Help Explaining Why Excess Speed Breaks our Boats

[Marty Gingras]

Hello all,

I need your help.

I have a background in mechanics (years ago I owned and operated a repair shop and boatyard) but am now a managing biologist.

I recently began managing a fisheries research and monitoring program that is boat-intensive.

Our field operation is in bad shape for many reasons, including crazy workload, lack of proper prior supervision, and lack of education.

The current crisis is that we have many broken boats, including a bunch of otherwise good high-quality aluminum boats with damage (broken welds, cracks through the bottom plate) that is clearly attributable use beyond design and/or construction specifications.

We work in a windy area with lots of 2-4ft wind waves and some of these boat can do 40 kts. Some of our boat operators beat the hell out of the boats.

I have instituted a 20 kt speed limit until I can fully understand the issues, and am getting feedback that the speed limit hurts the program because the program is built on speed. The usual assertion is that the operators have lots of experience and are the best judges of appropriate speed. This just ain't so!

Thus, I need to do two things: Understand the issues and explain the issues.

I hope you can help me explain the issues.

Can you give me some equations that explain how shock loads increase with speed or something similar that describes the adverse effects of speed?

I'd also love to learn about policies used by other organizations to address this issue.

Can you help?

Thanks much.

Marty Gingras
Supervising Biologist (Fisheries)
California Department of Fish and Game
Bay Delta Region
4001 North Wilson Way
Stockton, California 95205

Phone (209) 948-3702
email mgingras@dfg.ca.gov

[johnnyv]

Well it's fairly simple really.
The faster you go the harder you hit the water.
The harder you hit the water the stronger your hull needs to be for any given hull type.

As for equations the kenetic energy one works half mass x velocity squared.
Double the speed and you have four times the energy.

[buckknekkid]

After spending a lot of time throttling an Offshore race boat ,my only analogy is that its like having a car accident every 10 seconds for 60 minutes. thats why they break.

[SamSam]

You might find more direct, documented numbers and graphs looking at crash car test results. I would think they would parallel what happens to boats. It's got to be an exponential kind of thing, like double the speed quadruples the forces or something.

The policy I always ran into was if you didn't do what the boss wanted, you got fired. Abusing equipment was not what the boss wanted. Sam

[ted655]

Are they ALL breaking? All the same way, in the same places? All , in spite of who is operating them? All the same boat? Doing rthe same job?They say Lindberg could fly farther on the same fuel others had to land, & on overhauls, his engines always had less wear. Some truck drivers in a fleet of identical trucks NEVER have a problem.
It's obvious to blame speed and that may be a big factor, but I would gather complere & minute details on each boat, all the conditions I could think of. Time, length of operation, water conditions, operator, load & placement, etc. I would track at least 25-30 data inputs on each boat Then I would plot/ chart it on something like Powerpoint.
Welds may be suspect @ construction time OR the welding plan may be wrong for a particular joint. The material may be beyond it's ability. The structural size or spacing may be wrong. What & where is breaking? Are there splits, cracks or wjoint failures? Operators may be keeping the boats at a harmful harmonic level. Are other owners experiencing any problems? It will be a job to gather and match all the data, BUT I bet the answer is there.
Find as many "sames" of all the boats & as many differences and plot them all. See where they cross or paralell and the reason your boats break will read like a cheap novel

[Raggi_Thor]

Dynamic pressure = some constants x speed ^ 2
If you double the speed you have four times as high pressure.

[tom28571]

The energy equations above are correct but the actual forces are likely to be much greater. At high speed the boats will be leaping off waves and slamming down into the next one. Great fun for macho jockies if you don't own the boat. This is unpredictable in a specific case and you either need specially constructed boats (deep V hulls built for offshore work) or more discipline on the operators. The latter is the most reasonable path.

[Racemore]

After spending a lot of time throttling an Offshore race boat ,my only analogy is that its like having a car accident every 10 seconds for 60 minutes. thats why they break.

What he said.I think you should be able to find a better boat that can last better than the ones you have.If you have to have aluminium you need a RIB like the Coast Guard is using.



Jack who???:D

[Loveofsea]

Repower with smaller engines. Don't allow the hull to go fast enough to self-destruct.....

prop the new engines for longevity~

[Guillermo]

Marty,
What is the deadrise of those boats? Are they designed (and so scantled) for offshore or inland operation? Could you provide us with more info on them? Maybe also some photos?
Cheers.

[Poida]

G'day Marty, all the reasons you quote there are probably all the reasons why the last bloke quit the job

I run a maintenance department and Tom hit hit the nail on the head, if they don't own it they don't respect it. In our case we keep fixing it. Keeps me in a job anyway.

Loveofsea's suggestion could run into a safety hazard. As you are working in a windy area, you have to make sure the engine power is enough to bring you back to shore in a heavy wind. Unfortunately that means you have extra speed without the wind and even more when you are travelling with it.

