Boat Roll

[Irish Rambler]

Maybe you brought over to Waterford Richard !
Glad to hear your safe and well.

[CaptSteve53]

Originally Posted by Al

Is there a biblical formula in the maritime world in the proportions of rolling chocks in terms of construction to meet beam/length/depth? What determines the construction size of a given set of chocks? I have never read where measurement are included. Just that a boat had rolling chocks installed. Viewing many examples on boats on the hard, they vary in configurations/size.

As happy as I am with the ballast that I have mentioned numerous times on the forum, one wonders if installing a set of chocks would enhance the improved roll motion even more (cost being one consideration).
In speaking with a marine fiberglass repair/construction fellow in Wrangell AK, constructing chocks is a common enough project, in the same class as bulbous bow components , that a couple of days is all it would take to lay up a pair and install. Very tempting. Thoughts?

The only real way to have correct proportional rolling chocks fitted is using a Naval Architect, saying that however some naval architects don’t believe they are very effective at all, or cite roll magnitude reduction of only 10%, but other designers and builders report reduction of 30% to 50%.

Here are some General Considerations how ever:

1) Hard-chine boats and others with high initial stability benefit less from bilge keels/rolling chocks than do round or soft chine hulls, because the harshness of the hard chine edge creates its own turbulence and damping effect.
2) They can be made fairly long—half the length of the boat or more,depending on the curve of the hull. However, they should extend forward only to the point where they start converging due the curve of the bow; any more and they would add drag when underway. Besides, they would be ineffective if they were to come out of the water when the boat pitches.
3) Commonly they are only eight inch eight inches or so in width to avoid extending beyond the “envelope” of the hull, where they could be damaged by a trailer, carriage, or at the dock. If the keel is positioned down at the
turn of the bilge, and is placed perpendicular to the surface of the hull at that point, it can be made longer without extending far enough to attract damage. Some yards put bilge keels as wide as 16 to 18 inches on a 60-foot hull.
4) The trick is to place the keels such that they are within the water flow streamlines of the hull so they produce minimal drag.This can be a problem if the boat operates over a wide range of speeds, as do most semi displacement hulls, because the streamlines change with speed. Some engineers place rolling chocks high on the chines to produce a little lift, and they claim they work best when underway. But the more widely held view seems to be that they should be positioned lower and at a 45° downward angle,which precludes any lift effect. If correctly positioned they work quite well at anchor, and even better underway.
5) There is a drag penalty for chocks, and it’s there whether you need the roll control or not. But the increase in fuel consumption is estimated at less than 10%.
6) The fins should taper at both ends (rather than start and end with sharp corners) and should have a rounded or flat outer edge rather than a knife edge, to avoid damage to and by fishing gear and other obstacles in the water.

Cheers Steve

[FF]

Our boat LUCY is a US Navy Utility, that was converted to a lobster supply boat , then to a lobster boat, then to a cruiser to run the Loop and for cruising fun.

It was fitted with roll chocks about 8 inches deep and 30 ft long.

I have not been in the rough with an unmodified Navy Utility so can not compare how effective it is.

The boat still rolls , but there is no harsh check and rapid acceleration as a hard chine would have at the reversal of the roll.

I don't know if it does work , but it seems to have done no harm .

A beam sea is not comfortable but there is no snap roll to create a Vomitorium.

[Pgitug]

Don't want the roll?
Get a power cat.

[Wxx3]

Originally Posted by CaptSteve53

The only real way to have correct proportional rolling chocks fitted is using a Naval Architect, saying that however some naval architects don’t believe they are very effective at all, or cite roll magnitude reduction of only 10%, but other designers and builders report reduction of 30% to 50%.

Here are some General Considerations how ever:

1) Hard-chine boats and others with high initial stability benefit less from bilge keels/rolling chocks than do round or soft chine hulls, because the harshness of the hard chine edge creates its own turbulence and damping effect.
2) They can be made fairly long—half the length of the boat or more,depending on the curve of the hull. However, they should extend forward only to the point where they start converging due the curve of the bow; any more and they would add drag when underway. Besides, they would be ineffective if they were to come out of the water when the boat pitches.
3) Commonly they are only eight inch eight inches or so in width to avoid extending beyond the “envelope” of the hull, where they could be damaged by a trailer, carriage, or at the dock. If the keel is positioned down at the
turn of the bilge, and is placed perpendicular to the surface of the hull at that point, it can be made longer without extending far enough to attract damage. Some yards put bilge keels as wide as 16 to 18 inches on a 60-foot hull.
4) The trick is to place the keels such that they are within the water flow streamlines of the hull so they produce minimal drag.This can be a problem if the boat operates over a wide range of speeds, as do most semi displacement hulls, because the streamlines change with speed. Some engineers place rolling chocks high on the chines to produce a little lift, and they claim they work best when underway. But the more widely held view seems to be that they should be positioned lower and at a 45° downward angle,which precludes any lift effect. If correctly positioned they work quite well at anchor, and even better underway.
5) There is a drag penalty for chocks, and it’s there whether you need the roll control or not. But the increase in fuel consumption is estimated at less than 10%.
6) The fins should taper at both ends (rather than start and end with sharp corners) and should have a rounded or flat outer edge rather than a knife edge, to avoid damage to and by fishing gear and other obstacles in the water.

