length vs beam and trailer able

manyboats said:

Jeff,
Boats were narrow in the past mostly because they were easily driven when narrow and high power engines were not available. It's hard for me to believe most all boats are still wide (including my own) the way people complain about fuel consumption. And people don't like "tippy" boats ... even yachtsmen. Don't see any narrow inflatables. Actually I think there is one that is fairly narrow but I've never seen one.

But if your'e happy at 6 knots wide can be driven quite easily too ... almost as easily as narrow. And if my own Willy were widened to 12' beam my present engine would not need replacing and for all practical purposes Willy's not overpowered.

But if you get even close to hull speed narrow = easily driven.

Click to expand...

I wonder what would happen to get hit on the beam with a large wave in a 8.5 foot wide 40 foot boat?

bfloyd4445,

I'll answer your question w another question since the situation you presented is vague. Light boat heavy boat high CG low CG wct ect ect. But I'm sure the answer to your question would have more to do w hull shape and CG than beam.

If there was an 18' canoe w a 40" beam and a stretched version of the same boat that was 36' long and someone asked you to stand on the gunnel of one of them which one would you choose to stand on?

bfloyd4445 said:

I wonder what would happen to get hit on the beam with a large wave in a 8.5 foot wide 40 foot boat?

Click to expand...

First of all what's a "large wave"? Is it 3' high or 16' high?

Capsize studies in wave tanks have shown that, if a vessel is laying beam to the sea, a wave with a height (trough to crest) approximately 30% of her length will roll some vessels some of the time. With waves of 60% vessel length, all (of the models tested) will roll every time. So, in theory, a wave of 24' will roll your 40' boat. But much depends on frequency (crest to crest) or steepness of the waves. I've been in huge waves in the open Pacific but the crests were 1/2 a mile apart.....not really steep enough to capsize anything.

I've studied this a fair bit. And the reality is that few recreational boats are lost in North America due to capsize in waves. Most often capsize is due to loads shifting or downflooding......The motor quits and a wave comes over the stern, a combination of downflooding and free surface effect.

manyboats said:

bfloyd4445,

I'll answer your question w another question since the situation you presented is vague. Light boat heavy boat high CG low CG wct ect ect. But I'm sure the answer to your question would have more to do w hull shape and CG than beam.

If there was an 18' canoe w a 40" beam and a stretched version of the same boat that was 36' long and someone asked you to stand on the gunnel of one of them which one would you choose to stand on?

Click to expand...

the 36' one of course......hummmm, i think i see what your getting at. I'm useing my experiance in narrow beamed boats which tended to be very tippy compared to the same lenght style boat with wider beam. Even though a wider beam will not be affected as much by large loads shifted to port or starboard stability in a heavy sea may in fact be superior with the narrow beam. There would be less surface area for the breaking wave to impact on a longer vessel with narroe beam.

TAD wrote;
"The motor quits and a wave comes over the stern" No big surprise here as many boats look more like a Jacuzzi or a hot tub than a boat in the stern.

Also,
"And the reality is that few recreational boats are lost in North America due to capsize in waves" No surprise here either as almost all boats are wide. And beam = stability .. all other things being equal. And of course they never are but people think they KNOW wide is stable and safe and narrow will tip over. So people buy wide boats w lots of power .. power for safety of course.

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?

I think the percentage of boat length to wave height was based on a boat laying dead still in a beam sea Eric. The percentage would not apply to a vessel making headway. I may be confusing it though too.

Al said:

and now am budgeting for 60# commercial lead cannon ball trolling weights. (almost $2.00 per #)

Click to expand...

You can do what I do down in Missouri. Call around and find a recycle place and ask them if they will sell the scrap they take in. I got a local scrap yard that well sell lead to me at 0.75 cents a LB. We buy if for Scuba dive weights and fishing weights. Take and old cast iron skillet and fish cooker add your favorite drink and a little time, it won't take you long to get all the weight you need. scrap iron is 0.35 a LB. I picked up 10 ft of rail road track that weights about 90lb a foot, I have cut it up use it from time to time as weight for the tractor implements. We got a lot of guys in this area that race stock cars and they use big blocks of lead weight to off set the CG of the car you just need a few of them to melt down.

jeffnick said:

Narrow boats for sale, Canal boats for sale, narrowboats

Click to expand...

wow them are skinny boats, its like the one guy said before no wife or kids would ride in that after seeing the wider boats.

I have looked for boats like yours in your pic and can't find any when searching... got any tips on how you find one like yours. would you have any pics of the inside lay out? i could look at.

Water Rescure- Hummm. Living on an island far away from trains and no scrap yards, leaves me with the trolling leads to this point. Even though the cost is high, one can purchase one at a time. Placing them in bread baking pans will contain them. The other thought was using used zincs from commercial boats. The yard piles them up on removal and eventually they will ship 55 gallon drums of these south. I suppose they would melt easy enough, in your suggested fry pan. Thoughts? AMJ

Al said:

your suggested fry pan. Thoughts? AMJ

Click to expand...

Plumbers used to melt lead in cast iron kettles, no reason a pan wouldn't work fine too.

CPseudonym said:

Plumbers used to melt lead in cast iron kettles, no reason a pan wouldn't work fine too.

Click to expand...

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

manyboats said:

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?

Click to expand...

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.......

Tad Roberts said:

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.......

Click to expand...

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.

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.

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.

manyboats said:

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.

Click to expand...

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?

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.

manyboats said:

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.

Click to expand...

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

i still like pictures better

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.

"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.

FF,

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

Just say'in.

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