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Author Topic:   Boston Whaler Boats Tendency To Capsize

diveorfish posted 04-17-2009 01:31 PM ET (US)
After the recent loss of the NFL players, reading about other boat capsizing mishaps, and recent threads comparing Whalers to other boats, you come to the conclusion that boats, even boats with some foam in the hull, will capsize when swamped. Once the air inside the hull is replaced with water, there is no lateral stability because the buoyancy forces resisting the tendency to roll over are greatly diminished. Does this also hold true for Boston Whaler boats, especially the newer ones with really thick foam filled hulls clear up to the gunwales? When a Boston Whaler boat is swamped, the boat still has buoyancy. Lateral stability is still maintained to some extent because of the hull’s buoyancy. When the Whaler is swamped and it starts to lean over, is the buoyancy in the hull's sides strong enough to resist flipping compared to other boats that don’t have foam in the hull's sides?
Thirsty Whaler posted 04-17-2009 02:25 PM ET (US)
Having some foam in the hull, and having a hull made largely of foam, are two very different things.My one word answer would be-NO. I am sure some of the larger Conquests would likely capsize(have seen no evidence to support this),but, I have yet to view any article(s) that provide evidence that any of these hulls allowed their owners to get into that kind of trouble. It also is a very bad idea to anchor at the stern in six foot seas.
Buckda posted 04-17-2009 03:21 PM ET (US)
I do not believe that there will be an appreciable difference between a Whaler and other comparable self-bailing hull in the same situation. The seas were rolling and there were 4 heavy men aboard a small boat at anchor with a T-TOP. A similar Whaler would have capsized as well. The only possible difference is that it may have been slightly more stable – but once you get several hundred gallons flowing around in a small container, the weight of that water is going to overwhelm the minimal stabilizing power of the foam filled gunwales.
SJUAE posted 04-17-2009 06:05 PM ET (US)
I think we could look at this a slightly different way
Would a Whaler with and without foam be more stable?
With the foam the swamped capacity would be greater
Therefore, up to a certain point of water taken on board then I would think so
Once the mass of water taken on board and/or the sea state inducing severe rolling, accelerating the capsize, combined with the sloshing onboard water, then it's likely to be minimal.
So I think it would be reasonable to say under moderate conditions you should be slightly better off with foam filled.
Under severe conditions it would be marginal as the slight buoyancy advantage is too small to resist the other forces.
Other factor between similar boats boats (ie with and without T-Tops/Cabins etc) is likely to reduce this moderate condition advantage greatly.
The advantage under moderate conditions may make the difference before it accelerates to a severe
Regards
Steve
Jefecinco posted 04-17-2009 07:37 PM ET (US)
Beam to length ratio may have more to do with it than a foam filled hull. The last few "smallish" Edgewaters I've boarded seemed very beamy for the size.
Certainly any boat would be subject to capsize if the transom and one side of the boat was pulled below the surface while trying to break loose an anchor on the bottom by attempting to pull it out while it was attached to a stern cleat while pulling forward at close to WOT. Given sufficient power even a bow could be pulled under by a stuck anchor while proceeding forward at WOT unless a lot of rode was deployed.
Butch
highanddry posted 04-17-2009 08:15 PM ET (US)
There was a video I cannot find now that showed a Grady and a similar Whaler full of water and full of people and both had the same engine. The Grady filled completely with water, the stern sunk and it rolled over. The Whaler remained level, engine above water and stable. Clearly at least some Whalers are resistant to capsizing but that does not mean in an ocean with six foot seas, stern anchored with a fellow gunning the engine that it too would not roll over.
Jerry Townsend posted 04-18-2009 12:05 AM ET (US)
First off - the Florida fishing event involving the NFL players was, at least enhanced, by the anchor being tied to a gunwale cleat and rough water. Quite different than a boat capsizing from other than this situation.
The basic premise that "... that even have some foam in the hull will capsize when swamped ..." is not necessarily true. The capsizing depends on the way in which the swamping is done - i.e. from a side or the stern (or bow).
