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Old 07-25-2015, 10:03 AM   #41
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Rolly Polly ????

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Originally Posted by manyboats View Post

To dampen roll added weight should obviously be a considerable distance nice from CG. I thought that would be obvious.
Wrong choice of words. Lengthening the KG will make the roll snappier. She will come back quicker. It will likely not change much the length of the roll. Hull shape being what it is will make weather day delays, change in destination or tacking needed to make a trip.
I have lived through experimentation where the boats were made SO snappy your feet would almost get pulled out from under you in a beam sea.

The OP. You have a round bilged boat. They roll. These are a variant of a motor sailer. They stopped making them. Care to guess why? They roll. You have to plan your trip around the seas.

There's about 4 concepts to change the roll. (It's all a crap shoot, trial and error)

Add weight as far down low as possible.
Add weight right at (or just below) CB.
Add weight in the centerline.
Reducing weight aloft ( think flybridge)

It's not just about adding weight down low. A boat with too much tophamper is easy to fix

A boat with round bilges is tough. You can't change the shape of the hull. When she rolls is it a long, slow, deep roll? Or is it a sharp snappy roll?
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Old 07-25-2015, 01:39 PM   #42
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cappy,
What's KG and CB?

For serious roll control fishermen in Alaska always (as far as I know) employ paravanes. And many to most have round like hulls. However my Willard appears to have a rounded hull but actually dosn't. Just rounded bilges.
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Old 07-25-2015, 02:22 PM   #43
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KG = vertical center of gravity

CB = center of buoyancy
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Old 07-25-2015, 02:26 PM   #44
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Cappy, I agree the shape of the hull seems to be the determining factor. But maybe you can effectively change the shape of the hull. A resistance of some sort to the water movement under the hull. This brings me full circle to bilge keels. Manyboats, in beebes book he mentions an individual with a willard who had added bilge keels with excellent results. The paravanes effectively add a resistance to the movement of the boat utilizing water resistance.
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Old 07-25-2015, 03:17 PM   #45
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This might help.....


Hydrostatic Nomenclature

B or CB – Center of Buoyancy, the center through which the buoyant force acts. The CB moves as the underwater shape changes as the hull moves up and down (or rolls sideways) in the water. If the hull is floating free to trim or roll, the CB will always be directly under the center of gravity. During launching this doesn’t happen because the hull is “aground” forward.

M - Metacenter, the theoretical point around which the boat rolls or trims. There are separate transverse and longitudinal M’s.

K – Keel or baseline, the fixed line from which all vertical measurements are taken.

G – Center of Gravity of the vessel. The center of all the various weights that make up the boat. Addressed separately as VCG (Vertical Center of Gravity), LCG (Longitudinal Center of Gravity), and TCG (Transverse Center of Gravity). In computerese X is longitudinal, Y is athwartships, and Z is vertical.

GM – Distance from G to M in ft. or metres. Considered a general indication of a given vessel’s stability. To be stable G must be below M. A larger GM means the ship is stiff, a small GM (say less than one ft) is a tender vessel, a negative GM indicates an unstable ship.

GZ – Righting Arm in feet or metres. A horizontal distance between the CG acting downward and the CB acting upward.

V – Volume of the hull (underwater portion) in cubic feet or metres. The displaced volume (underwater) will be equal to the total weight of the vessel divided by the weight of the water she’s floating in. So if your boat weighs 5000 pounds(2273Kg) on the trailer, afloat she will displace 5000 pounds(2273Kg). Seawater weighs approximately 64 pounds(29Kg) per cubic foot so underwater volume (V) is 5000/64 = 78.1 cubic feet, or 2273/1000 = 2.27 cubic metres.

I – Inertia of Waterplane. The waterplane is a cut through the hull at the waterline. The distribution of this area affects stability. A barge and a needleboat could have the same waterplane area, but very different stability.

BM = I/V - Key stability equation. Inertia of the waterplane (I), divided by the displacement (V), is equal the distance from (B) the center of buoyancy, to (M) the meta center.

Ultimate Stability Angle- Called the angle of vanishing stability, this is the heel angle where righting force is zero.

Downflooding Angle- The heel angle where water starts coming through some hull opening (doors, windows, ports, hatches) and degrades stability of the vessel.

Free Surface- When the contents of a tank (fuel, fresh water, wet fish) slosh to one side it sets up a heeling force, which can degrade stability.

