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h2orescuemedic 11-30-2012 08:45 PM

length vs beam and trailer able
 
How come all the trailer able boats that have a 9 foot to 10 beam are under 28 foot. Why don't they make a 32 to 36 foot long boat that is only 9 ft wide? I would think you could add a few feet to the length and have a very cool trailer able boat.

bfloyd4445 11-30-2012 10:02 PM

Quote:

Originally Posted by h2orescuemedic (Post 116401)
How come all the trailer able boats that have a 9 foot to 10 beam are under 28 foot. Why don't they make a 32 to 36 foot long boat that is only 9 ft wide? I would think you could add a few feet to the length and have a very cool trailer able boat.

I think you need a wider beam on the longer lenghts for stability. To narrow and it can be treacherous in rough water

GFC 11-30-2012 11:28 PM

Rescuemedic, first if all, thank you for keeping boaters safe. You're a hero.

I'm not sure why you want a 32' boat with a 9' beam. On most highways once your load is over 102" wide you need to have trip permits, flags, oversize load banners, etc. So if eliminating the requirement for all of those things is your goal, and you want to be legal, you'd best stay at 8'6" or less in beam.

I had a 330 Sundancer with a 11'5" beam and towed it all over the place. It's not much of a hassle getting the permits (many states sell them online) and then you don't have to worry about towing as long as you stick with freeways. If you get off the freeways onto 2 lane roads you're supposed to have pilot cars, but I've towed on 2-lane roads without them and have never been stopped..

Nomad Willy 12-01-2012 12:03 AM

Most people like wide boats w LOTS OF STABILITY. They think a narrow boat will tip over. Just look at the typical dinghy.

The narrow boat takes much less power and is FAR more pitch stable than a wide boat. Wide boats have 2 speeds .... fast and really slow. They wallow their bows high in the air requiring lots of power at 7 to 17 knots. Nice speeds to be going especially when it a bit rough. And when it is a wide boat will pound worse and porpoise much more.

medic,
Do it. Cut a boat in half at the best spot and add more boat. Make it as long as you want. I think it will be better in all respects however on the road you may drag the stern on driveways and such. Quite a bit of work though but one can find these boats really cheap. And then you can put the engine where it belongs ... on the transom. With the outboard outboard engine mounts the engine is too far aft. They are just a quick and dirty modification.

markpierce 12-01-2012 12:26 AM

It's not unknown for ships to splice an additional section to the hull, lengthening the ship but maintaining the same beam, and offering more accommodation. Some of the ships I've sailed on (as a passenger) had this "operation."

sunchaser 12-01-2012 10:45 AM

bfloyd says:
"I think you need a wider beam on the longer lenghts for stability. To narrow and it can be treacherous in rough water"

Really, now that you are a designer, what treacherous narrow boats are you referring to? For starters, there are some are some lobster boat guys that would beg to differ. Sailors too.

RT Firefly 12-01-2012 11:03 AM

Greetings,
Mr. sunchaser.... +1

bfloyd4445 12-01-2012 12:31 PM

Quote:

Originally Posted by GFC (Post 116457)
Rescuemedic, first if all, thank you for keeping boaters safe. You're a hero.

I'm not sure why you want a 32' boat with a 9' beam. On most highways once your load is over 102" wide you need to have trip permits, flags, oversize load banners, etc. So if eliminating the requirement for all of those things is your goal, and you want to be legal, you'd best stay at 8'6" or less in beam.

I had a 330 Sundancer with a 11'5" beam and towed it all over the place. It's not much of a hassle getting the permits (many states sell them online) and then you don't have to worry about towing as long as you stick with freeways. If you get off the freeways onto 2 lane roads you're supposed to have pilot cars, but I've towed on 2-lane roads without them and have never been stopped..

sundancers are great boats, i even took my 270 1989 da to lake tahoe twice.

Nomad Willy 12-01-2012 12:48 PM

Consider;
If you add a section of hull to a boat that section adds stability. Quite a bit. So when you lengthen a boat the beam remains the same and the length to beam to length ratio is higher so most would consider it a narrower boat yet it has increased stability. You could consider the added section to be water wings.

