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-   -   length vs beam and trailer able (https://www.trawlerforum.com/forums/s37/length-vs-beam-trailer-able-7966.html)

bfloyd4445 12-06-2012 10:23 PM

Quote:

Originally Posted by CPseudonym (Post 117871)
Plumbers used to melt lead in cast iron kettles, no reason a pan wouldn't work fine too.

lead melts at a low temperature any old pot will do but be careful

Tad Roberts 12-07-2012 01:20 PM

Quote:

Originally Posted by manyboats (Post 117834)

Very interesting about the % of length capsize studies. As stated it says the longer a vessel is the less likely it will capsize from a given wave (in height).
Well Tad I'll be watch'in out for those 17' waves while out in my 30' boat. Only been in those once and I was in an 28' OB that I designed and built. Mus'ta done someth'in right as I'm still here. Actually I'll be watch'in out for for those 9 footers too. AND I'll be hang'in on white knuckl'ed to the helm also.
Does the % of length "rule" or findings take into consideration the CG change over long boats and short boats that are all the same size ... volume/disp ? Or are all the hypothetical short and long boats all the same beam? Or have I read this all wrong?

Those studies were done on "average" (whatever that is)hull models. The economics of most reseach means you use models borrowed from other studies. We can assume average types of hulls with typical length/beam/freeboard/depth. And the work was done with whatever waves that particular tank was capabile of generating, which may mean little in the real world.....

Which brings up another factor...keel tripping. Many folks have written about this and it's been studied a bit, again in test tanks. One theory is that as a wave passes under a boat, the keel (if there is one) holds the bottom back while the breaking top pushes the hull to leeward, increasing roll. Proponents of shallow draft boats cite this as a danger and claim a hull with no external keel will just slide over the wave with no "tripping".

Thus, perhaps, according to this theory, a deeper draft heavy displacement hull might be more prone to capsize (by wave action) than a lightweight shallow draft one.......

bfloyd4445 12-07-2012 04:02 PM

Quote:

Originally Posted by Tad Roberts (Post 117970)
Those studies were done on "average" (whatever that is)hull models. The economics of most reseach Thus, perhaps, according to this theory, a deeper draft heavy displacement hull might be more prone to capsize (by wave action) than a lightweight shallow draft one.......

Well if we look around us we see life raths are all shallow draft full enclousure type water craft and they seem to work in the worst seas. However, a deeper draft self righting craft will be much more comfortable to ride in and just as safe till u r in the rocks.

So, my recomendation is, take reasonable caution and the reat can go to .....just go enjoy the sea with a watchful eye with a good bottle of scotch in the emergency kit.

Nomad Willy 12-07-2012 05:00 PM

TAD,

OK good getting closer to apples and apples.

I designed a boat that had 45degree sides and it slid down the faces of waves bigger than 2 story houses just fine. After having survived that I consider non-tripping chines a very good thing. But get a keel big enough as on a very deep keel sailboat and she just lies down, slides a bit and let's the wave pass. So Ild say hull design has a lot to do w the ability to not capsize totally independent of beam. As is usually the case w design issues .. many variables.

TAD ther'e are lots of boats on the forum here that have at least the potential to trip on their keels but even a greater potential to trip on their chines. A good reason to be looking for plenty of beam, calm seas or both. Perhaps designers strive to give people that rock solid feel when they step aboard a boat w the salesman or a broker.

But a designer and/or manufacturer must design a boat to be appealing to buyers and I'm sure the lines get blurred a bit in the process. But I'm going to lean toward a boat that will slide sideways even if I've got to suffer from windage for it.

jeffnick 12-07-2012 07:05 PM

There's little adventure if there's zero risk...might just as well stay in your rocker on the heated, screened in front porch with the intruder alert.

The reason I go 'out there' is for adventure. If you're not in for a little excitement, fine, sit on the porch and debate about this and that...personally, I need a little more.

bfloyd4445 12-07-2012 07:09 PM

Quote:

Originally Posted by manyboats (Post 117999)
TAD,

OK good getting closer to apples and apples.

