area. They haul a lot of boats - I would not hesitate to take their advice on strength.

Peter

 

[Mambo42]

I hope they are going to work for your boat. On mine, a Defever 49, they did not work at all, our boat could go absolutely beserk in the marina or on anchor if we would be beam on. We really had to hold on for dear life, the rolling was very violent, so I had them removed and changed to stabilizers. We were in the water (last week) for 1 day, stabilizers were off, but obviously have a huge surface to keep the boat steady and we could already notice it. Normally, with the rolling chocks, in a marina with the wind from the side the boat would violently roll while the neighbors would not move an inchh.
That evenening we had strong winds on our port side, but the boat did not move an inch. For the first time we were actually lying steady in the water, amazing experience.

We had no problems with the rolling chocks with lifting out the boat, so don't need to worry about that.
Kind of curious to hear if these chocks will work for you, hope so, but let us know.

 

[sean9c]

North Harbor Diesel in Anacortes did a hard chine conversion for the round chine Bayliners. I haven't seen them do one in years but they probably still have the molds if someone wanted to do it

I have seen them called both. There used to be a company that made hard chines that could be added to the Bayliner motoryachts called Underhulls. They went out of business a few years after Bayliner stopped making the motoryachts. I understand that they made a big difference in the rolling of the boats. The rolling chocks will likely make a significant difference too. We were patrolling Americas Cup when it was in San Diego aboard a 4588 Bayliner. It certainly knew how to roll…

 

[DDW]

Cool, I love stuff like this. Is it the same guys that did DDW's American Tug?

I don't think that is the same company, as the construction method is different. Mine were a shop made molding that was fitted to the chine in the field and then tabbed on. I don't think it matters which way, but probably quicker to install the premade ones. On my boat they started at 8 in the morning and were finished by 5 the same day.

Regarding lifting the boat in slings: provided they are robustly made and attached, it is absolutely zero problem, and is given no consideration whatever. In a hard chine SD type hull, the sling spans the keel to the chine in free air, pressing inward on the chine. The rolling chock does not change this, and only makes the chine much stronger and stiffer than it was before.

They don't make a night and day difference, but reduce roll accelerations and increase roll dampening. On my boat is was a noticeable improvement and well worth the modest cost. They "take the snap out of the roll" is what the installer said, and that is an apt description. The only downside I have discovered from them is that the outboard surface of the chock is exposed to sunlight, and tends to grow algae and slime quicker. But it is easy to reach from the dock to brush off.

 

[Comodave]

North Harbor Diesel in Anacortes did a hard chine conversion for the round chine Bayliners. I haven't seen them do one in years but they probably still have the molds if someone wanted to do it

I think that was the company I was referring to. But I thought that I read somewhere that they weren’t available anymore, but not absolutely sure.

 

[ksanders]

This is how they look after shaping and before the fiberglass matt being applied.

Right now they are glued to the hull and the fiberglass matt will make them intergal to the hull

 

[Comodave]

You say they will be using mat to glass it on, are they going to use any glass like 1708?

 

[ksanders]

You say they will be using mat to glass it on, are they going to use any glass like 1708?

I do not know the exact glass they are using, nor the resin brand.

I just know that they are using fiberglass cloth and resin to make the keels intergal to the hull.

 

[O C Diver]

I do not know the exact glass they are using, nor the resin brand.

I just know that they are using fiberglass cloth and resin to make the keels intergal to the hull.

I'm sure they will do it correctly. The two primary terms for fiberglass cloth are matt and bi-axial cloth. The bi-axial cloth is multiple times stronger than matt. While there is strength in matt, it's advantage is to building up a surface more quickly with some amount of strength. Bi-axial cloth has much greater strength for each layer applied.

Ted

 

[DDW]

Does the boat have an underwater exhaust, or thru the transom? I think I see a transom exhaust exit in the first picture.

 

[Mako]

Nearly everyone who installs them makes the same statement that they make a “noticeable difference”.

Unfortunately no one seems to have taken roll acceleration and magnitude measurements before and after, in order to quantify that statement.

 

[Blissboat]

Unfortunately no one seems to have taken roll acceleration and magnitude measurements before and after, in order to quantify that statement.

Anecdotal observation may be as good as most of us can get. It seems like it would be hard to compare reliably without a tank test to exactly replicate the before / after conditions.

 

[socalrider]

Nearly everyone who installs them makes the same statement that they make a “noticeable difference”.

Unfortunately no one seems to have taken roll acceleration and magnitude measurements before and after, in order to quantify that statement.