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Old 07-25-2015, 05:12 PM   #46
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I have a 1973 36 Gulfstar mk1, and it rolls. Period. The steadying sail helps somewhat, but it still rolls in a beam sea. We tack underway when we have to, and stay at the pier to wait for favorable conditions. I keep the water tank full, and the fuel tank above 1/2. More than 2 feet on the beam is unacceptable for us, but we're retired, doing the loop, and don't have a schedule. I think it is a lot of boat for little money. Like all boats, you learn their quirks and deal with it. I have 2 Perkins 4-236 engines, but the trannys are not counter-rotating. So it prop walks to starboard when backing. OK, I know about it, I plan for it. All part of the fun.

As for numbers, Gulfstar made 98 36' Mk1 in 1973-1973. Then in 1975-1976, made 35 Mk IIs.
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Old 07-25-2015, 06:57 PM   #47
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I guess it's a bit extreme to put in a sea keeper gyro stabilizer for around 30 K but sure have read good things about them
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Old 07-26-2015, 06:53 AM   #48
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"They stopped making them. (MOTORSAILORS) Care to guess why? They roll. You have to plan your trip around the seas."

The early MS is mostly gone from the market because of lifestyle , hardly roll.

The usual MS is like any ocean voyaging a vessel where folks live IN the hull.

With diesels that are 1/5 the weight and size of early gas or diesels the fully powered sailboat is the result.

These actually do sail, at fine speeds , although most are 50-90ft + and may cost a few million.

Small sailors 30 ft up , can cross oceans , but not all the way under power.

Today folks want a view from above deck and the few (under 1-100) that will pay perhaps 300% extra for an ocean crossing motor boat scantlings enjoy the voyage.

That an inshore boat built as high and as fat as can be done (more room aboard ) with a short slip expense ,should not be amazed that their Roomaran does not like rough water.

All boats are a compromise , the mere volume boaters seem happy to do without seaworthy , sea kindly or easy to operate.They are found dockside most days.
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Old 07-26-2015, 09:15 AM   #49
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Quote:
Originally Posted by kpinnn View Post
Cappy, I agree the shape of the hull seems to be the determining factor. But maybe you can effectively change the shape of the hull. A resistance of some sort to the water movement under the hull. This brings me full circle to bilge keels. Manyboats, in beebes book he mentions an individual with a willard who had added bilge keels with excellent results. The paravanes effectively add a resistance to the movement of the boat utilizing water resistance.

I don't know how big bilge keels need to be before they are effective, but I can assure you that mine have only minimal effect on roll reduction. If you are considering it, don't skimp on the size. I suspect mine are far too small.
Then again, I suppose the same can be said for steadying sails.

Here's what mine look like.
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Old 07-26-2015, 09:58 AM   #50
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This thread's getting very informative.

Perhaps a keel extension the same area as a bilge keel would have the same effect .. roll wise? I'm not a fan of bilge keels.

Thanks for the thinking sheet TAD. A great lesson for those that are curious.
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Old 07-26-2015, 09:59 AM   #51
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motorsailors are still built

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"They stopped making them. (MOTORSAILORS) Care to guess why? They roll. You have to plan your trip around the seas."

The early MS is mostly gone from the market because of lifestyle , hardly roll.
That was not what I wrote. I was referring to this particular model, which in reality was a motorsailor hull, with the mast removed. Gulfstar made the 36 and a 43 I believe. They did the same on both models. Then they gave up on the trawler market. The concept of building motorsailors and when the trawler market heated up, simply removing the masts and calling it trawler was what stopped. The hull shape is the same on these vessels. The manufacturers (as I recall, I was really young in those days) had tried to experiment with removing the rig, lessening the molded in keel weight (to compensate for reduced or removed masts and sails), lessening the draft in the mold (thus making a shallower draft 'trawler') But the one thing they did NOT do was change the hull design. That is what killed the motorsailor conversions.

The people (as was mentioned by several people who actually live in, own and use in this blog) who own one now have to allow for weather.

I'm sort of surprised that no one from the 'Willard/Fales" community has commented on this, from both sides perspective (Under sail, versus power.)

here's a couple pics to show the difference. Click image for larger version

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ID:	42477or stays'l mast. Same hull. Name:  gulfstar underbody.jpg
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Size:  10.5 KBNice underbody shape ;-)
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