I designed a boat that had 45degree sides and it slid down the faces of waves bigger than 2 story houses just fine. After having survived that I consider non-tripping chines a very good thing. But get a keel big enough as on a very deep keel sailboat and she just lies down, slides a bit and let's the wave pass. So Ild say hull design has a lot to do w the ability to not capsize totally independent of beam. As is usually the case w design issues .. many variables.


But a designer and/or manufacturer must design a boat to be appealing to buyers and I'm sure the lines get blurred a bit in the process. But I'm going to lean toward a boat that will slide sideways even if I've got to suffer from windage for it.

what is a non-tipping chine?

Some boats like many of the DeFever 40-41's i've seen have a full keel with a deep hull towards the bow which begins to taper up a little past midship. Seems to me this shape may have similiar characteristics to what you describe?

Nomad Willy 12-07-2012 10:28 PM

bfloyd4445,
The best example of a non-tripping chine I can think of is the basic Sampan hull. There are 2 chines (turns or knuckles) in the area of the bilge instead of one. The hull between the 2 chines is typically about 45 degrees and as the boat slides sideways in a turn or on the face of a wave the shape of the double chine hull allows the water to slide transversely under the hull (especially aft) without causing extremely high lateral resistance very low that could capsize a hull especially abeam to breaking seas.

Yes the keel can have a similar affect depending on the size of the keel and how that keel can/could push the lee chine down and increase chine tripping probabilities. Or if the chine is soft like a lobster boat then the keel would be mostly what could cause tripping. This is one of the best features of the soft chine. But in a sharp turn a soft lee chine tends to pull the inbd chine down and the result can be over banking. I practically fell out of a soft chine OB w no keel because of that.

bfloyd4445 12-07-2012 11:46 PM

Quote:

Originally Posted by manyboats (Post 118062)
bfloyd4445,
The best example of a non-tripping chine I can think of is the basic Sampan hull. There are 2 chines (turns or knuckles) in the area of the bilge instead of one. The hull between the 2 chines is typically about 45 degrees and as the boat slides sideways in a turn or on the face of a wave the shape of the double chine hull allows the water to slide transversely under the hull (especially aft) without causing extremely high lateral resistance very low that could capsize a hull especially abeam to breaking seas.

Yes the keel can have a similar affect depending on the size of the keel and how that keel can/could push the lee chine down and increase chine tripping probabilities. Or if the chine is soft like a lobster boat then the keel would be mostly what could cause tripping. This is one of the best features of the soft chine. But in a sharp turn a soft lee chine tends to pull the inbd chine down and the result can be over banking. I practically fell out of a soft chine OB w no keel because of that.

Thanks Eric. u make me think and i like that. It will take a while to assimilate the double chine effect......would the second chine then be more like a hard chine? Sampan...i gotta check them out

h2orescuemedic 12-10-2012 10:21 PM

2 Attachment(s)
Attachment 14648

Attachment 14649

i still like pictures better

Nomad Willy 12-10-2012 10:43 PM

Hey Mr medic that's great.

Both A and B would work fine on the side of big waves. A because of lots of flare and deadrise. B is more like what I had in mind. B would be fine w a flat bottom as well.

The line dwg below the green shows a boat w only a small flared chine section (or flat) but even this much (anti-tripping chine (as it is usually called)) will help considerably.

I think it's easy to see in the line dwg that w/o the anti-tripping chine this hull could catch lots of heavy water moving sideways and act a bit like a bulldozer w it's side causing the lower part of the boat to slow tremendously w little to stop the upper part in it's plunge to leeward ..... probable capsize.

If the flat between the 2 chines is large (or wide) the effective beam in the water can be significantly reduced allowing less wave making resistance for more efficiency .. higher speed or lower power.

Some muli-chine dories are built so that each plank above the bottom is a chine flat so the overall shape is more round than hard angled like the single chine boat.

FF 12-13-2012 06:31 AM

"I'll be watch'in out for those 17' waves while out in my 30' boat."

Its the boats BEAM not LOA vs wave size that may cause a rollover.

A 30 ft boat , perhaps 9 ft beam , its the 10ft waves and bigger you need to be wary of.

Nomad Willy 12-13-2012 10:59 AM

FF,

I suggest you read post #33 by TAD Roberts NA.

Just say'in.

Average or "normal" beams were assumed for the studies made.


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