You didn't say what size the boats are. Can you get any new ones made of steel.

There are lots of cluey people on this forum and I would suggest you provide photos sizes etc. and you could probably get some good advice pertaining to correct engine size, optimum speed etc.

Could also be that the boats were built under the quotation system ie the manufacturer with the lowest quote won the job.

How old are they, can you get back to the manufacturer and get him to fix them and advise you wont be buying his boats next time if he doesn't.

Best of luck
Poida

[water addict]

Aluminum is very poor material in fatigue. If the boats are old, and have been run hard, and have cracks, most likely they are shot.
If you have the budget, sounds like you'd be better with some frp boats.
If you need to stick with the old boats, you will have to baby them.

Loads are only half the equation. The structural adequacy is the other. Sounds like you need stronger boats if you have experienced operators telling you that they aren't over-reaching the boats' speed capacity and they are coming back cracked. FRP is usually far superior in fatigue than aluminum if designed and built well.

[SailDesign]

Marty,
Talk to the manufacturer of the boats - ultimately it is he who is responsible if the boats canot hold together at the design speed.
You say "they can do 40knots", but is that what they were _designed_ to do? Are the engines on them bigger than mfr's specs?
Talk to the guy, make him responsible for his product.
Steve

[messabout]

Determine from the manufacturer whether they approve of 40 knot operation. I doubt that they will agree to that kind of abuse. Why do you need to go so fast ?? Are the operators running drugs are or they collecting samples ? How old are the main offenders ? (that'll give you some clues) I'm guessing that you are using fairly small boats with outboards. It is easy to be irresponsible with small boats and big power.

SamSAm has a sure fire solution. Without a seconds hesitation, **** can the guys who abuse the equipment. I have operated a manufacturing facility for many years. I learned the expensive way to put a screeching stop to equipment abuse as well as dangerous or stupid behavior. Dont dismiss the possibility that you may be held responsible for some one getting hurt or drowned, even though the accident was their own fault. Tort cases are really popular these days. Do what you have to do.

[longliner45]

dont be so fast to shitcan anyone ,,,find the root problem and go from there ,,you have time and money invested in the guys,,thier knowledge is worth something ,,,,,maybe its as simple as fatige on old boats ,,,or payload ,,a miriad of guesses,,, they may have good reasons to go fast ,,to get away from weather ,,or to deliver valuabe cargo ,,they are probably just trying to do the best they can ,,,,,youll be alright,longliner

[ted655]

:D Don't throw the babies out with the bathwater. Gather your data, plot it on a graph. You'll see the common thread, THEN act.

[Marty Gingras]

Hello all,

Thanks very much for your comments, questions and suggestions. They have me thinking along a couple of different lines for both the long-term and short-term.

Take care.

Marty

[tri - star]

To Marty Gingras:

" Read 'n Heed ! "
- it's all about...." Speed 'n Fatigue "
(To be posted soon - where ever your " boat jockeys " have coffee.)

You have just received enough info. to get you, half way through
Struc. Engineering 101.
From people with a combined experience of a 1000 yrs or more....
( Good job, guys, this is one of the best threads I've seen here.)

One of the most frustrating aspects of talking " boat " to clients:
Is; that most people live in a " 2 plus 2 = 4 world ".
i.e.
Twice as much carpet - costs twice as much.
Logical to presume...yes ?
Unless your brother - law, owns the store, that is.....
Whereas:
With boats, the forces involved, go up by at least the sq. - and
often by the cube root !
(3 x 3 = 9 and/or 3 x 3 x 3 = 27)

With costs moving up at the same rate of multiplication.
At least.......
...'Tis why a 36' vessel will cost, at least, four to nine times as
much as an 18' boat. Unfortunatly for the people, whom you toil for:
- Maintanance costs, also tend escalate, in a similer manner.......

Most lay people and sad to say, in my experience - many mariners
- have a hard time getting their heads around these Laws of
Physics stated.
Which includs; the guys that you work for.
(Who most likely went for the lowest bid.)
- And also, the guys who are busting up your boats.

You can tell them all: - I said so.
In fact, I will suggest, you pass on this entire Thread on to
both of these groups.

......................

To add my two bits...

In my opinion; welded alum. is over rated, for small vessel fabrication.
In the real world - it often fails to live up to expectations.

I have seen an entire fleet of identical alum. boats, all being
taken out of service, for extensive, major repairs.
(Including the failures, that you describe.)
- All at the same time.
- Note: - I repeat: All at the same time.
These boats; all designed and engineered by a well established
NA firm ?!

As ted655 says,
"......welds may be suspect."
I will go futher; ALL the welds are suspect. As the only weld you
can realy trust - is one that's been X - Rayed.

water addict; however, goes to the heart of the matter.
When he states,
"......very poor material in fatigue."