Regarding this basic subject, remember the USCG requires all boats of up to and including 18 feet (as I recall) must have level buoyancy - which I interprete as the boat being level when swamped. But all boats, which we are addressing, have some built in flotation devices (foam, tanks, et al.) to provide the buoyancy. A boat without any, or insufficient, flotation devices will, when swamped, sink - by definition.
A partially swamped boat is relatively stable, but if swamped from one side, the result will be enhanced as there will be less buoyancy on the up-side and more weight on the "down" side. This condition is maximized when the downside gunwald dips below the surface. Momentum will probably complete the capsize.
If the swamping is from the stern or bow, the loading will be somewhat uniform and as the swamping is compelte, the hull will be relatively stable - as the CG (center of gravity) is below the surface of the water and all forces acting on the boat are from below the surface. And remember that the heavier boat will be the more stable.
Now what would cause a boat to roll and to eventually swamp - - broaching in rough water, over-loading one side, tying an anchor to a gunwale cleat, some combination of these events or et al.
Now what can stop a capsize - one thing that I can think of - weight in the keel - a lot of it - so that as the keel were to be raised, the weighted keel would provide a moment which would tend to offset the capsizing and stabalize the boat. In the extreme it sounds almost like a sailboat. Can a sailboat capsize?
Having "... thick foam filled hulls clear up to the gunnels ..." does not necessarily affect a swamped boat - as any flotation above the water line does not provide any buoyancy.
But - having "... thick foam filled hulls clear up to the gunnels ..." will tend to stabilize the swamped boat if it tends to capsize. This results because this boat will have more weight (less buoyancy) on the up-side and the down-side will have more buoyancy - which tends to stabilize the boat. ---- Jerry/Idaho
A T-top really agravates the situation - as with the boat being swamped in a hoaling wind, there will be a very significant lateral load several feet above the water surface - which tends to roll the boat.
SJUAE posted 04-18-2009 01:44 AM ET (US)
Jerry
I agree,
Although having foam filled hulls clear up to the gunnels should reduce the free surface effect over a the same boat without as there is ~6" of less space for the water to run too in a broaching swamped from one side scenario.
This could be a significant moment as it's at the maximum distance from the at rest CoG and CoB.
An old trick to dampen rolling when at anchor overnight was to drop a bucket port and starboard.
Regards
Steve
jimh posted 04-18-2009 09:24 AM ET (US)
A capsize as being discussed here means a hull not overturning and inverting from lateral motion. The ability of a hull to resist overturning from lateral rotation is known as its righting moment. The righting moment is most influenced by the shape of the hull form and the distribution of weight in the boat. I believe the construction technique of the hull does not directly influence the righting moment, other than through an influence of how the weight is distributed.
In an open boat that has rolled so far that it has put its gunwale under, water is going to rapidly fill the interior. In this situation, a double-bottom boat like a Boston Whaler will have less interior space that can be filled with water. This will cause the boat to take on less water. The less water, the less weight free to move.
The only reason that a Boston Whaler rides higher in the water when swamped than an identical hull without the foam is that there is less water in the Boston Whaler boat. There is less water in the boat because much of the interior of the boat is filled with foam.
SJUAE posted 04-18-2009 04:26 PM ET (US)
Jim
I think the actual definition of righting moment is the torque trying to return a boat upright, when the boat is heeled, which is slightly different but same same for our purposes of discussion :)
The torque can be calculated by multiplying the horizontal distance between the CoG of the boat and CoB of the underwater part of the hull by the boat displacement.
The speed that it rights or resists heeling (what we would commonly consider as stability) is a function of the hull shape.
Flat bottom being the best and curved being the worse, leaving V somewhere in the middle.
Although a high heel resistance does not always equate to comfort. A boat with less heel resistance but a large righting moment would feel better say from the wake of a passing boat.
Probably the biggest safely factor to consider first would be the available free board as this would determine the maximum heel angle permissible before taking water over the gunwale.
Although the original question was for a fully swamped boat resistance to capsize I think we all agree that the difference between a fully foamed filled boat and not, is marginal as both are very near to neutral buoyancy and have a small righting moment. Although you would have less water to bail out in a Whaler
However in a partially swamped scenario there could be an advantage for Whalers.
