Bilge Keels - A real life evaluation of their effectivness

[ksanders]

In 2023 I completed the Baja Bash in my Bayliner 4788.

After that journey I had bilge keels installed.
I just completed the exact same journey yesterday.

Here's what I found.

The area north of Cedros Island on the Baja Peninsula is one of those areas in the world that is always windy. The wind is out of the Northwest, and it makes for a difficult crossing of 80 miles of open ocean in order to procede up or down the Baja Peninsula.

We all know how powerboat travels go. You want to get from point a to point b but you cannot always go directly. If the wind has a beamy component you need to veer off course to control the rolling of the boat to a level that is tolerable. We have all done it.

When I completed this segment in 2023 the wind was measuring in the 30 mph range on my davis weather system. With my approx 7 knots of speed the wind was running 23-25 MPH actual.

In 2023 i had to tack back and forth to control the roll.
This week I was able to make a straight line course
And... the winds were actually a couple MPH higher this year. Not a lot higher, but a couple miles an hour.

The effect of the bilge keels is nothing short of impressive! One of the best investments I have made on the boat in terms of comfort.
I have been thinking the bilge keels were really great at reducing the roll but until now I had zero real data for a comparison.


Here is a marked up photo to demonstrate

 

[trawlercap]

In 2023 I completed the Baja Bash in my Bayliner 4788.

After that journey I had bilge keels installed.
I just completed the exact same journey yesterday.

Here's what I found.

The area north of Cedros Island on the Baja Peninsula is one of those areas in the world that is always windy. The wind is out of the Northwest, and it makes for a difficult crossing of 80 miles of open ocean in order to procede up or down the Baja Peninsula.

We all know how powerboat travels go. You want to get from point a to point b but you cannot always go directly. If the wind has a beamy component you need to veer off course to control the rolling of the boat to a level that is tolerable. We have all done it.

When I completed this segment in 2023 the wind was measuring in the 30 mph range on my davis weather system. With my approx 7 knots of speed the wind was running 23-25 MPH actual.

In 2023 i had to tack back and forth to control the roll.
This week I was able to make a straight line course
And... the winds were actually a couple MPH higher this year. Not a lot higher, but a couple miles an hour.

The effect of the bilge keels is nothing short of impressive! One of the best investments I have made on the boat in terms of comfort.
I have been thinking the bilge keels were really great at reducing the roll but until now I had zero real data for a comparison.


Here is a marked up photo to demonstrate

View attachment 162198

Good report, do you have any pics of your keels?

 

[Mako]

Do you have some feedback of how well they work while anchored in a rolly anchorage? Tougher to quantify this of course, but you’ve owned and cruised your boat long enough.

 

[ksanders]

Good report, do you have any pics of your keels?

This was today in the travellift.

The bilge keels are 12" wide x 24' long

 

[ksanders]

Do you have some feedback of how well they work while anchored in a rolly anchorage? Tougher to quantify this of course, but you’ve owned and cruised your boat long enough.

That is more difficult to quantify, except I made a before and after video showing the motion when i intentionally got the boat rolling in its slip.

My opinion they work great at anchor at reducing the size of the roll. The roll period is not changed, but since the size of the roll is reduced, the velocity and acceleration/deceleration are reduced, making for a more comfortable experience.

 

[Mac2]

Great addition! The test in your slip was impressive. Definitely slowed the roll and seemed to half the roll period. Who made them and how are they attached? I would be worried about damaging them at haul out, but it looks like they did a good job placing supports for the slings.

 

[Mambo42]

Great to hear your bilge keels do work. Mine were a complete disaster, did not work at all and in the end were the reason I had to install stabilizers. Never found out why my bilge keels did not do anything, perhaps not wide enough, perhaps installed on the wrong spot, no idea really.

 

[mvweebles]

A handful of Willard 40s had bilge keels installed. Owners reported a meaningful reduction in roll and were happy with the cost and effort.

Peter
(Moderator of Willard Boat Owners group since 2002)

 

[Judy at JWY]

Cape Horn Trawlers, from 52' - 81', were all built with bilge keels. Their performance is best in beam seas, but also beneficial at anchor. Precise placement is critical for the best performance. One huge advantage for steel boats is that they can sit on their own bottom - makes bottom cleaning and inspection easy when beached in shallow water but also eliminating the need for jacks at haulout.

 

[ksanders]

Great addition! The test in your slip was impressive. Definitely slowed the roll and seemed to half the roll period. Who made them and how are they attached? I would be worried about damaging them at haul out, but it looks like they did a good job placing supports for the slings.