Boeing considers alum. is maxed out in only 20 yrs.
(So when I book a flight I'm more concerned with the age of the
aircraft - than how cheap a flight I can get.)
Also note:
Planes are subjected to far fewer, point loadings than boats are.
How long does an aircraft last if it hits the water hard ?
......Just once, in a crash landing ?

More to the point, how many planes are welded together ?
Rivets cause less local stressing - and are far easier to
trouble shoot.

Also, you will see much less electroiysis damage to commercial
aircraft....If any. As the operaters, wisely, keep them as far from
sea water as possible.

Given the above:
20 yrs is way, too optimistic to consider. In my book - for a small
craft's life expectancy. Harshly treated, that has been
constructed in alum.

As the fleet, I mentioned, were showing " catastrophic failures "
- within only a season or two.
So sight un - seen, I'd suggest that your boats will be lucky to
go - even five years with out, serious maintance concerns.

Almost any other material, commonly used in boat building, has
better resistance to fatigue.
Including: Steel, F. Glass and " Old School "...Epoxy / Wood.

I do not envy the tasks that stretch before you.

' Regards.

[ALowell]

I worked many years for a little sailing club that bought outboards that were way to big. They always said they got more power for safety. I'd say just the opposite -- less power means more safety! Who would get a Corvette for their kid and claim it's safer? Get engines big enough to get the boat on plane, plus a little more for heavy loads, and make sure you have high thrust props (low pitch) for load carrying ability. Unless they are traveling 10+ miles a day, anything over 20 mph is too much. 40 is WAY too much.


~ ALowell

[FAST FRED]

"Boeing considers alum. is maxed out in only 20 yrs.
(So when I book a flight I'm more concerned with the age of the
aircraft - than how cheap a flight I can get.)"

There are many many THOUSANDS of commercial aircraft that are far older than 20! years old in fine condition.

The USAF is using B-52's built in the 1950's today , and there is NO plan to replace them before 2040.

Having flown DC-3's built long before I was , I'm sure 20 years is too short a useful commercial life.

How long the new Plastic aircraft will go IS up to consideration.

FF

[water addict]

"Boeing considers alum. is maxed out in only 20 yrs.
(So when I book a flight I'm more concerned with the age of the
aircraft - than how cheap a flight I can get.)"

There are many many THOUSANDS of commercial aircraft that are far older than 20! years old in fine condition.

The USAF is using B-52's built in the 1950's today , and there is NO plan to replace them before 2040.

Having flown DC-3's built long before I was , I'm sure 20 years is too short a useful commercial life.

How long the new Plastic aircraft will go IS up to consideration.

FF

It's not the age, it's the number of loading cycles and load magnitude that counts - as you probably know. B-52's largely sit around doing nothing. A commercial plane that is in almost constant use, gets loaded and unloaded a lot more in a given time frame. I think it was Air Alaska plane operating in Hawaii doing shuttles betweens the islands that had part of the fuselage rip off in flight. Attributed to metal fatigue as the plane did many more than typical take-off / landings because the flight times were so short.

In general AL is not great in fatigue. It can be worked around if careful. Aye there's the rub. Careful.

[charmc]

Military aircrews are required to train on the aircraft to maintain proficiency, so B52's fly more than you think.

Military aircraft can undergo an overhaul process, actual more of a remanufacturing, that rerates the airframe to "zero hours" certification, meaning it's considered to be like new. Complete disassembly and exposure of bare metal, magnafluxing, etc., etc. Mega-costly, close to the original cost of the aircraft, so only governments can afford it. There's a somewhat less costly thorough overhaul procedure for commercial aircraft, still pretty expensive, but less than the cost of replacement. Forget it for boats, unless you're Larry Ellison or Paul Allen...:p :D

[tri - star]

Sorry FAST FRED,

the new metal " Foreverum " that the military received from the Alians
has not yet been released to the generel public yet...
Mostly due to the fact that nobody has found a way to drill holes in it.
Or find a saw that can cut into it.......

It is highly unlikely that all the pieces of alum. in an old aircraft,
are original - to the original airframe.

A great advantage to rivets, is that it is Common Practice to replace
suspect panels and/or rivets - with planes.
This is partly, why they " seem " to live so long.

As charmac says,
" ...aircraft...undergo an overhaul process...more of a remanufacturing..."

For very good reasons. As stated by water addict,
"....it's the number of loading cycles..."

Because, when a small US airline was not dilligent in inspecting their alum.
aircraft skin - of one of their planes...
As also stated by water addict,
"....had part of the fuselage ripped off....attributed to metal fatigue..."
A woman lost her life in the incident.

To water addict:
in these forums we often have to speak in wide generalities.
So I agree - loading cycles are key. To predict in years or months is hard.

