Keel walking

[cb34]

Can someone explain the dynamics of this and what it feels like?

 

[F/V First Team]

 

[F/V First Team]

Or are you talking about the phenomenon of a wide keel acting as a ski where it brings the boat further out of the water and then, due to the lack of running surface, it tips to one side.

It's not exactly a fun sensation the first time it happens, or subsequent times for that matter.

 

[plowin]

To add to Travis comment, to me keel walking feels like the boat is "flopping or falling" over from one side to the other. And yes I could not agree more with Travis, it is not a great feeling falling or flopping anywhere at 25 plus knots!!

 

[Blitzen]

Wasn't this a real problem with a well known 38 foot design above 22kts.?

 

[captainlarry84]

IMHO keel walk occurs when the hull speed of a given navel architects design is exceeded. The excessive speed is of caused by excessive power. As the boat starts to rise the keel of the boat starts to take control of the vessel leaving the rudder to fend of itself. With the fixed keel now in control it renders the movement’s rudder & steering of the captain almost useless. The sensation is a feeling of helpless as the vessel starts to tip from side to side in a manor all on its own. When it happens the instant fix is to slowdown.

Keel walking can be lessened by using a large reduction gear to accommodate the largest possible propeller along with a larger rudder. With these to items in place. It will lessen the ability of the vessel to take control of itself. What also helps it keel design. In some of the new and even older boats the keel is step forward and away from the wheel. Usually a skeg is need to be added or a beefy wet tube. Removing this part of the keel adds for better rudder control. However less keel = more roll… so you cannot have it both ways.

The one thing that I have found which can increase keel walking is the use of trim tabs.
With the boat at speed the tab just makes thing worst. With the bow down the keel has even more control.

 

[BillD]

To add to Travis comment, to me keel walking feels like the boat is "flopping or falling" over from one side to the other. And yes I could not agree more with Travis, it is not a great feeling falling or flopping anywhere at 25 plus knots!!

Mike, have you ever done any "keel walking" in the 31 BHM ????

 

[F/V First Team]

800 lbs of sand slung under the washrail works too

Then you don't need to slow down :-D

If it is just the flat running surface of the keel itself, easy fix is to just glass on a half round piece. Could be a cardboard tube sliced down the middle or a small diameter exhaust tubing if you want it to be all glass. Doesn't have to be fiberglassed all crazy either, just enough to hold it on. Think of it as a crumple zone for your boat if you do happen to touch something, no big deal to fix/replace.

 

[plowin]

If you are serious Bill, no the BHM has never keel walked. My BHM and most others make a steady 14-16kts in almost all conditions, within reason. I know of a couple with 500 hp and they do not keel walk either. I am sure the wet keel and the ability to put a 28" wheel under it has a lot to do with it.

 

[BillD]

If you are serious Bill, no the BHM has never keel walked. My BHM and most others make a steady 14-16kts in almost all conditions, within reason. I know of a couple with 500 hp and they do not keel walk either. I am sure the wet keel and the ability to put a 28" wheel under it has a lot to do with it.

Wasn't serious Mike!

I figure the only way a 31 BHM would see 28 knots is on a trailer being towed down a highway !

 

[Kaiser]

Wasn't this a real problem with a well known 38 foot design above 22kts.?

what well known 38 was this?

 

[Powderpro]

what well known 38 was this?

He is talking about the 38' Wesmac. I don't know how it would keel walk as the keel doesn't even start until about 8' back from the bow and it is very narrow all the way back until about the last 6' - 7' where it does widen out and has a stout skeg to mount the rudder to. The keel on my 34' Calvin was wider and much longer (by longer I mean the keel started at the very forward portion of the bow) than the 38' Wesmac, and my Calvin run arrow straight at 33 mph and had zero sign of keel walking. So I will be very shocked if the 38' Wesmac has a keel walking issue above 22 knots. I have attached a pic of a 38' Wesmac hull to show you how it would be impossible, in my opinion, for the keel to cause the hull to become unstable or veer at higher speeds.

I've built/owned a boat that keel walked a bit once you got to 22 knots+, and you could see why it would as the keel started at the bow, and was flat and very wide the entire length of the keel. It actually provided enough lift at 22 knots+ to where the boat would wander a bit. I usually ran the boat at 19 knots, so keel walking was never an issue, but it would do it if the throttle was down.

 

[Powderpro]

In this pic of my 34' Calvin Beal, you can see how the keel starts right at the bow and it is way wider than the 38' Wesmac for almost the entire length of the keel, and as I said, zero keel walk at 33 mph on my Calvin. The 38 Wesmac's keel is about 1" - 1.5" wider than the Calvin's keel in the last 3' - 4', but that will not create keel lift.



Here is a pic of my last boat that did have a little keel walk at 22+ knots. Any idiot can see that this keel is going to create some lift at higher speeds, and even as bad of a design as this keel is, and as light as the boat was (the Patriot is probably 2,500 pounds lighter than my Wesmac will be), it still only keel walked once you got above 22 knots. So that's my 2 cents on the subject .

 

[Fish220sr]

Nice treatise on the keel walk phenomenon.


Any idiot can see

 

[JasonD]

An easy way to avoid Keel Walking, go slow! Fuel is expensive anyway.
16 knots to glory!!!!

 

[cb34]

keel

Thanks guys, Capt Larry what hull have you experienced keel walking?

 

[captainlarry84]

Doing the Dance.....

Thanks guys, Capt Larry what hull have you experienced keel walking?

Under advice of council and to keep this post in harmony….. I plead the 5th amendment!

I will give into some info on the designs.

One vessel was only a 23 footer overpowered with a keel and a 240 Yanmar. It was direct drive with a very small propeller and spade rudder. At WOT the boat danced on it s keel like an elephant on ice. Great boat but just way too much power.

Second one was a DE with twin screw and a full keel at the high end of performance the boat just would not steer. Once again just too much power at total of 600 plus.

The last vessel was a 30 footer well respected with 450 plus HP. Ran fine until it went WOT then she walked.

A 38 Wesmac is our mystery vessel? I find that very hard to believe. Wesmac is one of the vessels with a cut back rear keel and shaft tube that I admire.

Three of the best current keel designs I have seen are on the following boats, which if any did the walk then I would have to say that the power was well over a reasonable limit:
Flowers
Wesmac
Northern Bay

On a new build or used buy I would target one of these three vessels.

 

[Powderpro]

You plead the 5th? Come on .

I have to agree, the Flowers, Wesmac, and NB (and Calvin Beal) have superb water flow to the prop, best I know of. Although my personal favorite is the Wesmac which has the sweetest looking keel/shaft tube design I've ever seen, but that's just me.

 

[captainlarry84]

I did not put them in order. If I did it would be a photo finish horse race for sure.

Every once in a while even an old war horse like me seeks council.

 

[Tuckerman]

Here's the vid for first teams post..

Alex Thomson attempts the Keel Walk - YouTube