The Alaska Marine Highway lengthened two ferries about 50' (I believe). I would love to know but don't know how that changed performance. I think they kept the same engines.

bfloyd4445 12-01-2012 01:12 PM

Quote:

Originally Posted by manyboats (Post 116579)
Consider;
If you add a section of hull to a boat that section adds stability. Quite a bit. So when you lengthen a boat the beam remains the same and the length to beam to length ratio is higher so most would consider it a narrower boat yet it has increased stability. You could consider the added section to be water wings.

The Alaska Marine Highway lengthened two ferries about 50' (I believe). I would love to know but don't know how that changed performance. I think they kept the same engines.

The width of beam is increased as well as the length for proper stability. If you lengthen a boat and keep the beam the same it would only improve stability if the beam were already much wider than it should be for the current length. I've had experience with a long narrow boat and that thing was dangerous in a beam sea. it was very, what's the correct term, roily. I think the Alaskan ferries in your example was already of a very wide beam to facilitate loading and likely too square so the additions of 50 feet to the hull would likely bring the beam to length ratio back into the realm of correct proportions for stability. Can you imagine trying to handle a boat configured like a pudgy rectangle?

no, i cannot believe that making a skinny boat longer will improve its stability

theran5317 12-01-2012 01:30 PM

I'm thinking there is a lot more to this question than just the beam.

All the mass calculations related to Center of Gravity vs Center of Buoyancy that are affected by the weight distribution in the boat.

bfloyd4445 12-01-2012 03:24 PM

Quote:

Originally Posted by theran5317 (Post 116592)
I'm thinking there is a lot more to this question than just the beam.

All the mass calculations related to Center of Gravity vs Center of Buoyancy that are affected by the weight distribution in the boat.

absolutely! Height, width, length ratio of beam width change in relation to length overall, waterline length, tons displacement, ....geezz...could go on and one. Ok out there, what's the answer u engineer types? I guess many of the variables could be dropped out of the equation as they have little effect for standard trawler configuration.
Ever heard the term, she handles like a pig? Heard this often used to discribe an under powered wallowing vessel. Are trawlers pigs?

sunchaser 12-01-2012 03:52 PM

bfloyd says :
"absolutely! Height, width, length ratio of beam width change in relation to length overall, waterline length, tons displacement, ....geezz...could go on and one."

You havn't come up with the important ones yet, keep guessing.

Tad Roberts 12-01-2012 04:06 PM

It gets complex.....remember we are talking about a boat shaped object. Most above are talking about transverse stability, but remember longitudinal stability is also an issue.

Transverse stability is dependent on a number of factors. The displacement(V), the center of buoyancy (all underwater volume)(B), the vertical center of gravity (the vessel, her crew, fuel, water, etc)(G), and the waterplane area and distribution (Iw). There's another point involved called the metacenter (M), it's mythical (an invention) and it's the point around which the boat is said to rotate when heeling.

The distance between G and M is called GM, and it's length (in feet or metres) is another basic measure of stability.

When a hull is floating level and upright the center of buoyancy (B) is on the centerline somewhere below the waterline. Not far below if the hull is a shallow barge, a long way below if its a deep and narrow type. G is (hopefully) also on centerline somewhere above B. In modern powerboats it's well above the waterline, in ballasted sailboats it's close to or slightly below the waterline. M must be above G for the hull to be positively stable.

As the hull heels B moves to the low side and the area of the waterplane changes shape (depending on hull form). In a flat shallow barge B moves quickly while in a narrow and deep hull B moves slowly. If you visualize B as an upward force and G as the downward force you see that as long as G stays on the centerline and B moves to one side there is a righting force created between the two.....Forcing them back into line(upright).

The distance (in feet or metres) between those opposing forces is called the righting arm (RA or GZ). The RA multiplied by V (displacement) is called the RM, righting moment. Most stability curves are of RA values.

You can increase stability by lowering G or raising M. Lower G by adding ballast on the keel or removing weights up high (dinghy on the roof, etc). Raise M by changing the shape of the waterplane or the displacement.

