Bilge Keels

I am looking at a Cape Horn with bilge keels, but no active stabilization. Does anyone have experience with this kind of set up? I'm wondering how effective the bilge keels are in reducing roll, especially in a beam sea?

No experience, but this is an interesting article.

http://www.kastenmarine.com/roll_attenuation.htm

Twin keels on a sailboat may have their advantages but are deeper then twin bilge keels on a power vessel, thus providing more stability. The CH65 is a heavy displacement (200K lbs) vessel and that should help with stability, though I notice that the other CH for sale does have stabilizers. Three suggestions: (1) contact the designer Bob Johnson for more information; (2) get a sea trial under very rough conditions; (3) confirm you are able to fit stabilizers if they are necessary - adequate access to appropriate positioning. That CH65 is a lot of boat for the money. Good luck.

Bilge keels do more than sinply slow the roll rate.

They can assist the boat staying level when on the hard.

This opens a huge cruising area in high tidal areas.

Navy Dave said:

I am looking at a Cape Horn with bilge keels, but no active stabilization. Does anyone have experience with this kind of set up? I'm wondering how effective the bilge keels are in reducing roll, especially in a beam sea?

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Beebe speaks generically to bilge keels (and other stabilization methods) in his book. You might review that, if you haven't already...

-Chris

That CH 65 has a hydraulic drive. That's interesting.

Also from the listing it said the PO removed the active fins because they felt they didn't really work well and were not needed, and slowed the boat down 1 knot.

Bilge keels is #1 on my list of future stabilizing. I talk to several mfg about active fins, they said for the 30 grand they would have little effect on the eagle being heavy full displacement and slow hull speed. They recomended fix keels of para vane. The reason bilge keels are passive enquiring no activation, working all the time and as Fred mentioned will help keep the boat vertical if grounded and on the hard.

I would keep an open mind about them. I am a firm believer a boat should be stable with out stabilizers first. Stabilizers are to make the ride more comfortable not to stabilize the boat.

What makes a sea kindly boat is good design .

A slow roll rate with no hard check at the roll reversal.

This can be improved a bit with add ons , but its the boat that counts , paravanes will help the distance the boat rolls , but thats all.

cardude01 said:

No experience, but this is an interesting article.

Roll Attenuation and Bilge Keels

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Great article! Thank you!

Thank you all for your comments! I really appreciate the feedback! I'll make a better informed decision after speaking with the designer and taking her out to some rough water (hope we find some that day) during the sea trial. My current trawler, a Fisher 38 Pilothouse, has a round bottom, so certainly the hard chines and bilge keels have to be an improvement!

Dave

"so certainly the hard chines and bilge keels have to be an improvement!"

Perhaps, but probably not in a sea kindly way.

The flatter the bottom the more the boat will follow the wave surface , both in shape and rate of inclination change.

Watch a floating bottle next to a plank in active water.

FF said:

Bilge keels do more than sinply slow the roll rate.

They can assist the boat staying level when on the hard.

This opens a huge cruising area in high tidal areas.

Click to expand...

A number of thoughts:

I really found the Kasten Marine article informative and in line with my experience.

I seriously considered adding bilge keels to Dauntless this spring. Even got the plans from Kadey Krogen!
As FF pointed out.
The pros were:
Most fishing boats my size has them in Ireland. So they must be somewhat effective.
Low cost, a few $k, to add
The ability to easily let the boat dry out at low water.

Ultimately I decided not to do it. Why:

On my round bottom, I thought the roll reduction would be on the order of 10 to 30% at best. But I'd be paying a 5 to 10% fuel/speed penalty 100% of the time.
(My paravanes EACH take about 10%+-2%)

The paravanes stop sympathetic rolling. On a beam sea they reduce rolling 75 to 90%. In a following sea, 50 to 75%

If I HAD NOT already done the paravanes, I would have probably added the bilge keels, but having them, the penalty wad to great for the conditions I would expect them and not the paravanes to mitigate.

Lastly, just because James Krogen designed them, doesn't mean he felt they were a good fit on a kk42.