Regards
Steve


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Author	Topic: Boston Whaler Boats Tendency To Capsize
diveorfish	posted 04-17-2009 01:31 PM ET (US) After the recent loss of the NFL players, reading about other boat capsizing mishaps, and recent threads comparing Whalers to other boats, you come to the conclusion that boats, even boats with some foam in the hull, will capsize when swamped. Once the air inside the hull is replaced with water, there is no lateral stability because the buoyancy forces resisting the tendency to roll over are greatly diminished. Does this also hold true for Boston Whaler boats, especially the newer ones with really thick foam filled hulls clear up to the gunwales? When a Boston Whaler boat is swamped, the boat still has buoyancy. Lateral stability is still maintained to some extent because of the hull’s buoyancy. When the Whaler is swamped and it starts to lean over, is the buoyancy in the hull's sides strong enough to resist flipping compared to other boats that don’t have foam in the hull's sides?
Thirsty Whaler	posted 04-17-2009 02:25 PM ET (US) Having some foam in the hull, and having a hull made largely of foam, are two very different things.My one word answer would be-NO. I am sure some of the larger Conquests would likely capsize(have seen no evidence to support this),but, I have yet to view any article(s) that provide evidence that any of these hulls allowed their owners to get into that kind of trouble. It also is a very bad idea to anchor at the stern in six foot seas.
Buckda	posted 04-17-2009 03:21 PM ET (US) I do not believe that there will be an appreciable difference between a Whaler and other comparable self-bailing hull in the same situation. The seas were rolling and there were 4 heavy men aboard a small boat at anchor with a T-TOP. A similar Whaler would have capsized as well. The only possible difference is that it may have been slightly more stable – but once you get several hundred gallons flowing around in a small container, the weight of that water is going to overwhelm the minimal stabilizing power of the foam filled gunwales.
SJUAE	posted 04-17-2009 06:05 PM ET (US) I think we could look at this a slightly different way Would a Whaler with and without foam be more stable? With the foam the swamped capacity would be greater Therefore, up to a certain point of water taken on board then I would think so Once the mass of water taken on board and/or the sea state inducing severe rolling, accelerating the capsize, combined with the sloshing onboard water, then it's likely to be minimal. So I think it would be reasonable to say under moderate conditions you should be slightly better off with foam filled. Under severe conditions it would be marginal as the slight buoyancy advantage is too small to resist the other forces. Other factor between similar boats boats (ie with and without T-Tops/Cabins etc) is likely to reduce this moderate condition advantage greatly. The advantage under moderate conditions may make the difference before it accelerates to a severe Regards Steve
Jefecinco	posted 04-17-2009 07:37 PM ET (US) Beam to length ratio may have more to do with it than a foam filled hull. The last few "smallish" Edgewaters I've boarded seemed very beamy for the size. Certainly any boat would be subject to capsize if the transom and one side of the boat was pulled below the surface while trying to break loose an anchor on the bottom by attempting to pull it out while it was attached to a stern cleat while pulling forward at close to WOT. Given sufficient power even a bow could be pulled under by a stuck anchor while proceeding forward at WOT unless a lot of rode was deployed. Butch
highanddry	posted 04-17-2009 08:15 PM ET (US) There was a video I cannot find now that showed a Grady and a similar Whaler full of water and full of people and both had the same engine. The Grady filled completely with water, the stern sunk and it rolled over. The Whaler remained level, engine above water and stable. Clearly at least some Whalers are resistant to capsizing but that does not mean in an ocean with six foot seas, stern anchored with a fellow gunning the engine that it too would not roll over.