So adding length might change the waterplane if new volume is greater than the structural weight added (boat floats higher). The added displacement will increase RM, righting moment, because that's our RA multiplied by displacement. But unless we make the boat wider RA will not change. So it will take more force to heel the boat, but she will capsize at the same heel angle as the shorter boat........

bfloyd4445 12-01-2012 04:32 PM

Quote:

Originally Posted by Tad Roberts (Post 116621)
It gets complex.....remember we are talking about a boat shaped object. Most above are talking about transverse stability, but remember longitudinal stability is also an issue.

Transverse stability is dependent on a number of factors. The displacement(V), the center of buoyancy (all underwater volume)(B), the vertical center of gravity (the vessel, her crew, fuel, water, etc)(G), and the waterplane area and distribution (Iw). There's another point involved called the metacenter (M), it's mythical (an invention) and it's the point around which the boat is said to rotate when heeling.

The distance between G and M is called GM, and it's length (in feet or metres) is another basic measure of stability.

When a hull is floating level and upright the center of buoyancy (B) is on the centerline somewhere below the waterline. Not far below if the hull is a shallow barge, a long way below if its a deep and narrow type. G is (hopefully) also on centerline somewhere above B. In modern powerboats it's well above the waterline, in ballasted sailboats it's close to or slightly below the waterline. M must be above G for the hull to be positively stable.

As the hull heels B moves to the low side and the area of the waterplane changes shape (depending on hull form). In a flat shallow barge B moves quickly while in a narrow and deep hull B moves slowly. If you visualize B as an upward force and G as the downward force you see that as long as G stays on the centerline and B moves to one side there is a righting force created between the two.....Forcing them back into line(upright).

The distance (in feet or metres) between those opposing forces is called the righting arm (RA or GZ). The RA multiplied by V (displacement) is called the RM, righting moment. Most stability curves are of RA values.

You can increase stability by lowering G or raising M. Lower G by adding ballast on the keel or removing weights up high (dinghy on the roof, etc). Raise M by changing the shape of the waterplane or the displacement.

So adding length might change the waterplane if new volume is greater than the structural weight added (boat floats higher). The added displacement will increase RM, righting moment, because that's our RA multiplied by displacement. But unless we make the boat wider RA will not change. So it will take more force to heel the boat, but she will capsize at the same heel angle as the shorter boat........


whew. but thats almost exactly what i said the diference being u know what i am talking about and i only know from my experiances at the helm. I would love to see the math. Thank you very much for the explanation. I gotta think about ewhat u posted...distance between G and M????

Tad Roberts 12-01-2012 06:08 PM

1 Attachment(s)
This might help.......

Attachment 14389

bfloyd4445 12-01-2012 06:10 PM

Quote:

Originally Posted by Tad Roberts (Post 116657)
This might help.......

Attachment 14389

Thanks. I get the picture.
from your picture it is obvious a narrow beam in relation to length is gonna cause stability problems

RT Firefly 12-01-2012 06:36 PM

Greetings,
Slightly tardy welcome aboard Mr. Roberts. Um, your vessel wouldn't happen to be named "Reluctant" would it?

theran5317 12-02-2012 12:09 AM

Quote:

Originally Posted by bfloyd4445 (Post 116658)
Thanks. I get the picture.
from your picture it is obvious a narrow beam in relation to length is gonna cause stability problems


I'm thinking that a well balasted keel, would make for quite a long righting arm, and make the boat more stable.

https://www.businessupnorth.com/images/virginia2.jpg

Tad Roberts 12-02-2012 04:12 PM

Quote:

Originally Posted by bfloyd4445 (Post 116658)
from your picture it is obvious a narrow beam in relation to length is gonna cause stability problems

Well.....perhaps.....But we recently did a stability study over on the Woodenboat forum of a Bolger Windemere design. This is a flat-bottomed plywood box about 30' by 8', draft is a bit more than a foot. Her stability was surprisingly good, more than expected for a sheltered water cruiser. Part of the reason for that is her relitivly high sides, and also no double-decking or raised cabin, the house is set down in the hull. Stability is as much dependent on height vs beam as anything....Low is good, high (tall or double-decked) is less good.....