Yeah more data would certainly be nice, but on the other hand it's also difficult to imagine (for me at least) how, say, a "20% reduction in roll acceleration and a 35% reduction in roll magnitude" would be perceived. At the end of the day, it's the qualitative perception that makes the most difference.

Further complicated by the fact that different people are sensitive to different types of motion... it's a mess really.

 

[Comodave]

Probably just give us your feelings about how they work.

 

[Taras]

If you're looking for just roll attenuation while at anchor, buy the Magma "Flopper stopper". It reduced the roll at anchor for our boat by at least 50% (and that was with just one flopper stopper. 2 would have made an incredible difference). I attached it to the davit arm on the flybridge and swing it out all the way away from the boat to get the most leverage and keep it about 6 feet under water. It was the best $350 bucks I spent.

 

[SteveK]

I think Kevin has almost enough hours of real life on the water to know if there is a difference and can estimate the amount.

What Mako says is true for most mods people make. Once the money is spent, few will say I wasted that money, so it is always better than before.

 

[DDW]

Nearly everyone who installs them makes the same statement that they make a “noticeable difference”.

Unfortunately no one seems to have taken roll acceleration and magnitude measurements before and after, in order to quantify that statement.

I have certainly tried. I collected some data before the install using a logging AHRS. Then I tried afterwards. There are a huge number of problems:

1) roll excursions are typically not very great even when you think it's "rough" on a powerboat (at least, my powerboat). At about 12 deg heel, things are sliding all over the place. 12 deg heel on a sailboat is just the start of a good days sailing.

2) It is impossible to duplicate conditions next week, next day, or even next minute. I thought I might be able to use the Washington state ferry wake as a "standard wave". But it is highly dependent on their speed, your speed, angle of crossing, background seastate etc. Even in a 10 minute period encountering the same ferry the resulting data capture is remarkable different.

3) Aggregated data (say, roll excursions averaged over time) suffers from the same data scatter due to all of the above.

It did prove to my satisfaction that the rolling chocks don't reduce roll excursions much. They seem rather to reduce roll accelerations, jerk, and dampening. I believe I can see that in the data, but it is pretty noisy.

The only possibly successful method would be two-boat testing, which would be feasible with my production boat. Take an unmodified sistership, in the same displacement state, run side by side over a range of conditions, record AHRS data on both, then statistically analyze for differences. I tried to organize this a couple of times but it isn't easy. You'd get a pretty good subjective comparison just running around for an hour and then trading places.

Another possibility is simply to collect large data sets. I now record all boat motions (roll, pitch heave, and yaw) and have for several 2000+ mile trips. This could be analyzed and compared against a similar pre-rolling chock data set, and would probably tell the story unless weather conditions were on average markedly different. Unfortunately I do not have the pre-chock data set.

 

[mvweebles]

I think Kevin has almost enough hours of real life on the water to know if there is a difference and can estimate the amount.



What Mako says is true for most mods people make. Once the money is spent, few will say I wasted that money, so it is always better than before.

I too was skeptical of confirmation bias. But enough old school Willard owners had them done and their reviews had the ring of truth. Not enthusiastic endorsements, but given the ease and cost, they felt they were a worthwhile value. Plus many (most?) Commercial fishing boats have them.

Peter

 

[ksanders]

This idea of how to quantify the effects of the installation has generated some good thought.

What I did is the day of haulout, I induced a rolling motion at the dock and took video of how the boat responded.

I'll record a similar video when I return to my slip with the rolling chocks installed.

That is about as scientific as I can do it.

 

[SteveK]

This idea of how to quantify the effects of the installation has generated some good thought.

What I did is the day of haulout, I induced a rolling motion at the dock and took video of how the boat responded.

I'll record a similar video when I return to my slip with the rolling chocks installed.

That is about as scientific as I can do it.

Do not be disapointed when you will see no difference. Rocking the boat at the dock I expect to show no difference as the force you apply is well, too gentle compared to the force of tons of water.

 

[DDW]

My impression with passing wakes when at anchor is that the roll is about the same but the number of oscillations before it settles is about 1/2 or 2/3 what it was. You could in theory do this at the dock, get it rocking and see how many cycles. But it is very hard to get a big boat rocking at the dock.

 

[mvweebles]

My sense from other owners is effect is minimal when not moving. But noticeable when underway. Given Kevin did something like 5000 nms going from Alaska to La Paz without them and will do close to 1000 nms over the same waters when he returns, I'd give his evaluation enormous credibility.

Importantly, there is virtually no downside to adding chocks (okay, some addl wetted surface and, of course, the cost).

Peter