On the subject of paravanes, in the last few months, I've run with just the windward bird in the water. Why? Just to save speed or fuel. It's remarkably effective, probably 80% of the two, BUT with more sympathetic rolling, but with much less amplitude.

Oh, and running with just the lee side bird, will heel the boat over like a racing sailboat. Don't ask how i know.

Richard on Dauntless in Rota, Spain

Seems like when I travel to the UK it is always low tide!!
Wherever we go there are boats sitting in/on the mud in rivers or harbors!!
Makes bilge keels kind of essential unless you want to roll over.
But, have not been able to work out how the owners manage to get back an forth to their vessels without very large Wellington boots.

They will keep the boat upright IF they are A) deep enough and B) the boat comes to rest on level, solid ground. I notice a lot of trawlers (the real ones) that come to rest on the mud at the dock up in the Maritimes. Virtually none have bilge keels, but rather pull chocks under the boat with bridles. May have a pic somewhere of that. A few looked like they were sized to match the contour of the slip, but I can't say for sure.

My take has always been that they are rarely seen for a reason (s). Richard may have covered the main of those reasons. Just one more thing to snag on or hit something would be another.

I'll bilge keel extend latterly at the turn of the bilge. I have both bilge keels and paravanes stabilizers. Although the bilge keels only extend about 6" and run about 3/4 of the hull. seas over 6' the paravanes are just about a must. I beach my boat at least once a year. And the bilge keels do allow me to refloat easily when the tide comes back in

I have to say that boats with para vanes out look like real working trawlers. ?


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"Makes bilge keels kind of essential unless you want to roll over."

Plan B for folks that wish to take the ground is a set of legs,

These are 2 stiff wooden legs with pads on the bottom , that have a line or chain between them.

Passed from front to mid ship where a set of chain plates have been installed.

They are simply attached with a 4 part or more tackle so they can be adjusted to level the boat , if the bottom is uneven.

Many boats will spend a winter with just sheer legs , instead of being hauled out.

Manatee HEY JUDE Bilge Keels



Only having HJ on a lake since purchase in '11, we have no idea how effective the bilge keels are. We're moving her to the TX coast soon with plans to travel E someday. Hopefully we'll meet another Manatee driver who can evaluate HJ's roll.

Manatee on a trailer !!

?

Phil: Hey Jude is looking good. Sure would like to have that trailer when you're finished.

Cardude01...due to Lake Travis's fluctuating level, +/- 60' since '09, there's no travel lift that actually lifts a boat out of the water. Initially all boats ride out on a trailer & then transferred using a travel lift to either blocks & stands or to transport trailer as ours will Sept 30 for ride to Clear Lake. After we get some work done we'll motor to Rockport & be your neighbor at Cove Harbor.

Healhustler...at $1K for haul & tranfer, be happy with your travel lift fees. Ref our discussion about fuel tank access...I was almost giddy with excitement when I confirmed I have at least two 6" plates, one port & other centered & possibly one starboard but under AC unit.

HeyJude said:

Cardude01...due to Lake Travis's fluctuating level, +/- 60' since '09, there's no travel lift that actually lifts a boat out of the water. Initially all boats ride out on a trailer & then transferred using a travel lift to either blocks & stands or to transport trailer as ours will Sept 30 for ride to Clear Lake. After we get some work done we'll motor to Rockport & be your neighbor at Cove Harbor

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Very cool! Glad to have another neighbor. Will you be in one of the covered slips?

Yeah Travis water level has been crazy the last few years. We had a boat on Travis back in 1996-1999. Had a houseboat hauled from Lake Conroe to Travis for some reason. Don't know what I was thinking. ?

Chrisjs said:

contact the designer Bob Johnson for more information; Good luck.

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I've done a couple of surveys with Bob on old converted steel tugs (early 1900's). I did not feel qualified so passed the work on to Bob on condition that I got to hang over his shoulder. I learned a lot and can tell you he is a unique, funny, grumpy, witty, acerbic no nonsense, rule of thumb type character. You will be entertained in any conversation with the man.