1. ## Bottom strength

So with all this discussion on bottom strength got me thinking...

If all the material used is the same quality...which one is "stronger?"

1/8" on a 2000 lb boat?
3/16 on a 3000 lb boat?

supposedly 3/16 is 1.5 times stronger than 1/8, right?

Kinetic energy = Mass x Velocity

2000 lb (907 kg) * 30 mph (13.4112 m/s) = 81566 Joules
3000 lb (1361 kg) * 30 mph (13.4112 m/s) = 122394 Joules

122394 / 81566 = 1.5

so, theoretically, the 3000 lb boat has `1.5 times the energy.

Which bottom is stronger?

How bout mine...

1/2" on a 2100 lb boat....Thanks River Wild

Before the stomp grate was installed. You dont want to know how big a rock that mark was from!

thoughts?

2. Originally Posted by c-bolt
thoughts?
I say with 1/2" you win in the strength department...

I can't help but notice, where's the stomp grate?...

3. Originally Posted by tjm
I can't help but notice, where's the stomp grate?...

4. While I agree with your premise... adding thickness doesnt necessarily add strengh if the boat ends up heavier in the end, one needs to also factor in the structure inside, which adds a great deal of the strenght (and weight as well) I guess to illustrate my point...

If you laid an 8 foot piece of that 1/2" aluminum and only braced it on each end with a structural piece, and right beside it an identical 8 foot piece of 1/2" and added only one additional structural support in the middle of it. Then took a big block V8 motor and dropped it in the middle of each piece from a height of say 3 foot, which one will have the least deflection and deformity?

Obviously there is a point where you can go overboard with the structure and add more weight than its worth, but your reputable builders all seem to have their forumulas perfected so far as whats needed to make the boats work well. Then guys like you and me sit here on our easy chairs with our laptops and digital pics and either brag on them or dis them to no end!

It just becomes really difficult to accurately comparitively analysis them when you try to factor in how much bracing they use inside, what its made of, and so on. Every industry out there has evolved the the point of stackng angles, and spanning distances between supports to maximise strength and effciency compared to weight and mass, weather it be the aviation industry, bridge builders, hi-rise construction and so on. Todays boat builders have so many options available to them and employ so many different techniques to give us the most strength and longevity per pound that we're a bit like kids in a candy store here!

Generally speaking, I'm in your camp on this one, thicker is better for my purposes as well, but I'm still a firm believer in that t-1 steel armoring to boot! Even if it does add the weight on there! But I'm still aware that possibly the superstructure inside to boat contributes even more to the overal strengh equation than that steel does!

By the way, is the whole bottom on your boat 1/2", or just the keel section? How long is the boat? How many hours did you put on it last season? and what rivers did you run on mostly? I've heard nothing but good stuff about your brand, I'm really curious to know how well their formula holds up. Also... how about that jet/powerplant combo? Have you hauled any really heavy loads with it? Have you owned a SJ before? Is it substantially more thrust, or is it a case of possibly greater longevity/reliability?

Thanks for sharing your thoughts and experiences... Chris

5. My 1/2" is 4' x 10'. it is 3/16 on the sides. Its a 6 ft bottom so there is still some "lighter" material as well.

I know there is more to it than just thickness, structure and material selection has everything to do with real world strength. It is really hard to beat the ol T-1 for toughness though. How much does a 4 x 10 sheet of titanium cost. I found a 2' by 4' x 1/2" for about \$4000...hehehe

My real point was about how much more energy a heavier boat has moving through the water. With bottom widths being the same, a lighter boat should move in less water than a heavier one. With a narrower boat, even a few inches, the boat begins to sit down in the water more at comparable speeds, and also at rest. In reality, the action of the water being pulled up into a tunnel also creates a force that the boat must counteract by being pulled down into the water the same amount. Using this thinking, the narrower boat should draft more water while on step than the other (obviously strake design, deadrise, and chine angles have HUGE impacts on this as well). We all know when it gets shallow, the less you run in, the better (If the pilot knows what they are doing).

Just because somebody says their bottom is 1.5 times stronger because the material is thicker doesn't mean it will make a difference when the going gets tough. Structure and design are where it counts. But I would hope a heavier boat has a thicker bottom, because it will need it.