Cheers Steve

You basically said everything I was going to say.

While in New Ross, having my bottom done, I did consider adding them. The cost would have been about $2500.

The reasons I ended up deciding not to:
1. I estimated the roll reduction would at most be 10 to 20% on a beam sea. My paravanes would reduce roll 75% on the same beam sea. Therefore the window for me to use them would be relatively small.

2. I estimated that fuel consumption would go up 10%.. Since I used over 2000 gallons in the last two years, that's not an insignificant amount.

3. The final deciding factor, I asked someone at Kadey Krogen. Surprisingly, he informed me that in fact, James Krogen had designed some bilge keels my owners' request.
So when my follow up question was, "Does that mean it was a good idea?"
The response was, "James Krogen did a number of things at owners' request, but had it been a good idea, he would have done it for all the boats"
Nuff said.

[FF]

"Don't want the roll?
Get a power cat."

And learn about Multihullers Eyeballs!

FAr far worse in accelerations than even a box underwater.

Think of each hull snapping up 5 rapidly ft as each wave goes under.

[Rebel112r]

I have had chocks on the boat for 2 seasons of cruising. Installed cost around 4K. I have not noticed any speed reduction, no increased fuel consumption. They do not cause problems with docking or lifting the boat. They temper the roll, and help with pitch. This is actual observation and not speculation. I have talked to 4 other NP owners that have had them installed and all have had positive things to say about them. There are about 10+ NP's that have had them installed, but I have not talked to all these owners. Added maintenance is about zero, maybe an extra quart of paint every other year. I have crewed on a fish boat with paravanes, which I feel are more effective than the chocks, but there is a lot of highly stressed hardware involved and there definitely is drag, and they do catch crap in the water. Active stabilization or gyro stabilization would be great, but not available for 4K.

[Nomad Willy]

A boat that has very rounded cross sections like Dixie II (pics) stabilizers will be very effective and you'd love them. However if you put stabilizers on a wide and flat bottomed boat you may be very disappointed.

The stabilizers need to counteract the tendency for the boat roll. If Dixie was sideways on the face of a wave a little righting moment induced by her stabilizers would keep her from responding to her natural tendency to roll putting her lee rail down toward the wave trough. Very little rolling would take place. If you put stabilizers on a barge almost no reduction in roll would take place. The barge would assume a position on the wave that almost matched the shape of the wave. And as quickly as the wave changed shape. The barge would allow the wave to dictate her rolling position almost entirely .. and almost instantly. The barge would assume her natural position no matter how powerful a stabilizing system would be.

Lots of pleasure boats have hull bottoms that are more like a barge that the fish boat in these pics. So unless your boat resembles Dixie's hull cross section any stabilizer installed will need to work very hard to dampen the roll enough so most are comfortable on board.

I include a pic of my Willard to show that even FD pleasure boats are not round in cross section to the extent that Dixie is. And much of the suitability of boats to stabilizers are a result of length to beam ratio. But most SD trawlers are wide and largely flat too. Stabilizers on a pleasure trawler may work acceptably well and then maybe not.

In the first pic you can see Dixie II roll just from the weight of her extended spar.

[Nomad Willy]

Originally Posted by ff

"don't want the roll?
Get a power cat."

and learn about multihullers eyeballs!

Far far worse in accelerations than even a box underwater.

Think of each hull snapping up 5 rapidly ft as each wave goes under.

yes .... +1
Similar in some ways to a barge but every boat differs.
A very narrow barge could be controlable (roll wise) and her pronounced hard chines may act much like bilge keels chocks ect.

[dannc]

Originally Posted by Irish Rambler

...
I know which side my bread is buttered on ! (Irish expression). Meaning I know when I'm well off.

Originally Posted by Wxx3

I thought THAT was a New York expression.

I thought that was a Southern expression!

The more I watch UK and Irish TV programs the more I see how many American sayings are from the home countries. We were watching a British show last weekend and a character said, "I reckon" which I thought was a Southern saying.

Later,
Dan

[Irish Rambler]

dancc,
Some expressions in use today in UK/Ireland came from GI's over here during WW2.
Later expressions from the US TV (that's television) shows influenced our younger generations.
Many others sayings in America date back to the days of Irish/Scottish/English immigrants, for example 'Fall' as in seasons, is the original English expression for what we here in UK/Ireland as Autumn.
Many of the city and town names in both America and Australia come from British/Irish town names copied in the 'New World' by homesick immigrants.