But exposure TIME - has a significant and very unpredicable contribution.
Not incidental, that the aircraft you refer to, also operated in a
maritine local.

Well I remember, the sad sight of a very wealthy man, staring at the
pin holes spreading across the body of his beutiful Aston Martin G.T.
" Handmade. in aluminium..." he was heard to mutter, almost
drowned out, by the crash of the surf by his sea side cottage.

In summation:
When you combine - salt - water - unknown welding skills - with an
unpredicable, amount of loading cycles - and impact shocks....!

What value would you place on these boats - when Marty is told
to sell them ?

[ALowell]

Has anyone considered that these are BOATS we're talking about here? They're not multi-million dollar spaceframes, nor are they built light enough to fly. Aluminum boats have been used for hard-working utility craft for decades because they are cheap, light, and stronger than comparable materials. Everything is a compromise and as such, we should remember that FRP and wood have their drawbacks as well.

For example, mainers Down East swear by aluminum boats for bouncing on island rocks during loading because alum. bends but doesn't break. Can you say that for FRP? It depends on the application what material should be used. Comparing utility punts to Boeing 707's is like comparing your wheelbarrow to an Enzo Ferrari.

Let's not get carried away with the academics!

~ ALowell

[charmc]

Correct, we did digress a bit with the aircraft discussion. I would say that does apply to aluminum high speed commercial vessels, like hydrofoils and fast ferries.

I too have seen very old aluminum runabouts still operating far beyond 20 years. It comes down to conservative design, good construction and maintenance ..... and sensible operation.

[ALowell]

One thing they do Down East is layer the underwater portion of the hull with 4-5 layers of fiberglass for reinforcement against rocks. This is easy to do and creates a very long-lived work boat.

If you are going to buy new alum boats for institutional use, I would recommend this approach - especially for riveted boats - but only if weight is less of an issue.

~ ALowell

[SamSam]

One thing they do Down East is layer the underwater portion of the hull with 4-5 layers of fiberglass for reinforcement against rocks. This is easy to do and creates a very long-lived work boat.


~ ALowell

I don't understand. You say that above and that below. They don't seem to be compatible.

"For example, mainers Down East swear by aluminum boats for bouncing on island rocks during loading because alum. bends but doesn't break. Can you say that for FRP?"

[longliner45]

the big boats in maine are jc boats and bruno stillman and one or two more I cant think of right now ,,,all glassers

[speedboats]

The question is incomplete...

How long are the boats, this will have an effect as to wheather of not they can span shorter wavelengths.

What is the deadrise? As pointed out about speed compounding the load / shock issues, the greater the deadrise, the lesser the 'impact'

I assume at the speeds you are suggesting that they are planning hul forms?

Alot of it has to do with build quality and choice of materials, as pointed out earlier, are the boats operated inside their design parameters? We build alot of high speed boats, alot of them into the commercial sector, and capable of around 45 to 65 mph. Payload of around 12 to 18 passengers and at rest displacement of 5000 and 8000lbs (depending on the boat, heavy ship), and an expected life of 5 years (another 5 if the maintenance schedule includes something similar to a 'zero hour'. But higher maintenance is required during this period). Further more, we build primarily out of Aluminium.

As pointed out here, alot of jockeys simply don't care about someone elses gear. That is why the boats must be built and maintained with the 'lowest common denominator' in mind, or in other words for the biggest ******** on staff. Believe me, if it can't be wrecked, they'll find a way, so this must be remembered.

You say your boats are breaking, can the maintenance program extend to gradual replacement of the fleet? What parts are failing? Alloy is a hasstle to reweld once it's gone into service, real care must be taken to clean the area well before hand, even then in some cases it can become a 'best effort' attempt. Most steel workers I've seen atempt a repair have botched the job, making the owner believe they have the wrong material for their boats.

Sorry, but you guys are starting to sound like the local cops, more speed bigger mess, (true-ish), but speed kills (not likely). For speed to kill you must first have an accident (the old addage... it wasn't the fall that killed him, just the sudden stop at the bottom). You need to identify what is 'killing' the boat. If speed is a requirement of the job, then you need to soften the impact on the boat in another manner (deaper deadrise, narrower boat, less weight in the bow, etc..)

My 2 cents worth...

[ALowell]

the big boats in maine are jc boats and bruno stillman and one or two more I cant think of right now ,,,all glassers

You are right, however these are not the ones they use for beaching on islands. When they do go ashore, they use alum boats, often towed behind the glass lobster boats for just this occasion.

FRP reinforcement of alum boats gives you the advantages of both materials. If you used FRP alone, it would crack and sink. If you use alum alone you'd have a dinged up boat that would add running drag.

An acquaintance of mine who makes a business of beaching on rocks for puffin tours does exactly what I'm describing. He has spent decades doing this and he knows what works and what doesn't.

~ ALowell