I will hopefully have my upgrades done for this next little get together. More ponies (maybe up to 300hp), new impellers, and a trim nozzle are in store along with a couple other things...like a nice centrifugal gravel trap or two.

Joe

p.s. Thanks for all the advice you gave me a couple years ago. I was really set on having a Riddle or Firefish, but then I found this one used It suits me and the family just right!

7. The kinetic energy of a boat in motion has nothing to do with the strength of its bottom.

The strength of a sheet of aluminum when subject to forces that would cause it to bend is proporitional to the cube of the thickness. If spacing between supports (stringers) is equal, a 1/4" is eight times more resistant to bending than a 1/8" hull, with some caveats. If you wanted to stretch this out well beyond some logical limit, your 1/2" plate is 64 times more resistant to bending than the 1/8" material.

I don't know riverboats and riverboating, but my gut tells me that anything thicker than 3/16" or 1/4" is a heavy gimmick, and is representative of a builder who is one of two things: 1. too lazy or ignorant to install an appropriate number of stringers and bulkheads between the deck and the hull, or 2. ignorant of the economics and performance tradeoffs of his designs.

At very best, 1/2" hull thickness is a niche requirement, suited for guys running water that's full of canopener-shaped large rock and lots of it.

I'd consider a doubler covering the front third or so of the vee for a "normal" boat, but that's about it.

8. Stronger in what sense? Unless you discuss the length and beam of the boat and the stringers used, it's a moot point to say which is "stronger" because more information is needed.

If you're talking resistance to rocks, then you simply can't beat thickness, though there is a point where the added weights affect on handling as well as fuel consumption penalty isn't worth the added protection.

Structural design is always a tradeoff.

9. Originally Posted by Vek
The kinetic energy of a boat in motion has nothing to do with the strength of its bottom.

The strength of a sheet of aluminum when subject to forces that would cause it to bend is proporitional to the cube of the thickness. If spacing between supports (stringers) is equal, a 1/4" is eight times more resistant to bending than a 1/8" hull, with some caveats. If you wanted to stretch this out well beyond some logical limit, your 1/2" plate is 64 times more resistant to bending than the 1/8" material.

I don't know riverboats and riverboating, but my gut tells me that anything thicker than 3/16" or 1/4" is a heavy gimmick, and is representative of a builder who is one of two things: 1. too lazy or ignorant to install an appropriate number of stringers and bulkheads between the deck and the hull, or 2. ignorant of the economics and performance tradeoffs of his designs.

At very best, 1/2" hull thickness is a niche requirement, suited for guys running water that's full of canopener-shaped large rock and lots of it.

I'd consider a doubler covering the front third or so of the vee for a "normal" boat, but that's about it.
Great point Vek,

C-bolt, appears you truly have a 1/2 thick plate and it's not 1/8" with 3/16" sandwiched together. If it's 4' wide, what did they use to widen the bottom out the full bottom width? What is the width? What is your boat length as well? Besides width a boat length is critical on how it steps as well. A shorter boat needs more water to step then a longer boat. Boulton told me that they found that their 22' boat was more effiecient then there 20' boats even though the boat was heavier. Just plans better because it's balanced better.

Your calcualtion is also skewed but correct if you where dropping the entire boat onto a rock at 30mph. However you would actually have to determine the actual downward weight at that particular point of the boat at the time of impact and upward acceleration at the time of impact. The amount of draft on step would be what's critical rather then weight. Also the forward motion in this case wouldn't be as critical as the upward acceleration going from the depth of step to the height at which the boat has to travel to clear the object. You could calculate the upward acceleration with the speed but its been awhile since I had university physics and not something I want to spend time on at this point but it's this Force=mass x accerleration that is going to dent your bottom. If you were going to lift the entire boat out of the water you could us the entire boat mass but if your just hitting a rock like it appears you did near the grate, using the entire weight wouldn't be accurate.