Baja Naval in Ensenada Mexico fabricated them.

Before installation on the boat the keels were made using coosa board.

Two pieces 12" W X 1" thick were first glued together.
Then two 4" wide X 1" pieces were glued to that making for a wide base to attach to the boat.

That assembly was then form fitted to match the exact curve of my hull and glued onto the hull at a 45 degree angle to the hull sides.

This held them in place to start the fiberglass encapsulation process.

They used mat glass and biaxial cloth to form not an attached appendage, but a integrated part of the hull of my boat. All total they used over 50 gallons of West Systems 105 epoxy resin in the process.

 

[ksanders]

Great to hear your bilge keels do work. Mine were a complete disaster, did not work at all and in the end were the reason I had to install stabilizers. Never found out why my bilge keels did not do anything, perhaps not wide enough, perhaps installed on the wrong spot, no idea really.

I did a lot of research on Bilge Keels before installing them. It's funny because the online recreational boating community in general has a marginal outlook as to their effectiveness. This perception originates in the original "Voyaging Under Power" were Bebe wrote that they are only marginal at reducing roll. Many continue to quote the numbers he provided as evidence as to their ineffectiveness.

But... I thought, if Bebe was right, why are they fitted to almost every commercial fishing boat in Alaska?
Are all these commercial guys wrong, and only Bebe got it right?

So I did more research, decided to make them as large as possible, and took a chance.

Here is what I found...

There are two main reasons for a poor outcome.

The first is not making them big enough. If you think about it the counter force to rolling they provide is directly related to their size. Too small and they have little effect. When the yard asked me how wide I wanted them, I asked how wide is the Coosa Board you purchased? They said it came in 12" wide pieces, so I opted for 12" wide.

The next problem is they get installed at an angle to the natural water flow along the hull. This creates drag.

What we did was install them exactly even with the natural waterline of the boat. This was easy to see on the bottom paint, so before stripping for installation they took photos and measurements.

 

[DDW]

I like my bilge keels. On haul out, we pay them no attention whatever, just sling it as normal. On a hard chine hull, the slings are going to turn a hard corner right at the chine, now covered by the bilge keel. The bilge keel has made this hard point even stronger. The guy that put mine on has done > 300 of them (mostly fishing boats) and he says they never do anything special to haul.

 

[trawlercap]

My friend who ran Marco Shipyard in Seattle told me “If you want rolling chocks...Go big or don’t go at all”
Every boat in the Bering Sea has rolling chocks.
60 sec. good vid on chocks

 

[Mambo42]

I did a lot of research on Bilge Keels before installing them. It's funny because the online recreational boating community in general has a marginal outlook as to their effectiveness. This perception originates in the original "Voyaging Under Power" were Bebe wrote that they are only marginal at reducing roll. Many continue to quote the numbers he provided as evidence as to their ineffectiveness.

But... I thought, if Bebe was right, why are they fitted to almost every commercial fishing boat in Alaska?
Are all these commercial guys wrong, and only Bebe got it right?

So I did more research, decided to make them as large as possible, and took a chance.

Here is what I found...

There are two main reasons for a poor outcome.

The first is not making them big enough. If you think about it the counter force to rolling they provide is directly related to their size. Too small and they have little effect. When the yard asked me how wide I wanted them, I asked how wide is the Coosa Board you purchased? They said it came in 12" wide pieces, so I opted for 12" wide.

The next problem is they get installed at an angle to the natural water flow along the hull. This creates drag.

What we did was install them exactly even with the natural waterline of the boat. This was easy to see on the bottom paint, so before stripping for installation they took photos and measurements.

Interesting to read.
Mine were 12 inches wide, but they were basically at the position where the fin motors are now and that is much lower in the water than the natural water line.
So based on what you wrote it could be that the bilge keels were of the correct size, but installed in the wrong position and subsequently did not work at all.

Good part is that, where the bilge keels were, the hull is much thicker and that part I left on the hull. I just cut the 12 inch part off, the rest remained, so I have some extra strength in the hull and that I don't mind.

 

[rslifkin]

Interesting to read.
Mine were 12 inches wide, but they were basically at the position where the fin motors are now and that is much lower in the water than the natural water line.
So based on what you wrote it could be that the bilge keels were of the correct size, but installed in the wrong position and subsequently did not work at all.

