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]

Originally Posted by Taras

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]

Originally Posted by 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

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]

Originally Posted by Jim Cooper

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

Originally Posted by 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…

[DDW]

Originally Posted by sean9c

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]

Originally Posted by 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 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]

Originally Posted by Comodave

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]

Originally Posted by ksanders

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]

Originally Posted by Mako

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.