It appears you also think the tunnel applies more downward suction (force) then not having a tunnel. I actually think it's total opposite. The tunnel is more apt to break suction then not having a tunnel. That's why they tend to cavitate easier in a hard turns... A tunnel is less likely to hold suction and loss of added downward force (holding force) being applied as your boat hits a rock and you slide over it would reduce the force being applied at the point of impact. This is just a my theory of course. It would be interesting to test the difference in hold power each design offers.

10. Vek, I am glad you showed up with your strength comparisons. I was just going off of what was said in another thread. I agree that the energy of a boat in motion has nothing to do with the strength of its bottom. But the relative "strength" of the bottom should be somewhat proportional to the energy of the boat in question right? The more energy the boat has when its about to change direction from impact with a rock the stronger it should be.

I wouldn't argue that 1/2" is probably overkill for most, but I wanted a boat I can run up on the rocks, or take a hit with and NOT get a dent. Scratches are fine, but dents ruin performance and look horrible upon resale. I want a boat with a bottom that will still look good after years of use. I have seen some big dents in 1/4" aluminum from rocks in some pretty well respected brands with good structures from impacts, so 1/2" is not unreasonable depending on use.

As far as performance goes, my bottom weighs about the same as it would have if I had 1/4 on the whole thing. Instead I have 3/16 where the 1/2 isn't. Just because somebody uses a thick bottom material doesn't mean they dont have structure. Just ask Chriso with his Riddle Marine boats. He has STEEL skid plates in his for the same reason. Because they will take the abuse again and again. Dont even think Riddle doesnt know how to build a boat or they are too lazy to put enough stringers in. Im not sure why you would want the doubler in the front, that part hardly ever takes a hit on the rivers, its usually the back. Plus when your on step, only the back is in the water anyways.

Thanks again for your expertise in how strength relates to thickness.

Paul, I do believe we are on the same page. It is impossible to call which bottom would be the strongest without comparing them on some computer with all the exact data. But for discussions sake, lets assume they are comparable Cant you tell I love stirring the pot?

HG, I think you know what I mean. If a boat with 1.5 times more energy hits something, it will cause more damage than the other boat given the same hit/placement/circumstances...etc. Thats why I say given the same structure, the heavier boat should have a bottom that is that much stronger. The theoretical damage would be the same. If Vek's calculations are correct, than a 3/16 sheet would be 4 times more resistant to bending than a 1/8. Like others though, I dont think you can figure strength on just bottom strength, it is everything combined.

As far as the tunnel goes, I think you cavatate because the boat slides sideways creating a sharp change in flow and aerating the water. The air/water mix cavatates the pump. When traveling straight, the water is drawn up smoothly into the tunnel not creating turbulence or air pockets. This is why a good tunnel design is long enough and smooth enough to prevent turbulence. When you are sideways in a sharp corner and the back end slides it creates an effect similar to the step tech hull designs on the racers. It causes the surface friction to be broken and creates less drag. Chriso has this type of bottom in his riddle. If tunnel hulls were more efficient, everybody would have one. The are really only for keeping the pump out of the rocks when running shallow. As far as length goes, once its on step the only thing that matters is the wetted surface. But The more water that is displaced when sitting the better.

11. Originally Posted by c-bolt
How much does a 4 x 10 sheet of titanium cost. I found a 2' by 4' x 1/2" for about \$4000...hehehe
Where did you find that? I might have lost one up the river last fall!!!

I thought that was probably the way RW built their 1/2" bottoms, like you said, the keel section, and especially near the pump intake, is where all the abuse seems to take its toll. Like some of these guys are talking, a full 1/2" bottom would be overkill for most of our smaller boats, but it sounds like you've got a good compromise going there.

I've read so many discussions about how thick a bottom should be (usually they dont point out how much superstructure should be incorporated) and conversely, how much superstructure should be inside (and these discussions typically leave out the hull thickness component) and how heavy a boat should be (typically leaves out both of the other two considerations) then of course the power to weight ratio is often discussed as well... but in fact as you know these components are all so inter-related the physics would leave most engineers dumbfounded. Thats why its so cool to have a boat built by experienced and dedicated craftsman, and to have opportunities like this forum provide us to hear firsthand how the various packages work.