Good part is that, where the bilge keels were, the hull is much thicker and that part I left on the hull. I just cut the 12 inch part off, the rest remained, so I have some extra strength in the hull and that I don't mind.

I would expect the ideal position depends a bit on the hull shape. Effectiveness probably does too. And keep in mind that Kevin's bilge keels are somewhere around half the length of the boat, so there's a lot of surface area on them.

 

[Mambo42]

I found an old picture of my bilge boards and they are indeed a lot shorter and under a different angle than what is on the video. Guess that explains why they did not do anything.

 

[rslifkin]

I found an old picture of my bilge boards and they are indeed a lot shorter and under a different angle than what is on the video. Guess that explains why they did not do anything.

Yup, those were probably just too small to have more than a small effect. Plus your hull is hard chined, so the roll is likely more snappy. That can make it harder to get comfortable roll behavior as well.

 

[ksanders]

I found an old picture of my bilge boards and they are indeed a lot shorter and under a different angle than what is on the video. Guess that explains why they did not do anything.

I would agree that they should have been bigger. Mine are 24' on a 47' hull.

So... that is approx 48 sqft of area.

yours look from the image to be around 8' long. Hard to tell the depth but even at 1' that is 8 sqft each or 16 sqft total

My hull is also rounded, and that might make a difference.

 

[DavidM]

Kevin,

So, hydraulic fin stabilizers, gyro stabilizers, etc. cost upwards of $100k for a boat like yours and either draw hydraulic power or electric power to operate.

Bilge keels are totally passive and from what I have seen here, at least half as effective as active stabilizer’s.

So, what did it cost to add your bilge keels, Kevin?

David

 

[Mambo42]

Yup, those were probably just too small to have more than a small effect. Plus your hull is hard chined, so the roll is likely more snappy. That can make it harder to get comfortable roll behavior as well.

It was indeed a snappy roll, we could be lying in the marina or in a port and all of a sudden the boat would start rolling violently and at the same time all other boats were lying dead in the water. The wind was basically able to push the boat over, the bilge keels did nothing.
So they were removed and then I installed these electric fins, since that time no more rolling.

 

[ksanders]

Kevin,

So, hydraulic fin stabilizers, gyro stabilizers, etc. cost upwards of $100k for a boat like yours and either draw hydraulic power or electric power to operate.

Bilge keels are totally passive and from what I have seen here, at least half as effective as active stabilizer’s.

So, what did it cost to add your bilge keels, Kevin?

David

it's hard to judge the effectiveness of bilge keels vs active fin stabilizers. I just know they work very well, and make it possible to hold course comfortable in conditions impossible before.

The total cost of the bilge keels including bottom painting the entire boat was right at $20K USD. I had the work done at Baja Naval in Ensenada Mexico.

These were not a "glue on and go" addition. The technicians worked on the job every day for a month, and in the end used over 50 gallons of West systems 105 resin.

 

[dannc]

Regarding bilge keels and their location, per Kasten, https://www.kastenmarine.com/roll_attenuation.htm

Edited a bit to focus on location, sizing and such. There is more in the article.

"Benefits of Twin Keels...

Aside from the obvious benefits offered by twin keels published elsewhere such as when taking the ground, a few points emerge from Lord Riverdale's research that are more subtle, and that may be of some interest to those experimenting with Twin Keels, as defined by Lord Riverdale, on power vessels and motor sailers...
...
* Twin Keel Location: The most successful Twin Keels were located approximately amidships, with the root of the keel beginning roughly 45% of the DWL aft, and the largest section being perhaps 60% or more aft. Forward twin keel locations were not favorable, as that location tended to provide poor steering characteristics and a poor wave form at speed. Aft locations were not investigated, as they would not have located the ballast where needed for the sake of proper trim.
...
* Toe-in: A small amount of "toe-in" seemed to benefit the overall resistance upright as well as under sail. The best results were achieved using a toe in of between 0.5 degree and 1.25 degrees. For Lord Riverdale's purposes, some amount of toe-in was deemed to be desirable for better "lift" to windward when sailing. While upright, the observed benefit to there being some amount of toe-in was attributed to providing better alignment with the under water flow lines.

This latter assumption is correct, as larger vessel flow analyses have shown. The amount of toe-in is therefore a variable which will be different with each hull shape, and which will vary with the longitudinal location of the keels. It would be interesting to test the effect of toe-in on yaw while rolling. It is questionable whether any amount of toe-in will benefit a motor vessel, since one would expect to observe that any amount of toe-in would enhance yaw, and therefore be undesirable in terms of directional stability.