[Hamrow]

Originally Posted by makobuilders

I agree that some sort of stabilization is needed for any long distance motor cruiser...

This thread seems tilted towards full displacement but i have to throw in a good word for the many folks on the forum with semi-displacement boats, and can't fully agree with the statement above. Yes my tug can go into the teens but if i keep her down in traditional trawler speed I can go well over 1000 mi on a full tank.
My 43' has no stabilization nor do i want it. Fin stabs are not without their drawbacks as far as maintenance and the addition of extra thru-hulls. Don't get me wrong, I suspect they're definitely a plus in some of the full displacement designs, but just not necessary on all long distance cruisers. We've been in some pretty sporty conditions in Admiralty inlet but i have to say the tug handles it pretty comfortably.
Just want the OP to know there are many hull options out there.....

[BruceK]

Originally Posted by Irish Rambler

...
I know which side my bread is buttered on ! (Irish expression). Meaning I know when I'm well off.

As long as it`s Irish soda bread, all good.
We know a slice of bread falls to the floor butter side down. And a falling cat always lands on its feet. So, if you tape a slice butter side up on the back of a cat.....

[markpierce]

Always thought boating was a lot about rolling. Expensive to minimize. Consider other non-small-boat options. Have experienced severe rolling even in large ships with stabilizers.

[Nomad Willy]

Mark most ships have flat bottoms .. not rounded.

The cheeks (bilge area) lifts one side.

[dannc]

Originally Posted by Irish Rambler

dancc,
Some expressions in use today in UK/Ireland came from GI's over here during WW2.
Later expressions from the US TV (that's television) shows influenced our younger generations....

Never thought about the influence of US TV and GIs on UK language...

One of the first US expressions we noticed on non US TV, was an Irish show that used the word, "Idjiots" or at least that is how I spell it. Idjiots = Idiots.

We were just watching a UK show, can't remember which one, and they used an expression my granny used. I think it was, "Waste not, Want not", which might have been documented by Ben Franklin, and if so, it almost certainly came from the UK. There are other little pronunciations, sometimes just a syllable, that we thought we "American" but maybe not. The Outer Banks of NC, until recently, was rather isolated and the accent and language of the natives was supposed to have been very similar to Elizabethan English.

NC had a huge influx of people from Scotland and Ireland. We have a Scotland country and many place names from derived from these immigrants. Many of the first Scottish settlers came from Campbeltown, Scotland.

Later,
Dan

[Simi 60]

Originally Posted by FF

"Don't want the roll?
Get a power cat."

And learn about Multihullers Eyeballs!

FAr far worse in accelerations than even a box underwater.

Think of each hull snapping up 5 rapidly ft as each wave goes under.

Have you actually had one?
I have and didn't experience any of the issues you mention.

[Simi 60]

Originally Posted by Pgitug

Don't want the roll?
Get a power cat.
Attachment 68462

I agree but to get the level of comfort, load carrying ability and range that we enjoy now we would have to spend at least $1 million more than we did.

[Gordon J]

Originally Posted by Nomad Willy

A boat that has very rounded cross sections like Dixie II (pics) stabilizers will be very effective and you'd love them. However if you put stabilizers on a wide and flat bottomed boat you may be very disappointed.

The stabilizers need to counteract the tendency for the boat roll. If Dixie was sideways on the face of a wave a little righting moment induced by her stabilizers would keep her from responding to her natural tendency to roll putting her lee rail down toward the wave trough. Very little rolling would take place. If you put stabilizers on a barge almost no reduction in roll would take place. The barge would assume a position on the wave that almost matched the shape of the wave. And as quickly as the wave changed shape. The barge would allow the wave to dictate her rolling position almost entirely .. and almost instantly. The barge would assume her natural position no matter how powerful a stabilizing system would be.

Lots of pleasure boats have hull bottoms that are more like a barge that the fish boat in these pics. So unless your boat resembles Dixie's hull cross section any stabilizer installed will need to work very hard to dampen the roll enough so most are comfortable on board.

I include a pic of my Willard to show that even FD pleasure boats are not round in cross section to the extent that Dixie is. And much of the suitability of boats to stabilizers are a result of length to beam ratio. But most SD trawlers are wide and largely flat too. Stabilizers on a pleasure trawler may work acceptably well and then maybe not.

In the first pic you can see Dixie II roll just from the weight of her extended spar.

Our beam is 15'8" in our length is 45 1/2 feet. We are semi displacement. I can tell you that the stabilizers make a world of difference and comfort.

[Nomad Willy]

Gordon J,
As I said all boats are different.
If you were to take a ride on Dixie II you would think it was magic.
There's many variables involved and most SD boats would benefit from stabilizers. But there's a wide range of results. And to get the stabilizing effects that you enjoy a narrow and round hulled boat would only need small stabilizers.