Tad Roberts 12-02-2012 04:19 PM

Quote:

Originally Posted by theran5317 (Post 116741)
I'm thinking that a well balasted keel, would make for quite a long righting arm, and make the boat more stable.


Be careful with that idea.....it might be good up to a point. If you add ballast to a boat not intended to have it, she will float deeper in the water. This means the rail goes under water sooner as she heels, which could cause early flooding at a lower heel angle. Usually peak stability is just as the rail (deck edge) goes under water.

Yes, adding ballast to lower G is increasing stability, but whether the lower capsize angle is worth it is a question.....

Nomad Willy 12-02-2012 05:01 PM

Most designs that are narrow it seems are priority wise leaning toward more efficiency and weight even for a full disp hull is of great importance. The most common rule of thumb for determining the amount of power required for a disp hull is weight/power. More or less directly proportional. So we see most narrow boats built low w little top hamper.

So ballast has it's price.

bfloyd4445 12-02-2012 05:39 PM

Quote:

Originally Posted by theran5317 (Post 116741)
I'm thinking that a well balasted keel, would make for quite a long righting arm, and make the boat more stable.

https://www.businessupnorth.com/images/virginia2.jpg

Yes but thats another part of the equation that was taken into consideration when the center of gravity was calculated right?

oh, and veyr nice boat

h2orescuemedic 12-05-2012 11:20 AM

First thanks Tad, That was very help full. I did a little more looking but you got me in the right spot to look. And the right frame of mind too. For some reason when i made this post i was looking at the boats for sale. When I found the off shore "race boats" the 100mph or +, 2 and 3 engine boats and some of them are very long even 38 to 40 ft but only 11 feet wide. ....... I know just because it fits on a trailer and its a boat. its not the same lol I do understand but just got the wheels turning upstairs a bit.

Until i retire the only way i can justify a trawler or any other boat is I have to be able to put it on a trailer I can pull with a 1 ton truck. One of the down sides to living in the middle of the USA in Missouri.

Thanks again guys.

bfloyd4445 12-05-2012 10:02 PM

Quote:

Originally Posted by h2orescuemedic (Post 117550)
First thanks Tad, That was very help full. I did a little more looking but you got me in the right spot to look. And the right frame of mind too. For some reason when i made this post i was looking at the boats for sale. When I found the off shore "race boats" the 100mph or +, 2 and 3 engine boats and some of them are very long even 38 to 40 ft but only 11 feet wide. ....... I know just because it fits on a trailer and its a boat. its not the same lol I do understand but just got the wheels turning upstairs a bit.

Until i retire the only way i can justify a trawler or any other boat is I have to be able to put it on a trailer I can pull with a 1 ton truck. One of the down sides to living in the middle of the USA in Missouri.

Thanks again guys.

I don't think it takes much to get a permit to go over nine feet wide. I know in California it dosent

Al 12-05-2012 10:44 PM

Eric
As to the Alaska Ferries being extended and gaining speed. Yes, As I recall, the extension increased speed by almost a full knot at original setting.
In conversation with a now decested old tug boat master who knew engineers on the ferries, the increase in hull speed allowed the ferries to reduce RPM allowing maintaing the schedule speed (Fexablility when required, like making up for lost time during incidents) This was during the 70's fuel crunch when saving fuel was a factor. The Malaspina on the Bellingham run saved tons of fuel on each voyage. I believe that system was then running PS300 Lt Fuel (actually heavy fuel, but did not require quite the heat to make it flow from the tank to engine) Currently the system is running pure diesel.

Tad- On a earlier thread, I had opened a discussion on ballast as it related to vessel rolling. You echoed knowledgeable posters with your diagram and explanation. The conclusion of that discussion has me convinced to add ballast. The situation is locating ballast at a palatable cost. I have discarded the thought of using 60# bags of cement/sand mix (contained within plastic garbage bags till atmospheric moisture set them hard) and now am budgeting for 60# commercial lead cannon ball trolling weights. (almost $2.00 per #) How many? Darn'ed if I know, just keep adding till results are gained!
Thanks for the refresher.