* Sectional Foil Shape: The Twin Keels chosen for Bluebird were of an asymmetrical foil shape, flat outboard and cambered inboard, much like an airplane wing. This was done in order to achieve greater "lift" when sailing to windward.

It is questionable whether asymmetry would provide any benefit to a power vessel. For a power vessel, one would expect that a symmetrical section aimed at providing low drag would be the most appropriate. For a power vessel, one would expect that the foil shape chosen should be "stall tolerant" or able to take a large variation in the angle of attack, and therefore within the 00xx family of NACA shapes. In order to contain the ballast, and also for the sake of being "stall tolerant" one would also expect that the foil would not be too "skinny."
...

 

[DDW]

My rolling chocks cost $4000 and were complete in one day on an AT34. This is a guy who has done 300, so he premolds the section in the shop. In my case the finish was "work boat", not "yacht" as ksanders seem to be. The quotes for a Magnus rotor from two vendors was in the $50-60K range. The price/performance is hard to beat.

 

[ksanders]

My boat is on the hard for bottom paint right now.

Here is a great photo showing the bilge keels.

 

[ABfish]

@ksanders What's the effect of the bilge keels on planing speed? Apologies if that's been discussed.

 

[Kit_L]

A very significant proportion of the fishing trawlers here, and in Queensland, have rolling chocks. Here are the chocks on a vessel I'm considering presently; I feel they're not wide enough, having seen many commercial installations, but the commercial fishing boats might need wider chocks because of all of their heavy deck gear, weight up high I mean.

Having said that, the previous owners run the yard that does most of the installations in Queensland for commercial fishers, so they must know what they're doing! As well, the boat has parvanes for when it's rougher. If I do buy her, I will have the longish trip from Townsville to Brisbane (leg 1) to assess their effectiveness. It would be a very simple matter to make them wider, and not an expensive proposition either.

 

[Mac2]

Good looking boat! Steel? The chocks do look a little narrow, but you’ll be able to test them as you said. What is the purpose of the scoop where a bulbous bow would be?

 

[ksanders]

@ksanders What's the effect of the bilge keels on planing speed? Apologies if that's been discussed.

I do not have a whole lot of up on plane time, either before or after the installation.

The boat gets up on plane properly, and has about the same speed at different throttle settings.
The EGT shows the same temperature of a bit over 900F so that tells me that they have not unduly increased the stress on the engines.


I do not remember if the boost pressures are slightly different or not.

Sorry, I just do not have a lot of data to go by.

 

[Rsysol]

In 2023 I completed the Baja Bash in my Bayliner 4788.

After that journey I had bilge keels installed.
I just completed the exact same journey yesterday.

Here's what I found.

The area north of Cedros Island on the Baja Peninsula is one of those areas in the world that is always windy. The wind is out of the Northwest, and it makes for a difficult crossing of 80 miles of open ocean in order to procede up or down the Baja Peninsula.

We all know how powerboat travels go. You want to get from point a to point b but you cannot always go directly. If the wind has a beamy component you need to veer off course to control the rolling of the boat to a level that is tolerable. We have all done it.

When I completed this segment in 2023 the wind was measuring in the 30 mph range on my davis weather system. With my approx 7 knots of speed the wind was running 23-25 MPH actual.

In 2023 i had to tack back and forth to control the roll.
This week I was able to make a straight line course
And... the winds were actually a couple MPH higher this year. Not a lot higher, but a couple miles an hour.

The effect of the bilge keels is nothing short of impressive! One of the best investments I have made on the boat in terms of comfort.
I have been thinking the bilge keels were really great at reducing the roll but until now I had zero real data for a comparison.


Here is a marked up photo to demonstrate

View attachment 162198

Kevin,

Our 55’ trawler has bilge keels, since I’ve not run this boat without them I can’t comment on any improvement in ride but our boat does well in anything up to a 8-10’ beam with a short period. I can say that I’ve cruised with many large vessels and our performance at anchor is much better.

That said, we’re also adding Magnus Master stabilization this spring as we intend to cross an ocean in the near future and forecasting out 20 days is not possible.

Glad yours are working out.

 

[Kit_L]

Yes, steel. 53 ft x 16 ft beam x 5'9" draft. Twin 210hp Cummins, keel cooled and dry stack.

Re. that scoop: I don't know for sure, but I imagine it is to hook on to any fishing line or rope from fish traps or the like rather than let them go under the keel and possibly tangled in the props and rudders. I will be asking that question though!