Its all a tradeoff to find the most nearly perfect setup. I felt for my purposes in an all-around boat that the SJ package was a bit short on thrust (but couldnt bring myself to get rid of all of the SJ's because they are sooo fun in certain conditions!) so I did my best to keep a similar power to weight ratio when I built that aluminum v8 and hooked it up with my scott pump. It turned out really great, but at the time I would have seriously considered the ecotec setup you got had there been a few more installations under the belt back then. Even if it doesnt have more thrust than a SJ (I bet it does!) it's got to be longer lasting and more industrial strength. (SJ's arent bad once you spend the hundreds of dollars it takes getting them all bored and sleeved at all the places they start wobbling in the first season) I ran my old almar thousands of river miles with a 3 stage and only 230 hp out of that old 351 ford, which weighed in a lot more than your ecotec.

Bottom line is, if its heavier and you want it to ride as high in the water at the same speeds as a lighter boat, you've either got to put more bottom under it, wider, longer, whatever... and / or more thrust behind it (although that gvery quickly that equates to having to run faster to ride as high as the lighter boat)

I'd really enjoy a chance to check it out firsthand if we ever happen to be on the water together next summer. I really think that ecotec has a lot of promise for us up here, and I've long admired them RW's!

By the way... why did you ever drive over that rock like that? Most guys I know try to drive around 'em (I know, I should never have said that, but I couldnt help myself! Everybody always asks me that too)

12. Originally Posted by Halibutgrove
Boulton told me that they found that their 22' boat was more effiecient then there 20' boats even though the boat was heavier. Just plans better because it's balanced better.
I've found that most of these guys have done the majority of their R & D refinements in one particular length of boat so far as coming up with their exact proportions go, then they add a couple feet, or chop them off according to what length the customer orders. Over time, they start refining based upon things that might improve performance in the shorter boats, or longer ones, but most of them are optimum in the 21 to 22 foot range, although outfits like Firefish spent most of their design efforts around smaller boats, and Riddle and of course Outlaw in Canada has done a ton of R&D around all kind of sizes, and Bentz and HCM have done a ton of it on the bigger boats. If you have the chance to visit with the builder and ask them to honestly tell you which size they recommend for ultimate performance in whatever particular hull design you are looking at, and they get all glassy eyed and dreamy looking and say "I'd love to build one for myself in a XX? footer..." well, then you know what size to get dont you!

Originally Posted by Halibutgrove
Your calcualtion is also skewed but correct if you where dropping the entire boat onto a rock at 30mph. However you would actually have to determine the actual downward weight at that particular point of the boat at the time of impact and upward acceleration at the time of impact. The amount of draft on step would be what's critical rather then weight. Also the forward motion in this case wouldn't be as critical as the upward acceleration going from the depth of step to the height at which the boat has to travel to clear the object. You could calculate the upward acceleration with the speed but its been awhile since I had university physics and not something I want to spend time on at this point but it's this Force=mass x accerleration that is going to dent your bottom. If you were going to lift the entire boat out of the water you could us the entire boat mass but if your just hitting a rock like it appears you did near the grate, using the entire weight wouldn't be accurate.
While thats true, its still proportional to the boat weight and CG...

Originally Posted by Halibutgrove
It appears you also think the tunnel applies more downward suction (force) then not having a tunnel. I actually think it's total opposite. The tunnel is more apt to break suction then not having a tunnel. That's why they tend to cavitate easier in a hard turns... A tunnel is less likely to hold suction and loss of added downward force (holding force) being applied as your boat hits a rock and you slide over it would reduce the force being applied at the point of impact. This is just a my theory of course. It would be interesting to test the difference in hold power each design offers.
I think he was referring more to the actual lifting capabilities of the particular hull... a straight bottom will give more lift that one with a tunnel, or tunnels cut in it... and generally speaking, if you have a straight bottom boat and an identical one with tunnel / tunnels in it, the tunneled one will ride a bit lower in the water at any given speed, and require a bit more speed to ride the same as the straight bottomed one.

13. To those that are saying that the kenetic energy of a boat that is in motion does not matter, or only matters if it is dropped, I disagree. It has been a few years, but since others are shooting from the hip I will as well.