Jerry Townsend	posted 04-18-2009 12:05 AM ET (US) First off - the Florida fishing event involving the NFL players was, at least enhanced, by the anchor being tied to a gunwale cleat and rough water. Quite different than a boat capsizing from other than this situation. The basic premise that "... that even have some foam in the hull will capsize when swamped ..." is not necessarily true. The capsizing depends on the way in which the swamping is done - i.e. from a side or the stern (or bow). Regarding this basic subject, remember the USCG requires all boats of up to and including 18 feet (as I recall) must have level buoyancy - which I interprete as the boat being level when swamped. But all boats, which we are addressing, have some built in flotation devices (foam, tanks, et al.) to provide the buoyancy. A boat without any, or insufficient, flotation devices will, when swamped, sink - by definition. A partially swamped boat is relatively stable, but if swamped from one side, the result will be enhanced as there will be less buoyancy on the up-side and more weight on the "down" side. This condition is maximized when the downside gunwald dips below the surface. Momentum will probably complete the capsize. If the swamping is from the stern or bow, the loading will be somewhat uniform and as the swamping is compelte, the hull will be relatively stable - as the CG (center of gravity) is below the surface of the water and all forces acting on the boat are from below the surface. And remember that the heavier boat will be the more stable. Now what would cause a boat to roll and to eventually swamp - - broaching in rough water, over-loading one side, tying an anchor to a gunwale cleat, some combination of these events or et al. Now what can stop a capsize - one thing that I can think of - weight in the keel - a lot of it - so that as the keel were to be raised, the weighted keel would provide a moment which would tend to offset the capsizing and stabalize the boat. In the extreme it sounds almost like a sailboat. Can a sailboat capsize? Having "... thick foam filled hulls clear up to the gunnels ..." does not necessarily affect a swamped boat - as any flotation above the water line does not provide any buoyancy. But - having "... thick foam filled hulls clear up to the gunnels ..." will tend to stabilize the swamped boat if it tends to capsize. This results because this boat will have more weight (less buoyancy) on the up-side and the down-side will have more buoyancy - which tends to stabilize the boat. ---- Jerry/Idaho A T-top really agravates the situation - as with the boat being swamped in a hoaling wind, there will be a very significant lateral load several feet above the water surface - which tends to roll the boat.
SJUAE	posted 04-18-2009 01:44 AM ET (US) Jerry I agree, Although having foam filled hulls clear up to the gunnels should reduce the free surface effect over a the same boat without as there is ~6" of less space for the water to run too in a broaching swamped from one side scenario. This could be a significant moment as it's at the maximum distance from the at rest CoG and CoB. An old trick to dampen rolling when at anchor overnight was to drop a bucket port and starboard. Regards Steve
jimh	posted 04-18-2009 09:24 AM ET (US) A capsize as being discussed here means a hull not overturning and inverting from lateral motion. The ability of a hull to resist overturning from lateral rotation is known as its righting moment. The righting moment is most influenced by the shape of the hull form and the distribution of weight in the boat. I believe the construction technique of the hull does not directly influence the righting moment, other than through an influence of how the weight is distributed. In an open boat that has rolled so far that it has put its gunwale under, water is going to rapidly fill the interior. In this situation, a double-bottom boat like a Boston Whaler will have less interior space that can be filled with water. This will cause the boat to take on less water. The less water, the less weight free to move. The only reason that a Boston Whaler rides higher in the water when swamped than an identical hull without the foam is that there is less water in the Boston Whaler boat. There is less water in the boat because much of the interior of the boat is filled with foam.
SJUAE	posted 04-18-2009 04:26 PM ET (US) Jim I think the actual definition of righting moment is the torque trying to return a boat upright, when the boat is heeled, which is slightly different but same same for our purposes of discussion :) The torque can be calculated by multiplying the horizontal distance between the CoG of the boat and CoB of the underwater part of the hull by the boat displacement. The speed that it rights or resists heeling (what we would commonly consider as stability) is a function of the hull shape. Flat bottom being the best and curved being the worse, leaving V somewhere in the middle. Although a high heel resistance does not always equate to comfort. A boat with less heel resistance but a large righting moment would feel better say from the wake of a passing boat. Probably the biggest safely factor to consider first would be the available free board as this would determine the maximum heel angle permissible before taking water over the gunwale. Although the original question was for a fully swamped boat resistance to capsize I think we all agree that the difference between a fully foamed filled boat and not, is marginal as both are very near to neutral buoyancy and have a small righting moment. Although you would have less water to bail out in a Whaler However in a partially swamped scenario there could be an advantage for Whalers. Regards Steve