A.M.(Al) Johnson-Ketchikan
27' Marben

FF 12-06-2012 07:03 AM

For most trailering folks staying under 8ft 6 ,no permits, is the easy solution.

An allowed 40 ft trailer length will allow a pretty large boat , but many states limit the overall length of the combination to 65ft. A few are at 75 , a few in the NE are 55.

YES ,commercial trucks go way longer , but non commercial IS limited.

For our use we built up a 35 ft bus conversion (reinforced frame , 400hp engine) and the trailer LOA limit caused us to select a 23 ft boat , remember the fuzz will be tape measuring to the end of the tilted up out-drive.

There is also some space required at the trailer ball end to be able to go round corners.

As it is impossible to back a trailer that can not be seen, the simple solution is a front mounted ball hitch , that makes launch recovery a snap.

Works on cars and trucks too!

jeffnick 12-06-2012 11:58 AM

Quote:

Originally Posted by h2orescuemedic (Post 116401)
How come all the trailer able boats that have a 9 foot to 10 beam are under 28 foot. Why don't they make a 32 to 36 foot long boat that is only 9 ft wide? I would think you could add a few feet to the length and have a very cool trailer able boat.

Why don't 'they' make long narrow trailerable boats?
It's not a question of stability or seakeeping or performance, it's because nobody would buy them. Side by side not one American in a million would pick the skinny boat, especially if his wife and kids had anything to say about it.

Things are different elsewhere.
Narrow boats for sale, Canal boats for sale, narrowboats

Nomad Willy 12-06-2012 12:13 PM

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.

Tad Roberts 12-06-2012 12:20 PM

Quote:

Originally Posted by Al (Post 117697)
Tad- On a earlier thread, I had opened a discussion on ballast as it related to vessel rolling. You echoed knowledgeable posters with your diagram and explanation. The conclusion of that discussion has me convinced to add ballast. The situation is locating ballast at a palatable cost. I have discarded the thought of using 60# bags of cement/sand mix (contained within plastic garbage bags till atmospheric moisture set them hard) and now am budgeting for 60# commercial lead cannon ball trolling weights. (almost $2.00 per #) How many? Darn'ed if I know, just keep adding till results are gained!
Thanks for the refresher.

A.M.(Al) Johnson-Ketchikan
27' Marben

I don't suppose you have a foundry up there? Pig iron is about the cheapest/densest thing currently (bought at retail prices) available. Common cement bricks from the building supply (not hollow ones) will work if you have space. Steel flat bar cut into sections and painted with Primacon will stow nicely. The advantage with using steel is that it's easy to drill and bolt down. Here we have a recycler that will sell scrap lead (not perfectly clean) for about a dollar a pound.....

Whatever you use make sure it absolutely cannot move even if the boat is upside down.....

bfloyd4445 12-06-2012 03:37 PM

Quote:

Originally Posted by manyboats (Post 117783)
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.

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

Nomad Willy 12-06-2012 04:33 PM

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?

Tad Roberts 12-06-2012 04:38 PM

Quote:

Originally Posted by bfloyd4445 (Post 117811)
I wonder what would happen to get hit on the beam with a large wave in a 8.5 foot wide 40 foot boat?

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.

bfloyd4445 12-06-2012 05:00 PM

Quote:

Originally Posted by manyboats (Post 117816)
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?

the 36' one of course......hummmm,:facepalm: 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.

Nomad Willy 12-06-2012 06:09 PM

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?

CPseudonym 12-06-2012 06:30 PM

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.

h2orescuemedic 12-06-2012 06:46 PM

Quote:

Originally Posted by Al (Post 117697)
and now am budgeting for 60# commercial lead cannon ball trolling weights. (almost $2.00 per #)

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.

h2orescuemedic 12-06-2012 07:02 PM

Quote:

Originally Posted by jeffnick (Post 117780)

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.

Al 12-06-2012 09:52 PM

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

CPseudonym 12-06-2012 10:03 PM

Quote:

Originally Posted by Al (Post 117868)
your suggested fry pan. Thoughts? AMJ

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

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.


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