F = MA, Force = Mass times Acceleration

So if two boats are compared, one with a higher mass than the other, and they both hit the same object (a rock) at the same speed, then the force applied to the boat of higher mass would be greater to stop it (deAccelerate) than the lighter boat, right?

It seems clear to me that the heavier boat will take a bigger hit when it hits the rocks than a lighter boat if they are both at the same speed. The bigger question is how much weight, as a percentage of the total weight does changing the thickness of the bottom make? I cannot imagine it is that much, since changing the thinkness of the bottom does not effect most of the components on the boat.

14. that riverwild looks like a sweet boat. Please post any updates and experiences you have with your engine, pump set up.
I agree with what some have said in that the engineering of stringers/bulkheads is as important as thickness of bottom plate. Looks like you probably have both.

I'm just ramblin generally, not to anyone specific, just trying to help
I think in a lighter-constructed boat, a tunnel is a good idea

Regarding cavitation, it's the rough water and flatter hull that does it, not the tunnel. Most tunnels nowadays (finally) are pretty good and are in fact jet-tunnels.
Good water conditions don't present problems. You find tunnels in flatter hulls, which don't cut the water and keep it headed straight back to the intake, instead their keel even rides a litter more on top of the water and the flow is more easily interrupted. That being said, even in hard turns, I never cavitate unless I cut across a section of choppy water, like when spinning brody's on the lake and driving over your own wake while turning at the same time. Some will argue that you cannot avoid this rougher water. I can see their point.

A hull with more deadrise slides less, rides a little lower in turns, and feeds a bit cleaner water to the intake (great handling qualities) and cavitates less. As far as your intake, tunneled or not, it seems you're moving forward just as much as sideways, even in hard turns. You're not really getting water directly from the side, unless you slide out or purposely do a 180* turn.. and of course you'll cavitate. I don't think a tunneled boat rides or drifts any lower than without a tunnel. It's such a neglible amount at drift.

The forward motion is "compressing" the water from the front of the tunnel (flush but wider) to the back (2 1/2" deep but several inches narrower at top). The back end of the boat does not have to stay deeper in the water to feed the tunnel. They're great for protecting your jet foot on an outboard, or protecting an inboard-mounted pump, especially in a lighter-constructed hull. My keel is beat to HE*L, but the walls and top of the tunnel, including where the pump is mounted are clean and true as the tunnel clears the obstructions that the keel hit. In my case (lighter constructed hull), I most definitely would have problems with my pump suffering damage with regards to alignment or cracks/water leakage.

I still don't know which I prefer, how a jetboat with more deadrise handles, or the slightly out of control way that my shallower deadrise boat handles but is able to slide over things that I thought for sure were going to ground me. (usually when I said uh-oh and turned around). I really don't know. The sliding at times is very unnerving. I may simply need to add chines as a minimum. My only advice would be a guy can get away with thinner construction to some point if you have a tunnel, if not, I would want some additional protection. My feeling is that it's easier to get stranded if you can't get your engine pump running correctly than if you get a dent on the bottom.
But a good point is made, it's harder to get full asking price for a boat that's dented up.
Hopefully a few things to consider. I sure am curious about that wooly sport jet as it seems to capture many high points.
see ya

15. Originally Posted by jrogers
To those that are saying that the kenetic energy of a boat that is in motion does not matter, or only matters if it is dropped, I disagree. It has been a few years, but since others are shooting from the hip I will as well.

F = MA, Force = Mass times Acceleration

So if two boats are compared, one with a higher mass than the other, and they both hit the same object (a rock) at the same speed, then the force applied to the boat of higher mass would be greater to stop it (deAccelerate) than the lighter boat, right?

It seems clear to me that the heavier boat will take a bigger hit when it hits the rocks than a lighter boat if they are both at the same speed. The bigger question is how much weight, as a percentage of the total weight does changing the thickness of the bottom make? I cannot imagine it is that much, since changing the thinkness of the bottom does not effect most of the components on the boat.
Maybe I didn't make myself clear in the other post. Your correct in saying that the force will be greater if the mass is larger. If you run both into a brick wall at the same speed the large vessel will apply more force and more kinetic energy. It may even bust through while the smaller one goes "splat". Allot will depend on the internal construction as well. There's not that many walls on the river except a few bridge abutments so hopefully a guy steers around them. I guess my point was that a heavier boat could draft less then a lighter boat and most hits are probably as a result of the rocks you can't see. Hopefully your avoiding the ones you can. Yes the mass of the boat will effect the amount of force given the same draft at the same speed. Which is less likely to bend 1/8 or 3/16" Which will also be less likely to bend if it's 5052 or 5086 harden aluminum?

I guess as a look back at the original post that started this I have to laugh. C-bolt just used overall weight as some sort of measurement to ask which is stronger. Really C-boat the overall strength of the bottom has nothing to do with its weight.

I believe 3/16 is .5lbs heavier per sqft then 1/8. Anyone know what 1/4" is and 1/2"?

The difference between a typical 21' boat with 1/8 or 3/16 bottom is about 63lbs. Assuming 6'x21' bottom. If it's 5086, it would be even strong. I'll sacrifice the weight for the added strength any day. JMHO.

16. 63 pounds for 3/16, 63 more to go to 1/2", 63 more for the additional structure to make it worthwhile, 63 more for a t-1 keel strip, then you probably want tougher sides so they dont crack out... pretty soon it starts to add up... thats where the SJ filled such a unique niche, being so light and still giving you over 200 hp, compared to those thousand pound bigblocks making only some 400 horsepower. I figure I saved some 400 pounds out of the back of my boat when I put that alumium v8 in it. But probably added back in about a hundred and a half with the structure and the steel. It worked out well for me and my purposes although some times I wish I'd skipped the tunnels so it'd ride a bit higher at slower speeds. This ecotec looks like a great compromise to me, if you can build a boat with a 1/2inch bottom and get 300 ponies behing a 7" jet and keep it around that 2100 pound mark, I think most of us would be well satisfied with that performance and durability.

17. Chris, that aluminum big block probably saved you around 400 lbs In dollar bills to carry around too . The ecotec is only 252 horse for now, but hopefully that will change for next spring. It does get up and go pretty good though and still runs shallow. The size is obviously bigger than a sportjet but everything is a compromise.

I hope this thread didn't stir the pot too much. We all know bottom strength is way more than just thickness. I just wanted to show off my snazzy boat.

Hope everybody has a great Thanksgiving!

18. How bout a couple more pics for fun!

Oh, and Chris..The "scratch" wasn't from me. It was when Carl (the previous owner) pretty much dropped it off some rapids onto one of those big rocks. The boat was built to handle big rapids and rocks. Ive never run them, but I guess the Rogue, Snake and some of the others down in Oregon fit that bill.

I hit a nice rock and it barely made a mark. It is really nice not having to worry about a nice thud every now and then.

19. I'm getting a headache from all the formula's, All I know is some people need a 1/2" bottom and some people can get away with a .100 bottom,running the same rivers.

20. Originally Posted by chriso
63 pounds for 3/16, 63 more to go to 1/2"
Chriso are you just making up the number?

Here's weights per square foot reference here

1/8" 1.75lbs
3/16 2.63
1/4 3.49
5/16 5.24
1/2 6.98

So a 4x10 sheet on the bottom would add 174lbs over just being completely 3/16". Where are you getting 63lbs to go to 1/2"? I mistakenly recalled 3/16 being only .5lbs heavier then 1/8 but it's actually .88lbs/sqft. So on a 6x20' bottom at 3/16 would ad 105lbs going 1/4" adds 209lbs. over a 1/8" bottom.

C-bolt your boat is sharp looking but I'm suspicious about the claimed weight especially with a 1/2" bottom at 4'x10' Is there fewer longitudnal supports with this bottom thickness over conventional designs? Do they even use longitudinal supports? With a 1/2 bottom I suppose you could not even worry about supports. Did you weight it on the scales? Any pics of the inside structure? What's the deadrise? Did they bend the 1/2 or weld two sheets together. I'll bet bending 1/2" isn't easy. The boat is sleek but doesn't leave much room for carrying cargo. Looks like it would make a nice sprint boat.

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